FOR LIMITATION
OF CONTACT  SULFURIC ACID
PLANT EMISSIONS
 ENVIRONMENTAL PROTECTION AGENCY

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                        APTDOG02
GUIDELINES FOR LIMITATION
OF  CONTACT SULFURIC ACID
      PLANT EMISSIONS
    Division of Control Agency Development
      ENRIRONMENTAL PROTECTION AGENCY
       Air Pollution Control Office
     Research Triangle Park, North Carolina
            January 1971

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The APTD ( Air Pollution Technical Data )  series of reports is issued
by the Air Pollution Control Office of the Environmental Protection
Agency to report technical data of interest to a limited readership.
Copies of APTD reports are available free  of charge to APCO staff
members, current contractors and grantees,  and nonprofit organiza
tions - as the supplies permit  - from the Office of Technical Informa-
tion and Publications, Air Pollution Control Office, Environmental
Protection Agency, Research Triangle Park,  North Carolina 27709.
      Air Pollution Control Office Publication No. APTD-0602
                                   ii

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                            CONTENTS
INTRODUCTION	1
EMISSIONS AND CONTROL TECHNOLOGY	3
   Sulfur Dioxide	3
   Acid  Mist	5
   Sulfur Trioxide 	   5
SAMPLING AND  MONITORING	7
SUMMARY  OF  SUGGESTED LIMITS	9
REFERENCES	11
                                  iii

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         GUIDELINES  FOR  LIMITATION
          OF  CONTACT  SULFURIC  ACID
                  PLANT  EMISSIONS

                         INTRODUCTION

     This document was  prepared by  the Air Pollution Control Office
 (APCO)  to assist state  and local regulatory agencies in the preparation
 of emission control regulations for contact sulfuric acid plants.  It
 is advisory in nature,  not prescriptive; and it  in no way infers or
 represents national emission standards.  It recognizes the importance of
 of economic considerations, but it  does not specifically relate the
 suggested limits to the economy of  any sulfuric  acid plant to which
 they may be applied.  This is not to say that any of the emission limits
 suggested here are economically unrealistic.  Most of them have, in fact,
 been achieved in commercial installations.
     The types and sources of air pollution in the contact sulfuric
 acid plant are discussed, and guidelines based on optimal use of avail-
 able control technology are presented to assist  agencies in developing
 regulations compatible  with local conditions.  There is, however, no
 attempt to give detailed descriptions of either  the contact sulfuric
 acid process or the recommended control techniques.  The latter may be
 found in a study of the sulfuric acid industry sponsored by APCO's
 Division of Process Control Engineering1 and in  a joint study shared
 by the  Manufacturing  Chemists' Association and the U.S.  Public Health
 Service (MCA-PHS).2
     All emissions are  presented as pounds per ton of 98 percent sul-
 furic acid produced (Ib/ton)  and as pounds per hour emission rates.
 The conversion curve  (Figure 1) will assist the  reader in making
 a transition between  these mass emission rates and the commonly used
 concentration units,  parts per million (ppm)  and milligrams per stand-
ard cubic foot (mg/SCF).  Mass emission rates  have been used because
they  are recommended  as more  practical for assessing the output of
individual plants,  and are not subject to circumvention by dilution.

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    10,000
                         S02 EMISSIONS, Ib/ton acid

                       10            100           1000
                                                       10,000
  i
 UJ
 u
 o
 o
   CM
 8
      1000
100
       10
                                                           100   u.
                                                                u
                                                                CO
                                                                V,
                                                                 O>
                                                                O
                                                                I—

                                                           10    K
     U
     o
     o
      CO
     O
     co
1.0   o
         0.01            0.1            1.0            10           100
                 S03  AND ACID MIST EMISSIONS, Ib/ton acid
                                                                 0.1
                                                                       U
            Figure 1. Conversion scale relating concentration and mass
                    emissions for S02.  803, and acid mist.
     The recommendations presented  are  based on information gathered

from the two  Studies mentioned above; from discussions with members of

APCO  divisions   and representatives of private industries  and state

and local regulatory agencies; and  from the current literature.

     Ideal maximum and minimum emission levels for sulfur oxides are

dependent on  local conditions and cannot be recommended  in  a document

of this nature.   The emission levels given herein are offered as guide-

lines to be incorporated in local regulations.

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          EMISSIONS AND  CONTROL  TECHNOLOGY
     Sulfur  dioxide  (SO-),  sulfur  trioxide  (SO,), and acid mist in the
absorber tail gas  are  the principal air pollutants emitted from a con-
tact sulfuric acid plant.   All  three present potential health hazards,
and the emission levels  can be  greatly reduced with the careful appli-
cation of currently  available technology.
Sulfur Dioxide
     Sulfur  dioxide  is emitted  from a contact sulfuric acid plant
absorber when conversion of the S0_ to SO,  is incomplete.  Large quanti-
ties of unconverted  SO.  then pass  through the absorber and into the
atmosphere.   These emissions, left uncontrolled, can average about
60.0 Ib/ton  of acid  produced, in a  plant with a conversion efficiency
of 95 to 96  percent; this represents a range of 50 Ib/hr for a 20-ton/
day plant to about 12,000 Ib/hr for a 4800-ton/day plant.  It is tech-
nologically  possible,  however,  to  reduce SO- emissions to one of three
levels.
Alter Operating Conditions
     The emissions can be reduced  to about  35 Ib/ton acid by altering
operating conditions such as catalyst quantity and quality and reaction
gas composition,  temperature, and residence time in the converter.^
Commercial Control Processes
     Data from new plants using a dual absorption process in the con-
verter system show emission rates  reduced to 6.5 Ib/ton acid.3>^>5
Such plants are in commercial operation in  Europe and Japan.   In such
a process, the S02 is  first partially converted to SO,, which is absorbed
in  the primary absorber. Additional conversion is achieved by sending
the off-gases containing S02  through a second converter.  This gives
overall SO. to SO, conversion  efficiencies  of 99.5 percent, since
equilibrium favors greater  conversion at the high O./SO. ratio that is
normally present  in the primary absorber off-gases.
     No existing  contact plants have been converted to dual absorption
in  the United States,  but  the systems are being offered  commercially.
Conversion of an  existing  contact plant  to  dual absorption does not

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 represent anything unusual or exotic in the chemical  processing
 industry.  It only requires the installation of an  additional absorber,
 heat exchanger, and associated piping.
      Other commercially available control processes for  existing plants
 are also capable of reducing emissions to the  6.5-lb/ton-acid level.
 In most United States plants the Cominco process  is being used, but the
 Wellman-Lord process is operating in one acid  regeneration plant. '
                                                            •I  Q
 The Sulfacid process is in commercial operation in  Europe, >   and a
 slaked-lime scrubbing system is being used to  remove  SO. and  SO. from
 a plant in Japan.
 Pilot-Scale Reductions
     Absorption processes using magnesium oxide and  sodium carbonate
(Na.CO,) have also been evaluated on the pilot-scale level and show
particular promise of reducing the total SO., in tail  gas emissions
                   1                       ^
to 2.0 Ib/ton acid.
Relative Merits of Available Controls
      A  comparison of  the  total  S0_  emissions  from a contact sulfuric
acid plant  (1)  with no  control,  (2)  with either dual-absorption or
commercially  available  SO.  control  processes,  and (3)  with promising
pilot-scale SO. control processes  is presented in Figure  2.
  10,000
    10
                   100           1000          10,000         100,000     1,000,000
                 PLANT PRODUCTION OF 98% SULFURIC ACID, tons/day
         Figure 2. Attainable S02 emission levels from contact sulfuric acid plants.

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     Installation of a dual-absorption plant would not only reduce the
SC>2 emissions by 85 to 90 percent from conventional plant levels, but
the additional cost of an added heat exchanger and absorption tower
would also be partially offset by the increased conversion efficiency.^
It should, however, be emphasized that the installation of a dual-
absorption plant does not necessarily mean that further controls would
not be required or that use of the dual absorption process in the con-
verter will eventually solve all of the SO,, emission problems in the
contact sulfuric acid plant.  The short stack, high-SO- concentration,
and cool stack-gas temperature could still present other problems in
meeting ambient-SO. air quality standards.
Acid  Mist
     Acid mist formation occurs in the contact sulfuric acid plant in a
number of ways, any or all of which may be operative in an individual
situation.  Hydrocarbons in the sulfur burn and produce water vapor
that  subsequently  combines with SO, in the economizer or in the
absorber.   Operating  concentrations and temperatures can favor mist
formation  in  the absorber.  Nitrogen oxides formed in the furnace may
oxidize  the SO.  in the stack gas to SO..  When SO  is present in a
stack gas,  it will combine with water in  the atmosphere and form a
plume of  acid mist.
      Acid  mist usually appears as a dense white plume; however, the
absence of  a  plume does not mean that there is no mist present, only
that  few of the particles are in the visible-size range.  Mist particles
range  from  0.3 to  5.0 microns in diameter.  In plants with an oleum
tower, the  percentage of submicron particles is greater, compounding
the emission  problem because the smaller  mist is more difficult to
collect.
     Without  controls, the acid-mist emissions can amount to 3 to 12
Ib/ton acid.  Effective control is possible, however.  Commercially
available mist eliminators and electrostatic precipitators can reduce
the total acid mist emissions to about 0.5 Ib/ton of acid produced. ''^
Sulfur Trioxide
     Proper design and operation of the absorption tower is the best
assurance against serious SO, emissions.   Under ideal conditions
                                       12
they should not exceed 0.2 Ib/ton acid.  '    Serious SO, emissions
usually occur  with plant  startup and plant upsets, but continuous
SO, emissions  in  excess of 0.2 Ib/ton are indicative of inefficient
absorber  operation.

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      The SO. and acid emission levels recommended in Figure  3  are
 consistent with attainable levels  reported in  the literature.1'2
   1000
i  100
Q
U
Q
Z
c?
    10
   1.0
                   100           1000           10,000          100,000
                 PLANT PRODUCTION OF 98% SULFURIC ACID, tons/day
                 Figure 3. Attainable acid mist and 50$ emission levels.
                                                                       1,000,000

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                  SAMPLING  AND MONITORING

     Since the value of  any  chemical  determination of emission concen-
trations is only as good as  the  sampling procedures and analytical
techniques used, it is  strongly  recommended  that prescriptions for
sound analytical techniques,  and the  best available sampling equipment
and procedures be incorporated into proposed regulations.
     It is recommended  that  the  most  serious type of pollution, SO ,  be
monitored on a continuous basis.   Several manufacturers have commer-
cially available equipment that  can easily be adapted to do continuous
monitoring of the SO--tail-gas emissions.  It is also recommended that
the SO, and acid-mist emissions  be determined regularly, either once
each work shift or every 8 hours.
     The modified Monsanto Company technique has been used by APCO
for determining the sulfuric  acid  mist  emissions, as have the Shell
Development Company and  the  Chemical  Construction Company technique
for determining the sulfur trioxlde emissions.  Detailed descriptions
of these analytical techniques can be found  in the joint MCA-PHS study
mentioned earlier.^  While these techniques  have been acceptable, APCO
is currently developing  more  reliable standard sampling and analytical
procedures that will be  used  for monitoring  pollutants emitted from new
installations.  These procedures will be forthcoming in the near future
and it is strongly encouraged that they be adapted for monitoring
emissions at both new and existing plants.

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              SUMMARY OF  SUGGESTED  LIMITS

     1.   Contact sulfuric acid plants can be designed  to meet an SC>2-
tail-gas-emission ceiling of 6.5 Ib/ton of acid  produced.  This is
equivalent  to  the level attainable with both dual-absorption plants and
commercially operating S02-control processes.
     2.   Although, at present, commercially available  S02 control
processes and  dual-absorption modification schemes  can only reduce
the S02  emissions to 6.5 Ib/ton of acid produced, promising pilot-
scale studies  indicate that SC>2 emission levels  of  2.0 Ib/ton of acid
produced are attainable and probably could be applied  to commercial
installations.
     3.   Appropriate equipment is commercially available and could be
installed in all new and existing acid plants to reduce  the acid mist
emission levels to 0.5 Ib/ton of acid produced.
     4.   Efficient absorber operation can limit  sulfur trioxide levels
to 0.2 Ib/ton  acid produced on both new and existing  installations.

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                           REFERENCES
 1.   Chemical Construction Corp.  Engineering Analysis of Emissions
     Control Technology for Sulfuric Acid Manufacturing Processes.
     DHEW-NAPCA Final Report CPA 22-69-81, March 1970.
 2.   Atmospheric Emissions From Sulfuric Acid Manufacturing Processes.
     U.S. DHEW.  Public Health Service Publication No. 999-AP-13.
     Washington, D. C., 1965.

 3.   Moller, W. , and K. Winkler.  The Double Contact Process for Sulfuric
     Acid Production, Presented at 60th Annual Meeting APCA.  Cleveland.
     June 1967.
 4.   Burleigh, J.  Chemical Construction Corp.  Private communication,
     June 24, 1970.
 5.   Sulfuric Acid Process Reduces Pollution.  Chem. Eng. News.   42(40):
     42-43, December 21, 1964.
 6.   Lawler, C.  Air Pollution Control by a Sulfur Dioxide Scrubbing
     System.  Presented at Semiannual Technical Conference of APCA.
     Houston.  December 1967.
 7.   Wellman-Lord, Co.  Private communication, June 1970.
 8.   Scheidel, C.  Sulphur Dioxide Removal From Tail Gas by the Sulfacid
     Process.  Presented at the 61st Annual Meeting AICHE.  Los Angeles,
     December 1968.
 9.   Uno, T., S. Aramaki, and M. Kishi.  Full Scale Studies of the MHI
     Lime/Limestone Scrubbing Process.  Presented at International
     Symposium on Lime/Limestone Wet Scrubbing for SO  Control.   Pensa-
     cola, March 16-20, 1970.
10.   Meinhold, F.  Three-Way Payout for H.SO, Gas Cleaner.  Chem.
     Progress.  29:63-4, March 1966.
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