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. organics. These organics are present in the the feed water, water, in relatively small concentrations. 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. 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.
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
but 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
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
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
THE JAEGER ADVANTAGE
Typical Steam Stripping Applications
Benzene removal from waste waters Sour water (H 2S and NH3) 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
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 Your Reference Description of problem, diagram:
Fax Date
Utilities Available: Heating medium:
Saturated steam for steam:
Coolant:
Heat transfer oil
pressure
Hot water
psi,
Water
temperature
F
°
Brine
Temperature
Inlet--summer
F,
°
Outlet--maximum
F,
°
winter
F
°
minimum
F
°
Mass balance for continuous rectifying column
Streams
Feed Distillate Bottom product Steam
F D B S
= = = =
lb/h lb/h lb/h lb/h
Composition of streams or desired purities
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
1
2
3
4
5
Total
Data for separation problem
Column operated:
continuously
Maximum bottom temperature tolerated
°
or head pressure
intermittently
F, bottom pressure
psia
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
(section B)
=
-
%
Total
Loading
Nominal load = 100% (Load range)
Column head:
Gas
GD =
lb/h
M
=
lb/lbmol pD =
psia
Liquid
LD =
lb/h
ρL
=
lb/lbmol tD =
°
Gas
GB =
lb/h
M
=
lb/lbmol pB =
Liquid
LB =
lb/h
ρL
=
lb/lbmol tB =
Bottom:
Feed I h
liquid at boiling point d
f
i i
i ?
vapor /
partly vapor
F
psia F
°
flash
%
PHYSICAL DATA OF THE PURE COMPONENTS
Table 2 Designation of components Name of components Molecular Weight
Units
2
3
4
5
lb/lbmol
F (liquid)
lb/ft
Dynamic viscosity G: vapor _____ F
cp
Density
1
°
G
L
p/H
t( F)
G
L
G
L
G
L
G
°
L: liquid _____ F °
Heat of evaporation Boiling point (Vapor pressure curves) of the pure components) or Antoine constants log p = A - B/(C+t) or Henry s constants (H)
Btu/lb p or H in atmosphere
A= B= C=
°
A= B= C=
A= B= C=
JPI\1996STMT.DOC
A= B= C=
A= B= C=
L
