''
 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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