Hazardous Waste Disposal with Thermal Oxidation - John Zink ...

johnzink

Hazardous Waste Disposal with Thermal Oxidation - John Zink ...

HAZARDOUS

WASTE DISPOSAL

BY THERMAL

OXIDATION


INTRODUCTION

HAZARDOUS WASTE DISPOSAL

BY THERMAL OXIDATION

Thermal oxidation has proved to be an effective and safe method for the disposal of a wide variety

of hazardous industrial wastes. Virtually all organic compounds can be thermally oxidized with an

assured level of destruction. John Zink Company has over 2300 thermal oxidizer installations in

service worldwide, destroying an array of hazardous and non-hazardous organic wastes.

The basic thermal oxidation system, shown in Figure A, consists of a refractory-lined vessel called

the Thermal Oxidizer (T.O.), burner, stack, and combustion controls. The oxygen for combustion

comes either from ambient air or is contained in the waste gas stream. Ambient air may be

inspirated by natural draft or forced in by a fan.

Burner

Stack

Waste Stream

Fuel

Air

Figure A: Basic Thermal Oxidation

Ideally, the flue gas resulting from high-temperature oxidation of hydrocarbons (HC) contains

CO2 , H2O, N2 , O2 and some acceptable levels of oxides of nitrogen (NOx ) and oxides of

sulfur (SOx). In reality, the flue gas from a combustion process contains CO2 , H2O, N2 , O2 and some concentration of carbon monoxide (CO), unburned hydrocarbons (UHC), NOx and

SOx .

PRODUCTS OF COMBUSTION

IDEAL

CO , H O, O , N , NO

XA

*, SO *

2 2 2 2 XA

FG

* Sub A designates acceptable level.

1

Castable

Refractory

Lining

Brick Lining W/

Castable Refractory

Back-Up Lining

Thermal

Oxidizer

Castable

Refractory Floor

Combustion Control

Package

REAL

CO 2, H

2

O, O

2

, N 2, NO X,

SO

X

UHC,CO


Environmental concerns require that the flue gas exiting a TO meet certain emission

requirements mandated by local and/or federal regulatory authorities. Thus, it is important not

only to destroy the organic portion of the waste completely, but also to limit the quantities of

pollutants which are produced by the combustion process or were originally in the waste but

not destroyed by combustion. For example, oxides of sulfur and C12/HCI produced by

thermally oxidizing wastes containing sulfontated or chlorinated components must be removed

down-steam. Similarly, inorganic salts or ash contained in the waste are unaffected by

combustion and must be removed to meet particulate emission requirements.

Meeting CO and UHC regulations is accomplished by the correct selection of TO resident

time, operating temperature and turbulence -the three Ts of combustion. Figure B is a plot

or residence time versus destruction efficiency for CO and HC at various temperatures. It

shows that CO and HC destruction efficiency increase as residence time and operating

temperature increase.


Figure C is an example of how this information is used to determine concentration of UHC and CO

in the flue gas. In this example, we assume methane is being burned with 25% excess air in a

horizontal T.O., having a residence time of 1.0 seconds and operating at a temperature of T 2 . Air

injected into the T.O. is in addition to the 25% excess air and is used to lower methane’s 3200° F

adiabatic temperature to T 2 .

The destruction efficiencies obtained from the graph for CO and HC are 99.88 % and 99.985 %.,

respectively. The heat and mass balance calculations determine flue gas concentrations of 7.1 and

56.8 ppm V (dry) for unburned HC (assumed as CH 4 ) and CO, respectively.

EXAMPLE:

What is the concentration of CO and unburned hydrocarbon in the flue gas

when the residence time is 1.0 second and operating temperature is T 2 ?

Use air to cool operating temperature to T 2 .

CO graph reading = 99.88 %

HC graph reading = 99.985 %

Combustion Air

CH

4

Basis 1 mole of CH

CH4 + 2O2 CO2 +2H2O Stoichiometric Air = 9.52 ( 2/0.21 )

125% Air (Burner) = 11.90 ( 9.52 x 1.25 )

Flue Gas: N2 = 9.40 ( 11.9 x 0.79 )

O2 = 0.50 ((11.90 - 9.52) x 0.21)

Flue Gas @ 3200° F : ( Figure D)

CO = 1

H2O = 2

N2 = 9.4

O2 = 0.5

Assume after subtracting heat loss, 12 moles of air will cool flue gas to T2 .

Flue Gas @ T2 :

CO2 = 1

H2O = 2

= 18.88 ( 9.4 + (12 x 0.79) )

N2 O2 Figure C : Example Problem

3200° F

Horizontal T. O.

Heat Loss

= 3.02 ( 0.5 + (12 x 0.21) )

CH 4 = 1.5 x 10 -4 1 ( 1 - 0.99985 )

CO = 1.2 x 10 -3 1 (1 - 0.9988 )

Total dry flue gas = 22.9 moles

[CH4 ] = 6.6 ppmv dry basis

[CO] = 52.4 ppmv dry basis

3

Stack


Figure D is a plot of adiabatic flame temperature, volume percent combustibles and volume

percent oxygen versus percent of stoichiometric combustion air for # 2 fuel oil and natural gas.

The figure indicates a theoretical flame temperature of 3200°F when methane is burned with

125 percent of stoichiometric combustion air (25% excess). In the previous example, air was

used to cool the 3200°F products of combustion leaving the burner to the TO exit temperature

of T 2 .

Meeting stringent pollution control regulations governing the amount of inorganic acids (SOx,

NOx, H 3 PO 4 , Cl2/HCl) and particulate matter in the exit flue gases requires the use of

additional equipment downstream of the basic TO system. This paper furnishes the reader

with a method of selecting the most appropriate waste disposal process.

WASTE CATEGORIES

Wastes are supplied to a disposal process in the form of either gas, liquid or solid, or a

combination thereof. Thus, wastes can be systematically divided into the categories of gas,

liquid, solid, gas+solid, liquid+solid and gas+liquid. Table 1, Industrial Waste and Pollutant,

lists these categories in the left-hand column. Note the absence of a gas+liquid category. A

gas+liquid waste, both fluids, versus a gas-only or liquid-only waste, requires the choice of an

appropriate burner rather than a process.


The second column lists a typical waste for each category, with the related waste pollutant(s) listed

in the third column. For example, a fume stream which is predominantly air containing

approximately one percent (10,000 ppmV) HC is listed as a gas waste, whereas a biosludge is

listed as a liquid+solid waste. Obviously, this second column does not contain all known industrial

wastes. However, it is likely that a particular waste is sufficiently similar to a listed waste so an

appropriate process can be chosen.

The fourth column is a list of process numbers which identify processes applicable to dispose of

waste listed in the corresponding row. For example, Process 6 is used to treat a gas+solid stream

consisting of CO, H 2 O and small combustible particulate.

DISPOSAL PROCESSES

The eight similar but separate processes to dispose of industrial wastes are described by the

following text and diagrams.

Gas or Liquid Waste - High Levels of NOx and/or SOx

The following six diagrams illustrate each of the six configurations of a process to dispose of

either a gas or liquid waste which produces a flue gas containing acceptable amounts of SOx

and/or NOx. Configuration 1.1 is simply a T.O. which is supplied with waste, fuel and

combustion air. Fuel is required when the waste’s combustion energy is insufficient (endothermic)

to produce an appropriate operating temperature. An exothermic waste requires a cooling medium

such as excess air, steam, or water for temperature control.

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Air

Fuel

Tail Gas Organic

Acid

Waste

Configuration 1.1 : Waste Process

Configuration 1.2 is the T.O. fitted with a heat recovery boiler. A boiler with an economizer can

recover as much as 85 % of the heat energy supplied to the T.O. by the waste and the fuel.

Configuration 1.2 : Waste Process

T. O.

6

Stack

FG, NO XA ,SO XA

FG, NO XA

Flue Gas

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Air

Fuel

Waste

Tail Gas Organic

Acid

T. O.

Steam

Boiler

FG, NO XA, SO XA

FG, NO XA

Stack

Flue Gas


Configuration 1.3 shows a T.O. fitted with a gas-to-gas heat exchanger. In the heat exchanger, the

hot flue gas from the T.O. is used to heat the incoming waste gases. This method of heat recovery,

when heating a 60° F waste gas to 800° F with a 1600° F operating temperature, can reduce a

16.8 MM Btu/hr without preheat fuel requirement, to approximately 9 MM Btu/hr.

(Refer to Figure 1A for savings.)

Fuel Savings (%)

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Air

Fuel

Tail Gas Organic

Acid

Configuration 1.3 : Waste Process

70

60

50

40

30

20

10

T. O.

Waste

H. Exchanger

7

FG, NO XA ,SO XA

FG, NO XA

Stack

Flue Gas

Value of Recovered Flue Gas Heat

(Based on 5000 cfm of inert waste gas and 1600°F operating temperature)

0

0 200 400 600 800 1000 1200

Waste Preheat Temp (°F)


Configuration 1.4 is a T.O. fitted with a gas-to-gas exchanger and a heat recovery boiler. The heat

exchanger heats incoming combustion air or waste gases, and the boiler further extracts the heat

available in the flue gas discharged from the exchanger. This configuration offers flexibility in the

amount of steam produced versus fuel usage.

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Air

Fuel

T. O.

Tail Gas Organic

Acid

Waste

H. Exchanger

Configuration 1.4 : Waste Process

Steam

FG, NO XA ,SO XA

FG, NO XA

Boiler

Stack

Flue Gas

Configuration 1.5 illustrates a Catalytic Oxidizer fitted with a gas-to-gas exchanger. The

heat exchanger preheats contaminated air which is routed to chamber containing catalyst

material. The catalyst causes oxidation of the HC to occur at much lower temperatures than

in a thermal oxidizer, thus greatly reducing the fuel usage. The HC content of the air is

generally limited to less the 0.75 % because of temperature limits of the catalyst.

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Fuel

Tail Gas Organic

Acid

Contaminated Air

Catalytic Oxidizer

Configuration 1.5 : Waste Process

8

H. Exchanger

FG, NO XA ,SO XA

FG, NO XA

Stack

Flue Gas


Configuration 1.6 displays a regenerative oxidizer which uses refractory packing to absorb and

transfer heat to the outgoing or incoming air stream. Inlet and outlet ductwork, valves and an

induced draft blower provide the means for the contaminated air to enter and exit the chambers

independently. The paths of flow are controlled by action of inlet and outlet valves. HC contents

is usually limited by the lower flammability limit instead of by overall HC concentration.

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Chamber No 1

Contaminated Air

Fuel

Tail Gas Organic

Acid

Configuration 1.6 : Waste Process

T. O.

FG, NO XA ,SO XA

FG, NO XA

Chamber No 2

Chamber No 3

Stack

Flue Gas

Gas or Liquid Waste - High Levels of SOx or Cl 2 / HCl

The following two diagrams show configurations of a process to dispose of either a gas or liquid

waste which produces flue gas containing excessive amounts of SOx or Cl 2 / HCl.

Configuration 2.1 consists of a T.O., a quench section which cools the flue gas to its saturation

temperature by directly contacting it with water, two adiabatic absorbers which remove inorganic

acids and chlorine, and a vent stack. Water is used in the first absorber to remove a majority of the

HCl from the flue gas. The residual HCl and virtually all the entering Cl 2 leaves the absorber with

the flue gas. A second absorber with caustic is used when either the Cl 2 or HCl in the flue gas

exiting the first absorber exceeds allowable levels. This occurs when excessive Cl 2 is formed in the

T.O. (see Figure 2A for HCl/Cl 2 equilibrium) or when the first absorber is used to make acid.

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

VCM

H FG, NOXA ,Cl2 / HCl

2O

PCB

Caustic

Pesticides

Hydrochloric

Waste

Acid

Air

Fuel

T. O. Quench Absorber Caustic Scrubber

Configuration 2.1 : Waste Process

9

Purge

Salt

Effluent

Flue Gas

Stack


Figure 2A: Equilibrium Constant vs. Temperature

Configuration 2.2 consists of a T.O., a heat recovery boiler which produces steam in

cooling the flue gas to 500° F, two absorbers, and a vent stack. The first absorber is fitted

with a lower section of ceramic packing which cools the 500° F flue gas to saturation

temperature prior to its entry into the acid absorption section, and the second absorber

removes residual HCl and CI 2 .

WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Waste

VCM

FG, NOXA ,Cl2 / HCl

PCB

Caustic

Pesticides

Hydrochloric

H

Steam

2O

Acid

Flue Gas

Air

Salt

Effluent

Fuel

T. O.

Boiler

Configuration 2.2 : Waste Process

Acid

Absorber

10

Caustic

Scrubber

Stack


When the waste stream is highly exothermic, a cooling medium such as air or water or steam is

added to the T.O. to control the flue gases to the boiler.

Figure 2B is an equipment representation of the

system shown in Configuration 2.2., consisting of a

horizontal T.O., firetube boiler, quench column, acidabsorber,

caustic scrubber, and and integral stack.

Waste Liquid

(Exothermic)

Figure 2B : Waste Process

Gas or Liquid - High Levels of NOx

Figure 3 is a block diagram of a two-stage combustion process to dispose of either a gas or liquid

that, if oxidized in a single-stage combustion process, would produce a flue gas containing

excessive amounts of NOx. It consists of the following components:

A reduction furnace in which a high-temperature reducing (less than stoichiometric air)

environment converts the fuel into H 2 , H 2 O, CO, and CO 2 , and the NOx present into N 2 .

A quench section which cools the flue gas to approximately 1400° F by directly

contracting it with a cool recycle gas.

A ReOx furnace which converts the H 2 to H 2 O and CO to CO 2 .

A heat recovery boiler which produces steam in cooling the flue gas to 350° F

Anvent stack.

Waste Liquid

(Exothermic)

Combustion Air

Fuel

Steam

T. O. Boiler

11

Salt Solution

Stack

Make-Up

Caustic

Solution

Absorber

Flue Gas

Quench Section

Scrubber

Acid


WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Fuel

Air

Waste

CO 2

H 2

CO

H 2O

N 2

Figure 3 : Waste Process

Tail Gas Organic

Acid

Reduction Furnace Quench Section

Recycle flue gas cooling in lieu of steam or water is an integral part of this process and helps

maximize heat recovery.

The purpose of the cooling step between the reducing stage and re-oxidation stage is to lower

the fine T.O. temperature. As shown in Figure 3A, a plot of NOx concentration versus

temperature, the amount of thermal NOx produced is a function of operating temperature and

the amount to excess oxygen. For example, when 2% O 2 is present, an operating temperature of

1600° F has an equilibrium NOx value of 42 ppm V; and at 2000° F, it has NOx value of over

200 ppm V. Thus, it is desirable to operate at the lowest practical temperature. Another

consideration is to oxidize the H 2 and CO present to meet air quality regulations. The design

becomes a trade-off between the amount of H 2 and CO allowed and the amount of NOx

allowed in the final product of combustion. Figure 3B is a schematic of a NOxIDIZER®

system.

12

Recycle Flue Gas

Air

FG, NO XA ,SO XA

FG, NO XA

ReOx Furnace

Steam

Boiler

Stack

Flue Gas


WASTE EXAMPLE PRODUCTS OF OXIDATION

Gas

Liquid

Combustion Air

Fuel

Steam

Reduction Furnace

Figure 3B : NOxIDIZER® System

Gas or Liquid Waste - Produces Cl 2 /HCl and NOx

Figure 4 is a example of a process to dispose or either a gas or liquid that produces a flue

gas containing Cl 2 /HCl and excessive amounts of NOx. It consists of several equipment

systems as follows:

A reduction furnace in which a high-temperature reducing environment converts NOx

to N 2 , Cl to HCl and fuel to H 2 , H 2 O, CO and CO 2 .

A quench section which cools the water gas to approximately 1400° F by directly

contacting it with recycle gas.

A T.O. which converts the H 2 to H 2 O, CO to CO 2 and allows the HCl concentration to

reach equilibrium.

An adiabatic absorber fitted with a lower section of ceramic packing which cools the

500° F flue gas to saturation temperature prior to its entry into the acid absorption section

which removes the inorganic acids.

Anvent stack.

Tail Gas Organic

Acid

Recycled flue gas cooling is an integral part of this process to maximize heat recovery.

13

FG, NO XA ,SO XA

FG, NO XA

Recyled Flue Gas

Steam

ReOx Furnace Boiler

Feed Water

Stack


WASTE EXAMPLE PRODUCTS OF OXIDATION

Liquid

Chlorinated Amine FG, Cl2/HCl, NOX Waste

CO2 H2 CO

H2O N2 Recycled Flue Gas

Air

Steam

H2O Or

Caustic

Fuel

Air

Reduction Furnance Quench Section ReOx Furnace Boiler Acid Or Salt Absorber

Figure 4 : Waste Process

If the chlorine-bearing waste steams are separate from nitrogen-bearing waste streams, the

chlorine stream can be admitted to the T.O. directly. The segregation of streams would result

in a smaller reduction furnace and, for endothermic wastes, would reduce the amount of

auxiliary fuel used.

Gas or Liquid Waste - High Levels of Particulates

The following three equipment examples show configurations of a process to dispose of either

a gaseous or liquid waste which produces flue gas containing excessive amounts of particulate

matter.

Configuration 5.1 consists of the following equipment systems:

A T.O.

A quench section which cools the flue gas to its saturation temperature by directly

contacting it with water.

A wet scrubber which removes the particular matter.

A vent stack.

A major advantage of the wet scrubber is its ability to remove both particulates and any

corrosive gases (SO 2 , HCl) in a single operation.

WASTE EXAMPLE PRODUCTS OF OXIDATION

LIQUID/SOLID NaCI SOLUTION

POLYPROPYLENE/CATALYST

H 2O

FG, NOXA , PARTICULATE

2

FLUE GAS

AIR

FUEL

WASTE

T. O. QUENCH WET SCRUBBER

Configuration 5.1 : Waste Process

14

SALT SOLUTION

OR SUSPENSION

STACK

Flue Gas

STACK Stack


Configuration 5.2 consists of the following:

A T.O.

A conditioning tower which, by directly contacting with water cools the flue gas either

600° F or 350° F, depending upon the dry particulate removal system selected.

An electrostatic precipitator (ESP) or a baghouse

A vent stack

WASTE EXAMPLE PRODUCTS OF OXIDATION

LIQUID / SOLID

NaCI SOLUTION

FG, NOXA, PARTICULATE

POLYPROPYLENE/CATALYST

AIR

THERMAL OXIDIZER

CONDITIONING

TOWER

Figure 5.2 : Waste Process

Configuration 5.3 consists of the following major components:

A T.O.

A conditioning tower fitted with a SaltMaster TM system which lowers the flue gas to

below salt fusion temperature by directly contacting it with recycle flue gas.

A heat recovery boiler which produces steam in cooling the flue gas to 350 o F.

Either an ESP or baghouse for particulate removal.

And an unlined vent stack.

The SaltMaster TM system keeps the salt building up in the bottom of the conditioning chamber

Salt build-up can cause operating and maintenance problems. Recycle gas is used for cooling to

maximize heat recovery.

WASTE EXAMPLE PRODUCTS OF OXIDATION

LIQUID / SOLID

NaCI SOLUTION

FG, NOXA, PARTICULATE

POLYPROPYLENE/CATALYST

AIR

THERMAL OXIDIZER

AIR

AND / OR

H 2O

CONDITIONING

TOWER

SaltMaster TM

FUEL

AIR

AND / OR

H 2O

FUEL

Figure 5.3 : Waste Process

ESP

WASTE

INJECTION

600° F

OR 350° F

WASTE

INJECTION

WATER

STEAM

DRY SALT

DRY SALT

BOILER

15

ESP

350° F

SALT SOLUTION OR SUSPENSION

OR

BAG HOUSE

DRY SALT

DRY SALT

FLUE GAS

STACK

BAG HOUSE

FLUE GAS

STACK


Figure 5A is a schematic of a down-fired salt system with a wet particulate removal system

(High Velocity Scrubber). Alternatively, a venturi scrubber may be used. The schematic shown

in Figure 5B is of a down-fired salt system with heat recovery.

Natural Gas

Quench

Pot

Combustion

Air Blower

Figure 5A : Down-Fired Salt System

Natural Gas

Conditioning

Tower

Salt Master TM

Combustion

Air Blower

Fuel Oil or Waste Liquid (Exothermic)

Air or Steam Atomization

Burner Assembly

Waste Liquid Injection (Exothermic)

Air or Steam Atomization

Thermal Oxidizer

Make-Up Water

High Velocity Scrubber

Make-Up Water

16

Vent Stack

Mist Eliminator

Fuel Oil or Waste Liquid (Exothermic)

Air or Steam Atomization

Burner Assembly

Waste Liquid Injection (Exothermic)

Air or Steam Atomization

Thermal Oxidizer

Salt Solution

and / or

Suspension

Soot Blowers

Recycled Gas

Boiler Economizer

Steam Make-Up

Water

Figure 5B : Down-Fired Salt System with Heat Recovery

Recycled Gas

Vent Stack

BagHouse

Dry

Salt

Acid or Salt

Solution or

Suspension


Waste Containing Combustible Fine Solids -

Acceptable Levels of NOx and/or SOx

The following two block diagrams show configurations of a process to dispose of a waste-containing

combustible fine solids (less than 500 microns particle size), which produces flue gas containing

acceptable amounts of SOx and/or NOx.

Configuration 6.1 consists of a cyclonic T.O. in which a high radial gas velocity causes the denser

solid particles to be preferentially “slung” to the wall, thus markedly increasing their retention time.

WASTE EXAMPLE PRODUCTS OF OXIDATION

GAS / SOLID CO + H 2/C FG, NO XA

AIR

FUEL

HOPPER

Configuration 6.1 : Waste Process

CYCLONIC T.O.

Configuration 6.2 shows a cyclonic T.O. fitted with a heat recovery boiler which produces steam

to lower the flue gas temperature to 350° F.

17

STACK

FLUE GAS

WASTE EXAMPLE PRODUCTS OF OXIDATION

GAS / SOLID

CO + H2/C FG, NOXA AIR

FUEL

HOPPER

CYCLONIC T.O.

Configuration 6.2 : Waste Process

STEAM

BOILER

STACK

FLUE GAS


Gaseous Wastes Containing Combustible Fine Solids -

Acceptable Levels of NOx and/or SOx

The following two diagrams illustrate configurations of a process to dispose of a gaseous waste

containing a combustible fine solid (less than 500 microns) which produces flue gas containing

acceptable amounts of SOx and/or NOx and excessive amounts of particulate.

Configuration 7.1 consists of the following equipment:

A cyclonic T.O.

Either a quench column, which by directly contacting the flue gas with water, cools it to its

saturation temperature; and a wet scrubber which removes the particular matter or a conditioning

tower, which by directly contacting the flue gas with water and/or air cools it to either 600° F to

350° F, depending on the dry particulate removal system selected.

An ESP or baghouse.

An unlined vent stack.

WASTE EXAMPLE PRODUCTS OF OXIDATION

GAS / SOLID

SOLID

AIR

FUEL

HOPPER

CYCLONIC T.O.

Conditioning

Tower

CO + H 2/C + ASH

COAL FINES

Quench

OR

350° F

Configuration 7.1 : Waste Process

Configuration 7.2 consists of the following major equipment:

A cyclonic T.O.

A hot cyclone for large particulate removal and/or conditioning tower which by directly

contacting the flue gas with recycle gas cools it to below ash fusion temperature.

A heat recovery boiler which produces steam in cooling the flue gas to 350 F.

Either an ESP or baghouse for particulate removal.

An unlined vent stack.

Recycle gas is used for cooling to maximize heat recovery.

18

H O

2

Wet Scrubber

DRY ASH

DRY ASH

BAG HOUSE

FG, NO XA,PARTICULATE

FG, NO XA,PARTICULATE

Make-Up Water

ESP

STACK

FLUE GAS


WASTE EXAMPLE PRODUCTS OF OXIDATION

GAS / SOLID

SOLID

CO + H2/C + ASH

COAL FINES

FG, NOXA, PARTICULATE

FG, NOXA, PARTICULATE

STEAM

HOPPER

ESP

AIR

350° F

FUEL

CYCLONIC T.O.

Configuration 7.2 : Waste Process

Wastes Containing Combustible Solids

Figure 8 is a diagram of a process to dispose of a waste that contains combustible solids in the

particle size range of 10 to 500 microns that produces a flue gas containing excessive amounts of

NOx. It consists of the following major components:

• A cyclonic reduction furnace in which a high radial velocity, high temperature, reducing (less

than stoichiometric air) environment converts the bound nitrogen to N 2 and the fuel to water gas.

• A quench section which cools the water gas to approximately 1400° F.

• A heat recovery boiler which produces steam in cooling the flue gas to 350° F.

• An unlined vent stack.

DRY ASH CONDITIONING

TOWER

HOT CYCLONE

Recycle flue gas cooling is an integral part of the process to minimize NOx formation and

maximize heat recovery.

19

BOILER

Recycled Gas

350° F

DRY ASH

DRY ASH

BAG HOUSE

WASTE EXAMPLE PRODUCTS OF OXIDATION

GAS / SOLID

SOLID

HOPPER

FUEL

AIR

Water Gas

CO 2

H 2

CO

H 2O

N 2

CYCLONIC REDUCTION

FURNACE

Figure 8 : Waste Process

MELAMINE SLURRY

DNT CELLULOSE

QUENCH

RECYCLED GAS

AIR

FG, NOx

FG, NOx

T.O

OR

STEAM

BOILER

FLUE GAS

STACK

FLUE GAS

STACK


SUMMARY

The description of pollutant control processes found in this paper is a tool which can be used

to identify the basic process needed to destroy pollutants in various types of waste streams.

Although this “cookbook” approach is a simplified version of the real world method of

specific equipment selection, it provides a good general understanding of what process is

best-suited for the destruction of various pollutants found in today’s industries.

20

More magazines by this user
Similar magazines