ENVIRONMENTAL HEALTH SERIES
Air Pollution
ATMOSPHERIC
EMISSIONS
FROM NITRIC ACID
MANUFACTURING PROCESSES
-------
ATMOSPHERIC EMISSIONS FROM
NITRIC ACID MANUFACTURING PROCESSES
Cooperative Study Project
Manufacturing Chemists' Association, Inc.
and
Public Health Service
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Division of Air Pollution
Cincinnati, Ohio
1966
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CONTROL NOW-
FOR CLEAN AIR!
Public Health Service Publication No. 999-AP-27
For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington, D.C., 20402 - Price 40 cents
ii
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CONTENTS
PREFACE vii
ACKNOWLEDGEMENTS viii
USE OF THIS REPORT 1
SUMMARY
Manufacturing Processes 3
Nitric Acid Production 3
Emissions from Nitric Acid Processes 3
Control of Emissions 4
GROWTH OF NITRIC ACID INDUSTRY
Historical Background 5
Current Production and Uses 6
Future Trends 6
NITRIC ACID MANUFACTURE
Chemistry of the Process 9
The Pressure Process 9
Combination and Intermediate Pressure Processes 11
Atmospheric Pressure Process 13
Other Processes 15
Acid Concentration Processes 15
Abatement Methods and Equipment 16
EMISSIONS FROM NITRIC ACID PROCESSES
Nitric Acid Manufacture 21
Other Processes 25
Plant Operating Variables 27
SUMMARY OF SAMPLING AND ANALYTICAL TECHNIQUES
Total Nitrogen Oxides 31
Oxygen 32
Nitrogen Dioxide 32
Acid Mist 32
GLOSSARY OF TERMS „ 35
APPENDICES
A. Sampling and Analytical Techniques 39
B. Nitric Acid Establishments in the United States 69
C. Factors Causing High Emissions of Nitrogen Oxides 75
D. Physical Data—Nitric Acid 79
REFERENCES 87
SUBJECT INDEX 89
iii
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FIGURES
1. Flow Diagram of a Typical 120 Ton/Day Nitric Acid Plant Utilizing
the Pressure Process 10
2. Flow Diagram of a Typical 120 Ton/Day Nitric Acid Plant Utilizing
the Combination Pressure Process 12
3. Flow Diagram of a Typical 120 Ton/Day Nitric Acid Plant Utilizing
the Atmospheric Pressure Process 14
4. Nitric Acid Concentrating Unit - 16
5. Typical Nitric Acid Plant Tail Gas Catalytic Reduction Unit 17
6. Pounds of Total Nitrogen Oxides Calculated as Nitrogen Dioxide
Emitted Per Hour vs Daily Production of Nitric Acid 26
7. Percent Oxidation of Nitric Oxide to Nitrogen Dioxide by Air at
25°C and 1 Atmosphere 33
APPENDIX FIGURES
Al Apparatus for Integrated Grab Samples 43
A2 Apparatus for Grab Samples - 43
A3 Data Sheet for Field Evaluation of Total Nitrogen Oxides by
Hydrogen Peroxide Method - 45
A4 Sampling System for Model 4 Photoelectric Analyzer 56
A5 Equilibrium Data for 2NO0 ^ N.,0, 58
2 24
A6 Model 4 Analyzer Calibration 60
A7 Acid Mist Sampling Train Control Panel 61
A8 Acid Mist Sampling Train Collection Compartment 62
A9 Data Sheet for Sampling N/tric Acid Mist 64
A10 Typical Orifice Calibration Curve at 70°F and 29.9 in Hg 65
Dl Boiling Point and Vapor Equilibrium Diagram for Nitric Acid—
Water Solutions at Atmospheric Pressure 82
D2 Effect of Concentration on Normal Freezing Points of Nitric Acid
—Water Solutions 83
D3 Nomograph Relating Specific Gravity and Acid Strength for Weak
Nitric Acid 84
D4 Nomograph Relating Specific Gravity and Acid Strength for Strong
Nitric Acid ; 85
iv
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TABLES
1. Growth of Nitric Acid Industry in United States 7
2. Emission and Operating Data for Nitric Acid Plants Without Waste
Gas Treatment Equipment 22
3. Emission and Operating Data for Nitric Acid Plants Having
Catalytic Waste Gas Treatment Equipment 24
4. Emission and Operating Data for Nitric Acid Plants Having Alkaline
Scrubbing Equipment 25
5. Nitric Acid Feeds and Compositions for a 3000-Pound-Per-Hour
(100% basis) Nitric Acid Concentrator 27
6. Atmospheric Emissions from a 3000-Pound-Per-Hour (100% basis)
Nitric Acid Concentrator 27
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PREFACE
To provide reliable information on the nature and quantity of emissions
to the atmosphere from chemical manufacturing, the Manufacturing Chemists'
Association, Inc. and the Division of Air Pollution, United States Public
Health Service, Department of Health, Education, and Welfare entered into
an agreement on October 29, 1962. A cooperative program was established
to study emissions from selected chemical manufacturing processes and to
publish information about them in a form helpful to air pollution control
and planning agencies and to chemical industry management.* Direction
of these studies is vested in an MCA-USRHS Steering Committee, presently
composed as follows:
Representing USPHS Representing MCA
Austin N. Hellerf Willard F. Bixbyt
John H. Ludwig Louis W. Roznoy
Stanley T. Cuffe Clifton R. Walbridge
Robert Porter Elmer P. Wheeler
Information to be published will describe the range of emissions during
normal operating conditions and the performance of established methods
and devices employed to limit and control these emissions. Interpretation
of emission values in terms of ground-level concentrations and assessment
of potential effects produced by the emissions are both outside the scope of
this program.
*The initial report in this series is Atmospheric Emissions from Sulfuric Acid
Manufacturing Processes, PHS Publ. No. 999-AP-13, U. S. Government
Printing Office, Washington, D. C., 60 cents.
fPrincipal representatives
vii
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ACKNOWLEDGEMENTS
Many companies and individuals in the nitric acid industry have been
helpful in carrying forward this study, and for their contributions the
project sponsors extend their sincere gratitude.
Special thanks are due the following organizations for their participa-
tion in a program of stack sampling and analysis specifically for this study:
E. I. du Pont de Nemours and Company
Hawkeye Chemical Company
The Tennessee Valley Authority
Several companies also have provided from their records additional
stack sampling and analytical data, which have been incorporated into
this report.
Richard W. Gerstle of the Public Health Service and Ralph F. Peterson
of E. I. du Pont de Nemours and Company were the investigators in the
study and are the principal authors of this report. The sponsors acknowledge
the contribution of E. I. du Pont de Nemours and Company in providing the
services of Mr. Peterson.
vui
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USE OF THIS REPORT
This report, one in a series concerning the atmospheric emissions from
chemical manufacturing processes, has been prepared to provide information
on nitric acid manufacture.
Background information is included to define the importance of the nitric
acid industry in the United States. Basic characteristics of the industry are
discussed, including growth rate in recent years, manufacturing processes,
uses for the product, and the number of producing establishments, i.e.,
manufacturing sites, in existence at the present time.
A description is given for the ammonia oxidation process—the principal
process in commercial use today—including the pressure variations used
for reaction and absorption. Process information includes discussions of the
normal operating variables that affect the types and quantities of emissions,
the normal range of emissions, and methods of controlling emissions. Sup-
plemental material provides detailed descriptions of sampling and analytical
methods.
The emission data represent results from approximately 30 percent of
the present number of establishments.* Most of these data have been
gathered from production records of nitric acid producers. Data also include
results from several stack-sampling programs conducted jointly during 1964
by the Manufacturing Chemists' Association and the United States Public
Health Service. Results obtained are consistent with the values of the
emissions otherwise reported.
The production of nitric acid has been a basic industry in the United
States for at least 40 years, and the manufacturing procedures have become
well established.
Emissions to the atmosphere from a nitric acid plant depend upon a
number of factors, such as plant design, skill of operation, efficiency of
absorption, and the use of special devices to reduce emissions. This report
should be reviewed from time to time to determine whether revision is
needed to reflect prevailing conditions.
Although this report has been prepared as a technical review for those
concerned with the control of air pollution, it is expected that this in-
formation will also be helpful to chemical plant management and technical
staffs. It may also be useful to engineering students, medical personnel, and
other professional people interested in the atmospheric emissions from nitric
acid manufacturing plants.
*Establishment: A works having one or more nitric acid plants or units,
each being a complete production entity.
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SUMMARY
MANUFACTURING PROCESSES
Since 1930 most of the nitric acid made commercially in the United
States has been produced by the ammonia oxidation process. Although
various types of plants have been constructed for carrying out this synthesis,
the basic chemistry is the same in all plants. It involves high-temperature
oxidation of ammonia with air over a platinum catalyst to form nitric oxide,
followed by oxidation of the nitric oxide to nitrogen dioxide and absorption
in water to produce an aqueous solution of nitric acid. The nitrogen that
enters the system in the air supplied to the process and small amounts of
unreacted oxygen and nitrogen oxides, mainly NO and NO2, are discharged
from the absorber to the atmosphere. This discharge represents the main
source of atmospheric emissions from nitric acid plants today. The composi-
tion of this exit gas, particularly its nitrogen oxides content, depends on the
type of process employed and on the operating conditions.
NITRIC ACID PRODUCTION
Production of nitric acid has increased sharply in the last 5 years. Since
1958, production has increased 70 percent to an annual rate of 4,609,000 tons
in 1964.(1) This growth rate of about 9 percent per year may continue for
several more years.
There are presently 74 nitric acid establishments having production
capacities ranging from 500 to 380,000 tons per year (100 percent HNO3 basis).
Product acid varies in strength from 50 to 65 percent; most of it is in the
range of 55 to 60 percent. The largest single use of the product is in the
manufacture of fertilizer-grade ammonium nitrate.
EMISSIONS FROM NITRIC ACID PROCESSES
Nitric Acid Manufacture
The major source of atmospheric emissions is the absorption column
in which nitrogen oxides are reacted with water to form nitric acid. The
exit gas from the column contains unreacted nitrogen oxides (largely in the
form of nitric oxide and nitrogen dioxide), oxygen, and nitrogen. Trace
amounts of acid mist or vapor may also be present. Nitric oxide is a colorless
gas; nitrogen dioxide is characterized by a reddish-brown color. The total
concentration of nitrogen oxides normally ranges from 0.1 to 0.6 percent by
volume of effluent prior to any treatment for control. Nitrogen dioxide
accounts for about one half of the total nitrogen oxides. Emission data are
shown in Tables 2, 3 and 4, (Pages 22, 24, and 25).
Other Processes
Emissions of nitrogen oxides occur also with certain chemical operations
where nitric acid is employed, as in nitration and oxidation. Small amounts
of nitrogen dioxide are also lost from acid concentrators and acid storage
tanks. These emissions are evidenced by their dense reddish-brown color,
but generally their volume is small.
SUMMARY
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CONTROL OF EMISSIONS
Factors that can cause heavy emissions of nitrogen oxides are (1)
operation above design capacity, (2) production of acid stronger than that
for which the plant was designed, (3) insufficient supply of oxygen to the
system, and (4) leaks from heat exchangers. High cooling-water tempera-
tures and atmospheric temperatures likewise reduce absorption efficiency
and increase emissions; for this reason emissions are usually more noticeable
in summer than in winter.
Emissions can be substantially reduced by installation of facilities to
remove nitrogen oxides from the tail gas. Alkaline scrubbing systems or
catalytic reduction equipment, presently used for this purpose, can reduce
nitrogen oxides emissions by as much as 90 percent.
Scrubbing with caustic solutions may involve a problem of liquid waste
disposal. Catalytic fume-abatement equipment is being used increasingly to
reduce nitrogen oxides emissions. Plants equipped with catalytic fume
eliminators usually operate with no visible plume. The heat generated in
these eliminators is recovered in heat exchangers and a waste heat boiler,
and also as power in recovery compressors or turbines. Catalytic fume
elimination equipment is now found on about 15 percent of nitric acid plants.
Capital costs range from $1.00 to $2.00 per scfm of tail gas, excluding such
auxiliary equipment as waste heat boilers and controls.
Emission Guidelines
Atmospheric emissions from nitric acid plants depend on plant operating
conditions, production rates, and the use of control devices. As shown in Table
2, plants operating within design capacities and producing 55 to 60 percent
nitric acid can limit nitrogen oxides concentration to 0.3 percent in the
effluent stream leaving the nitric acid absorption column. On this basis a
plant producing 300 tons per day will emit approximately 600 pounds of
nitrogen oxides per hour, as shown in Figure 6. Installation of scrubbers
or catalytic reduction equipment in the effluent gas stream can further reduce
these emissions by 50 to 90 percent when the equipment is operating properly.
Only trace amounts of nitric acid mist are normally emitted from a properly
operated plant.
Emissions from nitric acid concentrators amount to about 10 pounds of
nitrogen oxides per 1000 pounds of strong acid produced. Emissions during
startup or shutdown procedures are usually lower than those that occur
during normal operations.
SUMMARY
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GROWTH OF NITRIC ACID INDUSTRY
HISTORICAL BACKGROUND
The need for combined or "fixed" nitrogen in the growth and main-
tenance of all animal and plant life is well established and has been known
since 1862. Nitrogen is "fixed" by various types of bacteria and is thus
returned to the soil via the plant host upon which the bacteria may live. In
addition, bacterial action on dead organic matter produces fixed nitrogen
compounds. These amounts of fixed nitrogen compounds are not sufficient for
today's large agricultural needs, nor are these nitrates available for making
dyestuffs, explosives, nitrocellulose, and other products. Because of the in-
sufficient supplies of naturally occurring fixed nitrogen, much attention has
been given to the conversion of atmospheric nitrogen to various useful com-
pounds, especially nitric acid.
Until the early 1900's, fixed nitrogen was obtained largely from Chilean
saltpeter (sodium nitrate) or as a byproduct in coke manufacturing as
ammonium sulfate. The Chilean saltpeter was used directly as a nitrate
salt or converted to nitric acid by distilling with sulf uric acid. In the reaction
between sulfuric acid and saltpeter, cast iron retorts were charged with 1,500
to 5,000 pounds of sodium nitrate; sulfuric acid was added, and the mixture
was gently heated. The resulting nitric acid vapor was then condensed and
withdrawn. Sodium bisulfate (niter cake) remaining in the retort could be
sold occasionally as a byproduct.
The desire of manufacturers to reduce dependence on Chilean saltpeter
around the time of the First World War stimulated developments of other
methods of nitric acid production. The Haber process for ammonia produc-
tion had also been introduced by 1910, and the combination of these two
factors gradually caused a shift toward the newer and more economical
ammonia oxidation method for manufacturing nitric acid.
Modern methods of nitric acid production involve oxidation of ammonia
in air over a platinum catalyst followed by cooling of the resulting nitrogen
oxides and their absorption in water. Use of this basic method dates back
to about 1904, when Ostwald designed and built a small pilot plant for
this process.(2) This plant initially used relatively large amounts of catalyst;
however, developments in the use of preheated air and of electrically heated
gauze-type catalyst helped conserve the expensive platinum.
Nitrogen oxides were also made by passing air through an electric arc.
The intense heat caused about 2 percent of the nitrogen in the air to react
with oxygen to form nitric oxide. The emerging gases were cooled rapidly
to prevent decomposition and were oxidized to nitrogen dioxide and absorbed
in water to make nitric acid. This process required large amounts of electric
power and is presently not an economical method for nitric acid manufacture
in this country.
Work in the United States on the production of nitric acid by ammonia
oxidation was underway by 1916. Ammonia was obtained from calcium
cyanamide, CaCN2, and oxidized with air by passage through an electrically
heated platinum gauze. In 1918 the Air Nitrates Corporation, acting as
GROWTH OF THE INDUSTRY
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agent for the United States Government, built a large plant for the produc-
tion of nitric acid at Muscle Shoals, Alabama. This early plant •was con-
structed entirely of acid-resistant brick and operated at atmospheric pressure.
The slow absorption rates of the nitrogen dioxide in water at atmospheric
pressure necessitated a large absorption volume, comprising 24 towers, each
1,220 feet square by 60 feet high, to produce 280 tons per day of acid. Because
of the high initial building costs and the low strength of acid produced, the
brick type of plant has become extinct. A number of atmospheric pressure
plants were later constructed of stainless steel, and some of these are still
in operation.
With the further development of acid-resistant metal alloys in the mid-
1920's, nitric acid manufacturing techniques shifted toward the use of higher
pressures. Operation at high pressures enabled the manufacturer to build
a much smaller plant for the same acid production because nitrogen dioxide
is absorbed much faster by water at high pressures. In the early plants, the
high-pressure (80-psig) tail gas leaving the absorption system was simply
vented to the atmosphere. By the mid-1930's, process efficiency had been
significantly improved by reheating the 80-psig tail gas to about 500°F in a
heat exchange system and using it to drive a reciprocating expander. The
energy contained in the hot tail gas thus provided 30 to 40 percent of the
power used for process air compression.
A further development in power recovery technology occurred about
1950, when gas expander turbines were adapted for this purpose. Gas
turbines do not have the lubrication problems inherent in reciprocating
expanders and therefore can operate at much higher temperatures. Recovery
gas turbines may provide up to 90 percent of a plant's power requirements.
Almost all nitric acid in the United States is now manufactured by a process
in which the absorption portion, if not all of the process, operates at pressures
ranging from 50 to 120 psig.
CURRENT PRODUCTION AND USES
Table 1 shows the growth of nitric acid production over the past 25
years. The nitric acid industry is closely tied to the fertilizer industry; 75
percent of the nitric acid production goes into the manufacture of ammonium
nitrate, much of which is used as fertilizer. A significant quantity of
ammonium nitrate is used in commercial explosives. Substantial quantities
of nitric acid are also used for nitrating organic compounds and for certain
rocket fuels.
In January 1966, 74 establishments were producing nitric acid in the
United States. Missouri and Kansas were the leading states in the production
of nitric acid, with a combined capacity greater than 1 million tons of nitric
acid per year. The largest concentration of nitric acid plants is in the
midwestern and southeastern portions of the United States.
FUTURE TRENDS
The ammonia oxidation process for nitric acid manufacture seems firmly
entrenched as the most economical commercial process. The cost of ammonia
GROWTH OF THE INDUSTRY
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has shown a marked downward trend as a result of improved process
technology, and therefore the cost of nitric acid has likewise decreased. In
recent years much progress has been made in improving the efficiency of
nitric acid plants, particularly in power utilization through recovery of
energy from waste tail gas. The present trend is toward the building of larger
plants with capacities of 500 or more tons of nitric acid (100 percent basis)
per day. The proposed construction of an 800-ton-per-day unit was announced
in October, 1965.
TABLE 1. GROWTH OF NITRIC ACID INDUSTRY IN
UNITED STATES (1)
Production,
Year Thousands of short tons Increase, %
100% acid basis
1939 168
1947 1,189 608
1950 1,336 12.4
1955 2,592 94.0
1958 2,704 4.3
1959 3,074 13.7
1960 3,315 7.8
1961 3,380 2.0
1962 3,670 8.6
1963 4,243 15.6
1964 4,609 8.6
GROWTH OF THE INDUSTRY
GPO 828—664—2
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NITRIC ACID MANUFACTURE
CHEMISTRY OF THE PROCESS
Nitric acid in the United States is produced by the ammonia oxidation
process, which entails three principal steps:
One volume of anhydrous ammonia gas is mixed with about nine volumes
of hot air and passed through a pad composed of several layers of platinum-
rhodium wire-mesh catalyst at high temperature. Nitric oxide (NO) forms
according to equation (1).
4 NH3 + 502 = 4NO + 6 H2O (1)
When the NO stream is cooled, the NO reacts with oxygen remaining in
the mixture to form nitrogen dioxide (NO2) and the dimer, nitrogen tetroxide
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• MAIN INLET GAS STREAM
TAIL GAS STREAM
COMPRESSOR — EXPANDER
FLOW, Ib/hr
TEMPERATURE. °F
PRESSURE, psig
NH., Vol %
NO, Vol %
NO.., Vol %
0,, Vol %
H._.0. Vol %
HNO.,, Wt %
H..O. Wt %
N.., Vol %
CO.,, Vol %
1
AMMONIA
2,900
170
170
100
_
_
_
—
—
0.05
—
2
AIR
51,600
60
0
—
_
_
20.8
0.9
—
—
78.3
3
MIX
47,050
450
112
100
_
_
18.7
0.8
—
_
17.5
4
CONVERTER
PRODUCTS
47,050
1.650
112
0
9.3
0
6.3
15.4
—
—
69.0
5
COOLED
GAS
38,350
105
98
0
1.1
6.4
_
0.9
_
_
91.6
6
CONDENSATE
ACID
8,700
105
98
—
—
12
—
—
40-50
50-60
_
—
7
SECONDARY
AIR
7,450
450
120
—
—
—
20.8
0.9
_
_
78.3
8
NITRIC ACID
PRODUCT
16.650
135
95
—
—
_
—
_
60
40
_
—
9
WATER
3,350
100
125
—
—
—
—
—
_
100
—
—
10
TAIL GAS
41.200
85
92
—
0.10
0.15
3.0
0.6
_
—
96.15
11
STACK
EFFLUENT
42.600
450
0
—
0.01
Nil
Nil
3.8
_
_
94.2
2.0
Figure 1 — Flow diagram of a typical 120-ton-per-day nitric acid plant utilizing the pressure process.
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various arrangements of heat exchangers. A filter at the exit of the heat
exchanger train recovers catalyst dust.
Oxidation of nitric oxide to nitrogen dioxide is a continuing process
once the gas leaves the converter; however, oxidation is favored by low
temperatures, and no significant formation of nitrogen dioxide occurs until
the gas enters the cooler condenser. As the gas becomes cooled, water con-
denses and reacts with the newly formed nitrogen dioxide to produce a weak
nitric acid. Cooler condensers are usually designed with sufficient surface
and volume to allow for both cooling of the gas and oxidation of nearly all
nitric oxide to nitrogen dioxide.
The gas stream leaving the cooler condenser is passed through a cyclone
condensate separator before entering the base of the absorber. The separated
condensate, which is 40 to 50 percent nitric acid, enters the column at an
intermediate point. The absorber contains bubble cap plates to provide in-
timate countercurrent contact between the aqueous solution and the rising
gas stream. Because the absorption of nitrogen dioxide in this solution and
its reaction with water to form nitric acid are highly exothermic processes,
the tower is provided with internal cooling coils to remove the heat of
reaction. Water is fed to the top of the column for absorption, and secondary
air enters the bottom of the column to provide oxygen for the conversion of
nitric oxide to nitrogen dioxide in the absorber.
Unabsorbed gas, principally nitrogen, leaves the absorption tower at a
temperature of about 85 °F and is passed through an entrainment separator.
The tail gas is then heated by heat exchange with the hot process gases.
The energy contained in the resultant hot gas is recovered in a centrifugal
expander, which drives the air compressor. The gas leaving the expander
is then discharged to the atmosphere. The reheated tail gas may be passed
through a catalytic combustion unit or fume abater to reduce nitrogen
oxides, as shown in Figure 1, before entering the centrifugal expander.
COMBINATION AND INTERMEDIATE-PRESSURE PROCESSES
In the combination pressure process, the oxidation of ammonia occurs
at pressures from atmospheric to about 30 psig. The resulting oxides of
nitrogen are then cooled and generally compressed to about 30 to 50 psig
before being absorbed. Figure 2 illustrates the basic process. This system
provides the benefits of lower maintenance, reduced catalyst loss, and higher
conversion efficiency obtained by operating the ammonia converter at low
pressures. Further, it provides the benefits obtained by high-pressure absorp-
tion; these include smaller absorber size, greater absorption efficiency, and
higher-strength product acid. Such nitric acid plants are not common in
the United States; they are mentioned to provide a complete picture of
process variations.
The basic chemistry is identical with that encountered in the high
pressure systems; i.e. oxidation of ammonia over a catalyst, oxidation of
the resulting nitrogen compounds to nitrogen dioxide, and absorption of the
resulting oxides in water. Acid strengths up to 70 percent have been obtained
with these systems.(4)
NITRIC ACDD MANUFACTURE 11
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STACK
EFFLUENT
TAIL GAS STREAM
MAIN INLET GAS STREAM
CATALYST
i
AMMONIA
VAPOR Al"
STACK
FLOW, Ib/hr
TEMPERATURE, 'F
PRESSURE, psig
NH,, Vol %
NO. Vol %
NO.., Vol %
0._., Vol %
H_.O, Vol %
N... Wt %
HNO.,. Wt %
H.O. Wt %
1
AMMONIA
2,880
170
5
100
—
_
_
_
_
_
<0.5
2
AIR
53,550
60
5
_
_
_
20.8
0.9
78.3
_
-
3
MIX
45,680
270
5
10.2
_
_
18.7
0.8
70.3
_
-
4
CONVERTER
PRODUCTS
45,680
1.550
4
0
9.6
0
6.2
15.4
68.8
_
-
5
COOLED
GAS
52.730
160
40
0
5.1
32
8.0
4.6
79.1
—
-
CO
- -6 —
CONDENSATE
ACID
3,700
95
40
_
Nil
— 1
15.0
85.6
SECONDARY
AIR
10.750
?50
5
_
_
208
0.9" "
783
r -r
8
NITRIC ACID
PRODUCT
16,650
80
0
: -
60.0
40.0
9
WATER
3,600
60 4
50
_
— - -
100
10
TAIL GAS
43,450
85
40
0.10
0.10
40
1.5
94.3
— ~-
11
STACK
EFFLUENT
43.450
450
0
0.13
0.07
4.0
15
94.3
'"I -
Figure 2 — Flow diagram of a typical 120-ton-per-day nitric acid plan) utilizing the combination pressure process.
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The intermediate-pressure plant operates at pressures of 20 to 60 psig
throughout the plant. The basic process is identical to the high-pressure
system except that, because of the lower pressure, additional absorber
volume is required. A series of water-cooled horizontal drum absorbers
have been used for absorption in this type of plant.(5)
ATMOSPHERIC-PRESSURE PROCESS
Because acid-resistant materials were not available, absorption towers
in all of the early nitric acid plants were constructed of brick, which could
not withstand high pressures. The absorption towers therefore had to operate
at atmospheric pressure. With the advent of acid-resistant steel alloys
capable of withstanding high pressures, and with the demand for higher-
strength nitric acid, the atmospheric-pressure plant became outmoded.
Some of these early plants are still in existence today; however, most
are on a standby basis and are not normally in operation. Operation at
atmospheric pressure generally results in a high initial investment because
of the large absorber volume required. Maintenance and operating problems
and costs are minimal, however.
The basic chemistry of the atmospheric-pressure process for the pro-
duction of nitric acid by ammonia oxidation is also identical to that of the
pressure process except that all reactions occur at essentially atmospheric
pressure.
As shown in Figure 3, the ammonia-air mixture reacts across a 90:10
platinum-rhodium gauze catalyst at about 1550°F and is oxidized to nitric
oxide. This gas stream is cooled, and the resulting very weak acid condensate
is fed into the weak end of the absorption system. A typical analysis of
the cooled gas at this point is 6.4 percent NO, 4.0 percent NO2, 5.6 percent
H2O, 4.7 percent O_, and the balance N,. To promote the further oxidation
of NO to NO, the gas is next passed into large oxidation towers, where
residence time is sufficient for the substantial completion of the oxidation
to NO2. The gas stream then passes into a series of absorption towers. Be-
cause of the poor absorption characteristics of nitrogen dioxide in water at
atmospheric pressure and the very slow rate of re-oxidation of NO to
NO2, a large absorption volume is required, about 70 times the volume
required at a pressure of 110 psig. This is because the rate of oxidation of
nitric oxide to nitrogen dioxide varies directly with the square of the
pressure, and operation at atmospheric pressure thus requires greatly in-
creased time for oxidation to occur. Product acid concentrations range from
40 to 50 percent.
Conversion of ammonia to nitric oxide at atmospheric pressure is higher
than at elevated pressures (about 98 percent versus 95.5 percent). Com-
pared to a high-pressure-type ammonia converter, the atmospheric unit
has a much larger cross sectional area of catalyst and employs a larger quan-
tity of catalyst per daily ton of capacity. Catalyst life is improved largely
because of the lower temperature at which the catalyst operates (1550°F).
Gauzes are replaced only every few months, whereas in the high-pressure
converter they must be replaced every few weeks.
NITRIC ACID MANUFACTURE 13
-------
o
MAIN INLET GAS STREAM
• TAIL GAS STRtAM
WATER STACK
EFFLUENT
AMMONIA AIR
VAPOR
STACK
PRODUCT 48-52% HNO.,
FLOW, Ib/hr
TEMPERATURE. 'F
PRESSURE, psig
NH.,. Vol %
NO, Vol %
NO.., Vol %
0.,. Vol %
H.,0, Vol %
HN03, Wt %
H.,0, Wt %
N... Wt %
1
AMMONIA
2,850
100
5
100
_
<0.5
—
2
AIR
54,250
60
5
_
20.8
0.9
•—
78.3
3
MIX
46,100
270
5
10.0
18.7
0.8
—
71.5
4
CONVERTER
PRODUCTS
46,100
1,550
4
0
9.6
0
6.2
15.4
—
68.8
5
COOLED
GAS
44,350
95
3
0
6.4
4.0
4.7
5.6
_
_
79.3
6
CONDENSATE
ACID
1,750
95
_
_
_
Nil
_
25.7
74.3
-
7
SECONDARY
AIR
11,000
60
_
_
_
_
20.8
0.9
_
_
78.3
8
NITRIC ACID
PRODUCT
18,850
80
_
_
—
—
_
—
50.0
50.0
- -
9
WATER
6,750
100
40
_
—
—
_
—
—
100
-
10
STACK
EFFLUENT
45,000
85
0
_
0.1
0.2
4.0
4.2
—
—
91.5 1
Figure 3 — Flow diagram of a typical 120-ton-per-day nitric acid plant utilizing the atmospheric pressure process.
-------
An additional benefit is gained because ammonia evaporates at -28eF at
atmospheric pressure. Thus, no preheating is required to evaporate the
liquid ammonia, and its refrigerating value can be used advantageously to
cool the absorption system.
OTHER PROCESSES
The electric-arc process has found limited use. In this process, air is
passed through an electric arc and at the prevailing high temperatures about
1 or 2 percent of the nitrogen in the air is converted to nitric oxide. The
gases are rapidly cooled and oxidized to nitrogen dioxide.
Newer processes include the Wisconsin process (6) and nuclear nitrogen
fixation. (7) In the Wisconsin process about 1 percent of the nitrogen in
the air is converted to nitric oxide by heating the air to 4,000°F in a pebble
furnace. A double bed of magnesia pebbles preheats the incoming air and
also rapidly chills the combustion products and thus prevents dissociation
of the NO. The product, containing about 2 percent NO, is then concen-
trated in silica gel columns. Silica gel is used first to dehydrate the gas
stream and catalyze the oxidation of NO to NO2. The NO2 is then specifically
adsorbed on silica gel and finally released from the silica gel in concentrated
form by heating the bed. The resulting gas is absorbed in water and can
be used to make a 60 percent acid.
The nuclear nitrogen fixation process is not nearly so well developed
as the Wisconsin process, and neither process is in commercial use today.
Yields of 5 to 15 percent nitrogen oxides have been obtained by exposing
compressed air at 150 psi and 400°F to radiation from uranium-235. Nitrogen
and oxygen molecules are oxidized and decomposed by fission products and
alpha and gamma radiation.
ACID CONCENTRATION PROCESSES
The major portion of the 55 to 65 percent nitric acid produced by the
ammonia oxidation process is consumed at this strength. As previously
mentioned, much of it is used directly in the manufacture of ammonium
nitrate. There remains, however, a fairly substantial requirement for high-
strength (95 to 99 percent) nitric acid, which is obtained by concentrating
the 55 to 65 percent HNO,.
o
The nitric acid—water system forms a maximum boiling azeotrope at
a concentration of 68.4 percent HNO3 at atmospheric pressure; consequently,
nitric acid can not be concentrated beyond this strength by simple frac-
tional distillation. The distillation must therefore be carried out in the
presence of a dehydrating agent. Concentrated sulfuric acid is most com-
monly used for this purpose, although 70 to 75 percent magnesium nitrate is
also used to a limited extent.
Figure 4 is a simplified diagram of a typical nitric acid concentration
unit. As shown, the process consists of feeding strong sulfuric acid and 60
percent nitric acid to the top of a packed dehydrating column, through
which it flows downward countercurrent to ascending vapors. Concentrated
nitric acid leaves the top of the column as 98 percent vapor containing a
NITRIC ACID MANUFACTURE 15
-------
small amount of NO, and O, resulting from dissociation of nitric acid. The
vapors pass to a bleacher and countercurrent condenser system to effect
condensation of strong nitric acid and separation of the oxygen and nitrogen
oxides. These cooled noncondensable gases flow to an absorption column
for recovery of the nitrogen oxides as weak nitric acid in much the same
manner as in the pressure-process nitric acid plants. Auxiliary air is added
to the bottom of the column, and inert gases and unreacted nitrogen oxides
are vented to the atmosphere from the top of the column. The entire process
operates at approximately atmospheric pressure.
TAIL GAS TO
ATMOSPHERE (Volume %)
COUNTERCURRENT
CONDENSER
98% HNOs VAPOR
FEED
93% HoSO^ •*
60% HNO3-»
DEHYDRATING
COLUMN
LIQUI1
CTFAM
»^_
'W//////////A
3
" V
V
c
)
c
)
VAPORJ JCONDENSATE
NON-
CONDENSABLE
GASES
BLEACHER
^-»
TO COOLER AND STORAGE
APOR
70% H2SO.
Co,, > TO COOLER
74.3% N»
20.4% O-
1.0% NO + NO,
4.2% HoO
ABSORPTION
,COLUMN
AIR
55% HNOs
BOILER
Figure 4 — Nitric acid concentrating unit.
ABATEMENT METHODS AND EQUIPMENT
The emission of nitrogen oxides may be reduced by catalytic reduction
with certain fuels and by absorption, adsorption, and flaring. Catalytic
reduction is by far the most widely used method of abatement.
Catalytic Reduction Systems (8,9)
Catalytic reduction is particularly suited to the pressure ammonia oxida-
tion 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-system feed temperature. Efficiencies above 90 percent
16
NITRIC ACID MANUFACTURE
GPO 828-6641-3
-------
are possible, and in addition a significant economic return can be realized
through recovery of heat generated in the catalytic recovery unit.
In operation the tail gases from the absorber are heated to the necessary
catalyst ignition temperature, mixed with a fuel such as hydrogen or
methane (natural gas), and passed into the reactor and over a bed of
catalyst. A number of reactions take place resulting in the dissociation
and decompostition of nitrogen oxides:
CH4
CH
2 02 =
4 N0
4 2
CH, + 4 NO
c°2
4 NO + CO
2 H20
= 2 N
C0
2 + 2 H20
2 H20
(4)
(5)
(6)
Reactions (4) and (5) proceed rapidly, with evolution of considerable
heat. Since the nitrogen dioxide is all converted to nitric oxide in reaction
(5), the gas is now colorless even though there is yet no substantial destruc-
tion of nitric oxide. The reaction of further amounts of natural gas with
the nitric oxide in accordance with reaction (6), which takes place more
slowly, results in decomposition of the nitric oxide to nitrogen. When this
reaction is complete, total abatement is achieved.
A typical catalytic reduction unit is shown in Figure 5; the arrangement
of such a unit in conjunction with a pressure-process nitric acid plant is
shown in Figure 1. Temperatures and compositions are shown for illustrative
purposes. In practice, operating conditions are governed by the kind of
fuel employed, the gas composition, and the type of catalyst. When hydrogen
is used as fuel, the minimum ignition temperature is about 290eF and the
temperature rise is approximately 300 °F for each percent of oxygen in
the tail gas. With natural gas as fuel, minimum ignition temperature is
about 850°F and the temperature rise is 270°F for each percent of oxygen.
800—1000 °F
HEATED TAIL GAS
0.3-0.5% NO
2-4% N2 x
Balance N2
80 psig FUEL
FUEL
f]
S5S&BS
,
CATALYTIC
REDUCTION
UNIT
STEAM
t
900-1500 °F
800-
70
WATER
WASTE HEAT
BOILER
EFFLUENT
TO STACK
A 550 °F
0 psig
0.01-0.20% NO
0-2% CO. x
0.5-2% 0.
1^. 92.0-93.5% N»
' f>"^>^^, COMPRESSOR
1200 _ TAII ftic
psig EXPANDER
Figure 5 — Typical nitric acid plant tail gas catalytic reduction unit utilizing natural gas.
NITRIC ACID MANUFACTURE
17
-------
Usually the catalyst consists of 0.5 percent platinum or palladium on
a support such as woven Nichrome ribbon or ceramic material having a
pelleted or honeycomb structure. The honeycomb support offers the advantage
of low pressure drop. The catalyst will withstand temperatures as high as
1,400 to 1,500°F, which is also the approximate upper temperature limit for
the reaction vessels used in this service.
In a single-stage reduction unit, increasing the amount of fuel raises
the temperature of the gas as reactions (4) and (5) take place. Generally.
the temperature limit of about 1,500°F is reached before all oxygen has
reacted with the fuel, especially when natural gas is used. Under these
conditions the effluent is a colorless gas in which the nitrogen oxides are pres-
ent only as nitric oxide. As shown in Figures 1 and 5, the heat thus generated
can be recovered in a waste heat boiler and can also be recovered as energy
in driving the tail-gas expansion turbine.
Because temperature limits the extent of reaction in a single-stage
reactor, a two-stage reduction process may be required to split the heat
load. This would permit use of excess fuel, or operation on the reducing
side, whereby all oxygen in the tail gas is reacted and the nitrogen oxides
are decomposed in accordance with equation (6). The stack effluent will
contain 0.01 to 0.02 percent or less of nitrogen oxides. It is technically
possible to carry out essentially full reduction and decomposition of the
nitrogen oxides (for example, to 0.01 to 0.02 percent NOX) in a single stage if
the oxygen content of the absorber tail gas is kept well below the usual
3 percent so as to reduce the heat of reaction. Under these conditions,
however, there will be a loss in absorption efficiency in the nitric acid plant
with a consequent operating-cost penalty.
Performance of existing catalytic units varies widely and depends on
the method of operation. One operator may desire maximum reduction of
the nitrogen oxides, another may aim for a colorless plume, and a third,
for maximum heat generation. These variations are obtained by changes
in the amount and type of fuel, the amount of catalyst, oxygen content of
the tail gas, operating temperatures, and reaction time. The basic equipment
design is also a governing factor. Normally, a colorless effluent is accepted
as an indication of proper functioning but not necessarily of a reduction in
nitrogen oxides. In one known instance in which 1 percent methane was
reacted with a tail gas containing 1,100 ppm NO2, 1,900 ppm NO, and
4 percent O2, the exit gases contained 260 ppm NO2, and 2,300 ppm NO. (10)
The exit gas was nearly colorless, but its nitrogen oxides content was reduced
only slightly. As previously pointed out, the high oxygen content of the
tail gas and the consequent high temperature rise in the reactor may have
limited the quantity of fuel used to less than the stoichiometric amount
needed to react with all the oxygen and nitrogen oxides.
The cost of a catalytic tail-gas reduction unit, including catalyst, varies
from $1 to $2 per scfm of tail gas. Depending on the amount of steam pro-
duced and on costs of fuel, the systems will recover a substantial portion
of their capital cost. This steam can be used to furnish part of the power
to drive the nitric acid plant air compressor or it may be used as plant
process steam.
18 NITRIC ACID MANUFACTURE
-------
Large nitric acid plants equipped with catalytic tail-gas reduction units
may use no outside power after startup. The heat generated in the oxidation
of ammonia and in catalytic abatement combine to provide all the energy
necessary to drive the large air compressor. (11)
Ammonia can also be used as a fuel for the catalytic reduction of
nitrogen oxides. It differs from other fuels in that it reacts selectively with
NO and NO2 to form nitrogen without simultaneously reacting with the
oxygen in the tail gas. As a result, temperature rise in the catalytic reactor
is very small. A platinum catalyst supported on ceramic pellets is employed.
The reactions are
4 NH3 + 3 N02 = 3% N2 + 6 H2O (7)
2 NH3 + 3 NO =r 2V2 N~ + 3 H2O (8)
These reactions are carried out within the temperature range 410 to 520°F.
Below 410°F there is a chance that ammonium nitrate would be formed.
Above 520 °F, oxides of nitrogen are formed by the typical ammonia reaction.
In one known commercial installation, ammonia is used as the fuel in
catalytic reduction of nitrogen oxides. The potential presence of ammonium
salts in the effluent could be a deterrent to its use where the gas stream is sub-
sequently used to drive a turbine expander.
Absorption Systems
Various types of absorption towers, in which water is the absorbing
medium, can be used where the nitrogen oxide content, as NO2, of the
effluent stream is relatively high, perhaps 2 to 8 percent. Such a system
functions like an atmospheric-pressure nitric acid plant and is suitable for
application in the recovery and reduction of nitrogen oxides evolved from
nitration or nitric acid oxidation processes.
Best performance can be realized with a gas stream of steady flow
and uniform composition. Water absorbers are not very effective for reducing
emissions from nitric acid manufacturing plants, since these gas streams
represent the effluent from aqueous absorption systems and the nitrogen oxides
concentration, averaging 0.3 percent, is too low for efficient absorption. (12)
Absorption in alkaline solutions, such as sodium carbonate or sodium
hydroxide, is more effective than in water. Under proper feed stream com-
positions, nitrate and nitrite salts can be formed according to the following
reactions:
2 NaOH + 3 NO2 > 2 NaNOg + , NO + H2O (9)
2 NaOH + NO + NO2 + 2 NaNO2 + H2O (10)
An alternate scrubbing system utilizes two stages, with water in the
first stage and- sodium hydroxide in the second, again yielding nitrite and
nitrate salts. Disposing of the byproduct salt solutions may be a problem.
Adsorption Systems
Nitrogen dioxide may be removed by adsorption on activated charcoal
or silica gel. Adsorption on silica gel is actually the basis of the Wisconsin
process for recovery of NO2, which is present to the extent of 1 to 2 percent
NITRIC ACID MANUFACTURE 19
-------
in the gases from the thermal fixation process. The method has not been
used commercially for reducing emissions of nitrogen oxides.
Flaring:
Passing the gases that contain nitrogen oxides through a combustion
chamber or flame will usually reduce the nitrogen oxides to nitric oxide
and thereby provides a colorless emission. The extent of nitrogen oxides
destruction, to nitrogen, is influenced by the kind of burner or flare, the
type of fuel, and the initial concentration of nitrogen oxides in the waste
gas. The performance to be realized for any given set of conditions must be
determined experimentally.
f
Flaring is too costly for the abatement of effluents in nitric acid plants
because of the large volume of gas and low initial nitrogen oxides con-
centration. However, where there is intermittent discharge of nitrogen oxides
in concentrations of 1 percent or more, flaring may be the best means
of abatement.
Tall Stacks
Tall stacks aid in the dispersion of nitrogen oxide gases. Increased
temperature and velocity of the gases increase effective stack height and
further aid dispersion. Hot gases from adjacent processes may be added
to the effluent stack, thus raising the temperature and diluting the emission.
Some European plants use a venturi device on top of a tall stack. The
induction created by the discharge of tail gas through the venturi brings
about a 5:1, or greater, dilution of the effluent with air before it enters the
atmosphere. There is at least one such installation in the United States.
20 NITRIC ACID MANUFACTURE
-------
EMISSIONS FROM NITRIC ACID PROCESSES
NITRIC ACID MANUFACTURE
The main source of atmospheric emissions from the manufacture of
nitric acid is the tail gas from the absorption tower, which contains un-
absorbed oxides of nitrogen. These oxides are largely in the form of nitric
oxide and nitrogen dioxide. In addition, trace amounts of nitric acid mist
are present in the gases as they leave the absorption system. In the pressure
process these gases are reheated for power recovery purposes and discharged
to the atmosphere at 400 to 500°F; any nitric acid mist present is then
changed to its vapor state prior to discharge into the atmosphere. In the
a'tmospheric system, tail gases discharged to the atmosphere are cold, and
therefore any entrained particles of nitric acid in this gas stream would
appear as a mist. The quantity depends upon extent of entrainment and
the efficiency of entrainment separators.
The tail gas is reddish-brown; the intensity of the color depends on
the concentration of nitrogen dioxide present. Data in Table 2 show that
concentrations of 0.13 to 0.19 percent by volume of nitrogen dioxide produce
a definite color in the exit plume. Effluent gases containing less than 0.03
percent nitrogen dioxide are essentially colorless. Note that nitric oxide, as
distinguished from nitrogen dioxide, is colorless.
Table 2 presents emission and operating data from 12 plants. Emissions
range from 0.1 to 0.69 volume percent nitrogen oxides, with an average of
0.37. Limited data indicate that nitrogen dioxide accounts for approximately
Vs to Y2 of these values, the balance being nitric oxide.
Except for Plant 1, all plants listed in Table 2 were of similar design
and were operated at absorber pressures of 72 to 90 psig and at temperatures
of about 90 °F at the absorber outlet. All of the plants were producing acid
in the 55 to 60 percent range and were generally operating near nominal
capacity.
Plant 1 had been modified by the addition of another acid bleacher and
of 12 plates to the top of the absorber. Hot bleach air was injected into
the cooler-condenser, and changes had been made in the process piping in
an effort to produce acid more efficiently. This plant is thus not typical of
standard design.
In Plant 2 and probably Plant 8 leaks in the tail-gas reheater account
for the high emission values. If the values for Plants 1, 2, and 8 are
excluded, the average emission of nitrogen oxides is 0.32 percent.
Emission values for Plants 11 and 12 show that a decrease of 40 to 60
percent in oxygen tends to raise the nitrogen oxide content of the tail gas
by about 30 to 50 percent (compare with values for Plant 10.) The very
low nitrogen oxides content of the tail gas in Plant 3 is due partly to the
lower absorption-tower temperature.
Nitrogen dioxide was measured only at Plants 1 and 2; it constituted
54 and 28 percent, respectively, of the total nitrogen oxides content. At
Plant 2 the leak in the tail-gas reheater caused gas rich in nitric oxide (NO)
from the ammonia converter to leak into the tail-gas stream. The percent
nitrogen dioxide was thus a smaller part of the total.
EMISSIONS 21
-------
g TABLE 2
EMISSION AND OPERATING DATA FOR NITRIC ACID PLANTS
WITHOUT WASTE GAS TREATMENT EQUIPMENT
Plant number
Rated capacity, tons/day
(100% acid basis)
Normal acid strength, %
Percent of rated capacity
Ammonia feed rate, Ib/hr
Ammonia oxidation pressure, psig
Absorption column exit pressure, psig
Absorption column exit temp., °F
Stack gas rate, Mscfma
Total nitrogen oxides in stack gas, vol "%b
Nitrogen dioxide in stack gas, vol %
Oxygen in stack gas, vol %
Total nitrogen oxides emitted, tons/day0
Pounds of nitrogen oxides emitted per
ton of acid produced ( 100 % basis) c
Plume opacity
Plume color
1
55
60
88
100
72
96
3.5
0.24
0.13
4.1
0.8
33
med.
2
55
60
72
100
75
95
3.4
0.69
-------
Table 3 presents emission and operating data for 11 plants equipped
with catalytic combustors for the reduction and removal of nitrogen oxides
normally present in absorption-column tail gases. The general arrangement
of this equipment is as shown in Fig. 1. Hydrogen, natural gas, or a mixture
of the two are used as fuels. The data show the composition of the tail
gas leaving the absorber and of the effluent leaving the catalytic waste gas
combustor. Catalytic waste gas treatment reduced the total nitrogen oxides
emission by 36 to 99.8 percent. In all cases the stack effluent was clear and
colorless, indicating reduction of all nitrogen dioxide to nitric oxide. In
most cases there was substantial, if not total, removal of oxygen by com-
bustion with the fuel.
Only at Plant 22 was gas composition data available to show both total
nitrogen oxides (NO + NO2) and nitrogen dioxide. At this plant the
catalytic combustor reduced the nitrogen dioxide content of the absorber
tail gas by 92 percent and reduced the total nitrogen oxides content by
61 percent. As in the other examples, the stack effluent was clear and colorless.
Alkaline scrubbers also reduce the emission of nitrogen oxides effectively.
Data for five plants are presented in Table 4. The two-stage sodium
hydroxide-water scrubber (Plants 24 and 25) performed exceptionally well,
with an overall reduction of 91 percent in nitrogen oxides content. Scrubbing
with sodium carbonate solution, as illustrated by data on Plants 26 and 27,
left 0.4 percent nitrogen oxides in the gases after treatment. Efficiency of
scrubbing in this case cannot be evaluated because no data were available
on the composition of the tail-gas stream entering the scrubber. The data
on Plant 28 show a very high (2.5 percent) nitrogen oxides concentration in
gases entering the sodium carbonate scrubber; this high value might indicate
that the principal purpose of the scrubber here was to produce nitrite and
nitrate salts rather than to reduce emissions below the usual 0.15 to 0.40
percent nitrogen oxides concentration characteristic of untreated tail gas.
Figure 6 shows the pounds of total nitrogen oxides calculated as nitrogen
dioxide emitted per hour for various sized plants and various tail-gas con-
centrations.
Small amounts of acid mist may be present in the emissions from some
plants. A small quantity of entrained acid is generally present in the gases
leaving the absorption system. In the pressure process, the tail gases are
reheated and expanded before being released to the atmosphere at 400
to 500°F; this treatment results in vaporization of any traces of acid mist
that may have been present in the gases from the absorber. In the atmos-
pheric process the cold tail gas discharged to the atmosphere may contain
some entrained acid mist, the quantity depending on the efficiency of entrain-
ment separators prior to discharge.
Based on typical operating data, the tail gas from the usual pressure
process may be considered to have the following average composition:
Total nitrogen oxide (NO + NO2) 0.3%
Oxygen. 3.0 %
H2O 0.7 %
N2, etc Balance
EMISSIONS 23
-------
to
Iffc
TABLE 3
EMISSION AND OPERATING DATA FOR NITRIC ACID PLANTS HAVING CATALYTIC
WASTE GAS TREATMENT EQUIPMENT
Type of fuel*
Plant number
Rated capacity, tons /day
(100% acid basis)
Normal acid strength, %
Percent of rated capacity
Ammonia feed rate, Ib/hr
Ammonia oxidation pressure, psig
Absorption column exit pressure, psig
Absorption column exit temp., °F
Tail gas rate, Mscfmb
Gas temperature
and compositions
before treatment
equipment, vol. %
Gas temperature
and compositions
after treatment
equipment, vol. %
Percent reduction
Temperature, "F
Oxygen
Total nitrogen oxides0
Nitrogen dioxide
Temperature, °F
Oxygen
Total nitrogen oxides
Nitrogen dioxide
Carbon dioxide
in nitrogen oxides
Total nitrogen oxides emitted, tons/day*1
Pounds of nitrogen oxides emitted per
ton of acid produced (100% basis) d
Plume opacity
Plume color
NG
13
110
51
127
3346
105
70
85
10.9
840
3.5
0.21
1250
0.04
81
o.4q
5.7
Clear
None
H2
14
120
60
100
2880
120
94
78
9.3
375
2.4
0.10
915
None
<0.0005
None
99.8
Nil
Nil
Clear
None
NG
15
140
57
100
3500
110
90
100
11.3
1.5
0.50
1500
None
0.015
1.0
97
0.15
2.2
Clear
None
H2
16
150
56
100
3675
105
80
90
11.7
502
2.2
0.3
1120
None
0.01
Nil
97
0.11
1.5
Clear
None
NG
17
170
53
106
4100
20
24
13.7
250
3.0
0.22
900
1.9
0.14
0.88
36
1.8
19.6
Clear
None
75%H2
25%NG
18
185
57
100
4471
102
79
83
14.5
660
2.5
0.3
1190
None
0.005
98
0.07
0.75
Clear
None
H2
19
220
57
95
6150
105
82
86
20
2.7
0.3C
0.5
0.1
Nil
67
1.85
17.6
75%H2
25%NG
20
230
58
119
6700
115
80
98
20.5
570
1.6
0.54
930
None
0.008
98.5
0.15
1.1
Clear
None
NG
21
280
57
110
6800
132
100
65
21.2
2.1
0.36
0.9
0.04
0.67
89
0.78
5.1
Clear
Clear
NG
22
340
57
100
8600
98
27.1
1.9
0.54
0.26
1.7
0.21
0.02
0.6
61
5.25
30.9
Clear
None
NG
23
350
57
100
8460
108
92
104
28.6
3.0
0.2
1250
1.73
0.044
0.74
78
1.16
6.6
Clear
None
I
05
a H2 = hydrogen; NG = natural gas.
b All volumes corrected to 32°F and 29.9 in. Hg.
c Does not include N2O.
d Calculated on the basis that all nitrogen oxides are NO2.
-------
This gas has a distinct reddish-brown color due to its nitrogen dioxide
(NO2) content, but it is generally free of nitric acid mist.
OTHER PROCESSES
Emissions from nitric acid oxidation processes, especially those used to
make polymer intermediates such as adipic acid and terephthalic acid, vary
widely and may, in contrast to emissions from nitric acid plants, contain
high concentrations of nitrous oxide, N2O (laughing gas). In many of these
processes the evolved nitrogen oxides are passed first to an absorption
TABLE 4
EMISSION AND OPERATING DATA FOR NITRIC ACID PLANTS
HAVING ALKALINE SCRUBBING EQUIPMENT
Scrubber
Type of control equipment NaOH & H2Oa Na2CO3
Plant number
Rated capacity, tons/day
(100% acid basis)
Normal acid strength, %
Percent of rated capacity
Ammonia feed rate
, Ib/hr
Ammonia oxidation pressure, psig
Absorption column
Absorption column
exit pressure, psig
exit temp., °F
Stack gas rate, Mscfma
Gas compositions
before treatment
equipment, vol. %
Gas compositions
after treatment
equipment, vol. %
Oxygen
Total nitrogen oxidesb
Nitogen dioxide
Oxygen
Total nitrogen oxides
Nitrogen dioxide
Carbon dioxide
Percent reduction in nitrogen oxides
Total nitrogen oxides emitted, tons /day0
Pounds of nitrogen oxides emitted per
ton of acid produced (100% basis)6
24 25
55 55
60-64
105 105
110 110
85 85
70 70
4.3 4.3
3.8 4.0
0.31 0.34
0.23 0.18
d
0.03
0.03
91
0.23
4
26 27 28
50 120 830'
54 56 40
100 100 95
1200 2900 23850
60 110 13-24
45 90 0
100 100 86
3.5 8.9 77
3.2
2.5
d
1.5 1.5
0.4 0.15
1.5 1.5
94
4.6 10.7
54 27
a In two stages.
b Does not include N2O.
c More than one unit.
d Gas streams combine into one recovery device.
EMISSIONS
25
-------
1,200
BASED ON 85 scfm OF EFFLUENT
PER DAILY TON OF ACID
100
200
300
400
PRODUCTION OF NITRIC ACID, tons/day
(100% HNOs BASIS)
Figure 6 — Total nitrogen oxides (calculated as nitrogen dioxide) emitted per hour vs. daily
production of nitric acid.
system, where a substantial portion is recovered as nitric acid. The residual
gases (N2O, CO2, and inerts) containing small amounts of nitrogen oxides
(NO and NO2) are then discharged to the atmosphere. In nitration processes
there is some evolution of gaseous NO and NO2.
Emissions from acid storage tanks may occur during tank-filling opera-
tions. The gases displaced are equal in volume to the quantity ( of acid
added to the tank. ! j
Some nitrogen oxides are discharged to the atmosphere from nitric
acid concentrators. The data in Table 5 show typical nitric acid feeds and
compositions for a unit that produces 3,000 pounds per hour (100 percent
basis) of 98 percent nitric acid.
EMISSIONS
-------
TABLES
NITRIC ACID FEEDS AND COMPOSITIONS FOR A 3,000-POUND/HR
(100% BASIS) NITRIC ACID CONCENTRATOR
Lb HNO3 (100% basis)
per hour
Amt of 60% acid fed to unit 3110
Amt of 98% acid produced 3000
Amt of 55% acid recovered in absorber 90
Amt of NO2 vented to atmosphere 20
(as HN03)
The loss to the atmosphere is equivalent to 0.7 percent of the strong nitric
acid produced.
The composition and quantity of gases discharged to the atmosphere
are shown in Table 6 for a single nitric acid concentrator using sulfuric acid
as a dehydrating agent.
TABLE 6
ATMOSPHERIC EMISSIONS FROM A 3,000-POUND/HR
(100% BASIS) NITRIC ACID CONCENTRATOR
Component
N2
O2
N02
TOTAL
Composition,
volume %
74.4
20.4
1.0
4.2
100
Flow Rate,
Ib/hr
630
196
15
30
871
Emissions, Ib per
1000 Ib of HNO3 Produced
210
65
5
10
290
The composition and quantity of gases emitted when the magnesium
nitrate concentration system is used are essentially the same as those shown
in Table 6.
Red fuming nitric acid, of interest as a rocket fuel oxidizer, is a mixture
of concentrated (98 percent) nitric acid and an equilibrium mixture of
nitrogen tetroxide (N2O4) and nitrogen dioxide (NO2). It can be made by
dissolving N2O4 in concentrated nitric acid, and is sometimes produced by
total condensation of HNO3 and NO2 vapors, which distill from a nitric acid
concentration column. Emissions associated with manufacture of red fuming
nitric acid are of the same order of magnitude as those given for the pro-
duction of strong nitric acid.
PLANT OPERATING VARIABLES
Emissions of nitrogen oxides may vary widely with changes in plant
operation and with faulty equipment. The main operating variables that
EMISSIONS 27
-------
affect tail-gas concentrations adversely are insufficient air supply to the
system, low pressure in the system (especially in the absorber), high tempera-
tures in the cooler-condenser and absorber, the production of an excessively
high-strength product acid, and operation at high through-put rates. Faulty
equipment includes such items as improperly operating compressors and
pumps, and leaks between rich and lean nitrogen oxide gas streams.
Insufficient air supply may be due to an undersized compressor, mal-
functioning of the compressor and power-recovery equipment, or leaks in
the air supply system. Oxygen is normally supplied to the system by the
initial air compressor, which mixes air with ammonia before the converter
and also supplies "bleach" air to the base of the absorption tower. The
oxygen remaining in the gas stream leaving the ammonia converter, oxidizes
the nitric oxide before the gas enters the absorption tower. Most of this
oxidation occurs in the cooler-condenser system. Additional air is also heated
and pumped through the product acid to remove dissolved nitrogen dioxide.
This "bleach" air then enters the base of the absorption tower and is used
to oxidize the nitric oxide resulting from the formation of nitric acid:
3NO, + ELO = 2HNO, + NO (11)
z, £ a
Lack of oxygen will hinder the oxidation of NO to NO2 and result in high
nitric oxide emissions.
Routine Orsat readings will detect a lack of oxygen in the system, and
corrective measures can be taken. Oxygen concentrations in the tail gas
should be kept at about 3 to 4 percent oxygen.
Recent improvements in plant design include injecting additional air
into the .cooler-condenser to provide an increased oxygen supply. An increase
in the number of plates in the absorber or in spacing of plates also provides
increased oxidation time and absorption capacity, thus reducing emissions
and increasing plant efficiency.
Pressure in the absorber is fixed by basic design of the unit, by com-
pressor capacity, and by the pressure drop in the lines leading to the
absorber. The rate of oxidation of nitric oxide to nitrogen dioxide increases
as the square of the pressure; a small increase in absorber pressure therefore
will provide a substantial increase in the rate of oxidation and indirectly
in the rate of formation of nitric acid.
High temperature also causes a decrease in absorption efficiency. The
rate of oxidation of nitric oxide and the rate of absorption of nitrogen dioxide
vary inversely with the temperature and are favored by low temperatures.
Absorption towers are cooled by circulating water in cooling coils on each
plate. Temperature in the absorber is largely a function of entering gas
temperature, ambient air temperature, and temperature and flow of cooling
water. Cooling water throughput is dictated by pump design, and its tempera-
ture is fixed by the source of the water supply. Temperatures of the tail gas
leaving the absorber normally range from 70 to 90°F.
The desire for increased acid strength often leads to higher concentra-
tions of nitrogen oxides in the tail gas and to reduced operating efficiency.
For production of stronger acid, e.g., over 60 percent, in an existing plant,
28 EMISSIONS
-------
the make-up water to the absorber must be reduced and the nitrous gases
passed through a stronger, more acidic solution in the absorber. The nitrogen
oxides are not absorbed nearly so well in a strong acidic solution, and the
emissions are thus increased. This situation cannot be corrected easily with-
out modifying the plant structure. Increased absorber capacity, increased
oxygen content, decreased temperature, and increased absorption pressure
all tend to decrease tail-gas emissions while stronger acid is produced.
Leaks in process piping are easily detected and are usually repaired
promptly because of the danger to operating personnel. Not so easily observed
are internal leaks, which allow rich gases to leak into the lean tail gases,
such as the tail-gas reheater before the final power-recovery equipment.
Rich gases from the ammonia converter contain approximately 10 percent
total nitrogen oxides. Only a slight leak from this stream into the tail-gas
stream within the countercurrent heat exchanger will cause a definite increase
in stack emission, evidenced by the darker color of the gas stream. Correc-
tion of this situation requires that the plant be shut down and the reheater
section dismantled and repaired.
EMISSIONS 29
-------
SUMMARY OF SAMPLING AND ANALYTICAL TECHNIQUES
In nitric acid plants the nitrogen oxides content of the effluent streams
is measured to determine the operating efficiency of the plant. In addition,
oxygen concentrations are measured to check air rates to the unit. An
operator usually makes these tests every 2 or 3 hours. Detailed descriptions
of the methods used in the nitric acid industry to determine the oxides of
nitrogen are given in Appendix A and are summarized here.
TOTAL NITROGEN OXIDES
The hydrogen peroxide test is most commonly used in nitric acid plants
to determine total nitrogen oxides. This method measures all of the various
oxides of nitrogen except N2O. Nitric acid mist and vapor are also measured.
,' Although many variations are used, the technique basically involves collecting
a known volume of tail gas in a glass container charged with 25 cc of 3
percent hydrogen peroxide solution. The container is sealed and allowed to
react for 30 minutes, the container being shaken frequently. After 30
minutes, the container is washed with distilled water and five drops of
methyl red are added. The solution is then titrated to a copper-colored
endpoint with standard sodium hydroxide. The oxides are calculated as
percent nitrogen dioxide. Two variations of this technique are presented
in Appendix A.
This method gives accurate and reliable results in a nitric acid plant;
it cannot be used in other process gas streams where interfering substances
such as ammonia or sulfur dioxide are present, since they affect the acidity
of the solution and the titration endpoint.
The phenoldisulfonic acid method (13) may also be used to determine
total nitrogen oxides. The method gives comparable results, but is much
more tedious. The phenoldisulfonic acid method is not subject to interference
by any other compounds and thus is useful in gas streams containing ammonia,
sulfur dioxide, or other interferences. It is more accurate than the peroxide
method at concentrations below about 500 ppm. In the phenoldisulfonic
acid method, a measured volume of tail gas is collected in a flask and reacted
for approximately 24 hours with a dilute solution of sulfuric acid and
hydrogen peroxide. The hydrogen peroxide oxidizes the oxides of nitrogen
(with the exception of nitrous oxide) to nitric acid. The resultant solution
is then neutralized and evaporated to dryness and treated with phenoldisul-
fonic acid reagent and ammonium hydroxide. The resulting yellow trialkali
salt concentration is measured colorimetrically in a spectrophotometer at
326 niju, and the corresponding concentration of nitrogen oxides determined
from a calibration curve.
If the total nitrogen oxides content of a gas stream is below 500 ppm,
the Saltzman method (24) may prove useful and more accurate than the
hydrogen peroxide method. Concentrations in this range may be encountered
at the outlet of tail gas reduction equipment. This method is applicable
only to gas streams containing sulfur dioxide in amounts less than the
nitrogen oxide content.
SAMPLING AND ANALYSIS: SUMMARY 31
-------
OXYGEN
A standard Orsat kit is normally used to determine the oxygen content
of the tail gases. When used carefully, the kit measures oxygen concentrations
to the nearest 0.2 percent by volume. The absorbing solution for oxygen is
usually an alkaline pyrogallol or a chromous chloride solution. To preclude
the absorption of nitrogen oxides in the oxygen-absorbing solution, the
gas should first be passed through a caustic scrubber. The potassium hydrox-
ide scrubber in the Orsat kit commonly used for CO2 will serve this function.
Care must be used when sampling tail gases under high pressures. The
standard Orsat kit should not be subjected to excessive pressures, since
it may be damaged. A bleed off in the sample line is recommended.
NITROGEN DIOXIDE
Nitrogen dioxide is not usually measured as a separate compound but
is included in the determination of total nitrogen oxides. The measurement
of nitrogen dioxide is complicated by the presence of nitric oxide, which is
being constantly converted to nitrogen dioxide in the presence of oxygen.
Determination of nitrogen dioxide is of interest because its photochemical
reactions are important in air pollution and because the oxidation state of
the tail gases affects plant operations.
Once the tail gases enter the atmosphere they are rapidly diluted, and
at a concentration of 1 ppm, 70 hours are required for 50 percent conversion
of NO to NO2 (Figure 7). In photochemical reactions, the NO2 dissociates
to form NO and atomic oxygen, which in turn combines with molecular
oxygen to form ozone.
The Tennessee Valley Authority has developed a method in which a
solution of mixed nitric and sulfuric acids is used for determining the
ratio of NO to NO2. The method has been used successfully in absorption
towers where the total nitrogen oxides range from 5 to 6 percent. It has
shown poor reproducibility in use on tail gases.
The United States Public Health Service has developed a method for
determining NO, with the Saltzman reagent. This method involves carefully
diluting the tail gases by about 400:1 with nitrogen to obtain concentrations
at which this reagent may be used and at which the oxidation rate is
much slower.
Photoelectric instruments can be used to determine nitrogen dioxide
concentrations by measuring the light absorption of the gas stream. These
instruments, if carefully calibrated in the proper range, should give reliable
results. An instrument procedure developed by the Du Pont Company is
included in Appendix A.
ACID MIST DETERMINATION
Acid mist is collected by drawing a measured volume of tail gas through
a cyclone and a fiberglass filter. The train components are then carefully
washed with distilled water and titrated with a standard base. This type
32 SAMPLING AND ANALYSIS: SUMMARY
GPO 828-664-4
-------
of sampling collects only nitric acid in an actual mist form and not in the
vapor state.
Stack gases are usually well above the dew point of the nitric acid mist,
and no mist is present. Cooling the gas before passing it through the filter
causes condensation of nitric acid present in the vapor state.
1,000
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INITIAL NITRIC OXIDE CONCENTRATION, ppm by volume
Figure 7 — Percent oxidation of nitric oxide to nitrogen dioxide by air at 25°C and 1 atmos-
phere.(15)
SAMPLING AND ANALYSIS: SUMMARY
33
-------
GLOSSARY OF TERMS
ABBREVIATIONS
«B<§
°C
cc
ft
ft2
ft*, cf
oji
Ibs
mg
mm
Mscfm
ppm
psig
®
scfm
scfh
sp.gr.
°TW
yr
degrees Baume
temperature, degrees Centigrade
cubic centimeter
feet
square feet
cubic feet
temperature, degree Fahrenheit
pounds
milligram
millimeter
millimicron
thousands of standard cubic feet per minute
parts per million by volume
pounds per square inch gauge
Registered trade mark
cubic feet per minute measured at standard condi-
tions: O°C (32°F) and 760 mm (29.92") Hg
standard cubic feet per hour
specific gravity—compared to water at 60 °F
degrees Twaddell
year
CHEMICAL SYMBOLS
C°2
Hg
HN03
NaOH
Na2C03
NH
N20
NO
N0
methane
carbon dioxide
mercury
water
sulfuric acid
nitric acid
sodium hydroxide
sodium carbonate
ammonia
nitrogen
nitrous oxide (laughing gas)
nitric oxide
total nitrogen oxides in a mixture
nitrogen dioxide
nitrogen tetroxide
oxygen
GLOSSARY
35
-------
GLOSSARY OF TERMS (Contd.)
DEFINITIONS
Absorber
Bourne (°B(§)
Catalyst
Catalytic reduction
system
Converter
Effluent
Emission
Establishment
Fuming nitric acid
Nitric acid mist
Nitric acid (strong)
Nitric acid vapor
Nitric acid (weak)
Nitrogen oxides
Tail gas
Twaddell (°TW)
The absorber in a nitric acid plant is usually a
stainless steel tower with bubble cap plates.
Acid strength is determined by use of a floating
instrument (hydrometer) calibrated to read degrees
of Baume and by a conversion chart. The Baume
can also be calculated if the specific gravity of the
acid at 60°F is known:
145
"Be
= 145- (->»-.}
\ sp. gr.)
to
sp.gr.
In a nitric acid plant "catalyst" usually refers
the platinum-rhodium woven wire gauze on
•which the ammonia is oxidized to nitric oxide and
water.
A device for reducing the emissions of nitro-
gen oxides to the atmosphere by passing the gas
over a catalyst in the presence of a reducing fuel
such as natural gas, hydrogen or ammonia.
The chamber in which the ammonia is con-
verted to nitric oxide and water by reacting it with
air over a platinum-rhodium catalyst.
Waste gas stream that enters the atmosphere
from the process.
Any gas stream emitted to the atmosphere.
A works having one or more nitric acid plants
or units, each being a complete production entity.
A mixture of 98 percent nitric acid and an
equilibrium mixture of nitrogen tetroxide (N2O4)
and nitrogen dioxide (NO2).
Extremely small particles of acid in the liquid
state.
Concentrated 98 percent nitric acid.
Nitric acid in the gaseous state.
55 to 65 percent nitric acid.
A general term pertaining to a mixture of nitric
oxide (NO) and nitrogen dioxide (NO2).
The gas leaving the nitric acid absorber.
A measure of acid density and strength.
sp. gr. — 1
°TW =
0.005
36
GLOSSARY
-------
APPENDICES
A. SAMPLING AND ANALYTICAL TECHNIQUES
Nitric Oxide (NO) Plus Nitrogen Dioxide (NO2) in Gas
Samples, Modified Gaillard Method—DuPont Co 40
Determination of Oxides of Nitrogen as Nitrate—Hydrogen
Peroxide Method, Public Health Service 43
Phenoldisulfonic Acid Method for Total Nitrogen Oxides,
Public Health Service 47
Nitrogen Dioxide or Total Nitrogen Oxides Determination
with Griess-Saltzman Reagent, Public Health Service 51
Nitrogen Dioxide—Determination in Gas Streams by use of
the Model 4 Photoelectric Analyzer, DuPont Co 55
Determination of Acid Mist 61
B. NITRIC ACID ESTABLISHMENTS IN THE UNITED STATES 69
C. FACTORS CAUSING HIGH EMISSIONS OF NITROGEN OXIDES .... 75
D. PHYSICAL DATA—NITRIC ACID 79
APPENDICES 37
-------
APPENDIX A: SAMPLING AND ANALYTICAL
TECHNIQUES
The sampling and analytical techniques described here were used to
obtain the emission data presented in this report and are those generally
used in the nitric acid manufacturing industry. Format and wording for
most of these procedures are those of the company that supplied the
description.
39
-------
NITRIC OXIDE (NO) PLUS NITROGEN DIOXIDE (NO2) IN GAS
SAMPLES — MODIFIED GAILLARD METHOD —
E. I. duPONT de NEMOURS AND COMPANY
PRINCIPLE AND STATUS
This method determines NO plus NO2 in a gas sample of known volume
by converting the oxides of nitrogen to nitric acid with excess aqueous
hydrogen peroxide and titrating the acid with standard sodium hydroxide.
Equations for the reactions with peroxide may be written:
2N02 + H202 —> 2HN03
2ND + 3H202 -> 2HN03 + 2H2O
The method does not differentiate between NO and NO2. Any N2O4 that
may be present is counted as NO2. N2O does not interfere.
A trace of cupric sulfate is added to the hydrogen peroxide to increase
the rate of absorption of NO. Cupric sulfate catalyzes decomposition of
peroxide; the liberated oxygen reacts with NO to form NO2, which is absorbed
more rapidly than NO.
Because accurate measurement of sample volume is necessary, the
method is not applicable to gases that contain significant amounts of con-
densed liquids such as water or nitrogen tetroxide. It is applicable to
product gas from an NO generator, sampled downstream from the cooler
condenser, and to other gas samples containing no condensed phase.
Standard deviation (95% confidence level) is ± 0.12 percent at the 20
percent NO level based on 30 determinations by one analyst over a period
of one week.
SAFETY PRECAUTIONS
Wear rubber gloves and an apron when handling 30 percent hydrogen
peroxide, avoiding all contact with the skin and inhalation of vapor. If the
peroxide contacts the skin, flush immediately with large amounts of water
to prevent severe burns. Open new bottles carefully behind a shield in a
hood. Store in a cool area away from alkalies, ammonia, and chlorides; fer-
rous, mercurous, or gold salts, hypophosphites, iodides, permanganates, sul-
fites; and organic matter in general.
The maximum allowable concentration of NO2 in air is 5 ppm. The
greatest hazard of exposure to NO2 is that its serious effects are not felt
until several hours after exposure and that dangerous amounts may be
inhaled before any real discomfort occurs. NO is an extremely toxic gas,
which is rapily converted to NO2 by the oxygen of the air.
NO PLUS NO2
Apparatus and Reagents
Gas sampling bulb—300-500 ml, Corning Glass Co., Cat. No. 9500 or
equivalent.
40 APPENDIX A
-------
Thermometers:
EL-2 -5° to +25°C, Specification 1009.
EL-3, +20° to +50°C, Specification 1010.
30-ml syringe.
3 percent Hydrogen peroxide—Dilute 50 ml of 30 percent H2O? to 500 ml
with distilled water. One ml of this solution is equivalent to about 0.6
millimoles of NO. Three percent H2O2 designated "U.S.P." is not suitable
because it contains acetanilide, which interferes with the end point.
Methyl Purple® indicator—Fisher Scientific Co., Cat. No. So-I-9.
0.11V standard sodium hydroxide.
Kel-F® stopcock grease.
1 percent Copper sulfate solution—Dissolve 1 g of reagent grade an-
hydrous CuSO4 in 100 ml of distilled water.
Calibration of Gas Sampling Bulbs
Care in cleaning and lubricating gas sampling bulbs is essential for
precise analytical results. Clean new bulbs with chromic acid cleaning
solution. Use Kel-F® to lubricate the stopcocks. Never use silicone grease,
because it coats the interior walls of the bulb and interferes with proper
drainage. Bulbs contaminated with silicone grease may be cleaned with
hot 5 percent sodium hydroxide solution.
Weigh the clean, dry bulb to the nearest 0.01 gram.
Fill the bulb with water so the bore of one stopcock contains water.
Use a pipe cleaner to remove water remaining in the stopcock stem. Record
the temperature of the water and reweigh the bulb to the nearest 0.01 gram.
Calculation:
A - B
Capacity of bulb at t°C, ml =
dt - 0.0010
where A = weight of bulb plus water, grams
B = weight of bulb, grams
dt = density of water at observed temperature, t°C.
0.0010 = buoyancy constant, grams per ml
Analysis of Samples
Rinse a gas-sampling bulb with distilled water and dry in a stream of
clean air. If the water does not wet the bulb evenly, or if the water drains,
leaving droplets adhering to the walls, clean the bulb with chromic acid
cleaning solution. Check the bulb again for cleanliness before using.
Connect a clean, dry gas-sampling bulb to the source of gas to be analyzed
and purge for 5 to 10 minutes at a flow rate of at least 1 liter per minute.
Reduce the flow rate and pressurize the sample slightly by closing the
APPENDIX A *1
-------
outlet stopcock first, then the inlet stopcock. If there is a regulator on the
sample source, adjust to about 2 psig before closing the stopcocks.
Place the sample bulb in an area not subject to large temperature varia-
tions and allow to stand for 30 minutes to reach room temperature. Open
one stopcock for about 1 second to equilibrate with atmospheric pressure.
Repeat previous step. Record the^oom temperature to the nearest 0.1 °C
and atmospheric pressure to the nearest 0.1 mm.
Add one drop of 1 percent CuSO4 to 30 ml of 3 percent HXO2 in a 50-ml
beaker. Since CuSO4 acts as a decomposition catalyst for H2O2, do not
prepare this solution until ready to use.
Attach a 3-inch length of rubber tubing to a 30-ml syringe and draw
25 ml of the CuSO4-H,O2 solution into the syringe. Attach the other end of
the rubber tubing to the stopcock stem at one end of the sample bulb,
apply gentle pressure, and open the stopcock just long enough to admit
the solution.
Allow the bulb to stand 1 hour with occasional vigorous shaking to com-
plete the oxidation and absorption of nitrogen oxides. This period may be
shortened by placing the sample bulb on an automatic shaker and shaking
continuously. If the red-brown color of NO2 persists after 1 hour, indicating
incomplete absorption, repeat the period of standing and shaking.
If no NO, is visible, wash the contents of the bulb into a 250-ml beaker
with about 100 ml of distilled water. This may conveniently be done by
holding the bulb in a vertical position, opening both stopcocks, and inserting
the tip of a wash bottle into the stem of the upper stopcock while rinsing.
Titrate with 0.1N NaOH to a Methyl Purple® end point. When a new
bottle of 30 percent H2O2 is opened, determine a blank to make certain the
H2O2 is not acidic enough to interfere with the analysis. Normally, correc-
tion for a blank is not necessary.
Calculation:
Mole percent total (NO + NO,) =
ml NaOH x normality x Vm x 100
2 volume of sample bulb, ml
t = room temperature, °C
P = pressure, mm Hg, at the time of the final pressure equilibra-
tion.
Clean the sample bulb with acetone and lubricate the stopcocks with
Kel-F® after each analysis.
42 APPENDIX A
-------
DETERMINATION OF OXIDES OF NITROGEN AS NITRATE —
HYDROGEN PEROXIDE METHOD —
PUBLIC HEALTH SERVICE
SCOPE
This method comprises a nonspecific test for the oxides of nitrogen
(with the exception of N2O) and is easily completed in the field. It actually
determines total acidity of the gas stream; precautions must be taken in
interpreting the results since many other compounds may interfere if present
in the gas stream. These include SO,, SO3, and NH3. Results are reported
as ppm NO2 by volume.
APPARATUS (Figures Al and A2)
Sampling probe—Stainless steel (type 304 or 316) or glass tubing of
suitable size (%-inch-OD, 6-foot-long stainless steel tubing has been used).
Collection flask—A clean 2-liter round-bottom flask with an outer
24/40 joint for integrated samples or a 250-ml sampling tube for grab samples.
Adapter with stopcock—Adapter for connecting collection flask to sam-
pling "T".
Three-way stopcock.
Manometer—A 36-inch Hg manometer.
THREE-WAY
STOPCOCK
PROBE
fl2/5
$12/5
STAINLESS STEEL
PROBE
/"A
ORIFICE
ASSEMBLY
TEFLON GLASS
v SLEEVE CAPILLARY
,JBE
TYGON
SLEEVE
TO VACUUM
PUMP
- MERCURY
MANOMETER
GLASS FIBER
FILTER
DETAIL A
Figure Al — Apparatus for integrated grab samples.
TO VACUUM PUMP
250-ML FLASK
MERCURY MANOMETER-
Figure A2 — Apparatus for grab samples.
APPENDIX A
43
-------
REAGENTS
30 Percent hydrogen peroxide (reagent grade).
3 Percent hydrogen peroxide—Dilute 30 percent H2O2 with distilled water
at 10:1 ratio. Prepare fresh daily.
0.01 sodium hydroxide—Dissolve 40 grams NaOH in 40 grams H20.
Decant the clear solution and dilute about 2000:1. Standardize against potas-
sium acid phthalate or similar reagent.
0,1 Percent Methyl Red Indicator.
SAMPLING PROCEDURE
Add 25 ml of freshly prepared 3 percent hydrogen peroxide solution to
the sampling flask. Evacuate the sample flask, record pressure in flask.
Record all values on data sheet, shown in Figure A3. Purge the sample line
for about 1 minute. With probe valve still open, hold probe directly in the
gas stream and open flask stopcock. When flask has reached approximately
90 percent of atmospheric pressure, close stopcock and record final vacuum
in flask.
SAMPLE PREPARATION
Shake flask thoroughly every 10 minutes for % hour and then set aside
for an additional % hour.
ANALYTICAL PROCEDURE
Remove sample line and wash the region between the stopcock and
joint with distilled water, catching the washings in the sample flask. Wash
the joint and flask walls with a jet of distilled water. Add 5 drops of 0.1
percent methyl red indicator and titrate with standardized 0.0 IN NaOH to
a copper-colored endpoint. A blank should be run simultaneously.
CALCULATION
ppm NO2 by volume = (ml NaOH) x (N NaOH) x 24.1 x 106
_
("P "D \ i^n0!?
Cf Ci \ O«JU it
— I X T,
Vr = volume of reagent, ml
V0 = volume of flask at 70°F and 29.9 in. Hg, ml
Pj = absolute pressure in flask after evacuating, in. Hg
Pf = final absolute pressure in flask after sampling, in. Hg
Tj = initial temperature in flask, °R.
Tf = final temperature in flask, °R.
44 APPENDIX A
-------
DATE.
TEST NO..
LOCATION.
Type of Operation.
Samp I ing Flask No..
Flask Volume, Vo.
Volume of Reagent, Vr
Barometric Pressure,
.ml
-in. Hg
Initial Flask
Vacuum, P
leg 1
leg 2
Final Flask
Vacuum, ?2
pl=_
leg 1
leg 2
-in. Hg
?2= in. Hg
Initial Flask Temperature °F
Final Flask Temperature
460 =.
°F + 460 =.
.ml
Pi = Ph Pi =
P2=.
CALCULATIONS:
ppm HO = (nil HaOH) x (H HaQH) x 24.1 x 106
* " Vs (ml)
¥s =
-------
PHENOLDISULFONIC ACID METHOD FOR TOTAL
NITROGEN OXIDES — PUBLIC HEALTH SERVICE
SCOPE
When, sulfur dioxide, ammonia, or other compounds that interfere with
the hydrogen peroxide method are present in the gas to be sampled and/or
the concentration of the nitrogen oxides is below about 100 ppm, this method
is used. Accuracy below 5 ppm is questionable. This test is unsuitable for
atmospheric sampling.
APPARATUS (Figures Al and A2)
Sampling probe—Stainless steel (type 304 or 316) or glass tubing of
suitable size (%-inch-OD, 6-foot-long stainless steel tubing has been used).
Collection flask—A 2-liter round-bottom flask with an outer 24/40 joint
for integrated samples or a 250-ml MSA sampling tube for grab samples.
Orifice assembly—The size of the glass capillary tubing depends on the
desired sampling period (flow rates of about 1 liter per minute have been
used). Use of this orifice is not mandatory.
Adapter with stopcock—Adapter for connecting collection flask to sam-
pling "T".
Three-way stopcock.
Manometer—A 36-inch Hg manometer or accurate vacuum gage.
Spectrophotometer—Beckman Model "B" or equivalent.
REAGENTS
30 Percent hydrogen peroxide—(reagent grade).
3 Percent hydrogen peroxide—Dilute 30 percent H2O2 with water at 1:10
ratio. Prepare fresh daily.
Concentrated Sulfuric Acid.
0.1N (approximate) Sulfuric Acid—Dilute 2.8 ml concentrated H2SO4 to 1
liter with water.
Absorbing Solutions-Add 12 drops 3 percent H2O2 to each 100 ml 0.1N
H2SO4. Make enough for required number of tests.
IN (approximate) sodium hydroxide—Dissolve 40 gm NaOH pellets in
water and dilute to 1 liter.
Concentrated ammonium hydroxide.
Fuming sulfuric acid—15 to 18 weight percent free sulfuric anhydride
(oleum).
Phenol (reagent grade)
Phenoldisul/onic acid solution—Dissolve 25 grams of pure white phenol
APPENDIX A 47
-------
in 150 ml concentrated H2SO4 on a steam bath. Cool and add 75 ml fuming
sulfuric acid. Heat to 100 °C for 2 hours. Store in a dark stoppered bottle.
This solution should be colorless if prepared with quality reagents.
Potassium nitrate (reagent grade).
Standard potassium nitrate solution—Solution A: Dissolve 0.5495 gram
KNO3 and dilute to 1 liter in a volumetric flask. Solution B: Dilute 100 ml
of Solution A to 1 liter. One ml of Solution A contains the equivalent of
0.250 mg NO2 and of Solution B, 0.0250 mg NO2.
CALIBRATION
Calibration curves are made to cover different ranges of concentrations.
Using a microburette for the first two lower ranges and a 50-ml burette for
the next two higher ranges, transfer the following into separate 150-ml
beakers (or 200-ml casseroles).
1. 0-100 ppm: 0.0 (blank), 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 16,0, 20.0 ml of
KNO, Solution B.
o
2. 50-500 ppm: 0.0 (blank), 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 10.0 ml of
KNO, Solution A.
A
3. 500-1500 ppm: 0.0 (blank), 5.0, 10.0, 15.0, 20.0, 25.0, 30.0 ml of
KNO, Solution A.
A
4. 1500-3000 ppm: 0.0 (blank), 15.0, 30.0, 35.0, 40.0, 45.0, 50.0, 55.0,
60.0 ml KNO3 Solution A.
Add 25.0 ml absorbing solution to each beaker. Follow as directed in
the Analytical Procedure section starting with the addition of IN NaOH.
After the yellow color has developed, make dilutions for the following
ranges: 50 to 500 ppm (1:10); 500 to 1500 ppm (1:20); and 1500 to 3000 ppm
(1:50). Read the absorbance of each solution at 420m^.
Plot concentrations against absorbance on rectangular graph paper. A
new calibration curve should be made with each new batch of phenoldisul-
fonic acid solution or every few weeks.
SAMPLING PROCEDURE
Integrated Grab Sample—Add 25 ml freshly prepared absorbing solution
into the flask. Record the exact volume of absorbing solution used.
Set up the apparatus as shown in Figure Al, attach the selected orifice.
Purge the probe and orifice assembly with the gas to be tested before sampling
begins by applying suction to it. Evacuate the system to the: vapor pressure
of the solution: this pressure is reached when the solution i begins to boil.
Record the pressure in the flask and the ambient temperature. Open the
valve to the sampling probe to collect the sample. Constant flow will be
maintained until the pressure reaches 0.53 of the atmospheric pressure. Stop
before this point is reached. During sampling, check the rate of fall of the
mercury in one leg of the manometer in case clogging, especially of the
48 APPENDIX A
-------
orifice, occurs. At the end of the sampling period, record the pressure,
temperature, and barometric pressure.
An extended period of sampling can be obtained by following this pro-
cedure. Open the valve only a few seconds at regular intervals. For
example: Open the valve for 10 seconds and close it for 50 seconds; repeat
every 60 seconds.
Grab Sample—Set up the apparatus as shown in Figure A2 for high
concentrations (200-3000 ppm) or the apparatus as shown in Figure Al for
low concentrations (0-200 ppm) but delete the orifice assembly. The same
procedure is followed as in the integrated method except that the valve is
opened at the source for about 10 seconds and no orifice is used.
SAMPLE PREPARATION
Shake the flask for 15 minutes and allow to stand overnight.
ANALYTICAL PROCEDURE
Transfer the contents of the collection flask to a beaker. Wash the flask
three-times with 15-ml portions of H,O and add the washings to the solution
in the beaker. For a blank add 25 ml absorbing solution and 45 ml H2O to a
beaker. Proceed as follows for the blank and samples.
Add IN NaOH to the beaker until the solution is just alkaline to litmus
paper. Evaporate the solution to dryness on a water bath and allow to cool.
Carefully add 2 ml phenoldisulfonic acid solution to the dried residue and
triturate thoroughly with a glass rod, making sure that all the residue
comes into contact with the solution. Add 1 ml H2O and four drops con-
centrated H2SO4. Heat the solution on the water bath for 3 minutes, stirring
occasionally.
Allow to cool and add 20 ml H2O, mix well by stirring, and add 10 ml
concentrated NH4OH, dropwise, stirring constantly. Transfer the solution
to a 50-ml volumetric flask, washing the beaker three times with 4- to 5-ml
portions of H2O. Dilute to mark with water and mix thoroughly. Transfer
a portion of the solution to a dry, clean centrifuge tube and centrifuge, or
filter a portion of the solution.
Read the absorbance of each sample at 420 m^. If the absorbance is
higher than 0.6, make a suitable dilution of both the sample and blank and
read the absorbance again.
CALCULATIONS
(5.24 x 10") (C)
ppmNO2 =
» a
Where C = concentration of NO2, mg (from calibration chart)
VB = gas sample volume at 70°F and 29.92 in Hg, ml.
APPENDIX A *9
-------
NITROGEN DIOXIDE OR TOTAL NITROGEN OXIDES
DETERMINATION WITH GRIESS-SALTZMAN
REAGENT — PUBLIC HEALTH SERVICE
SCOPE
The technique employed for determination of nitrogen dioxide and of
total nitrogen oxides when concentrations are below 500 ppm is colorimetric
analysis with Griess-Saltzman reagent. This method is acceptable for nitric
acid plants or other sources where the interference of sulfur dioxide is not
encountered.
APPARATUS
Sampling Probe—Stainless steel (304 or 316) or glass tubing with
sampling tee (%-inch-OD tubing has been used).
Self-sealing serum cap—Rubber. (A serum cap with 11/32-inch sleeve
snd 7/32-inch plug has been used. Chemical Rubber Company, Catalog
No. 13-8855).
Gas syringe—5 ml, gas tight, with Teflon plunger and/or 100-ml glass
syringe (needle should be about No. 22).
Collection flask—A 2-liter glass flask for nitrogen dioxide and a 250-ml
gas-sampling tube for total oxides.
Flasfc adaptor—Any suitable fitting to reduce the 2-liter flask opening
to the size of the serum cap available.
Spectrophotometer—Beckman Model "B" or equivalent.
Thermometer—For ambient temperature.
Barometer—Barometric pressure, in. Hg.
REAGENTS
Nitrogen supply—Cylinder nitrogen with low oxygen content.
Glacial acetic acid.
Sulfanilic acid.
N- (1-Naphthyl) -ethylenediamine dihydrochloride.
Absorbing solution—To 6 liters of distilled water, add 1120 ml glacial
acetic acid, 40 gm sulfanilic acid, and 0.160 gm N-( 1-Naphthyl) -ethylenedia-
mine dihydrochloride. Dilute to 8 liters with water and store in a dark bottle
at about 45 °F.
Sodium nitrite—(reagent grade).
Standard sodium nitrite solution—Accurately weigh 2.03 gm NaNO, and
dissolve in water. Dilute to 1 liter. Transfer 10 ml of this solution to a 1-
liter volumetric flask and dilute to 1 liter. One ml of this standard solution
APPENDIX A 51
-------
is equivalent to 10 ^1 NO2 at 25°C and 760 mm Hg. It has been shown
empirically that 0.72 mole of sodium nitrite produces the same color as 1
mole of nitrogen dioxide.*
CALIBRATION
Transfer 0.2, 0.4, 0.6, 0.8, 1.0 and 1.2 ml respectively of the dilute standard
sodium nitrite solution to six 25-ml volumetric flasks and fill the flasks to
the mark with absorbing solution. Shake thoroughly and allow 15 minutes
for color development. Read the absorbance at 550 m^ in a spectrophotometer
using fresh absorbing solution as a blank. Plot concentrations against absorb-
ances on rectangular graph paper.
Make a new calibration curve for each new batch of absorbing solution.
SAMPLING PROCEDURE
Nitrogen dioxide—Add 50 ml of absorbing solution to a dry 2-liter
flask. Purge the flask and adapter with nitrogen and immediately seal with
a serum cap.
Insert the gas tight syringe through a serum cap in the sampling tee
and flush the syringe several times with sample gas. Draw into the syringe
exactly 5 ml of sample gas and quickly inject the sample into the 2-liter
flask. Allow the sample to absorb for 15 minutes, shaking several times
during this period.
After 15 minutes, drain the absorbing solution into a sealed container
(e.g. a 50-ml volumetric flask) and allow to stand 15 minutes longer for
color development (the transfer need not be quantitative).
Nitrogen oxides (1) syringe method—Fill a 100-ml glass syringe with
absorbing solution. Adjust to 90 to 100 ml, taking care to expel all air
bubbles. Cap the needle to prevent leakage of solution.
To sample, expel enough solution to reach the 80-ml mark and insert
the needle into the sampling tee. Carefully retract the plunger to the 100-ml
mark and then withdraw it from the sample line. Seal the needle tip with
a rubber stopper and place the syringe in a dark location for 24 hours.
(2) Gas Sample Tube—Fill a 250-ml gas tube with absorbing solution,
eliminating all air. Connect one end of the tube to the sample probe with a
short piece of Tygon tubing and insert the other end into a 110-ml volumetric
flask. (100 ml + 10 ml graduated neck). Open the bottom stopcock and by
•manipulating the top stopcock, drain 100± ml of reagent into the volumetric
flask. Close the bottom stopcock and set the tube in a dark location for
24 hours. (The 100+ ml should be drained quite rapidly and care taken
not to agitate the absorbing solution. These steps minimize absorption during
the sampling period).
*Molar volume at 25 °C and 760 mm Hg is 24.47 liters therefore:
2.03 x 10-ogm x —_— x —_ x 24.47 = 10 x 10-« 1 NO2 = 10 ^1NO2
52 APPENDIX A
-------
In all cases, record the barometric pressure (in. Hg) and ambient
temperature (°F).
ANALYTICAL PROCEDURE
After the specified waiting period has elapsed, shake the containers well.
Transfer the absorbing solution to 1 cm cells and measure the absorbance
at 550 m^ against unused absorbing solution as a reference. Dilutions with
fresh absorbing solution may be made if necessary.
CALCULATIONS
C = concentration of NO2 from calibration graph (ju,l NO2/ml reagent).
Vr = volume of reagent, ml
for nitrogen dioxide = 50 ml
for syringe = 80 ml
for gas tube, volume of tube minus reagent withdrawn
Vs = sample volume at 29.92 in. Hg and 25°C.
298
= V
29.92 J \ 273+Ta
V = sample taken, ml
for nitrogen dioxide — 5 ml
for syringe — 20 ml
for gas tube, volume of reagent withdrawn
Pb = barometric pressure, in. Hg.
Ta = ambient temperature, °C.
APPENDIX A 53
-------
NITROGEN DIOXIDE — DETERMINATION IN GAS STREAMS
BY USE OF THE MODEL 4 PHOTOELECTRIC ANALYZER
E. I. duPONT de NEMOURS AND COMPANY
PRINCIPLE AND STATUS
Nitrogen dioxide (NO2), a red-brown gas, dimerizes very rapidly and
reversibly to form colorless nitrogen tetroxide (N2O4) according to the
reaction:
At ordinary temperatures both NO? and N2O4 are always present in equili-
brium in the gas. A photometric measurement of the color intensity of
NO2 provides a rapid, continuous method for determining only NO2 without
affecting the NO2-N2O4 equilibrium. The wet chemical method uses per-
oxide to oxidize the nitrogen (IV)* oxides to nitric acid followed by
titration with a standard base. This method does not distinguish between
NO2 and N2O4, but gives total nitrogen (IV)* oxides calculated as mole per-
cent NO2, which is equivalent to mole percent NO2 plus twice mole per-
cent N2O4.
NO2 absorbs light strongly between 400 m^ and 600 m.ju,, while the other
nitrogen oxides do not absorb in this region of the spectrum. The Model 4
Photoelectric Analyzer, at an analyzing wavelength of 436 m/j. and a reference
wavelength of 546 m^, is used to determine NO2 in gas streams contain-
ing N2O, NO, N2O4, HNO3, N,, O2, CO2, and water vapor. The full-scale
range of the instrument with a 10-cm cell is from 1500 ppm NO2 to 2.0
mole percent NO2. This method is not recommended for concentrations of
NO2 greater than 2 mole percent. The Model 4 Photoelectric Analyzer can
be used to determine concentrations of NO2 greater than 2 mole percent by
changing the wavelengths and using a heated cell.
SAFETY PRECAUTIONS
Conduct all work in a well-ventilated area, venting the sample stream
in a hood or into an exhaust system.
NO and NO2 are extremely toxic gases. The maximum allowable con-
centration of NO2 in air is 5 ppm. Exposure to 100 ppm NO or NO2 for
30 to 60 minutes is dangerous. The greatest hazard of exposure to NO, is
that its serious effects are not felt until several hours after exposure and
that dangerous amounts may be inhaled before any real discomfort occurs.
*Valence of 4.
N02
APPARATUS AND REAGENTS
Model 4 Photoelectric Analyzer, Manufacturers Engineering and Equip-
ment Corporation, Hatboro, Pa., or Du Pont 400 Photometric Analyzer, Instru-
ment Products Division, Wilmington, Del., equipped with the following optical
niters:
APPENDIX A 55
-------
Measuring Beam—436
2 pieces Corning CS 3-73 (3389) Du Pont 400-340-6
1 piece Corning CS 5-58 (5113) Du Pont 400-340-8
Reference Beam—546 m/j,
1 piece Corning CS 3-69 (3486) Du Pont 400-340-7
1 piece Corning CS-1-60 (5120) Du Pont 400-340-9
Beam Splitter—50% Transmission Du Pont 400-330-3
Calibration Filter—Corning CS 3-75 (3060)
1 piece 0.23-0.26% NO, for 10 cm cell
J
2 pieces 0.45-0.50% NO, for 10 cm cell
Sampling system, Figure A4. Stainless steel needle valves should
be used. All lines should be made of stainless steel, glass, and/or Teflon.
All connectors should be stainless steel or Teflon. Beckman Teflon tube fit-
tings are excellent in this application. Rubber and Tygon connections should
be avoided. Keep sample lines as short as possible.
MANUAL VALVE AT
SAMPLE TAKEOFF
EXHAUST OR
SAMPLE RETURN
ANALYZER
SAMPLE CELL
SAMPLE FOR ^ ,
ANALYSIS "" 1 1 *1 ROTOMETER
~ (OPTIONAL)
MANUAL VALVES
NEAR ANALYZER
PURGE GAS
FILTER OR
STRAINER
Figure A4 — Sampling system for model 4 photoelectric analyzer.
Rotameter, Tru-Taper Tube, sizes 2-15-3 with stainless steel float, range
160-1600 ml/min., Brooks Rotameter Co., Lansdale, Pa.
Gas sampling bulb, 300-500 ml, Corning Glass Co., Cat. No. 9500 or
equivalent.
NO2 standard gas mixture. Mixtures of NO2 and N2 containing 0-2 per-
cent NO2 can be obtained from Matheson Co., Inc., P. O. Box 85, East
Rutherford, N. J. Determine total nitrogen (IV) oxides as mole percent
NOa in these mixtures by the modified Gaillard procedure.
ZERO ADJUSTMENT OF MODEL 4 ANALYZER
Purge the sample lines and cell with a dry, colorless gas (e.g instru-
ment air, nitrogen, clean laboratory air).
Make certain the calibration filter is not in the light path.
Adjust the COARSE ZERO and FINE ZERO controls until the recorder
56 APPENDIX A
-------
reads zero. Turn the COARSE ZERO and the FINE ZERO knobs clockwise
to move the recorder pen upscale and counterclockwise to move the pen
downscale.
If the instrument cannot be zeroed consult the operating manual.
Probable trouble sources are a dirty sample cell, weak batteries, an open
signal cable, gassy phototubes, broken optical niters, or defective amplifier
tubes. Major repairs and adjustments should be undertaken only by qualified
instrument shop personnel.
SPAN ADJUSTMENT
Purge the sample cell with a dry, colorless gas (e.g. instrument air,
nitrogen, clean laboratory air).
Make certain the calibration filter is not in the light path.
Check the instrument zero. If the zero has shifted, repeat zero
adjustment.
Insert the calibration filter in the light path by pulling up the calibra-
tion filter knob.
Adjust the SPAN control to give the desired recorder deflection for the
calibration filter being used. For example, to set the analyzer to read 2.0
mole percent NO2 full scale, use a 10 cm cell and a calibration filter made
of two pieces of Corning glass CS 3-75 (3060) having an equivalent NO2
value of 0.50 percent; adjust the SPAN control to give a recorder deflection
of 25 percent of full scale.
Recheck the zero setting after SPAN adjustment because a change in
the SPAN control may cause a shift in zero. Except for purging, the span
adjustment may have to be repeated several times before zero and span
settings are correct and stable.
DETERMINATION OF NO2
Purge the sample cell as before.
Zero the analyzer.
Make span adjustment.
Pass the gas stream to be analyzed through the sample cell, adjusting
the flow rate to not less than 500 ml/min for a 10 cm cell. This minimum
flow rate insures negligible photodecomposition of the NO2 which causes
low results.
Read from the recorder chart the concentration of NO2 in the sample.
From Figure A5, determine total nitrogen (IV) oxides as mole percent
NO, corresponding to the mole percent NO2 read on the analyzer recorder
chart. Figure A5 shows curves for three different temperatures. Select the
curve closest to the temperature of the sample cell. For example, the
analyzer indicates a gas stream contains 1.50 mole percent NO, at 35°C;
total nitrogen (IV) oxides as mole percent NO2 is 1.64.
APPENDIX A 57
-------
111
o
V)
HI
Q
HI
O
o:
AY
25°C.
35°C.
-------
Zero the analyzer.
Set the SPAN control so the calibration gas containing the highest
concentration of NO2 drives the recorder nearly to full scale.
Flush the cell with purge gas immediately before collecting each sample
in order to check the instrument zero.
Pass the NO2—N2 standard mixture from the gas cylinder through
the cell, adjusting the flow rate to not less than 500 ml/min for a 10 cm cell.
Collect a gas sample at the cell outlet in 300-to-500-ml gas-sampling bulb.
Purge the sampling bulb for 5 minutes with the gas sample. Note the
recorder deflection and record the designation of the corresponding sample
during the sample collection.
Determine total nitrogen (IV) oxides in the gas samples as described
in the H,O2 method.
After collecting the last sample, re-zero the analyzer and, without
changing the SPAN setting, insert the calibration filter and note the deflec-
tion on the recorder.
Plot recorder readings versus mole percent NO2 as in Figure A6. Mole
percent NO2 is obtained by converting the total nitrogen (IV) oxides value
obtained by the modified Gaillard procedure to mole percent NO2 by use
of the equilibrium data plotted in Figure A5. The plot of recorder readings
versus mole percent NO2 (Figure A6) is linear in the range from 0 to 2
percent NO2.
From the curve plotted, determine what mole percent NO2 is equivalent
to the recorder deflection for the calibration filter. For example, a single
3-75 (3060) filter gives a recorder reading of 24.3 percent of full scale,
which is equivalent to 0.24 mole percent NO2 according to Figure A6.
APPENDIX A 59
-------
0.9
0.8
0.7
0.6
I 0.5
<§
JE 0.4
0.3
0.2
0.1
0.0
0 10 20 30 40 50 60 70 80 90 100
RECORDER READING, % of full scale
Figure A6 — Calibration curve for model 4 analyzer (10-cm cell; span, 136).
60
APPENDIX A
-------
DETERMINATION OF ACID MIST
DESCRIPTION OF SAMPLING EQUIPMENT
The sampling equipment used for acid mist was constructed by the
Public Health Service and is based on the equipment used by the Monsanto
Company. This portable train allows collection of a wide range of mist
or dust concentrations in a minimum of time. Particles greater than 3 microns
diameter are determined separately from the smaller particles.
The Public Health Service sampling train, Figures A7 and A8, consists
of a glass probe, a high-efficiency glass cyclone to collect particles larger
than 3 microns diameter, and a filter that traps the smaller particles. A
calibrated orifice, dry gas meter, and pump complete the train. This train
was originally designed for the collection of sulfuric acid mist, but it serves
equally well for nitric acid mist.
To prevent condensation of moisture in the train, the collection system
is mounted in a heated, insulated box. Heating is accomplished by two
thermostatically controlled electric heaters mounted in a transite box within
the sampler. The heaters are rated at 1000 watts each at 110 volts. They
consist of cone-shaped ceramic holders wound with heating wire and are
commonly called bowl heaters. The transite box is open at each end, and
a small fan circulates hot air around the collection equipment. Temperatures
should be kept above the water dew point, but not above the acid dew point.
On the other side of the sampling box are mounted two manometers to
indicate flow rate through the train, two dial stem thermometers to measure
.-.. -'
Figure A7 — Acid mist sampling train, control panel.
APPENDIX A
61
-------
Figure AS — Acid mist sampling train, collection compartment.
temperatures at the cyclone and orifice, and a temperature-controlling
thermostat.
The filter consists of a 65-mm-diameter glass Buchner funnel with a
course-porosity filtering disc. Two layers of fiberglass filter paper (MSA
CT 75428) are placed on the filtering disc to form the acid mist filter. The
packed fiberglass wool filter (Pyrex 3950) as described by Monsanto is
also highly efficient. (16)
The dry gas meter may be omitted if the rate of flow through the cali-
brated orifice is carefully watched. In the field, however, circumstances may
prevent careful observation of flow rate, and a dry gas meter insures accurate
measurement of total volume flow.
SELECTION OF SAMPLING POINTS
• The location and number of sampling points are based on size and shape
of the duct, uniformity of gas flow in the duct, availability of sampling port,
and space required to set up sampling equipment.
Straight vertical ducts with no flow obstructions for at least 8 diameters
upstream of the sampling point are preferred. Sometimes one must settle
for less than these ideal conditions.
To insure a representative sample of stack gas, the duct should be
divided into a number of equal areas and sampled at the center of each of
these areas. The number of areas depends on the size of the stack. This
procedure prevents erroneous results due to stratification of the acid mist in
APPENDIX A
-------
the duct. Bulletin WP-50 of the Western Precipitation Company may prove
useful in determining the number of areas.
STACK GAS VELOCITY
The pitot tube is used for most velocity measurements. The basic equation
for calculating velocity is,
29.9 29.0
Vs = 174K V HTS x —_ x —— where Vs is the
"a MW
gas velocity in feet per minute, K is the pitot tube calibration factor, H is
the velocity head in inches of water, Ts is the stack gas temperature in °R,
Ps is the absolute pressure of stack gas in inches of mercury, and MW is
the molecular weight of the process gas. This equation simplifies to Vs =
174 V HTg when the stack pressure is approximately equal to 29.9 and the
molecular weight of the process gas is equal to that of air (29.0).
SAMPLING RATE DETERMINATION
In the use of the acid mist train, a sampling rate of about 1 cfm at 70°F
must be maintained in order to insure separation of particles larger than 3
microns diameter in the cyclone.
Nozzle area is then determined by dividing sampling rate by stack gas
velocity, i.e. _ Q, sampling rate at stack gas conditions
A... —
Vs, stack gas velocity
If the gas temperature is below the acid dew point at the sampling port, the
mist must be sampled isokinetically.
It is, of course, impractical to vary nozzle size once sampling has begun.
Therefore, if gas velocity varies considerably, the sampling rate must be
varied and either cyclone efficiency or isokinetic sampling must be sacrificed.
Isokinetic sampling is not necessary if previous testing has shown that
about 90 percent of the acid mist particles are below 3 to 5 microns diameter.
Sampling rates and the corresponding orifice pressure drop should be
computed for each sampling point before sampling is begun. These values
should be recorded on the data sheet, Figure A9. Care must be taken in
using the orifice calibration curve at various temperatures and pressures.
A typical orifice calibration curve is shown in Figure A10. The following
equations may prove useful:
„ / ,.ux 530 PH —P.
= AP (calib) x -—— x
Q T0 29.9
™O /-\/— — lil^\ ,- 0 ..
= Q (calib) x
530 Pb-P0
= pressure drop across orifice at orifice pressure and
temperature, in. H,O
Pb = barometric pressure, in. Hg
AP (calib) = pressure drop across orifice at orifice calibration con-
ditions, in. H2O
T0 = temperature at orifice, °R
p = gauge pressure at inlet to orifice, in. Hg.
APPENDIX A
63
-------
MW = molecular weight of gas
Q0 = fl°w through orifice at orifice temperature and pres-
sure, cfm
Q (calib) = flow through orifice at calibration conditions, cfm
Plant.
Location.
Date.
Test No..
PIT-
Posi tion
Time,
min
ORIFICE DATA*
Desired
flow, cfm
=*n * »s
AP0,
in. H20
TO-
°F
PO-
in. Hg
METER DATA
Reading, ft3
°m
Pr
in.Hg
V
°F
*At stack conditions.
... .. / 530
0 'ICBIIDJ ^460
Qs = Volume sampled in s
CYCLONE
FIBER FILTER
TOTAL
fT0 29.9 29.0^
ef - 0. x 53° * Pb Pm
°f ^ X 460 + Tra X
Tl THAT IONS
cc of NaOH, N=
29.9
mg HN03 =
cc x N x 63
CONC. mg/ft3
figure A9 — Data sheet for sampling nitric acid mist.
64
APPENDIX A
GPO 828-664-6
-------
20
10
°» 9.0
8.0
c
~ 7.0
< 6-°
Q- 5.0
0
tx.
s «•«>
ce
a3-0
£C
Q.
2 0
1 0
\
/
A
/
/
J
/
/
f
I
f
/
f
/
i
f
f
J
0.1 0.2 0.3 0.4 0.5 0.6 .7 .8 .9 1.0 2.0 3.
FLOW RATE (Q). cfm
Figure A10 — Typical orifice calibration curve at 70°F and 29.9 in. Hg.
A SAMPLE CALCULATION ILLUSTRATES THE PROCEDURE
Assume T0 = 100°F, P0 = 2 in. Hg, MW = 29.0, and Pb = 29.9 in. Hg.
Desired sampling rate at 70°P is 1 fts/min or 1.05 fta/min at 100°P (the
stack temperature). Stack velocity measured by pitot tube measurements
was 1350 ft/min. The sample nozzle area is then equal to
l.OSftVmin be gelected
1350 ft/min
10-8 ft.2.
APPENDIX A
65
-------
The required flow at the sampling point is the stack velocity times the
probe area or 1350 ft/min x 0.8 x 10~3 ft2 = 1.08 fts/min at stack temperature
and pressure.
The corresponding orifice pressure drop at this flow is obtained by (1)
entering the orifice calibration chart at the desired gas volume and reading
the orifice pressure drop and (2) converting this pressure drop to conditions
under which the orifice will operate.
i.e. 1. Enter chart at 1.08 cfm and read AP = 6.5 in. at calibration
conditions.
530 29.9-2.0 29.0
2. AP0 = 6.5m.x_ x __ x _ = 5.74m.
at orifice conditions.
Desired orifice setting is then 5.74 in. at this sampling point.
SAMPLE COLLECTION
Place two thicknesses of fiberglass filter paper in the glass filter
holder or firmly pack filter tube with glass wool to a depth of 2
inches, depending on which type of filtering system is used. Check
the packing by drawing air through the train at about 1 cfm. A
pressure drop of about 3 in. Hg indicates sufficient fiber wool packing.
Pressure check the train by plugging the probe and drawing a
vacuum of 6 in. Hg. Close the line leading from the train; the
vacuum should remain at 6 in. Hg if the train is leakproof.
Slowly remove plug from probe to release vacuum and open line
leading from train.
Close insulated door on sampling train and heat collection apparatus
to 10°F above stack temperature. Blower should be ON whenever
box is hot. Regulate temperature with the thermostat on front
of box.
Insulate probe to prevent condensation during cold weather.
When sample box reaches operating temperature, sampling can begin.
During testing, record all pertinent data on the data sheet. Compute the
desired flow and the corresponding pressure drop before sampling begins.
Normally a sample collection period of 20 to 30 minutes at a sampling
rate of approximately 1 cfm should be sufficient. If expected acid mist load-
ings are high, i.e. 50 mg per scf, it is possible to overload the glass filter
media regardless of which type is used. In any case, the glass tubing down-
stream of the filter should be inspected often. Any carryover of acid mist
will be indicated by droplets or liquid in the tubing.
SAMPLE ANALYSIS
When sampling is completed, allow train to cool. Remove collected
sample from probe and cyclone by rinsing with distilled water and collecting
66 APPENDIX A
-------
washings in a 500-ml beaker. Add five drops of phenolphthalein indicator
solution and titrate with a standardized NaOH solution. For lower acid
mist loadings of 0.5 to 50 mg/scf, use an NaOH solution of about 0.01 to
0.1N. For higher loadings, use a normality of about 1.0.
Remove the filter paper or glass wool from its holder and place in a
beaker. Rinse the cyclone outlet line and the glass filter holder with distilled
water and add this washing to the beaker with the filter. Add enough dis-
tilled water to thoroughly remove all of the acid mist from the filter and
form a slurry. Stir the solution of paper or glass wool and water vigorously
for 15 to 20 minutes to insure a uniform mixture. Vigorous stirring should
also be employed during the titration with NaOH solution to determine an
accurate end point. When glass wool is used as a filtering medium, a stain-
less steel stirring rod is recommended for stirring the rather thick fluffy
mixture of glass wool and water; many glass rods have been broken.
Since there are 63 mg HNO3 per cc of 1.0 NaOH solution, (cc NaOH)
(N NaOH) (63) = mg HNO3.
Take duplicate samples. Run blank titration on whichever filter medium
is used because some NaOH may be needed to neutralize the medium.
APPENDIX A
67
-------
APPENDIX B: NITRIC ACID ESTABLISHMENTS IN
THE UNITED STATES
The following tabulation was compiled largely on the basis of a ques-
tionnaire sent to all known nitric acid producers in September 1964, updated
with additional information obtained from the literature and by personal
contact with company representatives. The list indicates only the establish-
ment at a given location and not the number of individual producing units.
The "process" column relates to the operating pressures:
A—Atmospheric: Oxidation of ammonia and absorption at atmospheric
pressure (10 psig maximum).
I—Intermediate: Oxidation of ammonia and absorption at an intermedi-
ate pressure of 20 to 60 psig.
P—Pressure: Oxidation of ammonia and absorption of the resulting
nitrogen oxides at pressures of 80 to 120 psig.
69
-------
U. S. NITRIC ACID ESTABLISHMENTS
January 1966
Nominal*
Capacity,
short tons
of 100%
HNO3
Company Location Process per year
ALABAMA
Armour Agricultural Chemical Company Cherokee P 105,000
E. I. du Pont de Nemours & Company Mineral Springs P 20,000
Hercules Powder Company, Inc. Bessemer P 15,000
Ketona Chemical Corporation Ketona P 23,000
Tennessee Valley Authority Wilson Dam P 100,000
ARIZONA
Apache Powder Company Curtiss P 35,000
ARKANSAS
Monsanto Company El Dorado P 255,000
CALIFORNIA
Collier Carbon and Chemical Corporation Brea P 47,000
Hercules Powder Company, Inc. Hercules P 100,000
Ortho Div., Chevron Chemical Company Richmond P 80,000
Shell Chemical Company Ventura P 20,000
COLORADO
E. I. du Pont de Nemours & Company Louviers P 20,000
FLORIDA
Chemstrand Company, a div. of
Monsanto Company Pensacola P 220,000
Escambia Chemical Corporation Pensacola P 85,000
Southern Nitrogen Company, Inc. Tampa P 42,000
GEORGIA
Columbia Nitrogen Corporation Augusta I 145,000
Southern Nitrogen Company, Inc. Bainbridge P 43,000
Southern Nitrogen Company, Inc. Savannah P 142,000
a Rounded to nearest 500 net tons
b Unconfirmed
70 APPENDIX B
-------
Company
Location
Nominal"
Capacity,
short tons
of 100%
HN03
Process per year
ILLINOIS
Commercial Solvents Corp.
E. I. du Pont de Nemours & Company
Illinois Nitrogen Corporation
Nitrin, Inc.
Texaco Inc.
U. S. Industrial Chemicals Co., Div. of
National Distillers and Chemical
Corporation
INDIANA
Calumet Nitrogen Products Company
Central Nitrogen, Inc.
IOWA
Hawkeye Chemical Company
Ortho Div., Chevron Chemical Company
KANSAS
Cooperative Farm Chemicals Association
Spencer Chemical Div. —
Gulf Oil Corporation
KENTUCKY
Spencer Chemical Div. —
Gulf Oil Corporation
LOUISIANA
Commercial Solvents Corporation
Monsanto Company
Olin Mathieson Chemical Corporation
Rubicon (U. S. Rubber— ICI)
MAINE
Northern Chemical Industries, Inc.
MINNESOTA
St. Paul Ammonia Products, Inc.
MISSISSIPPI
Mississippi Chemical Corporation
Spencer Chemical Div. —
Gulf Oil Corporation
Ordill
Seneca
Marseilles
Cordova
Lockport
Tuscola
Hammond
Terre Haute
Clinton
Fort Madison
Lawrence
J
Pittsburg 1
Henderson
Sterlington
Luling
Lake Charles
Geismar
Searsport
Pine Bend
Yazoo City
Vicksburg
P
P
P
P
P
P
P
P
P
P
P
P
I
P
P
P
P
P
P
P
P
P
50,000
40,000
115,500
85,000
66,000
40,000
39,500
122,500
117,000
80,000
220,000
140,000
140,000
80,000
158,500
218,000
93,000
25,000
20,000
70,000
260,000
80,000
APPENDIX B
71
-------
Company
MISSOURI
Armour Agricultural Chemical Company
Atlas Chemical Industries, Inc.
Hercules Powder Company, Inc.
NEBRASKA
Allied Chemical Corporation, Nitrogen Div.
Feltex, Inc.
Cominco Products
NEW JERSEY
American Cyanamid Company
E. I. du Pont de Nemours & Company
Hercules Powder Company, Inc.
Hercules Powder Company, Inc.
NEW YORK
Allied Chemical Corporation, Nitrogen Div.
M. Ames Chemical Works, Inc.
NORTH CAROLINA
Carolina Nitrogen Corporation
OHIO
Allied Chemical Corporation, Nitrogen Div.
Solar Nitrogen Chemical Co.
Southern Nitrogen Company, Inc.
PENNSYLVANIA
Allied Chemical Corporation, General
Chemical Div.
Atlas Chemical Industries, Inc.
TENNESSEE
E. I. du Pont de Nemours & Company
Farmers Chemical Association
Location
Crystal City
Webb City
Louisiana
La Platte
Fremont
Beatrice
Bound Brook
Gibbstown
Kenvil
Parlin
Buffalo
Glens Falls
Wilmington
South Point
Lima
Cincinnati
Newell
Reynolds
Old Hickory
Chattanooga
Process
P
P
P
P
P
P
I
P
P
P
A
I
P
A
P
P
P
P
P
P
Nominal11
Capacity,
short tons
of 100%
HNO3
per year
100,000
91,500
350,000
93,500
30,000
125,000
21,500
220,000
15,000
40,000
25,000
500
130,000
239,000
65,000
76,000
65,000
17,500
42,000
125,000b
72
APPENDIX B
-------
Company
TEXAS
Celanese Chemical Company
E. I. du Pont de Nemours & Company
E. I. du Pont de Nemours & Company
Nipak, Inc.
Phillips Petroleum Company
El Paso Natural Gas
UTAH
United States Steel Corporation
VIRGINIA
Allied Chemical Corporation, Nitrogen Div.
Hercules Powder Company, Inc.
WASHINGTON
E. I. du Pont de Nemours & Company
Ortho Div., Chevron Chemical Company
Phillips Pacific Chemical Company
WEST VIRGINIA
American Cyanamid Company
E. I. du Pont de Nemours & Company
WISCONSIN
E. I. du Pont de Nemours & Company
Location
Bay City
Beaumont
Orange
Kerens
Etter
Odessa
Provo
Hopewell
Radford
Du Pont
Kennewick
Kennewick
Willow Island
Belle
Barksdale
Tons HNO3 per
Pressure Process
Intermediate
Atmospheric
6,190,000
366,500
264,000
Process
P
P
P
P
P
P
I
P
P
P
P
P
P
P
P
year
Nominal*
Capacity,
short tons
of 100%
HN03
per year
30,000
60,000
85,000
49,000
157,500
65,000
59,500
380,000
100,000
20,000
50,000
7,000
24,000
85,000
20,000
TOTAL 6,820,500
Number of Establishments — 74
APPENDIX B
73
-------
APPENDIX C: FACTORS CAUSING HIGH EMISSIONS
OF NITROGEN OXIDES
A number of factors, alone or in combination, can cause abnormally high
emissions of nitrogen oxides in the stack gases that are discharged to the
atmosphere. The causes and methods of control are tabulated on the fol-
lowing pages.
75
-------
PRESSURE AND COMBINATION PROCESSES
LEAKING HEAT EXCHANGERS
Cold exit gas from the absorption tower is generally reheated by heat
exchange with hot rich converter gas, before it passes to a power recovery
turbine and on to the atmosphere. A faulty heat exchanger allows rich gas
to leak into the exit gas stream, resulting in excessive nitrogen oxides con-
centration in the tail gas. Analysis of the exit gas for nitrogen oxides content
as it enters and as it leaves the reheater will show whether leakage is
occurring.
INSUFFICIENT OXYGEN SUPPLY TO PROCESS
Enough air must be supplied to the process to provide the oxygen
needed for oxidation of ammonia and for the subsequent reactions of
nitrogen oxides to form nitric acid. Under proper operating conditions there
should be a small excess of unreacted oxygen in the exit gas leaving the
absorber, usually about 3 or 4 percent. A deficiency of oxygen will result in
incomplete reaction and consequently in excess nitrogen oxides in the
stack gas. Proper control of air and ammonia flows can correct this situation.
COOLING WATER—INSUFFICIENT FLOW OR HIGH TEMPERATURE
Good cooling of the condensers and the absorption column is essential
for maximum absorption efficiency. An ample flow of cooling water is
mandatory. Best performance is obtained with cold water. In warm weather
the cooling water supply may reach temperatures of 90°F or more, with a
consequent decrease in absorption efficiency and increase in tail gas emis-
sion. The solution to the problem is to provide better cooling or to install
facilities for fume elimination.
PRODUCTION RATE AND ACID STRENGTH
Nitric acid plants can be operated above rated capacity by increasing
the flows of air and ammonia. The acid strength can also be increased
beyond design (usually 55 to 60 percent HNO3) by a few percent. Both
of these actions lead to a sacrifice in yield and an increase in tail-gas emis-
sion. Under these circumstances, fume elimination facilities may be required.
EQUIPMENT FAILURES
Performance of the absorption column can be adversely affected by
failure of the internal parts as a result of corrosion or mechanical break-
down. Usually this failure can be detected by determining the acid strength
gradient throughout the column.
Chlorides can cause severe corrosion of stainless steel; it is customary
to sample the nitric acid at an intermediate point in the absorber (where
the acid strength is about 23 percent HNO3), and determine its chloride
content. If the chloride content exceeds 0.03 to 0.05 percent, the 23 percent
nitric acid should be drained from the absorber tray; otherwise, a further
accumulation of chlorides would lead to serious corrosion.
76 APPENDIX C
-------
PROCESS FEED WATER
Distilled water (steam condensate) is fed to the top of the absorber and
takes part in the reaction with nitrogen oxides to form nitric acid. Failure
to supply the required quantity of process water to the absorber will result
in excessive emission of nitrogen oxides in the tail gas.
ATMOSPHERIC PROCESS
Emission problems in the atmospheric process are essentially the same
as those encountered in the pressure process. The two processes differ sub-
stantially, however, in the design of absorption systems. Whereas the pres-
sure process utilizes a single-pass bubble-cap absorber with internal cooling,
the atmospheric plant comprises a series of packed towers over each of
which acid is circulated by pumps. Generally, the circulating acid flows
through coolers.
Difficulties that could lead to excessive emission of nitrogen oxides in
an atmospheric plant absorption system are:
Failure of one or more of the acid circulating pumps to circulate suf-
ficient acid.
Poor acid distribution in the top of the absorbers.
Channeling due to dirty tower.
Inadequate cooling of the circulating acid, caused by dirty coolers or
insufficient water flow.
APPENDIX C 77
-------
APPENDIX D
PHYSICAL DATA
-------
PHYSICAL DATA —NITRIC ACID(17)
Be."
10.00
10.25
10.50
10.75
11.00
11.25
11.50
11.75
12.00
12.25
12.50
12.75
13.00
13.25
13.50
13.75
14.00
14.25
14.50
14.75
15.00
15.25
15.50
15.75
16.00
16.25
16.50
16.75
17.00
17.25
17.50
17.75
18.00
18.25
18.50
18.75
19.00
19.25
19.50
19.75
20.00
20.25
20.50
20.75
Sp. Gr.
1.0741
1.0761
1.0781
1.0801
1.0821
1.0841
1.0861
10.881
1.0902
1.0922
1.0943
1.0964
1.0985
1.1006
1.1027
1.1048
1.1069
1.1090
1.1111
1.1132
1.1154
1.1176
1.1197
1.1219
1.1240
1.1262
1.1284
1.1306
1.1328
1.1350
1.1373
1.1395
1.1417
1.1440
1.1462
1.1485
1.1508
1.1531
1.1554
1.1577
1.1600
1.1624
1.1647
1.1671
Tw.°
14.82
15.22
15.62
16.02
16.42
16.82
17.22
17.62
18.04
18.44
18.86
19.28
19.70
20.12
20.54
20.96
21.38
21.80
22.22
22.64
23.08
23.52
23.94
24.38
24.80
25.24
25.68
26.12
26.56
27.00
27.46
27.90
28.34
28.80
29.24
29.70
30.16
30.62
31.08
31.54
32.00
32.48
32.94
33.42
%HNO3.
12.86
13.18
13.49
13.81
14.13
14.44
14.76
15.07
15.41
15.72
16.05
16.39
16.72
17.05
17.38
17.71
18.04
18.37
18.70
19.02
19.36
19.70
20.02
20.36
20.69
21.03
21.36
21.70
22.04
22.38
22.74
23.08
23.42
23.77
24.11
24.47
24.82
25.18
25.53
25.88
26.24
26.61
26.96
27.33
Be."
21.00
21.25
21.50
21.75
22.00
22.25
22.50
22.75
23.00
23.25
23.50
23.75
24.00
24.25
24.50
24.75
25.00
25.25
25.50
25.75
26.00
26.25
26.50
26.75
27.00
27.25
27.50
27.75
28.00
28.25
28.50
28.75
29.00
29.25
29.50
29.75
30.00
30.25
30.50
30.75
31.00
31.25
31.50
31.75
Sp. Gr.
1.1694
1.1718
1.1741
1.1765
1.1789
1.1813
1.1837
1.1861
1.1885
1.1910
1.1934
1.1959
1.1983
1.2008
1.2033
1.2058
1.2083
1.2109
1.2134
1.2160
1.2185
1.2211
1.2236
1.2262
1.2288
1.2314
1.2340
1.2367
1.2393
1.2420
1.2446
1.2473
1.2500
1.2527
1.2554
1.2582
1.2609
1.2637
1.2664
1.2692
1.2719
1.2747
1.2775
1.2804
Tw.°
33.88
34.36
34.82
35.30
35.78
36.26
36.74
37.22
37.70
38.20
38.68
39.18
39.66
40.16
40.66
41.16
41.66
42.18
42.68
43.20
43.70
44.22
44.72
45.24
45.76
46.28
46.80
47.34
47.86
48.40
48.92
49.46
50.00
50.54
51.08
51.64
52.18
52.74
53.28
53.84
54.38
54.94
55.50
56.08
%HNO3.
27.67
28.02
28.36
28.72
29.07
29.43
29.78
30.14
30.49
30.86
31.21
31.58
31.94
32.31
32.68
33.05
33.42
33.80
34.17
34.56
34.94
35.33
35.70
36.09
36.48
36.87
37.26
37.67
38.06
38.46
38.85
39.25
39.66
40.06
40.47
40.89
41.30
41.72
42.14
42.58
43.00
43.44
43.89
44.34
80
APPENDIX D
GPO aae-664-7
-------
Be.0
32.00
32.25
32.50
32.75
33.00
33.25
33.50
33.75
34.00
34.25
34.50
34.75
35.00
35.25
35.50
35.75
36.00
36.25
36.50
36.75
37.00
37.25
37.50
37.75
38.00
38.25
38.50
38.75
39.00
39.25
39.50
39.75
40.00
40.25
Sp. Gr.
1.2832
1.2861
1.2889
1.2918
1.2946
1.2975
1.3004
1.3034
1.3063
1.3093
1.3122
1.3152
1.3182
1.3212
1.3242
1.3273
1.3303
1.3334
1.3364
1.3395
1.3426
1.3457
1.3488
1.3520
1.3551
1.3583
1.3615
1.3647
1.3679
1.3712
1.3744
1.3777
1.3810
1.3843
Tw.°
56.64
57.22
57.78
58.36
58.92
59.50
60.08
60.68
61.26
61.86
62.44
63.04
63.64
64.24
64.84
65.46
66.06
66.68
67.28
67.90
68.52
69.14
69.76
70.40
71.02
71.66
72.30
72.94
73.58
74.24
74.88
75.54
76.20
76.86
%HNO3.
44.78
45.24
45.68
46.14
46.58
47.04
47.49
47.95
48.42
48.90
49.35
49.83
50.32
50.81
51.30
51.80
52.30
52.81
53.32
53.84
54.36
54.89
55.43
55.97
56.52
57.08
57.65
58.23
58.82
59.43
60.06
60.71
61.38
62.07
Be.0
40.50
40.75
41.00
41.25
41.50
41.75
42.00
42.25
42.50
42.75
43.00
43.25
43.50
43.75
44.00
44.25
44.50
44.75
45.00
45.25
45.50
45.75
46.00
46.25
46.50
46.75
47.00
47.25
47.50
47.75
48.00
48.25
48.50
Sp. Gr.
1.3876
1.3909
1.3942
1.3976
1.4010
1.4044
1.4078
1.4112
1.4146
1.4181
1.4216
1.4251
1.4286
1.4321
1.4356
1.4392
1.4428
1.4464
1.4500
1.4536
1.4573
1.4610
1.4646
1.4684
1.4721
1.4758
1.4796
1.4834
1.4872
1.4910
1.4948
1.4987
1.5026
Tw.°
77.52
78.18
78.84
79.52
80.20
80.88
81.56
82.24
82.92
83.62
84.32
85.02
85.72
86.42
87.12
87.84
88.56
89.28
90.00
90.72
91.46
92.20
92.92
93.68
94.42
95.16
95.92
96.68
97.44
98.20
98.96
99.74
100.52
%HNO3.
62.77
63.48
64.20
64.93
65.67
66.42
67.18
67.95
68.73
69.52
70.33
71.15
71.98
72.82
73.67
74.53
75.40
76.28
77.17
78.07
79.03
80.04
81.08
82.18
83.33
84.48
85.70
86.98
88.32
89.76
91.35
93.13
95.11
Specific gravity determinations were made at 60°F, compared with
water at 60°F.
From the specific gravities, the corresponding degrees Baume were cal-
culated by the following formula:
Baume = 145 —
. gr.
Baume hydrometers for use with this table must be graduated by the
above formula, which formula should always be printed on the scale.
Atomic weights from F. W. Clarke's table of 1901. O = 16.
APPENDIX D
81
-------
ALLOWANCE FOR TEMPERATURE
At 10° —20° Be. — 1/30° Be. or .00029 sp. gr. = 1°F.
20° —30° Be. — 1/23° Be. or .00044 sp. gr. = 1°F.
30° — 40° Be. — 1/20° Be. or .00060 sp. gr. = 1°F.
40° — 48.5° Be. — 1/17° Be. or .00084 sp. gr. = 1°F,
250
240
230
220
- 120
Q.
LU
210
200
190
180
O
LU
- 95
- 90
85
20 40 60 80
NITRIC ACID CONCENTRATION, WT %
100
Figure D1 — Boiling point and vapor equilibrium diagram for nitric acid/water solutions of
atmospheric pressure)! 8).
82
APPENDIX D
-------
20 40 60 80
NITRIC ACID CONCENTRATION, WT %
- 0
100
Figure D2 Effect of concentration on normal freezing points of nitric acid/water solutions(19).
APPENDIX D
83
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PERCENT
HMOs
SPECIFIC GRAVITY
1.45-
1.44 -
1.43-
1.42 -
1.41-
1.40-
1.39 J
1.38-
1.37-
1.36-
1.35 J
1.34-
1.33-
1.32-
1.31-
1.30-
1.29-
1.28-
1.27-
1.26-
1.25-
1.24-
1.23-
1.22-
1.20-
1.19-
-40
-45
-50
-55
-60
-65
-70
D
DIRECTIONS:
CONNECT SPECIFIC GRAVITY ON SCALE A AND TEMPERATURE ON SCALE
B OR C WITH A STRAIGHT EDGE. READ STRENGTH AT INTERSECTION
WITH SCALE D.
Figure D3 — Nomograph relating specific gravity and acid strength for weak nitric acid.
APPENDIX D
-------
SPECIFIC GRAVITY
1.54 —
1.53-^
1.52 —
1.50 -^
1.49 -;
1.48 -
1.47 —
1.46 -
1.45 _I
1.44 —
1.43-1
TEMPERATURE:
°F °C
:r 5
50 L
60-; r
70 4-20
1-25
80-. '.
30
B C
PERCENT
HNO>
1-80
r81
j-82
r83
-84
r85
j-86
|-87
188
I-89
r-90
i-91
I-92
h93
1-94
1-95
E-96
r97
-38
DIRECTIONS:
CONNECT SPECIFIC GRAVITY ON SCALE A AND TEMPERATURE ON SCALE
B OR C WITH A STRAIGHT EDGE. READ STRENGTH AT INTERSECTION
WITH SCALE D.
Figure D4 — Nomograph relating specific gravity and acid strength for strong nitric acid.
APPENDIX D
85
-------
REFERENCES
1. Bureau of the Census, U. S. Department of Commerce, Statistical
Abstracts of the United States 1953-1964, Section on Chemical Products.
2. Hunt, L. B., The Ammonia Oxidation Process for Nitric Acid Manu-
facture, Platinum Metals Review, 2:129-134. Oct., 1958.
3. Chilton, T. H., The Manufacture of Nitric Acid by the Oxidation of
Ammonia. Chem. Eng. Progress Mono. Series No. 3, Vol. 56. Amer.
Inst. of Chem. Engineers. 1960.
4. Drake, G., Processes for the Manufacture of Nitric Acid. Brit. Chem.
Eng. 8:12-20. Jan., 1963.
5. Anon, Nitric Plant Optimizes at Medium Pressure. Chem. Eng. 65:56-58.
May, 1958.
6. Ermenc, E. D., Wisconsin Process for Recovery of Dilute Oxides of
Nitrogen. Chem. Eng. Progress. 52:488-492. Nov., 1956.
7. Harteck, P., Dondes, S., Producing Chemicals with Reactor Radiation.
Nucleonics. 14:22-25. July, 1956.
8. Donahue, J. L., System Design for the Catalytic Decomposition of Nitro-
gen Oxides. J.A.P.C.A. 8:209-212. Nov., 1958.
9. Anon, Where Tail Gas Oxidation Stands Today. Chem. Eng. 66:66-68.
Jan. 12, 1959.
10. Anderson, H. C., Green, W. J., and Steel, D. R., Catalytic Treatment of
Nitric Acid Plant Tail Gas. Ind. and Eng. Chem. 53:199-204. Mar., 1961.
11. Anon. Nitrogen Fertilizer Complex. Nitrogen. 28:21-22.
12. Peters, M. S., Stop Pollution by Nitrogen Oxides. Chem. Eng. 62:197-200.
May, 1955.
13. Beatty, R. L., Berger, L. B., and Schrenk, H. H., Determination of the
Oxides of Nitrogen by the Phenoldisulfonic Acid Method. R. I. 3687.
Bureau of Mines, U. S. Dept. Interior, Feb., 1943.
14. Saltzman, Bernard E., Colorimetric Determination of Nitrogen Dioxide
in the Atmosphere. Anal. Chem. 26:1949-1955. Dec., 1954.
15. Interbranch Chemical Advisory Committee, Division of Air Pollution,
Public Health Service. Selected Methods for the Measurement of Air
Pollutants. Public Health Service Publication No. 999-AP-ll, May, 1965.
16. Patton, W. F., and Brink, J. A., Jr., New Equipment and Techniques for
Sampling Chemical Process Gases. J.A.P.C.A. 13:162-166.
17. Mfg. Chemists' Assoc. Tech. Chart, Manual Sheet SD-5, Washington,
D. C.
18. Ellis, S. R. M., and Thwaites, J. M., J. Applied Chem. 7:152. 1957.
19. Kuster, F. W., and Kreman, R., Z. Anog. Chem. 51:1. 1904.
REFERENCES 87
GPO 828-664—8
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SUBJECT INDEX
Acid concentration processes, 15, 16
Acid concentrator, 26, 27
Acid mist, 3, 23
Ammonia oxidation process
atmospheric pressure process, 5,
13-15
combination process, 11-13
pressure process, 9-11
Analytical techniques
acid mist, 32, 61-67
nitric oxide, 40-42
nitrogen dioxide, 32, 51-53
nitrogen oxides, 31, 43-45
oxygen, 32
Control of emissions
absorption, 19
adsorption, 19
catalytic reduction, 4, 16-19
flaring, 20
scrubbing systems, 4, 23
tall stacks, 20
Cooler condensers, 11
Definitions, 35
Electric arc process, 5, 15
Emissions
acid mist, 3, 23
concentration, 3, 4, 21-29
control, 4, 16-20
nitrogen oxides, 3, 21-29
source of 3, 21, 75-77
Energy recovery, 6
Flaring, 20
Glossary, 35
Haber process, 5
Nitric oxide, 3, 40-42
Nitrogen dioxide, 3, 32, 51-53
Nitrogen oxides, 3, 31, 43-45, 75-77
Nuclear nitrogen fixation process, 15
Production, 3, 6, 69-73
Red fuming nitric acid, 27
Saltpeter—sulfuric acid process, 5
Scrubbing systems, 4, 23
Tall stacks, 20
Wisconsin process, 15
SUBJECT INDEX
GPO 828—664—9
89
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