FOR LIMITATION
OF CONTACT SULFURIC ACID
PLANT EMISSIONS
ENVIRONMENTAL PROTECTION AGENCY
-------
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
-------
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
-------
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
-------
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.
-------
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.
-------
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
-------
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.
-------
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.
-------
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
-------
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.
-------
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.
-------
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.
11
------- |