''
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-139 Sept. 1984
Project Summary
Process Design Manual for
Stripping of Organics
Harish M. Shukla and R. Edwin Hicks
Procedures and correlations for de-
signing and costing stripping towers for
the removal of organics from aqueous
streams are presented. The emphasis is
on practical methods suitable for engi-
neering estimates. The designs cover
steam strippers with and without con-
densers and reflux, as well as air
stripping. Steam stripping is treated as
an isothermal process and simplified
equations for determining tower height
may be used. Determination of the
height adiabatic air strippers involves a
tedious, iterative solution of heat and
material balances. A BASIC computer
program for carrying out these calcula-
tions is provided.
Capital costs are determined, essenti-
ally, by estimating the quantity of
materials required in conjunction with
material costs. Cost factors for a range
of materials and installation factors are
suggested. Methods for costing ancil-
lary equipment such as heat exchangers,
pumps, compressors, and storage ves-
sels are included. It is recommended
that vendor quotes be obtained wher-
ever possible. Typical operating costs
for energy and maintenance are also
given.
This Project Summary was developed
by EPA's Industrial Environmental He-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Stripping is one of several processes
used commercially for separating organ-
ics from water and wastewater. The
selection of the optimum process for any
given application is dependent on the
characteristics of the organics as well as
on other factors including cost and the
need to recover the separated organics.
In the case of a mixture of organics
having different properties, two or more
treatments in series may have to be
provided. The use of two different pro-
cesses, for example, one with cost de-
pendent on throughput, followed by a
polishing step having cost dependent on
feed concentration, can result in a lower
overall treatment cost. In a wastewater
treatment train, stripping is typically the
first process that separates dissolved
substances. It follows clarification or
filtration steps that are used for removal
of suspended solids and may precede
polishing steps such as carbon or resin
adsorption.
The essential characteristic that deter-
mines the effectiveness of stripping in
separating dissolved organics is the rela-
tive volatility or vapor pressure of the
organic above the aqueous phase. It has
been shown that at least half of the 186
organics on the USEPA's toxic pollutant
list are sufficiently volatile to be effectively
removed from aqueous waste streams by
stripping. Sixty-eight of these can be very
easily stripped by air at ambient tempera-
tures. Others can be stripped by air at
ambient temperatures with steam. The
remaining substances on the list have
relatively low vapor pressures and are not
easily stripped.
Stripping is emerging as a cost-effective
alternative for treating a wide range of
aqueous streams containing organics. It
may be used both as an in-plant process
for the recovery of organics from relatively
concentrated aqueous streams and as an
end-of-pipe treatment for removal of
dilute and even trace quantities of organ-
ics from wastewaters prior to discharge
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or recycle. Steam stripping is typically
used for in-plant separation, whereas air
or steam may be used for end-of-pipe
treatment, depending on the volatility of
the organics and post-treatments pro-
vided. In addition, air stripping is being
increasingly used for the removal of
trihalomethanes (THMs) and trichloro-
ethylene (TCE) from drinking water
supplies.
Purpose
The purpose of this manual is to provide,
within a single document, both data and
procedures for designing and costing
stripping systemsfor organics separation.
A major objective was to develop and
summarize simplified and practical engi-
neering procedures of study grade ac-
curacy. The designs and costs obtained
are suitable for evaluating the feasibility
and viability of stripping relative to other
control technologies and for checking
commercial designs. They are not in-
tended for detailed or definitive designs.
Scope
The design procedures cover:
1. Tray and packed towers
2. Air and steam stripping
3. Live and reboil steam
4. Refluxed and non-refluxed steam
stripping
5. Isothermal and adiabatic operation
6. Continuous operation
7. Ancillary equipment including heat
exchangers
The design and cost procedures are
summarized in a stepwise fashion to
facilitate their routine use. Procedures for
using the simplified analytical equations
appropriate to most stripping applications
are demonstrated by means of a worked
example. A BASIC program suitable for
desk-top computers is provided for the
case of adiabatic air stripping where the
usual simplified equations are less reli-
able. A comprehensive review of the
theory of stripping and the development
of the design equations is also included.
Although the manual is not intended as a
text, the reader may find the background
material useful as a refresher course in
stripping. We recommend that all users
scan the background sections, particularly
with reference to the limitations on the
procedures and data.
The process design is oriented towards
single-component relatively dilute sys-
tems. Other systems can nevertheless be
handled as well. For example, multicom-
ponent systems can be sized by designing
for the least volatile organic, and then
determining the distribution of the other
components separately. Use of the simpli-
fied design correlations for concentrated
streams may result in errors due to
thermal effects and deviations from
vapor-liquid equilibrium correlations. The
more rigorous design equations may,
however, be used without difficulty pro-
vided the necessary enthalpy and equi-
librium constant data are available.
The design of ancillary systems such as
decanters and other vapor handling
equipment is specifically not handled.
Multiple towers and batch stripping are
also not treated. Maintenance and opera-
tional problems are not discussed, and
controls, instrumentation, and civil design
are not covered. The cost of these items is
nevertheless included in the budget
estimates.
Harish M. Shukla andR. Edwin Hicks are with Water General Corp., Waltham, MA
02154.
Kenneth A. Dostal is the EPA Project Officer (see below).
The complete report, entitled "Process Design Manual for Stripping of Organics,"
(Order No. PB 84-232 628; Cost: $14.50, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
-Cf\JS GOVERNMENT PRINTING OFFICE, 1984 — 759-015/7811
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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