Air Pollution Engineering Manual Part5 1973

TYPES OF RESINS 

RESIN KETTLES 

A resin is defined by the American Society for 

Testing Materials (ASTM) as a solid or semisolid, 

water-insoluble, organic substance, with 

little or no tendency to crystallize. Resins are 

the basic components of plastics and are important 

components of surface-coating formulations. 

For both uses, growth in recent years has been 

phenomenal; more than 5, 000 companies in the 

United States now produce plastics. 

There are two types of resins--natural and synthetic. 

The natural resins are obtained directly 

from sources such as fossil remains and tree sap. 

These include Congo, Batu, and East India resins 

I from fossils; lac from insects; and damar and 

I rosin from tree sap. 

i 

I 

i 

Synthetic resins can be classified by physical 

properties as thermoplastic or thermosetting. 

CHAPTER 11 

CHEMICAL PROCESSING EQUIPMENT 

resisting qualities to cross-linked molecular 

structures. 

Phenolic Resins 

Phenolic resins can be made from almost any 

phenolic compound and an aldehyde. Phenol and 

formaldehyde are by far the most common ingredients 

used, but others include phenol-fukfural, 

resorcinol-formaldehyde, and many similar 

combinations. Since a large proportion of 

phenolic-resin production goes into the manufacture 

of molding materials, the most desirable 

process for this manufacture will be described. 

Phenol and formaldehyde, along - with an acid 

catalyst (usually sulfuric, hydrochloric, or 

phosphoric acid), are charged to a steamjacketed 

or otherwise indirectly heated resin 

kettle that is provided with a reflux condenser 

and is capable of being operated under vacuum. 

The following formula shows the basic reaction: 

j 

1 

1 

I, 

. . , . . 

... , 

- 

Thermoplastic resins undergo no permanent 

change upon heating. They can be softened, 

melted, and molded without change in their physi 

cal properties. Thermosetting resins, on the 

other hand, can he softened, melted, and molded, 

but with continued heating, they harden or set to 

a permanent, rigid state and cannot be remolded 

PHENOL FORMALDEHYDE 

0- 

",, t, ,, ",, C, 

un n n un n 

--c i -n- ! -0- i -Q + H ~ O 

HO OH 

In this section, several synthetic resins are dis- 

cussed briefly. For each, an example of ingre- 

dients is given and a typical manufacturing opera- 

tion is discussed. Each basic resin type requires 

many modifications both in ingredients and tech- 

niques of synthesis in order to satisfy proposed 

uses and provide desired properties (Kirk and 

Othmer, 1947; Plastics Catalog Corporation, 

1959; Shreve, 1956). Not all of these variations 

will be discussed, however, since not all present 

individual air pollution problems. 

Thermosetting resins are obtained from fusible 

ingredients that undergo condensation and poly- 

merization reactions under the influence of heat, 

pressure, and a catalyst and form rigid shapes 

that resist the actions of heat and solvents. 

These resins, including phenolic, amino, poly- 

ester, and polyurethane resins, owe their heat- 

TYPICAL ( INTERMEDIATE) CONDENSATION PRODUCT 

Heat is applied to start the reaction, and then 

the exothermic reaction sustains itself for a 

while without additional heat. Water formed 

during the reaction is totally refluxed to the 

kettle. After the reaction is complete, the upper 

layer of water in the kettle is removed by draw- 

ing a vacuum on the kettle. The warm, dehy- 

drated resin is poured onto a cooling floor or 

into shallow trays and then ground to powder 

after it hardens. This powder is mixed with 

other ingredients to make the final plastic mate- 

rial. Characteristics of the molding powder, 

as well as the time and rate of reaction, depend 

upon the concentration of catalyst used, the 

phenol-formaldehyde ratio used, and the reac- 

tidn temperature maintained.

702 CHEMICAL PROCESSING EQUIPMENT 

Amino Resins 

The most important amino resins are the urea- 

formaldehyde and melamine-formaldehyde resins. 

The urea-Cormaldehyde reaction is simple: 1 

mole of urea is mixed with 2 moles of formalde- 

hyde as 38 percent solution. The mixture is 

kept alkaline with ammonia pH 7.6 to 8. The 

reaction is carried out at 77°F for 2 days at 

atmospheric pressure without any reflux. 

The - melamine resins are made in much the same 

manner except that the reactants must be heated 

to about 176°F initially, in order to dissolve the 

melamine. The solution is then cooled to 77°F 

for 2 days to complete the reaction. 

The equipment needed for the synthesis of the 

amino resins consists of kettles for the conden- 

sation reaction (usually nickel or nickel-clad 

steel), evaporators for concentrating the resin, 

and some type of dryer. 

The amino resins are used as molding compounds, 

adhesives, and protective coatings, and ior treat- 

ing textiles and paper. 

Polyester ond Alkyd Resins 

There is much confusion concerning the mean- 

ing of the two terms polyester and alkyd. Ap- 

parently, by chemical definition, the product 

obtained by the condensation reaction between 

a polyhydric alcohol and a polybasic acid, whether 

or not it is modified by other materials, is prop- 

erly called a polyester. All polyesters can then 

be divided into three basic classes: Unsaturated 

polyesters, saturated polyesters, and alkyds. 

Unsaturated polyesters are iormed when 

either of the reactants (alcohol and acid) 

contains, or both contain, a double-bonded 

pair of carbon atoms. The materials usu- 

ally used are glycols of ethylene, propylene, 

and butylene and unsaturated dibasic acids 

such as maleic anhydride and furnaric acid. 

A typical reaction is as follows: 

MALEIC ANHYDRIDE ETHYLENE GLYCOL 

REPRESENTATIVE SEGMENT OF CHAIN-FORMED 

The resulting polyester is capable of cross- 

linking and is usually blended wlth a poly- 

merizable material such as styrene. Under 

heat or a peroxide catalyst, or both, this 

blend copolymerizes into a thermosetting 

resin. It has recently found extensive use 

in the reinforced-plastics field where it is 

laminated with fibrous glass. It is also 

molded into many forms for a variety of uses. 

2. Saturated polyesters are made from saturated 

acids and alcohols, as indicated by the follow- 

ing reaction: 

H 1 ,L - - - - - - H H 

H - O C - 0 - C - I ' O - I ! 

H H 

TEREPHTHALIC ACID ETHYLENE GLYCOL 

$__-__--i + H I - 0 - C - C - O - H - 4 

POLYESTER (REPERTING UNIT) 

The polyesters formed are long-chain, saturated 

materials not capable of cross-linking. 

Several of these are used as plasticizers. A 

special type made from ethylene glycol and 

terephthalic acid has been made into fiber 

(Dacron) and film ( ~ylara. Still others of 

this type with lower molecular weights are 

being used with di-isocyanate8 to form polyurethane 

resins. 

Alkyd resins differ from other polyesters 

as a result of modification by additions of 

fatty, monobasic acids. This is known as oil 

modification since the fatty acids are usu- 

ally in the form of naturally occurring oils 

such as linseed, tung, soya, cottonseed, and, 

at times, fish oil. The alkyds, thinned with, 

organic solvents, are used predominantly in 

the protective coating industry in varnishes, 

paints, and enamels. 

The most widely used base ingredients are 

phthalic anhydride and glycerol. Smaller 

quantities of other acids such as maleic, 

fumaric, and others and alcohols such as 

pentaerythritol, sorbitol, mannitol, ethylene 

glycol, and others are used. These are re- 

acted with the oils already mentioned to 

form the resin. 

The oils, as they exist naturally, are pre- 

dominantly in the form of triglycerides and 

do not react with the polybasic acid. They 

are changed to the reactive monoglyceride 

by reaction with a portion of the glycerol or 

other alcohol to be used. Heat and a cata- 

lyst are needed to promote this reaction,

which is known as alcoholysis. The resin 

is then formed by reacting this monoglyceride 

with the acid by agitation and sparging with 

inert gas until the condensation reaction prod- 

uct has reached the proper viscosity. The 

reaction takes place in an enclosed resin ket- 

tle equipped with a condenser and usually a 

scrubber, at temperatures slightly below 

500°F. The alcoholysis can be accomplished 

first and then the acid and more alcohol can 

be added to the kettle, or all the ingredients 

can be added simultaneously. 

An example of an alcoholysis reaction followed 

by reaction of the monoglyceride formed with 

phthalic anhydride is shown in the following: 

- 

C3 H5 (CI7 H33 COO)3 + C3 Hg (OH13 

Resin Kettles 703 

The flexible foams have found wide use in auto- 

mobile and furniture upholstery and in many 

other specialty items. 

By varying the ingre ents and adding other blowing 

agents such as Fre % ? 11, rigid foams with 

fine, close-cell structure can be formed. These 

can be formed in place by spraying techniques 

and are used extensively as insulating materials. 

Thermoplastic Resins 

GLYCEROL TRIESTER OF OLElC ACID GLYCERIN Polyvinyl Resins 

As already stated, thermoplastic resins are 

capable oi being reworked alter they have been 

formed into rigid shapes. The subdivisions in 

this group that are discussed here are the vinyls, 

styrenes, and the coal tar and petroleum base 

resins. 

H 

The polyvinyl resins are those having a vinyl 

HF - OH A ! 

(CH=CH2) group. The most important of these 

-HC - 0 - C - C17 H33 + 

I are made from the uolvmerization oi vinvl ace- 

HC - OH 

H d 

MONOGLYCERIDE OF OLElC ACID PHTHALIC ANHYDRIDE 

H H H 9 

.... 0 . C. C C. 0 . C R 

Polyurethane 

H A H 

I 

CI7 H33 - C = 0 

REPEATING UNIT FOR OIL-MOOIFIEO ALKYO 

A , 

tate and vinyl chloride. Other associated resins 

are also discussed briefly. 

Vinyl acetate monomer is a clear liquid made 

from the reaction between acetylene and acetic 

acid. The monomer can be polymerized in bulk, 

in solution, or in beads or emulsion. In the bulk 

reaction, only small batches can be safely bandled 

because oi the almost explosive violence of 

the reaction once it has been catalyzed by a small 

amount of peroxide. Probably the most common 

method of preparation is in solution. In this 

process, a mixture of 60 volumes vinyl acetate 

and 40 volumes benzene is fed to a jacketed, 

stirred resin kettle equipped with a reflux condenser. 

A small amount oi peroxide catalyst 

. . 

The manufacture of the finished polyurethane 

. . 

. , 

. 

... 

. 

resin differs from the others described in that 

no heated reaction in a kettle is involved. One 

of the reactants. however. ~-. is -~ a saturated ~.. mnlu- r --, 

ester resin. as alreadv mentioned. . or. , more - - 

recently, a polvether - . resin. To iorm a flexible 

foam product, the resin, typically a polyether 

such as polyoxypropylenetriol, is reacted with 

tolylene diisocyanate and water in an approximate 

100: 42: 3 ratio by weight, along with small quantities 

of an emulsifying agent, a polymerization 

is added and the mixture is heated until gentle 

refluxing is obtained. Aiter about 3 hours, approximately 

70 percent is polymerized, and the 

run is transferred to another kettle where the 

solvent and unreacted monomer are removed by 

steam distillation. The wet polymer is then 

dried. Polyvinyl acetate is used extensively in 

water-based paints, and lor adhesives, textile 

finishes, and production of polyvinyl butyral. 

catalyst, and a silicone lubricant. The ingredients 

are metered to a mixing head that deposits 

the mixture onto a moving conveyor. The resin 

and tolylene diisocyanate (TDI) polymerize and 

cross-link to form the urethane resin. The TDI 

also reacts with the water, yielding urea and 

carbon dioxide. The evolved gas forms a loamlike 

structure. The product forms as a continuous 

loaf. After room temperature curing lor 

about a day, the loaf can be cut into desired 

sizes and shapes, depending upon required use. 

Vinyl chloride monomer under normal conditions 

is a gas that boils at -14°C. It is usually stored 

and reacted as a liquid under pressure. It is 

made by the catalytic combination of acetylene 

and hydrogen chloride gas or by the chlorination 

of ethylene followed by the catalytic removal of hydrogen 

chloride. It is polymerized in a jacketed, 

stirred autoclave. Since the reaction is highly exothermic 

and can result in local overheating and poor 

quality, it is usually carried out as a water emulsion 

to facilitate more precise control. To ensure


quality and a properly controlled reaction, several with ethylene in presence of a Fridel-Crafts cataadditives 

are used. These include an emulsifying lyst such as aluminum chloride. During storage 

agent such as soap, a protective colloid such as glue, or shipment the styrene must contain a polymerizaa 

pH control such as acetic acid or other moderate- tion inhibitor such as hydroquinone and must be 

ly weak acid (2.5 is common), oxidation and re- kept under a protective atmosphere of nitrogen 

duction agents such as ammonium persulfate and or natural gas. 

sodium hisulfite, respectively, to control the oxidation-reduction 

atmosphere, a catalyst or initiator 

like henzoyl peroxide, and a chain length-con- 

Styrene can he polymerized in bulk, emulsion, 

or suspension using techniques similar to 

i 

1 

trolling agent such as carbon tetrachloride. The 

reaction is carried out in a completely enclosed 

vessel with the pressure controlled to maintain 

the unreacted vinyl chloride in the liquid state. 

As the reaction progresses, a suspension of latex 

or polymer is formed. This raw latex is removed 

from the kettle, and the unreacted monomer is 

removed by evaporation and recovered by compression 

and condensation. 

A modification oi the emulsion reaction is known 

as suspension polymerization. In this process, 

droplets of monomer are kept dispersed by rapid 

agitation in a water solution of sodium sulfate or 

in a colloidal suspension such as gelatin in water. 

During the the of monomer are 

converted to heads of oolvrner that are easily rethose 

mreviouslv described. The reaction is - ~ 

exothermic and has a runawav tendencv unless I 

the temperature is carefully controlled. Oxygen 

must he excluded from the reaction since it causes 1 

a yellowing of the product and affects the rate of 

nnlvmPrira+ion. --, ---.. .-.--. 

i 

! 

Polystyrene is used in tremendous quantities for 

many .. purposes. . Because of its ease of handline, 4 u~ ,, 

dimensional stability, and unlimited color possi- 1 

bilities, it is used widely for toys, novelties, i 

toilet articles. houseware marts. radio and tele- ~ ~ ! 

vision ~arts, wall tile. and other oroducts. Dis- I 

advantages include limited heat resistance, brit- .! 

tleness, and vulnerability to attack by organic 

solvents such as kerosine and carbon tetrachloride, i 

3 

covered and cleaned. This process is more 

troublesome and exacting than the emulsion reac- Petroleum and Coal Tar Resins 

tion hut eliminates the contaminating effects of 

the emulsifying agent and other additives. 

Petroleum and coal tar resins are the least expensive 

of the synthetic resins. They are made 

! 

from-the polymerization of unsaturated hydrocarbons 

found in crude distillate from coal tar in coke ovens ; 

or from cracking of petroleum. The exact chemical; 

nature of these hydrocarbons has not been determined, 

hut the unsaturates of coal tar origin are 

i 

known to be primarily cyclic while petroleum deriva 

tives are hoth straight- and close-chain types. 

Other vinyl-type resins are polyvinylidene chloride 

(saran@, polytetrafluoroethylene (fluoroethene), 

polyvinyl alcohol, polyvinyl hutyral, and others. 

The first two of these are made hy controlled poly- 

merization of the monomers in a manner similar to 

that previously described {or polyvinyl chloride. 

Polyvinyl alcohol has no existing monomer and 

is prepared from polyvinyl acetate by hydrolysis. 

Polyvinyl alcohol is unique among resins in that 

it is completely soluble in hoth hot and cold water. 

Polyvinyl butyral is made by the condensation 

reaction of butyraldehyde and polyvinyl alcohol. 

All have specific properties that make them super- 

ior for certain applications. 

Polystyrene 

Polystyrene, discovered in 1831, is one of the 

oldest resins known. Because of its transparent, 

glasslike properties, its practical application 

was recognized even then. Two major obstacles 

prevented its commercial development--prepara- 

tion of styrene monomer itself, and some means 

of preventing premature polymerization. These 

obstacles were not overcome until nearly 100 

years later. 

Styrene is a colorless liquid that boils at 145°C. 

It is prepared commercially from ethylbenzene, 

which; ,in turn, is made by reaction of benzene 

Most typical of the coal tar resins are those 

called Coumarone-Indene resin because these 

two compounds constitute a large portion of the 

distillate used for the reaction. The polymeriza- 

tion is initiated by a catalyst (usually sulfuric 

acid). After the reaction has proceeded as far as 

is desired, the unreacted monomer is removed 

by distillation. By controlling time, temperature, 

and proportions, many modifications of color and 

physical characteristics can be produced. The 

petroleum base distillate is polymerized in the 

same manner, yielding resins of slightly lower 

specific gravity than that of the coal tar resins. 

These resins are used in coating adhesives, in 

oleoresinous varnishes, and in floor coverings 

(the so-called asphalt tile). 

RESIN-MANUFACTURING EQUIPMENT 

Most resins are polymerized or otherwise reacted 1 

in a stainless steel, jacketed, indirectly heated ; 

vessel, which is completely enclosed, equipped j

with a stirring mcchanism, and generally contains 

an integral relluu condenser (Figure 549). Since 

most of the reactions prcviously iiescrihcd are 

exothermic, cooling coils are usually required. 

Some resins, such as thc phenolics, require 

that the kettle he under vacuum during part of 

the cyclc. This can be suppliecl either by a vac-' 

uum pump 01. by a steam or water jet ejector. 

Moreover, for somu reactions, that oi polyvinyl 

chlorirle [or example, the vessel must be capable 

of being operatcd uildcr pressure. This is nec- 

essary to kecp the norrnally gaseous monomer in 

a liquid state. The size of resin-processing ket- 

tles varies from a few hundred to several thou- 

sand gallons' capacity. 

Because oi Lhr rnany types of raw materials, 

ranging from gases to solids, storagc facilities 

vary accordingly--ethylene, a gas, is handled 

as such; vinyl chloride, a gas at standard condi- 

tions, is liquefieci easily under pressure. It is 

stored, therefore, as a liquid in a pressurized 

vessel. Most of the other liquid monomers do 

Res~n Kettles 705 

not present any particular storage problems. 

Some, such as styrene, must he stored under an 

inert atmosphere to prevent premature poly- 

merization. Some of the more volatile mate- 

rials are stored in cooled tanks to prevent ex- 

cessive vapor loss. Some of the materials have 

strong odors, and care must be taken to prevent 

emission of odors to the atmosphere. Solids, 

such as phthalic anhydride, are usually packaged 

and stored in bags or fiber drums. 

Treatment of the resin after polymerization varies 

with the proposed use. Resins for moldings are 

dried and crushed or ground into molding powder. 

Resins, such as the alkyd resins, to be used for 

protective coatings are normally transferred to 

an agitated thinning tank, as shown in Figure 550, 

where they are thinned with some type of solvent 

and then stored in large steel tanks equipped 

with water-cooled condensers to prevent loss of 

solvent to the atmosphere (Figure 551). Still 

other resins are stored in latex form as they 

come from the kettle. 

THE AIR POLLUTION PROBLEM 

The major sources of possible air contamination 

in resin manufacturing are the emissions of raw 

materials or monomer to the atmosphere, ernis- 

sions of solvent or other volatile liquids during 

the reaction, emissions of sublimed solids such 

as phthalic anhydride in alkyd production, emis- 

sions oi solvents during thinning of some resins, 

and emissions of solvents during storage and 

handling of thinned resins. Table 190 lists the 

most probable types and sources of air contami- 

nants from various resin-manufacturing opera- ,. 

tions. 

In the formulation of polyurethane foam, a slight 

excess of tolylene diisocyanate is usually added. 

Some of this is vaporized and emitted along 

with carbon dioxide during the reaction. The 

TDI fumes are extremely irritating to the eyes 

and respiratory system and are a source oi local 

air pollution. Since the vapor pressure of TDI 

is small, the fumes are minute in quantity and, 

if exhausted from the immediate work area and 

discharged to the outside atmosphere, are soon 

diluted to a nondetectible concentration. No 

specific controls have been needed to prevent 

emission of TDI fumes to the atmosphere. 

The finished solid resin represents a very small 

problem--chiefly some dust from crushing and 

grinding operations for molding powders. Generally 

the material is pne~rmatically conveyed 

from the grinder or pulverizer through a cyclone 

separator to a storage hopper. The fines escap- 

. . 

Figure 549. Typical resin-manufacturing unit 

showing process kettle and l iquid feed tanks 

ing the cyclone outlet are collected by a baghousetype 

dust collector. The collector should be de- 

\ 

1 

(Si lmar Chemical Company, Hawthorne, Cal if.). signed for a filter velocity of about 4 fpm or less. I 

. ,

706 CHEMICAL PROCESSING EOUIPMENT 

Figure 550. Resin-thinning tanks with water-cooled condensers (Allied Chemical Carp., Plastics Div. 

Lynnwood. Calif.). 

Most of the contaminants are readily condensable. 

In addition to these, however, small quantities 

of noncondensable, odorous gases similar to those 

irom varnish cooking may be emitted. These are 

morc prevalent in the manufacture of oil-modi- 

fied alkyds where a drying oil such as tung, lin- 

seed, or soya is reacted with glycerin and phtha- 

lic anhydride. When a drying oil is heated, 

acrolein and other odorous materials are emitted 

at temperatures exceeding about 350°F (see 

Iurther discussion under Varnish Cookers). The 

intensity of these emissions is directly propor- 

tional to maximum reaction temperatures. Thus, 

the intensity of noncondensable gases from resin 

formulation should he considerably less than 

that of gases from varnish cooking since the re- 

action temperature is approximately 100°F lower. 

AIR POLLUTION CONTROL EQUIPMEN1 

Figure 551. Resin storage tanks with condensers 

Control of monomer and volatile solvent emis- 

CAI I ied chemical c ~ plastics ~ ~ 0ivision, , ~ L ~ ~ ~ . 

wood, Calif.), 

sions during storage before the reaction and of

Resin Kettles 707 

Table 190. PRINCIPAL AIR CONTAMINANTS AND SOURCES OF EMISSION FROM 

RESIN-MANUFACTURING OPERATIONS 

Resin 

I 

Air contaminant 

I 

Possible sources 

of emission 

Phenol~c Aldehyde odor Storage, leaks, condenser outlet, 

vacuum pump discharge 

Amino / Aldehyde odor I Storage, leaks 

Polyester and alkyds 

Polyvinyl acetate 

Oil-cooking odors 

Phthalic anhydride fumes 

Solvent 

Vinyl acetate odor 

Solvent 

Polyvinyl chloride Vinyl chloride odor 1 

Polystyrene 

Styrene odor 

Petroleum and coal 

tar resins 

Polyurethane resins 

Monomer odors 

Tolylene diisocyanate 

solvent emissions during thinning and storage 

after the polymerization of the resin is relatively 

simple. It involves care in maintaining gastight 

containers for gases or liquefied gases stored 

under pressure, and condensers or cooling coils 

on other vessels handling liquids that might vapor- 

ize. Since most resins are thinned at elevated 

temperatures near the boiling point of the thinner, 

resin-thinning tanks, especially, require ade- 

quate condensers. Aside from the necessity for 

control of air pollution, these steps are needed 

to prevent the loss of valuable products. 

Heated tanks used for storage of liquid phthalic 

and maleic anhydrides should be equipped with 

condensation devices to prevent losses of sub- 

limed material. An excellent device is a water- 

jacketed, vertical condenser with provisions for 

admitting steam to the jacket and provisions for 

a pressure relief valve at the condenser outlet 

set at perhaps 4 ounces' pressure. During stor- 

age the tank is kept under a slight pressure of 

about 2 ounces, an inert gas making the tank 

completely closed. During filling, the displaced 

gas, with any sublimed phthalic anhydride, is forced 

through thc cooled condenser where the phthalic is 

deposited on the condenser walls. After filling is 

completed, the condensed phthalic is remelted by 

passing steam through the condenser jacket. 

Addition of solids such as phthalic anhydride to 

other ingredients that are above the sublimation 

temperature of the phthalic anhydride causes 

Uncontrolled resin kettle discharge 

Kettle or condenser discharge 

Storage, condenser outlet during 

reaction, condenser outlet during 

steam distillation to recover sol- 

vent and unreacted monomer 

Leaks in pressurized system 

Leaks in storage and reaction 

equipment 

Leaks in storage and reaction 

equipment 

Emission from finished foam result- 

ing from excess TDI in formulation 

temporary emissions that violate most air pollution 

standards regarding opacity of smoke or 

fumes. These emissions subside somewhat as 

soon as the solid is completely dissolved but remain 

in evidence at a reduced opacity until the 

reaction has been completed. The emissions 

can he controlled fairly easily with simple scrubbing 

devices. Various types of scrubbers can 

be used. A common system that has been proved 

effective consists of a settling chamber, commonly 

called a resin slop tank, followed by an 

exhaust stack equipped with water sprays. The 

spray system should provide for at Least 2 gallons 

per 1, 000 scf at a velocity of 5 ips. The settling 

chamber can consist of an enclosed vessel partially 

filled with water capable of being circulated 

with gas connections from the reaction vessel and 

to the exhaust stack. Some solids and water of 

reaction are collected in the settling tank, the 

remainder being knocked down by the water sprays 

in the stack. Another example is shown in Figure 

552. Here the vapors from a polyester resin 

process kettle are first passed through a spray 

chamber-type precleaner followed by a venturi 

scrubber. This system effectively reduces visible 

emissions. Scrubber water may be recirculated 

or used on a once-through basis, depending 

~ rimaril~ upon the available waste-water disposal 

system. The scrubber water can be odorous 

and should be discharged to a sanitary sewer. 

Many resin polymerization reactions, for example, 

polyvinyl acetate by the solution method, require

708 CHEMICAL PROCES SING EQUIPMENT 

Figure 552. Venturi scrubber venting resin-man- 

ufacturinn equipment (Silmar Chemical Corporation, 

Hawthorne; Calif. ). 

refluxing of ingredients during the reaction. Thus, 

all reactors ior this or other reactions involving 

the vaporization of portions of the reactor con- 

tents must be equipped with suitable reflux- or 

horizontal-type condensers or a combination oi 

both. The only problems involved here are prop- 

er sizing of the condensers and maintaining the 

cooling medium at the temperature necessary to 

effect complete condensation. 

When noncondensable, odor-bearing gases are 

emitted during the reaction, especially with alkyd 

resin production as already mentioned, and these 

gases are in sufficient concentration to create 

a public nuisance, more extensive air pollution 

control equipment is necessary. Such equipment 

is discussed thoroughly under other sections con- 

cerning odors (Varnish Cookers and Reduction of 

Inedible Animal Matter) and includes equipment 

for absorption and chemical oxidation, adsorption, 

and combustion, both catalytic and direct-ilame 

type. 

INTRODUCTION 

VARNISH COOKERS 

Varnish cooking processes discussed in this sec- 

tion include both the heated processes used to 

modify natural or synthetic oils or resins which 

will be the film-forming vehicles in inks or 

coatings (i.e., varnish, paint, enamel, lacquer) 

and those processes completely synthesizing 

iilm-forming vehicles. The effect of the various 

processes is to shorten the drying time and im- 

prove the qualities of chemicals which would, 

without modification, dry and form a film. Some 

varnish cooking processes will involve the manu- 

facture of a resin simultaneously with the rnodi- 

iication of the drying oils and in the same equip- 

ment. 

Varnish cooking, until the 19301s, involved only 

two basic processes: heat processing of natural 

oils to purify them or improve their drying time 

ior use in coatings and manufacture of oleoresin- 

nus varnish by heat processing the natural oils 

with natural resins. Since that time synthetic 

resins and synthetic film-forming compounds 

have greatly expanded the number of heating 

processes employed. Many new coatings do not 

use the film-forming products oi varnish cooklng. 

As a result, the products of varnish cooking con- 

stitute a much lower percentage of all coating 

materials than they did a decade ago. Neverthe- 

less, varnish cooking products still are exten- 

sively produced for use in the manufacture of 

surface coatings. 

DEFINITIONS - PRODUCTS AND PROCESSES 

Table 191 lists the various oils that are processed 

in varnish cooking equipment and the resins, both 

natural and synthetic, most frequently used in the 

manufacture of the iilm-forming materials. Var- 

nish cooking operations are varied, All opera- 

tions of this type, however, involve the applica- 

tion oi heat to these materials and their resultant 

polymerization, depolyrnerization, melting, 

esterification, isomerization, etc. Some of the 

most common processes are defined below. 

Boiled Oil. Linseed oil, soybean oil or other 

natural oils heated with small percentages oi 

oxides, acetates, or other salts of lead, manga- 

nese, or cobalt are known as boiled oils. During 

the process, the oil thickens, its density in- 

creases, and its color darkens, principally due 

to polymerization hut also to some oxidation. 

When catalysts, certain metal oxides, activated 

nickel, or sulfur dioxide are added, isomeriza- 

tion, or conjugation, occurs. This process is 

periormed to accelerate the normal drying time 

oi the oil. While oil so treated is known as

Table 191. VARNISH COOKING INGREDIENTS 

(Shreve, 1967) 

Oils 

Linseed oil 

Tung oil 

Dehydrated castor oil 

Castor oil 

Fish oils 

Tall oils 

Soya oil 

Cottonseed oil 

Coconut oil 

Natural resins 

Shellac, insect secretion 

Rosin 

East India 

Manila 

Kauri, old fossil resin 

Copal, fossil resin 

Dammar, recent fossil resin 

Synthetic resins 

Phenol-aldehvde (oil-soluble) 

Alkyd resins 

Mannitol esters 

Pentaerythritol esters and interesters 

Limed rosin 

Ester gum 

Cumarone-indene 

Melamine and urea-formaldehvde 

Chlorinated rubber and diphenyl 

Acrylates 

Vinyl resins 

Silicones 

Depolymerized copals 

Epoxies 

Polyurethanes 

boiled oil, the oil actually is heated only to tem- 

peratures of 360' to 580DF, which are below the 

boiling point. 

Heat-Bodied Oil. Linseed and other natural oils, 

including nut, vegetable, and marine oils, heated 

to temperatures from 485" to 620°F are known as 

heat-bodied oils. The viscosity of the oil, or its 

"body," is increased; the amount of increase de- 

pends upon the kind of oil and the time and tem- 

perature levels to which the oils are heated. 

Bodying is done principally for oils to be used in 

enamels and printing inks and results mainly from 

polymerization, although some oxidation also 

takes place. 

Blown Oil. Linseed oil and other natural oils may 

also be bodied by bubbling air through them and, 

in this case, are known as blown oils. The reac- 

tion is mainly oxidation; however, some polymeri- 

zation of the oxidized molecules also occurs. 

During the blowing process, the oil is heated to 

temperatures of 212 " to 390 "F. 

Varnish Cookers 709 

Esterification. The reaction of an organic acid 

(or acid anhydride) with an alcohol is known as 

esterification. In varnish cooking, copolymer 

oils, such as soyhean oil-maleic anhydride, are 

esterified with glycerol or other polyhydric alco- 

hols, or the vegetable oil may first be alcoholized 

and then treated with the anhydride. These opera- 

tions produce good drying oils from less desirable 

ones by increasing the double bond structures of 

the molecules. Polymeric esters, good synlhetic 

film-forming materials, are prepared by csteri- 

lication of glycerol, fatty acids, and phrhalic 

anhydride. These processes are performed in 

closed vessels at moderate temperatures. 

Spirit Varnish. Most spirit varnishes do not 

involve varnish cooking, but are mostly solutions 

of resins and volatile solvents mixed at room 

temperature. However, one spirit varnish, gloss 

oil, does involve varnish cooking. Resins are 

cooked at moderate to high temperatures with 

slaked lime, and the hot calcium resinate product 

is thinned with petroleum spirits. 

Oleoresinous Varnish. These varnishes are manu 

factured hy heating various combinations of natural 

oils with various svnthetic or natural resins 

to hlgh - temperatures, 520 " to 650 OF. The final 

product is thinned with solvent, and drying agents 

are added after thinning. 

Oil Breaking. Linseed oil, or other natural oils, 

contain some unsaponifiable matter, usually 1 to 

L percent. Those oils to be used in coatings 

without any other treatment will he cleared of 

most of this unsaponifiable material by the "break- 

ing" process. If the oils were allowed to age, 

this material would eventually separate and, along 

with other foreign matter, would settle as foots. 

Heating the oil to about 450 "F accelerates this 

separation and the oil is said to "break." 

Gum Running. Some natural resins, such as 

kauri gum, are insoluble in oil. In order to use 

them, they first are heated to temperatures of 

570 " to 700 "F. Then they are mixed with heated 

oils to produce the desired varnish product. This 

high temperature process, called gum running, 

serves to depolymerize the resin. 

MAJOR TYPES OF VARNISH COOKING EQUIPMENT 

Varnish cooking processes are conducted in two 

types of vessels--the open-topped portable kettle 

and the newer, totally enclosed, stationary kettle. 

The open kettles are cylindrical vessels with 

dished or flat bottoms. They usually are trans- 

ported on a three- or four-wheel truck, and are 

heated over an open flame. This type of kettle 

usually varies in capacity from 185 to 375 gallons


and is made of steel, copper, monel, aluminum, 

nickel, or stainless steel. Under most operating 

conditions, the kettle is charged in a loading 

room and then moved to the fire pit. It is heated 

over the fire pit and then, when the reaction is 

complete, transferred to another location for 

cooling. When the contents have cooled to the 

proper temperature, the kettle may be transferred 

to a third location for the addition of thinners 

and dryers or for transfer of its contents to 

a thinning tank. In the past, it was common to 

manually agitate the contents during cooking. 

Materials in open kettles now are seldom agitated 

manually. Agitation is provided by air-driven or 

electrically driven mixers and by sparging the 

contents with an inert gas, such as carbon dioxide 

or nitrogen. Figure 553 shows a kettle of this 

type. The open kettle still is employed extensively 

in paint manufacturing establishments. 

The enclosed stationary kettles are indirectly 

heated or cooled by jacketing or by coils. The 

kettles are vertical cylinders with dished tops 

and dished bottoms. They are constructed of an 

appropriate grade of stainless steel to resist cor- 

rosion. Some kettles are glass lined. An electri- 

cally driven agitator is mounted on the kettle. 

Batch weighing or metering equipment, pumps, 

and piping for the charging of liquid raw materi- 

als are installed with the kettle. The kettles are 

equipped with sealable openings through which 

solid or liquid materials can be charged manually. 

Inert gas is sparged into the bottom so as lo per- 

meate the entire contents of the kettle. For some 

types of production, condensers for reflux or 

vapor recovery are installed on the kettle. 

Figure 553. Uncontrolled open kettle far varnish 

cooking. 

Thinning for viscosity adjustment, or the addi- 

tion of dryers or unreacted monomers, usually 

is not done in the reaction kettle. Instead, the 

contents are pumped to other vessels designed 

for these purposes. These second vessels, or 

thinning vessels, also are closed and equipped 

with agitators. Jackets or coils for indirect 

heating or cooling, and nozzles for sparging 

with inert gas are installed. The thinning ves- 

sels are equipped with water-cooled vent con- 

densers mounted so that condensed solvent will 

drain back into the vessel. The closed station- 

ary kettles are almost exclusively found at chemi- 

cal companies engaged in manufacturing a wide 

variety of paint bases. 


Varnish cooking processes in both open and closed 

kettles are carried out at temperatures ranging 

from 200 " to 650 "F or higher. At times, rapid 

cooling of the cook is necessary to control the 

reaction or to control the composition of a parti- 

cular product. At approximately 350 "F, almost 

all of the solid or liquid materials begin to voli- 

tilize and emit vapors or gases from the vessel. 

As long as the ingredients are held at or above 

this temperature, the emissions continue. Some 

varnish cooking operations require 3 to 10 hours 

or longer. The quantity, composition, and rate 

of emissions depend upon ingredients in the cook, 

maximum temperature levels, method of intro- 

ducing additives, degree of stirring, cooking time, 

and extent of air or inert gas blowing (Stenburg, 

1958). Total emissions for oleoresinous varnish 

cooking can be as high as 6 to 12 percent by 

weight of the materials in the kettle, and those 

from oil cooking and blowing, 4 to 6 percent by 

weight. 

Cooker emissions vary in composition, depending 

upon the ingredients in the cook. Mattiello (1943) 

states that compounds emitted from cooking of 

oleoresinous varnish include water vapor, fatty 

acids, glycerine, acrolein, phenols, aldehydes, 

ketones, terpene oils, terpenes, and carbon diox- 

ide. Heat-bodying of oils causes the emission of 

these same compounds less the phenols, terpene 

oils, and terpenes. Gum running yields water 

vapor, fatty acids, terpenes, terpene oils, and 

tar. Besides the air contaminants listed by Mat- 

tiello, some highly offensive sulfur compounds 

such as hydrogen sulfide, allylsulfide, butyl mer- 

captan, and thiophene are formed when tall oil is 

esterified with glycerine and ~entaerythritol. 

These compounds are emitted as a result of small 

amounts of sulfur in the tall oil. Attempts to 

alleviate this problem involve further refining of 

the tall oil to remove as much sulfur as possible.

Of all the compounds emitted, acrolein is the one 

most generally associated with oil cooking because 

of its pungent, disagreeable odor and irritating 

characteristics. Some of the more odorous com- 

pounds have very low odor thresholds; acrolein, 

for example, has a threshold at 1.8 ppm and some 

of the sulfur compounds have a threshold at about 

0.001 ppm. 

A good portion of the emissions from these opera- 

tions are in the form of noncondensibles, insoluble 

gases or vapors, or condensible vapors which 

tend to form submicron size droplets. Emissions 

in the form of particulate matter have been found, 

upon examination under the microscope, to be in 

a size range between 2 and 20 microns in diame- 

ter. The median size of several samples varied 

from 8 to 10 microns. 

An important source of emissions is the thinning 

of varnish with solvent. In most of the newer 

stationary enclosed kettle installations, the 

cooked varnish is pumped from the reaction kettIe 

to a thinning tank that is equipped with an integral- 

ly mounted condenser. In the older portable open- 

kettle operations, however, the thinning operation 

is carried out near the boiling point of the solvent, 

and emissions of vapor can be considerable. Con- 

sequently, the thinning tank can be hooded and the 

vapors can be ducted to the same control system 

that removes the fumes from the cooker. While 

emission of solvents from the thinning tanks con- 

stitutes a greater potential for formation of photo- 

chemical smog than emissions from the varnish 

cooker, emissions from varnish cookers cause 

greater local nuisance problems because of nox- 

ious odors. Both operations result in the emis- 

sion of visible dense white plumes. 

HOODING AND VENTILATION REQUIREMENTS 

For air pollution control to succeed, all fumes 

emitted from the kettles and thinning vessels 

must be captured and conveyed to a control device 

under all operating conditions without hindering 

producti~n. 

Stationary closed kettle emission volumes are 

entirely dependent upon the type of operation per- 

formed, whether the kettle is sealed shut, oper- 

ated under partial vacuum, or merely vented with- 

out sealing so that air may be drawn into it and 

over its contents. Air volumes necessary to ex- 

haust open portable kettles are considerably 

reduced with properly designed close-fitting hoods. 

Sufficient air must continuously be swept through 

the open kettles so as to prevent the build up of 

explosive concentrations of the volatiles above 

the surface of the liquids within the kettle and in 

the exhaust ductwork. 

Figure 554 shows two open kettles in place over 


two open furnaces. The kettles are equipped with 

well designed removable hoods. The hoods are 

provided with openings for the manual addition of 

materials, for thermometers, and for agitators. 

The openings have hinged covers so that they can 

be kept closed except when being used. 

Indraft velocities of at least 100 to 150 fpm should 

be provided through the face of all the openings 

when the largest covered area is open to prevent 

the escape of contaminants from the kettle during 

charging or observation. Good hood design pro- 

vides the necessary indraft velocities when gas 

volumes of 100 to 300 cfm are exhausted from the 

kettle. Because the volatiles coming from a kettle 

condense on the hood, the hoods for open kettles 

should be provided with an outer trough to collect 

the condensed liquids whlch will appear on the 

hood surfaces. This trough should have provi- 

sions for drainage, usually to a small container. 

In the past, exhaust ductwork was sized for velo- 

cities of 1500 to 2000 fpm. Currently, ductwork 

frequently is designed for higher velocities, usual- 

ly 3000 to 3500 fpm. Higher velocities help reduce 

the rate of deposition of cond'ensed vapors on the 

duct walls. An exhaust gas blower in the exhaust 

system is necessary when venting open kettles. 

A blower also is required for closed kettles oper- 

ated at atmospheric conditions rather than under 

pressure or vacuum. When the air pollution con- 

trol system includes an afterburner, reliance upon 

the natural draft generated by its stack can be 

hazardous. Positive ventilation should be pro- 

vided to keep the vapor composition above the 

kettle below explosive limits and to maintain sd- 

ficient velocity in the exhaust system and at the 

entrance to the afterburner to prevent flashback. 

When the exhaust system includes an afterburner, 

the best placement of the exhaust blower is down- 

stream from the afterburner. If it is installed in 

front of the afterburner, serious maintenance and 

operating problems occur because deposits quickly 

build on the fan blades, resulting in unbalanced 

operation. With the blower on the discharge side 

of the afterburner, blower blades remain clean 

and in balance. Exhaust gases are cooled by dilu- 

tion with ambient air before entering the blower 

to a temperature of about 500 'F. Blowers of 

standard construction are available for operation 

at this temperature. 

The exhaust ductwork is subject to severe corro- 

sion and to heavy fouling. Use of appropriate 

corrosion-resistant material such as stainless 

steel will overcome most corrosion problems. 

Fouling problems require that the ductwork con- 

tain a number of sealed clean-out openings for 

access to the interior and that a regular cleaning 

schedule be maintained.


Figure 554. Open varnish-cooking kettles with exhaust hoods (Standard Brand Paints 

Company, Torrance, Calif.). 

Fouling has been reduced greatly or completely 

eliminated in some recent installations where the 

air pollution control device is an afterburner. In 

these installations, concentric type ductwork, 

with the outer duct insulated, has been used. A 

portion of the hot exhaust gas from the afterburn- 

er, after dilution to temperatures in the range of 

500" to 600 "F, is blown into the annular space 

between the inner and outer duct. The hot gas in 

the annular space heats the internal duct carry- 

ing the contaminated effluent from the kettles. 

The heated gases pass countercurrent to flow in 

the interior duct. The temperature of the wall of 

the duct carrying the contaminated effluent is 

raised, and condensation on the ductwork is 

limited. Condensation usually is restricted to 

low-viscosity liquids which may be carried along 

in the exhaust gas stream. The concentric duct- 

work is usually used only for the main section. 

Where dibasic acids, especially phthalic anhy- 

dride, are employed in the cooking operation, 

the concentric ductwork is extended to the ex- 

haust port on each kettle. Figure 555 illustrates 

one such exhaust system. Experience for 3 years 

with this system has demonstrated that cleaning 

of the duct has not been necessary. However, 

some provision for draining fluids from the duct 

should be included. Ln the installation illustrated, 

the downcomer duct to the afterburner is equipped 

with a well for fluid accumulation. The well has 

a removable cover, and it is cleaned after each 

week of operation. 

The cost of installing the concentric ductwork and 

its insulation adds approximately 150 percent to 

the cost of single ductwork. However, the reduc- 

tion of maintenance, the reduction of fire hazards, 

and the elimination of deposits inside the duct 

make the additional capital expenditure worthwhile. 


All operations in which varnish or paint base is 

cooked or in which drying oils are bodied or other- 

wise prepared by the application of heat should be 

vented to air pollution control devices. From 1 

to 5 percent or more of the total material charged 

to a kettle for these processes otherwise is emit- 

ted to the atmosphere during operation. The 

material emitted includes the odorous irritating 

compounds previously mentioned. In addition to 

odors, the emissions contain considerable parti- 

culate matter and frequently form a highly visible 

plume. The control devices applicable to varnish 

cooking are the same as those used for controlling 

other sources of organic vapors, particulates, 

odors, and visible emissions, with some modifi- 

cations to meet those situations unique to the var- 

nish cooking operations.

CONTAMINATED 

EXHAUST DUCT 

EXHAU TO AFTERBURNER 

BLOWE 


EXHAUST DUCT 

Figure 555. Varnish-cooking control system using heated concentric ductwork and an afterburner (Old Quaker 

Paint Co., Torrance. California). 

PHERE


Scrubbers 

Scrubbers, in the past, were the only devices 

installed to control emissions from varnish cook- 

ing. The inherent hazard of fire or explosion pre- 

vented serious consideration of afterburners. As 

the control of air pollution became more critical, 

direct-fired afterburners were chosen to comply 

with the more stringent regulations. For some 

processes, however, scrubbers still are adequate 

for controlling emissions of condensibles and are 

less costly to install and operate than afterburners. 

Sampling results (test 20, Table 192) for a spray 

scrubber venting a closed vessel producing alkyd 

modified varnish, illustrated in Figure 556, indi- 

cated that emissions from certain processes can 

be controlled sufficiently to meet stringent ernis- 

sion limitations. 

Many existing scrubbers have been left in place 

when afterburners were installed to serve as con- 

densers and to provide flashback protection before 

the contaminated emissions enter the afterburner. 

The various types of scrubbers which have been 

used include simple spray towers, sieve plate 

towers, chambers or columns with series of baf- 

fles and water curtains, agitated tanks, and water 

venturi jets. Scrubbers employing spray nozzles 

have suffered from a major disadvantage. The 

excessive maintenance required to keep the noz- 

zles free from clogging or to replace the nozzles 

because of erosion by recirculated scrubbing 

Table 192. SUMMARY OF RESULTS OF STACK DISCHARGE TESTS, VARNISH COOKING 

CONTROLLED BY AFTERBURNERSANDSCRUBBERS 

Itsm 

TOW proceaa time, hr 

Rots.. time of teat. 

hr 

Temperature of 

material. OF 

Teat No. 3 

Test No. 5 

1. Alkyd resin u=rnish Alkyd reeh vnrniah Heat body- 

2. Oleorealn varniah Two kettles ing oil 

Two - closed 

GO2 L~IOB. 

stage of procesa Heating to 

maldmum temperawre 

ExLaust volume. scfm 

Temperature of 

exhaust. OF 

Particulate loading. a 

grlecf 

Rate of particuloles. iblhr 

Organic acids, grlsci 

Aldehydes-ketone., p p 

Hydrocarbona, ppm 

Ait pollution control 

equipment 

Afterburner temperature, 

OF 

Total. 950 

Glycerine - fatty acid8 

Pentaerythrifol 

Phthalic anhydride 

Closed, gas fired 

N2 atmoa. 

106 147 

5.20 

0.174 

67 

I 

103 

3 spray towers 

vertical afterburner 

1200 to I240 

I 

Linseed 

oil 

ope. 

I 

Test No. 16 

Phenolic rcein varnish 

Linseed oil 

Phenolic resin 

Two. open 

rf 

Final f cook, f cooling 

i L 7 

Heating to mardmum 

temperature and 

cooling 

Sinale sorav in duct I Horizontal afterburner 

Teat No. 20 

Alkyd resin varninh 

Soy. chinasmod oils 

Glycerine 

Phthalic anhydride 

Closed 

N2 Ltmo.. . 

light vacvvm 

Major 

phthalic 

add. 

2bOf 

90 

I spray 

in stack 

Minor 

phthalic 

add. 

Organic acids, grlscf 1 0.066 1 None / . 1 . 1 0.15 / 0.082 

Efrlclcnolb 

*art>~"lates, % 

Chgmlc sclds. % 

Aldehydes-kctone., % 

Hydrocarbon#, % 

94 

48 

73 

99t 

.See Rule 2. in appendix. 

b 

&si. - reduction of total weight. 

'4ccur.q ~tmited to 10 ppm. 

d 

Wution air included. 

'hrulySi. of combustible gam. by CCLR method. Total ppm. 

'with ono md tao .toam let8 in stack. 

97.3 

99.9+ 

73 

85 

93 

94 

90d 

170

U 

GAS BURNER 

STEAM 

- 

F~gure 556. D~agram of a spray scrubber venting oleoresln 

rnanufacturlng equ~pment. Afterburners 

fluids has resulted in every scrubber of this type 

being taken out of service. Packed scrubbers 

have not been used in these operations because 

the condensed fumes rapidly plug the packing. 

1 

I 


WATER 

SEWER 

The scrubbers employed in these systems usually 

are designed with the flow of the contaminated gas 

stream countercurrent to that of the scrubbing 

medium. Generally, water is the scrubbing 

medium, and is not recirculated. Attempts have 

been made to use acids, bases, various oils, and 

solvents as scrubbing materials, but these scrub- 

bing solutions have not resulted in an increase in 

efficiency that would warrant their higher costs. 

Wetting agents have been added to scrubbing water, 

and in some special circumstances have resulted 

in increased collection efficiency. 

Condensers 

WATER 

Condensers have been used both to conserve sol- 

vent and to control visible emissions during the 

thinning operation. Varnish is thinned by the slow 

addition of the hot varnish to cold solvent or vice 

versa. Maximum solvent vaporization occurs 

during the initial contact between the solvent and 

hot varnish. Condensers must be designed to 

control the higher rate of emissions during the 

initial contact. When thinning vessels are vented 

directly to the atmosphere, loss of solvent, in the 

form of a dense white plume, is considerable. A 

condenser, usually a water-cooled shell-and-tube 

type, is mounted on the top of the thinning vessel 

vertically or at an angle so that the condensed sol- 

vent can drain back into the vessel. 

At one installation, a water -cooled shell-and-tube 

condenser having 52 square feet of transfer area 

and using copper tubes was mounted on a 350-gal- 

Ion hatch thinning tank. The condenser prevented 

visible emissions when 125 gallons of solvent was 

added to 195 gallons of varnish at 340 'F. The 

initial solvent flow rate was 7$ gallons per minute 

for 3f minutes: and the final flow rate was 12 gal- 

Ions per minute over an additional 14-minute 

period. 

Gas flow velocity from the condenser should be 

kept below 1000 fpm to minimize entrainment of 

condensate droplets. An entrainment separator 

should be installed on the discharge side of the 

condenser. The separator retains liquid particulates 

released during the initial high-volume surge 

of solvent vapors, which occurs when cold solvent 

and hot varnish first contact each other. Details 

on designing vapor condensers are given - in Chaater 

5 of this manual. 

Incineration of the effluent from varnish cooking 

processes has proved to be the most effective con- 

trol method and one relatively free of major main- 

tenance problems. Incineration has been effective 

for both open portable kettles and closed station- 

ary kettles. A direct-fired afterburner designed 

with appropriate parameters can reduce inlet odor 

concentration by 99 percent or more, and can 

oxidize 90 percent or more of the carbon in con- 

taminated effluent to carbon dioxide. Figures 555 

and 557 show two types of afterburners used to 

vent open kettle installations. Table 192 summar- 

izes results of stack tests conducted on direct- 

fired afterburners. 

In Los Angeles County, afterburners controlling 

emissions from varnish cookers have been pre- 

dominantly of the direct-fired type. Catalytic 

afterburners, however, are known to have been 

installed to control emissions from varnish cook- 

ers in other areas of the United States. Although 

a few catalytic units have been installed in the past 

in Los Angeles County, they have since been re- 

placed with direct-fired afterburners. 

One of the two most important design requirements 

for direct-fired afterburners is the capacity to 

operate at outlet temperatures of 1200" to 1400 "F 

under all conditions. When afterburner tempera- 

tures fall below 1200 "F. odor reduction is inade- 

quate and combustion efficiency for particulate 

matter and organic gases and vapors falls below 

90 percent an a carbon basis. The second impor- 

tant design requirement is the provision for direct 

flame contact with all vapors and gases emitted 

from the varnish cookers. Tests of afterburners, 

where direct flame contact of all the emissions 

did not occur, even with outlet temperatures of 

1400 'F and retention times greater than 0.3 

second, have revealed that combustion efficiencies 

for carbon have fallen well below 90 percent.


Figure 557. Direct-fired vertical afterburner (Great 

Western Paint Co., a division of Western Wood 

Preserving Co., Los Angeles, Calif.). 

A serious concern in venting varnish cookers and 

similar process equipment to an afterburner is 

the danger of flashback and fire. Where scrubbing 

equipment is used in the exhaust system prior to 

entry to the afterburner, this danger is usually 

overcome. Newer installations of afterburners 

on this type of equipment have not used a scrubber 

upstream from the afterburner. A short section 

of ductwork just prior to the entrance of the after- 

burner is designed so that the gases and vapors 

passing into this section are at a velocity consi- 

derably greater than the ilame propagation rate 

of the effluent gases in the reverse direction. 

Generally, flame propagation rates are 18 to 20 

fps, but the ductwork is designed for gas veloci- 

ties of about 50 fps. 

If there are considerable deposits inside the duct 

at the entrance to the afterburner, these deposits 

will start to burn after a lengthy afterburner oper- 

ation. Fire control dampers, when employed in 

the exhaust system ductwork, require constant 

maintenance and inspection if they are to be effec- 

tive. Several fires and explosions have been 

traced to failure of, or slow operation of, these 

devices. 

Heat-recovery equipment should be seriously con- 

sidered when an afterburner is used to control 

emissions. Heat exchangers can be installed so 

that the hot exhaust gases from the afterburner 

are cooled to below 600 "F by transferring waste 

heat to either Dowtherm, water (steam), or other 

heat-transfer media. The recovered heat then 

can be used in jacketed or coil-equipped kettles 

or in other plant process equipment. At a recent 

installation, a waste heat boiler utilizing the heat 

of the afterburner exhaust reduced fuel costs by 

supplying process steam in the plant. The payout 

time for the waste heat boiler is expected to be 

2 to 4 years. 

SULFURIC ACID MANUFACTURING 

Sulfuric acid is used as a basic raw material 

in an extremely wide range of industrial pro- 

cesses and manufacturing operations. Because 

of its widespread usage, sulfuric acid plants are 

scattered throughout the nation near every indus- 

trial complex. 

Basically, the production of sulfuric acid involves 

the generation of sulfur dioxide (SO2), its oxidation 

to sulfur trioxide (SO3), and the hydration of 

the SO3 to form sulfuric acid. The two main processes 

are the chamber process and the contact 

process. The chamber process uses the reduction 

of nitrogen dioxide to nitric oxide as the oxidizing 

mechanism to convert the SO2 to SO3 The 

contact process, using a catalyst to oxidize the 

SO2 to SO is the more modern and the more 

3 ' 

commonly encountered. For these reasons further 

discussion will be restricted to the contact 

process of sulfuric acid manufacture. 

CONTACT PROCESS 

A flow diagram of a "Type S" (sulfur-burning, 

hot-gas purification type) contact sulfuric acid 

plant is shown in Figure 558. Combustion air is 

drawn through a silencer, or a filter when the air 

is dust laden, by either a single-stage centrif- 

ugal blower or a positive-pressure-type blower. 

Since the blower is located on the upstream side, 

the entire plant is under a slight pressure, vary- 

ing from 1. 5 to 3. 0 psig. The combustion air 

is passed through a drying tower before it enters 

the sulfur burner. In the drying tower, moisture 

is removed from the air by countercurrent scrub- 

bing with 98 to 99 percent sulfuric acid at tem- 

peratures from 90" to 120°F. The drying tower 

has a topside internal-spray eliminator located 

just below the air outlet to minimize acid mist 

carryover to the sulfur burner.

WEAK hClO 

DRIlNG 

lDWER 

FILTERED AIR 

Molten sulfur is pumped to the burner where it 

is burned with the dried combustion air to form 

SO2. Normally a gas containing approximately 

9 percent SO2 is produced in a Type S plant. The 

combustion gases together with excess air leave 

the burner at about 1,600°F and are cooled to 

apprdximately 800°F in a water tube-type waste- 

heat boiler. The combustion gases then pass 

through a hot-gas filter into the first stage or 

"pass" of the catalytic converter at between 

750" and 800°F to begin the oxidation of the SO2 

to SO3. If the molten sulfur feed has been fil- 

tered at the start of the process, the hot-gas 

filter may be omitted. Because the conversion 

reaction is exothermic, the gas mixture from. 

the first stage of the converter is cooled in a 

smaller waste-heat boiler. Gas cooling after 

the second and third converter stages is achieved 

by steam superheaters. Gas leaving the fourth 

stage of the converter is partially cooled to ap- 

proximately 450 "F in an economizer. Further 

cooling takes place in the gas duct before the 

gas enters the absorber. The extent of cooling 

required depends largely upon whether or not 

oleum is to be produced. The total equivalent 

conversion from SO2 to SO3 in the four con- 

version stages is about 98 percent. Table 193 

shows typical temperatures and conversions 

at each stage of the four-stage converter. These 

figures vary somewhat with variations in gas 

composition, operating ra:e, and catalyst con- 

dition. 

The cooled SO3 combustion gas mixture enters 

the lower section of the absorbing tower, which 

is similar to the drying tower. The SO3 is ab- 

sorbed in a circulating stream of 99 percent 

sulfuric acid. The nonabsorbed tail gases pass 

overhead through mist removal equipment to 

the exit gas stack (Duecker and West, 1959). 

Sulfuric Acid Manufacturing 717 

MOLTEN 

SULFUR Ya"W>>w#:2:>>2.: 

A contact process plant intended mainly for use 

with various concentrations of hydrogen sulfide 

(H2S) as a feed material is known as a wet-gas 

Figure 558. ~ i o w diagram of a typical " Type S" 

sulfur-burning contact sulfuric acid pl.anf. 

~~~ .......... 

~~ .... 

WEAK IMPURE AClO 

Table 193. TEMPERATURES AND CONVERSIONS 

IN EACH STAGE OF A FOUR-STAGE CONVERTER 

FOR A "TYPE S" SULFUR-BURNING CONTACT 

SULFURIC ACLD PLANT 

Location of gas 

enter in^ 1st pass 

. 

1 

410 1 770 

Leaving 1st pass 601.8 1,115 

74.0 

Entering 2d pass 

Leaving 2d pass 

Entering 3d pass 

Leaving 3d pass 

Entering 4th pass 

Leaving 4th pass 

Total rise 

Temperatures, 

"C I "F 

t 

Equivalent 

conversion, 70 

plant, as shown in Figure 559. The wet-gas 

plant's combustion furnace is also used for burn- 

ing sulfur or dissociating spent sulfuric acid. A 

common procedure for wet-gas plants located near 

petroleum refineries is to burn simultaneously 

H2S, molten sulfur, and spent sulfuric acid from 

the alkylation processes at the refineries. In 

some instances a plant of this type may produce 

sulfuric acid by using only H2S or spent acid. 

In a wet-gas plant, the H2S gas, saturated with 

water vapor, is charged to the combustion fur- 

nace along with atmospheric air. The SO2 

formed, together with the other combustion 

products, is then cooled and treated for mist 

removal. Gas may be cooled by a waste-heat 

boiler or by a quench tower followed by Karhate 

and updraft coolers. Mist formed is removed


HYOROGEN SULFIDE 

HEAT EXCHANGERS 

STAGE 

CATALYTIC ABSORBER 

............... 

............... 

........... 

%AX ACID STRONG AClO 

CDMBUSTION 

CHAMBER 

820 

WASTE 

WEAK IMPURE 

C 

NEAT HUMIOIFYING MIST DRYING ACIO TO STORAGE 

BOILER TOWER PRECI PITAIOR TOWER 

Figure 559. Flow diagram of a contact-type wet-gas sulfuric acid plant. 

by an electrical precipitator. Moisture is re- Table 194. SULFUR TRIOXIDE AND SULFUR 

moved from the SO2 and airstream with con- DIOXIDE EMISSIONS FROM TWO ABSORBERS IN 

centrated sulfuric acid in a drying tower. A CONTACT SULFURIC ACID PLANTS 

centrifugal blower takes suction on the drying 

tower and discharges the dried SO2 and air to 

the converters. The balance of the wet-gas pro- 

cess is essentially the same as that of the pre- 

viously discussed sulfur-burning process. 


The only significant source of air contaminant 

discharge from a contact sulfuric acid plant 

is the tail gas discharge from the SO3 absorber. 

While these tail gases consist primarily of in- 

nocuous nitrogen, oxygen, and some carbon di- 

oxide, they also contain small concentrations 

of SO2 and smaller amounts of SO3 and sulfuric 

acid mist. Table 194 shows the SO2 and SO3 

discharged from two wet-gas sulfuric plant ab- 

sorbers. 

A well-designed contact process sulfuric acid 

plant operates at 90 to 95 percent conversion of 

the sulfur feed into product sulfuric acid. Thus 

a 250-ton-per-day plant can discharge 1.25 to 2.5 

tons of SO2 and SO3 per day. When present in 

sufficient concentration, SO2 is irritating to 

throat and nasal passages and injurious to vege- 

Gas flow rate, 

scfm 

Sulfur trioxide, 

grlscf 

70 by vol as SO2 

lblhr 

Sulfur dioxide, 

grlscf 

70 by vol 

Ib/hr 

Outlet of 

absorber No. 1 

9,600 

0.033 

0.002 

2.73 

2.63 

0.22 

216 

STACK 

Outlet of 

absorber No. 2 

7,200 

0.39 

2.4 

2.45 

151.2 

tation. SO2 concentrations greater than 0.25 ppm 

cause injury to plants on long exposure. The 

permissible limit for humans for prolonged ex- 

posure is 10 ppm. 

Tail gases that contain SO3, owing to incomplete 

absorption in the absorber stack, hydrate and 

form a finely divided mist upon contact with at- 

mospheric moisture. According to Fairlie 

(1936) the process temperature of gas going to 

the absorber should be on the lower side of a 

temperature range between 150" and 230°C.

The optimum acid concentration in the absorb- 

ing tower is 98.5 percent. This concentration 

has the lowest SO3 vapor pressure. The partial 

pressure of SO3 increases if the absorbing acid 

is too strong, and SO3 passes out with the tail 

gases. If a concentration of absorbing acid 

less than 98.5 percent is used, the beta phase 

of SO3, which is less easlly absorbed, is pro- 

duced. A mist may also form when the pro- 

cess gases are cooled before final absorption, 

as in the manufacture of oleum. 

Water-based mists can form as a result of the 

presence of water vapor in the process gases fed 

to the converter. This condition is often caused 

by poor performance of the drying tower. Effi- 

cient performance should result in a moisture 

loading of 5 milligrams or less per cubic foot. 

In sulfur-burning plants, mists may be formed 

from water resulting from the combustion of 

hydrocarbon impurities in the sul


SO2 concentrations resulting from acid plant 

startups and upsets could be handled adequately 

by a system such as this. 

Table 195. SULFUR TRIOXIDE AND SULFUR 

DIOXIDE EMISSIONS FROM A TWO-STAGE 

ELECTRICAL PRECIPITATOR SERVLNG 

Acid Mist Removal 

A CONTACT SULFURIC ACID PLANT 

Electrical precipitators 

Inlet of 

precipitator 

Outlet of 

prec~pitator 

Electrical precipitators are widely used for re- Gas flow rate, scfm 13,400 13,100 

moval of sulfuric acid mist from the cold SO2 

Gas temperature, "F 

160 80 

gas stream of wet-purification systems. The 

wet-lead-tube type is used extensively in this 

service. 

Average gas velocity, fps 

Collection efficiency, a 70 

Moisture in gas, % 

GOZ, 70 (stack conditions) 

36. 5 

0.8 

5.9 

20. 6 

93 

4.1 

6 

Tube-type precipitators have also been used for 

treating tail gases from SO3 absorber towers. 

More recently, however, two-stage, plate-type 

02, %(stack conditions) 

CO, 70 (stack conditions) 

N2. % (stack conditions) 

Sulfur trioxide, 

9.6 

0 

83.4 

8.4 

0 

81.2 

precipitators have been used successfully. One grlscf 

0.062 0.0048 

such unit, lead lined throughout to prevent corro- lhlhr 

7. 1 0.54 

sion, is designed to handle approximately 20, 000 %by volume 

0.0042 0.00032 

cfm tail gas from a 300-ton-per-day contact 

sulfuric acid plant. This wet-gas plant processes 

H7S, - sulfur, and spent alkylation acid. Dry 

gas containing SO2, carbon dioxide, oxygen, 

nitrogen, and 5 to 10 milligrams of acid mist 

per cubic foot enters two inlet ducts to the precipitator. 

The gas flows upward through distribution 

tiles to the humidifying section. This 

section contains 5 feet of 3-inch single-spiral 

Sulfur dioxide, 

grlscf 

4. 1 4.1 

lblhr 

470 460 

70 by volume 

0.345 0.345" 

aA mechanical rectifier was supplying only 36, 000 

volts to the precipitator. During normal operation, 

silicon rectifiers suIjply 75,000 volts to the electrode 

wires. This should increase the acid mist collection 

efficiencv appreciablv. 

. -- 

h~ule 53. 1 for "scavenger plants'' is applicable to 

tile irrigated by 800 gpm weak sulfuric acid. this plant rather than Rule 53a, which limits ernis- 

The conditioned gas then flows to the ionizing 

sions of SO2 to 0. 2 percent by volume. This plant 

section, which consists of about 75 grounded 

recovers SO2 that would otherwise be emitted to the 

curtain electrodes and 100 electrode wire ex- 

atmosphere. 

tensions. 

mechanical rectifier was, however, supplying 

only 36, 000 volts to the precipitator during this 

test. During normal operation, silicon rectifiers 

supply 75, 000 volts to the electrode wires. 

Ionized gas then flows to the precipitator section 

where charged acid particles migrate to the col- 

lector plate electrodes. There are twelve 14- 

by 14-foot lead plates and 375 electrode wires. 

The negative wire voltage is 75, 000. Acid mi- 

grating to the plates flows down through the pre- 

cipitator and is collected in the humidifying sec- 

tion. The gas from the precipitator section flows 

to a 5-foot-diameter, lead-lined stack that dis- 

charges to the atmosphere 150 feet above grade. 

The high-voltage electrode wires are suspended 

vertically by three sets of insulators. Horizontal 

motion is eliminated by four diagonally placed in- 

sulators, which are isolated from the gas stream 

by oil seals. All structural material in contact 

with the acid mist is lead clad. Electrical wires 

are stainless steel cores with lead cladding. Volt- 

age ia supplied from a generator with a maximum 

capacity of 30 kilovolt-amperes. A battery of 

silicon rectifiers supplies 75, 000 volts of direct 

current to the electrode wires. 

Table 195 shows the sulfur trioxide and sulfur 

dioxide emissions from the previously described 

two-stage electrical precipitator. The acid mist 

collection efficiency was only 93 percent. A 

Packed-bed separators 

Packed-bed separators employ sand, coke, or 

glass or metal fibers to intercept acid mist par- 

ticles. The packing also causes the particles to 

coalesce by reason of high turbulence in the small 

spaces between packing. Moderate-sized particles 

of mist have been effectively removed in a 12-inch- 

deep bed of l-inch Berl saddles with gas veloc- 

ities of approximately 10 fps. 

Glass fiber filters have not been very effective 

in mist removal because of a tendency on the 

part of the fiber to sag and mat. Nevertheless, 

experimental reports by Fairs (1958) on acid 

mist removal by silicone-treated glass wool are 

encouraging. A special fine-glass wool with a 

fiber diameter between 5 and 30 microns was 

used. The coarser fibers allowed adequate pene 

tration of the bed by the mist particles to ensure 

a reasonable long life and ~rovided sufficient 

support for the finer fibers in their trapping of 

the small acid mist particles.

The glass wool was treated by compressing it 

into a filter 2 inches thick to a density of 10 

pounds per cubic foot. It was then placed in 

a sheet metal container and heated at 500°C 

for 1 hour. By this treatment, the stresses 

in the compressed fibers were relieved, and 

the fiber mass could be removed from the mold 

without losing shape or compression. The 

fibers were then treated with a solution of meth- 

yl cblorosilane. 

The threshold concentration for mist visibility 

after scrubbing has been found experimentally 

by Fairs (1958) to be about 3.6 x gram 

SO3 per cubic foot. The discharge gases from 

the silicone-treated filter had an SO3 concen- 

tration of 1. 8 to 2. 5 x 10-4 gram per cubic 

foot and no appreciable acid mist plume. A 

faint plume became perceptible at approximate- 

ly weekly intervals but was eliminated by flush- 

ing the filter bed with water. The average tail 

gas-filtering rate for the treated filter was 

15. 6 cfm per square foot of filtering area for 

a pressure drop of 9-112 to 10 inches water 

column. According to Fairs, the effective 

life of the silicone fiber should be at least 

5,000 hours. Garnetted terylene was also 

used but was not as efficient as silicone-treated 

glass wool. It should, however, prove ade- 

quate for less stringent duties. Its life should 

be long since it does not require silicone pre- 

treatment. The use of untreated glass wool 

fiber proved unsatisfactory in reducing the 

opacity of the acid mist plume. 

Table 196 shows the SO2 and acid mist emis- 

sions from the outlet of a typical silicone- 

treated, glass fiber mist eliminator. This 

control unit processes absorber discharge gas 

from a contact sulfuric acid plant. The acid 

mist collection efficiency for the fiber glass 

mist eliminator was 98. 9 percent. A success- 

ful application of a mist eliminator using treat- 

Table 196. EMISSIONS OF SULFUR DIOXIDE 

AND ACID MIST FROM THE OUTLET OF 

A SILICONE-TREATED, GLASS FIBER MIST 

ELIMINATOR SERVING A CONTACT 

SULFURIC ACID PLANT 

Mist 

I inlet I 

Concentration, . - erlscf 0.035 

Concentration, ppm 

ZOO 

25 

Weight, lhlhr 

45 

0.5 

Collection efficiency, 70 I 98.9 

Gas 

1 

flow rate, scfm 

Avg gas velocity, fps 

Gas temoerature. ~F 

Sulfuric Acid Manufacturing 721 

1,300 

160 

ed fiber (Figure 560) bas been made by the 

Monsanto Chemical Company (Brink, 1959). 

exact treatment given to the fiber is not available 

since it is the property of the inventor, J. A. 

Brink, Jr. 

FIBER PRCKING 

Figure 560. Brink fiber mist eliminator (Brink, 

1959). 

Wire mesh mist eliminators 

Wire mesh mist eliminators are usually con- 

structed in two stages. The lower stage of 

wire mesh may have a bulk density of about 

14 pounds per cubic foot, while the upper stage 

is less dense. The two stages are separated 

by several feet in a vertical duct. The high- 

density lower stage acts as a coalescer. The 

reentrained coalesced particles are removed 

in the upper stage. Typical gas velocities for 

these units range from 11 to 18 fps. The kinet- 

ic energy of the mist particle is apparently too 

low to promote coalescence at velocities less 

than 11 fps, and reentrainment becomes a 

problem at velocities greater than 18 fps. The 

tail gas pressure drop through a wire mesh 

mist installation is approximately 3 inches 

water column.


Exit sulfuric acid mist loadings of less than 5 

milligrams per cubic foot of gas are normally 

obtained from wire mesh units serving plants 

making 98 percent acid. No type of mechan- 

ical coalescer, however, has satisfactorily 

controlled acid mists from oleum-producing 

plants. Corrosion possibilities from concen- 

trated sulfuric acid must be considered in se- 

lecting wire mesh material. The initial cost of 

wire mesh equipment is modest. The value of 

recovered sulfuric acid is usually sufficient to 

pay the first investment in 1 or 2 years (Duecker 

and West, 1959). 

Ceramic filters 

Porous ceramic filter tubes have proved success- 

ful in removing acid mist. The filter tubes are 

usually several feet in length and several inches 

in diameter with a wall thickness of about 318 inch. 

The tubes are mounted in a horizontal tube sheet, 

with the tops open and the bottoms closed. The 

tail gases flow downward into the tubes and pass 

out through porous walls. Appreciably more fil- 

tering area is required for the ceramic filter 

than for the wire mesh type. The porous ceramic 

filter is composed of small particles of alumina 

or similar refractory material fused with a binder. 

The maintenance costs for ceramic tubes is con- 

siderably higher than those for wire mesh filters 

because of tube breakage. Initial installation 

costs are also considerably higher than those for 

wire mesh. A pressure drop of 8 to 10 inches 

water column is required to effect mist removal 

equivalent to that of a wire mesh filter. Thus, 

operating costs would also be appreciable (Duecker 

and West, 1959). 

Sonic agglomeration 

The principle of sonic agglomeration is also 

used to remove acid particles from waste-gas 

streams. Sound waves cause smaller particles 

in an aerosol to vibrate and thereby coalesce 

into larger particles. Conventional cyclone sep- 

arators can then be used for removal of these 

larger particles. One installation treating exit 

stack gases from a contact acid plant has been 

reported to remove 90 percent by weight of acid 

in the gas stream. The tail gases leaving the 

sonic collector contained 2 to 3 milligrams of 

100 percent sulfuric acid mist per cubic foot. A 

nuisance factor must be taken into consideration, 

however, since some of the sound frequencies 

are in the audible range (Duecker and West, 1959). 

5 microns in size. A considerable amount of 

the larger size acid mist particles may he re- 

moved; however, the visibility of the stack 

plume is not greatly affected, since the smallest 

particle size contributes most to visibility. Vane- 

type separators operate at relatively high gas 

velocities and thus make better use of the parti- 

cles' kinetic energy. They have been found to be 

moderately effective for contact plants having 

wet-purification systems in reducing stack plume 

opacities (Duecker and West, 1959). 

SULFUR SCAVENGER PLANTS 

INTRODUCTION 

A sulfur scavenger plant scavenges elemental 

sulfur from the waste gases and fuel gases pro- 

duced in an oil refinery. Elemental sulfur has a 

wide variety of industrial uses and the amount of 

sulfur produced by scavenger plants is becoming 

increasingly important. As the demand for sul- 

fur increases and as natural sulfur deposits are 

depleted or their recovery becomes uneconomical, 

the price of sulfur will rise. Accordingly, the 

'recovery of sulfur from refinery gases containing 

high concentrations of hydrogen sulfide (H2S) 

becomes increasingly economical. From an air 

pollution standpoint, the vital function of the sul- 

fur scavenger plant is to prevent or reduce the 

emission of sulfur compounds to the atmosphere. 

SULFUR IN CRUDE OIL 

A11 crude oils contain sulfur and sulfur compounds 

in widely varying amounts. Some crudes contain 

as little as 0.1 percent while others contain 5.0 

percent or more, with most crudes having between 

1 and 2 percent by weight of sulfur and sulfur com- 

pounds. It is beneficial to refinery operations to 

remove the sulfur compounds because of their 

deleterious effects. The major effects are illus- 

trated in Table 197. 

In a variety of crude oil refining processes, most 

of the sulfur and sulfur compounds in the original 

crude oil are converted to H2S. This H2S gas is 

contained in the overhead off-gas streams from 

these processes and, after separation of ~roduct 

gas fractions, remains in the final waste gases 

which usually are used as fuel in refinery heaters. 

The burning of these gases results in large quanti- 

ties of sulfur dioxide (SO2) being formed and emit- 1 

Miscellaneous devices ted from the heater stacks. To reduce emissions 

Simple baffles and cyclone separators are not 

of SO2 from this source, it is necessary to remove 

as much H2S as possible from these gases 

effective in collecting particles smaller than before they are used as heater fuel.

Sulfur Scavenger Plants 721 

Table 197. EFFECT OF SULFUR COMPOUNDS DURING REFINING 

Purpose Primary Effect of contaminant 

contaminants 

Reduce Mercaptans Offensive product odors 0. 002% max. tolerable con- 

odor centration 

Reduce 

corrosion 

Reduce oper- 

ational pro- 

blems 

Improve 

gasoline octane 

Avoid catalyst 

poisoning 

Elemental S Attacks iron, copper, etc., forming sulfides 

Hzs Attacks zinc, copper, iron 

Mercaptans Mildly corrosive 

1 Corrosion compounds 

I 

H2S 

Iron sulfide 

Sulfur compounds 

Improve color, Disulfides 

reduce gum 

I 

Thiophenol 

(mercaptan) 

Plug exchangers, collect on fractionator trays; 

spontaneous combustion during cleanout 

Highly toxic (dangerous during cleanout) 

Foaming in amine systems (reduced efficiency) 

Foaming in caustic wash systems 

Oxidation (in simlight) to form acids and haze in gas- 

oline~ 

Catalyst in gum formation reactions 

Disulfides In the listed order of severity, sulfur compounds 

Sulfides reduce the effectiveness of TEL in raising octane 

Thiophene ratings 

Elemental S In reforming operations, sulfur compounds are con- 

Sulfur compounds verted to H2S which may react with catalyst to form 

sulfides 

Extend lube Sulfur in gasoline Sulfur compounds formed during combustion drastic- 

oil life ally reduce lube oil life 

REMOVAL OF H2S FROM REFINERY WASTE GASES RNHZ H2S G RNH3HS 

There are numerous methods by which H2S can be 

separated from hydrocarbon gas streams, and 

other methods are in the development stage. The 

three methods which are in common use in the 

petroleum industry are illustrated in Table 198. 

As noted in the table, the iron-sponge process is 

not practical for large gas streams or gas streams 

with a high H2S content. This process is used 

most commonly in desulfurizing natural gas 

streams, and the carbonate or amine absorption 

processes are used most commonly in petroleum 

refinery operations. Of the latter two processes, 

the amine is the most popular since refinery waste 

gases generally have H2S concentrations well 

suited to this process, and a greater removal effi- 

ciency is obtained than by the carbonate process. 

Both DEA (diethanolomine) and MEA (monoethano- 

lamine) are used, with DEA being preferred since 

chemical degradation and make-up rates are lower. 

Amine solutions will absorb both HzS and CO2 

according to the following reactions: 

Absorption of H2S occurs at 100 O F or below, and 

rejection of sulfide is active at 240 "F. The amine 

desulfurization process, therefore, involves con- 

tacting the sour (sulfur bearing) gas stream with 

a cool amine solution to absorb the H2S and then 

regenerating the amine and stripping the H2S from 

the amine solution by heating. A typical amine 

H2S removal system is shown in Figure 561. 

The treated gas leaving the amine desulfuriaation 

process will be used as refinery fuel or be burned 

in a flare. It is necessary, therefore, to ensure 

proper capacity and funcdoning of the amine sys- 

tem. The efficiency of an operating amine system 

can readily be determined by laboratory analysis 

of the sour inlet gas, treated outlet gas, and acid 

outlet gas streams. It may also be necessary to 

verify the adequacy of a proposed new amine sys- 

tem, and the following parameters may be used 

for this purpose:


Progress 

Iron sponge 

Hot potassium 

carbonate 

Arnine 

(MEA or DEA) 

Table 198. REMOVAL OF H2S FROM REFINERY GAS 

I Gas to be 

treated 

I process 

stages 

Advantages 

of method 

1. Low gas volume 

2. Low H2S content 

1. High volume 

2. Very sour gas 

(5 to 50% H2S) 

1. High volume 

2. Low or intermediate 

H2S content 

COOL WATER 

I I 

1. Reaction to 

2. Revivification 

or 

3. Repacking 

1. Absorption 

2. Regeneration 

by decrease in 

pressure 

1. Absorption 

2. Regeneration 

by heat striping 

I 

1. Low initial cost 

2. High efficiency 

for gas streams 

with low H2S content 

1. Will reduce H2S 

to less than 0.1% in 

very sour gas streams 

2. Extensive heat exchange 

equipment not 

required 

3. Absorbent (K2CO3) 

does not decrade 

readily. 

1. Will reduce H2S 

to less than 1 grain 

I100 ft3 in sour gas 

stream 

2. DEA preferred over 

MEA due to degradation 

of MEA by carbonyl 

sulfide and carbon 

disulfide in gas stream 

1. Actual H2S/DEA ratio versus H2SIDEA 

equilibrium ratio 

2. corrosion limitation 

3. absorber column sizing. 

Figure 561. Amine desulfurization process. standard parameters. 

The following example illustrates the calculations 

used in verifying the adequacy of a proposed 

amine (DEA) desulfurization system: 

Given: 

Total sour gas feed, scf/day 

= 20x106 

Specific gravity of sour gas = 0.8 

H2S in sour gas feed, weight % = 2.5 

DEA solution circulation rate, gal. /min 1.160 

DEA concentration, % = 20 

Absorber temperature, O F =lo0 

Absorber pressure, psig =I20 

Absorber diameter, feet = 5.0 

Absorber tray spacing, feet = 2.0 

Problem: 

Verify performance of proposed system against


Solution: H2S IDEA (actual) = 

1. Actual H2S/DEA ratio: 1907 lb Hzs 

2. 5% 20 x lo6 scf/day 

Total H2S in feed = -- 

100 24 hrlday 2. Corrosion limitation: 

1 

x - 1870 lblhr Total H2S = 

1 14 f b 

= 0. 109 

17,500 lb DEA - (OK) 

1907 lbIhr = 56. 0 mol/hr 

34 lb/mol 

Total H2S in DEA (based on 98% regeneration) 

Total DEA = 17' 500 lbIhr - 166.5 mol/hr 

= (1870)(0. 02) = 21 1b/hr 105.1 lblmol 

Total H2S to absorber = 1907 lb/hr 

Total DEA flow (20% solution) = (160 gallmin) 

x (60 minlhr) = 9600 gallhr 

H2S/DEA ratio (maximum recommended) = 

mol 

0. 4 - mol 

20% DEA = 1920 gallhr 

H2S DEA ratio (actual) = -- 56 0.336 (OK) 

166.5 - -- 

80% Hz0 = 7680 gallhr 

3. Absorber column sizing: 

Total DEA flow = (1920 gal/hr)(9.09 lblgal) + 

. Experience has shown that a satisfactory 

absorber tower cross-sectional area may be 

(7680 gal/hr)(8. 34 lblgal) derived from the following equation (Connors, 

1958): 

HzSIDEA ratio = - x 100 = 2. 34% (by 

81,500 

weight) 

Partial pressure H2S = (120 psi + 14. 7 psi*) 

x (760 mm Hgl14.7 psi) x (2. 34%/100) = 

163 mm Hg 

lb H2S 

HzSIDEA equilibrium = 0. 23 - 

lb DEA 

(from Figure 562) 

HzS PRESSURE, mm.Hg (GAS PHASE) 

Figure 562. Equilibrium plats of H2S in 20% DEA 

aqueous solution. 

*Atmospheric pressure. 

where 

A = absorber cross-sectional area, ft2 

B =Brown tray spacing factor 

(24 in. ) = 0. 82 

C = Barton plate correction 

factor (120 psig) = 1. 56 

D = specific gravity of sour gas = 0. 80 

K : specific gravity of liquid 

PEA) = 1. 09 

P = gas pressure, psia = 134.7 

Q = acid gas volume, lo6 scflday = 20. 0 

T = temperature, 'R = 560 

Required absorber diameter, Dr = (23.35)* 

- 

= 4. 83 ft 

- 

Actual absorber diameter, Da = 5.0 ft (OK)



The acid gas stream from typical refinery amine 

(or potassium carbonate) units will contain we11 

over 95 percent acid gas (HZS and carbon dioxide). 

I£ desired, there are processes for selective re- 

moval of the C02 from the acid gas, but this is 

not essential for processing the gas. The remain- 

der of the stream will be largely hydrocarbons, 

with small amounts of carried-over amine. With- 

out air pollution control equipment, this highly 

toxic and undesirable gas stream would have to be 

burned to convert the H2S to SO2, which is less 

toxic but also highly undesirable. Air pollution 

control equipment is required, therefore, for 

reduction of H2S emission to the atmosphere with- 

out a corresponding substitution of SO2 emission. 

This may be done by conversion of H2S to elemen- 

tal sulfur. 

AIR POLLUTION CONTROL EQUIPMENT 

There are numerous processes by which H2S 

can be removed from hydrocarbon gas streams 

by conversion to free sulfur, but these are pri- 

marily natural gas purification processes. The 

sulfur scavenger plant, however, serves solely 

to produce free sulfur from EZS streams which 

have been removed from hydrocarbon streams by 

other (amine, etc.) methods. The standard sulfur 

scavenger plant is based on the Claus process 

which involves oxidation of one-third of the H2S 

to SO2 and then catalytically reacting the remain- 

ing H2S with the SO2 to form water and free sul- 

fur: 

and 

The second (catalyzed) reaction usually is accom- 

plished in two stages, but more recently, three 

stages are being used for more complete conver- 

sion. Final off-gas is incinerated to prevent un- 

reacted HZS from being emitted into the atmos- 

phere. This results in some SO2 emission, al- 

though only a fraction of that which would have 

been emitted upon combustion of all the HZS. 

A variation of the basic Claus (split-stream) pro- 

cess is the partial-combustion process wherein 

the acid gas stream is partially oxidized by con- 

trolling the supply of air. The reaction gas is 

cooled to condense sulfur vapors and comingled 

with air and a slip-stream of acid gas, which are 

burned "in-line" so as to reheat the mixture be- 

fore it is passed to the first converter. This 

reaction gas is again cooled to condense sulfur 

vapors before being reheated by "in-line" com- 

bustion of additional slip-stream acid gas and 

being passed to the second catalytic converter. 

Again, the reaction gas is cooled for condensation 

of sulfur and then passed to a coalescer for 

removal of the remaining sulfur mist before being 

incinerated. All condensed sulfur drains to mol- 

ten sulfur storage, from which it may be pumped 

out and shipped in the molten state or may be 

solidified, by cooling in vats or blocks, for han- 

dling in the solid state. The basic split-stream 

process is illustrated in Figure 563, and the 

more commonly used partial-oxidation process 

is illustrated in Figure 564. 

However high the efficiency of a scavenger 

,$ant, the plant will be a source of SO2 air pol- 

lutlon slnce remaining sulfur compounds in the 

final vent gas will be incinerated to SO2 and then 

discharged through a stack to the atmosphere. 

Operation of the scavenger plant, however, re- 

duces the amount of SO2 emission in proportion 

to the amount of sulfur which is recovered, and 

this reduces overall emission of pollutants. In 

Los Angeles County. APCD Rule 53. 1 specifies 

that the scavenger plant must "substantially" 

reduce the amount of pollutants which would 

otherwise be emitted. In practice, a well- 

designed and properly operated scavenger plant 

can be expected to recover more than 90 percent 

of the sulfur contained in the acid gas feed. The 

criterion for evaluating scavenger plants has, 

therefore, been the achievement of a recovery 

efficiency of 90 percent or greater. Even at 

satisfactory plant efficiency, however, the SO2 

concentration in incinerated flue gas may exceed 

allowable limits and it may, therefore, be neces- 

sary to add dilution air to the incinerated gas 

(see Figures 563 and 564) before discharge to the 

atmosphere. 

The efficiency of an operating scavenger plant 

may be determined by methods similar to that 

illustrated by the following example: 

Given: 

Test period, hours 

- 24 

Total feed gas volume, scf = 600,000 

Feed gas composition: 

H2S, mol 70 - 65. 0 

Hydrocarbons, mol 70 - 2.0 

Sulfur produced, short tons = 15. 0 

Problem: 

Calculate efficiency of sulfur recovery.

ACID GAS 

I I 


2/3 STREAM FLUE GAS 

1/3 STREAM 

OXIDATION 

AIR BLOWER 

STEAM 

OXIDATION UNIT AND 

WASTE HEAT BOILER 

NO 1 

F~gure 563. Sulfur scavenger plant using the spllt-stream process (Giusti, 1965). 

Solution: 4. reheater 2: in-line combustion (or other 

1. Available sulfur in feed - gas 

means) to reheat gases to 450 "F 

5. converters 1 and 2: each to have sufficient 

600, 000 ft3 

379 ft3/mol 

0. 65 32 lblrnol 

2000 lb/ton 

= 16.45 tons 

bauxite catalyst that the 

ratio of H7S flow (cfs) to 

catalyst volume (f't3) does 

2. Sulfur recoyery efficiency not exceed 2:l. 

15. 0 tons x 100 = 91. 2% 

16. 45 tons 

In addition to supplying the correct amount of 

oxygen (air) to permit conversion reactions to 

take place, optimum operating conditions also 

must be maintained. The waste beat boiler, cool- 

ers, reheaters, and converters must be sized and 

operated to achieve conditions approximating 

those shown below: 

1. Waste heat boiler: boiler feed water to cool 

reaction gases Lo 450 "F 

2. coolers 1, 2, and 3: each to have capacity to 

cool gases to 300 "F 

3. reheater 1: in-line combustion (or other 

means) to reheat gases to 475 "F 

The above conditions can be achieved by various 

combinations of vessel sizing and/or flow rates 

and need not be further illustrated. 

Incineration Requirements 

Even in an efficient scavenger plant, a portion of 

the H2S in the acid gas is unreacted and passes 

through the plant. The final vent gas is composed 

of the products of reaction (other than recovered 

sulfur) and the inert nitrogen contained in the air 

used for supply of reaction oxygen, plus the com- 

ponents of the feed stream which do not take part 

in the conversion reactions and the unreacted H2S. 

Because of the remaining HZS, this vent gas must 

be incinerated to convert the H2S to SO2 before 

the vent gas is discharged to the atmosphere. 

Although the oxidation of H2S is exothermic, it 

may be necessary to supply additional heat at the


SLIP STREW" 

STEAM 

If If 

"3 

4 

LI) 

- m 

0 

4 

WASTE HEAT 

BOILER - AIR 

4 

AIR 

L 

I 

2 % 

C 

"7 

- Z 

4 

I 

OXIDATION 

- 

UNIT 

CONDENSER 

OXIDATION MOLTEN ! 

AIR BLOWER AIR FUEL GAS SULFUR -. I 

DILUTION 

AIR 

STORAGE 

PIT 

F~gure 564 Sulfur scavenger plant uslng the partlal ox~dat~on process (Giustl, 1965) 

incinerator in order to maintain incineration tem- 

perature for the total vent gas stream. Determina- 

tion of incineration requirements is illustrated by 

the following example for a scavenger plant simi- 

lar to that shown in Figure 563 and for the same 

feed stream used in the preceding example. All 

data are for a 24-hour period. 

Given: 

Feed composition: 

Total feed, scf = 600,000 

H2S, mol % 

- 65 

CO2, mol % 

- 3 3 

CH4, mol 70 

- 1.5 

CzH6, mol % 

- - 

Sulfur recovery efficiency, 70 = 91. 2 

Free sulfur carry-over (0. l%), lb = 30. 0 

Final vent gas temperature. "F = 320 

Problem A: 

Determine quantities of unreacted products pass- 

ing through the unit to the incinerator. 

Solution: 

1. Weight of unreacted H2S 

H 2 S - 100 - 91.2 = 8.8% 

- 0.5 = 3.77 mol/hr 

- 

\


2. Weight of unreacted GO2 6. Reaction quantities for hydrocarbon oxidation : 

Problem B: 

Using basic reaction formulas, determine quantities 

of reaction products from oxidation of both 

H2S and hydrocarbons. 

Solution: 

0.79N2 

N2 = 3.14 mollhr x = 11. 8 mollhr 

0.2102 - 

GO2 = l(0. 99) f 2(0. 33) = 1. 65 mol/hr 

HzO= 2(0. 99) t 3(0. 33) = 2.molIhr 

7. Total reaction products (other than sulfur): 

-- 

1. Basic reaction formulas for conversion of H2S: from 3 from 6 

HzS 

3 

- 02 -SO2 

2 

i Hz0 

H20 = 60.1 t 2.97 = 63. mollhr 

3 

3HZS + - 02- 

2 

2. Weight of reacted H2S : 

3S t 3H20 Problem C: 

Determine quantity of free sulfur carry-over. 

Solution: 

1. Weight of sulfur carrv-over 

= 60.1 mollhr 

15.0 tons (0.001)~2000 

S2 = lblton 

3. Weight of H2S reaction products (other than 

- 

sulfur) : 

24 hr x 64 lb/mol 

= 0.02 mollhr 

Oxidation of H2S to SO2 is rapid and essentially 

3 mol 

HO-- x 60.1 mollhr = 60.1 mol/hr 

2 - 3 mol 

complete at temperatures over 1050 "F, provided 

there is adequate air supply and mixing. For 

given operating conditions, additional fuel gas and 

air requirements may be determined and effectiveness 

of incineration may be verified. 

4. Reaction formulas for oxidation of 

hydrocarbons : 

CH4 t 202-C02 + 2H20 

7 

I CZH6 + 02- 2C02 i 3H20 

I 

5. Weight of hydrocarbons in feed stream: 

i = 0. 99 mollhr 

i 

= 0. mollhr 

Given: 

Vent gas temperature, "R = 320 t 460 = 780 

Incineration pressure, psia = 14.7 

Proposed incineration temperature. "R = 1700 

Excess air to be supplied, % = 25 

Dimensions of incinerator chamber = 4 ft diam 

x 8 it long 

Heat value (refinery gas), ~tu/ft~ = 800 

Temperature refinery gas and air, "F = 100 

Problem D: 

Determine air required for incineration of vent 

gas stream.


Solution: COz=21.70 + 1.65 = 23.35 mollhr 

Composition, 

mol/hr Oxidation reaction 

3 

H2S = 3.77 HZS + - 02 -SOZ + H20 

2 

GO2= 23.35 C02 C02 

N2 = 113. 0 (from reaction) = 113.00 mol/hr 

N2 = 21.45 (from 

incineration) = 21.45mollhr 

Air = 6.78 (excess, from 

incineration) = 6.78 mollhr 

H20= 63.07 H20 Hzo 2. Total heat required 

Hi (at initial 

N2 = 

124. 80 

215. Oi2 N2 

SO2 

H2(1700 'F) - temperature) = Btulmol 

25,350 16,200 (780 "R) 9,150 

1. Theoretical O2 required 

3 

02 = 2(0. 02) + $3.77) = 5.70 mollhr 

2. Amount N2 for required 02 

79% 

N = 5.70 x - = 21.45 mollhr 

2 21% 

3. Excess air for 25% excess 

Air = 0. 25 

Problem E: 

(5' 70 

(0.21) 

= 6. 78 mol/hr 

Determine heat evolved from incineration of vent 

gases. 

Solution: Heat 

value, 

mollhr x lb/mol x Btullb = Btulhr 

---- 

S2 0.02 64 3.984 5.100 

HZ 3.77 2 51,593 389,000 

S 3.77 3 2 3,984 480,500 

Total evolved heat 874,600 

Problem F: 

Calculate heat required to raise other (reacted) 

vent gases from 320 "F to 1240 "F. 

Solution: 

1. Total vent gases, after oxidation of comhustibles 

(from quantities in Problems A, C, and 

D, and reaction equations in Problem D) 

SO, = Z(0.02) + lf3.77) = 3.81 mollhr 

H20 34,450 21,650 (780 "R) 12,800 

C02 14,270 3,510 (780 a) lo, 760 

N2 9,600 2, 850 (780 "R) 6.750 

N i 9,600 1, 310 (560 OR) 8,290 

Air 9,680 1, 310 (560 "R) 8, 370 

3. Total heat required for incineration 

mollhr x Btulmol = Btu/hr 

s02 3. 81 9,150 34,800 

Hzo 66.84 12,800 856,000 

C02 23. 35 10,760 255,000 

N2 

113.00 6.750 763, 000 

N 2 21.45 8.290 177, 800 

Air 6.78 8, 370 56,700 

Total 

4. Additional heat required 

= 2,143, 300 

H = Heat required to raise products to 1240 

"F, minus incineration-evolved heat. 

H : 2,143, 300 - 874,600 = 1,268,700 Btulhr 

5. Refinery gas required for additional heat 

H = 800 Btu/ft3 x 379 ft3/mol = 313,000 

Btulmol 

1,268,700 Btu/hr = 4. O5 

Weight required = 

313,000 Btulmol mollhr 

Hz0 = (3.77) + 63. 07 = 66.84 mollhr Use 5. 0 mol/hr (for safety factor)


When burning refinery gas to obtain the required 

additional heat necessary to achieve the proposed 

Total = 2, 390,600 Btulhr 

incineration temperature, additional air for corn- 3. Anticipated incinerator temperature 

bustion of this gas must be supplied. The required 

air can be determined by calculations similar T - T - 

2 1- - 

to those above. A final incineration heat balance 

M C ~ 

can then be made, and the actual incineration 

temperature can be predicted. It is also neces- Where 

sary that the incinerator mixing velocity be such 

that the retention time exceeds 0. 3 second to T2 = final temperature, "F 

ensure adequate time for conversion of H2S to 

SO2. TI = initial temperature, "F 

Given: AQ = heat added, Btulhr 

Refinery gas essentially 75% CH4 and 25% C2H6. W = weight of gas, lb 

Excess air for combustion = 25% 

Problem G: 

Determine air requirement for fuel gas combus- 

tion and make final heat balance of combined vent 

gases, fuel gas, and air for fuel gas. Determine 

predicted incineration temperature and check 

against desired 1240 "F. Verify incinerator 

mixing velocity and retention time. 

Solution: 

1. Air requirement for 5. 0 mollhr fuel gas 

7 5 

02 = 2(-x 5. 0 mollhr) = 7. 5 mollhr 

100 

7 25 

02 = - (-x 5. 0 mollhr) = 4. 375 mol/hr 

2 100 

Required O2 = 7.5 + 4. 375 = 11. 875 mollhr 

Required N2 = - O' 79 x 11. 875 = 44.7 mollhr 

0. 21 

25 11. 875 

Excess air = - x --- mollhr = 14. 14 

100 0.21 

mollhr 

Additional C02 and H20 from fuel gas 

H20 = 2(3. 75) t 3(1. 25) = 11. 25 mol/hr 

C = specific heat of gas. 

P 

Assumed: 

(149) 

TI = 300 "F (vent gas at 320 "F; fuel and air 

at 100 O F ) 

Cp = 0.27 (based on weighted average of C 

P 

for major vent gas components) 

Incinerator heat loss = 15% 

W, weight of gases (Problem F and 1 above) 

mol/hr x lblmol = lb/hr 

C02 = l(3. 75) t 2(1. 25) = 6. 25 mol/hr (checks with assumed temperature of 1240 "F, 

allowing for heat-loss);. - , 

2. Total heat added 

! 4. Incinerator mixing velocity: 

I 

1 

.~.. , 

Incineration heat (Problem E) = 874.600 Btulhr 

Volume of gases 

mol 

Btu 

Fuel gas heat = 5. 0 - x 379 Gl ft3 x 800 - to incinerator 

hr 

= 311.57 mollhr x 379 ft3/hr 

ft3

7 32 CHEMICAL PROCESSING EQUIPMENT 

Area of 

incinerator 

- 3. 14(4)2 = 12. 56 ft2 

- 4 

119,700 ft3/hr 1 

Mixing velocity = 3600 sec/hr 12.56 ft 

5. Retention time: 

= 2. 65 fps 

Length of incinerator = 8. 0 ft 

Retention time = O ft = 3 seconds (OK) 

2. 65 ft/sec 

Stack Dilution Air 

As shown in the preceding problems, unconverted 

HzS and carried-over sulfur are burned in the 

incinerator to SO2. However, even when the 

scavenger plant is operating efficiently, the vol- 

ume concentration of SO2 in the flue gas from the 

incinerator may be high. To meet acceptable con- 

centration levels at the stack, dilution air may 

be added at the base of the stack. The required 

amount of dilution air may be determined as 

illustrated in the following problem. 

Maximum allowable SO2 = 0. 2 vol % 

Solution: 

1. Undiluted SO2 concentration 

3. 81 

volume 70 = - x 100 = 1.207% 

311.57 

2. Required dilution air 

Total volume required - 3. 8lmollhr x 379 ftlmol' 

for 0. 2% SO2 

60 minlhr x 0.002 

Total incinerator gas = 

= 12,040 cfm 

311. 57 mollhr x 379 ft3/mol = 1970 cfm 

60 minlhr 

Required air = total volume - incinerated gas 

: 12, 040 - 1970 = 10,070 cfm 

Use 11,-cfm blower 

In some localities, there may be no established 

criterion for maximum allowable SO2 concentra- ; 

tion in the flue gas. Nevertheless, SO2 is itself 

toxic and it is necessary to ensure that safe 

ground level concentrations are not exceeded. 

Additionally, some of the SO2 may be oxidized 

to SO3 which, in turn, could combine with atmo- I 

spheric moisture to form acid mist and lead to I 

extensive ground level damage. The additionof 

1 

dilution air, in addition to reducing SO2 concen- 

1 

tration, has the added advantage of "quenching" 

the incinerated gases and greatly reducing SO3 

formation. 

Incinerator Stack Height 

Where there is no set limit for stack SO2 concentration, 

an attempt may be made to keep 

ground level concentration to an acceptable level 

by providing a high stack. The required stack 

height may be determined by methods illustrated 

in the following example: 

i 

! 

Example 

Problem: 

Determine the SO2 concentration in the flue gas 

and the amount of dilution air required to lower 

the concentration to an acceptable level. 

Given: 

Total SO2 (from Problem G)= 3. 81 mollhr 

Given: 

Total flue gas volume, cfm 

SO2 concentration, vol % 

Allowable SO2 at 500 ft from base 

of stack, ppm 

Wind velocity, mph 

Solution: 

= 2000 

=0.5 

= 3 

= 10 

1 

I 1 

I 

! 

i 

! 

I 

Total gas = 311.57 mollhr The general concentration equation is 

I 

1 

where 

C = ground concentration, it3 50~/10~ ft3 air i 

M = SO2 emission rate, tonslday 

V = wind velocity, mph 

X = distance from stack base, ft ! 

K = e (-20 HIX) 

(Values of K are plotted in Figure 565. ) 

2000 cfm x 0.005 1440 min/day 

M = 

5. 93 ft31lb 2000 lblton 

= 121 tonslday 

1 

1 i 

I 

i 

! 

i

VALUE OF COEFFICIENT K 

stack for any stack height and wind veincity (Steinbock, 

1952). 

Stack height (from Figure 565). H = 130 ft 

Maximum ground level concentration will occur 

roughly at a distance of ten times the stack height 

from the stack. Since this distance derives from 

the stack height not yet determined, the required 

stack height to limit the ground concentration at 

any point must be determined. The height may be 

determined from Figure 566 by the following steps: 

1. Draw a vertical line at 121 tons per day until 

it intersects the 10-mph curve. 

2. From this intersection, draw a horizontal line. 

3. Draw a vertical line from 3 ppm mtil it inter- 

sects the horizontal line. 

RATE OF EMISSION OF POLLUTANTS, tons/day 

MAXIMUM SOZGROUND CONCENTRATION, ppm 

Figure 566. Maximum ground concentration of sulfur 

dioxide discharged from stacks of various heights 

(Steinbock. 1952). 


4. The pocnt of intersection is the required stack 

height. 

By interpolation of height curves, H = 230 ft. 

Plant Operational Procedures 

Even in properly designed plants, operational 

problems which result in decreased sulfur re- 

covery efficiency and consequent increase in H2S 

vented to the incinerator are often encountered. 

Most of these problems stem from either varia- 

tion in the feed gas stream or from inadequate 

reaction air and/or cooling water controls. 

Problems in these areas, in turn, affect the cata- 

lyst and may drastically reduce conversion 

efficiency. 

Based upon a fixed feed stream composition, the 

correct amount of oxidation air can readily be 

controlled by flow controllers. However, feed 

gas composition monitoring equipment is expen- 

sive and difficult to maintain and is therefore 

not generally used. The H2S content can be 

readily checked, and this is generally done on a 

periodic basis, with air supply adjustment as 

necessary. 

A more difficult problem is an increase in the 

hydrocarbon content, which may not be detected 

until the imbalance in feed is reflected in ahnor- 

ma1 temperature differentials in the waste heat 

boiler, coolers, and/or reactors. It is necessary, 

therefore, that operating temperatures he con- 

stantly monitored to detect hydrocarbon fluctua- 

tions. If not, the excess hydrocarbons will dis- 

rupt the oxygen supply and not permit full H2S 

conversion to SO2 in the first-stage reaction. 

Secondly, if not controlled, temperatures may 

rise to the point of equipment damage and pos- 

sible breakdown. Thirdly, the excess hydrocar- 

bons may not be fully oxidized in the controlled 

air supply and, particularly when the hydrocar- 

bons are heavier than C3 fractions, carbon may 

be deposited on the catalyst and thus reduce con- 

version efficiency. 

As discussed earlier, a two-stage conversion 

plant should attain a sulfur recovery efficiency of 

at least 90 percent. Many modern plants will 

yield 94 to 96 percent, and the efficiencies may 

he raised to as high as 98 percent where a third 

stage is used. Although the addition of a third 

stage to an existing two-stage plant may not be 

economical solely on a sulfur recovery basis, 

the provision of a third stage in new plants is 

relatively inexpensive. In either case, this third 

stage is highly desirable from an air pollution 

standpoint since large amounts of pollutant are 

represented by each percentage point of recovery 

efficiency. Also, the third stage can act as a 

stand-by for the other stages during upset con-

7 34 CHEMICAL PROCE :SSING EQUIPMENT 

ditions. As activity of catalyst in the first stage 

is reduced (by surface deposits of sulfur or car- 

bon), abnormal quantities of HzS will pass 

through. However, this can then be reaCtkd in 

the subsequent stages and high efficiencies can 

still be maintained until the first stage catalyst 

is reactivated. With the additional flexibility of 

three stages, any one of the stages can be by- 

passed for replacement of inactive catalyst. 

Generally, however, catalyst is reactivated rather 

than replaced, and this is done during periodic 

plant maintenance shutdown. Sour gas feed is 

shut off and fuel gas is burned with theoretical 

air in the combustion chamber until all sour gas 

is purged from the reaction system, Thereafter, 

air supply is raised to 25 percent excess for a 

period and then to 50 percent excess. In doing so, 

the hot excess air burns surface carbon and 

sulfur from the reactor catalyst, and this is 

reflected by a temperature rise across the re- 

actor. When the temperature becomes equal at 

inlet and outlet, surface material has been fully 

oxidized and the catalyst is reactivated. 

In all areas where either oil refining or sour 

natural gas processing operations take place, 

the sulfur scavenger plant may be one of the most, 

if not the most, important single air pollution 

control method. The provision of such plants, 

properly designed and efficiently operated, will 

prevent the emission to the atmosphere of intoler- 

ably high amounts of material which is toxic to 

both man and his environment. 

Inasmuch as the gas treating plants, as well as 

the sulfur recovery facilities, are processing a 

highly odorous and toxic gas, it is of utmost 

importance that the area be designed for easy 

cleaning oi spills, and that an efficient plant 

housekeeping program be followed. 

Tail Gas Treofmenf 

As previously discussed, the main portion of the 

sulfur from the crude oil can be removed and recovered. 

Recent attention to further reduced 

ambient air quality standards for sulfur oxides 

reauires added treatment to the tail u gases from 

the scavenger plants. Conversion efficiencies 

must be raised from the 90 to 95 percent range 

to a level greater than 99 percent. 

Two approaches are available to achieve the addi- 

tional clean-up. One requires the tail gas efflu- 

ent from the sulfur plant to be totally in an oxi- 

dize? *tate. The gas is then conditioned and 

treated by chemical scrubbing. The treated gas, 

containing less than 100 ppm sulfur compounds, 

discharges to the atmosphere, the chemical solu- 

tion is regenerated, and the resulting sulfur 

oxides are recycled back to the sulfur recovery 

units. This process was developed by Wellman- 

Power Gas, Inc.. of Lakeland, Florida. 

The other approach to this problem is to provide 

the tail gas in a reduced state of H2S before chemi- 

cally scrubbing. It is necessary to minimize car- 

bon disulfide and carbonyl sulfides to prevent high 

degradation of the scrubbing solution. Two pro- 

cesses of this type are known as the Beavon Stret- 

ford (R. M. Parsons Go. of Los Angeles, Califor- 

nia) and the Cleanair (The Pritchard Companies of 

Kansas City, Missouri). Both processes are 

capable of reducing the sulfur compounds to less 

than 100 ppm. 

Various other approaches to tail gas treatment 

are in development stages. Many involve chemi 

cal scrubbing of the gaseous streams although 

adsorption and molecular separation processes 

are being evaluated. 

PHOSPHORIC AClD MANUFACTURING 

During the past 20 years, the use of phosphorus- 

containing chemical iertilizers, phosphoric acid, 

and phosphate salts and derivatives has increased 

greatly. In addition to their very large use in 

fertilizers, phosphorus derivatives are widely 

used in food and medicine, and for treating water, 

plasticizing in the plastic and lacquer industries, 

flameproofing cloth and paper, refining petroleum, 

rustprooiing metal, and lor a large number of 

miscellaneous purposes. Most of the phosphate 

salts are produced for detergents in washing 

compounds. 

With the exception of the iertilizer products, 

most phosphorus compounds are derived from 

orthophosphoric acid, produced by the oxidation 

of elemental phosphorus. At present, elemental 

phosphorus is manufactured on a large enough 

scale to be classed as a heavy chemical and is 

shipped in tank cars from the point of initial 

manufacture, where the raw materials are inex- 

pensive, to distant plants for its conversion to 

phosphoric acid, phosphates, and other compounds. 

PHOSPHORIC AClD PROCESS 

Generally, phosphoric acid is made by burning 

phosphorus to form the pentoxide and reacting 

the pentoxide with water to form the acid. Spe- ~ 

cifically, liquid phosphorus (melting point 112'F) ! 

is pumped into a refractory-lined tower where it 

is burned to form phosphoric oxide, P4Ol0, which 

is equivalent algebraicly to two molecules of the 

theoretical pentoxide, PZ05, and is, therefore, 

commonly termed phosphorus pentoxide:

An excess of air is provided to ensure complete 

oxidation so that no phosphorus trioxide (P203) 

or yellow phosphorus is coproduced. The reac- 

tion is exothermic, and considerable heat must 

be removed to reduce corrosion. Generally, 

water is sprayed into the hot gases to reduce 

their temperature before they enter the hydrating 

section. 

Additional water is sprayed countercurrently to 

the gas stream, hydrating the phosphorus pent- 

oxide to orthophosphoric acid and diluting the 

acid to about 75 to 85 percent: 

The hot phosphoric acid discharges continuously 

into a tank, from which it is periodically rc- 

moved for storage or purification. The tail gas 

from the hydrator is discharged to a final col- 

lector where most of the residual acid mist is 

removed before the tail gas is vented to the air. 

A general flow diagram for a phosphoric acid 

plant is shown in Figure 567. 

Figure 567. General flow diagram for phosphoric 

acid production. 

The raw acid contains arsenic and other heavy 

metals. These impurities are precipitated as 

sulfides. A slight excess of hydrogen sulfide, 

sodium hydrosulfide, or sodium sulfide is add- 

ed and the treated acid is filtered. The excess 

hydrogen sulfide is removed from the acid by 

air blowing. 

The entire process is very corrosive, and 

special materials oi construction are required. 

Stainless steel, carbon, and graphite are com- 

monly used for this severe service. 

Special facilities are required for handling 

elemental yellow phosphorus since it ignites 

Phosphoric Acid Manufacturing 735 

spontaneously on contact with air at atmospher- 

ic temperatures and is highly toxic. Phosphorus 

is always shipped and stored under water to pre- 

vent combustion. The tank car of phosphorus is 

heated by steam coils to melt the water-covered 

phosphorus. Heated water at about 135°F is 

then pumped into the tank car and displaces the 

phosphorus, which flows into a storage tank. 

A similar system using hot displacement water 

is irequently used to feed phosphorus to the 

burning tower. 


A number oi air contaminants, such as phosphinc, 

phosphorus penlosiiie, hydrogen suliide, and phos- 

phoric acid niist, may be released by the phosphor- 

ic acid process. 

Phosphine (pH3), a very toxic gas, may be formed 

by the hyrlralysis of metallic phosphides that exist 

as impurities in the phosphorus. When the tank 

car is opened, the phosphine usually ignites spon- 

taneously hut only momentarily. 

Phosphorus pcntoxide (P4010), created when 

ptiosphorus is burned with excess air, forms 

an extremely dense fume. Our military forces 

takc advantage oi this property by using this con- 

pound to form srnolie screens. The fumes are 

submicron in size and are 100 percent opaque. 

Except for this military use, phosphorus pent- 

oxide is never released to the atmosphere unless 

phosphorus is accidentally spilled and exposed 

to air. Since handling elemental phosphorus is 

extremely hazardous, stringent safety precau- 

tions are mandatory, and phosphorus spills are 

very infrequent. 

Hydrogen sulfide (H2S) is released from the acid 

during treatment with NaHS to precipitate sulfides 

of antimony and arsenic and other heavy metals. 

Removal of these heavy metals is necessary for 

manufacture of good grade acid. H2S is highly 

toxic and flammable. Health authorities recom- 

mend a maximum allowable concentration of this 

gas of 20 ppm for an 8-hour exposure. The odor 

threshold is 0. 19 ppm (Gillespie and Johnstone, 

1955). In practice, however, H2S is blown from 

the treating tank and piped to the phosphorous- 

burning tower where it is burned to SO2. Source 

test information indicates that the concentration 

of SOZ in the gaseous effluent from the acid tower 

scrubberwillnot exceed 0.03 volume percent. Evo- 

lution of H2S is also minimized by restricting the 

amount of NaHS in excess of thatneeded to precipitate 

arsenic and antimony and other heavy metals. 

The manufacture of phosphoric acid cannot he 

accomplished in a practical way by burning 

phosphorus and bubbling the resultant products 

through either water or dilute phosphoric acid

736 CHEMICAL PROCESSING EQUIPMENT I 

(Slaik and Turk, 1953). When water vapor comes 

into contact with a gas stream that contains a 

volatile anhydride, such as phosphorus pentoxide, 

an acid mist consisting of liquid particles of var- 

ious sizes is formed almost instantly. An investi- 

gation (Brink, 1959) indicates that the particle 

size of the phosphoric acid aerosol is small, 

about 2 microns or less, and that it has a median 

diameter of 1.6 microns, with a range of 0. 4 to 

2.6 microns. 

The tail gas discharged from the phosphoric acid 

plant is saturated with water vapor and produces 

a 100 percent opaque plume. The concentration 

of phosphoric acid in this plume may be kept 

small with a well-designed plant. This loss 

amounts to 0.2 percent or less of the phosphorus 

charged to the combustion chamber as phosphorus 

pentoxide. 


All the reactions involved take place in closed 

vessels. The phosphorus-burning chamber and 

the hydrator vessel are kept under a slight neg- 

ative pressure by the fan that handles the effluent 

gases, as shown in Figure 520. This is neces- 

sary to prevent loss of product as well as to pre- 

vent air pollution. 

The hydrogen sulfide generated during the acid 

purification treatment must be captured and collected, 

and sufficient ventilation must be provided 

to prevent an explosive concentration, for 

hydrogen sulfide has a lower explosive limit of 

4. 3 percent. The sulfiding agent must be carefully 

metered lnto the acld to prevent excessively 

rap~d evolution of hydrogen sulfide. 


The hydrogen sulfide can he removed by chem- 

ical absorption or by combustion. Weak solu- 

tions of caustic soda or soda ash sprayed 

countercurrently to the gas stream react with 

the hydrogen sulfide and neutralize it: 

NaZC03 t H2S - NaHC03 t NaHS 

The hydrogen sulfide may also he oxidized in 

a suitable afterburner: 

The phosphoric acid mist in the tail gas is 

commonly removed by an electrical precip- 

itator, a venturi scrubber, or a Brink fiber 

mist eliminator (Brink, 1959). All are very 

effective in this service. 

The Tennessee Valley Authority has used elec- 

trical precipitators for many years to reduce 

the emission of phosphoric acid mist (Striplin, 

1948). Severe corrosion has always been a 

problem with these precipitators. Published 

data (Slaik and Turk, 1953) indicate that the 

problem has been partially solved by reducing 

the tail gas temperature to 135' to 185°F. 

The acid discharged amounts to about 0. 15 per- 

cent of the phosphorus pentoxide charged to the 

combustion chamber as phosphorus. The rela- 

tively low gas temperatures and consequently 

infrequent failure of the wires are given as the 

reason for the high mist recovery from the gas 

Stream. 

The TVA replaced one of the electrical precip- 

itators wlth a venturi scrubber in 1954. The 

venturi scrubber is constructed of stainless 

steel and is 14 feet 6 inches high, with a 30- 

inch-diameter inlet and outlet and a 11-112- 

inch-diameter throat (Barber, 1958). The 

scrubber is followed by a centrifugal entrain- 

ment separator. Stack analyses of emissions 

from this production unit are summarized in 

Table 199. 

Table 199. STACK ANALYSES OF EMISSIONS 

FROM A PHOSPHORIC ACID PLANT 

WITH A VENTURI SCRUBBER 

Phosphorus burning rate, lhlhr 2,650 

Temperature, *F 

Vaporizer outlet 1,650 

Burner outlet 880 

Venturi scrubber outlet 195 

Stack gas 175 

Pressure drop, in. WC 

Across venturi scrubber 25.2 

Across entrainment separator 1.9 

Emissions as % of phosphorous burned 0.2 

In 1962, the TVA constructed a stainless steel 

phosphoric acid unit that has an adjustable ven- 

turi scrubber, followed by a packed scrubber, 

and a wire mesh mist eliminator. When the 

venturi scrubber is adjusted to give a pressure 

drop of 37 inches of water column or higher, 

losses of P205 from the unit amount to only 

about 5 pounds per hour at phosphorus-burn- 

ing rates up to 6,000 pounds per hour. 

Considerable research and development work 

by the TVA demonstrated that good recovery of 

phosphoric acid mist could be achieved by intro- 

ducing water vapor into the hot gases from the 

combustion of phosphorus, passing the mixture 

through a packed tower, and condensing it 

(Slaik and Turk, 1953).

. . 

Soap, Fatty Acid, and Glycerine Manufacturing Equipment 737 

A large-scale plant using a Raschig ring-packed The Brink (1959) [iber mist eliminator is a relatower 

Sollowed by three gas coolers was built. tively new type of collector that has been used 

1 

1 

Overall p21aspRorus pcntoxide recovery exceeded 

99. 9 percent, hut the process was eventually 

alianiloneil bccausr of the ercessivc rate of corrosuccessfully 

on sulfuric acid mist, oleurn, phosphoric 

acid, ammonium chloride fume, and various 

organics. Collectors of this type have been dission 

of the gas coolers. cussed in the preceding section of this chapter. 

This same process, with a second packed scrubber 

or glass fiber-packed iiltcr unit for acid mist re- 

moval replacing the gas cooler, is used by a number 

of phosphoric acid producers throughout the country. 

Thcsr plants routinely operatc with phosphorus 

pentoxiclr recovery efiiciencies in exccss of 99. 8 

perccnt. H visible pliosphoric acid plume still 

rzmains, though the phosphorus content has been 

rccluced to lcss than 0. 1 grain pcr scS. A plant 

such as this is in opcration in Los Angeles County 

and is shoxm in Figure 568. Thc plume contains 

a large pcrcentagc of watcr vapor and does not 

violatc local air pollution prohibitions. Stack 

analyscs ol emissions irom this plant are shown 

in Table 200. 

The packed scruhber must be tl~oroughly and uniformly 

wctted with either water or weak acid and 

must have uniform gas distribution to achieve high 

collection cificiency. Gooci gas distribution is also 

niandatory iar glass fiber filter units, and a superficial 

gas velocity of less than 100 fpm is recommended. 

At one plant owned by Monsanto Chemical Company, 

the stack plume was very persistent and visible. 

Thirty milligrams of fine sulfuric acid mists per 

standard cubic foot and 80 to 200 milligrams of 

phosphoric acid particles per standard cubic foot 

were emitted from the stack. To correct the 

situat~on, a gas absorption apparatus followed 

by a flber mist collector was installed. Collection 

efficiencies of 99 percent on particles less 

than 3 microns in diameter and of 100 percent 

on larger particles were achieved. The stack 

plume, which consists of 15 percent water vapor, 

disappears within 40 to 50 feet of the stack on 

dry days and within 150 feet on wet days. No 

maintenance problems or changes in pressure drop 

through the apparatus have been encountered. 

SOAP, FATTY ACID, AND GLYCERINE 

MANUFACTURING EQUIPMENT 

INTRODUCTION 

Soap for washing and emulsifying purposes bas 

been manufactured and used for over two thou- 

sand years. Traditionally, soap has been manu- 

factured in batches by saponifying natural oils 

and fats with a solution of caustic soda, salting 

out the soluble soap formed, and drawing off the 

dilute glycerol produced. Shortly before World 

War 11, major changes started to occur in the 

industry. Pretreatment of the fats and oils was 

introduced and changes were made in plant pro- 

cedures and in finishing of the soap. Since World 

Was 11, with the advent of synthetic detergents, 

soap use has declined precipitously until its pro- 

duction today constitutes less than 20 percent of 

the combined production of soaps and detergents 

(Silvas, 1969). Figure 569 illustrates the vast 

change in relative production of soap and deter- 

gent since 1944. The manufacture of detergents 

is discussed in another section of this manual. 

When the direct neutralization of fatty acids by 

soda ash and/or caustic soda was introduced as 

a soap-making process, fat splitting, or hydrolysis, 

became a basic operation of the soap industry. 

Prior to 1955. the soap industry generated 

its own supply of fatty acids for use in soap making 

by splitting of natural fats and oils and provided 

fatty acids to other chemical process industries. 

Since 1955, however, fattv acids have 

also been synthesized from petroleum products, 

F~gure 568. Phosphor~c acld plant wlth a Raschlg so that today fatty acids are produced synthetlcalrine-packed 

scrubber. ly in greater quantities than by spllttlng natural

7 38 

CHEMICAL PROCESSING EQUIPMENT 

Table 200. STACK ANALYSES OF EMISSIONS FROM A PHOSPHORIC ACID 

PLANT WITH TWO RASCHIG RING-PACKED SCRUBBERS 

Phosphorus burning rate, lh/hr 

Gas rate, stack outlet, scfm 

Gas temperature, stack outlet, "F 

Diameter of first packed scrubber,ft 

Height of first scrubber's Raschig ring packing, ft 

Diameter of final packed scrubber, ft 

Height of final scrubber's Raschig ring packing, ft 

Final scrubber's superficial velocity, fpm 

P205 emitted, gr/scf 

P205 emitted, lblhr 

Emissions as 70 of phosphorus burned 

RAW MATERIALS 

Report series No. 

C-167 A C-167 B 

The soap industry applies the term "oi1"to those 

natural fats which are liquid at ambient conditions, 

excluding hydrocarbon oils obtained from petro- 

leum. "Fats, " in the soap industry, refers to 

all natural oils and fats, liquid or solid. Soap 

is produced almost exclusively from these natu- 

ral fats and oils. 

Ordinary soluble soaps are classifiable in a num- 

ber of ways. They may be generally classed as 

toilet soaps, household soaps or industrial soaps. 

Traditionally, sodium soaps have been called hard 

soaps, and potassium soaps called soft soaps. 

Today such classification is no longer meaningful, 

as the hard or soft quality of soap is much more ! 

0 drpident on the type and quality of fats and oils j 

1944 1948 1952 1956 1960 1364 

used to make the soap. 

YEAR i 

Figure 569. Production of soap and detergents in the 

United States, 1944 to 1968 (Chemical Week, 1969). 

fats and oils. The soap industry, however, still 

uses fatty acids produced almost exclusively by 

splitting natural oils and fats, and still supplies 

a significant amount of fatty acids to other chemi- 

cal process industries. The soap industry had 

been the principal supplier of glycerine to chemi- 

cal process industries. However, glycerine is 

now produced synthetically, and presently the 

soap industry supplies only about one-half of the 

total glycerine consumed in this country. 

Metallic soaps have uses entirely different from 

those for ordinary soaps, so that theyare not in 

direct competition. These soaps are alkaline 

earth, metal, or heavy-metal salts of fatty acids. 

They are made either by heating fatty acids with 

metallic oxides, carbonates, etc.. or by the re- 

action of soluble ordinary soap with solutions of 

heavy-metal salts. Their manufacture will not 

be discussed in this section. 

1,875 

12,200 

175 

8.5 

12 

2 0 

3 

47 

0.095 

9.9 

0.23 

895 

3,420 

162 

8. 5 

12 

2 0 

3 

13 

0.108 

3.2 

0. 16 

The properties of soaps are directly related to the !. 

type of fatty acids used. The most desirable fatty i. 

acids are lauric, myristic, paluitic, stearic, and ! 

1 . 

olsic, which are acids having 12 to 18 carbon 

I' 

atoms. These acids constitute the bulk of the 

fatty acids found in tallow and coconut oil. As a 

1' 

result, many soaps are combinations of these two i 

oils, usually in ratios of 3 or 4 parts of tallow to 1 

1 part coconut oil. Because of its favorable acid ! 

content, availability, and low price, tallow is the 1 

most predominant fat used for soap making. It 

constitutes 80 percent or more of the total fats 

used by the soap industry. Greases, the rendered j 

fats from hogs and other small domestic animals, 

are the next most often consumed fatty material 

(Shreve, 1967). Other natural oils, including 

marine oils, may also he used in the soap making 

processes. Many of the marine oils are used in i 

special applications. They represent only an ! 

insignificant portion of the total fats used. 

Sodlum hydroxide is the saponifying alkali used 

for most soap manufacture. Potassium hydroxide

Soa~. Fattv Acid. and Glvce? .ine Manufacturing Equipment 739 

still is used to some degree, and because potas- 

sium soaps are more soluble than the sodium 

soaps, they are used, or blended with sodium 

soaps, for making liquid soap solutions. Miner- 

als, including soda ash, caustic potash, sodium 

silicate, sodium bicarbonate, and trisodium 

phosphate, are used extensively as builders or 

fillers. Used in smaller quantities, but of ex- 

ceeding importance as synergetic soap builders, 

are tetrasodium pyrophosphate and sodium tri- 

polyphosphate. Carboxylmethylcellulose (CMC) 

also is an additive for most heavy-duty soaps. 

Finished soaps also may contain small quantities 

of chemicals used as preservatives, pigments, 

dyes, and perfumes, as well as antioxidants or 

chelating compounds. Bar toilet soaps and pow- 

der or granular laundry soaps may be manufac- 

tured as a combination of synthetic detergents 

and the neutralized fatty acid soluble soaps. 

Detergents used are either anionic or nonionic, 

but not cationic. 

FATTY AClD PRODUCTION 

Fatty acid production from natural fats may be 

performed by any one of several processes. The 

processes all result in "splitting" or hydrolysis 

of the fat. This may be represented as: 

I 

H-C -OH 

I I 

- 

H - COOR + 3H70-3RC00 + H - C -OH 

I 

H - COOR 

FAT 

I 

H-C-OH 

FATTY GLYCEROL 

AClD 

Three current processes for splitting or hydro- 

lyzing fats to produce fatty acids and glycerol 

utilizing either batch or continuous processes 

are detailed and compared in Table 201. Several 

older process methods, such as panning and 

pressing procedures, fractional distillation, and 

solvent crystalization, no longer are used. Of 

the three current processes, the continuous high- 

pressure hydrolysis process is the one most often 

used by the soap industry. A flow diagram of the 

process is shown in Figure 570. 

In the continuous high-pressure hydrolysis pro- 

cess, fat and water, both in liquid phase, are 

heated in contact with each other to temperatures 

in excess of about 400 "F, and some of the water 

becomes dissolved in the fatty matter. The pro- 

portion of water that becomes dissolved in the 

fatty layer increases rapidly with rise in tempera 

ture, causing a reduction in the aqueous layer. 

At temperatures approaching 550 "F, depending 

upon the type of oil used, the aqueous phase 

merges into the fatty phase, leaving but a single 

liquid phase (Ittner, 1942). In practice, the 

equipment is operated at temperatures and pres- 

sures where the two components show consider- 

able mutual solubility but below the temperatures 

where only one phase exists. The glycerine 

formed is continuously removed in the water 

stream, and at the same time the product fatty 

acids are removed as a separate stream. 

The equipment used for this process is a vertical 

column (Figure 570). The fats, in liquid form, 

are first vacuum deaerated, which prevents dar- 

kening, and then pmnped into the bottom of the 

column through a sparge ring. Deaerated, de- 

mineralized water is pumped at high temperature 

and high pressure into the top of the tower. High- 

pressure steam, at pressures of 700 to 750 psi, 

is introduced into the tower either along with the 

oil or directly into the reaction zone at the center 

of the tower, or, in some cases, at both the top 

and bottom of the tower. Tower operating pres- 

sures are usually 650 to 800 psi, and temperature 

of the fats is usually around 485 ' to 500 "F. The 

oil droplets travel up the column, while the water- 

glycerine solution flows down the column. The 

fatty acids then pass overhead to a flash tank for 

the removal of entrained water, or they may be 

decanted from the water after cooling and then 

passed to a settling tank where further separation 

occurs. 

As shown in Figure 570, the glycerine and water 

solution, called sweetwater, is drawn from the 

bottom of the hydrolyzer tower and is passed 

through a series of evaporators, or to a flash 

tank to remove some of the water, and then to 

storage as crude glycerine. 

The fatty acids produced are characteristic of 

the particular type oils being processed. Distil- 

lation is employed frequently on- stream with con- 

tinuous hydrolization to further refine fatty acids. 

When chemical and industrial products are manu- 

factured from these fatty acids, fractional distil- 

lation is used. When soap stock is produced. 

simple distillation in a continnous vacuum-type 

still is used as shown in Figure 570. 

In the vacuum still, the boiling fatty acids pass 

overhead through a series of condensers. They 

are then either drawn off and pumped to storage 

as fatty acids or passed through a line mixer 

where caustic soda or soda ash is added to pro- 

duce the salt of the fatty acids, which is a soluble 

soap. The soap stock thus produced is then held 

in storage for use in the various soap manufac- 

turing and finishing operations.


Table 201. COMPARISON OF THREE CURR 

Temperature, "F 

Pressure, psig 

Catalyst 

Time, hr 

Operation 

Equipment 

Hydrolyzed 

Advantages 

Disadvantages 

Twitchell 

212 to220 

0 

AIkyl-aryI sulfonic acids 

or cycloaliphatic sulfonic 

acids, both used with sul- 

furic acid, 0. 75 to 1. 25% 

of the charge 

12 to 48 

Batch 

Lead-lined, copper-lined, 

monel-lined, or 

wooden tanks 

85 to 98 % hydrolyzed: 

5 to 15 % glycerol solution 

obtained, depending on 

number of stages and 

type of fat 

Lorn temp-rature and 

pressure; adaptable to 

small scales; low first 

cost because of relatively 

simple and inexpensive 

equipment 

Catalyst handling; long 

reaction time; fat stocks 

of poor quality must 

often be acid-refined to 

avoid catalyst poison- 

ing; high steam consump- 

tion; tendency to form 

dark-colored acids; 

need for more than one 

stage for good yield and 

high glycerin concentra- 

tion; not adaptable to 

automatic control; 

:NT FAT-SPLITTING PROCE: 

Batch autoclave 

300 to350 (450 without cataly 

75 to 150 (425 to 450 without 

catalyst) 

Zinc 

calcium. 

or magne- 

sium 

oxides. 

1 to 2% 

5 to 10 

Batch 

Copper or stainless-steel 

autoclave 

85 to 98 %hydrolyzed; 

10 to 15 % glycerol, 

depending on 

number of stages and 

type of fat 

Adaptable to small 

scale; lower first cost 

for small scale than 

continuous process; 

faster than Twitchell 

High first cost; catalyst 

handling; longer 

reaction time than 

continuous process; 

not so adaptable to 

automatic control as 

continuous; high 

labor cost; need for 

more than one 

stage for good yield 

and high glycerin 

concentration 

5 (Shreve. 1967) 

Continuous 

counter current 

485 approx 

600 to700 

Optional 

2 to 3 

Continuous 

Type 316 stainless 

tower 

97 to 99 %, hydolyzid; 

10 to 25 % glycerol, 

depending on type 

of fat 

Small floor space; 

uniform product 

quality; high 

glycerin concen- 

tration; low 

labor cost; more 

accurate and 

automatic control; 

constant utility 

load 

High first cost; 

high temperature 

and pressure; 

greater operating 

skill 

The fatty acids, which may contain considerable soap stock. The hydrogenation operation is us=unsaturated 

organic acids, can be further pro- ally on-stream with the hydrolysis operation. 

cessed by hydrogenation. Hydrogenation, with 

the use of a catalvst, saturates the double bonds 

GLYCERINE PRODUCTION 

of the unsaturated fatty acids. The process helps The saponification of natural oils can be repre 

to eliminate objectionable odors and hardens the sented by the following reaction:

Soap, Fatty Acid, and Glycerine Manufacturing Equipment 

Figure 570. Flow diagram of a continuous process for hydrolysis of natural fats. 

H H 

I I 

H - COOCR H-C -OH 

I I 

H - COOCR + 3NaOH -+3NaCOOR + H - C - OH 

I I 

H - COOCR H-C-OH 

I I 

FAT SOAP GLYCEROL 

Whether soap is manufactured by the older method 

of saponification of natural oils illustrated by the 

preceding reaction or by the newer method of 

direct saponification of fatty acids, glycerine is 

always an accompanying product. 

Figure 571 illustrates a typical soap plant glyc 

erine purification operation. The crude weak 

glycerine solution derived from the hydrolysis 

process is refined to produce both commercial 

and pharmaceutical grades of glycerine. The 

processing of the glycerine obtained from the 

continuous hydrolysis process is a much easier 

operation than the processing of the spent soap 

741 

lye glycerine from the kettle or batch processes 

of soap making. The sweetwater drawn from 

the bottom of the hydrolizer column has a concentration 

of about 12 percent glycerol. This 

sweetwater usually is so hot that, upon passing 

through three evaporators in sequence, the glycerol 

concentration increases to about 75 to SO 

percent by weight: This crude glycerine then is 

held in a settling tank for at least 48 hours at 

elevated temperatures to reduce whatever fatty 

impurities are still present. It then is distilled 

under vacuum (60 mm Hg absolute) at temperatures 

of approximately 400 'F. Small amounts I 

of caustic are added to the still feed to saponify the ! 

! 

I

742 CHEMICAL PROCESSING EQUIPMENT - 

v 

STILL FEED TANK 

Y 

STEAM 

CAUSTIC 

FOOTS 

HOT WATER 

F~gure 571. Flow diagram for glycerine manufacture from hydrolys~s sweetwaters 

small amounts of fatty acid impurities which are 

present so that they will not boil off. The overhead 

product glycerine from the vacuum still then is 

condensed in a three-stage condensing system 

with progressively lower temperatures at each 

stage. The staged condensation yields different 

grades of glycerine. The highest temperature 

first-stage condensate usually contains 99 percent 

glycerol. Lower quality grades are collected 

from the lower temperature condensers. The 

glycerine is purified by bleeching and filtration 

or ion exchange. 

In the making of soap by alkaline saponification 

of fats, glycerine always is formed and common- 

ly is recovered in solution in the soap lye. The 

spent lye removed from the saponification process 

averages around 4 to 5 percent glycerine when 

removed directly, and may exceed 10 percent 

when other washing processes are used. The 

spent lye, in addition to the glycerine, contains 

roughly 10 percent by weight of salt and some 

small amount of soaps that are still soluble in 

the lye. 

Figure 572 illustrates a typical spent soap lye 

processing plant. The first step is the purifica- 

-L 

TO EJECTORS 

tion of the lye solution removed from the saponifi- 

cation operation. The lye is neutralized by trrat- 

ing with mlneral acids to form a salt. The neu- 

tralized solution is heated and agitated to precip- 

itate any remaining soap. After filtration, the 

solution then is evaporated. Vacuum evaporation, 

either in a series of batch vessels or continuously 

in cone bottom vessels, causes the salt crystal- 

lization point to be reached. 

As the salt concentration increases, salt crystal- 

lizes out and separates. In the continuous vessel, 

a portion of the separated salt is intermittently 

removed from the bottom. In the batch separation, 

the salt is removed from the slurry by pumping it 

through filters or centrifuges. Recovered salt is 

reused in the soap making process. The concen- 

trated glycerine is boiled down to remove even 

more salt until a concentrated crude soap lye 

glycerine is obtained. At this stage the crude 

glycerine constitutes 80 to 82 percent by weight 

of the solution with approximately 2 percent by 

weight of nonvolatile organic matter, the remain- 

der being a mild salt solution in water. Further 

treaixnent of this crude glycerine follows the same 

procedures used with the crude glycerine obtained 

from fat splitting operations.

FATTY ACID OR 

HIGH F.A. STOCK 

BOILING TANK 

SOAP MANUFACTURING 


SPENT SOAP LYE 

FROM SOAP MAKING 

SURGE TANK 

Figure 572. Spent soap lye plant for recovery of crude glycerine. 

The soap-making processes, either those utiliz- 

ing the alkaline saponification of fats and oils or 

those employing the saponification of fatty acids. 

are variously batch or continuous. The kettle or 

full-boiled process is a batch process which fol- 

lows the historical and traditional soap-making 

methods since the beginning of the industry. This 

process involves several steps or operations in a 

single kettle or, in large operations, a series of 

kettles. The kettles or pans used in these pro- 

cesses vary considerably in size depending upon 

production requirements. Small operations or 

producers of specialty soaps may employ a kettle 

which will only produce a few hundred pounds of 

soap. Large commercial producers of soaps may 

use kettles which will produce 150,000 pounds of 

soap per batch. 

4 

> 

Y 

743 

The steps or operations performed include sapon- 

ification of the fats and oils by boiling in a caustic 

solution using live steam, followed by "graining" 

or precipitating the soft curds of soap out of the 

aqueous lye solution by adding sodium chloride 

salt. The soap solution then is washed to remove 

glycerine and color body impurities to leave the 

settled or "neat" soap to form on standing. Neat 

soap is the almost pure soap produced in the full- 

boiled process and remains as the upper layer of 

soap from which "nigre" soap and lye solutions 

have settled. The steps described above in the 

full-boiled process, including that of the final 

settling, can require a period of several days. 

The smaller kettles using this process may re- 

quire up to 24 hours per batch, while the larger 

kettles may require up to a full week to complete 

a batch.


Other batch processes of saponification of fats 

and oils, still used for small production runs of 

specialty soaps, include the semiboiled process, 

the cold process, the autoclave process, the 

methyl ester process and the jet saponification 

process. 

Two proprietary processes for continuous sapon- 

ification of natural oils are used by some soap 

manufacturers. These are the Sharples Process 

and the Mon Savon Process. Both processes, 

while dissimilar, eliminate the large kettles and 

lengthy process time required by the old tradi- 

tional batch operations. All processes, however, 

accomplish the same steps of soap manufacture. 

The manufacture of soap by direct saponification 

of fatty acids is easily accomplished in continuous 

processes. However, many plants employ con- 

ventional soap kettle processes. Batch saponifi- 

cation also is performed in mixing kettles, com- 

monly called crutchers. Fatty acids obtained by 

continuous hydrolysis are usually neutralized with 

50 percent caustic soda continuously in a high- 

speed mixer-neutralizer to form soap. The neat 

soap produced is discharged at 200°F into an 

agitated blending tank to even out any inequalities 

of neutralization. The neat soap contains approx- 

imately 30 percent water at this stage. This soap 

stock then is held at an elevated temperature for 

use in the various soap finishing operations. 

SOAP FINISHING 

- 

Soap is finished for consumer use in various 

forms such as liquid, powder, granule, chip, 

flake, or bar. Part of the finishing operation 

for soap is the addition of various ingredients to 

accomplish the purposes for which the final product 

is designed. Toilet bars of the purest type 

of soap will have the minimum of additional ingredients. 

Heavy-duty laundry soaps will have a 

with whatever markings are desired, and wrapped 

for shipment. 

Most bar soap today is manufactured by a second 

process, the "milling" process. Milled soaps, 

as they are called by the industry, usually are 

manufactured in one of two processes. In the 

older and still more commonly used process 

shown in Figure 573, the soap stock is batched 

in a mixer, called a "crutcher", with other ingredients. 

The batch is then flowed onto chill 

rolls, and then flaked off and passed through a 

steam-heated hot:& dryer. The flakes can be 

packaged as flake soap or ground and packaged as 

powder. When soap bars are made, the flakes 

from the dryer are 'Lplodded'l (mixed in a screw 

or sugar tubular mixer) or mixed with final ingredients 

such as perfume. The plodded material 

then is fed to a roll mill. The flaky soap produced 

by the roll mill then is plodded again to throughly 

mix ingredients and improve texture and is extruded 

in a continuous bar shape for cutting, 

stamping, and wrapping. 

li 

MIXER 

STEAM 

maximum of other ingredients added. All soap, - - 

after finishing, contains some water, usually between 

10 and 30 percent, because anhydrous soap 

PLODDER 

ROLL 

would be too insoluble to use easily. The finished 

soap product contains perfume which, while fre- 

t - - quently not apparent, has been mixed in with the 

soap to disguise somewhat unappealing odors. 

CUTTER 

MIXER 

MILL 

v - 

STAMPER 

PACKAGING 

FLAKE 

PACKAGING 

BAR 

PACKAGING 

Bar soap is produced in three general processes. 

The oldest process, the framing -. process, seldom 

is used today except for some special types of 

soap. In this process, liquid soap, after mixing 

or crutching with other necessary ingredients, is 

Figure 573. Flow diagram of milling soap finishing 

n. - r- n- - - r . ~ ~ ~ 

poured as a semiliquid paste into large vertical In the second and more recent milled soap promolds. 

The soap hardens upon cooling in these cess, the basic blended soap stock is pumped 

molds. The sides of the molds or frames are through atomizing nozzles against the inside wall 

removed and the soap is cut by mechanical saw- of a vacuum chamber and dropped from the chaming 

processes into rough shapes and sizes of the ber into a plodder. Figure 574 is a diagram of 

hars. They are then stamped into the final shape, this process. The plodded soap is immediately

t 

LIQUID MIXER 

SOAP 

STOCK 

I 

- 

PLODDER CUTTER 

Soap, Fatty Acid, and Glycerine Manufacturing Equipment 745 

MINOR INGREDIENTS TO VACUUM 

- VACUUM 

n FLASH 

CHAMBER 

t 

STEAM 

MIXER 

PERFUME, ETC. 

Figure 574. Flow diagram of vacuum flash drying 

process for bar soap production. 

mixed with the necessary additional ingredients 

and then passed through a series of roll mills 

and plodders until it is extruded in a continuous 

bar for cutting, stamping, and wrapping. 

A third process, illustrated in Figure 575, pro- 

duces aerated soap bars. Neat soap is heated 

under pressure and then water is flashed off. 

Air is mixed with the soap, perfume is added, and 

the paste chilled and then extruded continuously. 

After cutting to rough shape, the bars are "aged" 

or cooled, and then stamped and wrapped. 

Soap also is finished for marketing in flake or 

chip form. In manufacturing this type of product, 

the same procedures are followed as were de- 

scribed for the framing process. The only ex- 

ception is that after hot air-drying, the soap is 

not milled or plodded. 

Soap powder formerly was produced by grinding 

the chips coming from the hot air-dryer discussed 

above and shown in Figure 573. This method of 

soap powder manufacture has been highly unsat- 

isfactory since it produced a product containing 

excessive fines. However, this process is still 

used occasionaly in some soap plants. Soap 

powders now are manufactured almost exclusive- 

ly by first crutching the soap stock with the fillers 

and other additives to produce the final composi- 

tion and then spray drying the slurry mix. The 

spray drying of soap and the spray drying of syn- 

L 

TI 

LIQUID SOAP ( 

I STOCK I ( I 

A 

1-i VAPOR 

FLASH TANK 1 

" 

I 

I I 

CONTIYUOUS 

I CRUTCHER - 

FREEZER- 

I I 

CUTTER 

04 

AGING ROOM 

H-H~I 

CUTTER STAMPER PACKAGING 

Figure 575. Flow diagram of aerated soap har 

production. 

thetic detergent compounds are very similar pro- 

cesses. Spray drying is discussed in much great- 

er detail in the section of this manual dealing 

with detergents. 

Liquid soaps very rarely are manufactured today 

except for some very specialized products such 

as "pure soap hair shampoo. " Top quality liquid 

soap is blended in tanks with the other ingredients 

desired and then packaged in standard bottle 

filling equipment. 


All chemical processes and some of the other 

operations involved in the making of soap, pro- 

duction of fatty acids, and the purification of 

glycerine have odors as a common air pollution 

problem. Blending, mixing, drying, packaging, 

and other physical operations are subject to the 

air pollution problems of dust emissions. 

Odors may be emitted from equipment used for 

the following operations:


1. Receiving and storage of animal and vege- 

table oils 

2. saponification of fats and oils or of fatty 

acids 

3. hydrolieation of natural fats and oils to 

produce fatty acids 

4. distillation of fatty acids 

5. hydrogenation of fatty acids 

6. concentration and distillation of glycerine. 

During their receiving and storage, natural fats 

and oils are heated to temperatures not over 150°~ 

to reduce viscosity for pumping. The fats and oils 

used by most soap manufacturers are of high qual- 

ity, and odors usually do not cause a local nuisance 

unless the equipment is located adjacent to homes 

or businesses. 

Fats and oils are heated during the direct saponi- 

fication, resulting in the emission of odors. 

These odors may cause a local nuisance, depend- 

ing upon the location of the equipment in the com- 

munity, and may require control equipment. 

Odors also are emitted during the deaeration and 

hydrolization of fats and oils to produce fatty acids. 

Distillation and hydrogenation of the fatty acids 

emit odors. Fortunately, the flash deaeration of 

fats and oils is performed under a vacuum, pro- 

duced usually by water or steam jets. Steam jets 

are followed by contact barometric condensers 

which in effect serve as scrubbers. This arrange- 

ment of equipment provides satisfactory odor con- 

lrol so that the installation of additional control 

equipment usually is not necessary. All stages of 

these operations are vented similarly. Figure 576 

illustrates several vacuum ejector and condenser 

systems. 

The flash dehydration of glycerine has been found 

to emit only mild odors. Equipment for glycerine 

distillation under vacuum is vented through steam 

jets and barometric condensers. Emissions again 

are very light and odors do not cause any nuisance 

problems. 

In soap-finishing operations, dust can be emitted 

from equipment performing the following opera- 

tions: Addition of powdered and fine crystalline 

materials to crutchers, mechanical sawing and 

cntting of cold frame soap, milling and plodding 

soap, air drying of soap in steam-heated dryers, 

milling, forming, and packaging. Although dust 

emissions from these equipment sources rarely 

violate existing air pollution regulations, the dust 

emissions cause an internal plant hygiene problem. 

Various pieces of process equipment must there- 

fore be vented to control equipment for worker 

comfort and safety. 

There are, however, other equipment sources of 

dust emissions which usually exceed air pollution 

regulations. The sources are: Grinding of soap 

chips, pneumatic conveying of powders, and spray 

drying of soap. Installation of control equipment 

is necessary for compliance with air pollution 

regulations as well as worker comfort and safety. 

The production of soap powder by spray drying 

creates the largest single source of dust in the 

manufacture of soap. Spray drying is designed to 

produce relatively coarse granules followed by 

highly efficient separation of soap granules from 

the drying air before the air is vented to the at- 

mosphere. Most towers for the spray drying of 

soap are the concurrent type where both the heat- 

ed air and soap slurry spray are introduced at 

the top of the tower. Heated air and soap granu- 

les are separated at the bottom of the tower in a 

baffled area which causes the granule-laden air to 

make sharp 180" turns. Most of the soap is de- 

posited in the baffled section and drops into the 

cone bottom of the spray dryer. However, a few 

soap particles still remain in the heated air after 

passage through the baffled area. The particles 

range in size from 2 to 200 microns, with a medi- 

ian particle size of over 20 microns. Air pollution 

control equipment is required before venting the 

contaminated air to the atmosphere. 

The hot soap granules removed from the bottom 

of the spray dryer must be cooled to prevent cak- 

ing and then screened and stored or sent to pack- 

aging equipment. The most common way to cool 

soap granules is by pneumatic conveying of the 

soap granules to elevated locations for gravity 

flow through screens into storage or packaging 

equipment. Cyclone separators or gravity settling 

chambers are used to remove the soap granules 

from the conveying air. Soap particles venting 

- - 

from the separator or settling chamber are finer 

in size than the soap particles in the exhaust air 

from the spray drying tower and are in such concentrations 

that they must be collected by control 

equipment in order to comply with air pollution 

regulations. 


The elimination of odors from the manufacture of 

raw soap, fatty acids, and glycerine can be accom- 

plished by scrubbers such as water ejectors or 

barometric condensers. Figure 576a shows a 

contact type scrubber which successfully vents 

odorous emissions from a vessel used for dehy- 

drating blends of tallow and foots oils by heating 

them above 200'F. This water jet contact scrubber

- 

60°F WATER 

8 PSlG 

6-in. dla. DUCT 

50 - 100 ft. 

1%-tn. INLET 

I I TO HOTWELL 

50,000 to 100,000 odor units per 113 


?-in OUTLET 

a. Barometric condenser and fan venting odorous oil b. Vacuum still which also provides odor reduction. 

blending operations. 

C. Flash tank which provides both jet exhaust 

and odor reduction. 

DRUM DRIER 

MAKEUP WATER PUMP 

d. Drum dryer which provides both vapor removal 

and odor reduction. 

Figure 576. Steam and water ejector and barometric condenser combinations which also effect odor reduction 

(condenser) reduces odor levels by over 90 per- Dust emissions from equipment used in the soap- 

cent. Tbe odor-containing gases vented from this finishing operations other than spray drying can 

scrubber are in very low volumes. The residual be controlled by dry filters and baghouses. Mois- 

odors are diluted in the atmosphere well below ture content of the dust-laden air is well below 

their threshold levels in traveling through the saturation and close to ambient so that condensa- 

atmosphere for only a short distance from the tion in the baghouse is not a problem. Dust col- 

scrubber exhaust. lected in filters or baghouses can be recycled 

747


to the process. Methods for hooding and ventila- equipment of higher collection efficiency than the 

tion of equipment emitting dust and the design of cyclones must be used in place of the cyclones or 

baghouses or filters are discussed in Chapter 4 be installed in series on the exhaust from the last 

of this manual. cyclone when this occurs. A baghouse presents 

problems because the exhaust air is usually saturated 

at tempzratures of 100" to 150 "F and, at 

Air pollution control equipment for soap spray this saturated condition, caking and blinding of the 

drying towers is designed specifically for the op- bag fabric can occur unless a special heated bagerating 

parameters of the particular tower. These house design is employed. Figure 577 is a flow 

parameters include: Materials sprayed, tower diagram illustrating the control of a soap spray 

operating temperature, tower dimensions, gas drying operation. Multistage centrifugal scrubbers 

velocities, and others. Because of the relatively or venhri scrubbers have proven to be satisfac~ 

large size of the particulates in soap drying, high- tory when additional control is required. Recirefficiency 

cyclones installed in series may be sat- culation of scrubbing liquid has not been employed 

isfactory in controlling emissions. Cyclones per- because soap slurry can cause severe foaming 

mit the recovery of materials for reuse in the 

' 

problems. Details on the design of scrubbers are 

process. However, small particulates may escape given in Chapter 4 of this manual. Further discollection 

by the second cyclone and may be in cussion which is applicable to spray drying towers 

such concentrations and quantities as to cause for soap also can be found in the following section 

emissions which violate regulations. Control on synthetic detergents. 

F~gure 577. Flow d~agram of soap spray drylng process wlth cyclones and baghouse for air pollution control.

Synthetic Detergent Surfactant Manufacturing Equipment 

SYNTHETIC DETERGENT SURFACTANT 

MANUFACTURING EQUIPMENT 

INTRODUCTION 

Surfactants are organic compounds that encom- 

pass in the same molecule two dissimilar struc- 

tural groups, e. g. , a water-soluble (hydrophilic) 

and a water-insoluble (hydrophobic) group. The 

composition, solubility properties, location, and 

relative sizes of these dissimilar groups in rela- 

tion to the overall molecular configuration deter- 

mine the surface activity of the compound (Kirk 

and Othmer, 1969). Every surfactant possesses 

detergent, dispersing, emulsifying, foaming, 

solubilizing, and wetting properties in varying 

degrees. The predominant property of any parti- 

cular surfactant dictates its use. Those surfact- 

ants with strong detergent properties when in 

aqueous solutions are used as the active agents 

in formulating various synthetic detergent pro- 

ducts. Detergent surfactant production for use 

in comp2unding of laundry and other cleaning com- 

pounds represents over 80 percent of all synthetic 

surfactant production. The remaining synthetic 

surfactants produced, of all types, are used in 

various industrial and chemical processes. 

Soap, as discussed earlier in this chapter, is a 

detergent type surfactant derived from saponification 

of natural oils and fats. It is generally 

not included in the present meaning of the term 

"detergent. I' Detergent is now almost exclusive 

'ly considered to apply to the synthetic organic 

surfactants. Synthetic detergents were first 

commerciallv emoloved in the textile industrv 

A , 

during the 1930's. Just prior to World War 11, 

some commercial production of laundry products 

containing detergents was started. Since the 

close of World War 11, products incorporating 

detergents greatly increased in use with a concomitant 

decline in the use of soap. By 1968, 

synthetic detergent products accounted for 83 

percent of the total combined production of soap 

and detergent cleaning compounds in the United 

States (Silvas, 1969). Figure 569 graphically 

illustrates this change in relationship. 

Surfactants are classified into four categories 

on the basis of their hydrophilic grouping: (1) 

Anionic surfactants have hydrophilic groups that 

are carboxylates, sulfonates, sulfates, or phos- 

phates, e. g., -OSO3- or S03-; (2) cationic sur- 

factants have hydrophilic groups that are primary, 

secondary, and tertiary amines and quaternary 

ammonium groups, e. g., -N(CH3)3f or C5~5~f-; 

(3) nonionic surfactants have hydrophilic groups 

that are hydroxyl groups and polyoxyethylene 

chains, e. g.. -(OCHZCHZ), OH; (4) amphoteric 

or zwitterionic surfactants include more than 

one solubiliaing group of differing types. 

749 

Table 202 shows the total 1966 U. S. production of 

surfactants divided among several major catego- 

ries. All soaps, both those for cleaning and 

washing products and those for metallic soaps 

for industrial and chemical processes, are in- 

cluded under carboxylates in the table. The over- 

whelming bulk of surfactant is produced by the i 

soap and detergent manufacturing companies, and 

consists almost exclusively of the anionic types. 

Limited amounts of anionic surfactants used in 

detergent cleaning and washing compounds are 

produced by petrochemical or chemical manufac- 

turing companies. The other two major catego- 

ries of synthetic surfactants, cationic and non- 

ionic, are almost entirely produced by chemical 

manufacturing companies. Their total produc- 

tion is relatively minor compared to anionic pro- 

duction. Therefore, cationic and nonionic sur- 

factants will not be discussed in this section. 

Row Materials 

The hydrophobic portion of most anionic surfac- 

tants is a hydrocarbon containing 8 to 18 carbon 

atoms in a straight or slightly branched chain. 

In certain cases, a benzene ring may replace 

some of the carbon atoms in the chain, e.g., 

C12H25-, C9H19. C6H4-. The hulk of anionic 

surfactants are made with dodecylbenzene, or 

commonly termed "detergent alkylate, 'I as the 

hydrophobic group. Prior to 1965, the alkylates 

were produced by reacting benzene or its homo- 

logs with branched-chain olefins such as propy- 

lene trimer or tetramer. Since 1965, the alky- 

lates used for detergents are "soft", or biode- 

gradable, and are made from long straight-chain 

normal paraffins, which are combined with ben- 

zene by the FriedelLCrafts reaction. Most deter- 

gent alkylates are produced at petroleum refiner- 

ies or petrochemical plants. Their production 

will not he discussed in this section. Some 

anionic detergents are made with normal fatty 

alcohols. Most of these alcohols are produced 

by large soap and detergent plants by hydro- 

genation of the fatty acxds obtained by the hydro- 

lization of natural oils and fats. Synthetic alco- 

hols are also used. The production of natural 

or synthetic alcohol will not be discussed in this 

section. 

The hydrophilic grouping in the anionic synthetic 

detergent surfactants is either a sulfonate or a 

sulfate. Sulfur trioxide or one of its hydrates, 

sulfuric acid or oleum, is reacted with alkylate 

or fatty alcohols to organic acids which are later 

neutralized to form salts. Neutralization is ac- 

complished hy empLoying sodium hydroxide, so- 

dium bicarbonate, or other sodium bases to form 

the sodium salts of the sulfonate or sulfate. Other 

neutralization procedures employ ammonia, po- 

tassium, diethanolamine, or triethanolamine to 

form their respective salts.

750 CHEMICAL PROCESSING EQUIPMEI'JT 

Processes 

Table 202. TOTAL U. S. PRODUCT-ION OF SURFACTANTS, DIVIDED 

I.V'IO hlA.IOK CAILtiOlllES. ALL FIGUIlL'S ARE FOR 100 I'LKCES I' 

SURI'ACL-I\C I'IVL' 11A ILKIALS 

(Kirk-Othmer, 1969) 

Nonionic-total all types 

Cationic-total all types 

Type 

Anionic synthetics 

Sulfonic acids and salts 

Sulfuric acids esters and salts (sulfates) 

Others 

Total anionic synthetic 

Amphoteric-total all types 

Carboxylic acids and salts-soaps and others 

Total-all surfactants 

There are several separate and distinctive pro- 

cesses for sulfonation or sulfation of various or- 

ganic bases to produce the detergents most com- 

monly manufactured. These processes variously 

employ oleum, sulfur trioxide in liquid or in va- 

port phase, sulfuric acid in high concentration, 

or chlorosulfuric acid. 

The attachment of the sulfonic acid group, 502 

OH, to a carbon atom of a hydrocarbon group 

(RH) is termed sulfonation. As 

with sulfur trioxide RH + S03-RSO2OH 

with sulfuric acid RHt H2SOqzRS020H 

with oleum t Hz0 

with chlorosulfuric RH t ClSO3H-RSOzOH 

acid (sulfone) t H CI~ 

Sulfation in detergent manufacturing denotes the 

attachment of an SO2OH group to an oxygen atom 

of an alcohol group. As 

with sulfur trioxide ROH t SO3-ROS020H 

with sulfuric acid 

with oleum ROH + HSOtROS020H 

with chlorosulfuric ROHt C1S03H-ROSOzOH 

acid (sulfone) 1 t HC11 

Production, 

pounds 

963,812,000 

111,925,000 

12,956,000 

1P88,693,000 

2,903,503,000 

Oleum is the most frequently used reactant for 

sulfonation. Oleum of 20 or 25 percent strength 

(20 or 25 parts by weight of sulfur trioxide liquid 

dissolved in 75 or 80 parts by weight or concen- 

trated sulfuric acid) is most frequently employed. 

During the early period of commercial production 

of synthetic detergents, all sulfonation processes 

employed 20 percent oleum in batch operations. 

Today almost all sulfonation of alkylate with oleum 

is performed in continuous operations. There are 

two typical processes: (1) Oleum sulfonation and 

(2) oleum sulfonation and sulfation. 

OLEUM SULFONATION I 

~ 

The most frequently encountered oleum sulfonation 

is the patented packaged plant illustrated in 

Figure 578. Although the feed equipment and discharge 

equipment may differ, the essential suli 

I 

i 

fonation and neutralization processes are the same 

for all of these plants. Oleum and alkylate are 

precisely metered and introduced to a centrifugal 

! 

mixing pump. The reacting mixture is then cooled 

in heat exchangers. Some reacting product ! 

recirculates to the mixing pump. The discharged 

I 

reacting product enters a digester tube section to 

allow the reaction to go to completion. The pro- 

duct is then diluted with water which hydrolizes 

sulfuric acid anhyrides and makes possible sub- 

sequent layer separation of spent sulfuric acid 

from the sulfonic acid. The layer separation 

step, which would normally require several hours, 

is effected in only a few minutes by adding sul- 

fonic acid product to the large mass of recycling 

spent acid. A centrifugal mixing pump is used

Synthetic Detergent Surfactant Manufacturing Equipment 

WATER ALKALI 1 

SULFONIC 

SULFONATION DILUTION CONCENTRATION NEUTRALIZATION 

Figure 578. Sulfonation of detergent alkylate with oleum in package plant with vacuum deodorizing 

(Chemithon Corp., Seattle, Wash.). 

to add dilution water, and the pump recirculates 

part of the dilute sulfonic acid along with part of 

the spent acid from the separation vessel. The 

spent acld is pumped from the bottom of the 

separation vessel, and sulfonic acid is pumped 

from the top. At this point in the process, differ- 

ences from one installation to another are found. 

Various arrangements of equipment provide for: 

Neutralization of the sulfonic acid followed by 

storage: deodorization by vacuum treating follow- 

ed either by storage or neutralization and storage; 

storage of the sulfonic acid without any further 

treating. 

The Air Pollution Problem 

Emissions of highly visible white opacity occur 

when oleum, formerly termed fuming sulfuric 

acid, is charged to a vessel and the displaced 

vapors are allowed to escape to the atmosphere. 

The visible emissions result from the reaction of 

sulfur trioxide vapor with water vapor in the air 

to form sulfuric acid particles in mist form. The 

particle size of this mist is directly comparable to 

the sulfuric acid mist in tail gases from sulfuric 

acid manufacturing. The particles of this mist 

are all less than 2 microns and 10 percent by 

weight are less than 1 micron. The threshold of 

visibility for this mist has been found experimen- 

tally to be of the order of 3.6 x grains/ft3 

(0.0203 mg/ft3), the precise value depending upon 

the temperature and humidity of the atmosphere 

(Fairs, 1958). Dense white emissions up to 100 

percent opacity occur from vents of storage tanks 

and process vessels during filling operations 

with oleum. 

Continuous sulfonation occurs in this equipment 

in a closed system without venting (except for 

751 

emergency relief). The sulfonic acid separation 

vessel is not vented, and the discharge of sul- 

fonic acid product and the waste sulfuric acid, 

after separation, to storage tanks does not cause 

emissions of more than trace opacities from vents 

of these tanks. When the sulfonic acid is neutra- 

lized, no visible emissions occur from the pro- 

cess equipment or from the final storage vessel. 

Depending upon the reagents used, the presence 

of long alkyl chains in the alkylate can lead to 

some dealkylation. Dealkylation results in the 

formation of small amounts of long-chain olefins 

which can cause product odor problems. To over- 

come odors, some plants deodorize the sulfonic 

acid product in a vacuum tank. The thresholds 

of the odorous materials removed depend upon 

the organic base feed stock. The ejectors and 

barometric condensers used for producing the 

vacuum scrub out odorous compounds from the 

gaseous stream. The odorous materials are 

skimmed from the water in the hot well. After 

skimming, the water may safely be cooled with- 

out creating odor emissions from the cooling 

tower. 

Air Pollution Control Equipment 

The transfer of liquid sulfur trioxide into vessels 

creates the same dense visible emissions as de- 

scribed for the transfer of oleum. When oleum 

and liquid SO3 were first introduced in industrial 

operations, control of emissions was attempted 

with simple water or caustic solution traps or 

scrubbers, but without success. Scrubbers and 

packed towers employing concentrated sulfuric 

acid as the scrubbing or absorbing medium were 

next employed. Many of these control installa- 

tions succeeded in reducing the opacity of the 

visible mist emissions, but did not reduce them

~. 

. .. . 


to a point that their corrosive effects on adjoin- 

ing equipment were eliminated. 

tured by Monsanto Company. Efficient operation 

of the filter is dependent upon adequately contact- 

ing the off-gases with water before entering the 

filter to convert all sulfur trioxide vapor to sul- 

furic acid mist for filtration. This is accomplish- 

ed by water sprayed concurrent with the gas flow. 

A 20 percent oleum was charged to the vented 

vessel at a rate of approximately 1000 pounds per 

minute, and the filter reduced the dense white 

emissions to a barely visible plume. 

Sulfur trioxide liquid is usually stored, shipped, 

and handled at a temperature between 90' and 

100 "F. Commercial stabilized SO3 has a melting 

point of about 62.2"F and a boiling point of 

about 112 "F. It is best handled and stored at 

92.2"F. Pure SO3 has a vapor pressure of 1 atmosphere 

at its boiling point, but the pressure 

will vary, at some lower value, from one supplier 

to another depending on the stabilizers employed. 

The vapor pressure of SO3 over 20 percent 

oleum, however, is only 0.8 mm Hg at 

OLEUM SULFONATION AND SULFATION 

35 "C (0.24 ounces~in.~ at 95°F). The vapor 

readily reacts either with water or water vapor 

to form sulfuric acid. Because it is a vapor 

phase reaction, and the sulfuric acid formed 

immediatley condenses to a liquid, the acid droplets 

are very small. Effective collection of these 

mists from tanks and vessels receiving SO3 or 

oleum will require exceedingly high-energy 

scrubbers or very high-efficiency filters. An 

Another continuous sulfonation process empLoys 

both sulfonation of an alkylate and sulfation of an 

alcohol in a two-stage series reaction with oleum 

in both stages. Figure 580 is a schematic flow 

diagram of this process. This process is proprietary 

and is operated by The Procter and Gamble 

Manufacturing Company. 

effective high-efficiency filter was constructed 

by Fairs (1958). The filter was made by com- 

Process 

pressing silicone treated ultrafine glass fibers 

to a bulk density of 10 pounds per cubic foot. Provision 

was made to throughly humidify the acid 

bearing exhaust gases before passing them to this 

filter. 

In this process, 20 percent oleum is continuously 

introduced to a mixing pump along with alkylate. 

The process proceeds according to what is termed 

the "dominant bath" principle to control the heat 

of sulfonation conversion and maintain the temp- 

A high-efficiency filter installation is illustrated 

in Figure 579. This oleum tank vent control consists 

of a Brink Mist Eliminator filter, manufacerature 

at a steady 130'F. A high recirculation 

ratio (volume of recirculating material divided 

by the volume of throughput) of at least 20: 1 is 

maintained ~~ to ~rodnce a favorable system. The 

discharged sulfonic mixture is passed through 

TO ATMOSPHERE coils to provide sufficient time for sulfonation to 

reach the desired high conversion. In the second 

stage of the process, fatty tallow alcohol, more 

oleum, and the first-stage sulfonic product are 

mixed in a centrifugal pump. This stage also 

OLEUM TANK 

HIGH-EFFICIENCY 

employs the dominant bath principle with a high 

recirculation ratio. The discharged sulfonicsulphate 

product then passes to a continuous line 

mixer where a sodium hydroxide solution is introduced 

for neutralization. Again, the dominant 

bath principle with a high recirculation ratio is 

used in the neutralization step. The surfactant 

slurry then is pumped to storage. This process 

makes no attempt to separate and remove any 

unreacted sulfuric acid as waste acid. All residual 

sulfuric acid is neutralized to sodium sulfate. 


SEWER 

The Procter and Gamble process requires an entirelv 

closed system. Venting - to the atmosphere 

Figure 579. High-efficiency mineral fiber filter installed 

ta vent acid mists from oleum storage tank; 

back flow not shown (Brink Filter. Monsanto Co.. St. 

iou!~. MO.). 

occurs only when the surfactant slurry is discharged 

into a storage vessel. Gaseous emissions 

from the storage vessel are minimal, and no air 

pollution control equipment is required.

CAUSTIC 

Synthetic Detergent Surfactant Manufacturing Equipment 753 

Figure 580. Continuous series sulfonation-sulfation with oleum, ending with neutralization, employing circulating 

heat-exchanging dominant bath to control heat (The Procter and Gamble Manufacturing Co., Long Beach, Calif.). 

SULFUR TRlOXlDE VAPOR SULFONATION 

When liquid detergent compounds were introduced 

as household products, it became necessary to 

reduce the sodium sulfate content of the surfac- 

tant. Sulfonation with oleum resulted in excess- 

ively high sodium sulfate content when the sur- 

factant was neutralized and used in liquid deter- 

gent products. The high sulfate content (11 to 12 

percent) caused cloudiness in the liquid deter- 

gent products and the sulfate settled out in the 

bottom of the containers. Sulfonation with pure 

sulfur trioxide vapor provided neutralized sur- 

factants with much lower sodium sulfate content 

(1 to 3 percent) and thus became an important 

process. The first ma'or installations of SO3 

vapor sulfonation equipLent included sulfur burn- 

ers for production of SO3. However, with the 

commercial development and availability of 

stabilized SO3 at low costs, many installations 

eliminated the SO3 production equipment (SO3 

production is discussed earlier in this chapter). 

Earliest processes for SO3 vapor sulfonation were 

batch operations. Several proprietary continuous 

operations are now used for this process. The 

continuous processes employ several types of 

reactors. One reactor is a mechanically agitated 

unit, and two others are film type reactors. The 

processes are similar and cause similar air 

pollution problems. SO3 is vaporized and diluted 

in a dry air stream (dew point 40 'F) to 29 to 8 

percent by volume before entering the reactor. 

Either alkylates or alcohols may be used in the 

processes. Figure 581 is a schematic flow dia- 

gram of one installation utilizing a film reactor. 

In this process, air is compressed, cooled, and 

dehydrated, then accurately metered to the reac- 

tion column. Simultaneously, stabilized liquid 

SO3 is weighed, then metered to a steam heat 

exchanger to be vaporized. Metered air is mix- 

ed with the SO3 vapor just before entering the 

reaction column, Al+late, alcohol, or other 

organic materials are metered and pumped to the 

reaction column. The reactor is a vertical cclumn 

designed for concurrent flow from top to bottom of 

the dilute SO3 vapor in air and the organic liquid. 

Cooling water flows on the outside of the reactor 

from the bottom to top in an opposite direction to 

the descending reactants. The sulfonic acid dis- 

charges from the bottom of the column to a cen- 

trifugal separator where liquid sulfonic acid is 

drawn from the bottom, and gas is vented from 

the top of the separator to the atmosphere (other 

installations may recycle the discharged gas and 

only vent some bleed-off). The liquid sulfonic 

acid then passes through a degassing column, 

maintained under vacuum, to remove unreacted 

SO3 vapors in the liquid phase. Depending upon 

the product manufactured, the product is pumped 

either to storage or neutralization tanks or to an 

"ageing tank" maintained under slight vacuum 

where it is agitated and cooled by water coils to 

ensure completion of the sulfonation reaction. 

It is then pumped either to storage or to neutra- 

lization equipment. Trace amounts of sulfuric


I 

COMPRESSED AIR AIR AIR TO 

DRYER 

t 

POLLUTION CONTROL 

COOL WATER 

.-... - VAPORIZER I I I I 

LlUUlU 

SULFUR TRlOXlDE I I I 

STEAM 'V 

- - 

ALKYLATEORALCOHOL I I l l 

V 

INTERNAL SEPARATOR 

- I 

SULFONIC ACID 

VACUUM LINE PRODUCT 

COOL WATER 

- --. I& 

VACUUM 

OR 

DEGASSER 

NEUTRALIZER 

r TO STORAGE 

OR PROCESS 

NEUTRALIZER WATER 

~ 

Figure 581. Sulfonation with sulfur trioxide vapor using a f i lrn reactor (Texti lana Corp., Hawthorne, Cal if.). 

acid anhydrides may be present in the sulfonic 

product, and form sodium sulfate when neutra- 

lized. Fatty alcohols must be neutralized immed- 

iately after the reaction with SO3 because sulfuric 

acid esters hydrolize rapidly. Some sulfonic 

acid is diluted with water to eliminate anhydrides 

before being stored. Neutralization of the sulfonic 

acid or sulfate is accomplished batchwise in an 

agitated water-cooled tank or in a dominant bath 

continuous neutralizer. The sulfonic acid or sul- 

fate products may be neutralized by sodium or 

potassium alkalies or by ammonia. 


COOLING TANK 

(AGING) 

In the SO3 vapor sulfonation process described, 

there are three point sources from which air 

contaminants can be emitted. The principal 

source of emission is the venting of gas separated 

from the sulfonic product upon discharge from the 

reactor. When the film reactor equipment was 

first installed, the emissions were believed to be 

_ 

: 

. 

., 

'= 

SURGE 

COOL 

WATER 

I 

STEAM 

TO HOTWELL 

__,. 

r 

QD I TO STORAGE 

mostly air with a small amount of SO3 vapor as 

acid mist. Control of this emission was attempt- i. 

ed by employing a mist eliminator followed by a 

packed scrubber using 99 percent sulfuric acid 

as the scrubbing medium. This method of control 

did not eliminate the visible emission ranging 

from 50 to 100 percent opacity. Upon investiga- 

I 

i 

tion, the emission was found to be almost com- 

pletely water soluble and to cause suds in water. 

The sulfuric acid in the scrubber did not in- 

crease in strength as would be the case if SO3 

were absorbed in the scrubber. Infrared spectro- 

meter analysis of the gaseous emissions indicated : 

the principle constituent of the visible emission to ~ 

be sulfonic acid. Fine mists are produced in the i 

reactor and may be formed in several ways. Some 1 

alkylate may vaporize in excess of normal equili- 

brium conditions due to localized hot zones in the 

reactor to later condense in the gas phase with 

the SO3 gas to produce sulfonic acid. Since the 

sulfonic acid is produced under conditions below 

its dewpoint, it immediately condenses from the 

!. 

1 

, ,


gas phase as a very fine mist. Some water is 

produced by side reactions. The water vaporizes 

and reacts with the SO3 gas in the vapor phase 

to form sulfuric acid below its dewpoint result- 

ing in a fine mist (Brink, et al. 1966). 

The other two paints of emissions have not been 

found to cause emissions of excessive opacities. 

One of these points is the exhaust from the single- 

stage steam ejector employed to provide vacuum. 

The ejector exhaust was found to contain little if 

any air contaminants and is not controlled. The 

third point of emission is the by-pass discharge 

from the reactor. The by-pass discharges liquids 

from the reactor during start-up procedures to a 

sump lor disposal to the sewer system. When 

carefully operated to avoid wasting materials or 

product, the start-up by-pass discharge is used 

for only a very short period, usually less than 

1 minute. Visible air contaminants from this 

source have been observed only during these 

short periods. 


The visible mist emitted from the vent of the re- 

actor is not readily controlled by scrubbing. In- 

cineration of the off-gasses eliminates visible 

emissions but results in emission of sulfur oxides. 

The high-efficiency filter discussed previously for 

SO3 acid mist control may be expected to control 

emissions from the reactor. The volume of ex- 

haust gas is determined by the operating para- 

meters of the sulfonation equipment. Pressure 

drop through the high-efficiency filter arranged 

for horizontal gas flow with velocities of 15 to 30 

fpm ranges between 5 and 8 inches of water col- 

umn. Provisions should he made for back-wash- 

ing of the filter elements. 

SULFUR TRlOXlDE LIQUID SULFONATION 

Since liquid sulfur trioxide with even a trace of 

moistur 2 present forms solid polymers at room 

temperatures, it was not a commerically feasible 

reactant until it was stabilized by addition of small 

quantities of suitable compounds. First processes 

employing liquid SO3 resulted in surfactants of 

poor color or with unpleasant odors. Liquid SO3 

added to undiluted alkylate causes heavy dealkyla- 

tion with the formation of odorous long-chain ole- 

fins. Pilot Chemical Company developed a com- 

mercial process employing the liquid, shown 

schematically in Figure 582. The process is op- 

erated in batches and employs liquid sulfur diox- 

ide as a diluent and as a refrigerant to maintain 

low batch temperatures (30°F) during the highly 

exothermic sulfonation reaction. 

Alkylate to be sulfonated is metered into the re- 

actor, and then the liquid SO2 and SO3 are meter- 

ed to the reactor. The heat generated by the sul- 

fonation reaction causes evaporation of the SOz, 

which holds the reaction mass at low temperature. 

The reactor is maintained under negative condition 

by pumping the SO2 vapor from it. The reaction 

is completed after several hours, and the sulfonic 

product is then heated to 85°F to drive off reemin- 

ing SO2 liquid as a vapor. The SOZ vapor removed 

from the reactor is compressed, scrubbed with 

concentrated sulfuric acid to remove any SO3, 

condensed, and returned to storage. The sulfonic 

product discharged from the reactor passes to a 

vacuum stripper to remove traces of SO2 and then 

to either storage or a neutralization tank. The 

vacuum pump for the vacuum stripper discharges 

to the compressors and returns any removed SO2 

to storage. 


The Pilot Chemical process emp?oys an entirely 

closed system u?til the sulfonic product is dis- 

charged to storage. The product in storage does 

not cause any air contaminant emissions other 

than very dilute and mild odors. The only air 

pollution problem found from the operation is 

from the necessary purge venting of the liquid 

SO2 storage tank. The tank must be continuously 

purged whenever the compressor is discharging 

SO2 back to it from the sulfonation reaction. This 

prevents any build-up of air which enters the 

system by leakage into the compressor and other 

equipment. SO2 vapors are present in the gas 

flow from the purge vent line. 


SO2 vapor emitted from the storage tank receiv- 

ing recovered SO2 from this process is readily 

controlled by absorption in a caustic solution. 

Moderate energy scrubbers such as packed 

columns and spargers using 10 percent sodium 

hydroxide solution as the scrubbing medium are 

effective. An air pollution control scrubber is 

schematically shown in Figure 583. At this 

installation, gas flow rate from the tank is limi- 

ted to approximately 1 to 2 cfm by a needle valve 

for the purge operation. SO2 vapor is sparged 

beneath the caustic solution contained in two 

scrubber vessels connected in series. The caus- 

tic solution is sampled regularly and maintained 

above 5 percent concentration. The same system 

can serve to vent the storage tank when it is fill- 

ed with liquid SO2 from a tank truck. The SO2 

vapor displaced during filling is returned to the 

truck tank so that the purge line vents only a low 

gas flow to the scrubber. The knock-out pot in 

the purge line between the tank and the scrubber 

principally serves to prevent back-flow of caustic 

solution to the SO2 storage tank.


SULFONIC AClD 

TO 

NEUTRALIZATION 

OR 

STORAGE 

Figure 582. Sulfonation with liquid sulfur trioxide diluted with liquid sulfur dioxide (Pilot 

Chemical Co., Santa Fe Springs, Calif.). 

CHLOROSULFURIC AClD SULFATION 

Chlorosulfuric acid as an acid reactant requires 

considerably different process equipment than 

any of the other processes discussed previously. 

The reaction is carried out with fatty alcohols. 

It is employed to produce surfactants used in for- 

mulating detergent products of high quality. Fig- 

ure 584 is a schematic flow diagram illustrating 

this process. Fatty alcohols are transferred 

from storage by a vacuum applied to the reactor. 

In the reactor, the alcohols are first cooled to the 

point of solidification by circulation of refrigera- 

ted water in the reactor jacket. The reactor is 

purged with inert gas (nitrogen) and chlorosulfuric 

acid is then slowly metered into the reactor. This 

reaction is characterized by the highly unbalanced 

pattern of heat and gas evolution. When the acid 

is first added to the alcohol, the exothermic for- 

mation of slkoxonium chloride occurs, and the 

hydrogen chloride generated by the sulfonation re- 

action is retained in the reactant mass. As acid 

addition continues, the HC1 is endothermically 

evolved as a gas and released from the reacting 

mass with considerable foaming. The heat evo- 

lution is highest at the start of the reaction, with 

approximately 60 percent of the total heat 

generated when only 20 percent of the total acid 

reagent has been added. Inert gas must be con- 

tinuously bled from the reactor along with the 

generated HC1. Off-gases containing HC1 pass to 

a falling film reactor for recovery of the HCI by 

absorption in water to form hydrochloric acid as 

a valuable byproduct. When the reaction has 

reached completion, the sulfated alcohol is trans- 

ferred to another vessel for neutralization. So- 

dium hydroxide, triethanolamine, or ammonia is 

used for neutralization. The sulfated alcohol must 

be neutralized immediately after completion of 

the reaction to avoid hydrolization. 


The receiving, storage, and handling of chloro- 

sulfuric acid results in more severe air pollution 

problems than those encountered with liquid So3 

and oleum. Chlorosulfuric acid is a fuming liquid 

which is extremely corrosive and reacts violently 

with water to produce hydrochloric and sulfuric 

acid. It is not normally exposed to air, and inert


NEEDLEVALVE 

SULFUR DIOXIDE RETURN SULFUR 

F-A AIR AND SULFUR 

( LIQUID SULFUR DIOXIDE 

TANK 

CAUSTIC 

OVER 

:&--- -x-- 

pH GUAGE . . 

TO SEWER 

LIQUID 

Figure 583. Air pollution control system venting 

liquid sulfur dioxide tank receiving recycled sulfur 

dioxide from sulfonation process (Pi lot Chemical Co., 

Sante Fe Springs, Calif.). 

gas under positive pressure is used in place of 

atmosphere when charging or discharging any 

containers or vessels. Venting of the displaced 

gas from vessels when filling with chlorosulfuric 

acid produces visible emissions of the acid mist. 

The chlorosulfation process evolves HC1 gas which 

is vented along with inert gas to a falling film ab- 

sorber. Most of the HC1 is absorbed in water, 

but a small amount of unabsorbed HCl is carried 

out with the inert gas to the atmosphere, causing 

visible emissions of acid mist. Hydrochloric 

acid produced by absorption of the HCl in water 

(usually 25 to 28 percent solution) is transferred 

to storage. Displaced vapors vented during fill- 

ing of the storage tank also consist of visible 

acid mist. The balance between the reactor op- 

eration and the absorber operation is critical if 

absorption of the HCl gas is to be reasonably com- 

plete. If absorption is inefficient, larger quanti- 

ties of acid mists are emitted from the storage 

tank vent. If inert gas flow volume to the reac- 

tor is excessively high, the absorption efficiency 

for HCl decreases. The flow of HCl from the re- 

actor is not constant. Therefore the feed water 

rate and other absorption variables must be con- 

trolled to keep the byproduct acid concentration 

from the absorber constant in spite of varying 

HCl gas loads. 


HCI acid mist displaced during filling of the stor- 

age tank is readily controlled with a caustic solu- 

tion scrubber or packed column. Two simple 

submersion type scrubbers illustrated in Figure 

585 serve to control emissions with high efficiency. 

The volume of HCl solution discharged from the 

chlorosulfation unit absorber is quite low, and 

this scrubber contains an excess of caustic for 

neutralizing all the HC1 vented during the batch 

operation. The caustic solution is tested after 

each batch operation to maintain the pH of the 

solution at 8 or greater. 

Sulfoalkylation is a condensation-type reaction 

producing a more complex sulfonate from a sim- 

ple one. One sulfoalkylation process, the manu- 

facture of N-acyl-N-alkyltaurate, is performed 

in the same equipment schematically illustrated 

in Figure 584 for a chlorosulfation process. 

Fatty acids are moved to the reactor, and phos- 

phorous trichloride is added as a reactant to pro- 

duce a fatty acyl chloride. Inert gas sparging is 

used, and hydrogen chloride is released by the 

reaction to be vented from the reactor with the 

inert gas. In this reaction, phosphoric acid is 

also formed in the reactor and settles out at its 

bottom. When the reaction is complete, remain- 

ing HCl is purged with the inert gas, and the 

phosphoric acid is drawn off. The fatty acyl 

chloride product of the first reaction is then re- 

acted with N-methyltaurine (taurine is 2-amino- 

ethane sulfonic acid) to form the final detergent 

surfactant (one of the "Igepon TI1 series of Gen- 

eral Aniline and Film Corporation). The HCl and 

inert gas vented from the reactor during the first 

reaction flows to the falling film absorber for 

HCl recovery. The surfactant is pumped from 

the reactor to a neutralization tank for final 

treatment with a caustic solution. 

Another sulfoalkylation process is a reaction be- 

tween fatty acids and isethionate, the sodium 

salt of isethionic acid (Z-hydroxyethane sulfonic 

acid), as the sulfating agent, and fatty acids in the 

presence of a catalyst to produce 8-sulfoesters. 

These detergents are sensitive to hydrolysis and 

are used only in specialty products. Hydrolysis 

does not deter their use in personal products. 

The sodium salt of 2-sulfoethyl ester of lauric 

acid or of coconut acid is used in manufacturing 

synthetic detergent bars. 

In this process, isethionic acid and coconut fatty 

acid are metered to a closed reactor, and a catalyst 

in ~owder form is added. The mix is agitated 

and circulated through a heat exchanger to 

add heat to the reactant mass. Inert gas is sparged 

into the reactor to prevent discoloration of pro-


Flgure 584. Chlorosulfonatian af fatty alcohols and recovery af hydrogen chloride (Textilana Carp., 

Hawthorne, Calif.). 

a. Low-volume hydrogen chlorlde ac~d mlst 

vented from chlorosulfonat~on process. 

VACUUM RELIEF VALVE 

b. Low-volume hydrogen chloride ac~d mlst vented 

from hydrogen chlorlde storage tank. 

Flgure 585. Submersion type scrubbers uslng caustlc solution (Textllana Corp., Hawthorne, Cal~f.).

Synthetic Detergent Product Manufacturing Equipment 759 

duct. Fatty acid vapor, water vapor, and inert 

SYNTHETIC DETERGENT PRODUCT 

gas are vented from the reactor through a condenser 

to a seaarator tank. Fattv acids seoara- MANUFACTURING EQUIPMENT 

ted are recycled to the reactor, the water is sent 

to the sewer, and the inert gas . is returned to a 

gas holder. The reaction is completed after several 

hours, and the product is then pumped to a 

jacketed vacuum stripper tank. The temperature 

is maintained, tallow fatty acid and more catalyst 

are added, and inert gas is sparged into the tank. 

The vessel is held under slight vacuum for a short 

period while the contents are agitated. The vacuum 

is then increased to strip any remaining unreacted 

fatty acid. Water vapor, inert gas, and 

fatty acid vapors are vented through a condenser. 

The condensate from the condenser consists primarily 

of coconut fatty acid and is returned to 

storage. The fresh surfactant is discharged 

through a line mixer where a small amount of water 

is added for cooling purposes. It is then transferred 

to a holding vessel for use in formulation 

of toilet bars. The water content flashes off in 

the holding vessel. 


The first of the two reactions involved in the production 

of alkyltaurates, the fatty acyl chloride 

reaction, also creates HCI acid mist emissions 

similar to those from the chlorosulfonation reaction. 

The second reaction, with the N-methyltaurine. 

is accomplished in the vessel without 

venting until the reaction is complete. 

The vacuum system employed in the second process 

to oroduce the sulfoester consists of compound 

steam ejectors with barometric condensers. 

The condensers discharge to a hot well. Visible 

and odiferous emissions, principally fatty acid 

vapors, occur from the hot well. Uncondensable 

gases in the reactor recirculation system also are 

vented and cause odors and visible emissions. 

The flashed off water vapor from the product hold 

tank can also contain contaminants of an odorous 

nature. No other air pollutant emissions occur 

from this process. 


The same control equipment shown in Figure 584 

for HC1 acid mist serves to control the emissions 

from the first sulfoalkylation process producing 

the alkyltaurate. 

The hot well receiving condenser water and uncon- 

densed gas and vapor from the vacuum jet systems 

in the second process for sulfoesters must be 

closed and vented to control equipment to eliminate 

odors and visible acid mist emissions. Scrubbers 

with gas pressure drops ranging from 7 to 12 in- 

ches water column usually control these emissions. 

INTRODUCTION 

"Synthetic detergent products" applies broadly to 

cleaning and laundering compounds containing surfactants 

along with other ingredients formulated 

for use in aqueous solutions. These products are 

marketed as heavy- or light-duty granules or liquids, 

cleansers. - - and laundrv or toilet bars. The heavvduty 

granules representthemajor portionof allproducts 

manufactured, with the light- andheavy-duty 

liquid or light-duty granules in far lesser production. 

The manufacture of all detergentproducts incorporates 

equipment andprocesses similar to those for 

manufacturing soapproducts. Themanufacture of 

the granular products is ofparamountinterest, with 

more severe air pollutionproblems than those encountered 

with soap granule production. The manufacture 

of liquid detergent andhar products is oflesser 

importance, withlittle or no difference from similar 

soap products in either process equipment or air 

pollution potential, and will not be discussed. 

Raw Materials 

The surfactants used in formulating synthetic detergent 

products are either anionic or nonionic. 

The products also contain other chemical compounds 

which supplement the detergent of the surfactant. 

Each particular formulation depends upon 

the ultimate design for consumer use. Table 203 

illustrates the formulations commonly used in 

large-volume granule and liquid detergent manufacture. 

Sodium tripolyphosphate (STP) or tetrasodium 

pyrophosphate (TSPP) are incorporated in most 

granular formulations as "builders" or seques- 

tering agents. They serve to eliminate inter- 

ference with the detergent action by the calcium 

and magnesium ions (hardness) in the water used 

in the wash solution. STP and TSPP may be used 

in powder, prill, or granule form, and are re- 

ceived in carlots. These ingredients are most 

often blended into the slurry before spray drying. 

Nitrilotriacetic acid (NTA) and its sodium salts 

have recently been incorporated in some heavy- 

duty granule products to replace part of the STP. 

It is more expensive than STP, but is a better 

sequestrant. The growing public concern with the 

role phosphates in detergents may play in deteri- 

oration of water quality has generated manufac- 

turers' interest in this substitute. Indications 

are that it will be employed in the near future in 

more formulations and in larger quantities. The 

acid is a crystalline powder and the salts (disodi- 

um or trisodium) are powders. They are receiv- 

ed in carlots. NTA is added to the slurry mix be- 

fore drying.


Surfactants 

Table 203. FORMULATIONS(1N PERCENT) FOR LARGE-VOLUME DETERGENT 

MANUFACTURE IN THE UNITED STATES 

Constituent 

Alcohol sulfate 

Alkyl sulfonate 

Ethoxulated 

fatty alcohol 

Alkyl amine oxide 

Soap 

Builders 

Fatty alcohol 

or amines 

STPINTA 

TS P 

Additives 

CMC 

Sodium silicate 

Sodium sulfate 

Enzyme 

Other 

Heavy duty Light duty 

p- 

High suds 

granules 

Low suds 

granules 

Brand A Brand B Brand C Brand D Liquid Granules Liquid 

Fillers, usually sodium sulfate or sodium car-- 

bonate, are incorporated in granule products. 

They are either powders or crystalline powders 

and are added in bulk form to the slurry before 

drying. 

8 

8 

- 

- 

- 

1. 5-2 

60 

- 

0. 5-0. 9 

5-7 

10-20 

Amides of various types are used as supplemen- 

tary surfactants in many formulations. They im- 

prove detergency of the sulfonic and sulfate sur- 

factants and act as foam boosters or stabilizers. 

Amides used include the higher fatty amides 

(e. g. cocomonethanolamide), ethanolamides, 

dialkyl and alkylol (hydroxyalkyl) amides, mor- 

pholides, and nitriles, as well as the lower acyl 

derivatives of higher fatty amines. These ma- 

terials are handled as liquids and received in 

tank cars or barrels. In granule manufacture, 

they are either incorporated in the slurry before 

drying or blended with the detergent granules 

after drying. 

18 

- 

- 

- 

0~0. 5 

50-60 

0. 5-0. 9 

5-7 

10-20 

0-35 

0-35 

0-35 

0-15 

- 

0-12 

- 

0-20 

0. 5-0. 9 

5-7 

- 

0.2-0.730.2-0.750.2-0.740.2-0.750.2-0.75 

0-5 0-5 0-5 0-5 0-5 

- 

6 

6 

- 

2 

50-60 

. 

0. 5-0. 9 

7-9 

10-30 

17 

- 

- 

. 

50-60 

- 

0. 5-0. 9 

7-9 

10-30 

25-32 

25-32 

- 

- 

. 

- 

. 

- 

0-5 

0-4 

60-70 

- 

0-5 

Function 

Cleaning 

agent 

for oily 

and organic 

s 011 

Foam booster 

or stabilizer 

Overcome 

water hardness 

and clean 

inorganic stains 

Antiredepositlon 

Corrosion 

inhibitor 

Flller 

Clean protein 

stain 

Perfume, dye, 

bleach, etc. 

Trisodium phosphate (TSP) is used in detergent 

granule formulations such as dishwasher com- 

pounds and wall cleaners which are designed to 

clean hard surfaces. TSP is considered func- 

tionally as an alkali rather than a sequestering 

agent. It is usually handled as a crystalline 

powder and is received in carlots, drums, or 

bags. 

Carboxy methylcellulose (CMC; sodium cellulose 

glycolate) usually is added to heavy-duty granules 

and serves to prevent redeposition onto the fabric 

of the dirt removed by the detergent. This chemical 

is received in bags or drums as a powder or 

granule. It is added to the slurry mixture before 

drying. 

Sodium silicate is added in most synthetic deter- 

gent formulations to inhibit the surfactant's ten- 

dency to corrode metal. It also is used to over- 

- 

20-25 

or 

20-25 

- 

10-12 

5-12 

2-15 

0-20 

- 

0-4 

0-5

come production and packaging problems encoun- 

tered with detergent granules. It is functionally 

used as a primary detergent alkali in compounds 

designed for hard surface washing, e. g. , machine 

dishwashing comp~unds. It can serve to retain 

uniform viscosity in the mixing and pumping of 

the slurry before it is dried, and it reduces the 

"tackiness" of the dried granules, facilitating 

their handling and reducing caking of the product 

after packaging. The sodium silicates are re- 

ceived in tank cars as water solutions. 

Optical brightners are added to many formulations. 

These are usually fluorescent dyes which absorb 

ultraviolet rays and reflect them as visible light. 

The dyes are received as powders in bags or as 

liquids in drums, and they are usually blended in 

the slurry before drying. 

Perfumes are added to almost all detergent pro- 

ducts to overcome unpleasant odors and impart a 

pleasing scent to laundered fabrics. The per- 

fumes are added by spraying onto the dried gran- 

ules or mixing with the liquid detergents. They 

are handled as liquids in small-size containers 

or drums. 

Bleaches of various kinds are frequently incor- 

porated in heavy-duty detergents. Sodium per- 

borate, along with magnesium silicate as a sta- 

bilizer, is commonly employed. They are re- 

ceived as powders or crystals in boxes or bags 

and are added to the granules after drying. 

Synthetic Detergent Product Manufacturing Equipment 

Enzymes have recently been introduced as part 

of the formulation of heavy-duty detergent pro- 

ducts to assist in the removal of protein-based 

stains from fabrics. The enzymes are received 

as powders in bags or drums. The enzymes are 

heat sensitive and are destroyed if heated to212"F. 

Most manufacturers blend the enzymes into the 

detergent granules after drying. 

Many other compounds may be incorporated in 

various products. Preservatives, antioxidants, 

foam- suppressors and other types of additives 

are used. The scouring cleansers are composed 

principally of finely pulverized silica, active 

detergent, small amounts of phosphates, and fre- 

quently a bleach. 

Detergent surfactants include alkyl sulfonic, 

alkyl sulfate, and alcohol sulfates, discussed 

above, and almost the entire range of anionic 

and nonionic detergents, including soap. Plants 

manufacturing their own sulfonic and sulfate sur- 

factants also use other surfactants in some or all 

of their products. The detergents are received 

and handled mostly as liquid solutions of varying 

strength, but some surfactants are received as 

flake or powder. Surfactants are principally mix- 

ed with the slurry before drying. 

Processes 

The only manufacturing process to be discussed 

here will be the production of detergent granule 

formulations incorporating spray-drying pro- 

cesses. All other products are produced in pro. 

cesses, such as drum drying, similar to soap 

production, discussed in the previous section. 

Manufacture of detergent granules incorporates 

three separate steps: Slurry preparation, spray 

drying, and granule handling (including cooling, 

additive blending, and packaging). Figure 586 

illustrates the various operations. 

SLURRY PREPARATION 

The formulation of slurry for detergent granules 

requires the intimate mixing of various liquid, 

powdered, and granulated materials. The soap 

crutcher is almost universally used for this mix- 

ing operation. Premixing of various minor ingre- 

dients is performed in a variety of equipment prior 

to charging to the crutcher or final mixer. The 

slurry, mixed in batch operations, is then held 

in surge vessels for continuous pumping to the 

spray drier. 


The receiving, storage, and hatching of the vari- 

ous dry ingredients creates dust emissions. 

Pneumatic conveying of fine materials causes 

dust emissions when conveying air is separated 

from the bulk solids. Many detergent products re- 

quire raw materials with high percentages of 

fines, viz.. typical specifications for some raw 

materials include the followiug percentage of 

fine materials passing a 200 mesh screen: Sodium 

sulfate - 12 percent; sodium tetrapyrophosphate - 

74 percent; sodium tripolyphosphate - 53 percent. 

The storage and handling of the liquid ingredients, 

including the sulfonic acids, sulfonic salts, and 

sulfates, do not cause emission problems other 

than mild odors. 

In the hatching and mixing of fine dry ingredients 

to form slurry, dust emissions are generated at 

scale hoppers, mixers, and the crutcher. Liquid 

ingredient addition to the slurry creates no vis- 

ible emissions but may cause odors. 


Control of dusts generated from pneumatic or 

mechanical conveying or from discharge of fine 

materials into bins or vessels is described in 

Chapters 3 and 4. There are no unique problems 

in hoodihg or exhaust systems for controlling dust 

emissions from conveying and slurry preparation.


Baghouses are employed not only to reduce and 

eliminate the dust emissions but for salvage of 

raw materials. None of the dusts causes any 

serious corrosion problems. Filter fabrics should 

be selected which have good resistance to alkalis. 

Filter ratios for baghouses with intermittent 

shaking cleaning mechanisms should be under 3 

cfm per square foot. 

SPRAY DRYING 

All spray drying equipment designed for detergent 

granule production incorporates the following com- 

ponents: Spray-drying tower, air heating and 

supply system, slurry atomizing equipment, 

slurry pumping equipment, product cooling equip- 

ment, and conveying equipment. The towers are 

cylindrical with cone bottoms and range in size 

from 12 to 24 feet in diameter and 40 to 125 feet 

in height. Single towers may be of varying dia- 

meter, being larger at the top and smaller at the 

bottom. Air is supplied to the towers from di- 

rect-heated furnaces fired with either natural gas 

or fuel oil. The products of combustion are tem- 

pered with outside air to lower temperatures and 

then are blown to the dryer under forced draft. 

The towers are usually maintained under slightly 

negativepressure, between 0.05 and 1.5 inches of 

water column, withexhaust blowers adjusted topro- 

vide this balance. Most towers designed for de- 

tergent production are of the countercurrent type, 

with the slurry introduced at the top and the heat- 

ed air introduced at the bottom. A few towers of 

the concurrent type are used for detergent spray 

drying, with both hot air and slurry introduced at 

the top. Some towers are equipped for either 

mode of operation as illustrated in Figure 586. 

In most towers today, the slurry is atomized by 

spraying through a number of nozzles, rather 

than by centrifugal action. The slurry is sprayed 

at pressures of 600 to 1000 psi in single-fluid 

nozzles, and at pressures of 50 to 100 psi in two- 

fluid nozzles. Steam or air is used as the atomiz- 

ing fluid in the two-fluid nozzles. 

Tower operations vary widely between manufac- 

turers and between products. Heated air supplied 

to the tower varies from 350' to 750°F. Temp- 

eratures of air supplied to countercurrent towers 

are generally lower, and most often range from 

500" to 650DF. Concurrent tower temperatures 

are somewhat higher. Solids content of slurrys 

for detergent spray drying varies from 50 to 65 

percent by weight, with some operations to as 

high as 70 percent. Moisture content of the dried 

product varies from 10 to 17 percent. Towers are 

designed for specific air-flow rates, and these 

rates are maintained throughout all phases of op- 

eration. Slurry temperatures may vary, but in 

most formulations they do not exceed 160°F. 

Frequently, they are as low as 8O0F. Exit gas 

temperatures range from 150" to 250°F with wet- 

bulb temperatures of 120" to 150°F. Air velocities 

in concurrent towers are usually higher than ve- 

locities in countercurrent towers. The concurrent 

towers produce granules which are mostly hollow 

beads of light specific gravity (0.05 to 0.20). 

Countercurrent towers produce granules which 

are multicellular and irreaularlv shaved and which 

have higher specific gravities ranging from 0.25 

to 0.45. 

In countercurrent towers, with lower air velocities 

and droplets descending against a rising column 

of air, most of the dried granules fall into the 

cone at the bottom of the tower. They are dis- 

charged through a star valve, or regulated open- 

ing, while still hot. Cooling of the granules is 

discussed below with other granule processing 

procedures. Unlike other product spray drying 

operations, e. g., powdered milk, the desired de- 

tergent granule product is comparatively large in 

size. The specifications for some well known 

granular products require 50 percent by weight 

or more to be retained on a 28-mesh screen. A 

certain amount of the product is dried to compar- 

atively small size. This amount is dependent on 

tower feed rates, the liquid droplet size in slurry 

atomization, the paste viscosity, the particular 

product, and other variables. Usually the exhaust 

air entrains 7 to 10 percent of that portion of the 

granular product which is too fine to settle out at 

the base of the tower. 

Concurrent towers, operate with higher air velocities 

than countercurrent towers. The air is vented 

just above the bottom of these towers through a 

baffle which causes violent changes of direction to 

the exhaust air to dynamically separate the dried 

granules, which then fall to the cone bottom for 

discharge. Concurrent towers producing very 

low-gravity granules vent air still conveying the 

~roduct to auxiliary equipment for separation. 

The loss of detergent fines entrained in the exhaust 

air stream will be somewhat higher from 

concurrent towers than from countercurrent 

towers. 


The exhaust air from detergent spray drying tow- 

ers contains two types of air contaminants. One 

is the fine detergent particles entrained in the 

exhaust air discussed above; the second consists 

of organic materials vaporized in the higher temp- 

erature zones of the tower. 

The detergent particles entrained in the exhaust 

air are relatively large in size. Over 50 percent 

by weight of these particles are over 40 microns. 

These particles constitute over 95 percent of the 

total weight of air contaminants in the exhaust air 

(Phelps, 1967). They consist principally of deter- 

-

Synthetic Detergent Product Manufacturing Equipment 763 

Figure 586. Detergent spray-drying with tower equ~pped for elther concurrent or countercurrent operation 

(dampers in countercurrent mode of operatlon). 

gent compounds, although some of the particles 

are uncombined phosphates, sulfates, and other 

mineral compounds. 

The second type of the air contaminant in the ex- 

haust air can create serious air pollution control 

problems. Various organic components in the 

slurry vaporize in the tower. The amount vapor- 

ized is dependent upon many variables, such as 

tower zone temperatures and volatility of the 

organics in the slurry mixture. The vaporized 

organic materials condense upon cooling in the 

tower exhaust air stream into micron- and sub- 

micron-size droplets or particles. Spray drying 

of one particular product resulted in the measured 

discharge of condensed organic particulates in the 

tower exhaust air ranging in size from 0.2 to 0.5 

micron. 

The variety of possible detergent compounds is 

almost infinite, and manufacturers are continually 

introducing new formulations or reformulating 

older ones. It is not always possible to predict 

how certain organic compounds in a slurry mix- 

ture will affect stack emission. If amides are 

present in the slurry in amounts greater than 0.5 

percent by weight, emission problems will occur. 

Source tests of exhaust air from an air pollution 

control scrubber with amides present in the slurry 

being dried in the spray tower revealed 0.08 grain 

of organic particulates per scf of exhaust gas. The 

presence of this relatively low concentration of 

submicron-size aerosols causes water vapor plumes 

to persist for long distances. Following the break 

or end of the water vapor plume, a highly visible 

contaminant plume persists for even greater dis- 

tances. The amide emission rate increases ex- 

ponentially with increases in tower operating tem- 

peratures. Many tower operating variables affect 

air contaminant emissions, but the temperature 

of the exhaust air probably is the most important. 

At one spray drier installation, opacities of organ- 

ic aerosol emissions were reduced by approximate- 

ly 30 percent when tower operation was altered to 

effect a reduction of exhaust gas temperature from 

2004 to 180°F. 

t 

i


Slurry formulations containing ethoqlated alcohol 

surfactants cause similar aerosol emissions. 

When this nonionic detergent is used in the slurry, 

source tests of the aerosol leaving the scrubber 

indicate a particle size range of 0. 2 to 1 micron. 

Plumes persist for long distances following the 

disappearance of the water vapor plume. 


The collection of air contaminants not only pro- 

vides for the economic return of detergent fines 

to the process, but also provides for control of 

submicron particles to ensure compliance with 

air pollution prohibitory rules. 

Manufacturers producing detergent granu!es have 

developed two separate approaches for capturing 

the detergent fines in the spray drier effluent for 

return to process. One method utilizes centrifugal 

separators to capture most of the product 

dust. The exhaust gases then are vented from 

the separators to scrubbers for removal of micron-size 

particles. The cyclone separators remove 

approximately 90 percent by weight of the 

detergent product fines in the tower exhaust air. 

The detergent dust remaining in the effluent 

vented from the cyclones consists of particles 

almost all of which are over 2 microns in size. 

Size distribution of these particles by weight will 

peak in the range of 7 to 10 microns. Particulate 

concentrations vary from 0.1 to 1.0 grain per scf. 

The cyclones are designed for relatively high 

efficiencies and operate at pressure drops from 

8 to 10 inches of water column (Phelps, 1967). 

A venturi type scrubber is used downstream of the 

cyclone, using water at 8 to 10 psig distributed 

through nozzles in the throat. Throat velocities 

of the exhaust gases average 8,500 fpm. With 

water supplied . to the throat at a ratio of 4.5 to 

5.0 gallons per 1,000 cubic feet of effluent, scrubber 

exhaust gases have loadings of about 0.085 grain 

per scf when slurries with amides are spray dried. 

A highly visible plume persists after the condensed 

water vapor plume has dissipated. 

In the second method of recovery of detergent 

fines, the centrifugal collector is eliminated, and 

only a scrubber is used. However, the scrubber 

uses detergent slurry as a scrubbing medium 

rather than water. The scrubbing slurry is main- 

tained at a high enough concentration to prevent 

foam, but at a low enough concentration to permit 

pumping and spraying. No further control device 

is used to cleanse the exhaust gases from the 

scrubber. When slurries with volatile organic 

materials are spray dried, highly visible plumes 

persist after the condensed water vapor plume 

has dissipated. A plume was even observed from 

a pilot venturi scrubber operating at a high pres- 

sure drop of 50 inches of water column. A 40 per- 

cent solids slurry was used as the scrubbing fluid 

delivered at gas scrubbing ratios of 60 to 100 gal- 

lons per 1000 cubic feet of gas. 

An alternative method for controlling emissions 

from the drier caused by volatile organics in the 

slurry is to reformulate the slurry to eliminate 

these offending organic compounds. When amide 

compounds were identified as causing the emission 

problems, some manuiacturers developed other 

formulations or methods for adding the amides 

to the spray dried granules to achieve a compar- 

able product. 

When reformulation is not possible, the tower 

production rate may be reduced, permitting oper- 

ation at lower air inlet temperatures and lower 

exhaust gas temperatures. When tower tempera- 

tures are reduced, lesser amounts of organic 

compounds are vaporized in the spray drier, and 

the scrubber is able to collect these emissions. 

GRANULE HANDLING 

Many manufacturers discharge hot granules from 

the spray tower into mixers where dry or liquid 

ingredients are added. The granules are usually 

mechanically conveyed away from the tower or 

mixer discharge and then are air-conveyed to 

storage and packaging. Air conveying serves to 

cool the granules and to elevate them for gravity 

flow through further processing equipment to 

storage and packaging. Air conveying of lowdensity 

granules usually is designed for 50 to 75 

scfm air per ~ound of granules conveyed. At the 

end of the conveyor, centrifugal separators remove 

granule product from the conveying air. 

Some manufacturers mechanically lift the granules 

from the spray tower to aeration bins where the 

granules are cooled or aged by injecting air at 

the bottom of the bin. This air percolates upward 

through the scrubber. 

The cooled granules are screened to deagglomerate 

the large granules and to remove undersize or 

oversize particles. Further mixing or blending 

may be performed to add heat-sensitive compounds 

to the detergent ~roducts. Many manufacturers 

do not store the finished granules, but convey 

them directly to packaging equipment. Some de- 

tergent products are held in storage, either in 

large fixed bins or small-wheeled buggy bins, and 

then are charged to packaging equipment. Pack- 

aging is done with either scale or volumetric fill- 

ing machines. 


Conveying, mixing, packaging, and other equip- 

ment used for granules can cause dust emissions. 

The granule particles, which are hollow beads, are 

crushed during mixing and conveying, and generate 

fine dusts. Dusts emitted from screens, mixers, 

bins, mechanical-conveying equipment, and air- 

conveying equipment are quite irritating to eyes 

and nostrils with continuous exposure. Some of

the additive materials, such as enzymes also 

cause serious health problems. Equipment in- 

volving enzymes requires very efficient ventila- 

tion in addition to proper dust collection. Dust 

emissions in most cases represent a significant 

product loss, and their collection and return to 

process (usually as an ingredient of the slurry to 

be spray dried) is necessary for economic plant 

operation as well as for air pollution control. 


Dust generated by granule processing, convey- 

ing, and storage equipment does not create unique 

air pollution control problems. Usually, bag- 

houses provide the best control. Collection effi- 

ciencies for baghouses are high; in many cases, 

efficiencies exceed 99 percent. No extreme con- 

ditions of temperature or humidity have to be met, 

but filter fabrics selected must show good resis- 

tance to alkaline materials. Baghouses utilizing 

intermittent shaking mechanisms should not have 

filtering velocities exceeding 3 fpm. Baghouses 

with continuous cleaning mechanisms may have 

filtering velocities as high as 6 fpm. 

GLASS MANUFACTURE 

Glass has been made for over 3,500 years, but 

only in the last 75 years have engineering and 

science been able to exploit its basic properties 

of hardness, smoothness, and transparency so 

that it can now be made into thousands of diverse 

products. 

The economics and techniques connected with 

mass production of glass articles have led to 

the construction of glass-manufacturing plants 

near or within highly populated areas. Un- 

fortunately, airborne contaminants generated 

by these glass plants can contrihute substantial- 

ly to the air pollution problem of the surround- 

ing community. Control of dust and fumes has, 

therefore, been, and must continue to be, in- 

herent to the progress of this expanding industry. 

Air pollution control is necessary, not only to 

eliminate nuisances, but also to bring substan- 

tial savings by extending the service life of 

the equipment and by reducing operating ex- 

penses and down time for repair. Reduction 

in plant source emissions can be accomplished 

by several methods, including control of raw 

materials, batch formulation, efficient com- 

bustion of fuel, proper design of glass-melt- 

ing furnaces, and the installation of control 

equipment. 

ufacture 765 

TYPES OF GLASS 

Nearly all glass produced commercially is one 

of five basic and broad types: Soda-lime, lead, 

fused silica, borosilicate, and 96 percent silica. 

Of these, modern soda-lime glass is well suited 

for melting and shaping into window glass, plate 

glass, containers, inexpensive tableware, elec- 

tric light bulbs, and many other inexpensive, 

mass-produced articles. It presently consti- 

tutes 90 percent of the total production of com- 

mercial glass (Kirk and Othmer, 1947). 

Typical compositions of soda-lime glass and 

the four other major types of commercial glass 

are shown on Table 204. Major ingredients of 

soda-lime glass are sand, limestone, soda ash, 

and cullet. Minor ingredients include salt cake, 

aluminum oxide, barium oxide, and boron oxide. 

Minor ingredients may be included as impuri- 

ties in one or more of the major raw ingredients. 

Soda-lime glasses are colored by adding a 

small percentage of oxides of nickel, iron, 

manganese, copper, and cobalt, and elemen- 

tal carbon as solutions or colloidal particles 

(Tooley, 1953). 

Although glass production results in tens of 

thousands of different articles, it can be divid- 

ed into the following general types (Kirk and 

Othmer, 1947): 

70 

- 

Flat glass 2 5 

Containers 5 0 

Tableware 8 

Miscellaneous instruments, scientific 

equipment, and others 17 

GLASS-MANUFACTURING PROCESS 

Soda-lime glass is produced on a massive scale 

in large, direct-fired, continuous melting fur- 

naces. Other types of glass are melted in small 

batch furnaces having capacities ranging from 

only a few pounds to several tons per day. Air 

pollution from the batch furnaces is minor, but 

the production of soda-lime glass creates major 

problems of air pollution control. 

A complete process flow diagram for the con- 

tinuous production of soda-lime glass is shown 

in Figure 587. Silica sand, dry powders, 

granular oxides, carbonates, cullet (broken 

glass), and other raw materials are transferred 

from railroad hopper cars and trucks to storage 

bins. These materials are withdraw from the 

storage bins, batch weighed, and blended in a 

mixer. The mixed batch is then conveyed to 

the feeders attached to the side of the furnace. 

Although dust emissions are created during


Table 204. COMPOSITIONS OF COMMERCIAL GLASSES (Kirk and Othmer, 1947) 

Component 

Si02 

Na20 

K2O 

CaO 

PbO 

B2°3 

AlZ03 

MgO 

. Soda-lime 

70 to 75 (72) 

12 to 18 (15) 

0 to 1 

5 to 14 (9) 

- 

- 

0.5 to 2.5 (1) 

0 to 4 (3) 

Figure 587. Flow diagram for soda-lime glass manufacture (Kirk 

and Othmer, 1947). 

these operations, control can be accomplished 

by totally enclosing the equipment and install- 

ing filter vents, exhaust systems, and bag- 

houses. 

Screw- or reciprocating-type feeders contin- 

uously supply hatch-blended materials to the 

direct-fired, regenerative furnace. These dry 

materials float upon the molten glass within 

Composition, qoa 

a~he figures in parentheses give the approximate composition of a typical member. 

SILICA SAND SODI ASH LIMESTONE 

or burn, ,me 

~andlonrr (in ~s., 

wva. I,,. MO., "D 

(rushed. wd$hzd. 

@pro*. 20.120 me* 

Oc8,a"Ylar 

M ~ atlo O relulfr 

,,raw mateldl 

ionIans MgCO, 

screenad to APProx. 2[il20 rn8.h 

8PP'o.. 20-100 mash 

CO"ti""0UI tan* turnsre ioo*mg Mdtlng 

doxnt"r.ugh top (crown,. about 2. 70o0i CYilPlcrYIhlng 

suhmera~ tnroat in aridaera,, 

Lead 

53 to 68 (68) 

5 to 10 (10) 

1 to 10 (6) 

0 to 6 (1) 

15 to 40 (15) 

- 

0 to 2 

- 

2 

Relining: 

fining and 

~orosilicate 96% silica 

73 to 82 (80) 

3 to 10 (4) 

0.4 to 1 

0 to 1 

0 to 10 

5 to 20 (14) 

2 to 3 (2) 

- 

96 

- 

- 

- 

- 

3 

- 

- 

Silica glass 

99. 8 

- 

- 

- 

- 

the furnace until they melt. Carbonates de- 

compose releasing carbon dioxide in the form 

of bubbles. Volatilized particulates, com- 

posedmostly of alkali oxides and sulfates, 

are captured by the flame and hot gases pass- 

ing across the molten surface. The particu- 

lates are either deposited & the checkers and 

refractory-lined passages or expelled to the 

atmosphere.

Glass Ma1 

The mixture of materials is held around 2, 700°F 

in a molten state until it acquires the homogeneous 

character of glass. Then it is gradually cooled 

to about 2,200aF to make it viscous enough to 

form. In a matter of seconds, while at a yellow- 

orange hot temperature, the glass is dram 

from the furnace and worked on forming machines 

by a variety of methods including pressing, blow- 

ing in molds, drawing, rolling, and casting. 

One source of air pollution is hydrocarbon greases 

and oils used to lubricate the hot delivery systems 

and molds of glass-forming machines. The smoke 

from these greases and oils creates a significant 

amount of air pollution separate from furnace 

emissions. 

Immediately after being shaped in the machines, 

the glass articles are conveyed to continuous 

annealing ovens, where they are heat treated 

to remove strains that have developed during 

the molding or shaping operations and then 

subjected to slow, controlled cooling. Gas- 

fired or electrically heated annealing ovens 

are not emitters of air contaminants in any 

significant quantity. After leaving the anneal- 

ing ovens, the glass articles are inspected and 

packed or subjected to further finishing opera- 

tions. 

Glass-forming machines for mass production 

of other articles such as rod, tube, and sheet 

usually do not emit contaminants in significant 

amounts . 

HANDLING, MIXING, AND STORAGE SYSTEMS 

FOR RAW MATERIALS 

Material-handling systems for batch mixing 

and conveying materials for making soda- 

lime glass normally use commercial equip- 

ment of standard design. This equipment is 

usually housed in a structure separate from 

the glass-melting furnace and is commonly 

referred to as a "batch plant. " A flow dia- 

gram of a typical batch plant is shown in Figure 

588. In most batch plants, the storage bins are 

located on top, and the weigh hoppers and mixers 

are below them to make use of the gravity flow. 

Major raw materials and cullet (broken scrap 

glass) are conveyed from railroad hopper cars 

or hopper trucks by a combination of screw 

conveyors, belt conveyors, and bucket eleva- 

tors, or by pneumatic conveyors (not shown in 

Figure 588) to the elevated storage bins. Minor 

ingredients are usually delivered to the plant 

in paper bags or cardboard drums and trans- 

ferred hy hand to small bins. 

Ingredients comprising a batch of glass are 

dropped by gravity from the storage bins into 

weigh hoppers and then released to fall into 

the mixer. Cullet is ground and then mixed 

with the dry ingredients in the mixer. Ground 

cullet may also bypass the mixer and be mixed 

instead with the other blended materials in the 

bottom of a bucket elevator. A typical batch 

charge for making soda-lime flint glass in a 

mixer with a capacity of 55 cubic feet consists 

of: 

Silica sand 

Cullet 

Soda ash 

Limestone 

Niter 

Salt cake 

Arsenic 

Raw materials are blended in the mixer for peri- 

ods of 3 to 5 minutes and then conveyed to a 

charge bin located alongside the melting furnace. 

At the bottom of the charge bin, rotary valves 

feed the blended materials into reciprocating- or 

screw-type furnace feeders. 

In a slightly different arrangement of equipment 

to permit closer control of batch composition, 

blended materials are discharged from the mixer 

into batch cans that have a capacity of one mixer 

load each. Loaded cans are then conveyed by 

monorail to the furnace feeders. Trends in 

batch plant design are toward single reinforced- 

concrete structures in which outer walls and 

partitions constitute the storage bins. Complete 

automation is provided so that the batch plant is 

under direct and instant control of the furnace 

foreman. 


The major raw materials for making soda-lime 

glass--sand, soda-ash, and limestone--usually con- 

tain particles averaging about 300 microns in size, 

Particles less than 50 microns constitute only a 

small portion of the materials, but are presentin 

sufficient quantities to cause dust emissions during 

conveying, mixing, and storage operations. More- 

over, minor raw materials such as salt cake and 

sulfur can create dust emissions during handling. 

Dust is the only air contaminant from batch plants. 

and the control of dust emissions poses problems 

similar to those in industrial plants handling simi- 

lar dusty powder or granular materials. 

Hooding and Ventilation Requirements 

Dust control equipment can be installed on con- 

veying systems that use open conveyor belts. 

A considerable reduction in the size of the dust


CULLET 

- > - 2 - * - = 

MAGNETIC E 

SEPARATOR + 

< 

- 

CRUSHER = rn 

RAW MATERIALS 

RECEIVING 

HOPPER 

V 

SCREW 

CONVEYOR 

C 

- 

-1 

BELT CONVEYOR 

Figure 588. Process flow diagram of a hatch plant. 

control equipment can be realized by totally en- cfm per foot of belt width, with 200 fpm minimum 

closing all conveying equipment and sealing all 

covers and access ooenines with easkets of 

velocity through the hood openings. 

polyurethane foam. In fact, by totally enclos- 

- 


ing all conveying ~. equipment, . - exhaust systems 

become unnecessary, and relatively small filter 

Because dust emissions contain particles only i 

vents or dust cabinets can be attached directly 

! 

a few microns in diameter, cyclones, and cento 

the conveying equipment and storage bins. 

I 

On the other hand, exhaust systems are re- 

quired for ventilating the weigh hoppers and 

mixers. For example, a 60-cubic-foot-capacity 

mixer and a 4,500-pound-capacity mixer each 

require about 600 cfm ventilation air. Seals of 

polyvinylchloride should be installed between 

the rotating body of the mixer and its frame td 

reduce ventilation to a minimum. 

Railroad hopper cars and hopper bottom trucks 

must be connected to sealed receiving hoppers 

by fabric sleeves so that dust generated in the 

hoppers during the loading operation is either 

filtered through the sleeves or exhausted tbrough 

a baghouse. 

Local exhaust systems for dust pickup are de- 

signed by using the recommended practice of the 

Committee on Industrial Ventilation (1960). For 

example, the ventilation rate at the transfer 

point between two open belt conveyors is 350 

- - 

trifueal scrubbers are not as effective as haehouses 

or filters are in collecting these small 

I 

; 

particles; consequently, simple cloth filters and I 

I 

baghouses are used almost exclusively in con- 1. 

trolling dust emissions from batch plants. 

Filter socks or simple baghouses with intermittent 

shaking mechanisms are usually de- 

I 

signed for a filter velocity of 3 fpm, but bag- 

i 

I 

houses with continuous cleaning devices such as i 

pulse jets or reverse air systems can be de- 

! 

signed for filter velocities as high as 10 fpm. i' 

Filtration cloths are usually cotton, though ny- i 

lon, orlon, and dacron are sometimes used. 

Dusts collected are generally noncorrosive. 

Filters or baghouses for storage bins are designed 

to accommodate not only displaced air 

from the filling operation but also air induced 

by falling materials. Filtration of air exhaust 

from pneumatic conveyors used in filling the 

bins must also be provided. Filters with at least 

a 1-square-foot area should be mounted on the 

hand-filled minor-ingredient bins. 

4 

I 

! 

i 

! 

~

Glass Man1 

Transfer chutes of special design are used for 

hand filling the minor ingredient bins. They are 

first attached securely with gaskets to the top of 

the bins. The bags are dropped into a chute 

containing knives across the bottom. The knives 

split the bag, and as the materials fall into the 

bin, the broken bag seals off the escape of dust 

from the top of the chute. 

CONTlNUOUS SODA-LIME GLASS-MELTING FURNACES 

While limited quantities of special glasses such 

as lead or horosilicate are melted in electrically 

heated pots or in small-batch, regenerative fur- 

naces with capacities up to 10 tons per day, the 

hulk of production, soda-lime glass, is melted 

in direct-fired, continuous, regenerative furnaces. 

Many of these furnaces have added electric induc- 

tion systems called "boosters" to increase capac- 

ity. Continuous, regenerative furnaces usually 

range in capacity from 50 to 300 tons of glass 

per day; 100 tons is the most common capac- 

ity found in the United States. 

Continuous, regenerative, tank furnaces differ 

in design according to the type of glass products 

manufactured. All have two compartments. In 

the first compartment, called the melter, the dry 

ingredients are mixed in correct prcportions and 

are continuously fed onto a molten mass of glass 

having a temperature near 2,700-F. The dry mate- 

rials melt after floating a third to one-half of the 

way across the compartment and disappearing into 

the surface of a clear, viscous-liquid glass. Glass 

flows from the melter into the second compartment, 

commonly referred to as the refiner, where it is 

mixed for homogeneity and heat conditioned to 

eliminate bubbles and stones. The temperature 

is gradually lowered to about 2,200-F. The 

amount of glass circulating within the melter 

and refiner is about 10 times the amount with- 

drawn for production (Sharp, 1954). 

Regenerative furnaces for container and tableware 

manufacture have a submerged opening or throat 

separating the refiner from the melter. The throat 

prevents undissolved materials and scum on the 

surface from entering the refiner. Glass flows 

from the semicircular refining compartment into 

long, refractory-lined chambers called forehearths. 

Oil or gas burners and ventilating dampers ac- 

curately control the temperature and viscosity of 

the glass that is fed from the end of the forehearth 

to glass -forming machines. 

Continuous furnaces for manufacturing rod, tube, 

and sheet glass differ from furnaces for container 

and tableware manufacture in that they have no 

throat between the melter and refiner. The com- 

partments are separated from each other by float- 

ing refractory beams riding in a drop arch across 

the entire width of the furnace. Glass flows from 

the rectangular-shaped refiner directly into the 

forming machines. 

Regenerative firing systems for continuous glass 

furnaces were first devised by Siemens in 1852, 

and since then, nearly all continuous glass fur- 

naces in the United States have used them. In 

Europe, continuous glass furnaces employ both 

recuperative and regenerative systems. 

Regenerative firing systems consist of dual 

chambers filled with brick checkerwork. While 

the products of combustion from the melter pass 

through and heat one chamber, combustion air 

is preheated in the opposite chamber. The func- 

tions of each chamber are interchanged during 

the reverse flow of air and combustion products. 

Reversals occur every 15 to 20 minutes as re- 

quired for maximum conservation of heat. 

Two basic configur~tions are used in designing 

continuous, regenerative furnaces - end port. 

Figure 589, and side port, Figure 590. Ir, the 

side port furnace, combustion products and 

flames pass in one direction across the melter 

during one-half of the cycle. The flow is reversed 

during the other half cycle. The side 

port design is commonly used in large furnaces 

with melter areas in excess of 300 square feet 

(Tooley, 1953). 

In the end port configuration, combustion products 

and flames travel in a horizontal U-shaped path 

across the surface of the glass within the melter. 

Fuel and air mix and ignite at one port and dis- 

charge through a second port adjacent to the first 

on the same end wall of the furnace. While the 

end port design has been used extensively in small- 

er furnaces with melter areas from 50 to 300 

square feet, it has also been used in furnaces with 

melter areas up to 800 square feet. 

Continuous furnaces are usually operated slightly 

above atmospheric pressure within the melter to 

prevent air induction at the feeders and an over- 

all loss in combustion efficiency. Furnace draft 

can be produced by several methods: Induced- 

draft fans, natural-draft stacks, and ejectors. 


Particulates expelled from the melter are the re- 

sult of complex physical and chemical reactions 

that occur during the melting process. 

Glass has properties akin to those of crystalline 

solids, including rigidity, cold flow, and hard- 

ness. At the same time, it behaves like a super-

. . 

. . 

. .~ 

. . . ~. 


Figure 589. Regeneratlve end port glass-melting furnace. 

cooled liquid. It has nondirectional properties, 

fracture characteristics of an amorphous solid, 

and no freezing or melting point. To account for 

the wide range of properties, glass is considered 

to be a configuration of atoms rather than an aggregate 

of molecules. Zachariasen (1932) proposed 

the theory that glass consists of an extended, 

continuous, three-dimensional network of ions with 

a cet.tain amount of short-distance-ordered arrangement 

similar to that of a polyhedral crystal. 

These dissimilar properties explaln in part why 

predictions of particulate losses from the melter 

based solely upon known temperatures and vapor 

pressures of purp compounds have been inaccurate. 

Other phenomena affect the generation of par- 

ticulates. During the melting process, carbon 

dioxide bubbles and propels particulates from the 

melting batch. Particulates are entrained by the 

fast-moving stream of flames and combustion 

gases. As consumption of fuel and refractory tem- 

peratures of the furnace increase with glass ton- 

nage, particulates also increase in quantity. Par- 

ticulates, swept from the melter, are either col- 

lected in the checkerwork and gas passages or 

exhausted to the atmosphere. 

Source test data 

In a recent study, many source tests of glass 

furnaces in Los Angeles County were used for 

determining the major variables influencing stack 

emissions. As summarized in Table 205, data 

include: Particulate emissions, opacities, pro- 

cess variables, and furnace design factors. 

Particle size distributions of two typical stack 

samples are shown in Table 206. These particu- 

late samples were obtalned from the catch of a 

pilot baghouse venting part of the effluent from 

a large soda-lime container furnace.

Chemical composition of the particulates was 

determined by microquantitative methods or by 

spectrographic analysis. Five separate samples, 

four from a pilot baghouse, and one from the 

stack of a soda-lime regenerative furnace, are 

given in Table 207. They were found to be com- 

posed mostly of alkali sulfates although alkalies 

are reported as oxides. The chemical composi- 

tion of sample 5 was also checked by X-ray 

crystallography. In this analysis, the only 

crystalline material present in identifiable 

amounts was two polymorphic forms of sodium 

sulfate. 

Opacity of stack emissions 

From the source test data available, particu- 

late emissions did not correlate with the opacity 

of the stack emissions. Some generalizations on 

opacity can, however, be made. Opacities usu- 

Glass Manufacture 771 

Figure 590. Regenerative side port glass-melting furnace. 

ally increase as particulate emissions increase. 

More often than not, furnaces burning U. S. Grade 

5 fuel oil have plumes exceeding 40 percent white 

opacity while operating at a maxim- pull rate, 

which is the glass industry's common term for 

production rate. Plumes from these same fur- 

naces were only 15 to 30 percent white opacity 

while burning natural gas or U. S. Grade 3 

(P.S. 200) fuel oil. Somewhat lower opacities 

may be expected from furnaces with ejector 

draft systems as compared with furnaces with 

natural-draft stacks or induced-draft fans. 


In order to determine the correct size of air 

pollution control equipment, the volume of dirty 

exhaust gas from a furnace must be known. Some 

of the more important factors affecting exhaust 

volumes include: Furnace size, pull rate, com-


Test No. 

C-339b 

C-339 

C-382-1 

C-382-2 

C-536 

C-383 

Pri Lab 

Pri Lab 

Pri Lab 

Pri Lab 

Pri Lab 

Pri Lab 

Pri Lab 

C-101 

C-120 

C-577 

C-278-1 

C-278-2 

C-653 

C-244-1 

C-244-2 

C-420-1 

C-420-2 

C-743 

C-471 

Table 205. SOURCE TEST DATA FOR GLASS-MELTING FURNACES 

x1 

Type Type (particulate 

of of 

furnacea fuel 

x33 

wt fraction 

of cullet in 

chargeC 

0.300 

0.300 

0. 300 

0.300 

0.199 

0.300 

0. 094 

0. 094 

0. 157 

0. 094 

0. 365 

0.269 

0. 175 

0.300 

0. 320 

0. 134 

0.361 

0. 360 

0. 131 

0. 182 

0.100 

0. I00 

0.100 

0.047 

0.276 

x4 

(checker volumd, 

ft3/ft2 of melter 

a~~ = end port, regenerative furnace; SP = side port, regenerative furnace. 

bG = natural gas; 0-200 = U.S. Grade 3 fuel oil; 0-300 = U.S. Grade 5 fuel oil. 

CConstants: Sulfate content of charge 0. 18 to 0. 34 wt 70. 

Fines (-325 mesh) content of charge 0.2 to 0.3 wt %. 

bustion efficiency, checker volume, and furnace 

condition. 

Exhaust volumes can be determined from fuel 

requirements for container furnaces given by 

the formula of Cressey and Lyle (1956). 

where 

F = total beat, 10 

6 

Btulday 

A = melter area, ft2 

T = pull rate, tonsfday. 

This straight-line formula includes minimum 

heat to sustain an idle condition plus additional 

heat for a specified pull rate. Fuel require- 

ments for bridgewall-type, regenerative fur- 

naces are also given by Sharp (1955) and are 

Maximum 

opacity 

of stack 

emissions, 

5 0 

10 

10 

10 

10 

2 0 

2 5 

2 5 

25 

2 5 

-- 

45 

20 

2 0 

2 0 

3 5 

2 0 

2 0 

40 

2 5 

25 

10 

5 

2 5 

30 

shown in Figure 591. The melter rating para- 

meter of 4 square feet of melter surface area 

per daily ton of glass should be used to estimate 

the fuel requirements of container furnaces at 

maximum pull rates, but 8 square feet per ton 

can be used for estimating fuel requirements 

for non-bridgewall furnaces supplying glass 

for tableware and for sheet, rod, and tube 

manufacture. Fuel requirements given are 

averages for furnaces constructed before 1955; 

consequently, these furnaces generally require 

more fuel per ton of glass than do furnaces con- 

structed since 1955. After the fuel require- 

ments are determined, exhaust volumes are com- 

puted on the basis of combustion with 40 percent 

excess combustion air. Forty percent excess 

combustion air is chosen as representing av- 

erage combustion conditions near the end of the 

campaign/ (a total period of operation without shut- 

ting down for repairs to the furnace). 

Exhaust volumes determined from fuel require- 

ments are for furnaces with induced-draft sys-


Table 206. SIZE DISTRIBUTION OF in temperature from 600" to 850°F, but exhaust 

PARTICULATE EMISSIONS gas temperatures from furnaces containing ejec- 

(MICROMEROGRAPH ANALYSES) tors are lower and vary from 400" to 600°F: 

- In Table 208 are found chemical analyses of gas- 

Furnace 1 

D~ameler (D), 

W 

36.60 

22.00 

18. 30 

16.50 

14.60 

12.80 

12.20 

11.60 

11.00 

10.40 

9. 80 

9.20 

8.5G 

7. 30 

6. 10 

4. 88 

3. 66 

3. 05 

2.44 

1. 83 

1. 52 

1.22 

Fhnt glass 

70 (by wt) 

Less than D 

100 

99. 5 

98. 6 

97.7 

94.0 

84. 6 

80.7 

76.6 

72. 7 

67. 7 

62.4 

58. 3 

51.8 

43.1 

34.4 

28. 0 

21.3 

18. 6 

14. 9 

11.0 

8. 3 

4. 1 

Furnace 2 Amber @ass 

Dlamcter (D), 70 (by wt) 

&. 

less than D 

17.40 100 

15.70 

99.8 

14. 00 

99.4 

12.20 

96. 8 

11.60 

92. 5 

11.00 

84. 5 

10.50 

87. 2 

9.90 

83.4 

9.30 

78. 7 

8.80 

75.0 

8. 10 

73.4 

7.00 

60. 3 

5.80 

47.6 

4. 65 

35. 6 

3.49 

25. 4 

2.91 

20. 5 

2.33 

16. 4 

1.74 

10.9 

1.45 

8.9 

1. 16 

5.3 

eous components of exhaust gases from large, 

regenerating, gas-fired furnaces melting three 

kinds of soda-lime glass. 

Air Pollution Control Methods 

As the furnace chmpaign progresses, dust carry- 

over speeds destruction of the checkers. Upper 

courses of the firebrick checker glaze when sub- 

jected to high temperatures. Dust and condensate 

collect on the brick surface and form slag that 

drips downward into the lower courses where it 

solidifies at the lower temperature and plugs the 

checkers. Slag may also act somewhat like fly- 

paper, tenaciously clinging to the upper courses 

and eventually sealing off upper gas passages. 

Hot spots develop around clogged checkers and 

intensify the destructive forces, which are re- 

flected by a drop in regenerator efficiency and a 

rise in fuel consumption and horsepower required 

to overcome additional gas flow resistance through 

the checkers. Checker damage can finally reach 

tems or natural-draft stacks. Exhaust volumes a point where operation is no longer economical or 

for ejector systems can he estimated by increas- is physically impossible because of collapse. Thus, 

ing the exhaust volume by 30 to 40 percent to successful operation of modern regenerative fur- 

account for ejector air mixed with the furnace naces requires keeping dust carryover from the 

effluent. melter to an absolute minimum, which also coin- 

cides with air pollution control ohjectives by prevent- 

Exhaust gases from furnaces with natural-draft ing air contaminants from entering the atmosphere. 

stacks or induced-draft fan systems usually range Aside from reducing air contaminants, benefits de- 

Table 207. CHEMICAL COMPOSITION OF PARTICULATE EMISSIONS 

(QUANTITATIVE ANALYSES), METALLIC IONS REPORTED AS OXIDES 

Sample source 

Test 

type of glass 

components 

Baghouse 

catch 

No. 1 

amber, 

wt % 

Silica (Si02) (SiO,) 

0. 03 

Calcium oxide (CaO) 

1. 70 

Sulfuric anhydride (SO3) ) 

Boric anhydride (B203) 

Arsenic oxide (As,O?) - - 

Chloride (Cl) 

46.92 

3. 67 

7. 71 

Lead oxide (PbO) 0. 39 

Fe203 

MgO 

ZnO 

Unknown metallic oxide (R203) 

Loss on ignition 

10.10 

Baghouse 

catch 

No. 2 

flint, 

wt Yo 

0.3 

2.3 

25. 1 

1.3 

30.8 

Baghouse 

catch 

No. 3 

amber, 

wt Yo 

0.1 

0.8 

46. 7 

0.1 

0.5 

25. 7 

Baghouse 

catch 

No. 4 

flint, 

wt % 

4.1 

19.2 

30.5 

0.6 

1.4 

7.5 

Millipore 

filter 

No. 5 

flint, 

wt % 

3.3 

39.4 

6. 5 

11. 6


By the method of Brandon (1959), particulate emis- 

sions, the dependent variable were found to corre- 

late with the following independent variables and 

nonquantitative factors: 

1. Process weight, lb/hr-ft2; 

2. cullet, wt % of charge; 

3 2 

3. checker volume, ft /ft melter; 

4. type of furnace, side port or end port; 

5. type of fuel, U.S. Grade 5 (PS300) oil or 

natural gas; 

2 

6. melter area, ft . 

Several simplifying assumptions are made so that 

furnaces of different sizes can be compared. Pro- 

cess weight per square foot of melter describes a 

unit process occurring in each furnace regardless 

of size. Cubic feet of checkers per square foot 

of melter not only defines the unit's dust-collect- 

ing capability but is also a measure of fuel economy. 

Source tests C-382 and C-536 in Table 205 (and 

other source tests) show no appreciable difference 

in particulate emissions from burning natural gas 

or U. S. Grade 3 fuel oil. 

MELTER AREA. f t 2 

Correlation of particulate emissions with weight 

percent sulfate (SO3) and minus 325-mesh fines 

in the charee - was not nossible because of insuffi- 

Figure 591' gas for 

regenerative furnaces (Sharp, 1955). 

I-type 

cient test data. Limited data available indicate 

that particulate emissions may double when total 

sulfate (SO2) content of the batch charge is in- 

A 

creased from 0. 3 to 1. 0 weight percent. Total 

rived from reducing dust carryover are many and sulfates (SO3) include equivalent amounts of eleinclude 

longer furnace campaigns, lower mainte- mental sulfur and all compounds containing sulfur. 

nance costs, and savings on fuel. 

Sulfates usually comprise over 50 percent of the 

particulate emissions. They act as fluxing agents 

In order to determine which design and operating preventing the melting dry-hatch charge from 

variables have the greatest effect upon dust carry- forming a crust that interferes with heat transover 

and particulate emissions, statistical analysis fer and melting (Tooky, 1953). Compounds of 

was performed on the source test data given in arsenic, boron, fluorine, and metallic selenium 

Table 205. 

are also expected to be found alone with sodium 

sulfate in the particulate emissions because of 

their high vapor pressures. 

Data roughly indicate that particulate emissions 

increase severalfold when the quantity of minus 

325-mesh fines increases from 0. 3 weight per- 

cent to 1 or 2 weight percent. 

Statistical analysis using the method of curvilinear 

multiple correlation by Ezekiel (1941) results in the 

following equation, which describes particulate 

emissions, the dependent variable, as a function 

Table 208. CHEMICAL COMPOSITION OF GASEOUS EMISSIONS 

FROM GAS-FIRED, REGENERATIVE FURNACES 

Gaseous components 

Nitrogen, vol 7% 

Oxygen, vol 70 

Water vapor, vol 70 

Carbon dioxide, vol % 

Carbon monoxide, vol % 

Sulfur dioxide (SO2), ppm 

Sulfur trioxide (SO3), ppm 

Nitrogen oxides (NO,NOZ), ppm 

Organic acids, ppm 

Aldehydes, ppm 

aNA = not available. 

Flint glass 

71. 9 

9. 3 

12.4 

6. 4 

0 

0 

0 

724 

NA" 

N A 

Amber glass 

81. 8 

10.2 

7.7 

8. 0 

0. 007 

61 

12 

137 

5 0 

7 

Georgia green 

72.5 

8.0 

12.1 

7.4 

0 

14 

15 

N A 

N A 

N A

of four independent variables and two nonquanti- 

tative independent factors. This equation is 

valid only when two other independent variables-- 

sulfate content and content of minus 325-mesh fines 

of the batch--lie between 0. 1 to 0. 3 weight percent 

and, also, when fluorine, boron, and lead com- 

pounds are either absent from the batch charge or 

present only in trace amounts. 

where 

XI = particulate emissions, lb/hr 

2 

X2 = process wt, lb/hr-ft melter 

X3 = 

wt fraction of cullet in charge 

X4 = 

3 2 

checker volume, ft /ft melter 

X5 = 

2 

melter area, ft 1100 

Glass Ma nufacture 77c 

(152) 

a = constant involving two nonquantitative 

independent factors relating the type 

of furnace (side port or end port) and 

the type of fuel (U. S. Grade 5 fuel or 

natural gas). 

a = -0.493 end port - U.S. Grade 5 

fuel oil 

a = -0. 623 side port - U.S. Grade 5 

fuel oil 

a = -1.286 end port - natural gas 

a = -1.416 side port - natural gas. 

Particulate emissions computed by this equation 

for 25 source tests show a standard deviation 

from measured particulate emissions of + 1.4 

pounds per hour. Further statistical refine- 

ment failed to yield a lower standard deviation. 

Emissions to the atmosphere can be predicted 

by using equation 152 or Figures 592 to 595, which 

are based upon this equation. The curves should 

be used only within the limits indicated for the 

variables. The curves should not be extrapolated 

in either direction with the expectation of any de- 

gree of accuracy, even though they appear as 

straight lines. Particulate emissions are first 

determined from Figure 592, then positive or 

negative corrections obtained from Figures 593 

to 595 are added to the emissions obtained from 

Figure 592. 

Design and operation of soda-lime, continuous, 

regenerative furnaces to alleviate dust carry- 

over and minimize particulate emissions are 

discussed in succeeding paragraphs. Advantages 

of all-electric, continuous furnaces for melting 

glass are also cited. 

Control of raw materials 

Although glassmakers have traditionally sought 

fine-particle materials for easier melting, these 

materials have intensified dust carryover in regenerative 

furnaces. A compromise must be 

reached. Major raw materials should be in the 

form of small particles, many of them passing 

U. S. 30-mesh screen, but not more than 0. 3 

weight percent passing U. S. 325-mesh screen. 

Because crystals of soda ash, limestone, and 

other materials may be friable and crush in the 

mixer, producing excessive amounts of fines, 

screen analyses of individual raw materials 

should not be combined for estimating the screen 

analyses of the batch charge. Crystalline shape 

and density of raw materials should be thoroughly 

investigated before raw material suppliers are 

selected. 

Since particulate emissions from soda-lime re - 

generative furnaces increase with an increase in 

equivalent sulfate (SO3) present in the batch 

charge, sulfate content should be reduced to an 

absolute minimum consistent with good glassmaking. 

Preferably, it should be below 0. 3 

weight percent. Equivalent sulfate (SO3) content 

of the batch includes all sulfur compounds and 

elemental sulfur. Compounds of fluorine, boron, 

lead, and arsenic are also known to promote dust 

carryover (Tooley, 1953), but the magnitude of 

their effect upon emissions is still unknown. In 

soda-lime glass manufacture, these materials 

should be eliminated or should be present in only 

trace amounts. 

From the standpoint of suppressing stack emis- 

sions, cullet content of the batch charge should 

be kept as high as possible. Plant economics may, 

nevertheless, dictate reduction in cullet where fuel 

or cullet is high in cost or where cullet is in short 

supply. Some manufacturing plants are able to 

supply all their cullet requirements from scrap and 

reject glassware. 

Batch preparation 

There are a number of ways to condition a batch 

charge and reduce dust carryover. Some sodalime 

glass manufacturers add moisture to the 

dry batch, but the relative merits of this process 

are debatable. Moisture is sprayed into the drybatch 

charge at the mixer as a solution containing 

1 gallon of surface-active wetting agent to 750 

gallons of water. Surface tension of the water is 

reduced by the wetting agent so that the water 

wets the finest particles and is evenly distributed


Figure 592. Particulate emlsslons versus checker 

volume per ft2 of melter. 

- x 

z 

w, 

- 

B 

B 

7 

6 

E 3 

+ 

c, u 2 

= 

- 

cz 

U I 

0 

I 

3 

0 B 12 16 20 24 28 31 

X2 PROCESS WEIGHT, Ib/hr Per 11' neller 

Figure 593. Correction to particulate emissions 

for process weight per ft2 melter. 

U.YI U,IU U. 13 U.IU 0.25 0.30 0.35 

X1. KEIGHT FRACTIOH OF CULLET IH CHIAGE 

Figure 594. Correction to particulate emissions for cullet content 

of the batch charge. 

Figure 595. Correction to particulate emissions 

for melter area. 

, Other 

throughout the batch (Wilson, 1960). Fluxing 

materials such as salt cake appear more effec- 

tive, since the unrnelted batch does not usually 

travel so far in the melter tank before it melts. 

Moisture content of the batch is normally in- 

creased to about 2 percent by weight. If the 

moisture content exceeds 3 percent, batch in- 

gredients adhere to materials-handling equip- 

ment and may cake in storage bins or batch cans. 

batch preparation methods have been em- 

ployed on a limited-production or experimental 

basis to reduce dust carryover from soda-ash 

glass manufacture. One method involves prer 

sintering the batch to form cullet and then charg- 

ing only this cullet to the furnace. Advantages

Glass Manx 

claimed are faster melting, better batch con- 

trol, less seed formation, reduced clogging in 

the checkers, and lower stack losses (Arrandale, 

1962). A Dutch oven doghouse cover also reduces 

dust carryover by sintering the top of the floating 

dry batch before it enters the melter. This meth- 

od is probably not as efficient as is complete pre- 

sintering in reducing dust carryover. 

Other methods include: (1) Charging briquets, 

which are made from regular batch ingredients 

by adding up to 10 percent by weight of water; 

(2) charging wet hatches containing 6 percent 

moisture, which are made by first dissolving 

soda-ash to form a saturated solution and mix- 

ing this solution with sand and the other dry 

materials: (3) charging the dry batch (Submerged) 

in the melter; (4) enclosing batch feeders (Fabri- 

anio, 1961); and (5) installing batch feeders on 

opposite sides of end port, regenerative furnaces 

and charging alternately on the side under fire. 

Checkers 

The design concept of modern regenerative fur- 

naces, with its emphasis on maximum use of 

fuel, is also indirectly committed to reducing 

dust carryover. All things being equal, less 

fuel burned per ton of glass means less dust 

entrainment by hot combustion gases and flames 

flowing across the surface of the melting glass. 

Although container furnaces constructed over 

15 years ago required over 7,000 cubic feet of 

natural gas per ton of glass at maximum pull 

rates, container furnaces built today can melt 

a ton of glass with less than 5,000 cubic feet 

of natural gas. 

While several design changes are responsible 

for this improvement, one of the most important 

is the increase in checker volume. The ratio of 

checker volume (cubic feet) to meter area (square 

feet) has been rising during the years from about 

5 in earlier furnaces to about 9 today. Enlarged 

checkers not only reduce fuel consumption and 

particulate formation but also present a more 

effective trap for dust particles that are expelled 

from the melter. Source tests conducted by a 

large glass-manufacturing company indicated 

that over 50 percent of the dust carryover from 

the melter is collected by the checkers and gas 

passages instead of entering the atmosphere. 

Of course, the economics connected with regen- 

erative furnace operation dictates the checker 

volume. The law of diminishing returns oper- 

ates where capital outlay for an added volume 

of checkers will no longer be paid within a spe- 

cified period by an incremental reduction in fuel 

costs. Checkers have been designed in douhle- 

pass arrangements to recover as much as 55 per- 

cent of the heat from the waste gases (Sharp, 1954). 

Although dust collects within checkers by mechan- 

isms of impingement and settling, the relationship 

among various factors influencing dust collection 

is unknown. These factors include: Gas velocity, 

brick size, flue spacing, brick setting, and brick 

composition. Checkers designed for maximum 

fuel economy may not necessarily have the high- 

est collection efficiency. Further testing will 

he necessary in order to evaluate checker de- 

signs. Checkers designed for maximum heat 

exchange contain maximum heat transfer surface 

per unit volwne, a condition met only by smaller 

refractories with tighter spacing. Heat transfer 

surfaces can be computed by the method given in 

Trinks (1955). Since gas velocities are also 

highest for maximum heat transfer, less dust 

collects by simple settling than by impingement. 

Dust collection is further complicated in that 

smaller brick increases the potential for clogging. 

To prevent clogging in the checkers and ensure 

a reasonable level of heat transfer, checkers 

should be cleaned once per month or more often; 

an adequate number of access doors should be 

provided for this purpose (Spain, 195613). Com- 

pressed air, water, or steam may be used to 

flush fine particles from the checkers. Virtual- 

ly nothing can be done to remove slag after it 

has formed. Checkers can be arranged in a 

double vertical pass to reduce overall furnace 

height and make cleaning easier. Access doors 

should also be provided for remqving dust de- 

posits from the flues. 

Preheaters 

Further reductions in fuel consumption to re- 

duce dust emissions may be realized by install- 

ing rotsry, regenerative air preheaters in series 

with the checkers. Additional benefits include 

less checker plugging, reduced maintenance, and 

increased checker life. Rotating elements of 

the preheater are constructed of mild steel, low- 

alloy steel, or ceramic materials. Preheaters 

raise the temperature of the air to over 1, 000°F. 

and the increased velocity of this preheated air 

aids in purging dust deposits that block gas pas- 

sages of the checkers. Exhaust gases passing 

through the opposite side of the preheater are 

cooled below 800°F before being exhausted to 

the atmosphere. A heat balance study of a plate 

glass, regenerative furnace shows a 9 percent 

increase in heat use by the installation of a 

rotary, regenerative air preheater (Waitkus, 

1962). To maintain heat transfer and prevent 

re-entrainment, dust deposits on the preheater 

elements must he removed by periodic cleaning. 

Ductwork and valves should he installed for by- 

passing rotary air preheaters during the cleaning 

stage.


Refractories and insulation 

Slagging of the upper courses of checkerwork 

can be alleviated in most cases by installing 

basic (high alumina content) brick in place of 

superduty firebrick (Robertson et al., 1957). 

Basic brickcourses extend from the topdown- 

ward to positions where checker temperatures 

arebelow l,50O0F. Atthis temperature, fire- 

bricknolonger "wets" and forms slagwithdust 

particles. Dust usually collects in the lower 

courses of firebrick in the form of fine particles 

that are easily removed by cleaning. Although 

basic brick costs 3 or 4 times as much as super- 

duty firebrick, some glass manufacturers are 

constructing entire checkerworks of basic brick 

where slagging and clogging are most severe. 

In some instances, basic refractories are re- 

placing fireclay rider tiles and rider arches 

in checker supports (Van Dreser, 1962). A 

word of caution, basic brick is no panacea for 

all ills of checkers. Chemical composition of 

the dust should be known, to determine com- 

patibility with the checkers (Fabrianio, 1961). 

Regenerative furnaces can be designed to con- 

sume less fuel and emit less dust by proper 

selection and application of insulating refrac- 

tories. A heat balance study of a side port, re- 

generative furnace shows that, in the melting 

process, glass receives 10 percent of heat 

transfer from convection and 90 percent from 

radiation. Of the radiation portion of heat 

transferred, the crown accounts for 33 percent 

(Merritt, 1958). Since heat lossesthrough the un- 

insulated crown can run as high as 10 percent of 

the total heat input, there is need for insulation 

at this spot. 

Most crowns are constructed of silica brick 

with a maximum furnace capacity restricted to an 

operating temperature of 2,850"F (Sharp, 1955). 

Insulation usually cons is ts of insulating silica 

brick backed with high-duty plastic refractory. 

Furnaces are first operated without insulation, 

so that cracks can be observed. Then the cracks 

are sealed with silica cement, and the ~nsulation 

is applied. 

Insulation is needed on the melter sidewall and 

at the port necks to prevent glassy buildup caused 

by condensation of vapors. Condensate buildup 

flows across port sills into the melter and can 

become a major source of stones. 

While insulation of sidewalls shows negligible 

fuel reduction for flint glass manufacture, it 

does show substantial fuel reduction for colored 

glasses. The problem in manufacturing colored 

glass is to maintain a high enough temperature 

below the surface to speed the solution of stones 

and prevent stagnation. Insulation on sidewalls 

raises the mean temperature to a point where 

stones dissolve and glass circulates freely. 

Six inches or more of electrofusion cast block 

laid over a clay bottom in a bed of mortar (Baque, 

1954) not only saves fuel but is also less subject 

to erosion than is fireclay block. 

Insulation is seldom needed on the refining end 

of the furnace since refiners have become cool- 

ing chambers at today's high pull rates. Nose 

crowns, however, are insulated to minimize con- 

densation and drip (Bailey, 1957). Checkers are 

sometimes encased in steel to prevent air infiltra- 

tion through cracks and holes that develop in the 

refractory regenerator walls during the campaign. 

Combustion of fuel 

Furnace size also has an effect upon use of fuel, 

with a corresponding effect on the emissions of 

dust. Large furnaces are more economical than 

are small furnaces because the radiating surface 

or heat loss per unit volume of glass is greater 

for small furnaces. 

Slightly greater fuel economy may be expected 

from end port furnaces as compared with side 

port furnaces of equal capacity. Here again, the 

end port furnace has a heat loss advantage over 

the side port furnace because it has less exposed 

exterior surface area for radiating heat. Side 

port furnaces can, however, be operated at great- 

er percentages in excess of capacity since mixing 

of fuel with air is more efficient through several 

smaller inlet ports than it is through only one 

large inlet port. In fact, end port furnaces are 

limited in design to the amount of fuel that can 

be efficiently mixed with air and burned through 

this one inlet port (Spain, 1955). As far as dust 

losses are concerned, there are only negligible 

differences between end port and side port furnaces 

of equal size. Reduced fuel consumption to re- 

duce dust carryover can also be realized by in- 

creasing the depth of the melter to the maximum 

consistent with good-quality glass. Maximum 

depths for container furnaces are 42 inches for 

flint glass (Tooley, 1953) and about 36 inches for 

amber glass and emerald green glass. 

Dust emissions as well as fuel consumption can 

also be reduced by firing practice. Rapid changes 

in pull rates are wasteful of fuel and increase 

stack emissions. Hence, charge rates and glass 

pull rates for continuous furnaces should remain 

as constant as possible by balancing loads be- 

tween the glass -forming machines. If possible, 

furnaces should be fired on natural gas or U. S. 

Grade 3 or lighter fuel oil. Particulate emis - 

sions increase an average of about 1 pound per 

hour when U. S. Grade 5 fuel oil is used instead

of natural gas or U. S. Grade 3 fuel oil, and 

opacities may exceed 40 percent white. 

Combustion air should be thoroughly mixed with 

fuel with only enough excess air present to en- 

sure complete combustion without smoke. Ex- 

cess air robs the furnace of process heat by 

dilution, and this heat loss must be overcome 

by burning additional fuel. Volume of the melter 

should be designed for a maximum fuel heat re- 

lease of about 13.000 Btu per hour per cubic foot. 

Furnace reversals should be performed by an 

automatic control system to ensure optimum 

combustion. Only automatic systems can pro- 

vide the exact timing required for opening and 

closing the dampers and valves and for co- 

ordinating fuel and combustion airflow (Bulcraig 

and Haigh, 1961). For instance, fuel flow and 

ignition must be delayed until combustion air 

travels through the checkers after reversal to 

mix with fuel at the inlet port to the melter. Fur 

nace reversals are usually performed in fixed 

periods of 15 to 20 minutes, but an improvement 

in regenerator efficiency can be realized by pro- 

gramming reversal periods to checker tempera- 

tures measured optically. Reversals can then 

occur when checker temperatures reach preset 

values consistent with maximum heat transfer 

(Robertson et al., 1957). 

An excellent system for controlling air-to-fuel 

ratios incorporates continuous flue gas analyzers 

for oxygen and combustible hydrocarbons. With 

this system, the most efficient combustion and 

best flame shape and coverage occur at optimum 

oxygen with a trace of combustible hydrocarbons 

present in the flue gas. Sample gas is cleaned 

for the analyzers through water-cooled probes 

containing sprays. The system automatically 

adjusts to compensate for changes in ambient 

air density. Fuel savings of 6 to 8 percent 

can be accomplished on furnaces with analyzers 

over furnaces not so equipped (Gunsaulus, 1958). 

Combustion of natural gas in new furnaces occurs 

efficiently when the.oxygen content of the flue 

gases in the exhaust ports is less than 2 percent 

by volume. As the campaign progresses, air 

infiltration through cracks and pores in the 

brickwork, air leakage through valves and damp- 

ers, increased pressure drop through the regen- 

erators, and other effects combine to make 

combustion less efficient. To maintain maxi- 

mum combustion throughout the campaign, pres- 

sure checks with draft gages should be run peri- 

odically at specified locations (Spain, 1956a). 

Fuel savings can also be expedited by placing 

furnace operators on an incentive plan to keep 

combustion air to a minim-. 


Electric melting 

Although melting glass by electricity is a more 

costly process than melting glass by natural 

gas or fuel oil, melting electrically is a more 

thermally efficient process since heat can be 

applied directly to the body of the glass. 

Electric induction systems installed on regen- 

erative furnaces are designed to increase max- 

imum pull rates by as much as 50 percent. These 

systems are called boosters and consist of sev- 

eral water-cooled graphite or molybdenum elec- 

trodes equally spaced along the sides of the melt- 

er 18 to 32 inches below the surface of the glass. 

Source test results indicate that pull rates can 

be increased without any appreciable increase in 

dust carryover or particulate emissions. Fur- 

nace temperatures may also be reduced by 

boosters, preventing refractory damage at peak 

operations. 

Furnace capacity increase is nearly proportional 

to the amount of electrical energy expended. A 

56-ton-per-day regenerative furnace requires 

480 kilowatt-hours in the booster to melt an addi- 

tional ton of glass, which is close to the theoret- 

ical amount of heat needed to melt a ton of glass 

(Tooley, 1953). 

Electric induction can also be used exclusively 

for melting glass on a large scale. Design of 

this type of furnace is simplified since regen- 

erative checkerworks and large ductwork are no 

longer required (Tooley, 1953). One recently 

collstructed 10-ton-per-day, all-electric furnace 

consists of a simple tank with molybdenum elec- 

trodes. A small vent leads directly to the at- 

mosphere, and dust emissions through this vent 

are very small. The furnace operates with a 

crown temperature below 600°F and with a 

thermal efficiency of over 60 percent. Glass 

quality is excellent, with homogeneity nearly 

that of optical glass. After the first 11 months 

of operation, there was no apparent wear on the 

refractories (Peckham, 1962). First costs and 

maintenance expenses are substantially lower 

than for a comparable-size regenerative furnace. 

An electric furnace may prove competitive with 

regenerative furnaces in areas with low-cost 

electrical power. 

Baghouses and centrifugal scrubbers 

Air pollution control equipment can be installed 

on regenerative furnaces where particulate 

emissions or opacities cannot be reduced to 

required amounts through changes in furnace de- 

sign, control of raw materials, and operating 

procedures. Regenerative furnaces may be 

vented by two types of common industrial con- 

trol devices--wet centrifugal scrubbers and 

baghouses.

780 CHEMICAL PROCESSJI \iG EQUIPMENT 

Figure 596 shows a low-pressure, wet, centrifugal 

scrubber containing two separate contacting 

sections within a singk casing. Separate 

50-horsepower, circulating fans force 

dirty gas through each section containing two 

to three impingement elements similar to fixed 

blades of a turbine. Although the collection 

efficiency of this device is considered about the 

highest for its type, source tests show an over- 

.~ . 

. . all efficiency of only 52 percent. This low efficiency 

demonstrates the inherent inability of 

the low-pressure, wet, centrifugal scrubbers 

to collect particulates of submicron size. 

Figure 596.~et, centrifugal-type scrubber con- 

trolling emissions from a glass-melting furnace 

(Thatcher Glass Co., Saugus, Calif. ). 

On the other hand, baghouses show collection 

efficiencies of over 99 percent. Although 

baghouses have not as yet been installed on 

large continuous, regenerative furnaces, they 

have been installed on small regenerative fur- 

naces. One baghouse alternately vents a l, 800- 

pound- and a 5,000-pound-batch regenerative 

furnace used for melting optical and special 

glasses used in scientific instruments. Bags 

are made of silicone-treated glass fiber. Off- 

gases are tempered by ambient air to reduce the 

temperature to 40OSF, a safe operating temper- 

ature for this fabric. 

Another baghouse, although no longer m operation, 

venteda 10-ton-per-day regenerative furnace for 

melt~ng soda-lime fllnt glass. Stack gases were 

cooled to 250°F by rad~ation and convect~on from 

an uninsulated steel duct before entering the baghouse 

contaming orlon bags. 

To determine the feasibility of using a cloth fil- 

tering device on large continuous, regenerative 

furnaces, a pilot baghouse was used with bags 

made of various commercial fabrics. An air- 

to-gas heat exchanger containing 38 tubes, each 

1-112 inches in outer diameter by 120 inches in 

length, cooled furnace exhaust gases before the 

gases entered the pilot baghouse. The baghouse 

contained 36 bags, each 6 inches in diameter by 

111 inches in length, with a 432-net-square-foot 

filter area. A 3-horsepower exhaust fan was 

mounted on the discharge duct of the baghouse. 

When subjected to exhaust gases from amber 

glass manufacture, hags made of cotton, orlon, 

dynel, and dacron showed rapid deterioration 

and stiffening. Only orlon and dacron bags ap- 

peared in satisfactory condition when controlling 

dirty gas from flint glass manufacture and when the 

dirty gas was held well above its dew point. This 

difference in corrosion between amber and flint 

glass was found to be caused by the difference in 

concentrations of sulfur trioxide (SO3) present in 

the flue gas. 

To reduce the concentration of SO3 from amber 

glass manufacture, iron pyrites were substituted 

for elemental sulfur in the hatch, but this change 

met with no marked success. Stoichiometric 

amounts of ammonia gas were also injected to 

remove SO3 as ammonium sulfate. Ammonia in- 

jection not only failed to lessen bag deterioration 

but also caused the heat exchanger tubes to foul 

more rapidly. 

In all cases, the baghouse temperature had to be 

kept above the dew point of the furnace effluent 

to prevent condensation from blinding the bags 

and promoting rapid chemical attack. At times, 

the baghouse had to be operated with an inlet 

temperature as high as 280°F to stay above the 

elevated dew point caused by the presence of SO3. 

Additional pilot baghouse studies are needed to 

evaluate orlon and dacron properly for flint glass 

manufacture. Experiments are also required for 

evaluating silicone-treated glass fiber bags in con- 

trolling exhaust gases from regenerative furnaces 

melting all types of glass. 

Information now available indicates that glass 

fiber bags can perform at temperatures as 

high as 500 "F, well above the elevated dew 

points. They are virtually unaffected by rela- 

tively large concentrations of SOZ and SO3, and 

there is less danger from condensation. One 

advantage of glass fiber is that less precooling 

of exhaust gases is required because of the high- 

er allowable operating temperatures. Reverse 

air collapse is generally conceded to be the best 

method of cleaning glass fiber bags, since this

Glass Manu 

material is fragile and easily breaks when regu- 

lar shakers are installed. 

Furnace effluent can be cooled by several meth- 

ods: Air dilution, radiation coollng columns, 

air-gas heat exchangers, and water spray 

chambers. Regardless of the cooling method se- 

lected, automatic controls should be installed to 

ensure proper temperatures during the complete 

firing cycle. Each cooling method has its ad- 

vantages and disadvantages. Dilution of offgases 

with air is the simplest and most troublefree 

way to reduce temperature but requires the larg- 

est baghouse. Air-to-gas heat exchangers and 

radiation and convection ductwork are subject to 

rapid fouling from dust in the effluent. Automatic 

surface-cleaning devices should be provided, or 

access openings installed for frequent manual 

cleaning to maintain clean surfaces for adequate 

heat transfer. If spray chambers are used, se- 

vere problems in condensation and temperature 

control are anticipated. 

GLASS-FORMING MACHINES 

From ancient times, bottles and tableware were 

made by handblowing until mechanical production 

~. began in the decade preceding the turn of the cen- 

! 

tury with the discovery of the "press and blow" 

I 

and the "blow and blow" processes. At first, 

- machines were semiautomatic in operation. 

Machine feeding was done by hand. Fully automatic 

machines made their appearance during 

World War I and completely replaced the semiautomatic 

machines by 1925. Two types of automatic 

feeders were developed and are in use today. 

The first type consists of a device for dipping and 

evacuating the blank mold in a revolving pot of 

glass. The second type, called a gob feeder, 

consists of an orifice in the forehearth combined 

with shears and gathering chutes (Tooley, 1953). 

Glass container-forming machines are of two 

general types. The first type is a rotating ma- 

chine in which glass is processed through a 

sequence of stations involving pressing, blowing, 

or both. An example of this type of machine is 

a Lynch machine. A second type is used in con- 

junction with a gob feeder and consists of inde- 

pendent sections in which each section is a com- 

plete manufacturing unit. There is no rotation, 

and the molds have only to open and close. An 

example of this type is the Hartford-Empire 

Individual Section (I.S.) six-section machine 

shown in Figure 597. Mechanical details and 

operations of various glass-forming machines 

for manufacturing containers, flat glass, and 

tableware are found in the Handbook of Glass 

Manufacture (Tooley, 1953). 

Figure 597. Hartford-Empire I.S. six-section glass- 

forming machine. (Thatcher Glass Co., Sangus, Calif.). 


Dense smoke is generated by flash vaporization 

of hydrocarbon greases and oils from contact 

lubrication of hot gob shears and gob delivery 

systems. This smoke emission can exceed 40 

percent white opacity. 

Molds are lubricated with mixtures of greases 

and oils and graphite applied to the hot internal 

surfaces once during 10- to 20-minute periods. 

This smoke is usually 100 percent white in 

opacity and exists for 1 or 2 seconds. It rapid- 

ly loses its opacity and is completely dissipated 

within several seconds. 

Air Pollution Control Methods 

During the past decade, grease and oil lubri- 

cants for gob shears and gob delivery systems 

have been replaced by silicone emulsions and 

water-soluble oils at ratios of 90 to 150 parts 

of water to 1 part oil or silicone. The effect 

has been the virtual elimination of smoke. The 

emulsions and solutions are applied by intermittent 

sprays to the delivery system and shears only when 

the shears are in an opened position.


Lubricating properties of silicone-based emul- when mounted at the point of transfer of gobs 

sions appear in some respects superior to those from the blank mold to the blow mold. 

of soluble oil solutions. Gob droo soeeds are 

a 

increased by 20 to 25 percent. Apparently, the 

gob rides down the deliverv chute on a cushion 

- 

of steam. Heat from the gob breaks the silicone 

emulsion, forming an extremely stable resin, a 

condensation product of siloxane, which acts as 

a smooth base for the cushioning effect of steam. 

This resin is degraded in a matter of seconds 

and must be reformed continuously hy reapply- 

ing the silidone emulsion. 

While graphite gives no apparent advantages to 

emulsions, a combination of water soluble oil and 

silicone emulsion appears to be most effective 

(Singer, 1956). Oil aids the wetting of metal 

surfaces with silicone and coats metal surfaces, 

retarding rust formation. Sodium nitrite is also 

helpful in inhibiting rust when added to silicone 

emulsion. Water for mixtures must be pure, and 

in most cases, requires treatment in ion ex- 

changers or demineralizers. 

Water treatment is most critical for soluble oil to 

prevent growth of algae and bacteria. Oil solutions 

form gelatinous, icicle-like deposits upon drying 

on the surfaces of pipes and arms of the I.S. ma- 

chine. These particles should not be allowed to 

fall into the mold. Optimum results are obtained 

by flood lubrication'of the delivery system to the 

maximum amount that can be handled by a runoff 

wire or blown off by air. Dry lubrication of 

delivery systems has been tried on an experi- 

mental basis by coating the metal contact sur- 

faces with molybdenum disulfide or graphite. 

Although future developments in the application 

of emulsions to molds look promising, present 

practice still relies upon mixtures of hydro- 

carbon greases, oils, and graphite. Silicone 

emulsions and soluble oils eliminate smoke, 

but several difficulties must be overcome be- 

fore they can be widely used for mold lubrica- 

tion. Water emulsions with their high specific 

heat cause excessive cooling if they are not ap- 

plied evenly to the mold surfaces by proper 

atomization. Fine sprays meet with wind re- 

sistance, and these sprays cannot be effectively 

directed to cover the shoulder sectipns of some 

molds. Because of the low viscosity of water 

emulsions, the emulsions are very difficult to 

meter through existing sight oil feeders. One 

company has equipped its machine with individual 

positive-displacement pumps for each nozzle. 

Invert-post cross-spraying is found to be most 

effective in giving a uniform coating to the molds 

of I. S. machines (Bailey, 1957). 

INTRODUCTION 

FRlT SMELTERS 

Ceramic coatings are generally divided into two 

classes, depending upon whether they are applied 

to metal or to glass and pottery. In the case of 

metal, the coating is widely referred to in this 

country as;porcelain enamel. The use of the 

term vitreous enamel seems to be preferred in 

Europe. Glass enamel is sometimes used inter- 

changeably with both terms. On the other hand, 

the coating applied to glass or pottery is known 

as ceramic glaze. 

Ceramic coatings are essentially water suspen- 

sions of ground frit and clay. Frit is prepared 

by fusing various minerals in a smelter. The 

molten material is then quenched with air or 

water. This quenching operation causes the 

melt to solidify rapidly and shatter into numerous 

small glass particles, called frit. After a drying 

process, the frit is finely ground in a ball mill, 

where other materials are added. When suspend- 

ed in a solution of water and clay, the resulting 

mixture is known as a ceramic slip. Enamel 

slip is applied to metals and fired at high tem- 

peratures in a furnace. Glaze slip is applied to 

pottery or glass and fired in a kiln. 

Raw Materials 

The raw materials that go into the manufacture 

of various frits are similar to each other whether , j 

the frit is for enameling on steel or aluminum or 

1. 

for glazing. The basic difference is in the chem- i. 

I 

ical composition. 

The raw materials used in enamels and glazes 

may he divided into the following six groups: 

i 

Refractories, fluxes, opacifiers, colors, floatl 

ing agents, and electrolytes (Andrews, 1961). ~ 

The refractories include materials such as I ! 

quartz, feldspar, and clay, which contribute to 

the acidic part of the melt and give body to the 

glass. The fluxes include minerals such as 

borax, soda ash, cryolite, fluorspar, and litharge, 

which are basic in character and react with the 

acidic refractories to form the glass and, more- 

over, tend to lower the fusion temperatures of 

the glasses. These refractory and flux materials 

chiefly comprise the ingredients that go into the 

raw batch that is charged to the smelter. 

Rotating machines are much easier to lubricate Materials falling into the other four groups are 

than are individual section machines. Emulsion introduced later as mill additions and rarely exsprays 

are most effective on rotating machines ceed 15 percent of the total frit composition. 

I 

i 

j

They include opacifiers, which are compounds 

added to the glass to give it an opaque appear- 

ance such as the characteristic white of porce- 

lain enamels. Examples are tin oxide, anti- 

mony oxide, sodium antimonate, and zirconium 

oxide. The color materials include compounds 

such as the oxides of cobalt, copper, iron, and 

nickel. The floating agents consist of clay and 

gums and are used to suspend the enamel or 

glaze in water. Electrolytes such as borax, 

soda ash, magnesium sulfate, and magnesium 

carbonate are added to flocculate the clay and 

further aid the clay in keeping the enamel or 

glaze in suspension (Parmelee, 1951). 

Types of Smelters 

Frit Smt 

Smelters used in frit making, whether for 

enamel or glaze, may be grouped into three 

classes: Rotary, hearth, and crucible. The 

rotary smelter is cylindrical and can be rotated 

in either direction to facilitate fusing, as shown 

in Figure 598. It can also be tilted vertically 

for the pouring operation, as demonstrated in 

Figure 599. The smelter is open at one end for 

the introduction of fuel and combustion air. It 

is similarly open at the opposite end for the dis- 

charge of flue gases and for charging raw mate- 

rials. Operated solely as a batch-type smelter, 

it is normally charged by means of a screw con- 

veyor, which is inserted through the opening. 

Rotary smelters are normally sized to take 

batches varying from approximately 100 to 3,000 

pounds. Fired with either gas or oil, the smelter 

is lined with high-alumina, refractory firebrick 

with an average life of from 400 to 600 melts. 

Firing cycles vary from 1 to 4 hours. 

The hearth smelter consists of a brick floor, on 

which the raw materials are melted, surrounded 

by a boxlike enclosure. This type of smelter 

can be either continuous, as illustrated in Figure 

600, or batch type, as shown in Figure 601. In 

either case, the hearth (or bottom) is sloped 

from one side to a point on the opposite side 

where the molten material is tapped. The con- 

tinuous type is usually screw fed. A flue stack 

is located on the opposite end. Oil or gas is 

normally used as fuel for the one or more burn- 

ers. The walls and floor are lined with a first- 

quality, refractory firebrick. The batch type is 

sized to take batches ranging from 100 to several 

thousand pounds. About 30 pounds of batch can 

be smelted for each square foot of hearth area. 

The typical continuous-hearth smelter can pro- 

cess 1, 000 to 1, 500 pounds of raw materials 

per hour. 

The crucible smelter consists of a high-refrac- 

tory, fireclay, removable crucible mounted 

within a circular, insulated, steel shell lined 

with high-grade firebrick, as shown in Figure 

602. Heating is usually accomplished with oil 

or gas burners, though electricity can be used. 

The combustion chamber surrounds the crucible, 

occupying the space between the crucible and the 

shell lining. Because the heat must be trans- 

mitted through the crucible to the batch, re- 

fractory and fuel costs are high. Crucibles can 

be sized to smelt a 5-pound batch for laboratory 

purposes, but the commercial crucibles are 

sized to take batches from 100 pounds to 3, 000 

pounds. Smelting cycles vary from 2 to 3 hours 

at temperatures around 2,200mF, depending 

upm the size of the batch and its composition. 

The steel shell is supported by trunnions so 

that the crucible can be tilted for the pouring 

operation. 

Frit Manufacturing 

Since the raw materials that comprise the 

smelter batch consist of refractories and 

fluxes, thorough and uniform mixing of these 

ingredients before the charging operation is 

essential for efficient smelting. Smelting 

involves the heating of raw materials until a 

fairly homogeneous glass is formed. The 

fundamental changes that occur are inter- 

action of acids and bases, decomposition, 

fusion, and solution. A considerable quanti- 

ty of steam is evolved as the borax begins to 

melt. The order of melting for some of the 

materials is: Sodium nitrate at 586"F, borax 

at 1, 366"F, soda ash at 1,564"F, litharge at 

1, 630°F, feldspar at 2,138"F, and quartz at 

3,llO"F. 

If white or light-colored frits are being smelted, 

smelter refractory linings must be high in alumi- 

na and low in iron to prevent discoloration and 

dark specks in the frit. The batch is protected. 

from contact with fuel gases during the-early 

stages of smelting by the evolution of gases 

within the smelter. To illustrate, a batch 

containing 35 percent borax and 10 percent 

soda ash loses about 165 pounds of water and 

42 pounds of carbon dioxide for a 1,000-pound 

batch of frit. This is equivalent to 483 cfm 

water vapor and 60 cfm C02 at a smelter tem- 

perature of 1,700°F and for a smelting period 

of 30 minutes. 

The rate and period of heat application is criti- 

cal in smelting enamels and glazes. A temper- 

ature too low may be sufficient only to vaporize 

the more fusible materials instead of volatilizing 

them, and thereby result in a very slow reaction 

with the more refractory ingredients. A higher 

operating temperature eliminates this low pro- 

duction rate. If the batch is heated too rapidly, 

however, the more fusible elements are melted


Figure 598. Rotary-type frit smelter (Ferro Corp., 

Los Angeles, Calif.). 

Figure 599. Rotary-type frit smelter in pouringposition (Ferro Corp., 

Los Angeles, Calif.).

Frit Smelters 785 

Figure 600. Continuous-hearth-type frit smelter '(~erro Corporation, 

Las Angeles, Calif.). 

Flgure 601. Batch-hearth-type frlt smelter (Ferro Corporatlon. 

Los Angeles, Cal~f.).

786 CHEMICAL PROCESS11 VG EQUIPMENT 

Flgure 602. Crucible-type f r ~ smelter t 

(Californla 

Metal Enamel lng Company, Los Angeles, Cal lf.). 

and volatilized hefore they have a chance to react 

with the more refractory materials. Driving off 

the fluxes in this manner results in a harder (less 

fusible) final batch. Excessive smelting, after the 

melt is ready to pour, results in a similar condi- 

tion and, if permitted to continue, necessitates a 

further increase in temperature to facilitate 

pouring. Oversmelting also causes loss of opac- 

ity, poor gloss, and discoloration in the frit. 

Insufficient smelting, on the other hand, causes 

blistering, loss of acid resistance, and poor 

texture in the finished coating. Batch composi- 

tion is the determining factor in selecting op- 

timum smelter temperatures and cycles. 

After the smelting operation, the molten material 

is quenched. Rapid cooling can be accomplished 

with either air, water, or a combination of the 

two. Air quenching produces a better product 

but is not normally practiced, owing to the quench- 

ing Znd storage space required. Water quench- 

ing is commonly practiced in the industry by 

pouring the molten material from the tilted 

smelter into a large pan of water. Water quench- 

ing is also frequently done by pouring molten mate- 

rial into a metal trough in which a continuous 

stream of water is flowing. The trough empties 

into a large wire basket suspended in a well, 

which holds the shattered frit but permits the 

water to flow out through an overflow. Rapid 

cooling is somewhat impeded by this method 

owing to a layer of steam that forms over the 

glass. Air-water quenching appears to be the 

most economical and effective method since a 

more thorough shattering of the glass results. 

In this method the molten material is poured 

from the smelter and passed through a blast of 

air and water. Quenching causes the molten ma- 

terial to solidify and shatter into numerous small 

glass particles (called frit) ranging from 114 inch 

in diameter down to submicron sizes. Its main 

purpose is to facilitate grinding. 

After draining, the frit contains 5 to 15 percent 

water and may be milled in this condition or 

may first he dried. Three types of dryers are 

employed: The drying table, the stationary 

dryer, and the rotary dryer. The drying table 

is a flat hearth on which the frit is placed. Heat 

is applied beneath the hearth, and the frit is 

raked manually. The stationary dryer consists 

of a sheet iron chamber in which a basket of 

frit is placed. Heated air from an exchanger on 

the smelter flue is passed through the basket of 

frit. The rotary dryer consists of a porcelain- 

lined rotating cylinder that is inclined slightly, 

causing the frit to move through continuously. 

The typical size is approximately 2 feet in di- 

ameter and 20 feet long, though larger cylinders 

are used. The rotary dryer, which is economical 

and efficient, can he heated by waste heat or by 

oil or gas. The frit can he further refined by 

using magnetic separation to remove small iron 

particles, which would otherwise cause black 

specks in the enamel. 

The final step in frit making is size reduction, 

which is normally done with a ball mill. Frits 

used in porcelain enamel are required to pass 

a No. 100 seive (150 microns), though a certain 

percent of fines must remain as residue on a 

finer sieve. In the case of ceramic glaze frits, a 

finer grind is necessary. About one-half of a 

batch must he less than 2. 5 microns with the 

remainder no greater than 10 microns. Effi- 

cient milling is best obtained when the speed of 

rotation is such that the balls ride three-fourths 

of the way up one side of the cylinder, and the inner- 

most balls slide back down over the outermost 

balls. This is achieved, for example, at a speed 

of 25 rpm for a 4-foot-diameter cylinder. Porce- 

lain balls or flint pebbles are used in the mill. The 

diameter of the balls ranges from 1 to 3 inches, 

and the charge should be maintained at about 55 

percent of the mill volume. Ball wear amounts to 

5 to 10 pounds in milling 1,000 pounds of frit. 

Colors, opacifiers, floating agents, and electro- 

lytes are mixed with the frit before it is charged 

to the ball mill. After the milling operation be- 

gins, water is added at a constant rate to keep 

the specific gravity of the slurry (referred to as 

slip) at the correct value at all times. After the 

milling operation, the ceramic slip is screened 

to remove large particles. A 1- to 2-day aging 

process then takes place at a temperature close

to that at which the enamel or glaze is to be ah- 

plied. Aging is necessary to set up an equilibrium 

among the clay, frit, and solution. The enamel 

or glazs slip is now ready for application. 

Application, Firing, and Uses of Enamels 

Enamels and glazes may be applied to ware 

blanks by immersion or spraying (Hansen, 

1932). The pouring and brushing methods are 

seldom employed today. In the dipping opera- 

tion, the blank is immersed in the slip and then 

withdrawn and allowed to drain. If the slip is 

thick, the excess enamel must he shaken from 

the ware, a process called slushing. Spraying 

is the application of enamel or glaze slip to 

ware by atomizing it through an air gun. 

After the enamel or glaze has been applied, it 

must then be burned or fired on the ware to 

fuse the coating to a smooth, continuous, glassy 

layer. The firing temperatures and cycles for 

porcelain enamel on steel and aluminum are 

approximately 1, 500°F (Shreve, 1945) for 5 

minutes and 1,000"F for 5 minutes, respective- 

ly. Ceramic glaze, however, is fired on pottery 

at about 2, 300°F for several hours or even days. 

The firing is accomplished in what is called a 

furnace in the porcelain enamel industry, and a 

kiln in the ceramic glaze industry. 

Porcelain enamel is used as a protective coating 

for metals--primarily steel, cast iron, and 

aluminum. Familiar items are bathtubs, water 

heater tanks, refrigerators, washing machines, 

and cooking ranges. Coated aluminum is being . 

used more and more in recent times for signs 

such as those installed on highways. Ceramic 

elazes are used as a decorative or orotective 

" 

coating on a wide variety of pottery and glass 

articles. Examples are lavatory basins, water 

closets, closet bowls, chinaware, and figurines. 


Significant dust and fume emissions are created 

by the frit-smelting operation. These emissions 

consist primarily of condensed metallic oxide 

fumes that have volatilized from the molten charge. 

They also contain mineral dust carryover and 

sometimes contain noxious gases such as hydro- 

gen fluoride. In addition, products of combus- 

tion and glass fibers are released. The quanti- 

ty of these air contaminants can be reduced by 

following good smelter-operating procedures. 

This can be accomplished by not rotating the 

smelter too rapidly, to prevent excessive dust 

carryover, and by not heating the batch too rapid- 

ly or too long, to prevent volatilizing the more 

fusible elements before they react with the more 

refractory materials. A typical rotary smelter, 

Frit Smelters 7 87 

for example, discharges 10 to 15 pounds of dust 

and fumes to the atmosphere per hour per ton of 

material charged. In some cases, where ingredi- 

ents require,high melting temperatures (1, 500°F 

or higher), emissions as great as 50 pounds per 

hour per ton of material have been observed, 

Depending upon the composition of the batch, a 

significant visible plume may or may not be 

present. Tables 209 to 212 indicate the extent of 

emissions from uncontrolled, rotary frit smelters 

for various-sized batches and compositions. 

Table 209. DUST AND FUME DISCHARGE FROM 

A 1,000-POUND, ROTARY FRIT SMELTER 

process wt, lh/hr 

Stack vol, scfm 1,390 1,540 1,630 

Stack gas temp, .F 

Concentration, grlacf 0.118 0.387 0.381 

Stack emissions. Ihlhr 1.41 5.11 5. 32 

CO, vol % (stack condition) 0.002 0.001 0.002 

NZ. "01 % (stack condition) 76.9 

Process wf, lblhr 

Stack vol, scfm 1,310 1,400 1,480 

Stack gas temp, OF 

Concentration. . erlscf 0.111 0. 141 0. I24 

Stack emissions, iblhr 1. 25 1.79 1.57 

to. "01 % (stack condition) 0 

N. 1 % k d o 1 7 1 0 1 73. 30 

I I I 

aThese three tests represent approximately the 1st. 2d, and 3d 

hour. of a 248-minute smelting cycle. The total charge amounted 

to 717 pounds of material con$isting of borax. feldspar, sodium 

fluoride, soda ash, and zinc oxide. 

b~hese three fesis represent approximately the 1st. Zd, and 3d 

hours of a 195-minute smelting cycle. The total charge amounted 

to 949 pounds of material consi3ting of litharge, silica, boric 

acid, feldspar, fluorspar. borax, and aircon. 


A 3,000-POUND, ROTARY FRIT SMELTER 

c 

Test data 

Process wt. Iblhr 

47Za 

Stack vol, scfm 

Stack - nas , temo. .. 'F 

. - 

2.240 

630 

Stack emissions, iblhr 

CO. "01 70 (stack condition) 

N ~ "01 , 70 (stack condition) 

2.70 

0.02 

75. 30 

7 1 8 I 9 

I I I 

472' 

2,270 

800 

Concentration. erlscf 1 0. 143 1 0. 114 1 0.172 

2.20 

0.02 

75.60 

=These three tests repreoent approximately the 1st. 2d, and 3d 

hours of a 248-minute smelting cycle. The total charge 

amounted to 1,951 pounds of material consisting of litharge, 

silicb, boric acid, feldspar, whiting. borax, and zircon. 


472' 

2,260 

Rotary smelters require a detached canopy-type 

hood suspended from the lower end of a vertical 

stack as shown in Figures 598 and 599. It is 

suspended far enough above the floor to trap the 

discharge gases from the smelter when in the 

horizontal position. Refractory-lined, it is of 

sufficient size to prevent gases from escaping 

840 

3.30 

0.02 

76.30


Table 211. FLUORIDE DISCHARGE FROM owing to the occasional presence of fluorides in 

A ROTARY FRIT SMELTER the effluent. The discharge gases must be cooled 

by heat exchangers, quench chambers, cooling 

Test data 

Process wt. lblhr 

stark "01, scrm 

Stack gas temp, .B 

Concentration, grlscl 

Stack emiasionr. . lbihr . 

174= 

1.400 

130 

0. 061 

0. 73 

~ert NO. 

'There two tests were of 90 minutesm dvration each and represented 

approximately the iirrt half and the second haU of a 248-minute 

smelting cycle. The total charge amounted fa 717 pounds of mntcrial 

~"nrirfing oi borax, feldspar, SOdivm fluoride, soda ash, and zinc 

oxide. 

b~hela two 60-minute t~ais reprerented approximately the 1st and the 

4th hours of s 450-mhufe am~iting cycle. Thm total charge amounted 

to i.211 pounds of malcrial consistin8 ol sodium carbonatm, calcium 

carbonate, pyrobar, and silica. The test was specifically conducted 

lorn batch containing maximum carbonaten (19%) and no liiharge. 


A 2,000-POUND ROTARY FRIT SMELTER 

Test data 

14' 

174= 

1,600 

840 

0. 035 

0. 48 

162~ 

1.000 

480 

0. 196 

1.68 

Process wt, lblhr 

857' 890~ 890b 

Stack vol. scim 

3 

2,430 4,347 

4,347 

Stack gas temp, 'P 600 600 340 

340 

Canrcnlration. crizcf 0.130 0.112 0.111 0. 103 

Stack emissions, lblhr 2.710 2.340 4. 110 3. 320 

"T~EJF two b0-minute testa rrprcaent the 1st and LC! hours of a 140minvtr 

rmclfing cycle. The total char~e amountad to 2.000 poimr,. 

oi rnatrria, containini: lilica, lifharge. an

Food Processing Equipment 789 

Figure 603. Venturi water scrubber venting 

three frit'smelters (Ferro Corporation, Los 

Angeles, Calif.). 

Table 213. EFFICIENCY OF VENTURI WATER SCRUBBER ON PARTICULATE 

MATTER AND FLUORIDES WHEN VENTING THREE FRIT SMELTERS 

Test data 

Process wt, lb/hr 

Stack "01, scim 

Stack gas temp, "F 

Dust concentration, gr/scf 

' Inlet 

Outlet 

Dust emissions, lb/hr 

Inlet 

Outlet 

Control efficiency, 7'0 

18 

1,360 

4,280 

570 

0.228 

0. 074 

8. 37 

2.72 

67.50 

19 

Dust and fumes 

Test No. a 

Fluorides 

1, 360 1, 360 1,360 1,360 

4.280 1 4.280 4.280 4.280 

552 564 570 552 

0.234 

0.077 

8.60 

2.85 

67.20 

a~ests No. 18 and 21 represent the first 54 minutes of the 107-minute smelting cycle, tests No. 19 

and 22 represent the last 54 minutes, and tests No. 20 and 23 represent the 23-minute tapping 

period. Total process weight was 3, 000 pounds of material consisting of borax, potassium carbonate, 

potassium nitrate, zinc oxide, titanium oxide, ammonium phosphate, lithium carbonate, 

sodium silico-fluoride, fluorspar, silica, and talc. Pressure drop across throat was 21 in. WC. 

Water flow rate to throat was 50 gpm. 

2 0 

0.127 

0.088 

1. 78 

1. 35 

30.70 

21 

0.092 

0.006 

3. 38 

0.22 

93.20 

2 2 

0.137 

0.008 

5. 03 

0.29 

94 

2 3 

1,360 

4.280 , 

564 

0.034 

0.017 

0. 48 

0. 26 

5 0

. . 


various preserving processes. More recently 

we find food purveyors increasingly concerned 

with processes that render foods more flavorful 

and easier to prepare. The trend toward greater 

presale food preparation has possibly caused 

a shift of at least some alr pollutants from many 

domest~c kitchens to a significantly smaller number 

of food-processing plants. 

Food processing includes operations such as 

. . .. . slaughtering, smoking, drying, cooking, baking, 

frying, boiling, dehydrating, hydrogenating, 

fermenting, distilling, curing, ripening, roasting, 

broiling, barbecuing, canning, freezing, 

enriching, and packaging. Some produce large 

volumes of air contaminants; others, only insignificant 

amounts. Equipment used to process 

food is legion. Some of the unit operations in- 

. . 

. . volved are the following (Kirk and Othrner, 1947): 

Material handling. Conveying, elevating, pump- 

ing, packing, and shipping. 

Figure 604. Baghouse with radiant cooling 

columns venting four rotary frit smelters 

(Glostex Chemicals, Inc., Vernon: Calif.). 

Separating. Centrifuging, draining, evacuating, 

filtering, percolating, fitting, pressing, skimming, 

sorting, and trimming. (Drying, screening, sifting, 

and washing fall into this category. ) 

Heat exchanzing. Chilling, freezing, and refrig- 

erating; heating, cooking, broiling, roasting, bak- 

ing, and so forth. 

Mixing. Agitating, beating, blending, diffusing, 

dispersing, emulsifying, homogenizing, kneading, 

stirring, whipping, working, and so forth. 

Disintegrating. Breaking, chipping, chopping, 

crushing, cutting, grinding, milling, maturating, 

pulverizing, refining (as by punching, rolling, 

and so forth), shredding, slicing, and spraying. 

Forming. Casting, extruding, flaking, molding, 

pelletizing, rolling, shaping, stamping, and die 

casting. 

Coating. Dipping, enrobing, glazing, icing, pan- 

ning, and so forth. 

Decorating. Embossing, imprinting, sugaring, 

topping, and so forth. 

Controlling. Controlling air humidity, temperature, 

pressure, and velocity; inspecting, measuring, tem- 

pering, weighing, and so forth. 

Packaging. Capping, closing, filling, labeling, 

packing, wrapping, and so forth. 

Storing. 

forth. 

Piling, stacking, warehousing, and so 

A description and discussion of each type of equip- 

ment used for food processing is not within the

scope of this manual. The following discussion 

will be limited to food processes in which air pollu- 

tion problems are inherent and in which typical 

food-processing air contaminants are encountered. 

This section is not concerned with the production 

of pet foods or livestock feeds, though in some 

instances, these materials are byproducts of food 

processes. 

COFFEE PROCESSING 

Most coffee is grown in Central and South America. 

After harvesting and drying at or near the coffee 

plantation, most "green" coffee beans are exported 

and further processed before sale to the consumer. 

Coffee processing in the United States consists es- 

sentially of cleaning, roasting, grinding, and packag 

ing. 

Roasting is the key operation and produces most 

of the air contaminants associated with the indus- 

try. Roasting reduces the sugar and moisture 

contents of green coffee and also renders the bulk 

density of the beans about 50 percent lighter. An 

apparently desired result is the production of 

water-soluble degradation products that impart 

most of the flavor to the brewed coffee. Roasting 

also causes the beans to expand and split into 

halves, releasing small quantities of chaff. 

Botch Roosting 

The oldest and simplest coffee roasters are directfired 

(usually by natural gas), rotary, cylindrical 

chambers. These units are designed to handle 

from 200 to 500 pounds of green beans per 15- to 

20-minute cycle and are normally operated at 

about 400DF. A calculated quantity of water is 

added at the completion of the roast to quench the 

beans before discharge from the roaster. After 

they are dumped, the beans are further cooled 

with air and run through a "stoner" air classifier 

to remove metal and other heavy objects before 

the grinding and packaging. The roaster and 

cooler and all air-cleaning devices are normally 

equipped with cyclone separators to remove dust 

and chaff from exhaust gases. Most present-day 


Flgure 605. A recirculating-batch coffee 

roaster (Jabez Burns - Gump Division,Blaw 

Knox Company, New York, N.Y.). 

An Integrated Coffee Plant 

A process flow diagram of a typical large integra- 

ted coffee plant is shown in Figure 606. Green 

beans are first run through mechanical cleaning 

equipment to remove any remaining hulls and 

foreign matter before the roasting. This system 

includes a dump tank, scalper, weigh hopper, 

mixer, and several bins, elevators, and convey- 

ors. Cleaning systems such as this commonly 

include one or more centrifugal separators from 

which process air is exhausted. 

The direct, gas-fired roasters depicted in Figures 

606 and 607 are of continuous rather than 

batch design. Temperatures of 4000F to 5000F 

are maintained in the roaster, and the residence 

time ~- --- is -~ adinrted bv controlline ~ - the drum soeed. 

~~ ~ ~~2 --- ~ - ~~ 3 

~- 

Roaster exhaust products are drawn off through 

a cyclone separator and afterburner, with some 

recirculation from the cyclone to the roaster. 

coffee roasters are of batch design, though the 

Chaff and other particulates from the cyclone 

newer and larger installations tend to favor con- are fed to a chaff collection system. Hot beans 

tinuous roasters. are continuously conveyed through the air cooler 

and stoner sections. Both the cooler and the 

In the batch roaster shown in Figure 605, some stoner are equipped with cyclones to collect parof 

the gases are recirculated. A portion of the ticulates. 

gases is bled off at a point between the burner 

and the roaster. Thus, the burner incinerates The equipment following the stoner is used only 

combustible contaminants and becomes both an to blend, grind, and package roasted coffee. 

air pollution control device and a heat source for Normally, there are no points in these systems 

the roaster. 

where process air is emitted to the atmosphere. 

1


Fiaure 607. A continuous coffee roaster and cooler:(left) continuous 

roister. showine course of the heated eases as thev are drawn throueh 

the coffee beans in the perforated, heiical-flanged cylinder and then 

into the recirculation svstem; (right) left-side elevation of contin- 

uous roaster, showing relationship-of reci rculating and cooler fans 

and the respective collectors on the roof (Jabez Burns - Gump Division, 

Blaw-Knox Company, New York, N.Y.).

At the plant shown on the flow diagram, chaff is 

collected from several points and run to a hold- 

ing bin from which it is fed at a uniform rate to 

an incinerator. Conveyors in the chaff system 

may be of almost any type, though pneumatic con- 

veyors are most common. The design of the in- 

cinerator depicted is similar to that of the saw- 

dust burners described in Chapter 8 but the 

incinerator is much smaller. 


Dust, chaff, coffke bean oils (as mists), smoke, 

and odors are the principal air contaminants 

emitted from coffee processing. Ln addition, 

combustion contaminants are discharged if chaff 

is incinerated. Dust is exhausted from several 

points in the process, while smoke and odors are 

confined to the roaster, chaff incinerator, and, in 

some cases, to the cooler. 

Coffee chaff is the main source of particulates, 

but green beans, as received, also contain ap- 

preciable quantities of sand and miscellaneous 

dirt. The major portion of this dirt is removed 

by air washing in the green coffee-cleaning sys- 

tem. Some chaff (about 1 percent of the green 

weight) is released from the bean on roasting and 

is removed with roaster exhaust gases. A small 

amount of chaff carries through to the cooler and 

stoner. After the roasting, coffee chaff is light 

and flaky, partlcle sizes usually exceeding 100 

microns. As shown in Table 214, particulate- 

matter emissions from coffee processing are well 

below the limits permitted by typical dust and 

fume prohibitions. 

Table 214. ANALYSIS OF COFFEE 

ROASTER EXHAUST GASES 

I contaminant concentration 

Collt~nnous roaster Batch roaster 

-- 1 I75 

Particulate matter, grlscf 0. 1891 0.006 I 0.160 

/ 1 

Aldehydes 

(as formaldehyde), ppm 139 .- 42 

Organic acids 

(as acetic acid), ppm . . 213 

Oxides of nitrogen 

(as NOZ). P P ~ 

26. 8 -- 21.4 

Coffee roaster odors are attributed to alcohols, 

aldehydes, organic acids, and nitrogen and sulfur 

compounds, which are all probably breakdown 

products of sugars and oils. Roasted coffee odors 

are considered pleasant by many people, and in- 

deed, they may often be pleasant under certain 

conditions. Nevertheless, continual exposure to 

uncontrolled roaster exhaust gases usually elicits 

widespread complaints from adjacent residents. 

The pleasant aroma of a short sniff apparently 

develops into an annoyance upon long exposure. 

Food Proces~ ;ing Equipment 793 

Visible bluish-white smoke emissions from coffee 

roasters are caused by distilled oils and organic 

breakdown products. The moisture content of 

green coffee is only 6 to 14 percent, and thus 

there is not sufficient water vapor in the 400" 

to 500°F exhaust gases to form a visible steam 

plume. From uncontrolled, continuous roasters, 

the opacity of exhaust gases exceeds 40 percent 

almost continuously. From batch roasters, ex- 

haust opacities normally exceed 40 percent only 

during the last 10 to 15 minutes of a 20-minute 

roast. Smoke opacity appears to be a function 

of the oil content, the more oily coffee producing 

the heavier smoke. The water quenching of 

batch-roasted coffee causes visible steam emis- 

sions that seldom persist longer than 30 seconds 

per batch. 

Hooding ond Ventilotion Requirements 

Exhaust volumes from coffee-processing sys - 

tems do not vary greatly from one plant to 

another insofar as roasting, cooling, and stoning 

are concerned. Roasters equipped with gas re- 

circulation systems exhaust about 24 scf per 

pound of finished coffee. Volumes from nonre- 

circulation roasters average ahout 40 scf per 

pound. A 10,000-pound-per-hour, continuous 

roaster with a recirculation system exhausts 

about 4, 000 scfm. A 500-pound-per-batch, non- 

recirculation roaster exhausts about 1, 000 scfm. 

Each hatch cycle lasts about 20 minutes. 

Coolers of the continuous type exhaust about 

120 scf per pound of coffee. Batch-type cool- 

ers are operated at ratios of about 10 scfm per 

pound. The time required for batch cooling 

varies somewhat with the operator. Batch-cool- 

ing requirements are inversely related to the 

degree of water quenching employed. 

Continuous-type stoners use about 40 scf air per 

pound of coffee. Batch-stoning processes require 

from 4 to 10 scfm per pound, depending upon duct- 

work size and batch time. 


Air contaminants from coffee-processing plants 

have been successfully controlled with afterburn- 

ers and cyclone separators, and combinations 

thereof. Incineration is necessary only with roaster 

exhaust gases. There is little smoke in other coffee 

plant exit gas streams where only dust collectors 

are required to comply with air pollution control 

regulations. 

Separate afterburners are preferable to the com- 

bination heater-incinerator of the batch roaster 

shown in Figure 605. When the afterburner serves 

as the roaster's heat source, its maximum operat-


ing temperature is limited to about 1,00O0F. A 

temperature of 1,200°F or greater is necessary 

to provide good particulate incineration and odor 

removal. 

A roaster afterburner should always be preceded 

by an efficient cyclone separator in which most 

of the particulates are removed. A residence 

time of 0. 3 second is sufficient to incinerate 

most vapors and small-diameter particles at 

1,200°F. Higher temperatures and longer resi- 

dences are, however, required to burn large- 

diameter, solid particles. Afterburner design 

is discussed in Chapter 5. 

Properly designed centrifugal separators are 

required on essentially all process airstreams 

up to and including the stoner and chaff collec- 

tion system. With the plant shown, cyclones 

are required at the roaster, cooler, stoner, 

chaff storage bin, and chaff incinerator. In 

addition, the scalper is a centrifugal classiiier 

venting process air. Some plants also vent the 

green coffee dump tank and several conveyors and 

elevators to centrifugal dust collectors. 

For best results. the chaff incinerator should be 

of the design discussed in Chapter 8 in which 

combustible material is fed at a uniform rate. 

It is, however, considerably smaller and has 

burning rates usually below 100 pounds per hour. 

The inorganic ash content of the chaff, at approxi- 

mately 5 percent by weight, is considerably great- 

er than that of most combustible refuse fed to 

incinerators. Provisions should be made in the 

incinerator design so that this material does 

not become entrained in the exhaust gases. If 

most of the noncombustible material is dis- 

charged with products of combustion from the 

incinerator, the combustion contaminants then 

exceed 0.3 grain per cubic foot calculated to 

12 percent carion dioxide. 

SMOKEHOUSES 

Smoking has been used for centuries to preserve 

meat and fish products. Modern smoking opera- 

tions do not differ greatly from those used by our 

forefathers, though the prime purposes of smoking 

today appear to be the imparting of flavor, color, 

and "customer appeal" to the food product. Cur- 

ing and storage processes have been improved 

to the point where ,preservation is no longer the 

principal objective. 

The vast majority of smoked products are meats 

of porcine and bovine origin. Some fish and 

poultry and, in rare instances, vegetable prod- 

ucts are also smoked as gourmet items. 

The Smoking Process 

Smoking is a diffusion process in which food 

products are exposed to an atmosphere of hard- 

wood smoke. Table 215 is an analysis of smoke 

produced through the destructive distillation of 

a hardwood. As smoke is circulated over the 

food, aldehydes, organic acids, and other 

organics are adsorbed onto its outer surface. 

Smoking usually darkens the food's natural color, 

and in some cases, glazes the outer surface. 

Table 215. ANALYSIS OF WOOD SMOKE 

USED IN MEAT SMOKEHOUSES 

(Jensen, 1945) 

Contaminant Concentration, ppm 

Formaldehyde 20 to 40 

Higher aldehydes 140 to 180 

Formic acid 90 to 125 

Acetic and higher acids 460 to 500 

Phenols 20 to 30 

Ketones 190 to 200 

Resins 1,000 

Regardless of smokehouse design, some spent 

gases are always exhausted to the atmosphere. 

These contain odorous, eye-irritating gases and 

finely divided, organic particulates, often in 

sufficient concentration to exceed local opacity 

restrictions. 

Smokehouses are also used to cook and dry food 

products either before or after smoking. Air 

contaminants emitted during cooking and drying 

are normally well below allowable control limits. 

Atmospheric Smokehouses 

The oldest smokehouses are of atmospheric or 

natural-draft design. These boxlike structures 

are usually heated directly with natural gas or 

wood. Smoke is often generated by heating 

sawdust on a steel plate. These smoke gener- 

ators are normally heated with natural gas pipe 

burners located in the bottom of the house. Hot, 

smoky gases are allowed to rise by natural con- 

vection through racks of meat. Large atmospheric 

houses are often built with two or three levels of 

meat racks. One or more stacks are provided 

to exhaust spent gases at the top of the house. In 

some instances the vents are equipped with ex- 

haust fans. During the smoking and drying cy- 

cles, exhaust gas temperatures range from 

120" to 150°F. Slightly higher temperatures 

are sometimes encountered during the cooking 

cycle.


Recirculating Smokehouses Smoking by Immersion 

Most large, modern, production meat smokehouses 

are of the recirculating type (Figure 608) 

wherein smoke is circulated at reasonably high 

velocities over the surface of the product. The 

purpose is to provide faster and more nearly 

uniform diffusion of organics onto the product, 

and nlore uniform temperatures throughout the 

house. These units are usually of stainless 

steel construction and are heated by steam or 

gas. Smoke is piped to the house from external 

smoke generators. Each unit is equipped with 

a large circulating fan and, in some instances, a 

smaller exhaust fan. During smoking and cooking, 

exhaust volumes of 1 to 4 cfm per square foot of 

floor area are maintained. The exhaust rate is 

increased to 5 to 10 cfm per square foot during . 

the drying cycle. Recirculating smokehouses 

are usually equipped with temperature and humidity 

controls, and the opacity and makeup of 

exhaust gas are usually more constant than those 

from atmospheric units. 

/-ALTERNATING 

AUTOMATIC 

Figure 608. A modern recirculating smokehouse 

(Atmos Corp., Chicago, II I.). 

Corlventional smoking operations can.be seen 

as an extremely devious method of coating food 

products with a myriad of hardwood distillation 

products. One might wonder why this coating 

is not applied by simple immersion. Unfortu- 

nately, many of the compounds present in smoke 

are highly toxic. If these were deposited heavily 

on the food product, results could be fatal. Smok- 

ing, therefore, provides a reasonably foolproof, 

if quaint, means of assuring that these toxic com- 

pounds do not accumulate in lethal concentrations. 

Many states have laws prohibiting the smoking of 

meats by liquid immersion. 

Smoking by Electrical Precipitation 

Some attempts have been made to precipitate 

smoke particles electrically onto food products 

in the smokehouse, and a few smokehouses so 

designed are in operation today. From the opera- 

tors' point of view, this arrangement offers the 

advantages of faster smoking and greater use 

of generated smoke. From the standpoint of air 

pollution control, it is desirable inasmuch as 

considerably lesser quantities of air contami- 

nants are vented to the atmosphere than are 

vented from a conventional, uncontrolled smoke- 

house. 

These units normally consist of a conveyorized 

enclosure equipped with an ionizer section similar 

to those used with two-stage precipitators. 

The foo'd product is usually passed 2 to 3 inches 

below tlie ionizing wires, which are charged with 

about 15, 000 volts. No electrical charge is aplied 

to the food products or the conveyor. These 

smokers are operated at ambient temperatures 

and do not lend themselves to use for either cooking 

or drying food products. As would be expected, 

spacing is a critical factor. 

There are very few precipitation smokehouses 

in the Unites States today, and for this reason, 

little reliable data about the operating characteristics 

or the air pollutants emitted are available. 

Smokehouses of this design have been 

reported to operate with visible emissions of 

only 5 to 10 percent opacity. Concentrations of 

air contaminants in gases from precipitationtype 

smokehouses would, under optimum conditions, 

be expected to be approximately equivalent 

to those from conventional smokehouses 

equipped with two-stage electrical precipitators. 

These units offer the potential of markedly reduced 

smoking times. Indeed, the few operating 

units have residence times of less than 5 minutes. 

If equipment such as this were perfected for a 

wider range of operation, residence times would 

not be expected to exceed 10 minutes.

796 CHEMICAL PROCESS1 LNG EQUIPMENT 

The application of precipitation smokehouses 

is today limited by a number of inherent problems, 

the foremost of which is the irregular shape of 

many smoked products, that is, hams, ham hooks, 

and salami. The degree of smoke deposition in 

a unit such as this is governed by the distance : 

between the ionizer and the food product. Irregu- 

lar spacing results, therefore, in irregular smok- 

ing of round and odd-shaped products that cannot 

be positioned so that all surfaces are equidistant 

from ionizer wires. The few existing installa- 

tions are used to impart a light smoke to regular- 

shaped, flat items such as fish fillets and sliced 

meat products. 


Smokehouse exhaust products include organic 

gases, liquids, and solids, all of which must 

be considered air contaminants. Many of the 

gaseous compounds are irritating to the eyes 

and relatively odorous. A large portion of the 

particulates is in the submicron size range where 

light scattering is maximum. These air con- 

taminants are attributable to smoke, that is, to 

smoke generated from hardwood, rather than 

from the cooked product itself. 

Exhaust gases from both atmospheric and re- 

circulating smokehouses can be periodically 

expected to exceed 40 percent opacity, the 

maximum allowable under many local air pollu- 

tion control regulations. With the possible ex- 

ception of public nuisance, smokehouse exhaust 

gases are not likely to exceed other local air 

quality standards. As shown in Table 215, con- 

centrations of particulate matter average only 

0. 14 grain per scf. 


Atmospheric smokehouses are designed with ex- 

haust volumes of about 3 cubic feet per square 

foot of floor area. Somewhat higher volumes are 

used with atmospheric houses of two or more 

stories. Inasmuch as there are no air recircula- 

tion and normally little provision for forced draft, 

the exhaust rate for an atmospheric house is es- 

sentially constant over the drying, cooking, and 

smoking cycles. Moreover, there is often some 

smoke in the house even during the cooking and 

drying cycles. This is particularly true where 

smoke is generated in the house rather than in 

an external smoke generator. If gases are to be 

ducted to air pollution control equipment, an ex- 

haust fan should be employed to offset the added 

pressure drop. When an afterburner is used, it 

can often be positioned to provide additional nat- 

ural draft. 

Recirculation smokehouses have a considerably 

wider range of exhaust rates. During smoking 

and cooking cycles, volumes of 1 to 4 cubic 

feet per square foot of floor area are exhausted. 

The rate increases to 5 to 10 cubic feet per square 

foot during the drying cycle. Recirculation houses 

are almost always equipped with external smoke 

generators, and a control of smoke flow is much 

more positive. There is essentially no smoke in 

the houses during the cooking and drying cycles. 

Most smokehouses do not require hooding. Ex- 

haust gases are normally ducted directly to the 

atmosphere or to control equipment. Some at- 

mospheric houses are, however, equipped with 

hoods over the loading doors to gather smoke that 

might escape during the shifting of meat racks. The 

latter situation is due to the inherently poor dis- 

tribution of smoke and heat in an atmospheric house. 

To maintain product uniformity, the meat racks 

must often be shifted while there is smoke in the 

house. Most atmospheric houses do not have ex- 

haust systems adequate to prevent appreciable 

smoke emissions from the door during these in- 

stances. Hoods and exhaust systems are some- 

times installed principally for worker comfort. The 

hoods or fans, or both, may be located in corridor 

ceilings immediately above the doors. These ven- 

tilators are often operated automatically whenever 

the doors are opened. Volumes can be appreciable, 

in some instances exceeding the smokehouse's ex- 

haust rate. 

There are normally no appreciable smoke emis- 

sions from doors of recirculation-type smoke- 

houses. Temperature and smoke distribution 

are sufficient so that there is no need to shift 

meat in the houses. Moreover, the doors are 

designed to provide tighter closures. Recircula- 

tion houses are operated under positive pressure, 

and any small opening causes large emissions of 

smoke. 


Afterburners 

Smoke, odors, eye irritants, and organic partic- 

ulate matter can be controlled with afterburners, 

provided temperature and design are adequate. 

Most of these contaminants can be eliminated at 

temperatures of 1, 000°F to 1,200"F in well-de- 

signed units. Larger diameter particulate matter 

is somewhat more difficult to burn at these tem- 

peratures; however, since concentrations of par- 

ticulate matter from smokehouses are reasonably 

small, this limitation is not critical.


Low-voltage, two-stage electrical precipitators 

were installed in the Los Angeles area as early 

as 1957 to control visible smokehouse air con- 

tamirlants. They have since been used at many 

other locations in the United States. Before 

1957, their use had been confined principally to 

. . . . air-conditioning applications. 

Electrical precipitators are, of course, effective 

only in the collection of particulate matter. They 

cannot he used to control gases or vapors. At 

smokehouse installations, their purpose is to 

collect the suhmicron smoke particles responsible 

for visible opacity. Two-stage precipitators 

.. ~ . . have been shown capable of reducing smoke opaci- 

~ ~ 

. . . . ~ .. ties to less than 10 percent under ideal conditions. 

A typical two-stage precipitator control system 

... . 

. . with a wet, centrifugal collector is shown in Figure 

609. The wet collector is used to control 

temperature and humidity and also remove a 

small amount of particulates. This is followed 

by a heater in which gas temperatures are regulated 

before the gases enter the ionizer. Voltages 

of 6, 000 to 15, 000 volts are applied to the ionizer 

I 1 and plate sections. Particulate matter collects 

on the plates and drains, as a gummy liquid, to 

1 the collection pan below. 

For sat~sfactory control of visihle emissions, it 

has been found that superficial gas velocities 

through the plate collector section should not exceed 

100 fpm. Some difficulty has been experience 

Food Processing Equipment 797 1 

owing to channeling in the collector. For best oper- 

ation, vanes or other means of ensuring uniform 

flow should bk used ahead of the plate section. 

Even under optimum conditions, a slight trace of 

smoke can he expected from the precipitator's 

outlet. At the discharge of the unit, eye irrita- 

tion is usually severe, and odors are strong 

though not overpowering. These odors and eye 

irritants can constitute a public nuisance, de- 

pending upon plant location. 

Electrical precipitation versus incineration 

Both electrical precipitation and incineration 

offer the classical choice of high initial cost 

versus high operating cost, but in addition, they 

differ markedly from the standpoint of air pollu- 

tion control. 

Electrical precipitators are capable of collect- 

ing particulate matter and thereby reducing 

visihle emissions to tolerable amounts. They 

have no effect on nitrogen oxides and little 

effect, if any, on gaseous eye irritants and 

odors. If arcing occurs, some small and proh- 

ably insignificant quantity of ozone is also pro- 

duced. The initial cost of precipitators is high, 

and their operating cost low in comparison with 

that of afterburners. Smokehouse precipita- 

tors do, however, require a relatively high 

degree of maintenance. If they are not proper- 

ly maintained, poor control efficiency and fire 

damage are probable. Fire damage can result 

d in extended outage periods during which uncon- 

Figure 609. A two-stage precipitator and wet centrifugal 

collector venting smokehouses (The Rath Pa-king Co., Vernon, Calif.).


trolled exhaust gases may vent directly to the 

atmosphere. 

Incineration is much more effective than elec- 

trical precipitation is in controlling gaseous 

organics and finely divided particulates. Large 

particles are, however, relatively difficult to 

burn at the normal operating temperatures and 

residence times of smokehouse afterburners. 

Under average conditionsl collection efficiency 

for particulate matter (about 65 percent) is 

roughly the same as that of a two-stage elec- 

trical precipitator. Fuel costs make the oper- 

ation of an incineration device more expensive 

than that of a precipitator. Nevertheless, 

maintenance is much less a problem. There 

is no buildup of tars and resins in the afterburner 

or stack to impede its operation. As with any 

smokehouse control device, tars accumulate in 

the ductwork between the house and afterburner, 

necessitating periodic cleaning. As shown in 

Table 216, incineration creates additional nitro- 

gen oxides, increasing concentrations from about 

4 ppm to approximately 12 ppm on the average. 

Comparative test data on smokehouse afterburners 

and electrical precipitators, as shown in Tables 

216 and 217, indicate that collection efficiencies 

for particulate matter, aldehydes, and organic 

acids are of the same magnitude for both types 

of control dequipment. These data fail to re- 

flect larger concentrations of odors and eye 

irritants from electrical precipitators that are 

readily apparent upon personal inspection of the 

devices. 

Bypassing control devices during nonsmoking 

periods 

Many operators of recirculation smokehouses 

find it desirable to bypass air pollution control 

devices during nonsmoking periods. From the " 

standpoint of air pollution control, this practice 

is not unreasonable. The major smokehouse air 

contaminant is smoke. Concentrations of air con- 

taminants during cooking and drying are relative- 

ly small, comparable to those of ordinary meat- 

cooking ovens. Drying-cycle exhaust gases are 

2 to 4 times more voluminous than those vented 

Table 216. ANALYSES OF MEAT SMOKEHOUSE EXHAUST GASES BEFORE AND 

AFTER INCINERATION IN NATURAL GAS-FIRED AFTERBURNERS 

Particulate matter, 

grlscf 

Aldehydes (as form 

aldehyde), pprn . Organic acids (as 

acetic acid) 

Oxides of nitrogen 

(as NO2), ppm 

Contaminant concentration 

Smokehouse 

Afterburner 

Range Average Range Average 

0.016 to 0.234 

8 to 74 

30 to 156 

1.2 to 7.2 

40 

0.141 

87 

3.9 

0.011 to 0.070 

5 to 61 

0 to 76 

3.7 to 33.8 

0.048 

Control 

efficiency, 

% 

Table 217. ANALYSES OF MEAT SMOKEHOUSE EXHAUST GASES BEFORE AND AFTER 

CONTROL IN TWO-STAGE ELECTRICAL PRECIPITATION SYSTEMS 

Contaminant concentration 

. Control 

Smokehouse 

Control systema efficiency, % 

Range Average Range Average 

Particulate matter, 

grlscf 

0.33 to 0.181 0.090 ' 0. 016 to 0. 051 0. 032 6 5 

Aldehydes (as formaldehyde), 

ppm 

--- 7 4 --- 47 

3 7 

Organic acids (as acetic 

acid), ppm 

--- 91 

>.- 48 

47 

aEach control system is equipped with a wet centrifugal collector upstream from the 

precipitator. 

2 5 

33.5 

11.7 

6 6 

3 8 

62 

Negative

during the smoking cycle. The size of control 

equipment is materially increased if drying 

gases are ducted to it. The initial cost and oper- 

ating cost of a smokehouse's air pollution control 

system can, therefore, be considerably reduced 

if exhaust gases are bypassed during drying and 

cooking cycles when no smoke is introduced into 

the house. 

If control devices are to be bypassed duringnonsmok- 

ing periods, the ductwork and valving should be de- 

signed to provide automatic or nearly automatic 

operation. Water seal dampers (Figure 610) are 

preferable. Mechanical dampers demand optimum 

maintenance for satisfactory closure. They are 

considerably more likely to malfunction owing to 

corrosion and contamination with greases and tars. 

Moreover, mechanical dampers are more suscepti- 

ble to physical damage than water dampers are. 

Ideally, damper operation should be keyed to other 

smokehouse auxiliaries such as fans and smoke 

generators. Where controls are manually oper- 

ated, there is a strong possibility that dampers 

will not be opened or closed at proper times, 

causing either overloading of the control device 

or the discharge of untreated air contaminants 

directly to the atmosphere. 

CASES FROM 

SMObEHOUSE 

10 CONTROL 

C- 

OtYlCt AIMOSPHERE 

F~gure 610. Diagram of a water-operated damper 

used to bypass the a1 r pol lut~on control dev~ce 

dur~ng nonsmoking per~ods. 

DEEP FAT FRYING 

Deep fat or "French" frying involves the cooking 

of foods in hot oils or greases. Deep-fried prod- 

ucts include doughnuts, fritters, croquettes, vari- 

ous potato shapes, and breaded and batter-dipped 

fish and meat. Most of these foods contain some 

moisture, a large portion of which is volatilized 

out as steam during frying. Some cooking oils, 

as well as animal or vegetable oils from tb". prod- 

uct, are usually steam distilled during the pro- 

cess. 


Deep fat frying is in common usage in homes, 

restaurants, and frozen food plants. In the home 

and in smaller commercial establishments, batch- 

type operation is more common. The principal 

equipment is an externally heated cooking oil vat. 

Oil temperatures are usually controlled to be- 

tween 325" and 400°F. Almost any type-of 

heating is possible. Where combustion fuels 

are used, burner gases are vented separately. 

The product to be fried is either manually or 

mechanically inserted into the hot grease and 

removed after a definite time interval. 

In large commercial establishments, highly 

mechanized, conveyorized fryers, such as that 

shown in Figure 611, are used. The raw food 

product is loaded onto an endless conveyor belt 

and passed through hot grease at a rate adjusted 

to provide the proper cook time. Almost all 

fryers are of one-pass design. Frequently, cook- 

ing units are followed by product coolers and pack- 

aging and freezing equipment. 


In a typical large industrial operation of this 

type, the cooking vat constitutes the principal 

source of air contaminants. Uncooked materials 

are usually wet or pasty, and the feed system 

produces little or no air pollution. Most cooked- 

product-handling systems are also innocuous, 

except in rare instances where fine, dusty mate- 

rials are encountered. 

TO - -+ Odors, visible smoke, and entrained fat particles 

are emitted from the cooking vats. Depending 

upon operating conditions and the surrounding 

area, these contaminants may or may not be m 

sufficient concentration to exceed the limits of 

local opacity or nuisance regulations. 

From the standpoint of air pollution control, the 

most objectionable operations involve foods con- 

taining appreciable fats and oils. Light ends of 

these oils are distilled during cooking. In gen- 

eral, the deep frying of vegetable products is 

less troublesome than that of fish and meat prod- 

ucts, which contain higher percentages of fats 

and oils. 

Most food products cooked in this manner con- 

tain between 30 and 75 percent moisture before 

the cooking. Almost all moisture is driven off 

in the cooking vat and appears as steam in ex- 

haust gases. Moisture concentrations in stack 

gases are usually between 5 and 20 percent, de- 

pending upon the volume of air drawn into the 

cooker hood and exhaust system. In highl!- 

mechanized installations, very little air enters 

under the cooker hood. As a result, the warm 

air-stream from a fryer such as this is often


Figure 611. A continuous deep fat fryer: (left) Interior view, 

(right) end view (J.C. Pitman & Sons, Inc., Concord, N.H.). 

saturated, and downstream cooling causes visi- 

ble condensation at or near the stack exit. 

Moisture has two effects: (1) It causes fats and 

oils to be steam distilled from the cooking vat, 

and (2) it masks visible stack emissions. Smoke 

observations of equipment such as this must be 

made at the point in the stack plume where water 

vapor has disappeared. This is best accomplished 

when the weather is warm and dry. On a cold, 

moist day, the vapor plume may extend as far 

as the smoke. 

Excessive smoking is most often due either to 

overheating or to the characteristics of the 

material being cooked. When, for instance, 

potato chip or corn chip fryers are operated 

in normal temperature ranges, there is usually 

no more than a trace of smoke in exhaust gases. 

On the other hand, several meat product fryers 

have been found to exhaust gases of high opacity, 

and control equipment was needed to bring them 

into compliance with local regulations. These 

visible emissions appear to be finely divided 

fat and oil particles distilled either from the 

product or the cooking oil. Cooking oils are 

usually compounded within reasonably narrow 

boiling ranges, and when fresh, very little of 

the oils is steam distilled. Most objectionable 

air contaminants probably originate, therefore, 

in the product or in spent cooking oil. 

The carryover of oil droplets can also cause a 

nuisance by spotting fabrics, painted surfaces, 

and other property in the surrounding area. 

1 

j 

This problem is most likely to occur when the 

I 

raw food contains relatively large concentrations j 

of moisture, a situation in which steam distillation 

is proportionally higher. 1 i 

I 


Deep fat fryers should always be hooded and 

vented through a fan. Axial-flow fans are pre- 

ferred. Exhaust volumes are governed by the 

open area under the hood. Where there is open 

area around the full hood periphery, the indraft 

velocity should be at least 100 fpm. In many 

modern units, the dryer sides are completely 

enclosed, and the only open areas are at the con- 

veyor's inlet and outlet. At these installations, 

exhaust volumes are considerably less, even 

though indraft velocities are well above 100 fpm. 

If control equipment is to be employed, exhaust 

volumes become an important factor. In these 

instances, redesigning the existing hoods to low- 

er the exhaust rates is often desirable. 


Incineration, low-voltage electrical precipita- 

tion, and entrainment separation have been used 

to control air contaminants from deep fat fryers. 

Since practically all air contaminants from fry- 

ers are combustible, a well-designed afterburn- 

er provides adequate control if the cperating tem- 

perature is sufficiently high. Temperatures from

1, 000' to 1, 200°F are often sufficient to eliminate 

smoke-causing particulates and to incinerate odors 

and eye irritants. The combustion of larger par- 

ticles usually requires higher temperatures, some- 

times as high as 1,600-F. The concentration of 

particulates in fryer exit gases is, however, nor- 

mally less than 0. 1 grain per scf, which is well 

below common limits for particulate emissions. 

Two-stage, low-voltage electrical precipitators 

(6, 000 to 15, 000 volts) can be used to collect a 

substantial portion of the particulates responsible 

for visible air contamination. These devices, 

unfortunately, do not remove the gaseous con- 

taminants that are usually responsible for odors 

and eye irritation. As would be expected, the 

effectiveness of a precipitator depends upon the 

particular fryer it is serving. If particulates 

are the only significant contaminants in the ex- 

haust gases, a precipitator can provide an ade- 

quate means of control. If, on the other hand, the 

problem is due to odors of overheated oil or prod- 

uct, a device such as this is of little benefit. For 

optimum performance, the temperature, humidity, 

and volume of gases vented to a two-stage pre- 

cipitator must be controlled within reasonably 

narrow limits. The oils collected are usually 

free flowing and readily drain from collector 

plates. A collection trough should be provided 

to prevent plate fouling and damage to the roof 

or other supporting structure on which the pre- 

cipitator is located. 

Entrainment separators have been employed 

with varying success to remove entrained oils 

in fryer exhaust stacks. These are most use- 

ful where the concentration of oils is relatively 

large. The material collected can represent a 

savings in oil and can prevent damage to ad- 

jacent roofing. Because of the inherently low 

collection efficiency of these devices, their 

use is not recommended where smoke or 

odors constitute the major air pollution prob- 

lem. Some cooking oils usually collect on the 

inner surfaces of uninsulated exhaust stacks 

and drain back towards the cooker. Most com- 

mercial fryers are .equipped with pans to col- 

lect this drainage at the bottom of the stack. 

LIVESTOCK SLAUGHTERING 

Slaughtering operations have traditionally 

been associated with odorous air contaminants, 

though much of these odors is due to byproduct 

operations rather than to slaughtering and meat 

dressing itself. Slaughtering is considered to 

include only the killing of the animal and the 

separation of the carcass into humanly edible 

meat and inedible byproducts. The smoking 

of edible meat products, and reduction of edi- 

ble materials are discussed in this subsection, 

Food Processii ng Equipment 801 

while the reduction of inedible materials is 

covered in another part of this chapter. 

Cattle-, sheep-, and hog-killing operations are 

necessarily more extensive than those concerned 

with poultry, though poultry houses usually han- 

dle appreciably larger numbers of animals. 

A flow diagram of a typical cattle-slaughtering , 

operation is shown in Figure 612. The animal 

is stunned, bled, skinned, eviscerated, and 

trimmed as shown. Blood is drained and col- 

lected in a holding tank. After removal, en- 

trails are sliced in a "gut hasher, " then washed 

to separate the partially digested food termed 

"paunch manure. " Many slaughterers have 

heated reduction facilities in which blood, in- 

testines, bones, and other inedible materials 

are processed to recover tallow, fertilizer, 

and animal feeds. The firms that do not oper- 

ate this equipment usually sell their offal to 

scavenger plants that deal exclusively in by- 

products. Hides are almost always shipped to 

leather-processing firms. Dressed beef, nor- 

mally about 56 percent of the live weight, is 

refrigerated before it is shipped. 


Odors represent the only air contaminants 

emitted from slaughtering operations. The 

odors could be differentiated as (1) those 

released from the animal upon the killing and 

cutting, and upon the exposure of blood and 

flesh to air; and (2) those resulting from the 

decay of animal matter spilled on exposed sur- 

faces or otherwise exposed to the atmosphere, 

Odors from the first source are not appreciable 

when healthy livestock is used. Where nuisance- 

causing odors are encountered from slaughter- 

ing, they are almost always attributable to in- 

adequate sanitary measures. These odors are 

probably breakdown products of proteins. Amines 

and sulfur compounds are considered to be the 

most disagreeably odorous breakdown products. 

In addition to these sources, there are odors 

at slaughterhouse stockyards and from the stor- 

age of blood, intestines, hides, and paunch 

manure before their shipping or further process- 

ing. 


As has been explained, odorous air contami- 

nants are emitted from several points in a 

slaughtering operation. Installing control equip- 

ment at each source would be difficult if not im- 

possible. Methods of odor control available in- 

clude: (1) Rigid sanitation measures to prevent


STORAGE 

RENDERING 

STORAGE 

Figure 612. Typical livestock-slaughtering and processing area 

(The Globe Company, Chicago, Ill.). 

RENDERING 

the decomposition of animal matter, and (2) com- EDIBLE-LARD AND TALLOW RENDERING 

plete enclosure of the operation to capture the 

effluent and exhaust it through a control device. Methods used to produce edible lard and tallow 

Where slaughtering is government inspected, 

the operators are required to wash their kill 

rooms constantly, clean manure from stock 

pens, and dispose of all byproducts as rapidly 

as possible. These measures normally hold 

plant odors to a tolerable minimum. 

When a slaughterer is located in a residential 

area, the odor reduction afforded by strict 

sanitation may not be sufficient. In these in- 

stances, full-plant air conditioning might be 

necessary. Filtration with activated carbon 

would appear to be the only practical means 

of controlling the large volume of exhaust 

gases from a plant of this type. The latter 

method has not yet been employed at slaughter 

houses in the United States. Nevertheless, 

activated-carbon filtration of the entire plant 

has been employed to control similar odors 

at animal matter byproduct plants. With in- 

creasing urbanization, this method of control 

may, conceivably, be used in the near future. 

are similar to those described later in this 

chapter for rendering of inedibles. As with 

processes for inedibles, feedstocks are heated 

either directly or indirectly with steam to effect 

a phase separation yielding fats, water, 

and solids. Moisture is removed either by 

vaporization or by mechanical means. Tallow 

and solids are mechanically separated from 

one another in presses, centrifuges, and filters. 

The only major process differences between 

rendering edibles and rendering inedibles are 

due to the composition and freshness of the 

materials handled. Edible feedstocks contain 

80 to 90 percent lard or tallow, 10 to 20 per- 

cent moisture, and less than 5 percent muscle 

tissue. Inedible feedstocks contain appreciably 

higher precentages of both moisture and solids. 

Edible feedstocks, in addition to being more 

select portions of the animal, are generally 

much fresher than inedible cooker materials 

are.


Whenever its products are intended for human material in direct contact with live steam. 

consumption, the process is much more stringent- - 

ly supervised and regulated by Federal and local 

The principal advantage of this type of renderagencies. 

There are numerous government regulations 

concerning the freshness of edi,,le-rendering 

is that large quantities of lar* Or tallow 

ing feedstocks, the cleanliness of processing 

can be produced without finely grinding the feed 

equipment, and the handling of rendered fats. material. Low-cost equipment and labor can 

For instance, paragraph 15. 1 of the United States 

be used. 

- - 

Department of Agriculture's Meat Inspection 

Regulations specifies that inspected feed mate- 

Wet rendering, however, necessarily requires 

higher temperatures (280" to 300°F) and inrial 

must be heated to a temperature not lower 

than 170°F for a period of not less than 30 

ternal pressures of 38 to 40 psig, The quality 

minutes when edible lard or tallow is being proof 

the lard or tallow produced is relatively low, 

duced. 

owing to the high temperatures to which it is 

subjected. 

Dry Rendering 


Batchwise renderine - The only noteworthy air contaminants generated 

Most of the high-quality edible lard and tallow 

from edible-rendering processes are odors. In 

are produced in indirectly steam-heated cookers. 

comparison with odors generated from inedible- 

These processes are frequently carried out at 

rendering processes, however, those from 

temperatures of less than 212°F. The lower 

edible-rendering processes are relatively minor. 

operating temperatures are afforded either by 

vacuum cooking or by finely grinding the feed- 

In Los Angeles County, rendering of edibles acstocks. 

The vacuum process is usually percounts 

for only about 10 percent of the total aniformed 

batchwise in a horizontal, steam-jacmal 

matter rendered. Rendering of inedibles 

keted cooker very similar to those used for 

at packing houses constitutes approximately 32 

rendering of inedibles. The vacuum is usually 

percent and that at scavenger plants accounts 

created through the use of steam- or waterfor 

the remaining 58 percent of the tonnage. 

operated ejectors. Variations in dry, ediblerendering 

processes are usually concerned 

In addition, rates of odor emissions from renwith 

temperatures and the degree of comminu- dering of edibles are low compared with those 

tion of fats. Where raw materials are ground from inedible-rendering processes. Inasmuch 

into fine particles, operation at lower tem- 

as edible feedstocks contain relatively low perperatures 

is usually possible, even without 

centages of water, the resultant steam generated 

a vacuum-producing device. 

from cookers, 6,300 scf per ton, is not appre- 

Continuous low-temperature rendering 

ciable. Feedstocks contain approximately 15 percent 

moisture, as compared with 50 percent 

from inedible cooker materials. Odor concentrations 

in cxhaust gases from the rendering 

of edibles are significant at 3, 000 odor units 

per scf but not excessive. Equipment at plants 

rendering edibles is kept scrupulously clean, 

which substantially reduces odors from inplant 

handling operations. 

Dry rendering processes have been developed 

to produce edible lard and tallow on a continu- 

ous basis from high-fat feedstocks. A typical 

process is shown in Figure 613. Feedstocks 

are first introduced to a grinder, where they 

are finely shredded at 120°F. and then heated 

to approximately 185°F before being passed 

through a desludging centrifuge in which solids 

are removed from the water and tallow. Lia- 

uids are then reheated to about 200°F in a 

steam jet heater. The remaining moisture is 

removed from the hot tallow in a second cen- 

trifuge from which edible lard or tallow is 

run to storage. The separated water is piped 

to a skimming pond where it is cooled before 

being sewered. Vapors from the several 

vessels are vented to a fume scrubber (con- 

tact condenser). 


Almost always, cooker gases from rendering of 

edibles can be piped directly to air pollution con- 

trol devices. Where condenser odor control de- 

vices are used, there is usually enough vacuum, 

that is, pressure differential, in the ductwork 

to cause vapors to flow from the cooker at a 

sufficiently high rate. Steam or water ejectors 

are sometimes employed to lower operating 

temperatures or to remove water vapor more 

Wet Rendering 

rapidly. Uncondensible gases do not exceed 

5 percent of cooker gases unless there is ap- 

The wet rendering process involves rendering preciable leakage into the system, as through 

of fats in a vertical, klosed tank with the feed seals on shafts, doors, and so forth.


HEADER SLOPE TO SCRUBBER. NO POCKETS OR TRAPS 

r'&..p AZZ-F-7 

PUMP PURIFIER TO STICKWATER PLANT 

OR CATCH BASIN 

1 

\scE!kEy 

1 

I 

i 

J 

--- 

VAPOR VENT LINES 

COLD WATER 

1 i,L 

CATCH BASIN. 

B C 

TO SEWER 

80' TO 190°F 1185" TO 215OF 

Figure 613. DeLaval continuous centriflow process for edible protein recovery 

and edible fat rendering (The DeLaval Separator Co., Millbrae, Calif.). 

Where cooking is performed at pressures 

greater than 1 atmosphere, piping must usually 

be arranged in a manner that prevents surging 

when high-pressure gases are released. If 

the main valve is released quickly, the high- 

pressure vapors usually cause slugs of grease 

and solids to be carried over into the control 

system. Severe surging can cause siphoning 

of all the material from cooker to the control 

system. To prevent this, the piping is often 

arranged with a small pipe, 1 to 2 inches in 

diameter, that bypasses the main cooker's 

exhaust line. High pressures are reduced by 

venting first through the small pipe to the con- 

trol device. Once the high pressure is relieved, 

the large valve can be opened to provide great- 

er flow. 


lower volume of steam exhausted from the cook- 

er. Exit water temperatures should be held 

below 140°F to prevent the release of volatile, 

odorous materials from downstream piping 

and sewers. 

Surface condensers are also satisfactory con- 

trol devices for edible-rendering processes. 

At the same condensate volume and tempera- 

ture, however, surface condensers by them- 

selves are not as effective as contact con- 

densers. This is due to the inherently lower 

condensate volume and larger concentration 

of odorous materials in the condensate of sur- 

face condensers. 

That an edible-rendering process would require 

more extensive odor control than would be afforded 

by an adequate condenser is unlikely. 

Nevertheless, uncondensed offgases from condensers 

could be further controlled by incineration 

or carbon adsorption, as outlined for 

processing of inedibles later in this chapter. 

Water spray contact condensers are the simplest 

devices used for controlling odorous air contaminants 

from rendering . of edibles. These condense 

a major portion of the steam-laden effluent 

vapors and dissolve much of the odorous materi- 

FlSH CANNERIES AND FlSH 

als. Water requirements of the contact condenser 

for edible-rendering operations are considerably 

REDUCTION PLANTS 

lower than those for the contact condenser used Canning is the principal method of preserving 

to control cooker gases from rendering of in- highly perishable fish foodstuffs. Canneries 

edibles. This is due primarily to the lower fcr this purpose are usually located near harmoisture 

content of feedstocks and the resultant bors where fish can be unloaded directly from

oats. Byproduct reduction plants are operated 

at or near fish canneries to process scrap ma- 

terials, and much of the odorous air contami- 

nants generally attributed to canneries emanate 

from byproduct processes. Only choice por- 

tions of sound fish are canned for human con- 

sumption. The remainder is converted into by- 

products, notably fish oil and high-protein 

animal feed supplements. 

Basically there are two types of fish-canning 

operations in use today. In the older, so-called 

"wet-fish" method, trimmed fish are cooked 

directly in the can. The more popular "pre- 

cooked" process is used primarily to can tuna. 

The latter method is characterized by the cook- 

ing of whole, eviscerated fish, and the hand 

sorting of choice parts before canning. 

WET-FISH CANNING 

Wet-fish canning is used to preserve salmon, 

anchovies, mackerel, sardines, and similar 

species that can be obtained locally and brought 

to the cannery quickly. The distinctive feature 

of the wet-fish process is the complete removal 

of heads, tails, and entrails before the cooking. 

Fish Canneries and Fish Reduction Plants 805 

Trimmed and eviscerated raw fish is packed 

into open cans that are conveyed through a 100- 

to 200-foot-long hot-exhaust box. Here live 

steam is employed to cook the fish. Hot-ex- 

haust boxes are vented through several stacks 

located along their lengths (Figure 614). At 

the discharge end, cans may he mechanically 

upended so that "stick water" is decanted from 

the cans while the cooked fish remains. Stick 

water consists of condensed steam, juices, and 

oils that have cooked out of the fish. This liq- 

uid is collected and retained for byproduct 

processing as described later in this section. 

The cans of drained fish are filled with tomato 

sauce, olive oil, or other suitable liquid before 

being sealed. Sealed cans are pressure cooked 

before their labeling, packing, and shipping. 

TUNA CANNING 

The precooked canning method was developed 

to improve the physical appearance of canned 

fish. It is confined to the commercial canning 

of larger fishes, principally tuna. Whole, 

cviscerated fish are placed in wire baskets and 

charged to live-steam-heated cookers such as 

those of Figure 615. The cookers are operated 

Figure 614. Unsealed cans of cooked mackerel beina conveved from

806 CHEMICAL PROCE :SSING EQUIPMENT 

Flgure 615. A bank of 11ve-steam-heated cookers 

used to process raw, whole tuna (Star-Klst Foods, 

Inc., Termlnal Island, Calif.). 

at about 5 psig pressure, condensate being dis- 

charged through steam traps. Air, steam, and 

any uncondensed, odorous gases are bled from 

the cookers through one or more small vents in 

'the ceiling. 

As the fish are cooked, juices, condensed steam, 

and oils are collected, centrifuged, and pumped 

to stick water and oil storage tanks. Cooking 

reduces the weight of a fish by about one-third. 

After the cooking, the flesh is cooled so that it 

becomes firm before it is handled. It is then 

placed on a conveyorized picking line. Operators 

stationed along the conveyor select the portions 

to be canned for human consumption. After being 

packed and sealed in cans, the fisb is pressure 

cooked for sterilization before its labeling, pack- 

ing, and shipping. Much of the dark meat is 

canned for pet food. Only about one-third of the 

raw tuna weight is canned as food for humans and 

pets. The remaining skin, bone, and other scrap, 

roughly amounting to one-third of the raw weight, 

is fed to the fish meal reduction system. 

CANNERY BYPRODUCTS 

A large fraction of the fish received in a cannery 

is processed into byproducts. In the precook 

process, about two-thirds of the raw fish weight 

is directed to byproduct reduction systems as 

stick water or solid scrap. The wet-fish process 

usually produces somewhat less offal, depending 

principally upon the size of fish. Typical head- 

and-tail mackerel scrap is pictured in Figure 616. 

In addition, whole fish may be rejected at the can- 

ning line because of spoilage, freezer burns, bad 

color, and so forth. Any fish or portions of fish 

Figure 616. Typical raw head-and-tail mackerel j 

scrap awaiting processing in a fish meal reduction 1 

system (Star-Kist Foods, Inc., Terminal Island, 

Calif.). i 

not suitable for human consumption or for pet 

food are handled in the reduction plant. In order 

of volume and relative importance, the byproducts 

are: Fish meal, used almost exclusively as an 

animal feed supplement; fish oil, used in the 

paint industry and in vitamin manufacture; and 

"liquid fish" and "fish solubles, " high-protein 

concentrates. The latter are manufactured 

somewhat differently, but both are used as ani- 

mal feed supplements and as fertilizers. 

.FISH MEAL PRODUCTION 

Fish scrap from the canning lines, including 

any rejected whole fisb, is charged to continuous 

live-steam cookers in the meal plant. 

Flow through a typical fish meal plant is diagrammed 

in Figure 617. Cookers of the type 

shown in Figure 618 are operated at between 10 

and 25 psig steam pressure. Material charged 

to the cookers normally contains 20 to 30 percent 

solids. Cooked scrap has a slightly smaller 

solids content owing to the condensed steam 

picked up in cooking. After the material 

leaves the cooker, it is pressed to remove 

oil and water, and this pressing lowers the 

moisture content of the press cake to approximately 

50 percent. The press cake is broken Up, 

usually in a hammer mill, and dried in a directfired 

rotary drier or in a steam-tube rotary 

drier. Typical fish meal driers ~ield 2 to 10 

tons of meal per hour with a moisture content 

of 4 to 10 percent. Both types of driers em-

Fish Canneries and Fish Reduction Plants an7 

1 

FISH SCRAP VAPORS TO CONDENSER 

t t 

1 WATER 

LIVE STEAM COOKER CENTRIFUGE 

AN0 SOLUBLES 

STEAM 5 PSlg DRIER GASES TO 

GRINDER 

SOLIDS 

SEPARATOR 

SOLlOS LlQUlOS rv 

ROTARY FISH MEAL DRIER 

t 

, TO STORAGE MEAL + 

I I FINES I 

GRINDER 

Flgure 617. Flow d~agram of a fish meal reduct~on system includ~ng 

011-separat~ng and 011-clar~fy~ng equ~pment. 

Figure 618. A live-steam reduction cooker and a 

continuous press (Standard Steel Corp., Los Angeles, 

Calif.). 

ploy air as the drying medium. Moisture is 

removed with exhaust gases, which are volu- 

minous. 

Direct-fired driers include stationary fireboxes 

ahead of the rotating section, as shown in Fig- 

ure 619. They are normally fired with natural 

gas or fuel oil. Combustion is completed in 

the firebox. Hot products of combustion are 

mixed with air to provide a temperature of 400" 

to 1,000"F at the point where wet meal is initial- 

ly contacted. Hot, moist exhaust gases from 

the drier contain appreciable fine meal, which 

is commonly collected in a cyclone separator. 

The essential feature of steamtube driers is 

a bank of longitudinal, rotating steamtubes 

arranged in a cylindrical pattern, as shown in 

Figure 620. Steam pressures range from 50 

to 100 psig in the tubes. Heat is transferred 

both to the meal and air. As with direct-fired 

units, gases pass parallel to meal along the 

axis of the drier and are vented through a cy- 

clone separator. Meal produced in steamtube 

driers is less likely to be over-heated and is 

generally of higher quality than that from direct- 

fired units. 

FISH SOLUBLES AND FlSH OIL PRODUCTION 

Fish solubles is the term used to designate the 

molasses-like concentrate containing soluble 

proteins and vitamins that have been extracted 

from fish flesh by cooking processes. The 

flow diagram of Figure 617 includes the sep- 

aration of press water and fish oil. The sources 

of solubles and oils are the juices and conden- 

sate collected as press water and stick water.

808 CHEMICAL PROCESSLNG EQUIPMENT 

AUTOMATIC OIL 

OR GAS BURNER 

VAPOR LADEN GASES - 

VAPOR AND PRODUCT EXHAUST 

TEMPERATURE LIMIT 

SAFETY CONTROL \ 

THERMOSTATIC 

TEMPERATURE 

CONTROL 

\ / I 

CONTINUOUS BED FRAME ROLLER BEARING MOTORIZED VAPOR AND 

PRODUCT 

OPTIONAL TRUNNIONS REDUCER 

PRODUCTFAN DISCHARGE 

Figure 619. A parallel-flow, direct-fired, rotary, fish meal drier 

(Standard Steel Corp., Los Angeles. Gal if.). 

Figure 620. A stearntube, rotary, fish meal drier (Standard Steel Corp., 


! 

I 

I 

i

Thesetwo liquids may be processed separately 

or blended before their processing. The liq- 

uids are first acidified to prevent bacterial de- 

composition. Some protein is flocculatdd up- 

on the addition of acid. The floc and other 

suspended solids are removed in a centrifuge 

and recycled to the fish meal reduction process. 

Liquids pass through a second centrifuge, where 

the fish oils are removed. The water layer is 

pumped to multiple-effect evaporators where 

the solids content is increased from approxi- 

mately 6 to 50 percent by weight. Uncondensed 

gases are removed from the process at one of 

the evaporator effects, which is operated under 

high vacuum. The vacuum is held by a water 

or steam ejector. Where steam ejectors are 

used they are equipped with barometric-leg 

aftercondensers. 

DIGESTION PROCESSES 

Fish viscera are usually digested by enzymatic 

and bacterial action rather than by thermal reduction. 

The product is a liquid that is concentrated 

by evaporation and marketed as a highproteln 

livestock feed supplement very similar 

to fish solubles. 

Most cannery-operated digestion processes are 

of the enzymatic type and are used only to pro- 

cess viscera. Stomach enzymes, under con- 

trolled pH and temperature, reduce the viscera 

to a liquid. The process is u'sually carried out 

, in a simple tank at atmospheric pressure, near- 

ambient temperature, and an acid pH. Essen- 

tially no moisture is evaporated during digestion. 

Before concentration, the digested liquid is fil- 

tered and centrifuged to remove small quantities 

of scales, bones, and oil. The evaporation pro- 

cess is identical to that used for fish solubles, 

yielding a liquid of 50 percent solids. 

Bacterial digestion is used to reduce all types 

of fish flesh. It is carried out at an alkaline 

pH in equipment similar to that used for en- 

zymatic processes. Again, there is no appre- 

ciable moisture evaporation, but odors evolved 

are considerably stronger and more likely to 

elicit nuisance complaints. 


Air contaminants emanate from a number of 

sources in fish canneries and fish reduction 

plants, including both edible-rendering and 

byproduct processes. Odors are the most ob- 

jectionable of these contaminants, though dust 

and smoke can be a major problem. In a fish 

cannery, some odor is unavoidable owing to 

the nature of the species. Heavy odor emis- 

Fish Canneries and Fish Reduction Plants 

sions that cause nuisance complaints can usu- 

ally, however, be traced to poor sanitation or 

inadequate control of air contaminants. Tri- 

methyl amine, (CH3)3N, is the principal com- 

pound identified with fish odors. 

Reduction processes produce more odors than 

camlery operations do. Materials fed to re- 

duction processes are generally in a greater 

state of decay than the fish are that are pro- 

cessed for human consumption. Edible por- 

tions of the fish are always handled first, and 

great care is maintained to guarantee the qual- 

ity of edible products. The portions that are 

unsuitable for human consumption have much 

less value, and it is not uncommon for opera- 

tors to allow reduction plant feedstocks to 

decompose markedly before the processing. 

The largest sources of reduction plant odors 

are fish meal driers. Lesser quantities of 

odors are emitted from cookers preceding 

meal driers, from digestion processes, oilwater 

separators, and evaporators. Dust 

emissions are lxmited to driers and the pneu- 

matic conveyors and grinders following them. 

Smoke can be created by overheating or burn- 

ing meal m the drier. 

Odors From Meal Driers 

809 

Fish meal driers exhaust large vollunes of gases 

at significantly large odor concentrations. Dur- 

ing the processing of fresh fish scrap, odor con- 

centrations in exhaust gases range from 1,000 to 

5,000 odor units per scf (see Appendix B for defi- 

nition of odor units and method of measuring odor 

concentrations). If the feedstocks are hlghly de- 

cayed, much greater odor concentrations can 

be expected. The result is an extremely heavy 

rate of odor emission, even when fresh fish 

scrap is processed. For example, a direct-fired 

drier operating under "low-temperature " condi- 

tions and producing 4 or 5 tons of dried fish meal 

per hour exhausts about 30 to 40 million odor 

units per minute if the concentration is about 

2,000 odor units per scf and the exhaust rate is 

15,000 to 20.000 scfm. Drier exit temperatures 

average about 200" F, and the moisture content 

normally ranges between 15 and 25 percent by 

volume. 

A more startling example is that of the direct- 

fired rotary drier operating under "high-tempera- 

ture" conditions. It produces 10 tons of dried 

fish meal per hour and exhausts 600 to 800 million 

odor units per minute. The odor concentration is 

about 40,000 odor units per scf with an exhaust 

rate of 15,000 to 20,000 scfm. Drier exit tem- 

peratures average above 300" F during high- 

temperature operation.


Emissions from steamtube driers are less 

water aggravates the problem by lowering the 

voluminous and can he less odorous than those temperature, which increases condensation and, 

from direct-fired units. With steamtube driers, 

there is less likelihood of burning or overheatthereby, 

the opacity. 

ing the meal and, therefore, excessively heavy 

odor concentrations are encountered less often. 

Dust From Driers and Conveyors 

Moisture contents are comparatively greater 

in gases from steamtube driers. Typical gases 

from emitted steamtube driers during tuna scrap 

processing contain about 25 percent moisture as 

compared with approximately 15 percent from 

a direct-fired unit processing the same material. 

As a result, volumes from steamtuhe driers are 

30 to 45 oercent lower than those from com-oar- 

The only major points of dust emission in canneries 

and reduction plants are the driers themselves 

and the grinders and conveyors used to 

handle dried fish meal. Driers and pneumatic 

conveyors are equipped with cyclone separators, 

and emissions are functions of collection efficiencies. 

able direct-fired units. Odor concentrations 

from steamtuhe driers are generally in the same 

range as those from direct-fired units when 

fresh fish scrap is being processed under proper 

operating conditions, that is, when meal is 

not overheated. 

Fish meal does not usually contain a large fraction 

of fines. A particle size analysis of a typical 

meal is provided in Table 218. This meal 

sample was collected in a pneumatic conveyor 

handling ground fish meal. It can he seen that 

the sample contains only 0.6 percent by weight 

less than 5 microns in diameter, and 1. 4 per- 

Smoke From Driers 

Excessive visible air contaminants can be created 

in fish meal driers by the overheating of 

meal and volatilization of low-boiling oils and 

cent less than 10 microns in diameter. Ninetysix 

percent is larger than 20 microns. 

other organic compounds. Smoke is more likely Table 218. PARTICLE SIZE ANALYSIS OF 

to be emitted from direct-fired driers than from 

A TYPICAL GROUND, 

steam-tube units, particularly if the drier is 

operated under high-temperature conditions. 

DRIED FISH MEALa 

Range of particle diameter, I 

IL 

,t qo 

b 

All driers have limits for gas discharge tempera- 

tures above which excessive visible contaminants 

appear in the elrit gas steam. The smoking lim- 

it is a function of drier design as well as of feed- 

stocks and varies somewhat from unit to unit. 

For direct-fired units, this limit is about 300" F. 

Direct-fired driers operated under low-tempera- 

ture conditions process fish meal at about one- 

half the rate for high-temperature conditions, 

and the limit for gas discharge temperature is 

about 200" F. Only low-temperature operation 

is suitable for control by chlorinator-scrubbers. 

Chlorination of a drier exit gas steam which is 

in excess of 200' F will predictably produce an 

opacity coupled with a corresponding rise in odor 

level. 

The addition of certain low-boiling materials to 

drier feedstocks can also create visible emis- 

sions when there is essentially no overheating 

of meal in the drier. One such material is di- 

gested fish concentrate. Some operators add 

this high-protein liquid to drier feedstocks to 

upgrade the protein content of meal. Digested 

fish concentrate can contain low-boiling com- 

pounds that are vaporized into exhaust gases and 

condense upon discharge to the atmosphere. 

These finely divided, organic, liquid particulates 

can impart greater than 40 percent opacities to 

drier gases. Scrubbing the drier gases with 

0 to 5 

5 to 10 

10 to 20 

20 to 44 

44 to 74 

74 to 149 

149 to 246 

246 to 590 

590 to 1,651 

1, 651 to 2,450 

more than 2,450 

0.6 

0.8 

2.6 

7.5 

11. 5 

29. 9 

16.4 

22.8 

7.4 

0.4 

0.1 

asample drawn from a pneumatic conveyor 

following a direct-fired drier and hammer 

mill. 

b~ize determination by micromerograph. 

Concentrations of fines in exit gases are usually 

less than 0.4 grain per scf. The pneumatic con- 

veyor cyclone handling the meal of Table 218 was 

found to be better than 99.9 percent efficient, 

with an exit dust concentration of less than 0. 01 

grain per scf. This efficiency is much greater 

than would be predicted on the basis of cyclone 

design and particle size. It indicates that ap- 

preciable agglomeration probably takes place 

in the cyclone.

. . 

. . 

Odors From Reduction Cookers 


condensers, are used to produce the vacuum, 

odor emissions to the atmosphere are much 

The cookers preceding fish meal driers exhaust greater. Contact condensers (water ejectors) 

gases of heavy odor concentration. Nevertheless, provide a dilution of condensate 10 to 20 times 

: the volumes of these offgases are appreciablyless greater than that produced by surface-type con- 

than those from driers. Cooker gases are simi-. densers used with steam ejectors or vacuum 

lar to those from indirectly heated rendering Pumps. 

cookers. They consist almost entirely of water 

vapor but contain significant quantities of extremely 

odorous organic gases and vapors. Odor 

Odors From Edibles Cookers 

concentrations from live-steam-heated cookers 

range from 53 000 to over loo, 000 odor units Per 

scf, depending to a large degree upon the state 

of feedstocks. Any malodorous gases contained 

While most odorous air contaminants are considered 

to emanate from fish reduction processes, 

the handling and cooking of edible fish also produce 

measurable odors. The largest single sources 

in the cellular flesh structure are usually liberated 

when the material is first heated in the cooker. 

are the cookers described earlier in this section. 

... 

. .~ . .~ 

~ . . . . . 

. . ... . . 

Essentially no solids are in the effluent from the 

cookers, though some entrained oil particulates 

are usually present. The volumes of exhaust 

vapors depend upon the degree of sealing provided 

in the cooker. All the steam can be contained in 

the cooker with no leakage. Most cookers, however. 

are desiened - to bleed off 100 to 1. 000 cfm 

through one or more stacks. The latter arrangement 

is recommended, since it provides a positive 

exhaust point at which air contaminants can 

be controlled. Otherwise the malodorous gases 

would be liberated at the press and grinder where 

they are difficult to contain. 

The precooked process is less productive of odors 

than the wet-fish orocess L - ~ is -~. ~ When - . --....-..-.. 

~ tvna ~ iq cnnkod 

in the live-steam cookers of Figure 615, much of 

the odorous gases and vapors is condensed in the 

cooker and the steam trap. Only the volatile, 

albeit highly odorous, compounds are vented 

through the steamtrap. 

The hot-exhaust boxes of wet-fish production 

systems are commonly vented directly to the 

atmosphere. These offgases consist mostly of 

steam with some noncondensihle air and malodorous 

gases entrained. Hot-exhaust boxes 

are the points of initial cooking of wet fish, and 

are, therefore, origins of large quantities of 

Odors From Digesters 

gases and vapors. 

The digestion of fish scrap produces only small 

volumes of exhaust gases, though these gases 

can have a large odor concentration. The en- 

zymatic, acid-pH decomposition of viscera 

does not normally produce odor concentrations 

greater than 20,000 odor units per scf, depend- 

ing again upon the quality of feedstocks. Alka- 

line digestion of fish scrap, on the other hand, 

is productive of strong odors that are likely to 

create a public nuisance. 

Odors From Evoporotors 

The evaporation of the water-soluble extracts-- 

stick water and press water--does not generally 

result in heavy odor emissions. This is pri- 

marily due to the use of water ejector-condensers. 

Odors could be considerably heavier if different 

types of vacuum-producing equipment were em- 

ployed. Most fish canneries are located near 

large bodies of water,and it is common to use 

water jet ejectors to maintain a vacuum on the 

evaporator system. All uncondensed gases and 

vapors from the evaporators are vented to the 

ejectors, which act as contact condensers. Most 

of the odorous compounds are condensed or dis- 

solved in the effluent water. If steam ejectors 

and surface condensers, rather than contact 


When air pollution control is employed, most 

fish cannerv and reduction orocesses are vented 

directly to the control device. Cookers, presses, 

grinders, and the hot press-water auxiliary 

equipment require hooding. Hot material from 

the cooker evolves appreciable steam and odors 

when the oil and water are pressed from it 

and when the resultant press cake is broken 

up before the drying. The vapors liberated at 

these points consist principally of steam. When 

the gases are vented to a condenser, hooding 

should be as tight as possible to prevent dilu- 

tion with air. Indraft velocities of 100 fpm 

across the open area under the hood are nor- 

mally satisfactory. Where possible, the source 

itself should be totally enclosed and ducted to 

control equipment. Unfortunately, the designs 

of many presses and grinders are not conducive 

to complete enclosure, and hoods must be em- 

ployed. 

The largest contaminated gas streams are ex- 

hausted from fish meal driers. As shown in 

Table 219, volume rates are lower from steam- 

tube driers than from direct-fired units. For 

the hypothetical comparison made in this table,


Table 219. CHARACTERISTICS OF EXHAUST tion is preferable if it can be adapted to the pro- 

GASES FROM TYPICAL DIRECT-FIRED AND cess. Incineration provides the most positive 

STEAMTUBE FISH MEAL DRIERSa control of nuisance-causing - odorous comoounds. 

Steamtube 

drier ..... 

~ o ~ evapora~ed s t ~ from ~ meal. ~ scfmb 320 320 

Natural gas fuel, sctmC 

Moisture in product. of combustion. scfm 

Total moisture in exhaust gases, scfm 

I6 

3 1 

ory exhaust gases, scfm 

Total exhaust gases, ostm 

Moisture content, %by volume 

Direct-fir,?d 

drier 

Temperature of exhaust gases, 'F 180 I 205 

a~asis: 1 ton of feed per hour to drier. ~oist~re content of press 

cake to drier. 50% by weight. 

b~oisture content of dried meal, 8% by weight. 

C~atural gas o* I. LOO Bt" per scf gross heating value 

the fired drier exhausts 70 percent more gases 

than the steamtube drier does and the moisture 

content is comparatively less, 15 percent com- 

pared with 24 percent. A 10-ton-per-hour fired 

drier would exhaust 22,830 scfm at about 200aF, 

while a steamtube unit of the same size would 

exhaust only 13, 500 scfm at about 180°F. 

Exhaust volumes from live-steam-heated cook- 

ers range from 100 to 1,000 cfm and depend 

to a large degree upon cooker design. Inlet 

and exit seals should be tight to prevent leakage. 

Most cookers are vented through a single stack. 

Digestion tanks with a capacity of 2,000 gallons 

or less seldom exhaust more than 50 scfm. Ex- 

haust volumes from digesters vary appreciably 

during the processing of a batch, exit rates being 

negligible much of the time. 

Where water ejector contact condensers are em- 

ployed on evaporators, exhaust rates are well 

below 50 scfm. If surface condensers or vacuum 

pumps are employed instead of contact condensers, 

exhaust volumes can exceed 100 cfm. 

Fish meal pneumatic conveyors are designed to 

provide from 45 to 70 cubic feet of air per pound 

of meal conveyed. A pneumatic conveyor handling 

5 tons of dried meal per hour exhausts about 

10,000 cfm. 

Exhaust'gases from cookers used in the precooked 

tuna process are relatively small in volume and 

include only those gases that are not condensed or 

dissolved at the steamtrap or the cooker itself. 

Gases evolved from the hot-exhaust boxes of the 

wet-fish lines are considerably more voluminous. 


Fish cannery and fish reduction equipment are 

controlled principally with condensers, scrubbers. 

afterburners. and centrifueal - dust collectors. 

Where odors are concerned, incinera- 

Condensers are effective where exhaust gases 

contain appreciable moisture, while centrifugal . 

collectors are usually satisfactory to prevent 

excessive dust emissions. Scrubber-chlorina- - -- 

tors find particular use in the control of odors 

from fish meal driers. 

Controlling Fish Meal Driers 

Because of the exceedingly large volume of mal- 

odorous exhaust products from driers, they 

cohstitute the most costly air pollution control 

problem in a reduction plant. Drier gases nor- 

mally contain only 15 to 25 percent moisture. 

Thus, even after condensation, the volume is 

great. Moreover, there are enough entrained 

solids in drier exit gases to make incineration 

difficult. 

Incinerating Drier Gases 

Incineration of odorous air contaminants from 

fish meal driers is possible, though costly. It 

is, however, the only feasible method presently 

available to control driers operated under high- 

temperature conditions. This occurs when the 

operator processes fish meal at such a rate that 

the drier gases emerge at a temperature above 

300" F, and the feed scrap is subjected to hot 

gases between 1,200" and 1,700" F. 

A properly designed afterburner control system 

requires a dust collector ahead of the afterburner 

to remove solids that cannot readily be burned. 

The incineration of solid particulates at 1, 2OO'F 

or lower can result in partial oxidation of partic- 

ulates, which tends to increase rather than de- 

crease odor concentrations. A contact condenser- 

scrubber removes much of the difficult-to-burn 

particulates and materially reduces the volume 

rate by condensing the moisture. If the partic- 

ulate matter concentration in gases to the after- 

burner is sufficiently small, incineration at 

1,200°F reduces odor concentrations to about 

50 odor units per scf. Owing to the high cost 

of fuel in such an arrangement, few large in- 

stallations of afterburners serve fish meal 

driers. To make incineration economically at- 

tractive, heat from the afterburner should be 

reclaimed in some manner. The most likely 

arrangement is the preheating of air to the drier. 

An afterburner operating at 1,200°F provides 

all the heat necessarv to oaerate the drier, which 

thus eliminates the need for a firebox. 

Chlorinoting and Scrubbing Drier Gores 

A unique scrubber-chlorinator design has been 

developed to control the odors from fish meal

driers. Units of this design have proved to be 

satisfactory, provided the driers are operated 

under low-temperature conditions. During lowtemperature 

operation, the drier exit gas temperature 

is not allowed to exceed 200" F. The 

driving force for drying air and products of combustion 

is maintained below 6 Btu per scf, and 

the temperature at the zone where the fish scrap 

enters is maintained below 600" F. Such stringent 

conditions placed upon the operation of the 

drier cause the production rate to be reduced to 

approximately one-half of design if the moisture 

content of the dried meal is to be maintained at 

an acceptable level. This unit is demonstrated 

in the flow diagram - of Figure - 621 and pictured in 

Figure 622. 

The process depends largely upon the reaction of 

chlorine gas with odorous compounds at drier exit 

temperatures. As shown in Figure 621, gases 

from the drier are first directed through a cyclone 

separator to remove fine particulates. Chlorine is 

then added at a rate calculated to provide a concentration 

of 20 ppm by volume in the gas stream. 

The reactionis allowed to ~roceedat about 200" F-the 

drier exit temperature--in the ductwork for 

approximately 0.6 second before the stream is 

chilled and scrubbed with sea water in a packed 

tower. Gases pass up through the packing countercurrently 

to the sea water. 

In Figure 623, odor concentrations from the 

scrubber exit are plotted against the chlorine 

addition rate at constant gas and sea water 

throughput. As can be seen from the curve, 

odors reach a minimum at about 20 ppm chlo- 

rine. When more than 20 ppm is added, chlo- 


rine odors become readily detectable in treated 

gases, and odor concentrations tend to increase. 

All the odor measurements used to draw this 

curve were made on drier gas.samples taken ! 

between 170" and 205"F, when there was es- 

sentially no overheating of meal in the drier. 

This method provides an overall odor reduction 

of 95 to 99 percent when fresh fish scrap is being 

processed in the drier. Chlorination itself pro- 

vides a 50 to 80 percent reduction in odor con- 

centration. Scrubbing reduces the remaining I 

odor concentration by another 50 to 80 percent. 

Condensation provides a 12 to 22 percent re- 

duction in volume, depending upon the original 

moisture content of the gases. i 

The exact mechanism of the chlorination reac- 

tion is uncertain, but it is assumed that chlorine 

reacts with odorous compounds, probably amines, 

to form additional products that are less odorous 

than the original compounds. Chlorine is not 

considered to be a sufficiently strong oxidizing 

agent to oxidize fully the odorous organic mate- 

rials present in drier gases. 

Controlling Reduction Cookers and Auxiliary 

Equipment 

There is a tendency for the operator to use more 

live steam to cook fish scrap before it is fed into 

the rotary drier if low-temperature operation of 

the drier itself is employed. The entire prepara- 

tion of the drier feed is carried out at tempera- 

tures above 170nF, and large volumes of contam- 

inated steam are released to the atmosphere. 

These occur at the cooker, press, grinder, and 

press-water screen and sump. They can be con- 

- 

CHLORINE GbS 

Figure 621. A chlorinator-scrubber odor control system venting a fish 

meal dr~er. 

. ,


Figure 622. A chlorinator-scrubber odor control 

system venting a fish meal drier (Star-Kist 

Foods, Inc., Terminal Island, Calif.). 

trolled by hooding the component parts and ex- 

hausting to a condenser followed by an after- 

burner. The firebox of the rotary drier may 

provide a satisfactory substitute for the after- 

burner if adequate control is maintained on the 

drier exit gases. 

Controlling Digesters 

Digester gases are most easily controlled with 

afterburners. These gases are small in volume 

and require only minimal fuel for incineration. 

Digester offgases contain no appreciable moisture 

or particulates. Odor concentrations can normal- 

ly be reduced by 99 percent or more at 1,200-F 

in a properly designed afterburner. 

Controlling Evoporotors 

Evaporators for stick water, press water, and 

digested liquor can be controlled with condensers 

and afterburners and combinations thereof. Most 

Figure 623. Exit odor concentrations from a chlo- 

rinator-scrubber as a function of the chlorine eas 

addition rate. Temperatures of gas discharged from 

drier are less than 205O~. 

evaporators are equipped with water ejector con- 

tact condensers to provide the necessary vacuum 

in the one effect of the multiple evaporator effects. 

Condensate temperatures from these ejectors are 

usually less than 80°F. As a result, they con- 

dense and dissolve most of the odorous compounds 

that would otherwise be discharged to the atmo- 

sphere. Condensate cannot be circulated through 

cooling towers without causing the emission of 

strong odors. Ideally, sea water or harbor 

water is used for this purpose, with no recircu- 

lation. The entrained air contaminants do not 

add enough material to tail waters to create a 

water pollution problem. 

If water ejectors are not used, odorous air con- 

taminants are emitted in much heavier concen- 

tration. The most likely alternative is a steam 

ejector and surface-type aftercondenser, possi- 

bly with multiple ejector stages. Noxious odors 

from an operation such as this are stronger and 

more voluminous than those emitted from contact 

condensers. Hooding of the condenser hot-well 

and exhausting to an afterburner operating at 

1.200" F or greater is usually the most feasible 

means of controlling these processes. Activated 

carbon can be used in lieu of an afterburner.

Collecting Dust 

As previously noted, fish meal does not contain 

a large amount of extremely fine particles, that 

is, those less than 10 microns. For this reason, 

cyclone separators are normally sufficient to 

prevent excessive emissions from the drier and 

subsequent pneumatic conveyors. If the meal 

from a particular plant were to contain appre- 

ciably more fine material than the sample shown 

in Table 218, more efficient dust collectors, 

such as small-diameter, multiple cyclones or 

baghouses, would have to be used. 

Controlling Edible-Fish Cookers 

Exhaust gases from both precooked and wet-fish 

process cookers consist essentially of water 

vapor. At tuna cookers, most of this vapor is 

condensed in the steamtraps on the cookers. If 

further control is desired, an afterburner, 

carbon adsorber, or low-temperature contact 

condenser is recommended. 

Reduction of Inedible Anlrnal Matter 815 

which are operated solely for the byproducts. 

In Figure 624, "deadstock" is shown awaiting 

dismemberment at a scavenger plant. Com- 

mon rendering cooker feedstocks are pictnred 

in Figure 625. In general, the materials pro- 

cessed in captive packing house systems are 

fresher than those handled at scavenger plants 

where feedstocks can be highly decayed. Typ- 

ical slaughterhouse yields of inedible offal, 

bone, and blood are listed in Table 220. 

The hot-exhaust boxes of wet-fish processes 

represent large odor sources that can be controlled 

with contact condensers, often at little 

expense to the operator. Most canneries are 

located near large bodies of water. Sea water 

or harbor water can be directed to contact condensers 

at little cost in these instances. Since 

exhaust box - eases are orincioallv water, there 

& , 

is a marked reduction in volume across a condenser 

such as this, in addition to a decrease Figure 624. Dead stock awaiting skinning and dismemberment 

at a scavenger renderine plant (Califorin 

odor concentration. 

nia Rendering Co.,Ltd.. Los Angeles, Calif.). 

REDUCTION OF INEDIBLE 

ANIMAL MATTER 

Animal matter not suitable as food for humans 

or pets is converted into salable byproducts 

through various reduction processes. Animal 

matter reduction is the principal waste disposal 

outlet for slaughterhouses, butcher shops, 

poultry dressers, and other processors of 

flesh foods. In addition, it is used to dispose 

of whole animals such as cows, horses, sheep, 

poultry, dogs, and cats that have died through 

natural or accidental causes. If it were not 

for reduction facilities, these remains would 

have to be buried to prevent a serious health 

hazard. The principal products of reduction 

processes are proteinaceous meals, which find 

primary use as poultry and livestock feeds, and 

tallow. 

Much reduction equipment is operated in meat- 

packing plants to handle only the "captive" blood, 

meat, and bone scrap offal produced on the 

premises. Other reduction cookers and driers 

are located in scavenger rendering plants, 

Figure 625. Inedible animal matter in the receiving 

pit of a rendering system (California Rendering Co., 

Ltd., Los Angeles, Calif.).


Table 220. INEDIBLE, REDUCTION PROCESS 

RAW MATERIALS ORIGINATING 

FROM SLAUGHTERHOUSES 

(The Globe Co., Chicago, Ill. ) 

Source, lb live wt 

Steers, I, 000 

Cows 

Calves, 200 

Sheeo . . 80 

Hogs, 200 

Inedible offal and bone, 

lblhead 

90 to 100 

110 to 125 

15 to 20 

(I to 10 

10 to 15 

Blood, 

Iblhead 

55 

55 

5 

4 

7 

The animal mstter reduction industry has been 

traditionally considered one of the "offensive 

trades. " The reputation is not undeserved. 

Raw materials and process exhaust gases are 

highly malodorous and capable of eliciting nuisance 

complaints in surrounding areas. In 

recognition of these facts, specific air pollution 

control regulations have been enacted requiring 

the control of odorous process vapors. 

BATCHWISE DRY RENDERING 

The most widely used reduction process is dry 

rendering, wherein materials containing tallow 

are heated indirectly, usually in a steam-jac- 

keted vessel. Heat breaks down the flesh and 

bone structure, allowing tallow to separate 

from solids and water. Ln the process, most 

of the moisture is evaporated. Emissions con- 

sist essentially of steam with small quantities 

of entrained tallow, solids, and gases. 

Dry rendering mav be performed batchwise or 

continuously and may be accomplished at pressures 

greater or less than atmospheric. A 

typical batch-type, steam-jacketed, dry rendering 

cooker is shown in Figure 626. These vessels 

are normally charged with 3,000 to 10,000 

pounds of animal matter per batch. The cookers 

are equipped with longitudinal agitators that are 

driven at 25 to 65 rpm. Each batch is cooked 

for 314 to 4 hours. 

Rendering is a specific heated reduction 

process wherein fat-containing materials are 

reduced to tallow and proteinaceous meal. 

Blood drying, feather cooking, and grease reclaiming 

are other reduction operations usually 

performed as companion processes in rendering 

plants. 

Pressures of 50 psig and greater are used to 

digest bones, hooves, hides, and hair. At the 

resulting temperature (about 300°F), these 

materials are reduced to a pulpy mass. In typical 

dry-pressure-rendering cycles, the cooker 

vent is initially closed to cause pressure and 

temperature to increase. Some materials are 

cooked as long - as 2 hours at elevated pressure 

Reduction processes are influenced largely by 

the makeup of feedstocks. As can be seen from 

Table 221, some materials, such as blood and 

feathers, are essentially grease free, while 

to obtain the necessary digestion. After pressures 

are reduced, the batch is cooked or dried 

to remove additional moisture and to complete 

tallow-solids separation. 

others contain more than 30 percent tallow. Some dry rendering operations are carried out 

Where no tallow is present, the reduction pro- under vacuum to remove moisture rapidly at 

cess becomes primarily evaporation with, possi- temperatures sufficiently low to inhibit degradahly, 

some thermal digestion, tion of products. Vacuum rendering processes 

Table 221. COMPOSITION OF TYPICAL INEDIBLE RAW MATERIALS 

CHARGED TO REDUCTION PROCESSES 

(The Globe Co., Chicago, Ill. ) 

Source 

Packlng house offal and bone 

Steers 

Cows 

Calves 

Sheep 

Hogs 

Dead stock (whole anlmals) 

Cattle 

Cows 

Sheep 

Hogs 

Blood 

Feathers (from poultry houses) 

Butcher shop scrap 

Tallow or grease, 

wt % 

15 to 20 

10 to 20 

8 to 12 

25 to 35 

15 to 20 

12 

8 to 10 

22 

3 0 

. 

3 7 

Solids, 

wt % 

30 to 35 

20 to 30 

20 to 25 

20 to 25 

18 to 25 

25 

23 

2 5 

25 to 30 

12 to 13 

20 to 30 

25 

Moisture, 

wt % 

45 to 55 

50 to 70 

60 to 70 

45 to 55 

55 to 67 

6 3 

67 to 69 

5 3 

40 to 45 

87 to 88 

70 to 80 

3 8

are essentially all of the batch type. Thevacu- 

um is usually produced with a precondenser, 

steam ejector, and aftercondenser. Cooker 

pressures are close to atmospheric at the start, 

then diminish markedly as the moisture content 

of the charge decreases. Vacuum rendering 

produces high-quality tallow but has a disadvan- 

tage in that ternperatures are low and incomplete 

cooking of bones, hair, and so forth, may occur. 

CONTINUOUS DRY RENDERING 

Because of the increased demand for processing 

meat, bone, and offal, highly mechanized con- 

tinuous dry rendering processes are used today. 

The advantages readily become apparent when it 

is shown that one operator can process 1 - 114 

million pounds of material in 16 hours. It would 

Reduction of Inedible Animal Matter 817 

Figure 626. A horizontal, batch-type, dry-rendering 

cooker equipped with a charging elevator (Standard 

Steel Corp., Los Angeles, Calif.). 

otherwise take 40 batch cookers and an undeter- 

mined crew of men to produce the same volume 

of throughput. Some processes consist essen- 

tially of a series of grinders, steam-jacketed 

conveyor-cookers, and presses. The continuous 

system of Figure 627 uses recycle tallow and a 

vertical-tube vacuum cooker. Selected meat and 

bone scrap is ground and slurried withhottallow 

before being charged to the cooker. Slurry is 

circulated through the tubes, and vapors are 

vented to a contact condenser. Steam is con- 

densed ahead of the ejector, and a barometric 

leg is employed. Tallow and solids are continu- 

ously withdrawn from the bottom of the cooker. 

In another continuous system, material is con- 

veyedto ahasher or hogger before it is fed to the 

first cooker. Here the temperature is brought 

up to approximately 180" F. Then the material is 

fed to a high-speed hammer mill or blender be- 

fore it is conveyed to the next cooker. The mate- 

rial is brought up to a temperature of about 21 0" F 

in the second cooker and then continuously con- 

veyed to a stacked set of finishing cookers. The 

finishing cookers consist of long jacketed continu- 

ous-tube screw conveyors where the material is 

brought up to 275" F before it is discharged onto 

a screen or into a prepresser. The prepresser, 

a press with extra spacing, gently squeezes the 

crax before it is fed to a press, or many presses 

in parallel. The press-cake is ground in a high- 

speed hammer mill and emerges as a meat meal 

product. Pressed and free-running tallow is 

settled, centrifuged, bleached, dried, and fil- 

tered to a premium grade tallow. 

Another continuous process consists of a hasher 

and one large continuous-tube cooker without


FLUlDlllNG TANK 

TRAMP METAL OISCHhRGF 

WATER SUPPLY 

STEAM SUPPLY 

BAROMETRIC CONDENSER STEhM SUPPLY 

FIUIOIIINO PUMP 

KlTER OISCHIIROE 

-AIR IN0 NUN CONOENSIBLE EJECTOR 

EAM CONOENSAI 

,. Y'8 . . 

FIT OISCIARGE 1 

STORAGE IANK 

Figure 62i. A continuous, vacuum rendering system employing tallow recycl ing (Carver-Greenf ield 

Process, The V.D. Anderson Co., Cleveland, Ohio). 

finishing cookers. The material is brought to 

250" to 300" F before being discharged to the 

prepresser. The feed rate to a unit without 

finishing cookers must necessarily be adjusted 

to allow more residence time in the single cooker. 

Another variation in the finishing cycle involves 

the use of a multiple-effect evaporator. The 

feed rate through the continuous-tube cooker may 

be approximately doubled and the material 

emerges half-cooked at approximately 210" to 

220" F. The steam driven off from the half- 

cooked material goes to an evaporator, where 

the remainder of the moisture is cooked off at a 

temperature of approximately 190" F and a 

vacuum of approximately 27 inches of water 

column. 

WET RENDERING 

One of the oldest reduction methods is the wet 

process, wherein animal matter is cooked in a 

closed vessel with live steam. There is little 

evolution of steam. Most of the contained mois- 

ture is removed as a liquid. Live steam is fed 

to a charge in a closed, vertical kettle until the 

internal pressure reaches approximately 60 psig 

(about 307°F). Heat causes a phase separation 

of water, tallow, and solids. After initial cook- 

ing, the pressure is released, and some steam 

is flashed from the system. The charge is then 

cooked at atmospheric pressure until tallow 

separation is complete. Water, tallow, and 

solids are separated by settling, pressing, and 

centrifuging. 

The water layer from a wet rendering process 

contains 6 to 7 percent solids. Soluble proteins 

can be recovered by evaporation, as in the 

processing of stick water at fish reduction 

plants. 

Wet rendering finds some use today in the han- 

dling of dead stock, namely whole animals that 

have died through accidents or natural causes. 

It has given way to dry rendering at most pack- 

ing houses and scavenger plants. Wet rendering 

is used to a limited degree in the production of 

edible fats and oils, as noted previously in this 

chapter.

REFINING RENDERED PRODUCTS 

At the completion of the cook cycle, tallow and 

sblids are run through a series of separation 

equipment as in the integrated plant of Figure 

628. Some systems are more complex than 

others, but the essential purpose is to produce 

dry, proteinaceous cracklings and clear, mois- 

ture-free tallow. In almost all cases, the cook- 

ers are discharged into perforated percolator 

pans that allow free-running tallow to drain from 

hot solids. The remaining solids are pressed to 

remove residual tallow. Dry cracklings are usu- 

ally ground to a meal before being marketed. In 

Figure 629, grease-laden cracklings are being 

dumped from a percolator pan after free tallow 

has been drained. 

Tallow from the percolators and presses is 

further treated to remove minor quantities of 

solids and water. Solids may he removed in 

desludging centrifuges, filters, or settling tanks. 

Traces of moisture are often removed from it 

by boiling or blowing air through heated tallow. 

Some operators remove moisture by settling in 

cone-bottom tanks, often with the aid of soda 

ash or sulfuric acid to provide better phase 

separation. 


Belgian De Smet process, in which hexane is 

employed, has been adopted by some renderers 

in the United States and Canada. The entire 

process is enclosed in a vaportight building to 

minimize the explosion hazard. After extrac- 

tion, hexane is stripped from tallow and solids. 

The only measurable air contaminants, solvent 

vapors, are vented at one or more condensers. 

DRYING BLOOD 

Animal blood is evaporated and thermally di- 

gested to produce a dry meal used as a fertiliz- 

er, as a livestock feed supplement, and, to a 

limited degree, as a glue. Blood contains only 

10 to 15 percent solids and essentially no fat. 

At most packing houses, it is dried in horizontal, 

dry rendering cookers. In typical slaughtering 

operations, blood is continually drained from 

the kill floor to one or more cookers, throughout 

the day. Initially, while there is appreciable 

moisture in the blood, heat transfer through the 

jacket is reasonably rapid. As the moisture 

content decreases, however, heat transfer be- 

comes slower. During the final portion of the 

cycle, drying is extremely slow, and dusty meal 

can be entrained in exit gases. 

In some instances, solvents are used to extract In some instances, a tubular evaporator is used 

tallow from rendered solids. Solvent extraction to remove the initial portion of the water. When 

allows extremely fine control of products. he the moisture content decreases to about 65 per- 

Figure 628. An integrated dry rendering plant equipped with batch 

cookers, percolators, a crack1 ings press, and a tal low-settl ing tank.

820 CHEMICAL PROCESSJNG EQUIPMENT 

Figure 629. Tallow-laden crack1 ings being dum~ed 

from a percolator after free tallow has been allowed 

to drain (California Render~ng Co., 

California). 

Ltd., Los Angeles, 

cent, the material is transferred to a dry ren- 

dering cooker for final evaporation. 

Continuous dry rendering is also used to process 

blood into blood meal. The raw or green blood 

is screened and air blown, then fed to a continu- 

ous coagulator where the blood is "set" with live 

steam. It then goes to a separator, where serum 

is removed from the coagulated blood. The co- 

agulated blood is then fed into a recycling hot-air 

drying system called a Ring drier. The Ring 

drier system consists of a feed port and hammer 

mill where the coagulated blood is fed into the 

system. It is pulverized in an atmosphere of 

180" to 200" F and blown to the manifold where 

it meets the air from the furnace. The furnace 

gases of 600" to 800" F provide the make-up air 

to the system and enter at the control manifold. 

Control dampers are located in the manifold and 

regulate the recirculation rate of the material as 

well as the product take-off ratio. A cyclone col- 

lecting system also is ducted to the control mani- 

fold and driven by an exhaust fan at the outlet. 

Product is withdrawn through star valves located 

in the solids discharge leg of the cyclones. 

Some animal blood is spray dried to produce 

a plywood glue that commands a price con- 

siderably higher than that of fertilizer or live- 

stock feed. This is an air-drying process, and 

exhaust gases are markedly more voluminous 

than those of rendering equipment. Feedstocks 

are usually concentrated in an evaporator be- 

fore the spray drying. 

PROCESSING FEATHERS 

Poultry feathers are pressure cooked and sub-, 

sequently dried to produce a high-protein meal 

used principally as a poultry feed supplement. 

Feathers, like blood, contain practically no fat, 

and meal is the only product of the system. 

Feathers are pressure cooked at about 50 psig 

to hydrolyze the protein keratin, their principal 

constituent. Initial cooking is usually carried 

out in a dry rendering cooker. Final moisture 

removal may be accomplished in the cooker at 

ambient pressure or in separate air-drying 

equipment. Rotary steamtube air driers, such 

as that shown in Figure 630, are frequently 

used for this purpose. If separate driers are ! 

employed, the material is transferred from 

cooker to drier at a moisture content of about 

50 percent. 

The Ring drier described under "Drying Blood'' 

can also be used to dry feather meal. However, 

continuous dry rendering of poultry feathers still 

appears to be in the pilot stage. The pressure 

required to break down the feathers requires 

choking in the continuous-tube cookers. Another 

problem is the lack of free-running tallow for 

heat transfer. Economically, although a large 

continuous supply of feed feathers is available, 

continuous rendering does not show the tremendous 

advantage for feathers that it does for meat 

and bone for tallow and meat meal because of the 

relatively lower price for feather meal. 

ROTARY AIR DRIERS I 

Dlrect-fired rotary driers are seldom used in 

the reduction of inedible packing house waste 

or dead stock. As noted previously in this 

chapter, they find wide use in the reduction of 

fish scrap. Fired driers have been used to a 

limited degree to dry wet rendering tankage 

and some materials of low tallow content. 

Where air driers are required, steamtube 

units are generally more satisfactory from the 

standpoint of both ~roduct quality and odor emission. 


Malodors are the principal air contaminants 

emitted irom inedible-rendering equipment and 

from other heated animal matter reduction pro- 

cesses, Reduction plant odors emanate from 

the handling and storage of raw materials and 

products as well as from heated reduction pro- 

cesses. Some feed materials are highly decayed, 

even before delivery to scavenger rendering 

plants, and the grinding, conveying, and storage 

of these materials cannot help but generate some 

malodors. Cooking and drying processes are, 

I

SIDE ELEVATION SHOW1 NG 

ARRANGEMENT OF TUBES 

Reduction of Inedible Animal Matter 

FRONT ELEVATION SHOWING STEAM FLOW 

CUTAWAY OF PIPES 

Figure 630. A rotary steamtube air drier of the type commonly 

used for the continuous drying of cooked feathers (The V.D. 

Anderson Co.. Cleveland, Ohio) 

nevertheless, considered the largest odor sources, 

and most odor control programs have been di- 

rected at them. Handling and storage odors can 

usually be kept to a tolerable minimum by fre- 

quently washing working surfaces and by pro- 

cessing uncooked feedstocks as rapidly as possible. 

McCord and Witheridge (19491, who discuss 

the "offensive trades" at length, attribute 

rendering plant malodors to a variety of com- 

pounds. Ronald (1935) identifies rendering 

odors as principally ammonia, ethylamines, 

and hydrogen sulfide, all decomposition products 

of proteins. Skatole, other amines, sulfides, 

and mercaptans are also usually present. Tallow 

and fats do not generate as great quantities of 

odorous materials. Aldehydes, organic acids, 

and other partial oxidation products are the 

principal odorous breakdown products of fats. 

Putrescine, NH2 (CH2)4 NH2, and cadaverine, 

NH2(CH2)5NH2, are two extremely malodorous 

diamines associated with decaying flesh and 

rendering plants. Several specific compounds 

have extremely low odor thresholds and are de- 

tectable in concentrations as small as 10 parts 

per billion (ppb). Odor threshold concentra- 

tions of compounds are listed in Table D2, 

Appendix D. Many suspected compounds have 

not been positively identified nor have their 

odor thresholds been determined. 

821


Cookers As Prominent Odor Sources Odors From Air Driers 

When animal matter is subjected to heat, the 

cell structure breaks down liberating volatile 

gases and vapors. Further heating causes some 

chemical decomposition, and the resultant prod- 

ucts are often highly odorous. All these mal- 

odorous gases and vapors are entrained in ex- 

haust gases. 

Exhaust products from cooking processes con- 

sist essentially of steam. Entrained gases and 

vapors are, nevertheless, highly odorous and 

apt to elicit nuisance complaints in areas sur- 

rounding animal matter reduction plants. Odor 

concentrations measured in exhaust gases of 

typical reduction processes are listed in Table 

222. Evidently there is a wide variation in 

odor concentrations from similar equipment. 

For instance, dry-batch rendering processes 

range from 5,000 to 500,000 odor units per scf, 

depending principally upon the type and "ripe- 

ness" of feedstocks. Blood drying can be even 

more odorous, with concentrations as great as 

1 million odor units per scf if the blood is allowed 

to age for only 24 hours before processing. High- 

ly odorous steam emissions also are generated 

whenever fresh feed material is dropped into a 

hot cooker. Approximately 4 hours rest time 

would be required between loads to prevent fresh 

material from being distilled during the loading 

operation. 

Source 

- 

Renderine cooker. 

dry-batch typeb ' 1 

Blood cooker, 

dry-batch type b 

Feather drier, 

s teamtuheC 

Blood spray 

drierc' 

Grease-drying tank, 

air blowing 

156°F 

170°F 

2Z5'F 

As can be seen from Table 222, feather drier 

odor concentrations, though generally smaller, 

are more variable than those from rendering 

cookers. Their largest odor concentrations-- 

25,000 odor units per scf--are associated with 

operations where feedstocks are putrefied or 

not completely cooked beforehand or where the 

meal is overheated in the drier. Under optimum 

conditions, odor concentrations from these driers 

should not exceed 2,000 odor units per scf. With 

blood spray driers, where extreme care is main- 

tained to ensure freshness of feedstocks, con- 

centrations can be less than 1,000 odor units per 

scf. In general, air drier odor concentrations 

are less than those of cookers for the following 

reasons: (1) In most instances feedskocks are 

cooked or partially evaporated before the air 

drying; (2) odorous gases are more dilute in 

drier exit gases; (3) feedstocks are often fresher. 

Odors and Dust From Rendered-Product Systems 

Some odors and dust are emitted from cooked 

animal matter as it is separated and refined. 

The heaviest points of odor emission are the 

percolators into which hot cooker contents are 

dumped. Steam and odors evolve from the hot 

material, particularly during times of cooker 

unloading. Cookers are normally dumped at or 

near 212°F. 

Table 222. ODOR CONCENTRATIONS AND EMISSION RATES FROM 

INEDIBLE REDUCTION PROCESSES 

Odor concentration, 

odor unit/scf 

Range ITypical average 

Typical moisture 

content of 

feeding stocks, 70 

5. 000 to I 50,000 

50 

500,000 1 I I 

10,000 to 

1 million 

600 to 

25, 000 

600 to 

1,000 

100,000 

2,000 

aAssumi~~g 5 percent moisture in solid products of system. 

b~oncondensable gases are neglected in determining emission rates. 

CExhaust gases are assumed to contain 25 percent moisture. 

d~lood handled in spray drier before any appreciable decomposition. occurs. 

800 

4, 500 

15,000 

60,000 

90 

5 0 

6 0 

< 5 

Exhaust products, 

scf/ton of feeda 

20.000 

38, 000 

77,000 

100,000 

100 scfm 

per tank 

Odor emission 

rate, odor unit/ 

ton of feed

Table 223 shows odor threshold concentrations of 

emissions from cookers during the dumping oper- 

ation. The type of material being rendered has a 

great effect on the odor concentration. As indi- 

cated, meat and bone trimmings from restaurants, 

which contain large quantities of rancid grease. 

produce high odor concentrations which would 

require hooding and incineration in an afterburner. 

Entrails from turkeys and chickens would be bor- 

derline, as shown in the table. The type of mate- 

rial, quantity of tallow or grease in the batch, 

freshness of the material, and unloading tempera- 

tures all are factors which influence the odor con- 

centration. Each rendering operation should be 

sampled for odors before deciding whether or not 

air pollution control equipment is required for 

the dump operation. 

Odorous steam emissions and smoke generated 

by the presses usually require control. Centri- 

fuges and settling tanks where meal and tallow 

are heated to accomplish the desired separation 

also emit odorous steam. 

I The grinding of pressed solids, and subsequent 

meal conveying are the only points of dust emis- 

! sion from rendering systems. These particulates 

1 are reasonably coarse, and dust is usually not 

1 excessive. 

i Grease-Processing Odors 

I 

! 

I 

! 

, . 

Some odors are generated at processing tanks 

when moisture is removed from grease or tallow 

by boiling or by air blowing or both. If air is 

used for this purpose, exhaust volumes seldom 


exceed 100 scfm, but odor concentrations are 

measurable. Odor concentration is a function 

of operating temperature. As shown in Table 

222, measured concentrations have been found 

to range from 4,500 odor units per scf at 150" F, 

to 60,000 odor units per scf at 225" F. Odor 

concentrations vary greatly with the type of 

grease processed and the air rate, as well as 

with temperature. 

Row-Materials Odors 

Some malodors emanate from the cutting and 

handling of raw materials. In most instances 

these emissions are not great. Odors usuaiiy 

originate at the point where raw material is 

first sliced, ground, or otherwise broken into 

smaller parts. Most feedstocks are ground in 

a hammer mill before the cooking. Large, 

whole animals (dead stock) must be skinned, 

eviscerated, and at least partially dismembered 

before being fed to rendering equipment. If the 

animal is badly decomposed, this skinning and 

cutting operation can evolve strong odors. 


All heated animal matter reduction processes 

should be vented directly to control equipment. 

Hooding is used in some instances to collect 

malodors generated in the processing of raw 

materials and cooked products. 

The loading of material into a hot batch cooker 

generates highly odorous steam emissions. It is 

impractical to require a cooker to be cooled be- 

Table 223. ODOR CONCENTRATIONS OF EMISSIONS FROM INEDIBLE RENDERING COOKERS 

DURING THE DUMPING OPERATION 

Poultry feathers 

Type of material cooked 

Entrails from turkeys and chickens 

Meat and bone trimmings with large quantities 

of rancid restaurant grease 

Emissions during 

dump from cooker. 

odor unitslcf 

200 

2,000 

25,000 

40,000 

Fresh meat and bone trimmings from a beef 100 

slaughterhouse 

Mixture of dead cats and dogs, fish scrap, 

poultry offal, etc. 

Slaughterhouse viscera and bones 

a 

x = 7 minutes. 

b 

x = 18 minutes. 

1,000 

150 

200 

Emissions 5 

minutes after 

dumping, 

odor units/cf 

2 0 

500 

3,000 

200 

7 0 

1,500 

150 

Emissions x 

minutes after 

dumping, 

odor unitslcf 

- 

. 

- 

800a 

150b


fore receiving the next charge. One method to 

prevent escape of air contaminants during the 

loading of a cooker is to provide a choked feed 

arrangement. A hopper may be constructed above 

the cooker that holds one full load. The material 

is dumped quickly and there is enough mass of 

material to prevent steaming. Another method 

is to blow the material into the cooker through a 

closed feed system. 

The methods described above, unfortunately, are 

not feasible for loading poultry feathers because 

of their density and texture. Grinding the feathers 

beforehand has not proven to be satisfactory. A 

successful method to control the loading of feathers, 

however, has been developed. The feather cooker 

is provided with a separate dome and vent at the 

drive end. Both exhaust systems may be valved 

at the dome. An indraft of 100 fpm through the 

charge door is usually adequate. The exhaust 

system used for cooking must be closed during 

the loading cycle and vice ver,sa. 

If highly decayed dead stock is being processed, 

the entire dead stock room should be ventilated 

at a rate of 40 or more air changes per hour for 

worker comfort. Areas should also be ventilated 

where raw materials are stored unrefrigerated 

for any appreciable time before processing. 

Hooding may be employed on raw-material 

grinders preceding cookers and percolator 

pans and expeller presses used to handle 

cooked products. Although the volume of 

steam and odors evolved at any of these points 

does not exceed 100 cfm, greater volumes are 

normally required to offset crossdrafts. In- 

draft velocities of 100 fpm under hoods are usu- 

ally satisfactory. 

Emission Rates From Cookers 

The ventilation rates of cookers can be esti- 

mated directly from the quantity of moisture 

removed and the time of removal. Maximum 

emission rates from dry cookers are approxi- 

mately twice the average moisture evaporation 

rates. In the determination of exhaust volumes, 

noncondensablegases can normally be neglected. 

Consider a batch cooker that removes 3, 000 

pounds of moisture from 6,000 pounds of animal 

matter in 3 hours, a relatively long cook cycle. 

The average rate of emission is 16.7 pounds 

per minute or 450 cfm steam at about 212°F. 

The instantaneous evaporation rate and cumula- 

tive moisture removal are plotted in Figure 

631. The maximum evolution rate apparently 

occurs near the initial portion of the cook at 

29 pounds per minute or 790 cfm at ZlZ'F. As 

moisture is removed from a batch cooker, the 

heat transfer rate decreases, the temperatures 

Figure 631. Steam emission pattern f ram a 

batch-type, dry render~ng cooker operated 

at ambient pressure. 

rise, and the evaporation rate falls off. The 

general shapes of the curves in Figure 631 are 

typical of batch-cooking cycles. Where cook 

times are appreciably shorter, evaporation 

rates are greater; nevertheless, the ratio of 

maximum to average evaporation rate is main- 

tained at approximately 2 to 1. 

The length of a cooking cycle, and the evapo- 

ration rate are dependent upon the temperature 

in the steam jacket, and the rotational speed 

of the agitator. The highest permissible agita- 

tor speeds (about 65 rpm) can result in cooking 

times of 45 minutes to 1 hour. Many operators, 

particularly at packing houses, use slower 

agitator speeds, and cycles are as long as 4 

hours. 

If vacuum cooking is employed, volume rates 

and temperatures decrease as the batch pro- 

gresses. With these systems, the vacuum- 

producing devices largely govern cooking times. 

The evaporation rate in a vacuum system is lim- 

ited by the rate at which steam can be removed, 

usually by condensation. If vapor cannot be 

condensed as fast as it is evaporated, the cycle 

is merely lengthened. 

Pressure cookers have a slightly dsferent emis- 

sion pattern, but maximum emission rates are 

again twice the average. During the initial 

portion of the cycle, there are no emissions 

while pressures are increasing to the desired 

maximum. The cooker is vented at elevated

pressure, usually about 50 psig. High-pres- 

sure vapors are relieved through small bypass 

lines so that the surge of steam is not more than 

the control system can handle. Most of the con- 

tained moisture is evaporated after pressures 

are reduced to ambient levels. 

Vapor emission rates from wet rendering cook- 

ers are considerably lower than those from dry 

cookers, comparable to initial volumes during 

pressure cooking. Only enough steam is flash 

evaporated to reduce the pressure to 1 atmos- 

phere. The large percentage of moisture in 

a wet rendering process is removed as water 

by physical separation rather than by evapora- 

tion. 

Emission rates from continuous, dry rendering 

processes are steady and can be calculated 

directly from the moisture content of feedstocks 

and products. To lower the moisture content 

from 36 to 6 percent in typical meat, bone, and 

offal scrap, 2,750 scfm or 110 pounds of steam 

per minute would be evaporated if the charge 

rate to the cooker were 20,000 pounds per hour. 

Since it is difficult to operate continuous systems 

gas-tight, it is necessary to produce an indraft 

at the feed and outlet ends of the system in order 

to ensure that cooker effluent does not escape 

into the atmosphere. Thus, another 490 scfm, 

or 15 percent by volume, must be accounted for 

in the emission rate from continuous tube systems. 

Emission rates from blood cookers are general- - 

ly lower than those from dry rendering cookers 

owing to the longer cook cycles employed. Blood 

is continually added to an operating cooker during 

a typical packinghouse workday. The emission 

rate fluctuates as a function of the moisture content 

in the cooker. A cook cycle may extend 

over 8 or 10 hours, and charging patterns can 

vary tremendously. Emission rates do not 

normally exceed 500 cfm, and at times, are considerably 

lower. 

Emission rates irom feather cookers follow the 

same pattern as those from other dry pressure 

cookers though rates are lower and cooking 

times usually longer. Inasmuch as feathers 

contain no appreciable tallow, heat transfer is 

relatively slow. At some plants, batches of 

feathers are cooked as long as 8 hours. Where 

separate driers are used, feathers are still 

cooked 2 to 4 hours, which reduces the moisture 

content to 50 percent before the charging to a 

drier. 

Emission Rates From Driers 

Most air-drying processes are operated on a 

continuous basis with no measurable fluctua- 


tions in exhaust rates. Enough air and, in some 

instances, products of combustion are added to 

yield a moisture content of 10 to 30 percent by 

volume in the exit gas stream. To dry 2,000 

pounds of cooked feathers per hour from 50 to 

5 percent moisture requires a drier (steamtube) 

exhaust volume of 1,660 scfm at 20 percent 

moisture in the gases. Volumes from air driers 

are always much greater than those from cook- 

ing processes, and they contain far greater 

quantities of noncondensable gases . 


The principal devices used to control reduction 

plant odors are afterburners and condensers, 

installed separately and in combination. Ad- 

sorbers and scrubbers also find use. Dust is 

not a major problem at animal matter reduction 

plants, and simple cyclones are usually suffi- 

cient to prevent excessive emissions. 

Selection of odor control equipment is influenced 

greatly by the moisture content of the malodorous 

stream, or conversely, by the percentage of non- 

condensable gases. It is usually more costly to 

control noncondensable gases than moisture. 

Reduction plant exhaust streams fall into two 

general types: (1) Those consisting almost en- 

tirely (95 percent or greater) of water vapor, 

as from rendering cookers and blood cookers, 

and (2) air drier exhaust gases, which seldom 

contain more than 30 percent moisture by volume. 

Controlling High-Moisture Streams 

Condensing moisture from wet cooker gases is 

almost always economically attractive. Some 

malodors are usually condensed or dissolved in 

the condensate. In any case the volume is re- 

duced by a factor of 10 or more. The remaining 

noxious gases can be directed to a further control 

device such as an afterburner or carbon adsorber 

before being vented to the atmosphere. 

Selection of the condenser depends upon the par- 

ticular facilities of the operator. The principal 

types of condensers noted in Chapter 5 are adapt- 

able to reduction cooker exhaust streams. Con- 

tact condensers and air-cooled and water-cooled 

surface condensers have been successfully used 

for this purpose. 

Contact condensers are more efficient control 

devices than surface condensers are, though 

both types are highly effective when coupled with 

an afterburner or carbon adsorber. This is 

illustrated by data in Table 224. Odor concen- 

trations are seen to be considerably greater in 

gases from surface condensers than in those 

from contact condensers. With condensate at


a 

Table 224. ODOR REMOVAL EFFICIENCIES OF CONDENSERS OR AFTERBURNERS, 

OR BOTH, VENTING A TYPICAL DRY RENDERING COOKER^ 

(Calculated from Mills et al., 1963) 

Odors from cookers 

Concentration, 

odor unitslsci 

50,000 

80"F, a contact condenser reduces odor concen- 

trations by about 80 percent and odor emission 

rates by 99 percent. At the same condensate 

temperature, odor concentrations increase across 

a surface condenser. Either type of condenser, 

however, reduces the volume of cooker vapors 

by 95 percent or more. Thus, even a surface 

condenser lowers the odor emission rate by about 

50 percent. 

Contact condensers are relatively inexpensive 

to install hut require large quantities of one- 

pass cooling water. From 15 to 20 pounds of 

cooling water is necessary to condense and sub- 

cool adequately 1 pound of steam. Since cooling 

water and condensate are intimately mixed, the 

resultant liquid cannot be cooled in an atmospheric 

cooling tower without emission of malodors to the 

almosphere. The large condensate volume that 

must be disposed of can overload sewer facili- 

ties in reduction plant areas. 

Subcooling Condensate 

Emission rate, 

odor unitslmi" 

25,000, 000 

Condenser 

None 

Surface 

Surface 

Contact 

Contact 

Condensate 

temperature, 

OF 

Surface condensers, whether air cooled or water 

cooled, should be designed to provide subcooling 

of condensate to 140°F or lower. This may be 

accomplished iri several ways, as noted in Chapter 

5. The need for subcooling is negated when high 

vacuum is employed. With vacuum operation, 

volatile, malodorous gases are drawn off through 

the ejector or vacuum pump, and condensation 

temperatures are often less than 140°F. At a 

vacuum of 24 inches of mercury (2.9 psia), the 

condensation temperature of steam is 140°F. 

- 

. 

80 

140 

80 

140 

Afterburner 

temperature, 

OF 

Odor removal 

efficiency, 

70 

~ a on ahypothetical ~ ~ d cooker that emits 500 scfm ofvapor containing 5 percentnoncondensable gases. 

1,200 

None 

1,200 

None 

I. 200 

Odors from control system 

Concentration, 

odors 

unitslscf 

100 to 150 

(Mode 120) 

100.000 to 

10 million 

(Mode 500,000) 

50 to 100 

(Made 75) 

2,000 to 

20,000 

(Mode 10,000) 

20 to 50 

(Mode 25) 

Condenser Tube Materials 

99.40 

50 

99.93 

99 

99.99 

Reduction process vapors can be highly corro- 

sive to the metals commonly used in surface 

condenser tubes. Both acid and alkaline vapors 

can be present, sometimes alternately in the 

same equipment. Vapors from relatively fresh 

meat and bone scrap renderir 7 are mildly acidic, 

and some brasses are satisfactory. Brasses 

fail rapidly, however, under alkaline conditions. 

Mild steel tubes are adequate where the pH is 

greater than 7.0 but quickly corrode under acid 

conditions. 

Some operations, such as dead stock rendering, 

can produce alkaline and acid gases alternately 

during the cook cycle. Here neither brass nor 

mild steel is satisfactory. In these cases, stain- 

less steels have been successfully employed. 

With a relatively constant pH condition, less ex- 

pensive metals could be used. 

Where acid-base conditions are uncertain, a 

pH determination should be made. The vapors 

should be sampled over the complete process 

cycle with all representative feedstocks in the 

cookers. 

Interceptors in Cooker Vent Lines 

Modal emission 

rate, odor 

unitslmin 

90,000 

12,500,000 

6,000 

250,000 

2,000 

Air pollution control systems venting cookers 

should be equipped with interceptor traps to pre- 

vent fouling of condensers and other control de- 

vices. So-called wild blows are relatively com- 

mon in dry rendering operations. They result 

from momentary plugging of the cooker vent. 

Steam pressures increase until they are suffi-

cient to unblock the line. In the unblocking, a 

measurable quantity of animal matter is forced 

through the vent line at high velocity. If there 

is no interceptor, this material fouls condensers, 

hot wells, afterburners, and other connected con- 

trol devices. Although a wild blow is an opera- 

tional problem, it greatly affects the efficiency 

of odor control equipment. 

The systems shown in Figures 632 and 633 in- 

clude interceptors in the vent lines between the 

cookers and condensers. The installation de- 

picted in Figure 633 uses an air-cooled con- 

denser and afterburner. Most tanks are of suffi- 

cient size to hold approximately one-haIf of a full 

cooker charge. They are designed so that col- 

lected materials can be drained while the cooker 

and control system are in operation. 

Figure 632. A condenser-afterburner control 

system with an interceotor located between 

the rendering cooker and condenser. 

Vapor Incineration 

For animal matter reduction processes, as with 

most odor sources, flame incineration is the most 

positive control method. Afterburners have been 

used individually and in combination with other de- 

vices, principally condensers. Rule 64 of the 

Los Angeles County Air Pollution Control District 

(see Appendix A), which specifically governs heat- 

ed animal matter reduction processes, uses incin- 

eration at 1,200-F as an odor control standard. 

Any control method or device as effective as 

flame incineration at 1,200°F is acceptable under 

the regulation. 

Total incineration is used to control low-mois- 

tnre reduction process streams, as from driers, 

and various other streams of small volume. At 

reduction plants, steamtube driers are normal- 

ly the largest equipment controlled in this manner. 


Gases from the driers are vented directly to after- 

burners, which are operated at temperatures of 

1,200" F or higher. Dustis usuallynotin sufficient 

concentration to impede incineration. If there is 

appreciable particulate matter in the gas stream, 

auxiliary dust collectors must be installed or the 

afterburner must be operated at 1.600" F or high- 

er. At 1,200" F, solids are only partially incin- 

erated. 

Flame incineration at 1.200" F reduces odor con- 

centrations from steamtube driers to 100 to 150 

odor units per scf where dust loading is not ex- 

cessive. Some variation can be expected when 

concentrations are greatly in excess of the nomi- 

nal 2,000 odor units per scf usually encountered 

in drier gases. 

Because of the large volumes exhausted from 

driers, afterburner fuel requirements are a 

major consideration. A drier emitting 3,000 

scfm requires about 4,800 scfh natural gas for 

1,200" F incineration. Several means of recov- 

ering waste heat from large afterburner streams 

have been used. The most common are the 

generation of steam and preheating of drier 

inlet gases. 

In the control of spray driers, dust collectors 

must often be employed ahead of the afterburner. 

High-efficiency centrifugal collectors, baghouses, 

or precipitators may he required as precleaners, 

depending upon the size and concentration of par- 

ticulates. 

Condensation-Incineration Systems 

As noted earlier, wet cooker vapors are seldom 

incinerated is a. While 100 percent incineration 

is feasible, operating costs are much greater 

than for condenser-afterburner combinations. 

Both types of control systems provide better than 

99 percent odor removal, but the combination system 

results in a much lower odor emission rate. 

The cooker control systems shown in Figures 632 

and 633 and in Chapter 5, illustrate typical com- 

binations of condensers and afterburners. Un- 

condensed gases are separated from condensate 

at either the condenser or hot well. Gases enter 

the afterburner near ambient temperature. Ei- 

ther contact or surface condensers serve to re- 

move essentially all particulates. The remaining 

"clean" uncondensed gases can be readily incin- 

erated at 1.200" F. In some instances there are 

minor concentrations of methane and other fuel 

gases in the stream. Uncondensed gases from 

surface condensers are richer in combustibles 

thanare those from contact condensers. As shown 

in Table 224, odor removal efficiencies greater than 

99.9 percent are possible with condenser-after- 

burner systems serving dry rendering cookers.


Figure 633. A cooker control system including an interceptor, 

air-cooled condenser, and afterburner (California Protein Products, 


When the moisture content of the contaminated 

stream is from 15 to 40 percent, the use of 

condensers may or may not be advantageous. 

In these cases, a number of factors must be 

weighed including volumes, exit temperatures, 

fuel costs, water availability, and equipment 

costs among others. 

Carbon Adsorption of Odors 

Most of the malodorous gases emitted from reduction 

processes can be adsorbed on activated 

carbon to some degree. The capacities of 

activated carbons for hydrogen sulficle, uric 

acid, skatole, putrescine, and several other 

specific compounds found in reduction plant gases 

are considered "satisfactoryr' to "high. " For 

ammonia and low-molecular-weight amines, 

they have somewhat lower capacities. The latter 

compoul~ds tend to be desorbed as the carbon becomes 

saturated with high-molecular-weight 

compounds (Barnebey-Cheney Co., Bulletin 

T-642). For the mixture of inalodorous materials 

encountered at reduction plants, a highquality 

carbon would be expected to adsorb 

from 10 to 25 percent of its weight belore the 

breakthrough point is reached. 

Carbon adsorbers are as efficient as afterburn- 

ers but have limitations that often make them 

unattractive for cooker control. Their most 

useful application is the control of large volumes 

of relatively cool and dry gases. Adsorhers 

usually cannot be employed in reduction process 

streams without auxiliary dust collectors, con- 

densers, or coolers. 

Carbon adsorbers cannot be used to control 

emissions from wet cookers unless the adsorb- 

ers are preceded by condensers. Activated 

carbon does not adsorb satisfactorily at tem- 

peratures greater than 120°F. To cool cooker 

vapors, which are predominantly steam, to 

this temperature, most of the moisture must 

be recovered. At l2OsF, saturated air contains 

only 11.5 percent water vapor by volume. Con- 

denser-adsorber systems are reported to re- 

move odors as efficiently as condenser-after- 

burner systems. No comparative odor con- 

centration data are available. 

Drier exhaust streams can be controlled with 

adsorbers if inlet temperatures and dust con- 

centrations can be held suiIiciently low and 

small, respectively. Many driers are exhausted

at temperatures higher than 200°F and contain 

enough fine particulates to foul adsorbers. A 

scrubber-contact condenser is often a satis- 

factory means of removing particulates and low- 

ering temperatures hefore adsorption. If, how- 

ever, there are appreciable particulates of less 

than 10 microns diameter, more efficient dust 

control devices are necessary. 

Regeneration of activated carbon is a major con- 

sideration at animal matter reduction plants. 

Carbon life between regenerations can be as 

short as 24 hours, particularly where malodors 

are in heavy concentration, and the carbon has 

a low capacity for the compounds being adsorbed. 

Regeneration frequency is a function of many 

- 

factors, including malodor concentration. the 

quality and quantity of carbon, and the kind of 

compounds that must be adsorbed. 

Some means must be employed to contain or 

destroy the desorbed gases; otherwise, mal- 

odors are vented to the atmosphere in essentially 

the same form that they were collected. Inciu- 

eration at 1,ZOO"F or higher is the most common 

method of controlling these gases. For streams 

of low volume, afterburners used during regen- 

eration can be as large and as costly as those 

used to incinerate odors from the basic reduc- 

tion equipment. The need for incineration of 

desorbed gases usually offsets the advantages 

of carbon adsorption for streams of low volume. 

If the exhaust rate is sufficiently small, incin- 

erating vapors directly, as they are evolved 

from the reduction equipment or condenser, is 

considerably simpler. 

Odor Scrubbers 

ELECTROPLATING 829 

Odor Masking and Counteraction 

Masking agents and odor counteractants have 

been used with some success to offset in-plant 

odors. These materials are added to cooker 

feedstocks and sprayed in processing and storage 

areas. They are repdrted to provide a degree 

of nuisance elimination and worker comfort, 

particularly in high-odor areas such as dead 

stock skinning rooms. Masking agents and 

counteractants, however, are not recommended 

for the control of odors from heated animal 

matter reduction equipment. 

ELECTROPLATING 

Electroplating is a process used to deposit, 

or plate, a coating of metal upon the surface 

of another metal by electrochemical reactions. 

In variations of this process, nonmetallic sur- 

faces have been plated with metals, and a non- 

metal such as rubber has been used as a plating 

material. Industrial and commercial applica- 

tions of electroplating are numerous, ranging 

from manufactured parts for automobiles, tools, 

other hardware, and furniture to toys. Brass, 

bronze, chromium (chrome), copper, cadmium, 

iron, lead, nickel, tin, zinc, and the precious 

metals are most commonly electroplated. 

Platings are applied to decorate, to reduce 

corrosion, to improve wearing qualities and 

other mechanical properties, or to serve as 

a base for subsequent plating with another metal. 

The purpose and type of plating determine the details 

of the process employed and, indirectly, 

the air pollution potential, which is a function of 

the type and rate of "gassing, " or release of gas 

bubbles from plating solutions with entrainment 

of droplets of solution as a mist. The degree 

of severity of air pollution from these processes 

may vary from being an insignificant problem 

to a nuisance. 

Conventional scrubbers are seldom used to 

control reduction process odors. Of course, 

contact condensers provide some scrubbing 

of cooker gases; nevertheless, these devices 

are principally condensers, and tail waters 

An electroplating system consists of two eleccannot 

be recirculated. It is conceivable that 

trodes--an anode and a cathode--immersed in 

alkaline or acid scrubbers would he effective 

for drier gases if all the odorous compounds 

an electrolyte and connected to an external 

source of direct-current electricity. The base 

reacted in the same manner. Unfortunately, 

material upon which the plating is to be deposited 

the malodorous mixtures encountered in typical 

makes up the cathode. In most electroplating 

reduction processes are not homogenous from 

systems, a bar of the metal to be deposited is 

the acid-base standpoint. 

used as the anode. The electrolyte is a solution 

containing: (1) Ions of the metal to be deposited 

Strong oxidizing solutions, such as chlorine and (2) additional dissolved materials to aid in 

dioxide, are reported to destroy many of the electrical conductivity and produce desirable 

odorous organic materials (Woodward and characteristics in the deposited plating. 

Fenrich, 1952). With any type of recirculating 

chemical scrubber, the contaminated stream When an electric current is passed through the 

would first have to be cooled to ambient tem- electrolyte, ions from the electrolyte are reperature, 

by condensation if necessary. duced, or deposited, at the cathode, and an

830 CHEMICAL PROCESS11 NG EQUIPMENT 

equivalent amount of either the same or a dif- 

ferent element is oxidized or dissolved at the 

anode. In some systems, for example, chrome 

plating, the deposited metal does not dissolve 

at the anode, and hence, insoluble anodes are 

used, the source of the deposited metal being 

ions formed from salts of that metal previously 

dissolved in the electrolyte. 

The character of the deposited metal is affected 

by many factors, including the pH of the electro- 

lyte, the metallic ion concentration, the sim- 

plicity or complexity of the metallic ion (includ- 

ing its primary and secondary ionization prod- 

ucts), the anodic and cathodic current densities, 

the temperature of the electrolyte, and the 

presence of modifying or "addition agents." By 

varying these factors, the deposit can be varied 

from a rough, granular, loosely adherent plat- 

ing to a strong, adherent, mirror-finish plating. 

If the electromotive force used is greater than 

that needed to deposit the metal, hydrogen is 

also formed at the cathode, and oxygen forms 

at the anode. When insoluble anodes are used, 

oxygen or a halogen (if halide salts are used in 

the electrolyte) is formed at the anode. Both of 

these situations produce gas sing. 

A potential air pollution problem can also occur 

in the preparation of articles for plating. These 

procedures, primarily cleaning processes, are 

as important as the plating operation itself for 

the production of high-quality finishes of im- 

pervious, adherent metal coatings. The clean- 

ing of metals before electroplating generally 

requires a multistage procedure as follows: 

1. Precleaning by vapor degreasing or by soak- 

ing in a solvent, an emulsifiable solvent, or 

an emulsion (used for heavily soiled items); 

2. intermediate cleaning with an alkaline bath 

soak treatment; 

3. 

electrocleaning with an alkaline anodic or 

cathodic bath treatment, or both (the chem- 

ical and mechanical [gassing] action created 

by passing a current through the bath between 

the immersed article and an electrode pro- 

duces the cleaning); 

4. pickling with an acid bath soak treatment, 

~ith or without electricity. 

The selection of an appropriate cleaning method 

in any given case depends upon three important 

factors: The type and quantity of the soil, com- 

position and surface texture of the base metal, 

and the degree of cleanliness required. In gen- 

eral, oil, grease, and loose dirt are removed 

first; then scale is removed, and, just before 

the plating, the pickling process is employed. 

The articles to be plated are thoroughly rinsed 

after each treatment to keep them from contami- 

nating succeeding baths. A cold rinse is usually 

used after the pickling to keep the articles from 

drying before their immersion in the plating bath. 

Electrocleaning and electropickling are generally 

faster than similar soak procedures; however, 

the electroprocesses always produce more gas- 

sing (hydrogen at the cathode and oxygen at the 

anode) than the nonelectroprocesses. The gas- 

sing from cleaning solutions tends to create 

mists that may, but usually do not, cause signi- 

ficant air pollution problems. 


The electrolytic processes do not operate with 

100 percent efficiency, and some of the current 

decomposes water in the bath, evolving hydrogen 

and oxygen gases. In fact, the chief advantage 

of electrocleaning is the mechanical action pro- 

duced by the vigorous evolution of hydrogen at 

the cathode, which tends to lift off films of oil, 

grease, paint, and dirt. The rate of gassing 

varies widely with the individual process. If 

the gassing rate is high, entrained mists of 

acids, alkaline materials, or other bath con- 

stituents are discharged to the atmosphere. 

Most of the electrolytic plating and cleaning pro- 

cesses are of little interest from a standpoint of 

air pollution because the emissions are inoffen- 

sive and of negligible volume, owing to low gas- 

sing rates. Generally, air pollution control 

equipment is not required for any of these pro- 

cesses except the chromium-plating process. 

In this process, large volumes of hydrogen and 

oxygen gases are evolved. The bubbles rise 

and break the surface with considerable energy, 

entraining chromic acid mist, which is dis- 

charged to the atmosphere. Chromic acid mist 

is very toxic and corrosive and its discharge 

to the atmosphere should be prevented. 

Chromic acid emissions have caused numerous 

nuisance complaints and frequently cause property 

damage. Particularly vulnerable are automobiles 

parked downwind of chrome-plating installations. 

Tne acidmist spots car finishes severely. 

The amounts of acid involved are relatively 

small but are sufficient to cause damage. In a 

typical decorative chromium-plating installation 

with an exhaust system but without mist control 

equipment, a stack test disclosed that 0.45 pound 

of chromic acid per hour was being discharged 

from a 1,300-gallon tank. 

Chromium-plating processes can be divided into 

two general classes, one of which offers a con-

siderably greater air pollution problem than the 

other. "Hard chrome" plating, which causes 

the more severe problem, produces a thick, 

hard, smooth, corrosion-resistant coating. 

This plating process requires a current density 

of about 250 amperes per square foot, which 

results in a high rate of gassing and a heavy 

evolution of acid mist. The less severe problem 

is presented by the process called "decorative 

chrome" plating, which requires a current 

density of only about 100 amperes per square 

foot and results in a definitely lower gassing 

rate. 

HOODING AND VENTILATING REQUIREMENTS 

Local exhaust systems are installed on many 

electroplating tanks to reduce the concentra- 

tions of steam, gases, and mists to what are 

commonly accepted as safe amounts for person- 

nel in the plating room. In the past, these ex- 

haust systems were often omitted altogether, 

and the resulting working conditions were often 

unhealthful. 

In 1951, the American Standards Association 

introduced Code Z9. 1 for Ventilation and Oper- 

ation of Open Surface Tanks. This code is an 

organized engineering approach designed to re- 

place the rule-of-thumb methods applied in the 

past. The use of this code in designing plating 

tank exhaust systems is recommended by public 

health officials and industrial hygienists. 

Mast exhaust systems use slot hoods to capture 

the mists discharged from the plating solutions. 

These hoods have been found satisfactory when 

properly designed. To obtain adequate distribu- 

tion of ventilation along the entire length of the 

slot hood, the slot velocity should be high, 2,000 

fpm or more, and the plenum velocity should 

be one-half of the slot velocity or less. With 

hoods over 10 feet in length, either multiple 

takeoffs or splitter vanes are needed. Enough 

takeoffs or splitter vanes should be used to re- 

duce the length of the slot to sections not more 

than 10 feet long. 

Ventilation rates for tanks, as previously dis- 

cussed in Chapter 3, are for tanks located in 

areas having no crossdrafts. In drafty areas, 

ventilation rates must be increased and baffles 

should be used to shield the tank. 


Scrubbers 

The device most commonly used to control air 

contaminants in hard-chrome-plating tank ex- 

haust gases is a wet collector. This type of 

Electr oplating 

831 

equipment is also suitable for controlling mists 

from any other type of plating or cleaning tank 

that may cause a problem. Figure 634 shows 

a ventilation system with a spray-type scrubber 

used to control mists from two 18-foot chrome- 

plating tanks. Many other types of commercial 

wet collectors are available, constructed of 

various corrosion-resistant materials. Water 

circulation rates are usually 10 to 12 gpm per 

1, 000 cfm. If the water is recirculated, the 

makeup rate is about 2.5 to 4 gph per 1,000 cfm. 

The scrubber water, of course, becomes con- 

taminated with the acid discharged from the plat- 

ing tank; therefore, efficient mist eliminators 

must be used in the scrubber to prevent a con- 

taminated water mist from discharging to the 

atmosphere. 

The scrubber water is commonly used for plat- 

ing tank makeup. This procedure not only re- 

moves the acid from the scruhber but also re- 

duces the amount of makeup acid needed for the 

plating solution. In some scrubbers, a very 

small quantity of fresh water is used to collect 

the acid mist; the resulting solution is continu- 

ously drained from the scrubber either into the 

plating tank or into a holding tank, from which 

it can be taken for plating solution makeup. 

The mists collected by the air pollution control 

system are corrosive to iron or steel; therefore, 

hood, ducts, and scrubbers of these materials 

must be lined with, or replaced hy, corrosion- 

resistant materials. Steel ducts and scrubbers 

lined with materials such as polyvinyl chloride 

have been found to resist adequately the corro- 

sive action of the mists. In recent years, hoods, 

ducts, and scrubbers made entirely of polyester 

resins reinforced with glass fibers have been 

used in air pollution control systems handling 

acid or alkaline solutions. These systems have 

been found to be very resistant to the corrosive 

effects of plating solutions. 

The scrubber removes chromic acid mist with 

high efficiency. A commonly used field method 

of determining chromic acid mist evolution 

consists of holding a sheet of white paper over 

the surface of the tank or scrubber discharge. 

Any mist contacting the paper immediately 

stains it. A piece of paper held in the discharge 

of a well-designed scruhber shows no signs of 

staining. 

Mist Inhibitors 

The mist emissions from a decorative-chromeplating 

tank and from other tanks with lesser 

mist problems can be substantially eliminated 

by adding a suitable surface-active agent to the 

plating solutions. The action of the surface-


Flgure 634. Two control systems wlth scrubbers venting four chrome- 

plating tanks. Each scrubber vents two tanks (Industrial Systems, Inc., 

South Gate, Calif.). 

active agent reduces the surface tension, which, 

in turn, reduces the size of the hydrogen bubbles. 

Their rates of rise, and the energy of their evolu- 

tion are greatly reduced, and the amount of mist 

is also greatly reduced. Several of these mist 

inhibitors are commercially available. 

If the proper concentration of mist inhibitor is 

maintained, a sheet of paper placed 1 inch above 

the bath surface shows no spotting. 

INSECTICIDE MANUFACTURE 

The innumerable substances used commercially 

as insecticides can be conveniently classified 

according to method of action, namely: (1) Stomach 

poisons, which act in the d~gestive system; 

(2) contact poisons, which act by dlrect external 

contact with the insect at some stage of its life 

cycle; and (3) fumigants, which attack the 

respiratory system. 

A few of the commonly used insecticides, clas- 

sified according to method of action, are shown 

in Table 225. The classification is somewhat 

arbitrary in that many poisons, such as nicotine, 

possess the characteristics of two or three 

classes. 

Table 225. SOME COMMON INSECTICIDES 

CLASSLFIED ACCORDING TO 

METHOD OF ACTION 

stomach po~sons I contact polsons I Fumigants 

Cryolite 

Nicotine 

Hydrocyanic acid 

Naphthalene 

Human threshold limit values of various insecticides 

are shown in Table 226. They represent 

conditions under which it is believed that nearly 

all workers may be repeatedly exposed day after 

day, without adverse effect. The amount by which 

these figures may be exceeded for short periods 

without injury to health depends upon factors such 

as (1) the nature of the contaminant, (2) whether 

large concentrations over short periods produce 

acute poisoning, (3) whether the effects are 

cumulative, (4) the frequency with which large 

concentrations occur, and (5) the duration of 

these periods. 

METHODS OF PRODUCTION 

Production of the toxic substances used in in- 

secticides involves the same operations employed 

for general chemical processing. Similarly,

chemical-processing equipment, that is, reac- 

tion kettles, filters, heat exchangers, and so 

forth, are the same as discussed in other sec- 

tions of this chapter. Emphasis is given, there- 

fore, to the equipment and techniques encoun- 

tered in the compounding and blending of com- 

mercial insecticides to achieve specific chemi- 

cal and physical properties. 

Insecticide Manufacture 

Table 226. THRESHOLD LLMIT VALUES OF VARIOUS INSECTICIDES 

Substance 

Aldrin (1, 2, 3, 4, 10, 10-hexachloro- 

1,4,4a, 5.8, 8a-hexahydro-1, 4, 5,sdimethanonaphthalene) 

Arsenic 

Calcium arsenate 

Chlordane (1, 2,4,5,6, 7, 8,E-octachloro-3a, 4, 7, 

7a-tetrahydro-4,7 -methanoindane) 

Chlorinated camphene, 60% 

2, 4-D (2,4-dichlorophenoxyacetic acid) 

DDT (2,Z-bis(p-chlorophenyl) 

-1, 1, l -trichloroethane) 

Dieldrin (1, 2, 3, 4, 10, 10-hexachloro-6, 7, 

epoxy-1, 4,4a, 5,6,7,8, Ba-octahydro- 

1, 4, 5, 8-dimethano-naphthalene) 

Dinitro-o-cresol 

EPN (O-ethyl O-p-nitrophenyl thionoben~ene~hosphonate) 

Ferbam (ferric dimethyl dithiocarbamate) 

Lead arsenate 

Lindane (hexachlorocyclohexane gamma isomer) 

Malathion (0, O-dimethyl dithiophosphate of 

diethyl mercaptosuccinate) 

Methoxychlor (2, 2-di-p-methoxyphenyl-1, 1,ltrichloroethane) 

Nicotine 

Parathion (0, O-diethyl-O-p-nitrophenyl 

thio~hos~hate) 

Pentachlorophenol 

Phosphorus pentasulfide 

Picric acid 

Pyrethrum 

Rotenone 

TEDP (tetraethyl dithionopyrophosphate) 

TEPP (tetraethyl pyrophosphate) 

Thiram (tetramethyl thiuram disulfide) 

Warfarin (3-(a-acetonylben~~l) 4- 

hydroxycoumarin) 

Most commercial insecticides are used as either 

dusts or sprays. Insecticides employed as dusts 

are in the solid state in the 0.5- to 10-micron 

size range. Insecticides employed as sprays 

may be manufactured and sold as either solids 

or liquids. The solids are designed to go into 

solution in an appropriate solvent or to form a 

colloidal suspension; liquids may be either solu- 

tions or water base emulsions. No matter what 

Threshold limit value, 

mg/meter3 

0. 25 

0.5 

1 

0.5 

0. 5 

10 

1 

0. 25 

0.2 

0.5 

15 

0. 15 

0.5 

15 

15 

0.5 

0.1 

0.5 

1 

0. 1 

5 

5 

0.2 

0. 05 

5 

0.1 

physical state or form is involved, insecticides 

are usually a blend of several ingredients in 

order to achieve desirable characteristics. A 

convenient means of classifying equipment and 

their related processing techniques is to differ- 

entiate them by the state of the end product. 

Equipment used to process insecticides where 

the end product is a solid is designated solid- 

insecticide-processing equipment. Equipment 

used to process insecticides where the end 

product is a liquid is designated as liquid-in- 

secticide-processing equipment. 

Solid-Insecticide Production Methods 

Solid mixtures of insecticides may be com- 

pounded by either (1) adding the toxicant in 

833

R34 CHEMICAL PROCESSING EQUIPMENT 

liquid state to a dust mixture or (2) adding a 

solid toxicant to the dust mixture. 

Figure 635 illustrates equipment used if the 

toxicant in liquid state is sprayed into a dust 

mixture during the blending process. After 

leaving the rotary sifter, the solid raw mate- 

rials are carried by elevator to the upper 

mixer where the liquid toxicant is introduced 

by means of spray nozzles. This particular 

unit has discharge gates at each end of the up- 

per mixer, which permit the wetted mixture 

to be introduced either directly into the second 

mixer or into the high-speed fine-grinding pul- 

verizer and then into the second mixer. From 

the sec0n.d mixer, a discharge gate with a built- 

in feeder screw conveys themixture toa second 

elevator ior transfer to the holding bin where the 

finished batch is available for packaging. Al- 

though as much as 50 percent by weight of liq- 

uid toxicant may be added to the blend, the di- 

luent clays are porous and absorb the liquid 

to such a degree that the ingredients of the mix 

are essentially solids and act as such. In in- 

secticide processing, the type of mixer general- 

ly employed to blend liquids with dusts is the 

ribbon blender. 

Figure 636 is an illustration of a ribbon blender 

screw. This screw consists of two or more 

ribbon flights of different diameters and opposite 

hand, mounted one within the other on the same 

shaft by rigid supporting lugs. Ingredients of 

the mix are moved forward by one flight and 

backward by the other, which thereby induces 

positive and thorough mixing with a gradual 

propulsion of the mixed material to the discharge. 

An example of an insecticide compound produced 

by this method is toxaphene dust. A commonly 

used formulation is: 

Toxaphene (chlorinated 

camphene) 40 

Kerosine 4. 5 

Finely divided porous clay 55. 5 

The toxaphene is melted and mixed with the 

kerosine, then sprayed into the clay and thor- 

oughly blended. 

When the toxicant is in the solid state, the in- 

gredients of the blend are intimately ground, usu- 

ally in stages, and blended by mechanical mixing 

operations. The equipment employed consists of 

standard grinding and size reduction machines 

Figure 635. Sol id-insecticide-processing unit (Poulsen Company, Los Angeles, Calif.)

Insecticide Manufacture 

Figure 636. R~hhon hlender screw (L~nk-Belt Company, Los Angeles, Cal I f.). 

such as ball mills, hammer mills, air mills, 

disc mills, roller mills, and others. A spe- 

cific example oi a grinding and blending facility 

for solid insecticide is shown in Figures 637 and 

638. This installation is used for compounding 

DDT dust. The grinding and blending operations 

are done in two stages. First, the material is 

processed in the premix grinding unit and then 

transferred to the final grinding and blending unit. 

Figure 637. Premix grinding unit. 

Figure 637 illustrates the equipment comprising 

the premix grinding unit. This unit is used for 

the initial grading and blending of DDT and silica 

mixtures. DDT flakes, 75 percent of which have a 

particle size of 1-centimeter diameter, are emp- 

tied from sacks into a hopper. A conveyor takes 

this DDT to a crusher irom which it is conveyed 

to a pulverizer. Finely ground silica (0. 2- to 

2-micron size) is introduced to the pulverizer. 

Silica is added because DDT becomes waxy at 

temperatures approaching its melting point and 

has a tendency to cake and resist grinding. 

Silica acts as a stabilizing agent. The coarsely 

ground silica-DDT mixture is then discharged 

into a ribbon blender for thorough mixing be- 

fore being conveyed to a barrel-filling unit, 

which packs the mixture for aging before its 

further grinding. 

835 

The final grinding unit shorn in Figure 638 takes 

the coarsely ground DDT-silica mixture and sub- 

jects it to fine grinding and blending. The aged 

DDT-silica mixture is fed into a ribbon blender 

where additional silica and wetting agents are 

added to the mix. The mix is then screw con- 

veyed to a high-speed grinding mill that uses 

rotating blades to shear the insecticidal mix- 

ture. A pneumatic conveying system carries 

the material to a cyclone separator from which 

it drops into another blender. After this mix- 

ing operation, the blend is finely ground by high- 

pressure air in an airmill. The blend is air 

conveyed to a reverse-jet baghouse that dis- 

charges into another blender. Additional air 

grinding is then repeated before the barrel 

filling and packing. 

1iquid.lnsecticide Production Methods 

Liquid insecticides may be produced as either 

solutions, emulsions, or suspensions. The 

most common means oi production consists of 

introducing a solid toxicant into a liquid carrier, 

which results in either a solution, emulsion, 

or suspension. 

Figure 639 shows equipment employed in a liq- 

uid-emulsion insecticide plant that makes the 

emulsion by introducing a solid toxicant into a 

liquid carrier in the presence of an emulsifying 

agent. A typical iormulation is: 

Ib 

- 

DDT (technical) 2 00 

Emulsiiying agent No. 1 12 

Emulsifying agent No. 2 12 

Organic solvent 569 (79. 5 gal)

836 CHEMICAL PROCESSWG EQUIPMENT 

The operation consists of adding the DDT to the 

mixing tank, the DDT being held on a horizontal 

wire screen located at the vertical midpoint of 

the tank. Organic solvent and emulsifying agents 

are then pumped into the mixing tank at the approximate 

level of the dry DDT. The mixture is 

continually agitated, both during and after the 

- 

addition of the liquids, until the desired emulsified 

state is achieved. The finished product is 

then pumped to the drum-filling station for packaging. 


As can be seen from the installations just de- 

scribed, air pollutants generated by the insecti- 

cide industry are of two types--dusts and or- 

ganic solvent vapors. 

To collect insecticide dusts, high-efficiency 

collectors are mandatory, since in many in- 

stances, the dust is extremely toxic and cannot 

be allowed to escape into the atmosphere, even 

in small amounts. The moderate fineness, 0.5 

to 10 microns, of the dust necessitates using 

collectors that are effective in these particle 

Figure 638. Final grinding and blending unit. 

size ranges. For the most part, the dusts en- 

countered are noncorrosive. 

Organic solvent vapors emitted from liquid-in- 

secticide production processes ordinarily orig- 

inate from relatively nonvolatile solvents. These 

vapors are of such concentration, nature, and 

quantity as to be inoffensive from a viewpoint of 

air pollution. 


Because of the toxicity of the dusts used in the 

manufacture of insecticides, it is important 

that all sources of dust be enclosed or tightly 

hooded to prevent exposure of this dust to per- 

sonnel in the working area. Wherever possible, 

the sources should be completely enclosed and 

ventilated to an air pollution control device. 

Some of the sources emitting dust are bag pack- 

ers, barrel fillers, hoppers, crushers, con- 

veyors, blenders, mixing tanks, and grinding 

mills. Of these, the crushing and grinding 

operations are the largest sources of emission. 

In most cases, these are not conducive to corn- 

plete enclosure, and hoods must be employed. 

i 

I 

! 

I 

I

Insecticide Manufacture 837 

The contaminants emitted are extremely 

fine dust and, since no elevated temperatures 

a.re encountered and the materials handled are 

n'dt particularly corrosive to cloth, can be 

easily collected by simple cloth bag filters. 

If extremely large throughputs are encountered, 

a conventional baghouse may be required. Since 

no extreme conditions of operation are general- 

ly involved, the most widely used filter material 

is a cotton sateen cloth. 

In larger installations, such as those illustrated 

in Figures 637 and 638 for compounding DDT 

dust, several baghouses are usually used. In 

the premix grinding unit shown in Figure 637, 

the air pollution control equipment consists of 

an exhaust system discharging into a baghouse, 

which is equipped with a pullthrough exhaust 

fan. The exhaust ducting connects to both the 

DDT and the silica hoppers, the DDT crusher, 

the blender, and the barrel-filling unit. Dust 

collected in the baghouse is conveyed to the 

barrel-filling unit for packaging. 

Figure 639. Liquid-insecticide-formulating unit. 

The final grinding unit, shown in Figure 638, 

uses air pollution control equipment consisting 

of a baghouse that serves the receiving hopper, 

the blenders, and the cyclone air discharge of 

the high-speed grinding mill. Dust collected 

in this baghouse is recycled to the feed blender. 

The final blenders and the barrel filler and 

Indraft velocities through openings in hoods 

around crushers and mills should be 400 fpm 

or higher. Velocities through hood openings 

for the other operations, where dust is released 

with low velocities, should be 200 to 

300 fpm. 

packer are vented to one of the reverse-jet 

baghouses serving the fluid energy mill. As 

in the case of mixing liquid toxicant with dust, 

the material collected is not corrosive to 

cotton cloth, and no elevated temperatures are 

encountered. In this installation, cotton sateen 

bags of 1.12 to 1.24 pounds weight per yard 

with an average pore size of 0.004 inch are 

AIR POLLUTION CONTROL EQUIPMENT employed as the filtering medium. 

Baghouses employing cotton sateen bags are the 

most common means of controlling emissions 

from the insecticide-manufacturing industry. 

In some applications, water scrubbers, of both 

the spray chamber and the packed-tower types, 

are used to control dust emissions. Inertial 

separators such as cyclones and mechanical 

centrifugal separators are not used because 

collection efficiencies are not high enough to 

prevent the smaller size toxic particles from 

being emitted into the atmosphere. 

In the solid-insecticide-processing unit previ- 

ously discussed and illustrated in Figure 635, 

air pollution control is achieved by dust pickup 

hoods located at the inlet rotary sifter and at 

the automatic bag packer. The dust picked up 

at these points is filtered by the use of cloth 

bags. Most units of this type are entirely 

enclosed, air contaminants being discharged 

only at the inlet to the unit and at the outlet. 

In liquid-insecticide manufacturing, air pollu- 

tion control problems usually entail collection 

of dusts in a wet airstream. Baghouses can- 

not, therefore, be used, and some type of 

scrubber must be employed. For the liquid- 

emulsion insecticide plant shown in Figure 639, 

the air pollution control equipment for the solid 

and liquid aerosols consists of a packed tower 

that vents the mixing tank. The tower is packed 

with l-inch Intalox saddles, the packing being 

4- 112 feet high, which equals a volume of 14 

cubic feet. The water rate through the tower 

is approximately 20 gpm. The tower is used 

to control dust emissions from the mixing tank, 

which occur when dry material is charged to the 

tank, and also occur during the first stages of 

agitation. Solvent vapors are not effectively 

prevented by the tower from entering the atmo- 

sphere since the solvent is insoluble in water. 

Solvent emissions originate from the storage 

tank and drum-filling unit. In the installation


described, no provision is made to prevent the 

solvint from escaping to the atmosphere since 

total solvent emissions are calculated to be 

only 5.4 per day. 

HAZARDOUS RADIOACTIVE MATERIAL 

Although the responsibility for overseeing the 

control of radioactive materials is predomi- 

nantly that of the Federal government, more 

and more responsibility is expected to be placed 

at state and local levels. For this reason, 

those concerned with air pollution must become 

acquainted with the problems associated with 

this new field, particularly those problems 

arising as more and smaller industries make 

use of radioactive materials. 

HAZARDS IN THE HANDLING OF RADIOISOTOPES 


Radioactive materials used in industry are a 

definite hazard today and will become an in- 

creasing rather than a diminishing hazard in 

the future. In industry, the maximum per- 

missible dose of direct, whole-body radiation 

of persons from all radioactive materials, 

airborne or nonairborne, is 5,000 millirem 

per year. There is greater likelihood that this 

limit will be reduced than that it will be in- 

creased. Airborne radiological hazards can 

result from routine or accidental venting of 

radioactive mists, dusts, metallurgical fumes, 

and gases and from spillages of liquids or 

solids. Presently existing governmental regu- 

lation of the rate of venting airborne, radio- 

active materials consists primarily of spe- 

cific limitations based upon individual chemi- 

cal compounds or upon concentrations of ra- 

dioactivity from single vents. No concepts 

have been promulgated concerning methods 

of controlling total radioactive air pollution 

from all sources in an entire area. Whether 

it will be either desirable or necessary to 

find a solution or solutions to these problems 

is an unanswered question. 

The characteristics of radioactive, gaseous 

or airborne, particulate wastes vary widely 

depending upon the nature of the operation from 

which they originate. In gaseous form they may 

range . from rare gases, such as argon (A~') 

from air-cooled reactors, to highly corrosive 

gases, such as hydrogen fluoride from chemical 

and metallurgical processes. Particulate 

The hazards encountered in handling of radioisotopes 

may be classified in order of importance 

as follows: (1) Deposition of radioisotope 

in the body, (2) exposure of the whole 

body to gama radiation, (3) exposure of the 

body to beta radiation, and (4) exposure of the 

hands or other limited parts to beta or gamma 

radiation. Deposition of a radioisotope in the 

.body occurs by ingestion, inhalation, or absorption 

through either the intact or injured 

body surface. Inhalation of a radioactive gas, 

vapor, spray, or dust may occur. Spray or 

matter or aerosols may be organic or inorganic 

and range in size from less than 0. 05 micron 

to 20 microns. The smaller particles originate 

from metallurgical fumes caused by oxidation 

or vaporization. The larger particles may be 

acid mist droplets, which are low in specific 

gravity and remain suspended in air or gas 

streams for longer periods (Liberman, 1957). 

dust is particularly hazardous because of the 

large fraction of contamination retained by the 

Characteristics of Solid, Radioactive Waste 

lungs (National Bureau of Standards, 1949). 

Solid, radioactive wastes are of two general 

Types of radiation are listed in Table 227. The 

ranges of activity may be defined as: (1) Tracer 

level, less than 1 x curie; (2) low level, 

1 x 10-6 to 1 x 10-3 curie; (3) medium level, 

1 x 10-3 curie to 1 curie; and (4) high level, 

1 curie and over. The handling of tracer quantities 

of radioisotopes usually presents no external 

hazard. Ordinary laboratory manipulaclasses 

--combustible and noncombustible. 

Typical combustible solid wastes are paper, 

clothes, filters, and wood. Noncombustible, 

solid wastes may include nonrecoverable scrap, 

evaporator bottoms, contaminated process equipment, 

floor sweepings, and broken glassware. 

If inadequate provisions are made for proper 

handling and disposal of these wastes, a distinct 

nuisance, and, under certain circumstances, 

tions are performed with special precautions even a hazard, could result. 

to prevent absorption of radioactive material 

by the body. 

Characteristics of Liquid, Radioactive Waste 

Liquid, radioactive wastes are evolved in all 

nuclear energy operations-from laboratory 

research to full-scale production. Liquid 

wastes with relatively small concentrations 

of radioactivity originate in laboratory oper- 

ations where relatively small quantities of 

radioactive materials are involved. Other 

sources are the processing of uranium ore and 

feed material; the normal operation of essen- 

tially all reactors, particularly water-cooled 

types; and the routine chemical processing of 

reactor fuels. High-activity liquid wastes

Type of 

radiation 

Alpha (a) 

. . Beta (8) 

~~ . . 

. . . 

. . . .. . . . . 

... .. . ... . 

Gamma (y) 

Neutron (r~) 

Physical nature 

Heavy particle, 

helium nucleus, 

double positive 

charge 

Light-particle 

electron, single 

negative charge 

Ray, similar to 

X-ray 

Moderately heavy 

particle, neutral 

charge 

are produced by the chemical processing of 

reactor fuels. 

Problems in Control of Airborne, Radioactive Waste 

Hazardous Radioactive Material 839 

Table 227. TYPES OF RADLATION 

Distance of 

travel in air 

Removal of radioactive suspended particles, 

vapors, and gases from "hot" (radioactive) 

exhaust systems before discharge to the atmosphere 

is a se~ious problem confronting 

all nuclear energy and radiochemistry installations. 

Removal is necessary in order to prevent 

dangerous contamination of the immediate 

and neighboring areas. Air pollution brought 

about through discharge of radioactive stack 

gas wastes from ventilation systems is only 

partially avoided by filter devices, no matter 

how efficient they may be, if the discharge 

contains radioactive gases. In systems using 

filter media such as paper, cloth, glass fiber, 

and so forth, activity eventually builds up in 

the filter media through dust loading; the same 

situation applies to electrical precipitators. 

I 

Few inches maximum 

Few yards maximum 

Very long 

Very long 

Another problem in the control of airborne, 

radioactive waste is the low dust loading of 

exhaust streams. The dust concentration of 

ambient air is usually about 1 grain per 1,000 

cubic feet. At installations handling radioactive 

material, owing to precleaning of the 

entering air, aerosols may have concentrations 

as small as 10- 

2 

to 10-3 grain per 1,000 

cubic feet. In contrast, loadings of some industrial 

gases may reach several hundred 

grains per cubic foot, though values of 20 

grains or less per cubic foot are more common. 

An outstanding feature to consider with air- 

cleaning requirements for many nuclear oper- 

Effective shielding 

Skin or thin layer 

of any solid mate- 

rial 

One-half inch of 

any solid material 

Lead, other heavy 

metals, concrete, 

tlghtly packed so11 

Water, paraffin 

Usual means of 

detection ~~-... 

Proportional counter, 

ion chamber, scin. 

tillation counter 

Geiger counter, film 

badge, dosimeter 

Geiger counter, ion 

chamber, film badge, 

dosimeter 

Proportional counter 

contalnlng borlc compound, 

lon chamber 

with cadmium shield 

ations is the extremely small permissible con- 

centrations of various radioisotopes in the at- 

mosphere (see Table 228). Often, removal ef- 

ficiencies of about 99. 9 percent or greater for 

particles less than 1 micron in diameter are 

necessary. This high removal efficiency lim- 

its the selection of control equipment for ra- 

dioactive applications. 


Hooding 

Hooding for radiochemical processes must pre- 

vent radioactive contaminants, such as dust 

and fmes, from escaping into thk work area 

and must deliver them to suitable control de- 

vices. Radioactive sources require proper 

shielding to prevent the escape qf radiation 

and are not considered in this section. The 

materials used for construction for hoods depend 

upon the type and quantities of radioactivity and 

the nature of the process. Stainless steel, 

masonite, transite, or sheet steel, surfaced 

with a washable or strippable paint, can be 

used (Ward, 1952). Where it is necessary in 

a process to handle material that may cause 

dusts or fumes to form, a completely enclosed 

hood should be used, equipped with a glove box 

or dry box. Any tools used for manipulation 

should not be removed from the hood. 

Ventilation 

The recommended airflow for toxic material 

across the face of a hood is 150 fpm (Manufac- 

turing Chemists' Association, 1954). Turbu- 

lence of air entering a hood can be reduced by


Table 228. PROPERTIES OF RADIOISOTOPES (Benedict and Pigford, 1957) 

the addition of picture frame airfoils to the edges. 

Hoods should not be located where drafts will 

affect their operation. When more than one hood 

is located in a room, fan motors should be oper- 

ated by a single switch. The fan should freely 

discharge to the atmosphere and be connected 

to the outlet side of any control device, the 

motors being located outside the air ducts to 

prevent their contamination. Hood and ducts 

should be equipped with manometers to indi- 

cate that they are operating under a negative 

pressure. 


Reduction of Radioactive, Particulate Matter at Source 

Reduction at the source has been defined as the 

design of processes so as to minimize the initial 

release of particulate matter at its source. The 

principle is not new; it is applied, for example, 

in the ceramics industry where dry powders 

are wetted and mixed as a slurry to minimize 

the production of dust. But its application to

adioactive aerosols is particularly worthwhile 

since it (1) provides a cleaner effluent, (2) re- 

duces radiation hazards involved in the mainte- 

nance of air-cleaning equipment or those re- 

sulting from the buildup of dust activity, (3) per- 

mits the use of simpler and less expensive air- 

cleaning equipment, and (4) becomes a part of 

the process once reduction has been established. 

In general, preventing the formation of highly 

toxic aerosols is preferable to cleaning by 

secondary equipment. 

The design or redesign of processes for reduc- 

tion at the source should be based upon a study 

of the quantity and physical characteristics of 

the contaminant, and the manner in which it is 

released. Examples of this concept are instal- 

lation of glass fiber filters on the lnlet of ven- 

tilating or cooling alr to minimize the irradia- 

tion of ambient dust particles, and treatment 

of ducts to minimlze corrosion and flaking 

(Friedlander et al., 1952). 

Design of Suitable Air-Cleaning Equipment 

The most satisfactory control of particulate 

contamination with air-cleaning equipment re- 

sults from using combinations of the various 

collectors. These installations should be de- 

signed to terminate with the most efficient 

separator possible, the nature of the gases 

being considered. To reduce maintenance, 

less efficient cleaners capable of holding or 

disposing of most of the weight load should be 

placed before the final stage. It is good prac- 

tice to arrange the equipment in order of in- 

creasing efficiency. A typical example of such 

an arrangement is a wet collector such as a 

centrifugal scrubber to cool the gases and re- 

move most of the larger particles, an efficient 

dry filter such as a glass fiber filter to remove 

most of the remaining particulate matter, and 

a highly efficient paper filter to perform the 

final cleaning. If the gases are moist, as in 

this example, the paper filter should be pre- 

ceded by a preheater to dry the gases (Fried- 

lander, 1952). 

An air-cleaning installation for highly toxic 

aerosols should fulfill the following require- 

ments (Friedlander et al., 1952): 

1. "It should discharge innocuous air. 

2. "The equipment should require only occa- 

sional replacement and should be designed 

for easy maintenance. Frequent replace- 

ment or cleaning entails excessive exposure 

to radiation and the danger of redispersing 

the collected material. 

Hazardous Ra rdioactive Material 84 1 

3. "The particulate matter should be separated 

in a form allowing easy disposal. The use 

of wet collectors, for example, poses the 

additional problem of disposing of volumes 

of contaminated liquid. Wet collection does, 

however, reduce considerably the danger of 

redispersion. 

4. "Initial and maintenance costs, as well as 

operating costs, should be as low as possi- 

ble while fulfilling the preceding three con- 

ditions. In this respect, pressure drop is 

generally an important consideration. " 

Reverse-jet haghouse 

One type of commercially available dust collector 

that meets the requirements of filtering airborne, 

radioactive particles from ventilation exhaust 

streams is a bag filter employing what is called 

reverse-jet cleaning. This type of baghouse 

(described in Chapter 4) has an efficiency as 

high as the conventional cloth bag or cloth screen 

collector and is particularly adapted to an in- 

stallation where the grain loading of the effluent 

is low. The bag material is a hard wool felt of 

the pressed type, about 1116-inch thick, or a 

cloth woven of glass fibers. The gas flow is 

likely to he around 10 to 40 cfm per square foot 

of bag area when the pressure drop is maintained 

at usual values such as 2 to 7 inches water col- 

umn (Anderson, 1958). 

The conventional cloth bag or cloth screen col- 

lectors, which are cleaned periodically by auto- 

matic shaking devices, may allow a puff of dust 

to escape after the shaking operation. The prob- 

lem of maintenance in this instance presents a 

contamination and radiation hazard. For this 

reason, the reverse-jet baghouse is generally 

preferred. 

Wet collectors 

Another method of treating contaminated ex- 

haust air before discharge to the atmosphere 

involves the use of wet collectors of various 

types. These collectors are relatively effec- 

tive on gases. Investigation covering changing 

of water supply or recirculating has shown the 

latter procedure useful for considerable periods 

of time without apparent adverse effect. Evapo- 

ration is compensated for by fresh supply. In- 

soluble radioactive salts, soluble salts, and 

other radioactive particles that may form a 

solution, suspension, or sludge in the reser- 

voir result in fairly high radioactivity of the 

scrubbing media. Precautions must be taken 

during maintenance to avoid carryover of the 

scrubbing media since the radioactive con- 

tamination of entrained liquid would be trans-


ferred to the preheater or filter, resulting in 2. "With uneven airflow, the air velocity 

high radiation levels at those points. through some of the collector cells may 

Some important disadvantages of wet collectors 

make them less attractive than other types . . of 

collectors. Wet collectors present the difficult 

problem of separating the radioactive, solid 

material from the water in which it is suspended. 

Maintenance and corrosion are serious problems. 

Considerable quantities of water are required, 

and, if the radioactive solids are not separated 

from the water, this in turn leads to a final 

storage and disposal problem. 


Radioactive, airborne particles, when given an 

electrical charge, can be collected on grounded 

surfaces. The fact that the particles are radioactive 

has very little to do with their behavior 

in an electrical precipitator. Experiments conducted 

with precipitators using the alpha emitter 

polonium and the beta emitter sulfur 35 indicate 

that neither material behaves in a way different 

from nonradioactive material. 

Water-flushed-type, single-stage, industrial 

precipitators, and air-conditioning-type, two- 

stage precipitators are used for separating ra- 

dioactive dusts and fumes from gases at atomic 

energy plants and laboratories. A small elec- 

trical precipitator of the water-flushed type with 

a design capacity of 200 cfm was installed to 

test efficiency of collecting and removing par- 

ticulate radioactivity from the offgas system 

of an isotope recovery operation. This precip- 

itator consists of 23 vertical collecting pipes 

with an ionizing wire centered in each pipe. The 

inside surfaces of the pipes serve as collecting 

walls. For wet operation, the collecting walls 

are water flushed by means of spray nozzles in- 

stalled at the top of each pipe. This water is re- 

cycled continuously at a rate of 35 gpm over the 

collecting walls while high voltage is applied to 

the electrodes. This unit reportedly collects 

more than 99. 99 percent of the particulate radio- 

activity in the offgas at 50 to 55 kilovolts when 

the concentration of radioactivity as solids is 

greater than 5.0 x microcuries per cubic 

centimeter of offgas (Anderson, 1958). 

Based upon tests made at the Oak Ridge Nation- 

al Laboratory, Anderson (1958) makes the follow- 

ing evaluation of precipitators used in radio- 

active applications: 

1. "Electrical precipitators are not intended 

to collect the ultra fine particles which 

may be discharged from radiochemistry 

installations. 

be sufficientlv above velocitv limits to blow 

off collected wastes which would then be 

discharged to the atmosphere. 

3. "Efficient operation depends a great deal 

on the regularity with which the unit is 

cleaned. At best the electrical precipitator 

is only approximately 90 percent 

efficient. This may he demonstrated by 

the fact that dense clouds of tobacco smoke 

fed into the precipitator will escape from 

it in concentrations great enough so that the 

escaping smoke can be seen. The blue 

color of tobacco smoke is evidence that 

most of its particles have a diameter less 

than the wavelength of light, which is 

roughly 0.5 micron. 

4. "For absolute efficiency an after-filter of 

the Cambridge or MSA Ultra-Aire type is 

necessary to catch the dirt should the pre- 

cipitator short circuit. 

5. "Difficulty may be experienced if the dust- 

load builds up faster than it can be removed, 

eventually becoming so heavy that arcing 

occurs between the dirt bridges resulting 

in a fire hazard. 

6. 

"Devices such as the single-stage indus- 

trial precipitator and the air-conditioning 

type two-stage precipitator accomplish 

only one phase of the problem. The final 

disposal of radioactive wastes collected 

and accumulated during operation and main- 

tenance still remains. " 

Glass fiber filters 

Glass fiber or glass fiber paper is often used 

as a filter medium and is effective in the oper- 

ation of :adiochemistry hoods, canopies, and 

gloved b'oxes. One of the most efficient light- 

weight, inorganic filters developed to date is 

made with a continuous, pleated sheet of micro- 

glass fiber paper. The pleats of the glass paper 

are separated by a corrugated material (paper, 

glass paper, aluminum foil, plastic, or as - 

bestos paper) for easy passage of air to the deep 

pleats of the filter paper. The assembly of the 

filter paper and corrugated separators is sealed 

in a frame of wood, cadmium plated steel, stain- 

less steel, or aluminum. This construction per- 

mits a large area of filter paper to be presented 

to the airstream of a correspondingly low re- 

sistance (Flanders Filters, Inc. , Riverhead, 

N. Y. ).

Glass fiber, from which filters are made, with- 

stands temperatures up to 1, OOO°F. It is non- 

combustible and has extremely low thermal 

conductivity and low heat capacity. The fibers 

are noncellular, are like minute rods of glass, 

and do not absorb moisture; however, water 

can enter the interstices. The material is 

relatively nonsettling, noncorrosive, and durable. 

It is resistant to acid fumes and vapors, except 

hydrogen fluoride. 

The installation and replacement costs of glass 

fiber filters are low. Final disposal of used 

filters may be accomplished by incinerating at 

over 1,000"F with provisions for decontaminating 

the stack gases. This melts the glass fibers, 

reducing the physical mass to the size of a glass 

bead. Thus, glass fiber filters provide, in part, 

a very good answer to the problem of control 

and final disposal of radioactive contaminants. 

Paper filters 

A highly efficient paper filter medium can be 

used with adequate effectiveness on incoming 

ventilating air and as a final cleaner in many 

instances. This type filter is composed of as- 

bestos cellulose paper. A more recently de- 

veloped filter has a glass fiber web. It is de- 

signed and manufactured in corrugated form 

to increase the available filter area and load- 

ing capacity and to reduce initial resistance. 

The filter units are tested at rated capacity 

with standard U.S. Army Chemical Corps test 

equipment for resistance and initial penetra- 

tion and are unconditionally guaranteed to be 

at least 99.95 percent effective against 0. 3- 

micron-diameter dioctyl phthalate particles. 

This filter performs as well as, or better 

than, the earlier paper types and under tem- 

peratures up to l,OOOeF. 

Airborne, radioactive wastes are only part of 

the control and disposal problem of nuclear 

energy and radiochemistry installations. Solid 

and liquid, radioactive wastes are subject to 

the same limitations on disposal to the environ- 

ment. 

The methods of disposing of the final waste from 

the collection systems present additional prob- 

lems, as follows (Anderson, 1958): 

1. "Incineration results in stack gas and par- 

ticle discharge which is a cycle of the en- 

tire problem repeated over again. 

2. "Direct burial results in redispersal and 

ground contamination with associated prob- 

lems related to the ground water table. 

Hazardous Radio active Material 843 

3. "High dust or particle loading capacity re- 

sults in high radioactivity of the collecting 

media. 

4. "Vapors, acid fumes and unfilterable gases 

may cause rapid deterioration and disinte- 

gration of filter media resulting in a main- 

tenance and health hazard problem. 

5. "Mechanical replacement costs are high 

because of the remote handling involved. 

6. "An auxiliary unit for emergency or main- 

tenance shutdown must be available to pre- 

vent the possibility of reverse flow of the 

air stream out of "hot" equipment into 

controlled rooms and areas. " 

Disposol and Control of Solid, Radioactive Waste 

The most common method of disposal of solid, 

radioactive wastes is Land burial at isolated 

and controlled areas. The earth cover over 

these burial pits is usually about 12 feet, and 

the surface is monitored regularly. A method 

used for disposal of low-level, radioactive, 

solid wastes consists of putting the wastes in 

concrete and dumping it at sea. Incineration 

of combustible, solid wastes is practiced, with 

provisions for decontaminating the flue gases 

(Shamos and Roth, 1950). 

Disposal and Control of Liquid, Radioactive Worte 

Low-level, radioactive, liquid wastes, under 

proper environmental conditions, are suscepti- 

ble to either direct disposal to nature or dis- 

posal after minimum treatment. Treatment 

processes used include coprecipitation, ion ex- 

change, biological systems similar to sewage 

treatment methods, and others. Only to the 

extent that it is absolutely safe, maximum use 

is made of the dilution factors that may be avail- 

able in the environment and that can be assessed 

quantitatively. 

High-activity, liquid wastes associated with the 

chemical processing of reactor fuels constitute 

the bulk of the engineering problem of disposal 

of radioactive wastes. Highly radioactive, liq- 

uid wastes are currently stored in specially de- 

signed tanks. Since the effective life of the fis- 

sion products constituting the wastes may be 

measured in terms of hundreds of years, tank 

storage is not a permanent solution to the dis- 

posal problem. Evaporation before storage is 

generally practiced to reduce storage volume 

and cost. The degree to which evaporation is 

carried out is limited in some instances by the

844 CHEMICAL PROCESSIl \iG EQUIPMENT 

percentage of solids present in the waste or by 

considerations of corrosion. 

There are several ~ractical approaches to 

ultimate, safe disposal of high-activity, liquid 

wastes. The actual fission products in radioactive 

waste material may be fixed in an inert, 

solid carrier so that the possibility of migration 

of the radioactivity into the environment 

is eliminated or reduced to acceptable and safe 

limits. The carrier containing the radioactive 

material could then be permanently stored or 

buried in selected locations. Fixation on clay, 

incorporation in feldspars, conversion to oxide, 

elutriation of the oxide, and fixation of the 

elutriant are examples of systems under development. 

Because of the particular radiotoxicity and long 

half-life of strontium-90 and cesium-137, the 

removal and separate fixation and handling of 

these two isotopes would substantially reduce 

the effective life and activity of the waste and 

facilitate its final disposal. With cesium and 

strontium removed, the possibilities of safe 

disposal into the environment under controlled 

conditions are greatly increased. 

It may be practical to dispose of the wastes 

underground in some cases without any treat- 

ment, into formations such as (1) spaces pre- 

pared by dissolution in salt beds or salt domes, 

(2) deep basins containing connate brines and 

with no hydraulic or hydrologic connection to 

potable waters or other potentially valuable 

natural resources, and (3) special excavations 

in selected shale formations (Liberman, 1957). 

OIL AND SOLVENT RE-REFINING 

Many millions of gallons of oils and solvents 

are used annually for lubricating vehicle en- 

gines and other machinery, transmitting pres- 

sure hydraulically, cleaning manufactured arti- 

cles and textiles, and dissolving or extracting 

soluble materials. In the course of their usage, 

these oils and solvents accumulate impurities, 

decompose, and lose effectiveness. The im- 

purities include dirt, scale, water, acids, de- 

composition products, and other foreign mate- 

rials. Reclaiming some of these oils and sol- 

vents for reuse by removal of the impurities 

can he effected in many instances by re-refining 

processes. 

Most re-refiners must practice stringent econ- 

omies to survive, and for this reason, second- 

hand, cannibalized, or makeshift equipment is 

often employed. Many re-refiners also neglect 

maintenance, repairs, and general housekeeping 

in order to keep operating costs low. As a result, 

air pollution control is minimal or lacking unless 

made mandatpry by legislation. 

RE-REFINING PROCESS FOR OILS 

Lubricating oils collected from service stations 

are the main source of supply. A typical scheme 

for re-refining lubricating oil is shown in Figure 

640. Re-refining is normally a batch process. 

Treating clay, for example, Fuller's earth, is 

added to the contaminated oil at ambient tem- 

perature to aid in the removal of carbon mate- 

rials. The mixture is next circulated through a 

fired heater, usually a pipe or tube still, to a flash 

tower for removal of diluent hydrocarbons and 

water. The oil being reclaimed and the products 

desired determine the final temperature (300" 

to 600°F). Live steam, introduced at the base 

of the flash tower, is used to assist in this phase 

of the operation. Besides distilling off the light 

fractions contained in the oil, the steam pre- 

vents excessive cracking of the oil at the higher 

temperatures. 

A barometric condenser maintains a vacuum on 

the tower. The overhead vapors containing 

steam, low-boiling organic materials, and en- 

trained hydrocarbons are aspirated through the 

condenser to a separator tank. The condensate, 

consisting of light gas, oil, and water, is col- 

lected and separated in the separator tank. Non- 

condensible gases are usually incinerated in 

fireboxes of adjacent combustion equipment. The 

light oil condensate is decanted from the water 

and is suitable as liquid fuel. The contaminated 

water is piped to a skimming pond where it is 

cooled and either reused or disposed of by drain- 

ing to a sewer. The oil..-clay mixture is with- 

drawn from the tower and filtered. The oil is 

blended with additives and is canned or drummed. 

The clay is usually hauled to a dump. 

In some re-refineries, the process is preceded 

by a dehydration operation. Water is removed 

from the oil by using sodium silicate, sodium 

hydroxide, and heat. Dehydrated oil is decanted 

from the mixture and charged to the still. Sul- 

furic acid treabent is also employed at some 

re-refineries before the refining process. The 

acid-treated oil is settled, decanted from the 

acid sludge, and neutralized with caustic. Be- 

fore the clay is added, sulfuric acid treabent 

or air blowing may also be used to improve 

color of the re-refined oil. 

RE-REFINING PROCESS FOR ORGANIC SOLVENTS 

The typical organic solvent re-refining process 

is similar to that described for oil re-refining. 

The prime difference between the processes is 

that the volatilities of the organic solvents re-

efined are much greater than those of lubrica- 

ting oils. Mineral spirits, benzene, toluene, 

xylene, ketones, esters, alcohols, trichloro- 

ethylene, and tetrachloroethylene from paint, 

lacquer, degreasers, and dry cleaners are ex- 

amples of solvents reclaimed by re -refining. 

Figure 641 illustrates a typical solvent recov- 

ery system. The mixture to he processed is 

introduced into a settling tank to permit the 

solids to settle out. The supernatant liquid is 

then preheated and charged to a pot still topped 

by a fractionating section, which may be under 

RECOVERABLE 

+ 

Oil and Solvent Re-Refining 845 

Figure 640. Composite flow sheet for re-refining process. 

CDNDENSER 

t lTER OUT 

FRACTlONIITlNG 

EsEcrloM ~ " SOGlUM cClRBONliTE ' E 

QRCHtIITER 

Sllll 

OEHIORATING 

CGNOENSIITI lATER PRODUCT 

TO SBtR 

Figure 641. Typical solvent re-refining installation. 

vacuum. Vapors from the still are condensed 

in a water-cooled surface condenser. Reflux- 

ing may or may not be done, depending upon the 

product, the degree of purity desired, and the 

contaminants present. The condensate is ac- 

cumulated in a holding tank, where a salt such 

as sodium carbonate is added to "break" the 

water from the solvent. After the water settles 

out, it is removed, and the solvent is drurnmed . . 

off as product. 

, . 

r. 

THE AIR POLLUTION PROBLEM i 

Air Pollution From Oil Re-refining ~ 

The two primary air pollution problems connected 

with oil re-refining are odors and hydrocarbon 

vapors. 

Chief odor sources are the contaminated water 

and the noncondensible gases from the separator 

tank and dehydration tank. Obnoxious odors ! 

emanate from the skimming pond. Odors also 

occur from the barometric condenser leg. If 

the process water is aerated in a cooling tower 

or spray pond, a serious odor problem occurs. 

Other odors can originate from the dehydration 

operation and from sulfuric acid sludges and 

clay filter cakes. ! 

i 

I 

I 

j


In addition to air pollution from odors, oil re- sions from the bottom drawoff of the still are 

refining processes can emit some hydrocarbons slight since most of the volatiles have been 

into the atmosphere. These originate from the flashed off. Emissions from the settling tank 

noncondensible gases and the layers of light, and the product receivers are normally too 

volatile hydrocarbons on the surface of the sep- small to create any problems, but they can be 

arator tank and the skimming pond. controlled by being vented also to a boiler firebox. 

Air Pollution From Solvent Re-refining 

As in oil re-refining, - the chief air pollution 

problems are odors but these are less severe 

than those occurring from re-refining of lubricating 

oil. Sources of emissions are the settling 

tanks during filling and sludge drawoff, the drawoff 

of bottoms from the still, the product receivers, 

and the water jet reservoir (if vacuum is 

produced by a barometric water jet). By creating 

a vacuum, the water jet entraps the solvent vapors 

from the still. 


Oil Re-refining 

The most acceptable method of controlling emis- 

sions from re-refining is incineration. Usually 

the firebox of a boiler or heater provides ade- 

quate incineration. The separator tank must be 

covered and vented to a firebox. The vent line 

should be equipped with a knockout drum and a 

flashback arrester. Additional safety protection 

can be achieved by introducing live steam into 

the vent line upstream from the firebox. Other 

vessels, for example, dehydrating tanks and 

mixing tanks, may be tied into this system. 

Emissions from the barometric, or contact, 

condenser can be controlled by maintaining a 

closed recycle water system or by modifying 

the operation by substituting a shell-and-tube- 

type condenser. 

Recycle water, highly odorous from contact 

with the oil and heated by contact with the hot 

vapors, must be allowed to cool before reuse. 

It can he controlled by cooling in a covered 

settling tank that is properly vented to an 

operating boiler or heater firebox. Con- 

taminated recycle water must not be cooled 

by aerating in a spray pond or cooling tower. 

Solvent Re-refining 

Usually, in the solvent re-refining industry, air 

pollution control is lacking without enforcement, 

and solvent vapors are allowed to escape into 

the atmosphere. If, however, control is re- 

quired, it can easily be accomplished by venting 

the barometric water jet vacuum system to a 

boiler firebox, provided appropriate flashback 

prevention measures have been taken. Emis- 

CHEMICAL MILLING 

The chemical milling process was developed 

by the aircraft industry as a solution to the 

problem of making lightweight parts of intri- 

cate shapes for missiles. These parts could 

not be formed if mechanically milled first, and 

no machines were available that could mill them 

after they were formed. Chemical milling is 

based upon the theory that an appropriate etch 

solution dissolves equal quantities of metal per 

given time from either flat or curved surfaces. 

The process was quickly adopted by the aircraft 

industry, and etchants were developed for 

chemically milling many metals used in aircraft 

and missiles, including aluminum, titanium, 

stainless steel, and magnesium. 

DESCRIPTION OF THE PROCESS 

Before an article can be chemically milled, the 

surface of the metal must be clean. The usual 

metal surface preparation includes (1) degreas- 

ing, (2) alkaline cleaning, (3) pickling, and 

(4) surface passivation. The cleaning is needed 

to provide a clean surface in order to ensure uni- 

form dissolving of the metal when it is submerged 

in the milling solution. The passivation is needed 

to protect the surface from oxidation in air and 

provide a surface that will accept and hold a 

masking agent or material. 

Maskings are either tapes with pressure-sensi- 

tive adhesives or paint-like substances that are 

applied by brushing, dipping, spraying, or flow- 

coating. Figure 642 shows a sheet of stainless 

steel being flow-coated with a rubber base mask- 

ing material. These paint-like maskings must 

be cured, usually in a bake oven. After curing, 

the masking is removed or stripped from those 

areas to be milled. Figure 643 shows one meth- 

od of scribing the masking by use of a template. 

Milling is accomplished by submerging the pre- 

pared article in an appropriate etching solution. 

The depth of the cut is controlled by the length 

of time the article is held in the etching solu- 

tion. To stop the milling action, the article is 

removed from the etchant and the adhering solu- 

tion is rinsed off with water. During the milling 

step, some metals are discolored by their etch- 

ing solutions. The smutty discoloration is re-

Chemical Milling 847 

This process is patented and licensed by 

Fieilre . .-- fi47. An 18- hv 6-foot stainless steel Turco Products Co., Wilmington, Calif. 

~ - ... - .. ., . ~~ ... . -.. ~ .-. . 

sheet being masked b; flow-coating with a rub- Figure 644. A flow diagram showing the typical 

ber-based masking (U.S. Chemical Milling Gorp., steps necessary to the chem-milling process 

Manhatten Beach, Calif.). (Scheer, 1956). 

Figure 643. The masking on a titanium part is being 

scribed bv use of a template. After scribing, the 

masking will be stripped from those areas shown by 

the holes in the templates. The stripped areas will 

then be milled. The black part in tile foreground and 

those in the background have not yet been scribed 

(U.S. Chemical Mi l ling Corporation, Manhatten Beach, 

Calif.). 

moved in a brightening solution such as cold, 

dilute nitric acid. A flow diagram of the pro- 

cess is shorn in Figure 644. 

percent high-boiling alcohols, and is then 

stripped off by hand. Figure 645 shows the in- 

spection of a part. The metal thickness is mea- 

sured before the masking is removed. Figure 

646 shows the masking being removed from a 

section of a wing skin. The entire side shown 

was masked, and some areas of the other side 

were etched. In Figure 647, the masking is 

being stripped from a milled part. 

Figure 645. Inspection of milled parts. The in- 

After the milling, the paint-like masking is strument measures the metal thickness before the 

softened in a solution consisting, for example, masking is removed (U.S. Chemical Mi l l ing Corpora- 

of 80 percent chlorinated hydrocarbons and 20 tion, Manhatten Beach. Calif.),


ETCHANT SOLUTIONS 

Figure 646. Stripping masking from a.section of a wing skin of a 

B-58. The entire side shown was masked. Some areas of the other 

side were mil led (U.S. Chemical Milling Corporation, Manhatten Beach, 

Calif.). 

Etchants range from sodium hydroxide solution 

for aluminum to aqua regia for stainless steel. 

For milling a specific metal, the concentration 

of the chemical in the solution may vary widely 

between different operators: however, each 

operator controls the concentration of his solu- 

tion to within very close limits. The concen- 

Figure 647. Masking being stripped, milled parts with masking still 

in lace, and mil led parts with masking removed (U.S. Chemical Mi l- 

ling Corporation, Manhatten Beach, Calif.). 

tration of the solution affects the milling rat'e; 

therefore, it must be closely controlled to ob- 

tain the desired rate. For milling aluminum, 

the solutions in use contain from 7 to 30 per- 

cent sodium hydroxide. For lnilling magnesi- 

um, dilute sulfuric acid solutions are adequate. 

Stainless steels require strong solutions, USU- 

ally aqua regia fortified with sulfuric acid. In 

most of the milling solutions, surface-active

agents are used to ensure smooth, even cuts. 

The surface-active agents also reduce the ten- 

dency toward mist formation by reducing the 

surface tension of the solution. The solutions, 

during milling operations, are generally main- 

tained at constant temperatures ranging from 

105" to 190" F. 


The air contaminants emitted in the prepara- 

tion of metals by chemical milling consist of 

mists, vapors, gases, and organic solvents. 

Mists 

A mist of the etching solution used in a milling 

process is discharged from the milling tank 

owing to entrainment of droplets of the solution 

hy the gas hubbles formed by the chemical 

action of the etchant on the metal. The amount 

of mist generated depends upon factors such as 

the nature of the chemical reaction, the solu- 

tion temperature, and the surface tension of the 

solution. Since the solutions from which the 

mists are formed are very corrosive, the mists, 

too, are very corrosive and are capable of caus- 

ing annoyance, or a nuisance, or a health hazard 

to persons, or damage to property. 

Some of the acid solutions used, such as hydro- 

chloric and nitric, have high vapor pressures 

at the temperatures used for the milling pro- 

cess; therefore, appreciable amounts of acid 

vapors are discharged. Unlike the discharge 

of mists, which occurs only during the milling, 

the vapors are discharged continuously from the 

hot solution. Under certain atmospheric condi- 

tions, the vapors condense, forming acid mists 

in the atmosphere. 

Gases 

Since hydrogen is formed in chemical milling, 

proper ventilation must be provided to prevent 

the accumulation of dangerous concentrations of 

this gas. 

Solvents 

Organic solvent vapors may be emitted from the 

vapor degreaser, the maskant area, and the 

curing station in the cleaning and masking pro- 

cesses. This type of air contaminant, and the 

method of controlling it are described elsewhere 

in this manual. Alkaline cleaning, pickling, and 

passivating tanks from the other phases of the 

cleaning processes have been found to be minor 

sources of air pollution. 

:a1 Milling 849 


The air contaminants released from chemical 

milling tanks can be captured by local exhaust 

systems. Since open tanks are used to provide 

unobstructed working area, most exhaust sys- 

tems employ slotted hoods to capture the mists 

and vapors. In designing slot hoods for chem- 

ical milling equipment, it is particularly im- 

portant to provide for the elimination of exces- 

sive cross-drafts as well as for adequate dis- 

tribution of ventilation along the entire length 

of the hoods. The minimum ventilation rates 

previously mentioned in Chapter 3 are for tanks 

located in an area having no cross-drafts. If 

the tank is to be located outside or in a very 

drafty building, either the ventilation rate will 

have to be greatly increased or baffles must be 

used to shield the tank from winds or drafts. 

In some instances, both baffles and increased 

ventilation are needed. 

Adequate distribution of ventilation along the 

entire length of a slot can be attained by pro- 

viding a high slot velocity and a relatively low 

plenum velocity. The slot velocity should be at 

least 2, 000 fpm, and the plenum velocity should 

be not more than half of the slot velocity. With 

hoods more than 10 feet in length, either multi- 

ple takeoffs or splitter vanes are needed. Enough 

takeoffs or splitters should be used to reduce 

the length of the slot to sections not more than 

10 feet long. 

Under excessively drafty conditions, a hood en- 

closing the tank can be used to advantage. The 

hood should cover the entire tank and have suf- 

ficient height to accommodate the largest metal 

sections that can be handled in the tank. Vari- 

ous methods have been used to get work into and 

out of the tank. In one installation, the hood has 

doors on one end, and a monorail, suspended 

below the hood roof, that runs out through the 

doors. The work is carried on the monorail 

into the hood and above the solution. After the 

work is lowered into the solution, the doors are 

closed, when necessary, to ensure complete 

capture of the air contaminants created. In 

another installation, the hood is left open on one 

end, and a slot hood placed across the opening. 

The top of the hood is slotted to provide for the 

movement of the crane cable. This slot is 

nominally closed with rubber strips, which are 

pushed aside by the cable during movement of 

the crane. 


Many types of wet collectors that can control 

the emissions from chemical milling tanks are 

commercially available. The one most common-

850 CHEhiIICAL PROCESS 

ly used is the spray and baffle type, owing prob- 

ably to its low cost. and ease of coating with cor- 

rosion-inhibiting materials. Moreover, the oper- 

ation and maintenance of this type are simple 

and inexpensive compared with those of other 

types of scrubbers. 

Figure 648 shows an exhaust and mist control 

system employing two scrubbers, one for each 

side oi a 24-foot-long by 6-foot-wide tank used 

for chemically milling stainless steel and ti- 

tanium. The etching solution is a mixture of 

hydrochloric, nitric, and sulfuric acids and is 

heated to 150°F. Acid vapors discharged from 

the solution are captured by slot hoods, one on 

each side of the tank. The ducts from each 

hood exit downward from the center. Each hood 

has four splitter vanes, which divide it into four 

sections. The overall hood length is 24 feet, 

the end-sections and those adjacent being 4 feet 

long each, and the center section being 8 feet 

long. Distribution of ventilation is excellent. 

Each hood is supplied with 18, 000 cfm ventila- 

Figure 648. A tank used for the chemical milling of 

stainless steel, and Dart of its air oollution 

control system. The hoods, ductwork, and scrubbers 

shown are made ent~rely of polyester resin reinforced 

wlth flberglas. The fans and discharge ducts, 

not shown, are steel-coated wlth polyester resln. 

(U S Chem~cal MI ll lnE Coraoratlon, Manhatten Beach, 

tion, and the slot is sized to give an intake ve- 

locity of 2, 000 fpm. The plenum velocity is 

less than 1, 000 fpm. It is estimated that this 

system provides sufficient ventilation to capture 

at least 95 percent of the vapors emerging from 

the process. 

The scrubbers are of the spray and baffle type, 

as shown in Figure 649. They are cylindrical, 

two baffles forming three concentric chambers. 

Gases enter at the top and flow down through 

the center cylindrical section. Water from a 

bank of sprays scrubs the gases as they enter 

this section. The bottom of the scrubber is 

filled with water to a depth of 1 foot. The gases 

and scrubbing water flow downward through the 

center section and impinge on the water. The 

gases turn 180 degrees and flow upward through the 

second chamber. Most of the scrubbing water 

remains in the sump. The depth of water in the 

sump is maintained at a uniform level with a 

float valve and an overflow line. The scrubber 

is equipped with a pump to circulate the sump 

water to the sprays. In this installation, how- 

ever, only fresh water is used, the sump being 

kept full and overflowing all the time. 

The gases flowupward throughthe second sectionand 

over the secondbaffle. Theyturn 180 degrees to enter 

the third section. In the third section, the gas- 

es flow down and around to the outlet port. Most 

of the entrained moisture entering the second 

section is removed either by impingement on 

the walls of that section or by centrifugal im- 

pingementduring the 180-degree change of direction 

into the third section. The last of the entrained 

water is deposited on the walls of the third sec- 

tion. The gases then flow from the scrubber to 

the fan, from which they are discharged to the 

atmosphere through ducts. 

The hoods, the scrubber, and the ductwork con- 

necting the hoods to the scrubbers and the scrub- 

bers to the fans are made entirely of polyester 

resin reinforced with glass fibers. The fans and 

discharge ducts are made of steel coated with 

polyester resin. 

The existing system provides satisfactory con- 

trol of the vapors. It captures an estimated 95 

percent of the vapors at the tank, and the gases 

discharged have only a slight acid odor. 

Corrosion Problems 

Whenever moisture is present in an exhaust 

system, the iron or steel surfaces should be 

coated to prevent corrosion. However, since 

zinc is soluble in both acid and alkaline solu- 

tions, galvanized iron cannot be used when 

chemical milling tanks are vented. A coating

Model 

Motora 

ho 

.". 

Chemical Milling 851 

DRA l N 

Pump Drain 

rac.htb A B C D E F 6 H I K L 

'~otor is 440/220 volts, 3 phase. 60 cycle. Exhaust fan and motor furnished upon request 

b D ~ ~ not s include recirculating motor and pump. 

Figure 649. A scrubber used to control the acid vapors discharged 

from a tank used to mill stainless steel (Lin-0-Coat scrubber, 

manufactured by Diversified Plastics. Inc., Paramount, Calif.). 

such as polyvinylchloride (PVC), which is not 

attacked by either dilute acids or dilute alkalies, 

should be used. It has been found, however, 

that the PVC linings in ducts and scrubbers can- 

not withstand the strongly oxidizing acids used 

for stainless steel and titanium milling. These 

highly corrosive acids have been successfully 

handled in exhaust systems made of polyester 

resins reinforced with fiberglas. Hoods, ducts, 

and scrubbers are available made entirely of 

polyester-fiberglas material. Figure 648 shows 

i 

Spray 

nozzles 

Drain 

size. it,. 

Mi".-range-max. 

lorn cfm i fom I r fm 

an air pollution control system venting a 24-foot- 

long tank for stainless steel chemical milling. 

The hoods, ductwork up to the blowers, and the 

scrubbers are made entirely of polyester-fiber- 

glas material. The steel blowers and discharge 

ducts are coated with polyester resin. Some 

blower manufacturers are now advertising blow- 

ers with scrolls made entirely of polyester- 

fiberglas and with steel wheels coated with the 

same material. 

! 

1

Air Pollution Engineering Manual Part5 1973

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