ATMOSPHERIC EMISSIONS
FROM
THERMAL- PROCESS
PHOSPHORIC ACID
MANUFACTURE
U. S. DEPARTMENT OF HEALTH, EDUCATION AND WELFARE
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ATMOSPHERIC EMISSIONS
FROM
THERMAL-PROCESS PHOSPHORIC
ACID MANUFACTURE
Cooperative Study Project
Manufacturing Chemists' Association, Inc.
and
Public Health Service
U.S. DEPARTMENT OF HEALTH, EDUCATION AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
National Air Pollution Control Administration
Durham, North Carolina
October 1968
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price 40 cents
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The AP series of reports is issued by the National Air Pollution Con-
trol Administration to,report the results of scientific and engineering
studies, and information of general interest in the field of air pollution.
Information reported in this series includes coverage of NAPCA intra-
mural activities and of cooperative studies conducted in conjunction
•with state and local agencies, research institutes, and industrial
organizations. Copies of AP reports may be obtained upon request,
as supplies permit, from the Office of Technical Information and Pub-
lications, National Air Pollution Control Administration, U.S. Depart-
ment of Health, Education, and Welfare, Ballston Center Tower No. 2,
801 North Randolph Street, Arlington, Virginia 22203.
National Air Pollution Control Administration Publication No. AP-48
ii
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PREFACE
To provide reliable information on the nature and quantity of
emissions to the atmosphere from chemical manufacturing, the Manu-
facturing Chemist's Association, Inc. , and the National Center for Air
Pollution Control, United States Public Health Service, Department of
Health, Education, and Welfare, entered into a study agreement on
October 29, 1962. A cooperative program was established to investi-
gate 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-USPHS Steering Committee, -which
is presently constituted of the following members:
Representing USPHS Representing MCA
Stanley T. Cuffe* Willard F. Bixby*
Robert L. Harris Louis W. Roznoy
David Monti Clifton R. Walbridge
Raymond Smith Elmer P. Wheeler
Information included in this report describes the range of emis-
sions during normal operating conditions and the performance of
established methods and devices employed to limit or control these
emissions. Interpretation of emission values in terms of ground-level
concentrations and assessment of potential effects produced by the
emissions are outside the scope of this program.
*Principal representative.
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ACKNOWLEDGMENTS
Many companies and individuals in the phosphoric acid industry
have been helpful in promoting this study, and for their contributions,
the project sponsors extend their sincere gratitude.
Special thanks is due the following companies for their participa-
tion in a program of stack sampling specifically for this study:
Hooker Chemical Corporation
The Tennessee Valley Authority
Monsanto Company
Stauffer Chemical Company
Don R. Goodwin, of the Public Health Service, and Fred G.
Rolater, of Stauffer Chemical Company, were the investigators in the
study and are the principal authors of this report. The sponsors
acknowledge the services of the Stauffer Chemical Company in pro-
viding the services of Mr. Rolater.
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CONTENTS
PREFACE iii
ACKNOWLEDGMENTS iv
USE AND LIMITATIONS OF THIS REPORT 1
SUMMARY 3
Phosphoric Acid Production 3
Emissions from Phosphoric Acid Manufacture 3
Control of Emissions 3
Emission Guidelines 4
GROWTH. OF PHOSPHORIC ACID INDUSTRY 5
THERMAL-PROCESS PHOSPHORIC ACID MANUFACTURE • • 9
Introduction 9
Raw Materials 9
Process Description 10
Yields and Losses 12
EMISSIONS FROM PHOSPHORIC ACID MANUFACTURE BY
THERMAL PROCESS 13
Phosphoric Acid Manufacture 13
Acid Treating 15
Operating Factors Affecting Emissions 15
Abatement Methods and Equipment 16
GLOSSARY OF TERMS 23
APPENDIX A. EMISSION" AND OPERATING DATA FOR THERMAL-
PROCESS PHOSPHORIC ACID PLANTS . . . • 27
APPEND DC B. SAMPLING AND ANALYTICAL TECHNIQUES . • 33
Determination of Phosphoric Acid Mist ... 34
Sample Analysis (Colorimetric Method) ... 43
Sample Analysis (Acid-Base Titration
Method) 47
Determination of Nitrogen Oxides in Stack
Gas (Phenoldisulfonic Acid Method) 49
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APPENDIX C. THERMAL-PROCESS PHOSPHORIC ACID
ESTABLISHMENTS IN UNITED STATES ... 59
APPENDIX D. PHYSICAL DATA 61
REFERENCES 67
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USE AND LIMITATIONS OF THIS REPORT
This report, one of a series concerning atmospheric emissions
from chemical manufacturing processes, * has been prepared to provide
information on phosphoric acid manufacture by the thermal process.
This report does not include information on the manufacture of phos-
phoric acid by the wet process.
Background information is included to define the importance of
the thermal-process phosphoric acid industry in the United States.
Basic characteristics of the industry are discussed, including growth
rate in recent years, uses for the product, and the number and location
of the producing sites.
A process description is given for the thermal process. Process
information includes discussion of normal process variables that affect
the quantity of emissions, the normal range of emissions, and methods
of controlling or reducing emissions. Supplemental material provides
detailed emission sampling and analytical methods.
The emission and operating data in Table A-l in Appendix A
represent results from approximately 90 percent of the present number
of establishments:**
Most of these data have been gathered from production records of
phosphoric acid producers. The data also include results from several
stack-sampling programs conducted during late 1966 and early 1967 by
*Two previous reports have been published in.this series: "Atmos-
pheric Emissions from Sulfuric Acid Manufacturing Processes, "
PHS Publ. No. 999-AP-13; and "Atmospheric Emissions from Nitric
Acid Manufacturing Processes, " PHS Publ. No. 999-AP-27. They
are available from the Manufacturing Chemists' Association,
Washington, D. C. , and Superintendent of Documents, U.S. Govern-
ment Printing Office, Washington, D. C. 20402.
**Establishment a -works having one or more thermal-process phos-
phoric acid plants or units, each of which is a complete production
entity.
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the United States Public Health Service. Results obtained from these
tests are consistent with the data received from other industry sources.
Emissions to the atmosphere from a thermal-process phosphoric
acid plant depend upon a number of factors, such as plant design, skill
of operation, efficiency of hydration, and the type and operation of
special devices to reduce emissions. This report should be reviewed
in 5 to 10 years to determine whether revision is necessary to reflect
prevailing conditions.
Although this report is an industry review primarily for public
officials concerned with the control of air pollution, the information
should also be helpful to chemical plant management and technical
staffs concerned with the control of air pollution. It may also be help-
ful to engineering students, medical personnel, and other professional
people interested in emissions from thermal-process phosphoric acid
plants.
THERMAL-PROCESS PHOSPHORIC ACID
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SUMMARY
PHOSPHORIC ACID PRODUCTION
Production of phosphoric acid by the thermal process has in-
creased at an annual rate of about 8 percent during the period from
1953 to 1963, and this growth rate is expected to continue in the imme-
diate future. Thermal-process acid is used primarily in the manu-
facture of industrial phosphates and generally has-been confined to non-
fertilizer use. In recent years high-purity thermal-process acid has
been used in increasing quantities for the production, of the new super-
phosphoric acids (up to 80 percent P?O ).
At the present time .27 operating establishments, several of which
have more than one furnace, produce more than 1,000, 000 tons of
phosphoric acid per-year (P,O basis). Strength of acids produced
& o
varies from 75 to 85 percent phosphoric acid, although a few plants
produce acid of up to 105 percent phosphoric acid.
EMISSIONS FROM THERMAL-PROCESS PHOSPHORIC ACID
The major atmospheric contaminant from thermal-process phos-
phoric acid manufacture is phosphoric acid mist discharged in the
absorber exit gas. This gas stream aiao contains-water vapor and
trace amounts of-nitrogen-t>xides. The concentration of acid mist from
the plants that supplied data varies from 0. 1 to 16. 9 milligrams of
acid mist (expressed as P^O,.) per standard cubic foot of stack gas.
Emission data are shown in Table A-l in Appendix A.
A second important emission is the acid treating tank discharge
gas, which can contain significant amounts of hydrogen sulfide. These
emissions are intermittent and may range from 10 to 2500 parts per
million of hydrogen sulfide, as shown in Table A-l.
CONTROL OF EMISSIONS
Operating practices have little effect on emissions of acid mist.
Several abatement devices have the ability to reduce emissions of acid
325-033 O - 68 - 2
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mist by as much as 99. 9 percent. Both high-pressure-differential
wire-mesh mist eliminators and high-efficiency glass-fiber mist
eliminators are capable of this high performance.
Emissions of hydrogen sulfide can be controlled by alkaline
scrubbing or by incinerating the hydrogen sulfide in the phosphorus
furnace.
EMISSION GUIDELINES
The emission and operating data in Table A-l show that acid
mist and spray can be controlled effectively by commercially available
abatement devices. Collection efficiencies range from 95 to 99. 9 per-
cent, with about one-third of the collection efficiencies reported being
99. 9 percent or better. This degree of control is possible in the pro-
duction of 75 to 105 percent phosphoric acid.
Stack effluent from thermal-process phosphoric acid plants
normally has a plume of from 50 to 100 percent opacity. The plume
dissipates in a few hundred feet, depending on acid mist concentration
and atmospheric conditions.
Since only trace amounts of nitrogen oxides are emitted from
these plants, abatement equipment is not used to reduce these emissions.
Hydrogen sulfide emissions from the acid treating facilities are
influenced by operating practices. The relatively small intermittent
emissions of hydrogen sulfide can be controlled by alkaline scrubbing
or can be oxidized in the phosphorus furnace to sulfur dioxide.
THERMAL-PROCESS PHOSPHORIC ACID
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GROWTH OF PHOSPHORIC ACID INDUSTRY
In 1938 low-cost electric power became available in large quan-
tities in the Tennessee River Valley. The availability of low-cost
power and the presence of thermal--quality phosphate rock in the Maury
County area of middle Tennessee brought about the production of
elemental phosphorus by the electric furnace process. The thermal
process of producing phosphoric acid was the natural outgrowth.
A very pure phosphoric acid can be produced by the thermal
process. This acid normally is used to produce high-quality phosphates
for food, drug, and detergent uses; and since 1940, production has in-
creased at the same general rate as the demand for these products. A
few installations now produce fertilizer-grade acid, but they account
for only a small part of the annual production.
In 1941 the production of thermal-process acid was about 108,500
tons (P O basis) while wet-process acid production was slightly higher
at 132, 000 tons. By 1945 production of thermal-process acid and wet -
process acid were equal at about 132, 000 tons each. Since 1945 both
segments of the industry have continued to grow, but since 1950 wet-
process acid production has exceeded thermal process production, as
is shown in Figure 1. Production data are given in Table 1.
The thermal process is now used to produce approximately one-
third of the phosphoric .acid annually in the United States. The thermal-
process acid industry can be expected to increase at the same rate as
the national economy unless technical changes (alter the cost differential
between thermal and wet acid. Should thermal acid ever become
economically attractive for fertilizer manufacture, production would
increase rapidly.
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c
o
4.0
3.5
3.0
2.5
o10 2.0
C\J
Q.
2 1.5
0.5
TOTAL PHOSPHORIC ACID PRODUCTION
.WET-PROCESS
\ACID PRODUCTION;
THERMAL-PROCESS'.:-.
ACID PRODUCTION..-'
1945
1950
1955
1960
1965
Figure 1. Production of phosphoric acid in
United States, 1941 through 1965.
THERMAL-PROCESS PHOSPHORIC ACID
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Table 1. GROWTH OF PHOSPHORIC ACID INDUSTRY IN UNITED STATES'
(tons/year 100& PO basis)
Year
1941
1942
1943
1944
1945
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
I960
1961
1962
1963
1964
1965
Thermal process
108,494
104,655
103,418
111,157
132,149
191,911
211,578
259,677
295,073
330,096
357,622
462 , 580
506,774
540,025
570,235
632,954
657,372
740,747
762,531
844,761
869,805
947,293
1,007,624
l,007,941a
Wet process
131,521
118,970
127,248
141,141
132,599
174,987
220,828
245,427
299,152
338,426
388,908
496,152
631,252
774,998
811,770
936,129
1,033,205
1,140,658
1,324,695
1,409,173
1,576,976
1,957,476
2,275,418
2,837,119
Subject to revision.
Growth of Phosphoric Acid Industry
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THERMAL-PROCESS PHOSPHORIC
ACID MANUFACTURE
INTRODUCTION
The process of producing phosphoric acid from elemental phos-
phorus is referred to by several names, including: the electric furnace
process, phosphorus burning process, and thermal process. In this
report it will be referred to as the thermal process.
Essentially all of the phosphoric acid produced in the United
States is manufactured by either of two commercial processes. The
wet process produces phosphoric acid from phosphate rock by treat-
ment with sulfuric acid. The thermal process produces phosphoric
acid by burning elemental phosphorus in air.
The cost of phosphorus pentoxide produced by the thermal process
is nearly twice the cost of that produced by wet-process acid. Thermal-
process acid as normally produced contains 75 to 85 percent phosphoric
acid (H.PO ), but a few plants produce an acid of 100 to 105 percent
phosphoric acid. Acids of up to 115 percent phosphoric acid can be
produced with modifications in process design and operation.
High-grade thermal-process phosphoric acid is normally used ift
the production of industrial phosphates, i.e., plasticizers, detergents,
fire retardants, pharmaceuticals, and food-grade acid. Only a small
quantity is used in the phosphate fertilizer industry.
RAW MATERIALS
Raw materials for the production of phosphoric acid by the
thermal process are elemental (yellow) phosphorus, air, and water.
Phosphorus is the basic raw material and is usually produced by the
reduction of phosphate ore in electric furnaces. Phosphorus is nor-
mally handled in the molten state and must always be submerged under
water or blanketed with inert gas because it ignites immediately when
exposed to air. Phosphorus is usually produced at a point remote
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from the thermal acid plant and is commonly shipped by rail as a
liquid under water.
PROCESS DESCRIPTION
Thermal-process phosphoric acid manufacture, as shown in
Figure 2, typically involves three steps.
1. Burning (oxidizing) the liquid elemental phosphorus in a
suitable chamber to produce phosphorus pentoxide.
2. Hydrating the phosphorus pentoxide with dilute acid or water
to produce phosphoric acid liquid and mist.
3. Removal of the phosphoric acid mist from the gas stream.
The following reactions are involved:
P. + 5 O •• ^A^in (Phosphorus pentoxide)
P O + 6 HO 4 H PO (orthophosphoric acid, nor-
mally called phosphoric acid)
Phosphorus is transferred from the liquid phosphorus feed tank
to the burner tower by a pump or by liquid displacement at feed rates
that range from 1 to 5 gallons per minute. At the burner the phosphorus
is mixed with air and is oxidized at temperatures of 3000" to 5000°F in
the combustion chamber.. The resulting mixture of phosphorus pen-
toxide vapor and excess air passes from the combustion tower and into
the hydrator.
Although many plants have refractory or graphite-lined combus-
tion towers, a few new burning towers are constructed of water-jack-
eted stainless steel. In stainless steel towers •weak phosphoric acid
introduced into the combustion tower flows down the walls to remove
excess heat. The phosphorus pentoxide vapors from the combustion
tower are contacted with weak and product acid to hydrate the oxide to
phosphoric acid and to absorb acid mist. This may be accomplished
in one unit, but many plants use separate absorbing towers. In some
new designs the acid sprayed into the hydrator is cooled prior to re-
cycle. This permits use of a smaller quantity of acid and allows the
10 THERMAL-PROCESS PHOSPHORIC ACID
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5
•S
2.
CL
iS.
STACK
EFFLUENT
(AIR + H3P04 MIST)
ACID TREATING PLANT
STACK EFFLUENT
(AIR
H2S)
HYDROGEN SULFIDE,
SODIUM HYDROSULFIDE.
OR SODIUM SULFIDE
PHOSPHORUS
COMBUSTION
CHAMBER
HYDRATOR-
ABSORBER COOLING WATER
PUMP
AIR TO
SPARGER
BURNING AND HYDRATION SECTION
BLOWER PUMP
ACID TREATING SECTION
(USED IN THE MANUFACTURE OF ACID
FOR FOOD AND SPECIAL USES)
Figure 2. Flow diagram for typical thermal-process phosphoric acid plant.
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production of higher strength acid.
Some product acid is drained from the bottom of the hydrator-
absorber. Gases containing acid mist leave the hydrator-absorber
and enter air pollution abatement equipment.
Venturi scrubbers, packed scrubbers, glass-fiber mist elimina-
tors, wire-mesh mist eliminators, and electrostatic precipitators are
used as abatement equipment at phosphoric acid plants. Weak acid
collected in this equipment flows to storage tanks and is recycled with-
in the process. Exhaust gas from the abatement equipment is dis-
charged to the atmosphere.
Raw acid may contain arsenic, lead, and other heavy metals that
make it unsuitable for use in food products. In the preparation of food-
grade phosphoric acid the raw acid is treated with a sulfide to precipi-
tate arsenic and other heavy metal ions. Hydrogen sulfide, sodium
hydrosulfide, or sodium sulfide is added in excess of theoretical quan-
tities to batches of raw acid to precipitate the metal sulfides. Sodium
hydrosulfide is usually used. In the treating operation the solution is
blown with air to remove excess hydrogen sulfide. The metal sulfides
are removed from the acid by filtration before the product acid is trans-
ferred to storage.
YIELDS AND LOSSES
The yields from thermal production of phosphoric acid are
exceptionally high. In efficient plants about 99. 9 percent of the phos-
phorus burned is recovered as acid. The loss of acid through leaks
and discharges to sewers is usually negligible. Losses of phosphoric
acid to the atmosphere represent direct product loss; therefore, effi-
cient collection devices are normally installed in the gas stream before
the gas is discharged from the plant. The collector efficiency data
given in Table A-l show that the collector efficiencies range from 95. 0
to 99. 9 percent and average 98. 0 percent. In most units, more than
90 percent of the acid is absorbed prior to the final collecting unit.
Under these conditions, yields will approach 99. 8 percent.
12 THERMAL-PROCESS PHOSPHORIC ACID
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EMISSIONS FROM PHOSPHORIC ACID
MANUFACTURE BY THERMAL PROCESS
PHOSPHORIC ACID MANUFACTURE
The principal atmospheric emission from the manufacture of
phosphoric acid by the thermal process is acid mist in the absorber
discharge gas. In the normal operation of the plants the hydration of
phosphorus pentoxide (P QI ) creates phosphoric acid mist. Acid
mist loadings within the process can be quite high. Loadings as high
as 6000 milligrams per dry standard cubic foot of stack gas have
been reported. It is not uncommon for as much as half of the total
phosphorus pentoxide to be present as liquid phosphoric acid particles
4
suspended in the gas stream. Economical operation of the process
depends on agglomeration of the acid mist particles and subsequent
separation from the gas stream. For this reason all plants are
equipped with some type of emission control equipment.
The gas stream from the hydrator contains phosphoric acid mist,
often incorrectly referred to as P O mist. Actually the acid mist is
in the form of orthophosphoric acid (H,PO ). Unhydrated phosphorus
pentoxide does not exist in stack gas. The particle size of the acid
mist ranges from 0. 4 to 2.6 microns with a mass median diameter of
1. 6 microns. Figure 3 from Gillespie and Johnston is a graph of
particle-size distribution developed from laboratory experiments.
Rough particle-size determinations made on three of the four plants
sampled by the U. S. Public Health Service showed that 90 percent of
the acid mist particles at the collector outlet were less than 5 microns
in diameter.
The stack gas stream may contain as much as 60 percent and as
little as 10 percent water vapor, depending on design and operating
conditions. Water vapor in the plume usually ranges between 40 and 50
percent. This usually results in a dense white plume of 100 percent
13
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opacity. Depending on weather conditions and acid mist concentration,
the plume usually dissipates in a few hundred feet.
E 2jO
^ 1.S
D.
S. 1.0
£ o-e
tn 0.6
s
^ O.«t
0.2
III 1 1 1 1 1 1 1 I 1
RETENTION
TIME, min
6 98
5 12
0 7U
0 08
III II I I I I I I I II III
0.5 1 2 5 10 20 i»0 60 80 95 99 99.9
CUMULATIVE MASS PERCENT LESS THAN D
P
Figure 3. Particle size distribution of phosphoric
acid mist. Mist loading, 1.0 mg/liter.
Table A-l presents emission and operating data from 25 plants
at which typical abatement equipment is used. Depending on plant
operating conditions and type of abatement device, emissions range
from 0. 10 to 16. 9 milligrams of phosphoric acid mist per standard
cubic foot of stack gas (expressed as P O ). The average emission of
all plants supplying data and those that were sampled is 7. 7 milligrams
of phosphorus pentoxide per standard cubic foot of stack gas. The
majority of the plants from which data are presented were producing
75 to 85 percent phosphoric acid and were operating within 10 percent
of rated capacity.
Thermal-process acid manufacture employs high-temperature
combustion that is normally conducive to the formation of nitrogen
oxides. Many factors such as flame temperature, residence time, and
quantity of excess air affect the amount of nitrogen oxides formed.
14
THERMAL-PROCESS PHOSPHORIC ACID
-------
Because data on the quantity of nitrogen oxides formed in the thermal
process is not generally available, two plants were sampled for nitro-
gen oxides. The data, listed in Table A-l, are from plants 12 and 24.
The results, expressed as nitrogen dioxide, average 10 ppm. Appar-
ently nitrogen oxide emissions are not significant in this process.
ACID TREATING
In the preparation of food-grade phosphoric acid the raw acid is
treated with hydrogen sulfide, sodium hydrosulfide, or sodium sulfide.
These chemicals are added in quantities slightly in excess of the theo-
retical amount. Heavy metals such as arsenic and lead are precipitated
and separated by filtration. Excessive amounts of the treating chemical
result in the formation of hydrogen sulfide, which is discharged from
the treating tank. This emission is not continuous and may vary from
substantial quantities for a short time to little, if any, detectable
quantity.
Of the 25 plants that supplied data, 21 produce food-grade acid
and, therefore, at times generate some hydrogen sulfide. Five plants
reported'hydrogen sulfide content of the acid-treater vent gas. The
concentration of hydrogen sulfide in these plants ranged from 10 to
2500 parts per million.
OPERATING FACTORS AFFECTING EMISSIONS
No serious problems are encountered in the startup or shutdown
of a thermal phosphoric acid manufacturing unit that affect losses
from the final collector. Maintenance of proper liquid flows and pres-
sure differentials on the absorbers and collectors allows little or no
increase in acid mist discharged to the atmosphere during either start-
up or shutdown.
Maintenance is not usually considered to be a major problem.
Sprays, fans, mist eliminators, and other equipment obviously must
be maintained in good operating condition. If a continuous emission
monitor is used on the collector exhaust, problems with the abatement
equipment will be apparent to the operator quickly. Operators are
normally concerned with keeping losses at a minimum because any
loss is a direct loss of product.
Emissions from Acid Manufacture 15
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ABATEMENT METHODS AND EQUIPMENT
Scrubbing
Packed and open tower scrubbers have been used widely to col-
lect phosphoric acid mist. Low initial cost and ease of construction
are advantages of these units. Conventional packing, e.g. Raschig
rings or Beryl saddles, may be used. Both water and weak phosphoric
acid are used as scrubbing media.
An important factor in efficient effluent collection for a given
packed height is gas velocity. In one pilot plant study, collection
efficiency increased from 40 to 95 percent while the gas velocity,
calculated on the basis of an empty tower, increased from 2 to 7 feet
per second. This is shown in Figure 4.
100
60
-------
Scrubbing is an inexpensive and simple abatement technique, but
high collection efficiency is not usually obtained. Some plants have
improved efficiency by installing wire-mesh mist eliminators after the
scrubber.
Emission and operating data for plants that use such devices are
presented (Plants 1 through 6, Table A-l), The emissions range from
3 to 14 milligrams P?O per standard cubic foot of stack gas. The
average emission concentration from the six plants is 7.5 milligrams
per standard cubic foot.
Venturi Scrubbers
Venturi scrubbers are capable of operating at high collection
efficiencies on phosphoric acid mist. The extremely small size of the
mist particles usually requires pressure differentials in excess of 40
inches of water. Collection efficiencies of venturi scrubbers are de-
pendent on mist particle size, pressure drop across the venturi and
spray liquid rate. The effect of particle size on efficiency is illustrated
by Figure 5. Collection efficiencies of 98 percent on 1-micron parti-
cles and 78 percent on 0. 5-micron particles are reported.
TOO
95
o 90
85
80
75
0.5
1.0
Dp, wm
1.5
2.0
Figure 5. Collection efficiency of venturi scrubber
as a function of particle size.
Emissions from Acid Manufacture
17
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Complete process data on a venturi gas scrubbing system are
given in Table D-2. Overall phosphorus pentoxide recoveries in ex-
cess of 99. 9 percent are shown.
Plants 9 through 16 in Table A-l provide operating and emission
data of venturi scrubber installations. Acid mist concentrations vary
from 6 to 17 milligrams of phosphorus pentoxide per standard cubic
foot of stack gas.
Cyclonic Separators with Wire-Mesh Mist Eliminators
Cyclonic-type collectors are used in some plants to separate
acid mist from hydrator-absorber effluent gas. Because of the small
particle size of the acid mist other abatement devices usually supple-
ment these collectors. Supplemental collectors are typically wire-
mesh mist eliminator pads of low pressure differential. Data on two
plants using this type of equipment are presented (Plants 7 and 8, Table
A-l). Emission concentrations of 8 and 15 milligrams per standard
cubic foot are given for these plants. High collector efficiency cannot
be expected because cyclonic separators are not effective on particles
of less than 10 microns in diameter.
In some plants venturi scrubbers are provided after the hydrator
to operate in series with cyclonic separators. These venturi scrubbers
have several functions and are not used solely for abatement. They
actually hydrate part of the phosphorus pentoxide vapor, agglomerate
the fine acid mist particles,and cool the stack gases. Up to half of the
product acid may be recovered by the venturi - cyclonic separator
system. Cool weak acid is added at the venturi throat. Gases are
cooled rapidly by the evaporation of water from the acid and the expan-
sion of the gas. A venturi scrubber followed by a cyclonic separator
can recover up to 99. 9 percent of the acid mist at pressure drops of 35
to 60 inches of water. In a system of this type the inlet loading to the
venturi may be as high as 6000 milligrams of phosphorus pentoxide per
standard cubic foot. Table A-l shows data for this type of system
(Plants 10, 11, 12, and 13). Emission concentrations range from 2.5 to
16. 9 milligrams of phosphorus pentoxide per standard cubic foot of gas.
18 THERMAL-PROCESS PHOSPHORIC ACID
-------
The average of the four plants is 10. 6 milligrams of phosphorus pent-
oxide per standard cubic foot of stack gas.
Fiber Mist Eliminators
Glass fiber mist eliminators are capable of high collection effi-
ciency in removing phosphoric acid mist from absorber effluent gas
streams. Table 2 reports collection efficiencies of 95.2 to 99 percent
with particles of less than 3 microns in size in pilot units using vapor
g
velocities of 1.4 to 4. 8 feet per second. Table A-l gives process and
emission data for plants with glass fiber mist eliminators (Plants 17,
18, 19, 20, 21, and 22). These plants operated with collector efficien-
cies of 96 to 99. 9 percent at gas velocities ranging from 0. 4 to 13 feet
per second. The pressure drop of these units varied from 7 to 22
inches of water. Emissions reported ranged from 0. 1 to 9. 0 milligrams
of phosphorus pentoxide per cubic foot of stack gas. The average emis-
sion of this group of plants was 2. 4 milligrams of phosphorus pentoxide
per cubic foot, which is well below the average of 7. 7 milligrams of
phosphorus pentoxide per standard cubic foot for all plants reported in
the study. When mist eliminators are operating at a superficial vapor
velocity of less than 1 foot per second and at pressure differentials of
about 20 inches of water, collection efficiencies of 99. 9 percent are
attainable. Plants 21 and 22, examples of this type of installation,
report emissions of 0. 1 and 0. 25 milligram of phosphorus pentoxide
per standard cubic foot of stack gas. Plants 21 and 22 also report
clear stacks.
The stack gases leaving phosphoric acid plants can be made com-
pletely invisible when the mist loading is reduced to 0. 02 milligram of
phosphorus pentoxide per standard cubic foot of stack gas, the concen-
tration of mist in the collector is at least 75 percent phosphoric acid,
and the stack gas temperature is above 80°C. Under these conditions,
the water vapor present in the gases disperses in the atmosphere
9
before the gases are cooled below their dew point.
Good gas distribution is mandatory for glass fiber mist elimina-
tors.
Emissions from Acid Manufacture 19
325-033 O - 68 - 4
-------
Table 2.
FIBER MIST-ELIMINATOR PILOT UNIT AT HIGHER VELOCITIES
PHOSPHORIC ACID MIST COLLECTION BY HIGH-EFFICIENCY
8
Hours of
operation
4
5
6
7
8
2,521
2,522
2,523
2,546
2,5*17
2,548
3,623
3,627
3,628
3,289
6,290
6,291
Flow through
pi lot unit,
cfm
219
219
219
68
68
146
146
146
224
224
224
142
142
142
142
142
142
fps
4.6
4.6
4-6
1.4
1.4
3-1
3.1
3.1
4.8
4.8
4.8
3.1
3-1
3.1
3-1
3.1
3.1
Mist loading
of gases into
pi lot uni t ,a
mg P205/scf
38.9
32.1
27.4
40.2
39.2
47.5
45.8
50.5
40.8
40.0
35.1
5-9
6.7
5.0
18.7
19.3
18.9
Mist loading
of gases from
pi lot uni t ,
mg P205/scf
0.53
0.57
0.60
0.60
0.31
1.45
2.20
2.03
1.35
1.27
1.21
0.04
0.08
0.18
0.50
0.49
0.41
Col lection
efficiency
on particles
3 microns and
smaller, %
98.6
98.2
97.8
98.5
99-2
97-0
95.2
96.0
96.7
96.8
96.6
99.3
98.8
96.4
97-3
97.5
97-8
The mist loading
in diameter.
values given are for particles 3 microns and smaller
High-Energy Wire-Mesh Contactors
The high-energy wire-mesh contactor is a. recently developed
abatement device, which is reported to give collection efficiencies that
exceed 99. 9 percent at pressure differentials ranging from 35 to 41
inches of water pressure drop. Data on one installation are presented
under plant 23, Table A-l. An emission concentration of 0. 63 milli-
gram of phosphorus pentoxide per standard cubic foot of stack gas is
reported at a pressure drop of 39 inches of •water. The unit has the
advantage of operating at relatively high superficial vapor velocities of
20 to 30 feet per second, which results in low capital cost. One opera-
ting company is reported to have this type of scrubber installed on four
of its plants. Capital cost of wire-mesh mist eliminators is reported
20
THERMAL-PROCESS PHOSPHORIC ACID
-------
12
to be approximately $1. 50 per actual cubic foot per minute of stack
10
gas.
Electrostatic Precipitators
Electrostatic precipitators are highly efficient when used to
collect acid mist regardless of the size of the acid mist particles.
Phosphorus pentoxide losses from electrostatic precipitators are
affected only slightly by rate of gas flow or by temperature, as long as
the design conditions are not exceeded. Acid mist losses are affected
by the cleanliness of the equipment and the electrical conditions
4
employed in its operation. Precipitators operate at a pressure drop
of about 0. 5 inch of water. One source reports collection efficiencies
of 98 to 99 percent when using electrostatic precipitators, but at high
maintenance cost. Data on plant 25 (Table A-l) show an emission
concentration of 12 milligrams per standard cubic foot of stack gas.
Table 3 shows electrostatic precipitator data from six installations.
14
Table 3. OPERATING CHARACTERISTICS OF PHOSPHORIC ACID MIST
ELECTROSTATIC PRECIPITATORS1/f
Instal-
lation
1
2
3
4
5
6
Gas
flow
rate3,
scfm
3,160
14,100
3,540
3,900
3,570
7,300
Inlet
temper-
ature,
°F
227
292
173
192
195
234
Inlet
mist
cone.
as noted
7.45b
I4.21b
3468C
3650C
4060C
278d
Outlet
mist
cone.
as noted
0.08b
0.4l5b
0.1 Oc
0.16C
0.24C
10.43d
Col lector
efficiency,
%
98.9
97.1
99-9+
99.9+
99.9+
96.3
Rated
capacity,
%
147
119
75
114
104
101
a29.92 in. Hg and 32°F.
Grains/scf dry gas as
Milligrams 80% H^PO^/cf dry gas at temperature.
Milligrams mist/scf dry gas at 60°F as PO^C-
Hydrogen Sulfide Emission Abatement
Many plants make no attempt to remove hydrogen sulfide from
the acid-treating-tank vent gas. This pollutant is vented directly to
Emissions from Acid Manufacture
21
-------
the atmosphere, usually through short stacks in the roof of the treating
building.
Hydrogen sulfide can be removed from the stack gases by com-
bustion or absorption. An inexpensive method is to vent the acid-
treater effluent gases to the phosphorus furnace and incinerate the
hydrogen sulfide to sulfur dioxide. Suitable flame arresters must be
provided in this line. Plants 2 and 17 (Table A-l) report the use of
this method.
Weak solutions of caustic soda or soda ash may be sprayed
counter-current to the gas stream in packed towers to remove the
hydrogen sulfide according to the following reactions:
Na2CO3 + H2S -NaHCO3 + NaHS
Z NaOH + H2S Na2S + HO
Of the 22 plants producing food-grade acid, Plants 11 and 25 (Table
A-l) report the use of this method of abatement.
22 THERMAL-PROCESS PHOSPHORIC ACID
-------
GLOSSARY OF TERMS
Abbreviation
°C
cc
cfpm
ft
ft2
ft3, cuft
fpm
fps
°F
gr
in. H2O
Ib
Ibs/hr
mg
mg/scf
mm
mscfm
NA
ppm
psig
scf
scfm
sp gr
Yr
Chemical Symbols
H2S
Hg
HZ°
HNO3
Temperature, degrees centigrade
Cubic centimeter
Cubic feet per minute
Foot (feet)
Square feet
Cubic feet
Feet per minute
Feet per second
Temperature, degrees fahrenheit
Grain
Inches of water
Pounds
Pounds per hour
Milligram
Milligram, per standard cubic feet
Millimeter
1000 standard cubic feet per minute
Data not available
Parts per million by volume
Pounds per square inch gauge
Standard cubic feet measured at 60 °F and
760 mm HG
Standard cubic feet per minute
Specific gravity
Year
Hydrogen sulfide
Mercury
Water
Hydrochloric acid
23
-------
HC1
H3P04
NaHCO
NaOH
NaS
NaHS
Na2C03
NO
x
NO
NO,
P2°5' P4°10
Definitions
C ontaminant
Combustion tower
Effluent
Emission
Establishment
Food-grade acid
Hyd rator-ab s orbe r
Phosphoric acid mist
Hydrochloric acid
Ortho phosphoric acid
Sodium bicarbonate
Sodium hydroxide
Sodium sulfide
Sodium bisulfide
Sodium carbonate
Total nitrogen oxides in a mixture
Nitric oxide
Nitrogen dioxide
Oxygen
Phosphorus
Phosphorus pentoxide
Any substance not normally present in the
atmosphere.
Refractory graphite-lined or water-jacketed
stainless steel tower in which phosphorus is
burned to phosphorus pentoxide.
Waste gas stream that enters the atmosphere
from the process.
Any gas stream emitted to the atmosphere.
A works having one or more phosphoric acid
plants or units, each of which is a complete
production entity.
Phosphoric acid that has been treated for
removal of heavy metals and is suitable for
use in food products.
A single or double tower in which phosphorus
pentoxide is hydrated to phosphoric acid and
the resulting acid mist is absorbed.
Extremely small particles of phosphoric acid
that are true aerosols.
24
THERMAL-PROCESS PHOSPHORIC ACID
-------
Phosphoric acid spray Large phosphoric acid particles introduced
into the gas by mechanical entrainment.
Raw acid Impure phosphoric acid that contains heavy
metallic impurities.
Glossary of Terms 25
-------
APPENDIX A: EMISSION AND OPERATING
DATA FOR THERMAL-PROCESS
PHOSPHORIC ACID PLANTS
Most of the emission and operating data in Table A-l, which
makes up Appendix A, were supplied by the manufacturers of phos-
phoric acid. Data from a variety of types and sizes of plants are in-
cluded. The emission data are from 90 percent of the present thermal
process establishments and include the results of the U. S. Public
Health Service stack sampling program.
The table lists data from 25 separate thermal-process phosphoric
acid manufacturing plants. Each plant is numbered; operating and
emission data are listed vertically under the number of each plant.
Capacity of each plant, feed rate at rated capacity, hydrator dis-
charge data, and acid treater discharge data are listed in the table.
Included as hydrator discharge data are type of collector used,
gas flow rate, stack gas temperature, collector pressure drop, super-
ficial gas velocity in collector, oxides of nitrogen contained in stack
gas, acid mist emitted, phosphorus emitted, level of production during
testing, plume opacity, and collector efficiency.
Acid treater discharge data includes that for type of collector,
gas flow rate, stack gas temperature, amount of hydrogen sulfide in
stack gas, and level of production during testing.
27
325-033 O - 68 - 5
-------
Table A-1. EMISSION AND OPERATING DATA FOR THERMAL-PROCESS PHOSPHORIC ACID PLANTS
Plant number
Rated capacity, tons/day
Feed rate at rated capacity
phosphorus, Ib/hr
Hvdrator discharge data
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, *F
Collector pressure drop.
in. water
Superficial gas velocity
in collector, fps
NOX (as N02) in stack gas,
ppm
Acid mist to collector,
Acid mist from collector,
mg P20g/scf
Acid mist emitted, lbP205/hr
P4 emission (% of P4 burned)
Percent of rated capacity
during sampling
Plume opacity
Collector efficiency
Acid treatar discharge
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, *F
H2S in stack gas, ppm
Percent of rated capacity
when sampled
1
1 16 of 85% H3P04
2.590
Packed tower
6,900
176
1
1.6
NA
NA
3
2.7
0.057
90
NA
NA
none
5,200
176
24 (maximum)
100
2
131.5 of 75% H3P04
2,600
Packed tower
7,870
189
3.3
60
NA
214
9.7
10.1
0.169
100
100%
95.5
Piped to phosphorus
burning tower
NA
NA
NA
NA
3
1 16 of 85% H3PO4
2,600
Packed tower and
wire-mesh mist
eliminator
6,940
175
1.5
2
NA
650
4.5
4.1
0.069
100
medium
99.4
none
870
70
10-20
100
4
407 of 75% HsPO4
8.640
Packed tower and
wire-mesh mist
eliminator
21 ,600
180
5
10
NA
NA
14
40.0
0.252
80
medium
NA
none
NA
NA
NA
NA
5
135 of 80% H3P04
2,870
Scrubber plus
wire-mesh mist
eliminator
9,740
176
7
9
NA
NA
5
6.4
0.097
100
100%
NA
Food-grade
not produced
NA
NA
NA
NA
-------
I"
CD
Table A-1 (continued). EMISSION AND OPERATING DATA FOR THERMAL-PROCESS PHOSPHORIC ACID PLANTS
Plant number
Rated capacity, tons/day
Feed rate at rated capacity
phosphorus, Ib/hr
Hvdrator discharge data
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, *F
Col lector pressure drop,
in. water
Superficial gas velocity
in collector, fps
NOX (as NC>2) in stack gas,
ppm
Acid mist to collector.
Acid mist from collector,
Acid mist emitted, lbP20g/hr
?4 emission (% of ?4 burned)
Percent of rated capacity
during sampling
Plume opacity
Collector efficiency
Acid treater discharge
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, *F
HZS in stack gas, ppm
Percent of rated capacity
when sampled
6
162 of 87% H3P04
3,750
Scrubber plus
wire-mesh mist
eliminator
12,700
170
3
9
NA
NA
9
15.1
0,151
116
medium
NA
none
NA
NA
NA
NA
7
179 of 85% H3P04
4,000
Cyclonic separator
wire-mesh mist
eliminator
9,890
184
8.5
9.5
NA
NA
15
19.6
0.246
87
medium
NA
none
NA
NA
NA
NA
8
189 of 80% H3PO4
4,000
Cyclonic separator
wire-mesh mist
eliminator
13,600
176
8
10
NA
NA
8
14.4
0.157
100
100%
NA
none
NA
NA
NA
NA
9
1 10 of 75% H3P04
2.250
Venturi plus
wire-mesh mesh
eliminator
6,370
150
0.5 (mist eliminator)
280 (venturi)
NA
NA
16.3
13.7
0.302
88
100%
NA
none
NA
NA
NA
NA
10
217 of 105% H3P04
5,700
Venturi, cyclonic
separator and wire-
mesh mist eliminator
13,075
150
NA
NA
NA
NA
6.5
11.2
0.086
NA
NA
NA
Food-grade acid
not produced
NA
NA
NA
NA
-------
Table A-1 (continued). EMISSION AND OPERATING DATA FOR THERMAL-PROCESS PHOSPHORIC ACID PLANTS
Plant number
Rated capacity, tons/day
Feed rate at rated capacity
phosphorus, Ib/hr
Hvdrator discharae data
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, 'F
Collector pressure drop,
in. water
Superficial gas velocity
In collector, fps
NOX (as N02) In stack gas,
ppm
Acid mist to collector.
Acid mist from collector,
mg PjOs/scf
Acid mist emitted, lbP20g/hr
?4 emission (% of PQ burned)
Percent of rated capacity
during sampling
Plume opacity
Collector efficiency
Acid treater discharge
Type of col lector
Gas flow rate (dry), scfm
Stack gas temperature, °F
H2S in stack gas, ppm
Percent of rated capacity
when sampled
11
100 of 75% H3P04
2,000
Venturi, cyclonic
separator, wire-mesh
mist eliminator
4,900
175
(excluding 6 venturi)
NA
NA
NA
2.5
1.6
0.037
95
100%
NA
Company design
NA
NA
NA
NA
12
165 of 87.5% H3P04
3,950
Venturi, cyclonic
separator, wire-mesh
mist eliminator
7,460
175
2.3 (excluding venturi)
-
9.5
-
16.9
16.7
0.185
100
100%
NA
none
NA
NA
NA
NA
13
217 of 105% HsP04
6,000
Venturi, cyclonic
separator, wire-mesh
mist eliminator
6,922
142
52 (venturi)
22 (separator)
201 (venturi)
5.9 (separator)
NA
5,989
6.7
6.1
0.048
91.5
light
99.95
Food-grade acid
not produced
-
-
-
-
14
270 of 75% H3P04
5.300
Venturi scrubber
6,600
201
33
360
NA
625
15
13.1
0.108
100
100%
97.5
none
107
174
2,500
100
15
350 of 75% H3P04
7,000
Venturi scrubber
15,500
168
34
400
NA
NA
9
18.5
0.121
95
medium
NA
none
NA
NA
NA
NA
-------
Table A-1 (continued.) EMISSION AND OPERATING DATA FOR THERMAL-PROCESS PHOSPHORIC ACID PLANTS
Plant number
Rated capacity, tons/day
Feed rate at rated capacity
phosphorus, Ib/hr
Hvdrator discharge data
Type of collector
Gas flow rate (dry), scfm
Stack gas temperature, °F
Collector pressure drop,
in. water
Superficial gas velocity
in collector, fps
NOX (as N02) in stack gas,
ppm
Acid mist to col lector,
mg P2Og/scf
Acid mist from col lector.
Acid mist emitted, Ib P2C>5/hr
PH emission (% of PH burned)
Percent of rated capacity
during sampling
Plume opacity
Collector efficiency
Acid treater discharge
Type of col lector
Gas flow rate (dry), scfm
Stack gas temperature, 'F
H2S in stack gas, ppm
Percent of rated capacity
when sampled
16
151 of 100% H3P04
4,000
Venturi scrubber
17,775
165
60
NA
NA
NA
6
14.1
0.192
80
100%
NA
Food-grade acid
produced
17
120 of 75% H3P04
2,600
Glass fiber
mist eliminator
5,000
185
7.5
0.92
NA
515
3.5
2.3
0.039
NA
light
99.2
Piped to phosphorus
burning tower
NA
NA
NA
NA
18
200 of 75% H3P04
4,033
Glass fiber
mist eliminator
6,140
180
22
13
NA
252
9
7.3
0.079
100
medium
96
Wire-mesh mist
eliminators
500
145
55 (calculated)
100
19
60 of 75% H3P04
1,500
Glass fiber
mist eliminator
3,440
136
9
0.4
NA
109
2
0.9
0.027
98
light
98.1
none
NA
NA
NA
NA
20
250 of 75% HaP04
5,000
Glass fiber
mist eliminator
17,000
170
7
7
NA
100
3
6.7
0.065
90
light
97
Food-grade acid
produced
-
-
-
-
-------
Table A-1 (continued). EMISSION AND OPERATING DATA FOR THERMAL-PfiOCESS PHOSPHORIC ACID PLANTS
Plant number
Rated capacity, tons/day
Feed rate at rated capacity
phosphorus, Ib/hr
Hvdrator discharge data
Type of collector
Gas flow rate (dry) , scfm
Stack gas temperature, °F
Collector pressure drop,
in. water
Superficial gas velocity
in collector, fps
NOX (as NC>2) in stack gas,
ppm
Acid mist to collector,
mg P2C>5/scf
Acid mist from collector,
mg P2d5/scf
Acid mist emitted, Ib P205/hr
?4 emission (% of Pi\ burned)
Percent of rated capacity
during sampling
Plume opacity
Collector efficiency
Acid treater discharge
Type of col lector
Gas flow rate (dry), scfm
Stack gas temperature, *F
H2S in stack gas, ppm
Percent of rated capacity
when sampled
21
504 of 77% H3P04
1 1 ,000
Glass fiber
mist eliminator
30,200
165
18
0.4
NA
1,300
0.1
0.40
0.002
100
0%
99.9
none
1,000
100
NA
NA
22
NA (79% H3P04)
11,100
Glass fiber
mist eliminator
19,433
182
21.5
0.4
NA
1,543
0.25
0.65
0.003
100
0%
99.9
none
NA
NA
NA
NA
23
405 of 75% H3P04
8,000
High A P wire-mesh
mist eliminator
12,250
172
39
27
NA
2,670
0.63
1.0
0.005
99.5
100%
99.9
none
NA
NA
NA
NA
24
100 of 90% HsPO/i
2,270
Wire-mesh mist
eliminator
8,690
175
NA
4
10
235
12.4
14.2
0.273
100
100%
95
none
NA
NA
NA
NA
25
150 of 75% HaP04
3,000
2 electrostatic
precipitators in series
3,600
117
11
6.8
NA
NA
12
5.7
0.083
100
light
NA
Packed tower
247
94
218
100
-------
APPENDIX B: SAMPLING AND
ANALYTICAL TECHNIQUES
The sampling and analytical techniques described are those used
by the Public Health Service to conduct source tests on four thermal-
process phosphoric acid plants in this study. The analytical procedures
are based on methods described in the literature and by manufacturers
of phosphoric acid.
33
-------
DETERMINATION OF PHOSPHORIC ACID MIST
Description of Sampling Equipment
The equipment used for sampling phosphoric acid mist is an adap-
tation of the particulate sampling train designed by the U. S. Public
Health Service. The design of the sampling train is based on flexibility,
portability, and ease of operation. The Public Health Service sampling
train permits separation of the acid mist particulate into two fractions
having particle diameters greater and less than 5 microns.
The sampling train is shown schematically in Figure B-l and as
it actually appears in Figures B-2 and B-3. The sampling train con-
sists of a probe, cyclone, filter, four Greenburg-Smith impingers,
pump, dry gas meter, calibrated orifice, and manometer.
14
PROBE TIP 10. IMPINGER
PROBE 11. VACUUM PUMP
CYCLONE 12. DRY GAS METER
FILTER 13. DUAL MANOMETER
5. HEATED BOX 14. CHECK VALVE
6. ICE BATH 15. THERMOMETER
7. IMPINGER
8. IMPINGER
9. IMPINGER
16. PRESSURE GAUGE
17. CALIBRATED
ORIFICE
Figure B-l. Flow diagram of phosphoric acid mist sampling train.
The probe tip (1), a stainless steel button-hook type, is shown in
Figure B-l. The probe (2) is made of 5/8-inch-diameter medium-wall
Pyrex glass tube and is wound with 25 feet of 26-gauge nickel-chromium
alloy wire to heat the probe during sampling. A variable transformer
controls the temperature of the probe. To protect the glass probe the
34
THERMAL-PROCESS PHOSPHORIC ACID
-------
Figure B-2. Phosphoric acid mist sampling train.
Figure B-3. Control panel of phosphoric acid mist sampling train.
Appendix B
-------
nickel-chromium alloy wire is wrapped with fiber glass tape, and. is
encased in a 1-inch stainless stee-1 tube. The probe connects to a
cyclone (3) and filter (4). The cyclone and filter are housed in an
electrically heated box (5), which thermostatically maintains, a tempera-
ture of 250°F. The cyclone is designed to make a size cut at about 5
microns. When phosphoric acid mist is sampled, the fritted glass and
filter paper are removed from the filter housing and all mist smaller
than approximately 5 microns is collected in the impingers.
Attached to the heated box-is- air ice bath-(6) containing four Green-
burg-Smith impingers connected in series by glass bail joints. The
first two impingers are fitted with the standard 'orifice plate impinger
tips while the second two have the orifice tip replaced with 1/2-inch-
diameter glass tubes extending to 1/2-inch from the bottom of the flask.
The first impinger (7) receives the stack effluent from the filter.
This impinger contains 250 milliliters of deionized water. The second
impinger (8) contains 150 milliliters of deionized water. The third
impinger (9) is dry, and serves as a knockout pot for entrained water.
The fourth impinger (10) contains 175 grams of silica gel, and removes
remaining moisture from the gas before it enters the pump and gas
meter.
The pump (11), dry gas meter (12), and manometer are housed
in a meter box. The gas from the fourth impinger passes through a.
check valve (14), thermometer (15), pressure gauge (16), vacuum pump
(11), dry gas meter (12), dual manometer (13), and calibrated orifice
(17). All of these parts are housed in the meter box, and are connected
to the impingers by an umbilical cord of rubber tubing to carry the
sample gas. Electrical lines, pitot tube, and pressure-sensing tube are
also included. This permits a remote location for the meter box and
the operator.
Figure B-3 shows the controls on the meter box that include a
powerstat for controlling heat to the probe; switches that control the
power to the fan, heated box, and pump; and the flow control valves
and manometers.
36 THERMAL-PROCESS PHOSPHORIC ACID
-------
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 that have no flow obstructions for at least 8
diameters upstream and 2 diameters downstream from the sampling
point are preferred. For this equipment a 3-inch sample hole is re-
quired. In non-cylindrical stacks the traverse should be made across
the largest dimension. In horizontal ducts the traverse should always
be vertical. The importance of selecting proper sampling point loca-
tions is paramount if representative reproducible results are to be
obtained.
To insure a representative sample of the stack gas, the duct
should be divided into a number of equal areas and samples should be
taken at the center of each of these areas. The number of areas de-
pends on the size of the stack. This procedure prevents erroneous
results due to stratification of the acid mist in the duct. Bulletin WP-
50 of the Western Precipitation Company may prove useful in deter-
mining the number of areas.
Thermal-process phosphoric acid plants employ continuous pro-
cesses and are not, therefore, subject to cyclic emission rates. The
major factor in selecting sampling time is the quantity of material
collected in the cyclone and impingers. The limiting factor is the
moisture content of the stack gas. Sample runs are usually terminated
before water entrainment occurs in the third impinger. Optimum time
is approximately 1 hour.
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 HTSX
•where:
Vg is the 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
Appendix B 37
-------
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 "VHTg 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 5 micrometer 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
n 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 when sampling
has begun. Therefore, if gas velocity varies considerably, the sampl-
ing 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 parti-
cles are below 3 to 5 micrometers 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 B-4). Care
must be taken in using the orifice calibration curve at various tempera-
tures and pressures. A typical orifice calibration curve is shown in
Figure B-5. The following equations may prove useful:
530 Pb - P
AP0 = AP (calib) x — x -^- x —
Qn = Q (calib) x 29- 9
,Q „ V / " COQ ~ p _ p
b o
AP = pressure drop-across orifice at orifice pres-
sure and temperature, in. t^O
Pit, = barometric pressure, in. Hg
38 THERMAL-PROCESS PHOSPHORIC ACID
-------
AP (calib) pressure drop across orifice at orifice cali-
bration conditions, in. H£O
To = temperature at orifice, °R
P0 = gauge pressure at inlet to orifice, in. Hg
MW = molecular weight of gas
Qo = flow through orifice at orifice temperature
and pressure, cfm
Q (calib) = flow through orifice at calibration conditions,
cfm
A sample calculation illustrates the procedure assume To =
100°F, P0 = 2 in. Hg, MW = Z9. 0, and Pb = 29.9 in. Hg. Desired
sampling rate at 70°F is 1 ft3/min at 100°F (the stack temperature).
Stack velocity measured by pitot tube measurements was 1350 ft/min.
The sample nozzle area is then equal to
' . ... min 0. 778 x 10~3 ft2. The area of the probe selected was
1350 ft/mm c
0.8 x 10"3 ft2.
The required flow at the sampling point is the stack velocity
times the probe area or 1. 350 fpm x 0. 8 x 10 = 1. 08 cfm 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 P = 6. 5 in. at calibration
conditions.
. . 530 29.9-2.0 5. 74 in. at orifice
2. AP- 6. 5 in. X -TT— X inn ~ ' j-f
° 560 29.9 conditions.
Desired orifice setting is then 5. 74 inches at this sampling point.
Sample Collection
Add distilled or deionized water to the first and second impingers
and silica gel to the fourth impinger. Turn heat on probe and cyclone
box and allow about 10 minutes until the system maintains a tempera-
ture of about 10°F above the stack gas temperature. Use a powerstat
Appendix B 39
-------
Plant.
Location.
Date_
Test No._
Pb=-
Position
Time,
min
ORIFICE DATA*
Desired
flow, cfm
=An x Vs
APQ,
in.H20
V
°F
Po'
in.Hg
METER DATA
Reading, ft3
«m
Pm>
in.Hg
V
°F
*At stack conditions.
APo= AP(Calib)
MW
29.9
Q = Volume sampled in scf = Qm x t/0 f
29.9
CYCLONE
IHPINGERS
TOTAL
cc of NaOH, N=
mg HHO =
cc x N x 63
Concentration,
mg/ft3
Figure B-4. Data sheet for sampling phosphoric acid mist.
40
THERMAL-PROCESS PHOSPHORIC ACID
-------
20
c 1.0
. eo
a.
•3 6.0
Q_
O
cc.
0
in
in
4.0
2.0
1.0
0.1 0.2 0.»» 0.6 0.8 1.0
FLOW RATE (Q),cfm
2.0
Figure B-5. Typical orifice calibration curve at 70°F
and 29.9 in. Hg.
to adjust temperature. Add crushed ice to the impinger water bath.
Pressure check the train by plugging the probe and drawing a
vacuum of 20 inches of Hg. Close the line leading from the train; the
vacuum should remain at 20 inches Hg if the train is leak proof. Slowly
remove the plug from the probe to release vacuum and open the line
leading from the train.
When train reaches operating temperatures, sampling can begin.
Record all pertinent data during the test. Compute the desired flow
and corresponding pressure drop before sampling begins.
The sampling period will depend on the size of the stack.
Appendix B
41
-------
Normally a 5-minute sample is withdrawn from each sample area; i.e. ,
eight sample areas will require 40 minutes.
When the sampling is complete, allow the train to cool. Remove
sample from probe, cyclone, and connecting tubing by rinsing with
distilled water into a suitable sample bottle. The acid mist collected
in the impingers should be washed into a second sample bottle.
42 THERMAL-PROCESS PHOSPHORIC ACID
-------
SAMPLE ANALYSIS (Colorimetric Method)
The ammonium phosphomolybdovanadate colorimetric method
used in the analysis of phosphate samples was adopted from standard
operating procedures of the U. S. Industrial Chemical Company and
the Association of Official Analytical Chemists. This method is
based on the spectrophotometric determination of the yellow ammonium
phosphomolybdovanadate complex formed when orthophosphate reacts
with ammonium molybdate-vanadate reagent in an acid medium. The
method is applicable to materials in which phosphorus compounds can
17 18 1Q
be quantitatively oxidized to the orthophosphate form. ' '
Acid hydrolysis (HNOj-HCl, 6 to 1) is used to destroy any organic
material present in the sample and to hydrolyze any phosphate in the
meta or pyrophosphate form to orthophosphate. The system obeys
Beer's law to about 2 milligrams of phosphorus pentoxide (P2Og) per
100 milliliters of solution. Results of analyses are reported in terms
of P205.
Reagents:
All reagents are prepared from ACS analytical reagent-grade
chemicals in phosphate-free distilled or deionized water. Re-
agents that will be used are:
1. Nitric acid (concentrated).
2. Hydrochloric acid (concentrated).
3. Perchloric acid (70%).
4. Ammonium molybdate solution (0.2 M). Dissolve 35.3 grams
of ammonium molybdate tetrahydrate [(NH ), Mo O . 4H2C>J
in distilled water and dilute to 1 liter. The reagent is stable
at room temperature and may be stored in a glass stoppered
bottle for at least 3 months.
5. Ammonium vanadate - perchloric acid solution (0.02 M
NH.VO - 4 M HC10 ). Dissolve 1. 17 grams of ammonium
metavanadate in 200 ml of distilled water and transfer to a
500-ml volumetric flask. Acidify with 172 ml of 70% per-
chloric acid, and dilute with distilled water to 500 ml. This
Appendix B
-------
reagent may be stored at room temperature for several
months.
6. Standard phosphate solution. Dry several grams of potas-
sium dihydrogen phosphate (KH^PO ) in an oven at 105°C.
Dissolve exactly 1. 917 grams of dried KH PO in distilled
water and dilute to 1 liter in a 1-liter volumetric flask. One
ml of this solution is equivalent to 1 mg of P O .
Ct D
Apparatus:
1. Analytical balance.
2. Volumetric flasks, 100-, 500-, 1000-ml.
3. Erlenmeyer flasks, 250-ml.
4. Hotplate.
5. Spectrophotometer. This instrument should be capable of
measuring color intensity at 400 mp. in 0. 5-in. absorbance
cells or larger.
6. Constant-temperature water bath. (20°C +_ 2 °C).
7. Filter paper (Whatman No. 42).
8. Filter funnels and rock.
9. Pipettes (1-, 2-, 5-, 10- and 20-ml).
Analysis:
1. Field samples arrive in two sample bottles. Probe and
cyclone -washings are in one bottle, and impinger solution
is in the other. Each field sample is made up to a known
volume.
2. Transfer an aliquot of the sample to a 250-ml Erlenmeyer
flask. Simultaneously, prepare a. blank (distilled water) and
treat in the same manner. Digest the sample and blank
(distilled water) with 30 ml of nitric acid and 5 ml of hydro-
chloric acid. Evaporate until HC1 fumes are produced (i. c.
almost to dryness) on a hotplate.
3. Cool, dilute to 25 ml with distilled water, and filter through
Whatman No. 42 filter paper into a 100-ml volumetric flask
to remove any insoluble material. Wash filter and flask
THERMAL-PROCESS PHOSPHORIC ACID
-------
seve-ral times with 5- to 10-ml portionsof distilled water,
and dilute to 100 ml.
4. Pipet 10 ml of the filtrate into another 100-ml volumetric
flask.
5. Add 10 ml of ammonium vanadate-perchloric acid solution
and 20 ml of ammonium molybdate solution to the 100-ml
volumetric flask and dilute to the mark with distilled water.
6. Place the samples in a water bath (20°C). Allow 15 minutes
for complete color development.
7. Measure the absorbance against the distilled water-reagent
blank, prepared simultaneously, at a wavelength of 400 m/i
using a spectrophotometer and 0. 5-in. cells.
8. Obtain the number of milligrams of P,O present from a
^ 3
previously prepared calibration curve, where absorbance
was plotted versus milligrams of P,O .
£ 5
9. If the amount of PpC" in the aliquot of the sample used is
greater than 2 mg, estimate the amount of P O present by
extrapolating the calibration curve and calculate the proper
aliquot size needed. Take an aliquot from the prepared
filtrate (i. e. the remaining 90 ml) calculated to have an
amount of P,O suitable for quantitative analysis (0. 5 to
£* 3
2 mg), and proceed with the analysis.
Calculation:
T P n - (m6 P2C*5 found) (volume of original solution)
25 aliquot volume
Preparation of Calibration Curve ,
1. Pipet exactly 0, 0. 5, 1. 0, 1. 5, and 2. 0 ml of standard P^O
solution (1 ml = 1 mg P O ) into 100-ml volumetric flasks.
2. Add the color developing reagents as in step 4 of the analysis
and dilute to the 100-ml mark. Place samples in a water bath
(20 °C) and allow 15 minutes for full color development.
3. Measure the absorbance at 400 m/i.
1*5
Appendix B
-------
4. Plot absorbance versus milligrams of PzC>5 on square grid
graph paper. The curve follows Beer's law up to 2 mg of
P2O5 per 100 ml of solution.
Discussion of Procedure
Precautions:
1. Use proper protective equipment and safety precautions when
handling perchloric acid. In case of contact, flush with
plenty of water for 15 minutes.
2. Temperature and final acid strength play, an important roll in
color development and stability. A constant temperature bath
(20°C +^2°C) should be used. Maximum color will develop in
15 minutes; absorbance will remain constant for at least 2
hours. Final acid strength should be constant at 0. 4 M
HC10, for each sample and blank. Slight increases in absorb-
ance are encountered when acid molarity is decreased from
0.40 to 0.20.2°
Interferences:
Certain substances interfere -with the ammonium phosphomolyb-
dovanadate color reaction.
1. Certain ions such as ferrous, stannous, hydrazonium, and
iodine should be absent because they reduce the color com-
plex to'molybdenum blue.
2. Oxalates, tartrates, and citrates complex molybdenum and
tend to bleach the color.
3. High concentrations of iron in the sample cause high results;
however, the iron salts can be converted to the perchlorate
15
complex ion which absorbs less light.
4. The interference of dichromate is well known and results
from the close resemblance of the color of the ion to the
yellow complex ammonium phosphomolybdovanadate. If
present, the simplest procedure seems to be the volatiliza-
tion of the undesired chromium as chromic chloride from hot
perchloric acid. Perchloric acid may be used as an oxidizer,
provided an HC10 . fume hood is available.
1*6 THERMAL-PROCESS PHOSPHORIC ACID
-------
Comments:
This method is applicable to the determination of total phosphates
in the concentration range of from about 50 jig to 2 mg. The pre-
cision encountered when replicate samples were analyzed was
^ 1.0 percent. The same reproducibility has been obtained in
the laboratory.
SAMPLE ANALYSIS (Acid-Base Titration Method)
The acid-base titration of phosphoric acid in stack gas samples
was adapted from the standard assay procedures for phosphoric acid
21
as described in Reagent Chemicals, ACS Specifications (I960). This
method is applicable to particulate samples collected from effluents of
furnace phosphoric acid plants. An aliquot of the sample is titrated
•with standard sodium hydroxide to the disodium hydrogen phosphate
equivalence point, using thymolphthalein as an indicator. One ml of
one normal sodium hydroxide is equivalent to 0. 049 gram of phosphoric
acid.
Reagents:
All chemicals used must be ACS analytical-reagent grade. Re-
agents that will be used are:
1. Water. Deionized or distilled water.
2. Thymolphthalein (0. 1 percent). Dissolve 0.10 gram of thy-
molphthalein in 100 ml of ethanol.
3. Sodium hydroxide (1 N). Dissolve 40 grams of sodium hydrox-
ide in 1 liter of deionized or distilled water. Standardize
against potassium acid phthalate by using phenophthalein as
an indicator.
t
4. Sodium hydroxide (0. 1 N). Dissolve 4. 0 grams of sodium
i
hydroxide in 1 liter of deionized or distilled water. Stan-
dardize against potassium acid phthalate by using pheno-
phthalein as an indicator.
Apparatus:
1. Absorber. Three Greenburg-Smith impingers or other col-
lection devices capable of removing phosphoric acid mist
from stack gases.
Appendix B 47
-------
2. Buret. Standard 50-ml buret.
3. Flasks. Erlenmeyer (250-ml).
Analysis:
Transfer the sample to a volumetric flask, and dilute to a known
volume. Pipet an aliquot of the sample into a 250-ml Erlenmeyer
flask. Wash down the sides of the flask with deionized-distilled
water, and add 10 to 12 drops of thymolphthalein indicator.
Titrate to the light blue endpoint with standard 0. 1 N or IN
sodium hydroxide, whichever is necessary. The strength of
sodium hydroxide used will depend on the amount of phosphoric
acid present in the aliquot. A reagent blank should also be run
with samples.
Calculations:
Calculate the number of grams of phosphoric acid present in the
sample by the following formula:
H,PO (grams) = (A-B) x C x D
Where:
A = ml of 0. 1 Nor 1 N NaOH required in titration
B = ml of 0. 1 N or IN NaOH required by reagent blank
C = 0. 049 gram H,PO4 per ml for 1 N NaOH, 0. 0049 gram
H3PO per ml for 0. 1 N NaOH
_ .. . , . Volume of sample (ml)
D aliquot factor = ^— —-—r ^ . '
Volume of aliquot (ml)
Calculate the parts per million concentration of H PO by the
following formula.
/tr T>r~> \ grams H3PO4 x 24. 1 liters/mole x 10°
ppm (H3P04) = 98 grams/mole x V
Where:
24. 1 ;— = gram molecular volume at 70 °F
mole 6
98 = gram molecular weight of H PO
V = Volume of gas samples (liters)
Discussion of Procedure
In this acid-base titration, phosphoric acid is converted to
48 THERMAL-PROCESS PHOSPHORIC ACID
-------
disodium hydrogen phosphate (Na?HPO ), and the pH at the equivalence
point is about 10. The equivalence point of the titration is detected by
a color change in the thymolphthalein indicator from colorless to blue.
Any other soluble acids or bases collected would interfere in the analy-
sis. This method is suitable, therefore, when only small amounts of
other acids or bases are present in the sample.
When this procedure is compared with the ammonium phospho-
molybdovanadate colorimetric procedure for phosphates, good agree-
ment is obtained. With standard solutions of phosphoric acid, the
results of the titration method are 2. 5 percent lower than those ob-
tained with the colorimetric procedure, which is well within experi-
mental error When both the titration and colorimetric procedures
are applied to samples collected from effluents of thermal phosphoric
acid plants, the results of the titration procedure are within +^7.6 per-
cent of those obtained using the colorimetric procedure.
DETERMINATION OF NITROGEN OXIDES IN STACK GAS
(Phenoldisulfonic Acid Method)
The phenoldisulfonic acid method is applicable to the determina-
tion of total oxides of nitrogen (nitrous oxides excepted) in stack gases
in the concentration range of from 5 to several thousand ppm. Nitro-
gen oxides are collected in an evacuated flask containing an absorbant
consisting of hydrogen peroxide in dilute sulfuric acid and are oxidized
to nitric acid. The nitric acid formed is used to nitrate phenoldisul-
fonic acid, which, when reacted with ammonium hydroxide, forms a.
yellow compound (5-nitro, 6 hydroxy, 1, 3-benzenedisulfonic acid,
triammonium salt). The intensity of the color produced is proportional
to the concentration of nitrogen oxides in the sample and is measured
spectrophotometrically at 420 m/*.
Inorganic nitrates, nitrites, or organic nitrogen-bearing com-
pounds easily oxidized to nitrates interfere with the method. The
method described in this report is an adaptation of Method D1608-60,
American Society for Testing Materials.
Appendix B 49
-------
Reagents:
All chemicals used must be of ACS analytical-reagent grade.
1. Water. Distilled or deionized water.
2. Hydrogen peroxide (30 percent). Reagent grade.
3. Hydrogen peroxide (3 percent). Dilute 10 ml of 30 percent
HO to 100 ml in a 100-ml volumetric flask with water.
4. Sulfuric acid (0.1N). Dilute 2.8 ml of concentrated H,SO
— 24
to 1 liter with water.
5. Absorbing reagent. Dilute 6 ml of 3 percent H?O to 1 liter
with 0. 1 N H,SO . This solution is stable and may be used
for at least 30 days. Analyses show that the percent HO
in the absorbing reagent remains constant over a 49-day
period.
6. Sodium hydroxide (IN). Dissolve 40 grams of NaOH pellets
in •water, and dilute to 1 liter.
7. Ammonium hydroxide (concentrated).
8. Sulfuric acid (fuming).
9. Phenoldisulfonic acid solution. Dissolve 25 grams of pure
white phenol in 150 ml of concentrated H?SO on a steam
bath. Cool, and add 75 ml fuming sulfuric acid. Heat to
100"C for 2 hours. Store in a dark, stoppered reagent
bottle.
10. Potassium nitrate solution (standard). Dissolve 0. 5495 gram
of KNO- in 1 liter of water in a volumetric flask. Dilute 100
ml of this solution to 1 liter in a volumetric flask. One ml
of the final solution is equivalent to 0. 025 mg NO..
Apparatus:
1. Flasks. Two-liter, Pyrex, round-bottom flask encased in
urethane foam with sleeve and accompanying three-way-stop-
cock with T-bore should be used. The T-bore has a cone for
the verticle leg and balls and sockets for the horizontal legs
(see Figures B-6 and B-7).
2. Vacuum system. The vacuum system consists of a vacuum
pump capable of pumping 0.1 cfm at 27 in. Hg or more
50 THERMAL-PROCESS PHOSPHORIC ACID
-------
1. GROUND-GLASS SOCKETS, 5 NO. 12/5, PYREX.
2. STOPCOCK - THREE-WAY, T-BORE, J, PYREX,
2-mm BORE, 8-mm OD.
3. GROUND-GLASS BALL JOINT, 5 NO. 12/5.
4. GROUND-GLASS CONES - STANDARD TAPER,
I SLEEVE NO. 24/40.
Figure B-6. Three-way stopcock and "L" used to sample
stack gases for oxides of nitrogen.
\ 1/4 in. /
c
•I—
f
I
CO
f
-7 in.-
1. BOILING FLASK - 2 LITER, ROUND BOTTOM, SHORT NECK,
WITH I SLEEVE NO. 24/40.
2. URETHANE FOAM ENCASEMENT.
Figure B-7. Urethane-encased flask used in sampling stack gases for
oxides of nitrogen.
Appendix B
51
-------
vacuum, connected by a quick disconnect to a vacuum gauge
capable of measuring vacuum with an accuracy of 0. 25 in.
of Hg (see Figure B-8).
3. Thermometer. Dial thermometer, range 25° to 125 °F, 5-
inch stem.
4. Probe. Pyrex glass tubing (10-mm diameter, 44 in. long).
(See Figure B-9.)
5. Glass "L". Connects three-way stopcock to probe (see
Figure B-8).
6. Variable transformer. Rated at 7-1/2 amps, 0 to 135 volts.
7. Spectrophotometer. This instrument should be capable of
measuring optical density at 420 my in 0. 5-inch absorbance
cells.
THREE-WAY STOPCOCK
INSERTED IN THIS LINE WHEN IT
IS NECESSARY TO PROTECT PUMP
FROM CORROSIVE GASES)
FEMALE BALLJOINT FOR
EASY CONNECTION TO
THREE-WAY STOPCOCK
7 \ TV
TYGON TUBE CONNECTS
VACUUM GAUGE TO
THREE-WAY STOPCOCK
VARIABLE
TRANSFORMER
PLYWOOD BOX - CONVENIENTLY
HOLDS SAMPLING TRAIN COMPON
QUICK DISCONNECT
Figure B-8. Apparatus used in sampling stack gases for oxides
of nitrogen.
52
THERMAL-PROCESS PHOSPHORIC ACID
-------
PYREX GLASS (10 mm)
GLASS WOOL
z
l-in.-OD, 0.035-in.-WALL
STEEL TUBE
44 in.
CORK
Figure B-9. Sampling probe for oxides of nitrogen.
Sample Collection
Emission sources containing oxides of nitrogen are sampled by
a grab sampling technique using an evacuated Z-liter flask. The equip-
ment, developed and used by the Abatement Program, National Air
Pollution Control Administration, is shown in Figure B-8.
The following procedure is used for the collection of samples:
Add 25 ml of absorbing solution to the flask. Place the three-way
stopcock in position on the flask, and insert the stem of the dial ther-
mometer into the urethane foam adjacent to the flask (Figure B-8).
Connect the female balljoint of the stopcock to the probe via a glass
"L". Insert a wad of glass wool in the intake end of the probe to mini-
mize the amount of particulate matter entering the flask. Connect the
male balljoint of the stopcock to the vacuum gauge and pump. Insert
the sampling probe into the stack, turn on the pump, and purge the
probe and stopcock with stack gas.
If a trap is required to protect the vacuum gauge and pump from
corrosive gases,fill a 500-ml plastic bottle with a caustic solution and
connect in the line (Figure B-8). If condensation occurs in the stopcock,
connect the probe heating element to a variable transformer. Apply
sufficient voltage to prevent condensation. Turn the stopcock to connect
the vacuum pump and vacuum gauge to the flask. Evacuate the flask to
Appendix B
S3
-------
the vapor pressure of the absorbing solution (approximately 20 mm Hg).
Disconnect the vacuum pump line at the quick disconnect, i.e. , close
the line to the vacuum gauge, and accurately measure the vacuum in
the flask. Turn the three-way stopcock to connect the flask to the probe
and vacuum gauge. Allow the flask to fill with a sample of stack gas
until very little or no vacuum remains; however, avoid pressurizing the
flask (a condition that is possible if stack pressure exceeds atmospheric
pressure). If the flask takes longer than 15 seconds to fill, the glass
•wool filter is plugging and should be replaced. Measure the final
vacuum in the flask accurately. Position the three-way stopcock so
that the flask is closed. Record the flask temperature indicated by the
dial thermometer. Disconnect the stopcock at the probe and vacuum
source connections. Shake the flask for 15 minutes, and allow to stand
overnight to insure complete reaction and absorption of the nitrogen
oxides.
Analysis:
Transfer quantitatively the contents of the collection flask to a
250-ml beaker. Wash the flask three times with 10 ml of water,
and add to the beaker. For a blank, add 25 ml of absorbing
solution and 30 ml of -water to a 250-ml beaker. Proceed as
follows for both the sample and blank.
Add 1 N NaOH solution to the beaker by drops until the solution
is alkaline to litmus paper. Evaporate to dryness on a steam
bath, and allow to cool. Add 2 ml of phenoldisulfonic acid solu-
tion to the residue, and triturate thoroughly with a glass stirring
rod. Make sure all the residue comes in contact with the solu-
tion. Add 1 ml H-.O and four drops of concentrated H,SO . Heat
2 24
the solution on the steam bath for 3 minutes with occasional
stirring. Allow the solution to cool, add 20 ml H_O, mix well,
and add 10 ml of concentrated NH OH by drops with constant
stirring. Transfer the solution to a 50-ml volumetric flask.
Wash the beaker three times -with 5-ml portions of water. Dilute
to 50 ml, and mix thoroughly. Transfer a portion of the solution;
to a centrifuge tube, and centrifuge for several minutes. If no
54 THERMAL-PROCESS PHOSPHORIC ACID
-------
centrifuge is available, the solution may be filtered, provided
that the same quality filter paper is used for both samples and
blanks.
Determine the absorbance of each sample at 420 m/i using 0. 5-
inch absorbance cells. If the absorbance is outside the range of
the calibration curve, i. e. , if absorbance is greater than 0. 6,
make a suitable dilution of the sample and blank and determine
the absorbance. Obtain the number of milligrams of NO present
in the sample from a previously prepared calibration curve,
where absorbance -was plotted versus concentration.
Calculations:
Calculate the concentration of oxides of nitrogen as NO., in parts
per million by volume as follows:
(5.24x 102) (C)
ppm N02 = i '-^-f-
S
where:
C concentration of NO,, mg
Vs = gas sample volume at 70°F and 29. 92 in. Hg, liters
Calculate the volume of gas sampled at standard conditions of
70°F, 29.92 in. Hg.
Vf(Pf-P.) x 530°R
Volume of gas sampled = Tf x 29/92 in. Hg
Where:
Vf = flask volume, liters
P£ = final flask pressure, in. Hg
Pj = initial flask pressure, in. Hg
Tf flask temperature, °R >
Preparation of Calibration Curve
Pipet exactly 0, 4, 8, 12, 16, and 20 ml of the standard solution
containing 0. 025 mg NO2 per ml into 250-ml beakers. Add 25 ml of
absorbing reagent to each beaker, and repeat the procedure indicated
under analysis of samples. Determine the absorbance at 420 rrifi, and
plot the absorbance of the solutions versus concentration (mg NO2).
Appendix B 55
-------
Discussion of Procedure
This method gives a reproducibility of +_ 1 percent when applied
23
to standard samples of inorganic nitrates. When used in motor
vehicle exhaust gas analysis, the precision is about +_ 5 percent and
24
the overall accuracy is about 3 percent. The precision and accuracy
obtained in analysis of stack gas samples should be the same as in the
analysis of motor vehicle exhaust gas.
Inorganic nitrates, nitrites, or organic nitrogen compounds
that easily oxidize to the nitrate interfere with the test and give high
results. Reducing agents such as SC>2, when present in high concentra-
tions, may interfere by reacting with the hydrogen peroxide in the
absorbing reagent to leave an insufficient amount for reaction with the
nitrogen oxides. Chlorides and halides also tend to interfere, and
produce lower results. The continued use of glassware that is etched
or becomes etched during the trituration process tends to yield low re-
sults and should be avoided.
The color produced is stable for several hours at room tempera-
ture (70°F). If the absorbance of the sample is above 0.6, appropriate
dilutions of both the sample and blank may be made with water. The
absorbing reagent can be prepared in the laboratory and used in the
field up to 30 days after its preparation. Reduction of the absorbing
reagent in the H-O concentration was found to be negligible in labora-
tory experiments conducted over a period of 49 days.
Emission Monitor
Five of the 25 plants from -which data are reported use a conduc-
tivity cell to monitor the emission of phosphoric acid mist. The system
used by the Tennessee Valley Authority is shown in Figure B-10. A
small sample stream is withdrawn from the stack by an ejector or a
small pump. The acid mist and water are condensed and passed
through a conductivity cell before being released to the sewer. A
recorder or indicator is attached to the conductivity cell to measure
microhms. Model CEL-JDI Industrial Instrument Company* conductivity
*Mention of company or product name does not constitute endorsement by
the U.S. Department of Health, Education and Welfare.
56 THERMAL-PROCESS PHOSPHORIC ACID
-------
cell, or equal, may be used. The recorder is calibrated by stack sam-
pling and can be used to give a continuous reading of the acid mist
emissions. Figure B-10 shows that a wet test meter or a calibrated
orifice may be used to measure the volume of the sample.
SAMPLE LINE
FROM STACK
,WATER
CONDENSER
ORIFICE OR
WET TEST METER
EJECTOR OR
PUMP
EXHAUST
TO
ATMOSPHERE
GAS CONDENSATE
TRAP
CONDUCTIVITY
CELL
CONDENSATE
TO SEWER
Figure B-10. Diagram of conductivity cell stack monitor.
Appendix B
57
-------
APPENDIX C: THERMAL-PROCESS PHOSPHORIC
ACID ESTABLISHMENTS IN UNITED STATES
The purpose of this tabulation of thermal-process phosphoric
acid manufacturing establishments (Table C-l) is to indicate the distri-
bution and principal areas of concentration of this segment of the indus-
try throughout the country.
Listings are without regard to the number of production units at
each location. As a result of sale, merger, or lease, company identi-
fications may in some cases differ from those presently in use.
The locations of 30 thermal-process phosphoric acid establish-
ments are shown on the accompanying map (Figure C-l). Three of
the establishments shown on the map are not now in operation.
Figure C-l. Location of thermal-process phosphoric acid plants.
-------
Table C-l. THERMAL-PROCESS PHOSPHORIC ACID ESTABLISHMENTS
IN UNITED STATES1'2'25
State
Alabama
Cal ifornia
Colorado
Georgia
Idaho
Illinois
Indiana
Kansas
Massachusetts
Michigan
Montana
New Jersey
New York
Ohio
Pennsylvania
South Carol ina
Tennessee
Texas
Wyoming
Company
Tennessee Valley Authority
F M C Corporation
Monsanto Company
Stauffer Chemical Company
Stauffer Chemical Company
Colorado Fuel and Iron
Corporation
Monsanto Company
El Paso Natural Gas Company
Monsanto Company
Stauffer Chemical Company
Stauffer Chemical Company
Hooker Chemical Company
Mobil Chemical Company
F M C Corporation
Hooker Chemical Company
Monsanto Company
Stauffer Chemical Company
Agrigo Chemical Company
Continental Oil Company
F M C Corporation
Monsanto Company
Hooker Chemical Company
Mobil Chemical Company
Monsanto Company
Stauffer Chemical Company
Mobil Chemical Company
Hooker Chemical Company
Stauffer Chemical Company
Hooker Chemical Company
F M C Corporation
Location
Wilson Dam
Newark
Long Beach
Richmond
South Gate
Pueblo
(not operating)
Augusta
Georgetown
(not operating)
Sauget
Chicago Heights
South Chicago
Jeffersonvi 1 le
Gary
Lawrence
Adams
Trenton
Butte
Carteret
Carteret
Carteret
Kearny
Niagara Fal Is
(not operating)
Fernald
Addyston
Morrisvi 1 le
Charleston
Columbia
Nashville
Dallas
Green River
60
THERMAL-PROCESS PHOSPHORIC ACID
-------
APPENDIX D: PHYSICAL DATA
Standard conversions for orthophosphoric acid, metaphosphoric
acid, pyrophosphoric acid, phosphorus and phosphorus pentoxide are
given in Table D-l. Specific gravity and density of phosphoric acid at
varying temperatures and concentrations are shown in Figure D-l.
Table D-2 gives process data on gas scrubbing systems of an
operating phosphoric acid manufacturing plant. Data on operating con-
ditions during testing and results of tests are given.
61
-------
Table D-l. CONVERSION TABLES
26
Name
Orthophosphorrc acid
Metaphosphoric acid
Pyrophosphoric acid
Phosphorus
Phosphorus pentoxide
Fo rmu 1 a
H3P04
H PO
H4P2°7
P4
P2°5
P4°10
Molecular
weight
98.14
80.05
1 78 . 1 1
124.16
142.16
284.32
To convert to
Pi, P205
multiply by
0.316
0.388
0.349
1.000
0.437
0.725
0.887
0.797
2.289
1.000
62
THERMAL-PROCESS PHOSPHORIC ACID
-------
75.95
100* H PO^; INTERNATIONAL CRITICAL TABLES
.8 - 115.7* H PO^; DURGIN, LUN, AND HALOWAN,
13.18
- 6.91
1<|.5 21.7 29.0 36.2 43.5 50.7 58.0 65.2 72.4 79.6 86.9
I i i i i 1 1 1 1 1 1
20 30 40 50 60 70 80 90 100 110 120
CONCENTRATION, I H PO
131.0
127.9
124.7
121.6
118.5
I 1S.li
112.3
109.1
106.0
102.9
U
I »•«.
«l
I 96'7
>f 93.6
I/I
1 90.1.
87.3
84. 2
81.1
78.0
74.8
71.7
68.6
65.5
62.4
Figure D-l. Specific gravity and density of phosphoric acid.
17.51
17.09
16.67
16.26
15.84
15.42
15.01
14.59
14.17
13.76
13.34
•
«*-
£ 12.92
- '2-51
z
o
12.09
11.67
11,26
10.84
10.42
10.00
8.59
8.17
8.75
8.34
27,28
Appendix D
63
-------
Table D-2. PROCESS DATA ON GAS SCRUBBING SYSTEMS OF TVA NO. 6 PHOSPHORIC ACID UNIT3
(Unit produces acid containing P.O,. equivalent to 85 to 115 percent H,PO.)
Operating condlt ons
Test
No.
Data
6
10
3
5
3
4
32
33
37
S3
50
58
51
48
53C
Data
1
2d
41
40
31
62
Data
16
13
14
11
12
7
8
17
15
18
K4
feed,
Ib/hr
for 85
2750
2320
2320
3000
3130
3170
3560
3650
4530b
5060b
5083*
5l30b
5270b
6050?
706ob
for 105
3800
3960
4040b
4330b
4330|>
l(880b
for 103
1530
2450
2600
2730
2780
2910
3000
3040
3080
3560b
Excess
air,
).
o 98 pe
42
36
34
42
40
36
40
3*
33
23
40
20
40
28
20
to 106
31
51
41
20
23
38
to 112
53
53
54
26
40
37
33
38
34
23
Acid, % HjPO^
Product
•cent H,P
87.5
85.7
86.7
86.8
84.9
87.0
34.0
89.7
98.7
35.1
95.8
95.0
97.3
90.2
91.7
Dilute
°4
38.2
39.0
37.6
42.1
37.6
41.3
45.8
43.3
58.8
47.9
54.8
49.0
53.0
39.9
40.9
percent hyo/.
106.3
106.3
105.3
105.9
105.9
106.0
70.7
72.3
74.4
70.0
73.3
69.7
percent HjPO,,
109.9
110.8
110.8
109.4
110.5
110. 8
III.O
111.0
III. 2
110.5
75.3
78.2
79.1
80.9
82.5
79.0
80.6
79.1
75.1
84.4
Cooling
water,
°F
84
85
84
86
86
86
86
86
75
81
79
82
80
62
84
78
78
45
57
82
56
84
85
84
84
85
84
85
84
83
82
Venturl scrubber
Gas entering
P2os,
Ib/hr
2540
2760
2650
2800
2340
3140
3630
3420
5440
5090
6440
5080
6340
7430
3720
3290
3240
5320
4860
2370
5780
1300
2240
2510
2370
2430
2720
2590
2740
2340
3510
Total,
1000
Ib/hr
26.2
26.3
26.4
26.3
28.3
28.8
33.2
31.1
38.7
41.2
50.8
41.0
50.6
56.1
68.6
28.9
31.7
36.6
32.6
30.1
41.0
16.6
23.7
24.0
23.5
23.2
23.7
23.1
22.3
23.2
24.3
1000
Btu/hr
3,530
4,530
4,120
3,430
3,500
3,210
4,730
3.560
6,080
6,730
3,630
7.170
8,820
12,800
13,810
2,030
2,260
3,540
3,130
3,040
4,330
,070
,800
,050
,660
,830
,880
,260
.750
.340
,840
Temp,
•F
260
400
315
260
240
250
300
230
480
380
525
450
415
350
440
330
328
400
370
440
370
270
330
350
330
370
330
430
340
360
340
Gas
4P,
water
26
32
30
27
37
23
37
2
43
49
51
30
30
35
53
<20
<20
53
30
53
53
32
34
40
30
31
30
30
45
32
25
Temp,
out,
•F
139
146
141
140
133
139
138
171
142
147
152
150
157
167
175
137
141
141
137
137
142
133
142
145
147
156
142
161
143
141
151
it,
•F
+2
-4
-3
+2
+1
+4
+1
*2t
-3
+2
+2
+2
+9
+7
*9
+7
+7
-3
-1
-7
-3
-1
-3
0
»2
-2
+2
+2
-1
+2
-3
Dilute
add
entering
1000
Ib
122
143
143
147
144
148
183
10
206
143
150
150
148
135
144
176
192
153
142
120
183.
192
159
160
201
138
201
203
134
156
217
•F
137
ISO
144
138
132
135
137
145
145
145
150
148
148
160
166
130
134
144
138
144
145
134
145
145
145
158
140
153
144
133
154
Gas
entering,
psig
2.0
2.0
2.0
2.0
1.6
1.6
1.0
0.9
0.3
0.8
0.3
0.3
0.9
1.0
0.3
I.I
2. 1
0.9
0.9
0.8
0.3
2.0
2.0
2.0
2.0
2.2
2.0
2.0
2.0
2.0
1.1
Separa
Flows, 1000 Ib/hr
Makeup
water
5.10
5.40
5.40
5.10
6.15
5.70
5.75a
5.35
6.11
7.45
8.00
7.75
8.00
13.0
20.2
3.60
3.60
4.01
4.16
4.00
4.81
1.50
2.25
2.00
I.6S
2.10
1.50
2.25
2.25
2.25
2.25
Weak
acid
37
38
97
38
105
107
0
116
135
109
112
107
110
104
109
128
123
133
123
143
127
125
125
88
128
130
126
127
131
33
137
"2°
out In
stack
gas
2.01
2.36
2.07
1.91
2.54
2.13
3.00
3.15
4.08
3.43
4.65
4.07
4.38
7.84
12.70
.67
.41
.49
.68
.73
.39
0.49
0.69
0.82
0.60
0.65
0.78
0.85
0.64
0.90
0.84
tor tower
Stack aas
Temp,
°F
130
142
136
131
127
128
132
140
137
138
142
141
141
150
162
125
128
132
126
137
135
126
137
140
135
143
135
147
136
130
144
P20S,
Ib/hr
20
2
3
12
7
37
4
26
1
8
1
5
5
8
30
50
36
2
5
2
3
16
9
11
4
9
13
15
6
9
15
1000 Btu/hr
In
jacket
water
710
880
810
800
700
810
620
620
740
740
780
880
820
1400
810
830
890
1730
1100
840
830
620
640
710
560
760
690
620
1010
790
670
In
stack
gas
2,540
2,990
2,640
2,430
3,120
2,630
3,720
3.980
5,020
4,340
5.880
5,070
5,560
3,440
15,120
2,210
2,000
2,140
2,240
2,440
2,770
780
,150
,300
,030
,150
,220
.360
,050
,320
.330
* of
total
to
plant
10.3
8.1
10.2
9.6
12.1
10.3
3.5
10.0
10.3
8.5
10.7
3.7
10.9
14.4
18.6
7.6
7.2
8.1
7.2
7.0
6.7
7.0
5.3
6.5
4.6
6.0
5.8
5.6
6.4
6.0
5.3
Recovery of P,05
Ib/hr
2520
2760
2650
2730
2930
3100
3620
3400
5440
5080
6440
5070
6340
7420
3690
3240
3210
5320
4850
2970
5780
1280
2230
2500
2360
2420
2710
2580
2730
2340
3500
* of
total
acid
unit
40.0
41.1
39.6
40.6
40.8
42.7
44.5
40.6
51.8
43.9
55.3
43.2
52.5
53.6
53.9
37-2
35-4
57.6
49.0
30.0
51.7
36.8
33-7
42.1
37.9
38.0
40.6
37-5
33.3
33.2
42.8
Over-all
In acid
unit, *
of total
from
P; feed
93.68
33.98
99.96
99.83
99.90
93.50
33.96
39.69
99.99
99.93
99.99
99.95
33.36
33.34
33.81
99.42
99.61
99.98
99.95
99.98
99.98
99.55
99.83
99.82
99.94
99.86
99.80
99.78
99.91
99.88
99.81
M
1
r
en
en
TJ
O
en
T3
a
o
>
o
-------
e
X
D
Table D-2 (continued). PROCESS DATA ON GAS SCRUBBING SYSTEMS OF TVA NO. 6 PHOSPHORIC ACID UNIT3
(Unit produces acid containing P?0|- equivalent to 85 to 115 percent H.PO.)
Operating conditions
Ho.
Data
25
26
24
13
57
27
22
3*
36
5"l
if
52
61
39
56
38
45
44
28
46
42
43
49
29
60
47
30
Data
23
35
21
Ib/hr
or 109
3640
3700
3720
3770'
38Mb
4060
4200b
4210'
4340b
4470b
M90b
4540b
4560b
466ob
4720b
4790b
4790?
1,9 lob
S020b
5070b
5190b
5300b
5370b
ss4ob
5S40b
60COI>
6280b
for II
3390"
3690b
438ob
4580b
«
to 112
16
27
16
20
32
11
26
40
2!
48
32
32
10
30
32
31
40
40
39
20
21
25
30
16
21
10
15
to 115
37
40
24
Product
ercent 1
109.7
no. 6
III. 3
111.6
109.2
110.3
III. 2
111.7
111.8
109.3
110. 0
109.3
109.6
109.6
109.2
109.4
110.6
110. 0
110.4
110.0
109.8
109.3
109.9
111.5
109.9
110.. 6
III. 9
percent
113.2
115.0
113. 1
114. 1
"A
Dilute
3P04 (eo
76.6
79.5
74.3
61.8
83.1
67.6
65.4
9«.7
87.3
85.2
84.8
82.4
77.5
82.0
87.5
80.S
85.1
81.9
61.8
60.0
78.1
76.3
79.7
82.5
76.8
78.0
81.8
'3'",
86 0
9o!s
91.7
85.5
•F
tinned)
54
58
55
78
82
S6
64
85
83
81
81
80
83
75
82
73
50
48
67
50
48
47
65
70
62
58
/3
78
64
85
(8
Venturl
PlV
Ib/hr
3700
3980
3330
3640
4750
3150
4370
3640
3340
6450
5900
5640
4760
5160
5570
5060
5560
6060
4950
5310
5460
6020
6640
6240
6760
7090
6950
4190
4540
4990
Gas en
Ib/hr
27.1
29.4
25.9
25.3
32.2
25.9
30.8
35.0
29.3
44.1
39.2
38.2
31.3
37.5
39.9
37.9
42.3
43.7
33.1
38.7
37.4
42.4
45.0
39.3
43.3
46.1
42.1
21 .3
30.1
35.9
31.7
terlno.
Btu/hr
3,240
3.710
2.530
1,080
3,090
2,690
3,080
3,570
2,670
5,890
4,750
4,510
3.760
4,760
4,850
5,220
5,560
4,760
4,600
4,270
4,670
5.340
6,170
5,910
6,300
6.650
6,980
3!450
3,540
2,890
Temp.
500
530
395
360
400
410
433
450
405
520
480
470
465
530
510
570
550
465
500
470
520
500
520
610
530
550
615
3*iO
493
433
400
scrubber
water
39
38
35
57
40
35
34
51
48
40
61
25
39
41
40
39
30
51
54
30
46
40
40
56
50
51
44
35
35
32
30
Gas
•F
149
157
140
155
154
137
171
199
170
172
168
171
147
167
178
165
185
166
162
154
156
158
163
•F
-4
-6
0
-2
-2
-1
0
-3
-5
-4
-3
+3
-9
-3
-5
-4
»I3
-2
-6
-4
-2
-4
-3
185 | -7
161
168
172
156
189
192
158
-4
-4
-6
0
*4
-1
Di lute
acid
Ib
146
ISO
146
200
166
140
210
249
236
185
189
179
181
230
194
228
199
191
ISO
189
184
180
175
148
182
179
144
221
245
206
•F
153
163
140
157
156
138
171
202
175
176
171
168
156
170
183
169
172
168
168
158
158
162
170
192
169
172
178
isfl
189
188
159
Separator tower
psl9
0.8
0.8
0.8
1.1
0.7
0.8
I.I
0.8
0.9
O.S
0.8
0.8
0.8
0.6
0.9
1.0
0.9
0.8
0.8
0.9
0.8
0.9
0.8
0.6
0.9
0.8
0.8
I.I
0.9
1.1
Flows, 1000 Ib/hr
water
3.01
.51
.51
.55
.20
.21
.55
.00
.75
.30
.60
.00
.90
.26
.00
4.51
3.51
3.86
4.26
3.81
4.21
4.51'
5.3'
4.51
5.30
5.86
5.61
2.25
2.50
2.50
2.50
acid
127
130
124
U7
137
120
138
166
159
137
136
137
134
153
142
152
142
138
161
135
132
0
127
160
134
128
161
149
163
135
"2°
gas
1.92
2.21
1.73
1.05
1.41
1.74
1.17
0.66
0.84
2.35
1.63
1.63
1.35
3.13
1.96
3.46
2.26
2.61
2.24
2.10
2.27
2.52
3.05
2.73
2.76
3.43
3.03
1.36
0.95
1.26
Stack
•F
136
145
131
144
148
122
IS?
187
164
164
161
160
147
160
172
-156
160
152
154
142
145
146
158
176
159
157
165
171
173
145
gas
Ib/hr
8
4
13
7
2
6
6
6
2
4
3
6
4
7
4
6
7
5
2
II
3
6
Jt
2
7
3
4
7
32
14
Heat removed,
1000 Btu/hr
water
1160
800
910
1300
650
700
1260
950
1080
760
880
860
610
990
660
940
1350
1360
860
1030
1290
1420
1150
760
740
1900
1320
1430
830
1280
gas
2,510
2,930
2,260
1,530
2,110
2,220
1,890
1,940
1.570
3.500
2.800
2.770
2,010
4,200
3,050
4.560
3.370
3,680
3,220
2,940
3.120
3.500
4.220
3.930
3,880
4,650
4,200
2,190
1.690
1.920
J of
plant
7.8
8.5
6.8
6.7
6.1
6.3
7.6
5.8
4.9
8.4
6.8
6.9
4.6
6.9
7.4
9.3
8.7
9.1
7.4
6.7
7.6
8.1
8.6
7.3
6.9
9.9
8.4
9.6
6.2
6.6
Recovery of P,oe
Ib/hr
3690
3970
3310
3630
4750
3150
4360
3450
3340
6440
5900
5630
4750
5170
5570
5050
5560
6060
4950
5300
5450
6010
6630
6240
6750
7090
6950
3350
4190
4500
4380
S of
total
to
acid
44.4
46.8
38.9
41.1
53.7
33.8
45.3
35.8
33.6
64.9
57.4
54.2
4S.S
48.4
51.5
46.0
50.7
53.9
43.0
45.6
45.3
49.5
53.9
49.2
53.2
51.6
48.3
*t3.5
49.6
44.9
47.5
Over-all
In acid
unit, »
of total
Pt feed
99.91
99.96
99.65
93.82
59.96
39.94
99.94
99.92
99.98
99.97
99.97
99.94
99.96
99.93
99.97
99.95
99.94
99.36
99.99
99.91
99.98
99.95
99.97
99.97
99.95
99.98
99.97
99.83
99.91
39.66
93.87
*To weak acid receiver.
Two combustion chambers In operation.
^Before test No. 59 was nade, the l-l/2-lnch carbon Intalox saddle packing was removed from the separato
After test Ho. 2 was made, a damper, or sliding gate, was Installed at the throa: of the venturl scrubb
os
en
-------
REFERENCES
1. Prombino, A. J., "Phosphates", Chemical Week, 109-132, Oct., 1964.
2. Bureau of the Census, U. S. Department of Commerce, Industrial
Statistics, Section on Industrial Inorganic and Organic Chemicals.
3. Allgood, H. Y., F.E. Lancaster, andJ.A. McCollum,"Operating
Experience with TVA's Stainless Steel Thermal Phosphoric Acid
Production Plant", Presented at 152nd National Meeting of .Ameri-
can Chemical Society, September 11-16, 1966.
4. Brink, J.A. , "Removal of Phosphoric Acid Mists", Chapter 15,
Part B, of Gas Purification Processes, edited by G. Nonhebil.
5. Brink, J.A.,.and C.E. Contant, "Experiments on anlndustrial Ven-
turi Scrubber", Industrial and Engineering Chemistry,50:1157-60.
August, 1958.
6. Gillespie, G. R. , andH.F. Johnstone, "Particle Size Distribution
in some Hygroscopic Aerosols", Chemical Engineering Progress,
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7. Striplin, M. M., "Development of Processes and Equipment for
Production of Phosphoric Acid", Chemical Engineering Report No.
2, Tennessee Valley Authority, 1948.
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10. Anon, "Collector 99. 9% Efficient: Pressure Drop Moderate",
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Ave. , New York, New York, 10017, Personal Communication.
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Health Service, PHS Publ. No. 999-AP-13, Cincinnati, Ohio, 1965.
13. Baskerville, W.H., "The Packed-Tower Collection of Phosphoric
Acid", American Institute of Chemical Engineers, 37:79-94, 1941.
67
-------
14. Walker, O. B. , Research Contrell, Inc. , Box 750, Bound Brook,
New Jersey, Personal Communication, February, 1967.
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Analysis, 9th Edition, I960.
17. Guinland, K. P., and M. A. DeSesa,"Spectrophotometric Deter-
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Analytical Chemistry, 27:1626, 1955.
18. Talvitic, N. A., E. Pereg, and D.P. Illustre/'Spectrophotometric
Determination of Phosphorus as Molybdovanadophosphoric Acid",
Application to Air Borne Particulate Matter, Ibid. 34:866, 1962.
19. Rogers, R. N. , "Determination of Phosphate by Differential
Spectrophotometry", Ibid. 32:1050, I960.
20. Gee, A., andV.R. Dietz, "The Determination of Phosphate in the
Presence of Calcium by the Molybdovanadate Method", Ibid. 25:1320,
1953.
21. Reagent Chemicals, American Chemical Society Specifications,
Allied Publications, 340-342, I960.
22. Beatty, R. L. , L. B. Berger, and H. H. Schrenk, "Determination
of Oxides of Nitrogen by the Phenoldisulfonic Acid Method", R.I.
3687, Bureau of Mines, U.S. Dept. Interior, February, 1943.
23. "Standard Method of Test for Oxides of Nitrogen(Phenoldisulfonic
Acid Procedure)", 1965 Book of ASTM Standards, ASTM Desig-
nation D-1608-60, 725-729, 1965.
24. Jacobs, M.. B., The Chemical Analysis of Air Pollutants, Inter-
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25. Douglas, J. R. , E.A. Hame, and E.L. Johnston,"Fertilizer
Trends", TVA, Wilson Dam, Alabama, 1964.
26. Waggaman, W.H., "Phosphoric Acid, Phosphates and Phospha-
tic Fertilizers", ACS Monograph Series, 2nd Edition, 1952.
27. International Critical Tables, McGraw-Hill Book Company,
1:102, New York, New York, 1926.
28. Ibid, P. 101.
68 THERMAL-PROCESS PHOSPHORIC ACID
H. S. GOVERNMENT PRINTING OFFICE : 1968 O - 325-033
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