EPA-450/3-79-013
A Review of Standards
of Performance
for New Stationary Sources -
Nitric Acid Plants
by
Marvin Drabkin
The MITRE Corporation
Metrek Division
1820 Dolley Madison Boulevard
McLean, Virginia 22102
Contract No. 68-02-2526
EPA Project Officer: Thomas Bibb
Emission Standards and Engineering Division
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
March 1979
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This report has been reviewed by the Emission Standards and
Engineering Division of the Office of Air Quality Planning and
Standards, EPA, and approved for publication. Mention of
trade names or commercial products is not intended to constitute
endorsement or recommendation for use. Copies of this report
are available through the Library Services Office (MD-35),
U.S. Environmental Protection Agency, Research Triangle Park,
N.C. 27711; or, for a fee, from the National Technical Information
Services, 5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-450/3-79-013
ii
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ABSTRACT
This report reviews the current Standards of Performance for
New Stationary Sources: Subpart G - Nitric Acid Plants. It includes
a summary of the current standards, the status of current applicable
control technology, and the ability of plants to meet the current
standards. Information used in this report are based upon data
available as of June 1978. The recommendations state that no change
be made at this time in the NOX NSPS for nitric acid plants, but that
a study be made of the NOX control capability of the extended
absorption process.
iii
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TABLE OF CONTENTS Page
LIST OF ILLUSTRATIONS vii
LIST OF TABLES viii
1.0 EXECUTIVE SUMMARY 1-1
1.1 Best Demonstrated Control Technology 1-1
1.2 Current NOX NSPS Levels Achievable with Best
Demonstrated Control Technology 1-2
1.3 Economic Considerations Affecting the NOX NSPS 1-3
1.4 Impact of Projected Growth of the Nitric Acid
Industry on NOX Emissions 1-4
1.5 Problems Encountered by the Extended Absorption
Process in Meeting the NO,. NSPS 1-4
X
2.0 INTRODUCTION • 2-l
3.0 CURRENT STANDARDS FOR NITRIC ACID PLANTS . 3_]_
3.1 Background Information . . 3_^
3.2 Facilities Affected 3_2
3.3 Controlled Pollutants and Emission Levels . 3.3
3.4 Testing and Monitoring Requirements 3_4
3.4.1 Testing Requirements 3_4
3.4.2 Monitoring Requirements 3_5
4-1
4.0 STATUS OF CONTROL TECHNOLOGY
4.1 Status of Nitric Acid Manufacturing Industry Since
the Promulgation of the ,NSPS 4_]_
4.1.1 Geographic Distribution 4_1
4.1.2 Production 4_3
4.1.3 Trends 4_8
4.2 Nitric Acid Manufacture 4_g
4.2.1 Single Pressure Process 4-12
4.2.2 Dual Pressure Process 4-16
4.3 Emissions from Nitric Acid Plants 4-18
4.4 Control Technology for NOX Emissions from
Nitric Acid Plants 4-19
4.4.1 Catalytic Reduction 4-20
4.4.2 Extended Absorption 4-28
4.4.3 Molecular Sieves 4-32
4.4.4 Wet Scrubbing 4-35
v
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TABLE OF CONTENTS (Concluded)
5.0 INDICATIONS FROM NSPS COMPLIANCE TEST RESULTS
5.1 Test Results from EPA Regional Sources
5.2 Analysis of NSPS Test Results
5.2.1 Control Technology Used to Achieve Compliance
5.2.2 Comparative Economics of the Catalytic
Reduction and Extended.Absorption Processes
for NOX Abatement
5.3 Indications of the Need for a Revised Standard
6.0 ANALYSIS OF THE IMPACTS OF OTHER ISSUES ON THE NSPS
6.1 Effect of Projected Nitric Acid Plant Construction
.on Emissions
6.2 Problems Encountered by the Extended Absorption
Process in Controlling NOX Emissions
7.0 FINDINGS AND RECOMMENDATIONS • ....
7.1 Findings
7.2 Recommendations
8.0 REFERENCES
Page
5-1
5-1
5-1
5-4
5-5
5-7
6-1
6-1
6-2
7-1
7-1
7-2
8-1
vi
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LIST OF ILLUSTRATIONS
Figure Number pa e
4-1 Nitric Acid Plants Built or Under
Construction After 1971 4-2
4-2 Growth of the Nitric Acid Industry 4-6
4-3 Nitric Acid Consumption in the U.S.
by Major Uses, 1970 (in Millions of
Tons of 100% Nitric Acid) 4-7
4-4 Single Pressure Nitric Acid Manufacturing
Process 4-14
4-5 Dual Pressure Nitric Acid Manufacturing
Process 4-17
4-6 Acid Plant Incorporating Catalytic
Reduction for NOX Abatement 4-23
4-7 Extended Absorption System for NO
Emissions Control X 4-30
4-8 Two-Bed Purasiv N Process (Vessel A
Under Adsorption and Vessel B Under
Regeneration Heating) for Control of
NOX in Nitric Acid Plant Tail Gas 4-33
5-1 Nitric Acid Plants NSPS Test Results
NOX Emissions 5_3
vii
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LIST OF TABLES
Table Number
4-1
4-2
4-3
4-4
4-5
4-6
4-7
5-1
5-2
6-1
6-2
6-3
Nitric Acid Plant Completions Subject
to NSPS
Nitric Acid Plants Planned or Under
Construction
U.S. Nitric Acid Production
Nitric Acid Plants Completed Since
Promulgation of the NSPS
NOX Abatement Methods for Nitric Acid
Plants
Typical Nitric Acid Plant Tail Gas
Emission Compositions (Percent by
Volume)
Operating Conditions for Treating Nitric
Acid Plant Tail Gas by Catalytic
Reduction
NSPS Compliance Test Results for
Plants
Cost of Producing Nitric Acid Using
Catalytic Reduction and Extended
Absorption NOX Control Methods for a
500-Ton/Day Plant
Projected Cumulative NOX Emissions from
New & Replacement Nitric Acid Plants
Added Between 1980 and 1983
Excess Emissions Data from Extended
Absorption Nitric Acid Plant Operations
Excess Emissions Data from Extended
Absorption Nitric Acid Plant Operations
4-3
4-4
4-5
4-13
4-21
4-22
4-26
5-2
5-6
6-3
6-5
6-6
viii
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1.0 EXECUTIVE SUMMARY
The objective of this report is to review the New Source Perfor-
mance Standard (NSPS) for nitric acid plants in terms of developments
in control technology, economics and new issues that have evolved
since the original standard was promulgated in 1971. The need for
possible revisions to the standard is analyzed in the light of com-
pliance test data available for plants built since the promulgation
of the NSPS. The NSPS review includes the NOX emission standard for
the nitric acid plant production unit. While included in the nitric
acid plant NSPS, the opacity standard is not reviewed separately
since it is directly related to the NOX standard. The following
paragraphs summarize the results and conclusions of the analysis,
as well as recommendations for future action.
1.1 Best Demonstrated Control Technology
A mixture of nitrogen oxides (NOX) is present in the tail gas
from the ammonia oxidation process for the production of nitric acid.
In modern U.S. single pressure process plants producing 50 to 60
percent acid, uncontrolled NOX emissions are generated at the rate
of about 21 kg/Mg* of 100 percent acid (42 Ib/ton) corresponding to
approximately 3000 ppm NOX (by volume) in the exit gas stream. The
catalytic reduction process** has been largely supplanted by the ex-
tended absorption process as the control technology of choice for
*Mg - Metric tons.
**The process used in the rationale for the present NOX NSPS as best
demonstrated control technology.
1-1
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controlling NOX emissions from new nitric acid plants to the level
required by the standard of performance.* The latter control system
has apparently been chosen by the nitric acid industry due to the
increasing cost and danger of shortages of the principal fuel (natural
gas) used in the catalytic reduction process. Since the energy crisis
of the mid-1970s, over 50 percent of the nitric acid plants that have
come on stream through mid-1978, and almost 90 percent of the plants
scheduled to come on stream through 1979, use the extended absorption
process for NOX control.
1.2 Current NOY NSPS Levels Achievable with Best Demonstrated
Control Technology
Fourteen of the new or modified operational nitric acid pro-
duction units subject to NSPS showed compliance with the current NOX
control level of 1.50 kg/Mg (3 lb/ton).** The average of seven sets
of test data from catalytic reduction-controlled plants is 0.22 kg/Mg
(0.44 lb/ton), and the average of six sets of test data from extended
absorption-controlled plants is 0.91 kg/Mg (1.82 lb/ton).*** All of
the plants tested were in compliance with the opacity standard. It
*It should be noted that standards of performance for new sources
established under Section 111 of the Clean Air Act reflect emission
limits achievable with the best adequately demonstrated technolog-
ical system of continuous emission reduction (taking into consider-
ation the cost of achieving such emission reduction, as well as any
nonair quality health and environmental impacts and energy require-
ments) .
**Five units had not been tested for compliance as of mid-1978. No
additional data have been obtained for this report since mid-1978.
***0ne set of data covers a nitric acid plant using a combination of
chilled absorption and caustic scrubbing for NOX control. This
plant is in compliance.
1-2
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appears that the extended absorption process, while it has become the
preferred control technology for NOX control, cannot control these
.emissions as efficiently as the catalytic reduction process. In
fact, over half of the test results for extended absorption, while
in compliance, were within 20 percent of the NOX standard. A prin-
cipal vendor of the extended absorption process only provides a 7
to 8 percent safety factor (in terms of absorber tray count) in
the performance guarantee. Thus, the extended absorption process
appears to have limitations with respect to NOX control, and com-
pares unfavorably with catalytic reduction in its ability to reduce
NOX emissions much below the present NSPS level. However, the
overriding consideration which leads to the recommendation of no
change in the NOX NSPS at the present time, is the sharply escalat-
ing cost and developing long-term shortages of natural gas which have
caused the present pronouced trend to the extended absorption process
for NOX control in new plants. It is also recommended that an in-
depth, EPA study be carried out to completely define the NOX control
capability of this process before any future consideration can be
given to making the current NOX NSPS more stringent.
1.3 Economic Considerations Affecting the NOY NSPS
Nitric acid plant operators opting for the extended absorption
process for NOX control for new plants (rather than catalytic
reduction) would not be penalized from an economic standpoint, since
the annualized costs of these two NOX control methods appear to be
1-3
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comparable. This is especially true now with the cost of fuel
(natural gas) for the catalytic reduction process experiencing sharp
*
rises. Capital cost, however, for this process is appreciably higher
than that for catalytic reduction, .thus, making the latter process
less capital intensive. Making the NOX standard more stringent at ^
this time would severely impact the investment cost of the extended ^
absorption process, since much larger absorption towers would have to
be incorporated in new plants in order to meet performance guarantees. ?
1.4 Impact of Projected Growth of the Nitric Acid Industry on NOY ,
Emissions
Based on an estimated nitric acid plant growth rate of four new ,
production lines per year between 1980 and 1983, a 50-percent reduc-
tion of the present NOX NSPS level—from 1.5 kg/Mg (3 Ib/ton) to 0.75
kg/Mg (1.5 Ib/ton)—would result in a drop in the estimated percentage
NOX contribution of these new nitric acid plants to the total na- |
tional NOV emissions, from 0.02 to 0.01 percent. . ,
A • ' .,
i'r-
1.5 Problems Encountered by the Extended Absorption Process in t'
Meeting the NOV NSPS f
i i .-...V ... ii- A. i —... i . . tf
V
Based on limited data, problems are encountered with the ex-
tended absorption process in meeting the NOX standard during cer-
t
tain startup periods and unscheduled shutdowns. During these periods,
'u<
process conditions are unstable and NOX concentrations tend to be
high while nitric acid production is low or nonexistent so that 3-hour
averaging is insufficient to bring the average NOX level below 1.5
kg/Mg (3 Ib/ton).
1-4
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2.0 INTRODUCTION
In Section 111 of the Clean Air Act, "Standards of Performance
for New Stationary Sources," a provision is set forth which requires
that "The Administrator shalls at least every 4 years, review and, if
appropriate, revise such standards following the procedure required
by this subsection for promulgation of such standards." Pursuant
to this requirement, the MITRE Corporation, under EPA Contract No.
68-02-2526, is to review 10 of the promulgated NSPS including the
nitric acid plant production unit.
The main purpose of this report is to review the current nitric
acid standards for NOX and opacity and to assess the need for revi-
sion on the basis of developments that have occurred or are expected
to occur in the near future. This report addresses the following
issues:
1. A review of the definition of the present standards.
2. A discussion of the status of the nitric acid industry and
the status of applicable control technology.
3. An analysis of NOX and opacity test results and review of
levels of performance of best demonstrated control technol-
ogies for emission control.
4. An analysis of the effect of projected nitric acid plant
construction on NOX emissions.
5. A study of problems encountered by recently developed
NOX control technology with the NSPS.
Based on the information contained in this report, conclusions
are presented and specific recommendations are made with respect to
changes in the NSPS.
2-1
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3.0 CURRENT STANDARDS FOR NITRIC ACID PLANTS
3.1 Background Information
Prior to the promulgation ;of the NSPS in 1971, only 10 of the
existing 194 weak nitric acid C50 to 60 percent acid) production
facilities were specifically designed to accomplish NOY abatement.
A-
Without control equipment, total NOX emissions from nitric acid
plants can range from 1000 to 6000 ppm by volume. In a typical
plant, total NOX emissions are approximately 3,000 ppm in the stack
gas, equivalent to a release of 21.5 kg/Mg (43 Ib/ton) of 100 percent
acid produced (EPA, 1971).
At the time of the NOX NSPS promulgation there were no state
or local NOX emission abatement regulations in effect in the U.S.
which applied specifically to nitric acid production plants. Ventura
County, California, had enacted a limitation of 250 ppm NOX to
govern nitric acid plants as well as steam generators and other
sources (EPA, 1971).
In 1971, NOX emission decolorization was practiced at 52
nitric acid plants by a method which also permitted maximum power
recovery from the pressurized absorber tail gas. The uncontrolled .
NOX tail gas emission consisted of approximately 50 percent nitro-
gen dixoide
-------
colorless NO in a highly exothermic reaction, with the heated exhaust
gas from the catalytic treatment being then passed through an ex-
pander to recover power for driving the air-compressor turbine used
in the nitric acid manufacturing process.
Stack gas decolorization enabled nitric acid plants in many
areas to meet visible emission regulations (with equivalent opacity
provisions), even though the catalytic decolorization technique has
little effect on the total NOX emissions (EPA, 1971).
It is estimated that NOX emissions from nitric acid plants
totalled 163,000 Mg (179,000 tons) in 1971 and 137,000 Mg (150,000
tons) in 1976 (Mann, 1978). This represented a 16 percent drop in
NOV emissions in the first 5 years after the promulgation of the
it
NSPS and implementation of State Implementation Plans (SIPs) for this
pollutant. By the end of 1977, nitric acid plants, in compliance
with NSPS, represented an estimated 23 percent of the industry capac-
ity.
3.2 Facilities Affected
The NSPS regulates nitric acid plants that were planned or under
construction or modification as of August 17, 1971. Each nitric acid
production unit (or "train") is the affected facility. The standards
of performance apply to new facilities producing so-called "weak
nitric acid" (defined as 50 to 70 percent strength). The standards
do not apply to the various processes used to produce strong acid by
extraction or evaporation of weak acid, or by the direct strong acid
process.
3-2
-------
An existing nitric acid plant is subject to the NSPS if: (1)
it is modified by a physical or operational change in an existing
facility thereby causing an increase in the emission rate to the
atmosphere of any pollutant to which the standard applies, or (2) if
in the course of reconstruction of the facility, the fixed capital
cost of the new components exceeds 50 percent of the cost that would
be required to construct a comparable entirely new facility that
meets the NSPS. • ,
3.3 Controlled Pollutants and Emission Levels
Total nitrogen oxide emissions from nitric acid plants are
controlled under the NSPS, as defined by 40 CFR 60, Subpart G (as
originally promulgated in 36 FR 24881 with subsequent modifications
in 39 FR 20794):
(a) On and after the date on which the performance test
required to be conducted ... is completed, no owner or
operator subject to the provisions of this subpart shall
cause to be discharged in to the atmosphere from any
affected facility any gases which:
(1) Contain nitrogen oxides, expressed as N02, in excess
of 1.5 kg per metric ton of acid produced; (3.0 Ib per
ton), the production being expressed as 100 percent
nitric acid.
(2) Exhibit 10 percent opacity, or greater.
This standard was based on inspections and stack tests of
existing nitric acid facilities; consultations with plant operators,
designers, and state local control officials; and a review of the
literature. Investigation of nitric acid plant control technology
showed that catalytic reduction systems could successfully control
tail gas nitrogen oxide emissions to levels within the proposed
3-3
-------
standard of 1.5 kg N0x/metric ton of .100 percent acid (3 Ib/ton).
A survey of 10 U.S. plants equipped with catalytic reduction systems
showed that all plants either consistently achieved that NOX level
or could be operated or repaired to meet the proposed standard (EPA,
1971).
All of the facilities equipped with catalytic NOX reduction
devices were found to operate with no visible emissions. Thus, any
facility meeting the mass NOX limit will produce no visible emis-
sions from the stack and therefore meet the promulgated opacity
standard (EPA, 1971).
Section 4.0 dicusses alternative NOX control technologies that
t
have come into use by the nitric acid industry since the promulgation
of the standard, or are under development. Chief among these new
technologies, and one that has been widely used since the mid-1970s,
is the extended absorption process.
3.4 Testing and Monitoring Requirements
3.4.1 Testing Requirements
Performance tests to verify compliance with the NOX standard
must be conducted within 60 days after the plant has reached its full
capacity production rate, but not later than 180 days after the ini-
tial start-up of the facility (40 CFR 60.8). The EPA reference
methods (40 CFR 60, Appendix A) to be used in conjunction with NOX
compliance testing include:
1. Method 7 for the concentration of NOX
2. Method 1 for sample and velocity transverses
3-4
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3. Method 2 for velocity and volumetric flow rate; and
4. Method 3 for gas analysis.
Each performance test consists of 3 runs, each consisting at least
four grab samples taken at approximately 15-minute intervals. The
arithmetic mean of the runs constitutes the value used to determine
whether the plant is in compliance.
3.4.2 Monitoring Requirements
The NOX levels in the tail gas from new nitric acid plants are
required to be continuously monitored to provide: (1) a record of
performance and (2) information to plant operating personnel such
that suitable corrections can be made when the system is out of ad-
justment. Plant operators are required to maintain the monitoring
equipment in calibration and to furnish records of excess NOX
emission values to the Administrator of EPA or to the responsible
State agency as requested.
Measurement principles used in the continuous gas analysis
instruments for NOX are (Apple, 1978):
1. Photometric
2. Nondispersive infrared absorption
3. Ultraviolet absorption
4. Electrochemical
5. Chemiluminescent emission
6. On-stack (in—situ) absorption
3-5
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A continuous NOX analyser in wide use in the nitric acid
industry is based on the principle of photometric analysis. This
analyzer consists of a split-beam design in which the difference in
light absorption by nitrogen dioxide (Np2) is measured at two
different wavelengths (a measuring wavelength and reference wave-
length). A basic requirement for this measurement principle is that
all the NO, which is transparent in the visible and ultraviolet
regions, is quantitatively converted to N0£ in the measuring
instrument (Dupont, 1974).
The continuous monitoring system is calibrated using a known air
NOo gas mixture as a calibration standard. Performance evaluation
of the monitoring system is conducted using the EPA Method 7. In
general, the system in use should satisfy the specifications as shown
in 40 CFR 60, Appendix B, Performance Specification 2.
Excess NOX emissons are required to be reported to EPA (or ap-
propriate state regulatory agencies) for all 3-hour periods of excess
emissions (or the arithmetic average of three consecutive 1-hour
periods). Periods of excess emission are considered to occur when
the integrated (or arithmetic average) plant stack NOX emission
exceeds the 1.5 kg/Mg (3 Ib/ton) standard.
3-6
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4.0 STATUS OF CONTROL TECHNOLOGY
4.1 Status of Nitric Acid Manufacturing Industry Since the Promul-
gation of the NSPS
4.1.1 Geographic Distribution
In 1972 there were approximately 125 nitric acid units in
i
existence, exclusive of government-owned units at ordnance plants
(Manderson, 1972). About 75 percent of these units were 10 years old
or older and, in general, had capacities of 270 Mg/day (300 tons/
day) or less. The remaining 25 percent of the units were of more
recent and larger design, having capacities exceeding 270 Mg/day (300
tons/day). The Bureau of the Census reported that there were 72
plants (involving one or more units) in 1972 producing nitric acid in
the U.S. and that by 1977 the ,net number of plants in production had
increased by only one.
As of June, 1978, 19 nitric acid units subject to NSPS had come
on stream. Table 4-1 summarizes data presented later in Table 4-4
for these 19 units and their design tonnage by EPA region. Figure
4-1 shows the geographic distribution of these units as well as the
locations of eight units still under construction. The latter units
are described in Table 4-2. The heaviest concentration of new or
modified nitric acid unit construction since 1971 appears in EPA
Regions IV and VI—along the coast of the Gulf of Mexico and within
the Mississippi River delta. Additionally, about half of the total
number of nitric acid plants are located in the southern tier of
states. The distribution of nitric acid, as shown in Figure 4-1
displays a spacial pattern similar to that of the major fertilizer
4-1
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TABLE 4-1
NITRIC ACID PLANT COMPLETIONS SUBJECT TO NSPS
EPA
Region
III
IV
VI
IX
X
Total
Average
New or Modified
Units
in Production
(1971-1977)
1
7
7
2
2
19
New or Modified
Plant
Design Capacity
(100% HN03)
Mg/day (tons/day
164(180)
3936(4325)
3265(3588)
319(350)
549(603)
8319(9046)
Percent of Total
New or
Modified
Design Capacity
2.0
47.8
39.6
3.9
6.7
100.0
Design Capacity/Unit: 438(476)
production centers (Chapman, 1973). Since the bulk of all nitric
acid produced is consumed captively in the manufacture of nitrogen
fertilizer used mainly in the Midwest cornbelt, the South Central
states, and the Southwest, the similarity in spacial patterns between
nitric acid plants and fertilizer manufacturing plants is to be
expected.
4.1.2 Production
EPA predicted the start-up of five new nitric acid units per
year for several years after promulgation of the NSPS (EPA, 1971).
The actual average rate of start-up between 1971 and 1977 has been
between two and three units per year.
In 1971, U.S. production of 100 percent nitric acid totalled
6,951,000 metric tons and increased at an average annual rate of 0.7
4-3
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percent to 7,167,000 metric tons in 1977. Figure 4-2 shows the
growth of nitric acid production from 1939, and Table 4-3 shows the
percent change per year.
Major end uses for nitric acid are shown in Figure 4-3. The
largest consumer of nitric acid is the fertilizer industry which
consumes 70 percent of all nitric acid produced; industrial explo-
sives use 15 percent of acid produced (Manderson, 1972). Other
end uses of nitric acid are gold and silver separation, military
munitions, steel and brass pickling, photoengraving, production of
nitrates, and the acidulation of phosphate rock.
TABLE 4-3
U.S. NITRIC ACID PRODUCTION
Year
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
Sources :
Production of
100% 'Acid (106 Mg)
2.4
2.5
2.8
3.0
3.1
3.3
3.6
4.3
4.7
5.0
5.8
6.2
6.6
6.8
6.9
7.2
7.6
7.3
6.8
7.1
7.1
Bureau of the Census, 1965; 1977.
Annual
Change (%)
4.1
12.0
7.1
3.3
6.4
9.0
19.4
9.3
6.3
1(5.0
6.8
6.4
3.0
1.4
4.3
5.5
-3.9
-6.8
4.4
0
4-5
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8.0
7.0
t>0
S
vO
O
6.0
5.0
I
4J
| 4.0
3.0
4J
•H
2.0
1.0
1935 1945
1955 1965
Year
1975 1980
Sources: Bureau of the Census, 1965; 1977.
FIGURE 4-2
GROWTH OF THE NITRIC ACID INDUSTRY
4-6
-------
PRODUCT FORM END USE
7
5
cc
a
o ,
EH 4
0
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H
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6.5 .other Organic Chemical
0 1 {
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49 .
(75%)
-
-* — "
Organic
Chemicals
Military
Munitions
Nitrophosphate
Based Fertilizers
Ammonium
Nitrate
(Solid & Liquid)
Potassium
•»-*• • *>•».
NitrateT
0.1
0.5J
1.9'
2.0<
Organ. Chem. Mfg.
Steel Pickling
Other
Military
Munitions
Industrial
Explosives
(Largely
Ammonium Nitrate)
~-^
Nitro-
Phosphate
Liquid
Ammonium
Nitrate
(in
Nitrogen
Solutions)
Solid
Ammonium
Nitrate
F
E
R
T
I
L
I
Z
E
R
S
1
[0.5
\
Jo,
1.0
J (15%)
\
4.5
(70%)
Source: Manderson, 1972.
FIGURE 4-3
NITRIC ACID CONSUMPTION IN THE U.S. BY MAJOR
USES, 1970(IN MILLIONSOFTONS OF
100% NITRIC AC ID)
4-7
-------
4.1.3 Trends
The average rate of production increase for nitric acid fell
from 9 percent/year in the 1960-1970 period to 0.7 percent from 1971
to 1977. The decline in demand for nitric acid parallels that for
nitrogen-based fertilizers during the same period (Bureau of the
Census, 1977).
Nitric acid production shows an increasing trend towards plant/
unit location and growth in the southern tier of states. In 1971, 48
percent of the national production was in the south. This figure
increased to 54 percent in 1976 (Bureau of the Census, 1977).
About 50 percent of plant capacity in 1972 consisted of small to
moderately sized units (50 to 300-ton/day capacity). Because of the
economics of scale some producers are electing to replace their
existing units with new, larger units (Manderson, 1972). Also, the
trend toward reduction of NOX emissions is stimulating the shutdown
and replacement of older units. New nitric acid production units
have been built as large as 910 Mg/day (1000 tons/day). The average
size of new units is approximately 430 Mg/day (500 tons/day).
4?
4.2 Nitric Acid Manufacture
Nitric acid is manufactured in the U.S. by the high temperature
catalytic oxidation of ammonia. The essential components of an
ammonia oxidation nitric acid plant are:
*Process information in Sections 4.2, 4.3 and 4.4 is taken from
Acurex/Aerotherm, 1977, unless otherwise noted.
4-8
-------
1. Converter or oxidation section where the ammonia vapor and
air are mixed and reacted catalytically to oxidize the
ammonia.
2. Cooler-Condenser section where the nitrogen dioxide is pro-
duced by cooling the reaction gases and weak nitric acid is
formed.
3. Absorber section where the cool nitrogen dioxide is absorbed
in water to form nitric acid.
In the first step of this process one volume of anhydrous ammonia is
mixed with nine volumes of preheated air and passed through a multi-
layered, silk fine platinum-rhodium gauze catalyst at 750° to 800°C.
Under these conditions, the oxidation of ammonia to nitric oxide pro-
ceeds in an exothermic reaction with a 95 percent yield:
4NH3 + 502 -> 4NO + 6H20> (1)
The second step involves the oxidation of the nitric oxide to
nitrogen dioxide:
2ND + 02 -»2N02 -»N204 (2)
The forward rate of reaction (2), which is rather slow compared with
reaction (1), is favored at lower temperatures and higher pressures.
Hence, reaction (2) is always carried out after cooling the gas to
38°C or less and, depending on the process design, at pressures up to
500 kPa* (73 psig).
In the final step, the nitrogen dioxide/dimer mixture is cooled
further and passed to an absorber where it reacts with water to pro-
duce an aqueous solution of 50 to 60 percent nitric acid, the concen-
tration depending on the temperature, pressure, number of absorption
*Kilopascal - 100 kPa = approximately 1 atm.
4-9
-------
stages, and concentration of the nitrogen dioxide entering the
absorber
3N02 + H20 -»2HN03 + NO
This reaction is also favored by low temperature and high pres-
sure, because the gases involved are more soluble at lower tempera-
tures and absorption results in a reduction in volume. In fact, some
processes utilize the low temperature/high pressure conditions to
increase yields.
The formation of nitric acid in Equation (3) involves the dis-
proportionation of nitrogen dioxide to form two moles of nitric acid
for every mole of nitric oxide. In order to reoxidize the nitric
oxide during absorption, secondary air (also known as bleacher air)
is introduced into the absorber along with the nitrogen dioxide.
However, the reaction to form nitric acid is never quite complete —
the overall process is 95 percent efficient, so that a small quantity
of nitrogen oxides, NOX (N02 and NO), is inevitably present in
the waste gas discharged from the absorption column. The NOX in
these waste gases is the target for air pollution regulations and
control.
Acid product is withdrawn from the bottom of the tower in con-
centrations of 55 to 65 percent. The air entering the bottom of the
tower serves to strip N02 from the product and to supply oxygen for
reoxidizing the NO formed in making nitric acid (Equation 3).
4-10
-------
The oxidation and absorption operations can be carried out at
low pressures (100 kPa), medium pressures (400 to 800 kPa) or high
pressures (1000 to 1200 kPa). Both operations may be at the same
pressure or different pressures.
Before corrosion-resistant materials were developed (precluding
the use of high pressures) the ammonia oxidation and absorption oper-
ations were carried out at essentially latmospheric pressure. The
advantages over higher pressure processes were longer catalyst life
(about 6 months) and increased efficiency of ammonia combustion.
However, because of the low absorption and NO oxidation rates, much
more absorption volume was required, and several large towers were
placed in series. Some of these low pressure units are still in
operation, but they represent less than 5 percent of the current U.S.
nitric acid capacity.
Combination pressure plants carry out the ammonia oxidation pro-
cess at low or medium pressure and the absorption step at medium or
high pressure. The increased pressure for the oxidation reaction
shortens the catalyst's lifetime (1 to 2 months) and lowers the
ammonia oxidation conversion efficiency. Thus, lower pressures in
the oxidation process are preferred. On the other hand, higher
pressures in the absorption tower increase the absorption efficiency
and reduce NOX levels in the tail gas. The advantages of higher
absorber pressures must be weighed against the cost of pressure
vessels and compressors.
4-11
-------
The choice of which combination of pressures to use is very site
specific and is governed by the economic tradeoffs such as costs of
raw materials, energy and equipment and process efficiency. In the
1960s combination low pressure oxidation/medium pressure absorp-
tion and single pressure (400 to 800 kPa) plants were preferred.
Since the 1970s the trend has been toward medium pressure oxi-
dation/high pressure absorption plants in Europe and single pressure
(400 to 800 kPa) plants in the U.S.
The two types of weak nitric acid production processes in use in
new U.S. plants, i.e., single pressure and dual pressure process, are
described in the following sections. Table 4-4 lists all of the new
and modified nitric acid plants subject to NSPS, together with their
capacities and the production and NOX abatement processes used.
4.2.1 Single Pressure Process
In the single pressure process both the oxidation and absorption
are carried out at the same pressure—either low (atmospheric) or
medium pressures of 400 to 800 kPa (60 to 120 psig). Single pressure
plants are the most common type in the U.S. Figure 4-4 is a
simplified flow diagram of a single pressure process. A medium
pressure process will be described in the following paragraphs.
Air is compressed, filtered, and preheated to about 300°C
(592°F) by passing through a heat exchanger. The air is then mixed
with anhydrous ammonia, previously vaporized in a continuous-steam
4-12
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evaporator. The resulting mixture, which contains about 10 percent
ammonia by volume, is passed through the reactor. The reactor
contains a platinum-rhodium (2 to 10 percent rhodium) wire-gauze
catalyst (e.g., 80 mesh and 75-mm diameter wire, packed in layers of
10 to 30 sheets) so that the gas travels downward through the gauze
sheets. Catalyst operating temperature is about 750°C (1382°F).
Contact time with the catalyst is about 3 x 10"^ second.
The hot nitrogen oxides and excess air mixture (about 10 percent
nitrogen oxides) from the reactor are partially cooled in a heat ex-
changer and further cooled in a water cooler. The cooled gas is
introduced into a stainless-steel absorption tower with additional
air for the further oxidation of nitrous oxide to nitrogen dioxide.
Small quantities of water are added to hydrate the nitrogen dioxide
and also to scrub the gases. The overhead gas from the tower is re-
heated by feed/effluent heat exchangers and then expanded through a
power recovery turbine/compressor used to supply the reaction air.*
The bottom of the tower yields nitric acid of 55 to 65 percent
strength. Fifteen of the 19 U.S. nitric acid plants subject to NSPS,
employ a single pressure process.
*In those plants using catalytic reduction as NOX abatement
method, the tail gas is first passed through the catalytic reduction
system and then expand ed through a power recovery turbine/compressor
used to supply the reaction air.
4-15
-------
4.2.2 Dual Pressure Process
In order to obtain the benefits of increased absorption (with
greater product yield) and reduced NOX emissions, some dual pres-
sure plants are in use in the U.S. Four of these plants subject to
NSPS have been built in the U.S. Recent trends favor moderate
pressure oxidation and high pressure absorption.
A simplified process flow diagram for a dual pressure plant is
shown in Figure 4-5. In the Uhde version of this process, liquid am-
monia is vaporized by steam, heated and filtered before being mixed
with air from the air/nitrous oxide compressor at from 300 to 500 kPa
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4-17
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4.3 Emissions from Nitric Acid Plants
The main source of atmospheric emissions from the manufacture of
nitric acid is the tail gas from the absorber tower. The emissions
are primarily nitric oxide and nitrogen dioxide with trace amounts of
nitric acid mist. Each of these pollutants has an effect on the
color and opacity of the tail gas plume. The presence of nitrogen
dioxide is indicated by a reddish-brown color. Since nitric oxide is
colorless, the intensity of the color and, therefore, plume opacity,
is directly proportional to the nitrogen dioxide concentration in the
plume. Concentrations of greater than 0.13 percent by volume of ni-
trogen dioxide produce a definite reddish-brown color in the exit
plume, whereas effluent gases containing less than 0.03 percent ni-
trogen dioxide are colorless.
The opacity of the plume is also a function of the amount of
nitric acid mist in the tail gas, which is dependant on the type of
process used, the extent of mist entrainment and the efficiency of
entrainment separators. For those acid processes operated above at-
mospheric pressure, the tail gases are reheated and expanded for
power recovery purposes and discharged to the atmosphere at 200° to
250°C. At this temperature, any acid mist present is converted to
the vapor state. In atmospheric pressure processes, however, the
temperature of the tail gas is below the dew point of nitric acid.
•As a result, the acid is emitted as a fine mist which increases the
plume opacity.
4-18
-------
The average emission factor for uncontrolled acid plants is 20
to 28 kg N0x/Mg of acid, with typical uncontrolled tail gas concen-
trations on. the order of 3000 ppm NOX. This concentration would be
experienced in a low pressure plant. The NOX concentration in the
tail gas of medium pressure plants ranges from 1000 to 2000 ppm.
Nitrogen oxide emissions vary considerably with changes in plant
operation. Several operating variables have a more significant ef-
fect on increasing NOX emissions. These include: (1) insufficient
air supply to the oxidizer and absorber; (2) low pressure, especially
in the absorber; (3) high temperatures in the cooler-condenser and
absorber; (4) production of an excessively high-strength product
acid; and (5) operation at high throughput rates. Finally, faulty
equipment, such as compressors or pumps, lead to lower pressures and
leaks which decrease plant efficiency and increase emissions.
4.4 Control Technology for NOY Emissions from Nitric Acid Plants
Nitric acid plants can be designed for low NOX emission levels
without any add-on control equipment. Such plants are usually equip-
ped with high efficiency absorbers, i.e., those having high inlet gas
pressures and effective cooling of the absorber solution. However,
all new U.S. plants built since the promulgation of the NSPS are
designed to meet the low NOX emissions required by the present
standards with some form of NOX abatement equipment.
A number of methods are available for reducing NOX emissions
from new nitric acid plants. These methods include catalytic
4-19
-------
reduction with certain fuels, extended ubuorptiott, wet butuhhtng,
chilled adsorption, and molecular sieve adsorption. The methods are
summarized in Table 4-5 and described in greater detail in the fol-
lowing paragraphs. Table 4-6 summarizes typical tail gas analyses
from uncontrolled plants and from plants incorporating the two most
important NOX abatement methods in use in new nitric acid plants
(catalytic abatement and extended absorption).
4.4.1 Catalytic Reduction
Catalytic reduction has been widely used as an NOX abatement
system installed on new nitric acid plants built since 1971. Cataly-
tic reduction was also used as a method of NOX decolorization on
over 50 percent of nitric acid plants built prior to the NSPS. The
reasons for the prevalance of this control technology until 1975*
were:
(1) Its relative ease and flexibility of operation
(2) The recovery of waste heat
(3) High NOX removal efficiencies.
In practice, the catalytic reduction unit is an integral part of
the plant (Figure 4-6). The tail gas from the absorption tower is
preheated by heat exchange with the converter effluent gas. Fuel is
added and burned in the catalytic unit to generate heat and abate
The advent of a proven alternate NOX control technology—the
extended absorption process—together with the developing natural
gas shortage at that time radically changed the entire nitric acid
plant NOX control situation (see Section 4.4.2).
4-20
-------
TABLE 4-5
NOX ABATEMENT METHODS FOR NITRIC ACID PLANTS
Method
Description
Comments
Catalytic Reduction
Nonselective
Selective
Extended
Absorption
Wet Scrubbing
Molecular Sieve
Adsorption
Chilled
Absorption
Reduction of NOX and 02
with CH^, CO or H2 over
a Pt or Pd catalyst to form
N2, C02 and H20; single-
stage unit reduces N02 to
NO (decolorization); two-
stage unit or single-stage
with temperature control
reduces NO to N2 (full
abatement).
Reduction of NOX only
with NH3 over 'a Pt
catalyst to form N2.
Use of a second absorption
column to increase recovery
and yield of HN03.
Scrubbing absorber tail
gases with solution of
urea, ammonia, sodium
hydroxide, sodium carbonate,
or potassium permanganate.
Removal of NOX using
adsorbent/catalyst bed con-
taining a synthetic zeolite;
thermal regeneration
recovers N02 for conver-
sion to HNOj.
Chilling absorbing solution
to increase N02 solubility
and yields of HNOj.
Prior to the promulgation of
NSPS, decolorization of the
absorber tail gas was often
profitable because of the
energy recovered from the
combustion of methane; full
abatement now requires addi-
tional methane and represents
a fuel penalty; may be oper-
ated at high or low pressure;
may be used in conjunction
with extended absorption.
Energy recovery not possible;
may be operated at high or
low pressures; often used
with extended absorption.
Required inlet pressure of
730 kPa may necessitate ad-
ditional compressor unit.
May be operated at low or
high pressure, but NOX
removal greater at higher
pressures.
High energy and capital
requirements; achieves ex-
tremely low NOX emissions
«50 ppm).
Primarily used as retrofit
on existing plants; usually
cannot meet NSPS without
other controls or lowered
acid product concentration.
4-21
-------
TABLE 4-6
TYPICAL NITRIC ACID PLANT TAIL GAS EMISSION COMPOSITIONS
(Percent by Volume)
Component
or Tail Gas
NO
N02
N2
02
H20
C02
Plant
Uncontrolled3
0.10
0.15
96.15
3.00
0.60
"~
Control Method
Catalytic
Reduction
0.01
trace
94.20
trace
3.80
2.00
Extended
Absorption"
—
0.015
96..00
3.50
0.50
"
Conventional design has been 98 percent absorption efficiency
(this composition is typical of the tail gas before catalytic
reduction).
control in this plant is done by increasing the absorption
efficiency to 99.8 percent plus.
Source: Wyatt, 1973.
4-22
-------
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4-23
-------
the tail gas. The hot gas from this unit passes to an expander which
drives the process air compressor for the ammonia converter. A waste
heat boiler removes the heat from the expander outlet gas in the form
of steam, and the treated tail gas is vented to the atmosphere. In
some cases, a waste heat boiler is required after the catalytic unit
to keep the expander inlet temperature below its design maximum -
usually 677°C (1250°F).
Catalytic reduction processes can be divided into two categor-
ies: nonselective and selective reduction. In nonselective reduc-
tion, the tail gases from the absorber are heated to the necessary
ignition temperature and mixed with a fuel such as methane, carbon
monoxide, or hydrogen. This mixture is passed to the catalytic re-
duction unit, where the fuel reacts with both NOX and 02 to form
C02, H20 and N2 over a catalyst consisting of 0.5 percent Pt or
Pd either in the form of spherical pellets or deposited in a honey-
comb ceramic material. When methane (natural gas) is used as the
fuel, the following reactions take place:
CH4 + 202 -»C02 + 2H20 (6)
CH4 + 4N02 -» 4NO + C02 + 2H20 (7)
CH4 + 4NO -> 2N2 + C02 + 2H20 (8)
The first two of these reactions proceed rapidly with the evolution
of considerable heat which is recovered in a waste heat boiler. In
the second reaction or decolorization step, the nitrogen dioxide is
converted to nitric oxide, so the gas is colorless even though there
4-24
-------
has been no decrease in the total nitrogen oxides. Only the reaction
with additional methane as shown in the last reaction results in the
reduction of the nitric oxide to nitrogen. The final reduction step
must be limited to an upper temperature of 843°C (1550°F), due to the
catalyst thermal limitation. If reduction has to be carried out in
the presence of high oxygen concentrations (above 3.0 percent), it
must be performed in two stages to prevent exceeding the upper tem-
perature limit. When this last reaction is complete, total NOX
abatement is achieved.
For a given fuel, there is a minimum ignition temperature re-
quired to initiate the reaction. Once reaction has started the heat
of. reaction will maintain the temperature. Ignition temperature is
lowest for hydrogen and carbon monoxide, 150° to 200°C, and highest
for natural gas, 480° to 510°C.
In practice, 90 to 95 percent of the nitrogen oxides in the tail
gas are decomposed by this process. Typical operating conditions are
summarized in Table 4-7. The particular process conditions chosen
depend upon the usefulness of recovering heat, the amount of capital
available for the cost of heat exchangers and related equipment, and
the availability and cost of fuels. Depending on the overall plant
heat balance, significant economic return can be realized through
recovery of heat generated in the abatement unit.
In the selective reduction process, ammonia is used to catalyti-
cally reduce N02 to N2 without simultaneously reacting with
4-25
-------
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oxygen. A ceramic-supported (either pellets or honeycomb) platinum
catalyst is used to effect the following reactions:
8NH3 + 6N02 -»7N2 + 12 H20 (9)
4NH3 + 6NO -»5N2 + 6 H20 (10)
Both of these reactions occur at relatively low temperatures (210° to
270°C). Typical operating conditions for selective reduction are
summarized in Table 4-7.
The advantage of this method is that less heat is evolved and
the installation of heat removal equipment is unnecessary. However,
the platinum catalyst required is more expensive and the ammonia cost
may not be competitive with other fuels even when less is required.
Close temperature control is required to prevent ammonia oxidation,
which would increase nitrogen oxide emissions. Start-up and shut-
down procedures must also be closely controlled to avoid formation of
ammonium nitrite salts.
Catalytic reduction is particularly suited to the pressure
ammonia oxidation process in which the absorption tower tail gas is
of uniform composition and flow, is under pressure, and can be
reheated by heat exchange to the necessary reduction unit feed
temperature. Of the 19 nitric acid plants subject to NSPS which are
currently on stream, eight feature catalytic reduction as the NO,,
X
control mechanism.
4-27
-------
4.4.2 Extended Absorption
The most obvious method of reducing NOX emissions in the tail
gas of a nitric acid plant is to increase the absorption efficiency.
Emission control by absorption is somewhat misleading, since no add-
on emission control equipment is necessary if the plant is designed
and built with sufficient absorption capacity. The majority of
nitric acid plants built since World War II have absorbers designed
for an absorption efficiency of 98 percent, allowing an emission
of 15 to 17.5 kg of NOX (as N02) per metric ton of nitric acid.
This design factor was established by economics and the lack of air
pollution regulations. However, with present day economics and the
advent of the NSPS, designing absorption plants for higher NOX
recovery has received more consideration. Nitric acid plants have
been constructed with absorption systems designed for 99.8 plus
percent NOX recovery. This recovery efficiency assures compliance
with the NOX NSPS of 1.5 kg/Mg (3.0 Ib/ton).
In the extended absorption process, a second absorption tower is
added in series to the existing absorber. The NOX is absorbed by
water and forms nitric acid. The economics of the extended absorp-
tion process generally require the inlet gas pressure at the absorber
to be at least 730 kPa (107 psig). Also, cooling is usually required
if the inlet NOX concentration is above 3000 ppm. There is normal-
ly no liquid effluent from extended absorption; the weak acid from
4-28
-------
the secondary absorber is recycled to the first absorber, increasing
the yield of nitric acid. Figure 4-7 is a schematic flow sheet of a
328 Mg/day (360 tons/day) nitric acid plant using extended
absorption. Also shown on Figure 4-7 are the. operating conditions
and utility requirements in effect at this plant. The system shown
is the Grande Paroisse* version of the extended absorption process.
In the D.M. Weatherly Company version of the extended absorption
system, a smaller volume and number of trays in the absorption system
is required as compared with the Grande Paroisse absorption system
due to the use of mechanical refrigeration for chilling part of the
cooling water employed. Two cooling water systems are used for
cooling the absorbers. The first part of the absorption process is
cooled by the normal cooling water available at the plant site.
Approximately one-third of the trays are cooled by normal cooling
water. The balance of the trays in the absorption system, are cooled
by cooling water at about 7°C (45°F), which is achieved by mechanical
refrigeration. The refrigeration process is a part of the ammonia
vaporization section of the nitric acid plant (Weatherly, 1976).
The extended absorption system operates without any problems as
long as design conditions are met. This means that the absorber
pressure and oxygen content in the gas to the absorber must not be
below design level; and the temperature and NOX content in the gas
stream must not exceed design level. With regard to temperatures,
^
Licensed by the J.F. Pritchard Co., Kansas City, MO.
4-29
-------
4-30
-------
this system is particularly vulnerable to high summer ambient
temperatures in the southern tier of states, i.e., temperatures in
excess of 95° to 100°F. Information from one extended absorption
nitric acid plant in Louisiana for the third quarter of 1978 seems to
confirm this problem. In August there were 2 days when 4-hour
periods of excess NOX emissions occurred due to high ambient
temperatures (Carville, 1978). Since the NOX vapor pressures can
be higher then the absorber can cope with during these periods of
excessive ambient temperatures, one extended absorption system vendor
will guarantee performance within the specified NOX emission limit
only 95 percent of the time (Russell, 1978).
Of the 19 nitric acid plants currently subject to NSPS, nine
feature extended absorption as the NOX control mechanism. It is
noteworthy that eight of these nine plants have come on stream since
the energy crisis of the mid-1970s.* Additionally, seven of the
eight plants scheduled to come on stream by the end of 1979 (Table
4-2) feature extended absorption for NOX emission control. It
appears that from a day-to-day operational standpoint, nitric acid
plant operators have decided that the increasing uncertainty of an
adequate natural gas supply, the principal fuel used in the catalytic
reduction units, together with the anticipated sharp increases in
natural gas price over the next few years,** have made extended
One of these plants (a U.S. Army installation) operates inter-
mittently and is currently down.
Interstate natural gas price (old gas) is expected to be in the
$1.50 to $2.00 per 1000 cubic feet range in the early 1980s, as
compared with the present price of approximately $1.25 per 1000
cubic feet (MITRE estimate).
4-31
-------
;v
absorption the preferred process for NOX abatement in the future.
In cases where the new nitric acid plant is located in a fertilizer
complex* with an available contract at favorable prices an assured
low-price, long-term natural gas supply, catalytic reduction eco-
nomics are more attractive than extended absorption, provided that
fuel consumption is only slightly in excess of the stoichiometric
amount needed for NOX abatement (Byrne, 1978).
J.*.
4.4.3 Molecular Sieves**
Molecular sieves can selectively adsorb NOX from nitric acid
plant tail gas. NOX removal is accomplished' in a fixed bed adsorp-
tion/catalyst system, providing recovery and recycle of the nitrogen
oxides back to the nitric acid plant absorption tower. A flow dia-
gram for a Purasiv*** control system is shown in Figure 4-8. The
water-saturated nitric acid plant absorption tower overhead stream
is chilled to 7° to 10°C (45° to 50°F),. the exact temperature level
being a function of the NOX concentration in the tail gas stream,
and passed through a mist eliminator to remove entrained water and
acid mist. The condensed water, which absorbs some of the N02 in
the tail gas to form a weak acid, is collected in the mist eliminator
and either recycled to the absorption tower or sent to storage. The
dried tail gas then passes through a molecular sieve bed where the
special properties of the NOX removal grade molecular sieve result
*Where ammonia is synthesized from natural gas.
**This information is taken from EPA, 1976, unless otherwise noted.
***purasiv is the molecular sieve system developed by Union Carbide
Corp.
4-32
-------
902
4-33
-------
in the catalytic conversion of NO to N02- This occurs in the
presence of the low concentrations of oxygen typically present in the
tail gas stream. Nitrogen dioxide is then selectively adsorbed. The
molecular sieve adsorbent/catalyst provides the most effective
performance and longest life when the tail gas is bone dry. This is
accomplished by drying with a desiccant which exhibits very little
coadsorption of NOX during water removal. The desiccant is located
in the same adsorber vessel as the NOX adsorbent/catalyst in a
compound bed arrangement.
Regeneration is accomplished by thermal swinging (cycling) the
adsorbent/catalyst bed after it completes its adsorption step and
contains a high adsorption loading of N02- The required regenera-
tion gas is obtained by heating a portion of the treated tail gas
stream which is then used to desorb the adsorbed N0£ from the bed
for recycle back to the nitric acid plant absorption tower. The
treated tail gas stream is passed through an oil or gas-fired heater
to provide heat for regeneration. The NC^-loaded gas is recycled
to the nitric acid absorption tower. The pressure drop in the sieve
bed averages 34 kPa and NOX outlet concentration of the molecular
stack gas averages 50 ppm.
The process has been successful in meeting NOX emission stan-
dards for existing plants. The principal criticisms have been high
capital and energy costs, and the problems of coupling a cyclic sys-
tem to a continuous acid plant operation. Furthermore, molecular
4-34
-------
sieves are not considered as state-of-the-art technology (Acurex/
Aerotherm, 1977).
There have been no nitric acid plants built and subject to NSPS
which incorporate molecular sieves as NOX control technology.
4.4.4 Wet Scrubbing
Wet scrubbing involves treatment of the absorber tail gas with
solutions of alkali hydroxides or carbonates, ammonia, urea, or po-
tassium permanganate to absorb NO and N02 in the form of nitrate
and/or nitrite salts in a scrubbing tower. In the case of caustic
scrubbing, the following reactions take place:
2NaOH + 3N02 ->2NaN03 + NO + H20 (11)
2NaOH + NO + N02 -»2NaN02 + H20 (12)
However, disposal of the spent scrubbing solution presents a serious
water pollution problem. One nitric acid plant subject to NSPS
employs a combination of chilled absorption and caustic scrubbing to
achieve NOX abatement.
One of the more novel scrubbing processes uses a urea solution
to convert the nitrogen oxides, after oxidation to their respective
acids, to nitrogen and marketable ammonium nitrate:
HN02 + CO(NH2)2 + HN03 -» N2 + C02 + NH4N03 + H20 (13)
This process has been reported to reduce NOX emissions from 4000
pptn to 100 ppm and can theoretically be designed for no liquid efflu-
ent; in practice, however, some effluent is produced requiring waste-
water treatment. Additionally, marketing of the ammonium nitrate is
not always possible, creating an additional storage/disposal problem.
4-35
-------
-------
5.0 INDICATIONS FROM NSPS COMPLIANCE TEST RESULTS
5.1 Test Results from EPA Regional Sources
The MITRE Corporation, Metrek Division, conducted a survey of
all 10 EPA regions to gather ;available NSPS compliance test data for
each of the 10 industries under review (MITRE Corp., 1978); This
survey yielded test data on two new nitric acid units. Data included
average NOX emissions and 100 percent nitric acid production .rates
for these units in effect at the time of the test. In both cases,
the nitric acid production rate was at the unit design maximum (the
actual production rates were within 5 to 10 percent of the nominal
design rates). The two units were stated to be in compliance with
respect to the opacity standard. Telephone contacts with EPA
regional personnel, nitric acid plant operators and a search of the
literature yielded NSPS compliance test data on an additional 12 new
nitric acid units. Five new operational nitric acid units have not
been tested for compliance under NSPS as of August, 1978. In all,
14 sets of data were obtained representing 14 new or modified nitric
acid units.
5.2 Analysis of NSPS Test Results
The NOX emission results of the NSPS compliance tests obtained
for the 14 nitric acid units are tabulated in Table 5-1 and displayed
in Figure 5-1. It should be noted that the data in Figure 5-1 are
displayed in terms of the three NOX control technologies used at all
of the plants subject to NSPS.
5-1
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FIGURE 5-1
NITRIC ACID PLANTS NSPS TEST RESULTS
NOX EMISSIONS
5-3
-------
5.2.1 Control Technology Used to Achieve Compliance
All 14 units tested showed compliance with the NSPS NOX con-
trol level. Of the 14 units tested, seven achieved compliance with
the NOV standard through use of the catalytic reduction process.*
A
Of the remaining seven units, six use the extended absorption pro-
cess and one employs a combination of chilled absorption and caustic
scrubbing to meet the standard. All of the new units meet the opac-
ity standard since opacity is directly related to NOX emissions.
It is evident from Figure 5-1 that catalytic reduction is more
capable of control to lower NOX emission levels than extended ab-
sorption. The arithmetic average of the NSPS NOX control results
is 0.22 kg/Mg of 100 percent acid (0.44 Ib/ton) where catalytic re-
duction control technology is employed, while the arithmetic average
of the NSPS test results for those plants using extended absorption,
is 0.91 kg/Mg of 100 percent acid (1.82 Ib/ton). Thus, both tech-
nologies can meet the present NSPS for NOX emissions. However, as
was discussed in Section 4.4.2, it 'is likely that the great majority
of nitric acid plants built in the future will employ extended ab-
sorption as the NOX control technology. Since extended absorption
absorption was not in use in any U.S. nitric acid plants at the time
*Most of these plants use the nonselective catalytic reduction pro-
cess. At least one plant uses the selective process (distinctions
between these processes are discussed in Section 4.4.1). All refer-
ences to catalytic reduction in later sections of this report refer
to the nonselective process.
5-4
-------
of promulgation of the NOX NSPS, EPA had only described catalytic
reduction as the control technology capable of achieving compliance
with the standard. With the demonstrated ability of extended ab-
sorption to control NOX emissions to within the present standard,
and the very pronounced trend to this technology for NOX control
in future plants, any changes in the NSPS must be considered in the
light of this newer technology.
5.2.2 Comparative Economics of the Catalytic Reduction and
Extended Absorption Processes for N0y Abatement
Relative costs of new nitric acid plants equipped with either
catalytic reduction or extended absorption processes for NOX con-
trol, have been developed and .are shown in Table 5-2. The costs
shown are in 1975 dollars.
Study of Table 5-2 indicates that in terms of 1975 dollars,
the total annual operating cost ,of the catalytic reduction process
is approximately 98 percent of this cost for extended absorption.
Escalation to current costs would affect both catalytic abatement
and extended absorption in similar amounts for nearly all the items
shown in the determination of total annual operating cost. However,
the fuel cost shown for catalytic reduction, i.e., $1.00/million BTUs
for natural gas, is not a realistic current cost. A MITRE estimate
for a realistic volume price for interstate natural gas at present
would be in the neighborhood of $1.25/million BTUs. This price is
likely to increase sharply in the near future. On this basis, the
5-5
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total annual operating cost (in current dollars) for the catalytic
abatement and extended absorption processes appears to be quite
comparable. However, the investment cost for extended absorption
appears to be appreciably greater than that for catalytic abatement
based on data in Table 5-2.
5.3 Indications of the Need for a Revised Standard
At this time, there is not sufficient justification for making
the present NOX NSPS (and the related opacity standard) moire strin-
gent, based on the following considerations:
• There are several alternative NOX control technologies
available to the nitric acid industry, two of which have
been the control systems of choice since the promulation
of the nitric acid plant NSPS. These are catalytic re-
duction and extended absorption
• Of these two systems, NSPS compliance test data have clearly
shown that catalytic reduction is the best demonstrated con-
trol technology (even though both NOX control systems meet
the present NSPS), since this system of NOX control produces
a much lower level of residual NOX in the exhaust gas than
extended absorption (based on NSPS compliance test data).
Additionally, catalytic reduction is a much more flexible
system than extended absorption in that it can deal with
upset conditions in the nitric acid plant which produce
large NOX excursions in a much more efficient manner.*
• However, the overriding consideration in determining choice of
NOX control systems at the present time and in both near and
long term, is the uncertainty of supply and sharply escalating
cost of natural gas— the principal fuel used in the cataly-
tic reduction process. For this reason, nitric acid producers
have opted for extended absorption NOX control in about 50
percent of the plants built in the last 4 years (through mid-
1978) and will have incorporated extended absorption NOX
control in about 90 percent of new plants to be completed by
*Section 6.2 presents data on NOX emissions resulting from upset
conditions.
5-7
-------
1980. On the basis of annualized costs, the catalytic reduc-
tion and extended absorption NOX control process appear to
be comparable, so that there would be minimal cost penalty for
new nitric acid plants incorporating the extended absorption
process.
• While the extended absorption process can maintain NOX
emissions at levels below the present standard, the emis-
sion levels achieved do not represent a very large margin
of safety. A principal vendor of this equipment provides
a normal performace guarantee of 200 ppm of NOX in the
nitric acid absorber tail gas (equivalent to approximately
3 Ib/ton) with only a 7 to 8 percent margin of safety in
terms of absorber tray count. The lowest performance
guarantee which has been provided by this vendor, is 150
ppm NOX (equivalent to approximately 2.25 Ib/ton) in the
latest plant design. Absorption towers get very large
and costly as the performance guarantee on NOX emission
level is tightened (Russell, 1978). Thus, limitations in
extended absorption performance appear to preclude making
the NSPS more stringent at the present time.
Other considerations, including effect of projected nitric acid
plant construction on NOX emissions and unique features of extended
absorption which affect the NSPS, are discussed in Section 6.0.
5-8
-------
6.0 ANALYSIS OF THE IMPACTS OF OTHER ISSUES ON THE NSPS
6.1 Effect of Projected Nitric Acid Plant Construction on Emissions
Based on the information presented in Section 4.1, the rate of
completion of new or modified nitric acid plants during the 1971 to
mid-1978 period has been approximately two to three per year. During
mid-1978 to 1980 period, the number of new nitric acid plants planned
or under construction continues to average about the same as the pre-
vious period. Based on this information, and an anticipated slowdown
in nitrogen-based fertilizer exports during the early 1980^ (Chemical
and Engineering News, 1978), MITRE estimates a maximum of two new ni-
tric facilities added to existing U.S. production capacity during the
1980-1983 period. This will result in a maximum of eight new nitric
acid production lines starting up during this 4-year period. In
addition, replacement of older nitric acid plants during this period
is assumed to occur at the same rate, i.e., eight replacement units
are anticipated to start-up during the 1980 to 1983 period. Thus,
a total of 16 nitric acid units subject to NSPS, are predicted to
come on-line during this period. Based on data in Tables 4-2 and
4-6 these new units are expected to average about 423 Mg/day (465
tons/day) each.
The total NOX emissions have been calculated at various NSPS
emission control levels for the 16 new units projected to be com-
pleted during the 1980-1983 period. The results of these calcula-
tions are shown in Table 6-1.
6-1
-------
Table 6-1 indicates that halving the present NSPS control level
from 1.5 Kg/Mg (3.0 Ib/ton) to 0.75 Kg/Mg (1.5 Ib/ton) would have
a relatively small effect on total U.S. NOX emissions, considering ,
both the relation to total emissions from NSPS-controlled plants and
to total emissions from all stationary sources. Approximately 1800
Mg/Yr ( 2000 tons/year) reduction in total NOX emissions from NSPS-
controlled plants, results from a 50-percent reduction in the NSPS
control level. The relative national environmental impact of these
projected new nitric acid plants comparing the present NOX NSPS
control level and a 50 percent reduction of this level is very small
when considered against the total NOX emissions from all stationary
sources.
6.2 Problems Encountered by the Extended Absorption Process in
Controlling NOY Emissions
The extended absorption process appears to be capable of con-
trolling NOX emissions from nitric acid plants subject to NSPS, to
less than 1.5 kg/Mg (3.0 Ib/ton) during normal operation, based on
NSPS compliance test results (see Section 5.0). However, communi-
cation with extended absorption nitric acid plant operators indi-
cates that problems are encountered during startup (where process
malfunctions may exist for several hours requiring several rest-
arts) and shutdown (particularly unscheduled or emergency shut-
down). During these periods process conditions are unstable, and
NOX emission concentrations tend to be high while production is low
6-2
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or nonexistent. No external control system is available in these
situations to reduce NOX emissions to below the control level (as
in the catalytic reduction process), and a period of excess emissions
occurs. Limited data from two plants in their third quarter, 1978
excess emissions reports to EPA Region VI illustrate this problem
(Tables 6-2 and 6-3).
6-4
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TABLE 6-2
EXCESS EMISSIONS DATA FROM EXTENDED ABSORPTION
NITRIC ACID PLANT OPEPATIONS
Plant: CF Industries, Donaldsonville, LA
a,b
Date
7/2/78
7/11/78
7/23/78
8/7/78-
8/16/78
8/20/78
8/22/78
8/24/78
8/25/78
8/29/78
Time Period
. 12-1 pm
1-2 pm
2-3 pm
3-4 pm
6-7 pm •
7-8 pm
8-9 pm
2-3 pm
3-4 pm
4 -5 pm
3-4 pm
4-5 pm
5-6 pm
6-7 pm
7-8 pm
6-7 pm
7-8 pm
8-9 pm
11-12 am
12-1 pm
1-2 pm
2-3 pm
11-12 am
12-1 pm
1-2 pm
2-3 pm
1-2 pm
2-3 pm
3-4 pm
1-2 pm
2-3 pm
3-4 pm
5-6 pm
6-7 pm
7-8 pm
Emissions
Lb. NOX Per
Ton of 100% HN03
3.83
4.52
4.26
3.52
5.89
4.99
4.15
5.71
6.65
3.76
4.27
4.23
3.27
5.20
3.48
4.25
5.65
2.32
2.81
3.29
3.40
3.07
2.88
3.23
3.24
3.00
5.49
4.17
3.74
4.25
2.89
2.46
3.23
2.63
3.55
Cause
Start up
Start up followed shutdown due
valve malfunction
to expander bypass
Start up
Start up followed shutdown due
temperature trip
Start up followed shutdown due
trip
to high guage
to NO compressor
Reduced absorption tower efficiency due to high
ambient temperature
Reduced absorption tower efficiency due to high
ambient temperatures
Start up followed shutdown due
trip
Start up followed shutdown due
Start up followed shutdown due
failure
to NO compressor
to mysterious trip
to electrical power
a. Increased emissions occur during start ups due to lag time in establishing required
absorption tower pressure and lowered circulating water temperature. No external
NO abatement system is used at this acid plant.
b. Pounds of NO are calculated based on 225 ppm(v) equal to 3 Ibs/ton at 100 percent
production rate.
Source: Carville, 1978.
6-5
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7.0 FINDINGS AND RECOMMENDATIONS
The primary objective of the report has been to assess the need
for revision of the existing NSPS for nitric acid plants, including
a review of the NOX standard. The existing opacity standard is di-
rectly related to the NOX standard and is not reviewed separately.
The findings and recommendations developed in this area are presented
below.
7.1 Findings
• The best demonstrated NOX control technology used in the
rationale for the original standard, the nonselective
catalytic reduction process, has been largely supplanted
in the last few years by a new control process—extended
absorption—due to increasing cost and shortages of the
principal fuel (natural gas) used in the former process.
Based on this overriding consideration it appears that
the NOx control process of choice by the nitric acid
industry for at least the next few years will be the
extended absorption process.
• Both catalytic reduction and extended absorption pro-
cesses can achieve NOX emission control levels below the
1.5 kg/Mg (3 Ib/ton) standard, based on NSPS compliance
test results. The average of seven sets of test data
from catalytic reduction controlled plants is 0.22 kg/Mg
(0.44 Ib/ton), and the average of six sets of test data
from extended absorption controlled plants is 0.91 kg/Mg
(1.82 Ib/ton). Thus/.catalytic reduction appears to be
capable of controlling NOX emissions to a level approx-
imately four times lower than the extended absorption
process based on NSPS compliance test results. In all
cases, the observed opacity was equal to or less than
the opacity standard.
• Based on available information on the NOX emission con-
trol capability of the extended absorption process and
performance guarantees from a principal vendor of this
process, there does not appear to be enough of a safety
factor available in the extended absorption process to
permit any substantial increase in stringency of the
NOX standard at this time.
7-1
-------
• While use of the extended absorption process for
NOX control in new nitric acid plants will not cause
any appreciable economic penalty as compared with the
use of catalytic reduction in meeting the present NOX
NSPS, making the standard more stringent would involve
greatly increased capital costs for the former process
since much larger absorption towers would have to be
incorporated in the new plants in order to meet tighter
performance guarantees. Investment cost for a plant
incorporating the extended absorption process may be
as much as 20 percent greater than that for a nitric
acid plant with a catalytic reduction NOX control unit
installed making the catalytic reduction controlled plant
less capital-intensive.
7.2 Recommendations
At this time it is recommended that no change be made in the
NOV NSPS for nitric acid plants. The overriding consideration
A
leading to this recommendation is that sharply escalating cost and
developing long-term shortages of natural gas — the principal fuel
used in the catalytic reduction process for NOX control — have
caused the nitric acid industry to switch to the extended absorption
process for NOX control. Approximately 50 percent of nitric acid
plants subject to NSPS built in the last 4 years and 90 percent of '
plants to be completed by 1980 will have incorporated the extended
absorption process for NOX control.
It is further recommended that an in-depth EPA study be carried
out to completely define the NOX control capability of the extended
absorption process before any future consideration can be given to
making the current NOX NSPS more stringent.
7-2
-------
8.0 REFERENCES
Acurex Corporation/Aerothenn Division, 1977. Control Techniques for
Nitrogen Oxide Emissions from Stationary Sources. Aerotherm
Report TR-77-87 prepared for U.S. Environmental Protection
Agency, Research Triangle Park, N.C.
Apple, G., 1978. Personal communication. Dupont Co., Glasgow,
Del.
Baker, J., 1978. Personal communication. Apache Powder Co., Benson,
Ariz.
Bain, R., 1978. Personal communication. IMC Corp., Fertilizer
Group, Sterlington, La.
Berlant, M., 1978. Personal communication. South Coast Air Quality
Management District, Anaheim, Calif.
Bland, J., 1978. Personal communication. Allied Chemical Corp.,
Newell, Pa.
Brown, M.L., 1976. Nitric Acid Plant Emisson Control Grande Paroisse
Extend Absorption. Proc. Fertilizer Institute, Env. Symposium,
New Orleans, La. January.
Byrne, D., 1978. Personal communications. • D. M. Weatherly Co.,
Altanta, Ga.
Carville, T.E., 1978. Personal communications. CF Industries, Inc.,
Donaldonsville, La.
Chapman, J.D., 1973. Oxford Regional Economic Atlas United States
and Canada. Clarendon Press, Oxford.
Chemical and Engr. News, August 21, 1978, p. 8.
Coop, D., 1978. Personal communication. N-Ren Corp., Cincinnati,
Ohio.
Dessert, W., 1978. Personal communication. Allied Chemical Corp.,
Geismar, La.
Dezariac, J., 1978. Personal communication. Rock Island Arsenal,
Rock Island, 111.
Dupont Co., 1974. 400 Series Analyzer Systems Brochure. A.D.
Snyder, et al., 1971.
8-1
-------
Gardner, R., 1978. Personal communication. U.S. EPA Region IV,
Atlanta, Ga.
Giles, C., 1978. Personal communication. U.S.S. Agricultural Chem-
icals, Crystal City, Mo.
Gillespie, G.R., et al., 1972. Catalytic Purification of Tail Gas.
Chemical Engineering Progress, Vol. 68, No. 4, April.
Kelly, M., 1978. Personal communication. Valley Nitrogen Producers,
Inc., Fresno, Calif.
Manderson, N.C., 1972. Nitric Acid: the Demand/Supply Outlook for
Nitric Acid. Chemical Engineering Progress, 68:4,57. April.
Mann, C., 1978. Personal communication. Requests and Information
National Air Data Branch, U.S. Environmental Protection Agency,
Research Triangle Park, N.C.
MITRE Corporation, 1978. Regional Views on NSPS for Selected Cate-
gories. MTR-7772. Metrek Division. McLean, Va.
Murphy, D., 1978. Personal communication. Agrico Chemical Co.,
Catoosa, Okla.
Read, M.J., 1978. Personal communication. Terra Chemicals, Inter-
national. Woodward, Okla.
Russell, C., 1978. Personal communication. J.F. Pritchard Co.,
Kansas City, Mo.
Snyder, A.D., E.G. Eimutis, M.G. Konieek, L.V. Parts, and P.L.
Sherman. Instrumentation for the Determination of Nitrogen
Oxides Content of Stationary Source Emissions, EPA Contract No.
EHSD 71-30.
Spaniel, J., 1978. Personal communication. Chevron Chemical, Inc.,
Kennewick, Wash.
Spruiell, S., 1978. Personal communication. U.S. EPA Region IV,
Dallas, Texas.
Stark, J., 1978. Personal communication. Mississippi Chemical Co.,
Yazoo City, Miss.
Thompson, J., 1978. Personal communication. Nitram, Inc., Tampa,
Fla.
8-2
-------
U.S. Dept. of Commerce, Bureau of the Census, 1965. Statistical
Abstracts of the United States, 1953-1964, Section on Chemical
Products. Washington, B.C.
U.S. Dept. of Commerce, Bureau of the Census, 1977. Current Indus-
trial Reports, Inorganic Fertilizer Materials and Related
Products. Washington, B.C.
U.S. Environmental Protection Agency, 1971. Background Information
for Proposed New Source Performance Standards. Office of Air
Programs. U.S. Environmental Protection Agency. Research
Triangle Park, N.C.
U.S. Environmental Protection Agency, 1976. Molecular Sieve NOX
Control Process in Nitric Acid Plants. EPA-600/2-76-015.
Research Triangle Park, N.C.
U.S. Environmental Protection Agency, 1976a. Priorities and Pro-
cedures for Development of Standards of Performance for New
Stationary Sources of Atmospheric Emissions, EPA-450/3-76-020.
Research Triangle Park, N.C.
Vick, J.J., 1978. Personal communication. Monsanto Textile Co.,
Escambia City, Fla.
Weatherly, B.M., 1976. Catalytic Abatement and Absorption ,for NOX
Removal or Recovery in Nitric Acid Plants. Proc. Fertilizer
Institute, Environmental Symposium, New Orleans, La.
Wolleson, W., 1978. Personal communication. J.R. Simplot Co.,
Pocatello, Idaho.
Wyatt, E.S., 1973. Technical Guide for Inspection of New Source
Nitric Acid Plants, Braft Report. Prepared for Office of
General Enforcement, U.S. Environmental Protection Agency,
Washington, B.C.
8-3
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-79-013
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
A Review of Standards of Performance for
New Stationary Sources — Nitric Acid Plants
5. REPORT DATE
January 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Marvin Drabkin
8. PERFORMING ORGANIZATION REPORT NO.
MTR-7911 - -
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Metrek Division of the MITRE Corporation
1820 Do!ley Madison Boulevard
Me Lean, VA 22102
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-2526
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
DAM for Air Quality Planning and Standards
Office of Air, Noise, and Radiation
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
14. SPONSORING AGENCY CODE
EPA 200/04
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report reviews the current Standards of Performance for New Stationary
Sources: Subpart 6 - Nitric Acid Plants. It includes a summary of the: current
standards, the status of current applicable control technology, and the ability
of plants to meet the current standards. Information used in this report is
based upon data available as of June 1978. The recommendations state that no
change be made at this time in the NOX NSPS for nitric acid plants, but that
a study be made of the NOX control capability of the extended absorption process.
17.
KEY WORDS AND DOCUMENT ANALYSIS
a.
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
13B
18. DISTRIBUTION STATEMENT
Release Unlimited
EPA Fofm 2220-1 (Rev. 4-77} PREVIOUS EDITION is OBSOLETE
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
72
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
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