ENVIRONMENTAL HEALTH SERIES
                            Air Pollution
ATMOSPHERIC
EMISSIONS
FROM  NITRIC ACID
MANUFACTURING PROCESSES

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       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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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

-------
                                                                                                                         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.

-------
    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
       2  100
       o  so
       LU
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             1                10              100             1,000
               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

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                          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

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        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

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 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

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    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

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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

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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

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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

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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  = 
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      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

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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

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 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

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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

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    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

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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

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     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

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    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

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          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

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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

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  APPENDIX D
PHYSICAL DATA

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           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

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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

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                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

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                        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

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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

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                            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

-------
                           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

-------