Literature - Steam Stripping

Steam Stripping
Stream stripping for water clean-up is essentially a distillation
process where the heavy product is water and the light product is a
mixture of volatile organics. These organics are present in the feed
water, in relatively small concentrations. Since the volatility of the
organics is a very strong function of temperature, the high stripping
temperature inherent in stream stripping allow for the removal of
heavier more soluble organics that are not strippable with air. No
off-gas treatment is needed ad the only wastestream generated is a
small amount of very concentrated organics.
The Jaeger Advantage
Jaeger Products, Inc. has extensive experience in the successful
design of steam stripping systems for organic removal and recovery.
Our engineering staff can provide you with a complete process
design, and with the necessary engineering, specify the contacting
column in detail. We have c complete line of packings, trays, and
tower internals that can satisfy any steam stripping need.
Typical Steam Stripping Applications
Benzene removal from wastewaters
Sour water (h2O and NH3) stripping
Acetone removal/recovery from wastewaters
Oxygenate (MTBE. MEK) removal/recovery
Removal of chloroform, bromoform and
other halogenated organics from water
Removal of organics from quench waters
Organics recovery from leachates
Alcohol (ethanol, propanol, IPA, butanol)
removal from water
Solvents recovery or removal
(tetrahydrofuran, hexane, heptane)
Superior performance by design
JAEGER PRODUCTS, iNC.
1611 Peachleaf, Houston, Texas 77039
Phone:(281) 449-9500 Fax: (281) 449-9400
(800) 678-0345
http://www.jaeger.com

Removal of Organics From Water Using Steam Stripping
Jaeger Products, Inc
Houston, Texas
Dilute mixtures of organic materials in water can be concentrated by a process known as steam stripping.
The end products of such operation are a clean water stream almost devoid of organic materials, and a
highly concentrated organic stream suitable for recycle to a process or for disposal. The use of heat in the
form of steam as a separating agent offers significant advantages over other methods, such as inert gas (air)
stripping.
WHY USE STEAM STRIPPING?
Steam stripping for water clean-up is essentially a distillation process where the heavy product is water and
the light product is a mixture of volatile organics. These organics are present in the feed water in relatively
small concentrations. The process of steam stripping takes place at high temperatures compared to air
stripping, usually very close to the boiling point of water. Since the volatility of the organics is a very strong
function of temperature, the high stripping temperatures inherent in steam stripping allow for the removal
of heavier, more soluble organics that are not strippable with air.
Another very important feature of steam stripping is the fact that no off-gas treatment is needed, and that
the only waste stream generated is a small amount of very concentrated organics. These are easily dealt
with by incineration, biological treatment, or recycled to process.
In summary, steam stripping is a good solution for wastewater streams that contain fairly soluble,
non-volatile organics and where no off-gas stream is desired. On the other hand, steam striping does
necessitate the presence of steam (or process heat) and would tend to be more capital intensive than air
stripping. Ideal settings for steam stripping are oil refineries, petrochemical, and chemical plants.
WHAT IS STEAM STRIPPING?
A wastewater stream is heated and put in intimate contact with steam in a packed or trayed tower. The
combined effects of the steam and heat, or temperature cause organic material to transfer from the liquid
to the vapor phase. This material is then carried out with the vapor. As contacting proceeds down the
tower, the wastewater becomes leaner in the organic material while the vapor phase becomes more
enriched as it travels up the tower.
Steam is injected at the bottom of the tower to provide heat and vapor flow. Clean water leaves the bottom
of the tower. The wastewater is fed at the top of the tower and the steam leaves the top heavily laden with
organic material. This steam/organic combination is condensed and processed further as detailed in the
next few pages. The net effect achieved in the steam stripper and condenser is that a contaminated
wastewater and steam are injected into the tower and a clean water stream is obtained. A low-volume,
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ut concentrated water/organic mixture, is also obtained as a by-product.
WHAT DOES A TYPICAL STEAM STRIPPING UNIT LOOK LIKE?
The configuration of a steam stripping unit can vary depending on the characteristics of the organic material
to be removed, and on what is to be done with it in terms of disposal and recycle. As a minimum, a steam
stripping unit will look like the unit depicted in Figure 1. It is important to note that heat recovery from the
bottom product is necessary for economical operation. Operations at reduced pressure do not need
recovery exchangers, but operate at lower temperatures and larger steam rates. The towers also tend to
be a bit larger in vacuum operations.
Steam requirements for stripping vary with the operating pressure, the type of organic, and the degree of
organic removal/recovery. Further, steam requirements for heat balance purposes need to be accounted
for. A very important consideration in the design of a steam stripper is the fact that the column needs to
be capable of handling enough steam flow to operate without the benefit of the recovery exchanger. This
feature will be needed during start-up and when the exchanger is out of service for cleaning.
Some organic materials are not totally miscible in water and separate into a distinct organic phase when
the concentration exceeds the solubility limit. Most aromatics and halogenated organics fall in this
category. Steam stripping applications for these types of compounds can be very effective, since a good
part of the concentration of the organic can be accomplished in a decanter as indicated in Figure 2. In this
case, the water layer is recycled to the stripping column for reprocessing. The design of the decanter poses
some interesting questions since the water flow is generally significantly larger than the organic flow.
Furthermore, in some cases (benzene, toluene, etc), the organic layer is the lighter of the two liquid phases.
In applications involving halogenated organics, the organic liquid is heavier than water. Needless to say,
good models to predict the phase behavior of the system in question are essential.
Figures 3A and 3B are refined versions of the flowsheet in Figure 2. These arrangements are needed when
better organic recoveries are needed from more dilute streams. The selection between Figure 3A and 3B
depends solely on the equipment sizing. Figure 3A is used when required steam flows are larger (less
volatile compounds).
Figure 4 is applicable when the organic material to be removed exhibits very high solubility in water. In this
case, a refluxed distillation column is needed to achieve high organic concentrations.
Other variations on the same flowsheets shown above include the use of reboilers instead of direct steam
injection and operation at reduced pressure to reduce operating temperature.
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CHEMISTRY, CHEMISTRY, CHEMISTRY!!
It is of crucial importance that the designers and operators of steam strippers understand the chemistry of
the system, since lack of operability and maintenance problems occur frequently because of faulty
chemistry.
This is of particular importance in systems that include a multitude of pollutants, since interaction among
them can be large. An excellent example is the typical mixed wastewater from a chemicals manufacturing
facility that includes inorganic acids, organic pollutants, and dissolved gases. As the gases, such as CO2
and or NH3, are stripped, the pH of the water changes causing potential solids precipitation. This is
aggravated by the fact that steam stripping temperatures often exceed the precipitation temperature for
salts, such as calcium carbonate.
The volatility of the compounds to be stripped is often affected by the water chemistry present. Accurate
predictions of the volatility are of extreme importance for proper stripper design; the operators of stripping
systems should always be aware that changes in the chemistry of the incoming water can affect the
removal efficiencies observed in the stripper.
Jaeger Products, Inc. has more experience than any other mass transfer supplier in tackling tough stripping
problems from the chemistry to the equipment.
SOME PITFALLS IN STEAM STRIPPING SYSTEM DESIGN.
Several aspects of the design of steam stripping systems are very crucial and not immediately obvious.
First is the accuracy and reliability of equilibrium data. Steam stripping is a situation where the old reliable
Henry's law just isn't applicable due to the broad concentration ranges, high temperatures, extensive
interactions between components, and the existence of two liquid phases. The thermodynamic model of
choice for steam stripping systems is one based on activity coefficients that can predict immiscibility. No
model fits this function better than the NRTL activity coefficient model (non-random two liquid model
developed by Prausnitz and co-workers). Pilot and laboratory tests to establish the adjustable parameters
in the NRTL model for the mixture in question are advisable, but solubility and vapor pressure data can
suffice as a good approximation.
Wastewaters can be very fouling, especially when the temperature is raised and inorganic salts precipitate.
In typical steam stripping configurations, most of the fouling will occur in the recovery exchanger and
design provisions are needed to allow for frequent cleaning. In the absence of a recovery exchanger, the
brunt of the fouling will be taken by the stripper itself. In such cases, the use of trays can be a way to avoid
plugging even though packings would yield better performance characteristics. The use of sequestering
agents is also a good solution for reliable and lengthy operation.
Materials of construction need be some grade of stainless steel or a high performance plastic due to the
varied and changing nature of the water chemistry. Capital savings by use of lesser materials of
construction generally translate into severe problems and added expense later.
Start-up of any steam stripper requires heating of the feed water to the operating temperature in the
stripper. This added heat has to be supplied in the form of steam at the bottom of the stripper. Design
provisions need to be made to accommodate this larger, but temporary, steam flow in the stripper. This
capability is also desirable to allow for continued operation while cleaning of a fouled recovery exchanger
takes place.
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Design at low stripping steam rates is desirable since it reduces the downstream processing requirements.
Figure 5 illustrates how sensitive the process is to steam flow. Optimum designs require stripping factors
between 1.5 and 4. These stripping factors mandate more stages for separation and taller packed heights.
Design under these conditions becomes very sensitive to the reliability of the equilibrium data and the mass
transfer models. This is also the case where excellent packings and internals are necessary and where
vendor experience in design of steam stripping systems is invaluable.
THE STEAM STRIPPER AND OTHER COLUMNS IN THE SYSTEM.
The contacting devices in the steam stripping system are where the mass transfer takes place. They are
vertical countercurrent vessels filled with a mass transfer device. In general, these devices are either sieve
trays, random packings, or structured packings (the level of efficiency and capacity follows the same order
and so does their sensitivity to fouling).
The columns are also equipped with liquid distributors and support plates for the packing. In the case of
deep bed requirements, intermediate liquid collectors and redistributors are also installed to ensure good
performance. Figure 6 shows different combinations of internals that can be installed in a steam stripper.
In most cases though, only combinations of trays and packings (with the associated internals) are used.
Jaeger Products, Inc. offers all internal devices necessary for steam strippers and distillation columns in
a variety of designs and materials to suit the application.
HOW CAN JAEGER HELP YOU IN STEAM STRIPPING APPLICATIONS?
Jaeger Products, Inc. has extensive experience in the successful design of steam stripping systems for
organic removal and recovery. Our engineering staff can provide you with a complete process design, and
with the necessary engineering, specify the contacting column in detail, and supply you with all process
specification for the peripheral equipment as illustrated in Figure 7. Our database is very extensive and
chances are there are very few organics we have not tackled. We can simulate and optimize a complete
steam stripping and solvent recovery unit using the most advanced and comprehensive models. Our
calculations will account for unusual vapor/liquid equilibria and will incorporate the best mass transfer
efficiency rating methods available.
We have a complete line of packings, trays, and tower internals that can satisfy any steam stripping needs.
The performance of the system depends heavily on the correct internals selection as well as on a good
process design; Jaeger can assist you with both so that total responsibility is easily identified. Although
we normally do not provide turn-key systems, we can direct and/or assist you in such a project. We can
also put you in contact with a systems manufacturer that would provide a turn-key project with Jaeger
engineering and hardware.
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THE JAEGER ADVANTAGE
Typical Steam Stripping Applications
Benzene removal from waste waters
Sour water (H 2S and NH 3) stripping
Phenol recovery
Acetone removal/recovery from waste waters
Oxygenate (MTBE, MEK) removal/recovery
Removal of chloroform, bromoform and other halogenated organics from water
Removal of various organics from quench waters
Concentration and organics recovery from leachates
Alcohol (ethanol, propanol, IPA, butanol) removal from water
Solvent recovery or removal (tetrahydrofuran, hexane, heptane)
Steam stripping facts
Capable of achieving very high removals and low effluent concentrations
Most economical removal technique at feed concentrations above 0.1% weight organics
Cost effective at feed concentrations as low as 200 ppm
Can produce a re-usable concentrated product
Minimizes air emissions
Reduces loads to incineration
Can be operated at vacuum or pressure depending on needs with little penalty
Can be made very energy efficient with heat recovery
Fouling is a continuous concern
Typical hardware for steam strippers
Sieve trays for fouling service (SS, Monel)
Metal random packings for most applications (SS, Monel)
Plastic random packings for acid service (GFPP, Noryl, PVDF, Teflon)
Metal structured packings for high efficiency/capacity (SS, Monel, Aluminum)
Column internals to include: distributors, redistributors, supports, and mist eliminators
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STEAM STRIPPING
Application information for design
(Copy, fill out, and fax pertinent information and we will be glad to assist you with a design.)
Company
Person Responsible
Address
Telephone Fax
Your Reference Date
Description of problem, diagram:
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Utilities Available:
Heating medium: Saturated steam Heat transfer oil Hot water
for steam: pressure psi, temperature °F
Coolant: Water Brine
Temperature Inlet--summer °F, winter °F
Mass balance for continuous rectifying column
Streams Feed F = lb/h
Distillate D = lb/h
Bottom product B = lb/h
Steam S = lb/h
Composition of streams or desired purities
Outlet--maximum °F, minimum °F
Please place a check against the units in which the specification is made:
lb/h Weight % Mole fraction PPM PPB
Table 1A
Component (I)
Name
Mole Mass
Feed F
Distillate D
Bottom
1 2 3 4 5 Total
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Data for separation problem
Column operated: continuously intermittently
Maximum bottom temperature tolerated °F, bottom pressure psia
or head pressure psia, and maximum pressure drop tolerated psi
Calculated pressure performance data (if separation problem has been calculated by the customer)
Number of theoretical stages in rectifying section (section D) =
in stripping section
Total
(section B) =
Loading Nominal load = 100% (Load range) - %
Column head: Gas G D = lb/h M = lb/lbmol p D = psia
Liquid L D = lb/h ρ L = lb/lbmol t D = °F
Bottom: Gas G B = lb/h M = lb/lbmol p B = psia
Liquid L B = lb/h ρ L = lb/lbmol t B = °F
Feed liquid at boiling point vapor partly vapor flash %
Is there danger of precipitation? yes/no
foaming? yes/no
Column sizing by Jaeger by customer
Column internal diameter in.
Packing type total h eight ft.
Number of sections , rectifying section , stripping section
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Table 2
PHYSICAL DATA OF THE PURE COMPONENTS
Designation of components Units 1 2 3 4 5
Name of components -
Molecular Weight lb/lbmol
Density °F (liquid) lb/ft
Dynamic viscosity
G: vapor _____ °F
L: liquid _____ °F
Heat of evaporation Btu/lb
Boiling point
(Vapor pressure curves)
of the pure components)
or
Antoine constants
log p = A - B/(C+t)
or
Henrys constants (H)
cp
p or H
in
atmosphere
G L G L G L G L G L
p/H t(°F)
A= A= A= A= A=
B= B= B= B= B=
C= C= C= C= C=
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