United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/3-79-038
November 1979
Air
Review of New Source
Performance Standards
for Phosphate
Industry
-------
EPA-450/3-79-038
Review of New Source Performance
Standards for Phosphate
Fertilizer Industry
by
William Herring
Emission Standards and Engineering Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
November 1979
-------
This report has been reviewed by the Emission Standards and Engineering
Division of the Office of Air Quality Planning and Standards, EPA, and
approved for publication. Mention of trade names or commercial products
is not intended to consitute endorsement or recommendation for use. Copies
of this report are available through the Library Services Office (MD-35) ,
U.S. Environmental Protection Agency, Research Triangle Park, N.C. 27711,
or from National Technical Information Services, 5285 Port Royal Road,
Springfield, Virginia 22161.
11
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TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS vi
LIST OF TABLES v1
1. INTRODUCTION 1-1
1.1 PURPOSE AND SCOPE 1-1
1.2 STUDY RESULTS 1-2
2. INDUSTRY GROWTH AND PROJECTIONS 2-1
2.1 PRODUCTION CAPACITY 2-1
2.2 REFERENCES FOR SECTION 2. 2-3
3. PRODUCTION PROCESS CHANGES 3-1
3.1 WET PROCESS PHOSPHORIC ACID 3-1
3.1.1 Dihydrate Processes 3-1
3.1.2 Hemihydrate (Hemidihydrate) Processes 3-4
3.2 SUPERPHOSPHORIC ACID 3-5
3.3 DIAMMONIUM PHOSPHATE 3-6
3.4 TRIPLE SUPERPHOSPHATE 3-9
3.4.1 TSP from Phosphate Rock Treatment 3-9
3.4.2 GTSP from Limestone Treatment 3-14
3.5 PHOSPHATE ROCK DRYING AND GRINDING 3-14
3.6 PRODUCTION PROCESS CHANGES SINCE NSPS PUBLICATION 3-15
3.6.1 Production Processes in Use at Time of NSPS Publication 3-15
3.6.2 Production Process Changes in the U.S. 3-15
3.6.3 Production Process Changes Outside the U.S. 3-16
3.6.4 Discussion of Limestone Treatment (Simplot) Process
for GTSP Production 3-17
3.6.5 Discussion of Wet-Rock Grinding 3-18
3.6.6 Discussion of Hemihvdrate (Hemidihydrate) Processes
for WPPA Production 3-20
3.7 STATUS OF POTENTIAL REGULATION OF RADIOACTIVE EMISSIONS
FROM PHOSPHATE PLANTS UNDER THE CLEAN AIR ACT 3-21
3.8 REFERENCES FOR SECTION 3. 3-23
iii
-------
4. FLUORIDE EMISSION CONTROL CHANGES 4-1
4.1 CONTROL SYSTEMS PREVIOUSLY AVAILABLE 4-1
4.2 NEW CONTROL SYSTEMS 4-3
4.2.1 Modified Scrubbing Systems for WPPA and TSP Production 4-4
4.2.2 Modified Scrubbing System for DAP Production 4-6
4.2.3 Discussion of the Modified Scrubbing Systems 4-7
4.3 REFERENCES FOR SECTION 4. 4-10
5. ADVANCES IN GYPSUM POND FLUORIDE CONTROL 5-1
5.1 PREVIOUS OPERATION AND CONSTRUCTION OF POND SYSTEMS 5-1
5.2 PRESENT OPERATION AND CONSTRUCTION OF POND SYSTEMS 5-7
5.2.1 Treatment of Pond Water for Discharge 5-7
5.2.2 Pond Lining 5-7
5.2.3 Pond Area Reduction by Cooling Towers and
Fluoride Recovery 5-8
5.2.4 Gypsum Pond Emission Reduction by Fluoride
Recovery from WPPA Evaporator Gas 5-9
5.2.5 Gypsum Pond Emission Reduction by Fluoride
Recovery from WPPA Process Water 5-11
5.2.6 Gypsum Pond Reduction by Hemihydrate WPPA Production 5-13
5.3 REFERENCES FOR SECTION 5. 5-14
v
6. NSPS ENFORCEMENT PROBLEMS AND COMPLAINTS 6-1
6.1 NEW SOURCES SINCE NSPS PUBLICATION 6-1
6.2 COMPLAINTS OF PHOSPHATE PLANT EMISSIONS AND SUGGESTED
IMPROVEMENTS OF REGULATIONS 6-2
6.2.1 Florida 6-2
6.2.2 Idaho 6-4
6.3 STATUS OF DEVELOPMENT OF FLUORIDE MONITORING 6-4
6.4 STATE PLANS FOR REGULATING EXISTING PHOSPHATE PLANTS 6-5
6.5 REFERENCES FOR SECTION 6. 6-8
7. CONCLUSIONS 7-1
7.1 HEMIHYDRATE PROCESS FOR WET PROCESS PHOSPHORIC ACID (WPPA) 7-1
7.2 SIMPLOT PROCESS FOR GRANULATED TRIPLE SUPERPHOSPHATE (GTSP) 7-2
7.3 WET GRINDING OF PHOSPHATE ROCK 7-2
7.4 SCRUBBING SYSTEMS, COOLING TOWERS, AND GYPSUM PONDS 7-3
7.4.1 Fluoride Recovery 7-3
7.4.2 Cooling Towers 7-3
-------
7.5 FLUORIDE EMISSION MONITORING 7-5
7.6 RADIOACTIVE EMISSIONS 7-5
7.7 AREAS FOR RESEARCH AND DEVELOPMENT 7-6
7.8 INDUSTRY GROWTH 7-6
7.9 REGULATION OF EXISTING SOURCES 7-7
7.10 REFERENCES FOR SECTION 7. 7-7
8. RECOMMENDATIONS 8-1
8.1 HEMIHYDRATE PROCESS FOR WET PROCESS PHOSPHORIC ACID (WPPA) 8-1
8.2 SIMPLOT PROCESS FOR GRANULATED TRIPLE SUPERPHOSPHATE (GTSP) 8-1
8.3 WET GRINDING OF PHOSPHATE ROCK 8-1
8.4 SCRUBBING SYSTEMS, COOLING TOWERS, AND GYPSUM PONDS 8-1
8.4.1 Fluoride Recovery 8-1
8.4.2 Cooling Towers 8-1
8.5 RADIOACTIVE EMISSIONS 8-2
8.6 RECOMMENDATION ON NSPS REVISION STUDY 8-2
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LIST OF ILLUSTRATIONS
Figure Number Page
3-1 Wet-Process Phosphoric Acid Process 3-2
3-2 Stauffer Superphosphoric Acid Process 3-7
3-3 TVA Diammonium Phosphate Process 3-8
3-4 Run-of-Pile Triple Superphosphate Process 3-10
3-5 TVA One-step Granular Triple Superphosphate Process 3-12
4-1 Spray-crossflow Packed Bed Scrubber 4-2
5-1 Typical Gypsum Pond Servicing a 1000 TPD-PJ),-
Plant * a 5-3
LIST OF TABLES
Table Number Page
j
2-1 Phosphate Production Capacity in the U.S. 2-2
5-1 Typical Material Balance of Fluoride in Manufacture
of Wet-Process Phosphoric Acid 5-4
5-2 Fluoride Emission Factors for Selected Gypsum Ponds
at 90°F; Ib /acre day 5-6
VI
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1. INTRODUCTION
1.1 PURPOSE AND SCOPE
On August 6, 1975, the Environmental Protection Agency promulgated
New Source Performance Standards (NSPS) for Five Categories of Sources
in the Phosphate Fertilizer Industry (40 FR 33152). These standards
establish emissions limits and require emission testing and reporting
for total fluorides from wet process phosphoric acid (WPPA) plants,
superphosphoric acid (SPA) plants, diammonium phosphate (DAP) plants,
triple superphosphate (TSP) plants, and granular triple superphosphate
(GTSP) storage facilities.
The Clean Air Act Amendments of 1977 require that the Administrator
of the EPA review and, if appropriate, revise established standards of
performance for new stationary sources at least every four years (Section
111(b)(1)(B)). This report includes reviews of recent and projected
growth of the phosphate fertilizer industry. Changes in process techno-
logy since 1975 are presented, and advances in the control of fluorides
from gypsum ponds are discussed. Inquiries were made on enforcement
problems of the current NSPS and on continuous monitoring of fluoride
control devices, and the results are presented. Compliance test results;
information from the literature; and discussions with representatives of
industry, control equipment vendors, phosphate fertilizer plant designers,
EPA regional offices, state agencies, and the Tennessee Valley Authority
form the basis for these reviews. The information obtained was analyzed
to determine whether potential benefits exist that would warrant NSPS
revision now.
1-1
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1.2 STUDY RESULTS
Based on results of this investigation, conclusions were drawn on
significant developments in the phosphate industry since NSPS promulga-
tion, and recommendations were formulated on action to be taken pertaining
to NSPS revision. These conclusions and recommendations are shown in
Section 7 of this report.
1-2
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2. INDUSTRY GROWTH AND PROJECTIONS
2.1 PRODUCTION CAPACITY
The total capacity of plants in the U.S. for production of wet
process phosphoric acid (WPPA), superphosphoric acid (SPA), ammonium
phosphate (AP), and triple superphosphate (TSP), for the years beginning
1974 and projected through 1985, is shown in Table 2-1. The Table 2-1
values were derived from TVA compilations. This data source was sup-
2
ported by recommendation of the Fertilizer Institute.
Table 2-1 shows that production capacity increased for WPPA, SPA,
AP, and TSP, during the years 1974 through 1979, by 3071, 496, 955, and
313 thousand tons P2^5' respectively. This amounts to an average annual
growth of 614, 99, 191 and 63 thousand tons P205 for each product,
respectively, over those 5 years;
Table 2-1 also shows that the projected capacity increases for
those products from 1979 to 1980 are 461, 350, 0, and 0, respectively.
For 1980 through 1985, the projected capacity increase is zero for
all aforementioned products.
Recent literature indicates that U.S.-located phosphate plants are
now producing at nearly full capacity due largely to high export demand;
but that further expansion would be contingent on continued current
export levels and increased domestic demand - conditions not assured.
Exports might be reduced because of potential high production outside
345
the U.S. ' ' Pertaining to domestic demand, U.S. and Puerto Rican
phosphate use decreased 9% in 1978; and there are strong indications
that some soils have been overferti1ized with phosphate. * These
factors support the expectation of little or no expansion of phosphate
production capacity in the U.S. between 1980 and 1985.
2-1
-------
TABLE 2-1. PHOSPHATE PRODUCTION CAPACITY IN THE U.S. (THOUSAND SHORT TONS P^)1
Product
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985
Phosphoric acid (WPPA)
Superphosphoric acid
Ammonium phosphate9
Concentrated (triple)
Superphosphate6 .
6680
747
3806
2127
8518
877
4548
2367
9001
1012
4721
2596
9346
1037
5267
*,
2440
9601
893
4794
2440
9751
1243
4761
2440
10212
1593
4761
2440
10212
1593
4761
2440
10212
1593
4761
2440
10212
1593
4761
2440
10212
1593
4761
2440
10212
1593
4761
2440
ro
ro
Includes monoammonium phosphate and diammonium phosphate.
Includes run-of-pile and granulated triple superphosphate.
-------
2.2 REFERENCES FOR SECTION 2.
1. Tennessee Valley Authority. World Fertilizer Capacity:
"Phos Acid WP," TVA-05/10/79; "Super Acid W," TVA-05/21/79; "AM Phosphate,"
TVA-05/21/79; "Cone Super," TVA-05/21/79. Muscle Shoals, Alabama. 22 p.
2. Letter from K.T. Johnson, The Fertilizer Institute, to W.O. Herring,
U.S. EPA. April 18, 1979. Subject: Phosphate Industry in U.S.
3. Key Chemicals, Phosphoric Acid. Chemical and Engineering News.
p. 18. April 30, 1979.
4. 1979 Fertilizer Situation. U.S. Dept. of Aqriculture.
Washington, D.C. Publication FS-9. Dec. 1978. D. 23.
5. Harris, G.T., and E.A. Harre. World Fertilizer Situation and
Outlook - 1978-85. International Fertilizer Development Center and
Tennessee Valley Authority. Muscle Shoals, Alabama 35660. Bulletin
IFDC-T-13, March 1979. pp. 8-13.
6. Reference 4, p. 11.
7. Situation 78 - TVA Fertilizer Conference. Tennessee Valley
Authority. Muscle Shoals, Alabama 35660. Bulletin Y-131. Aug. 1978.
p. 54.
2-3
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3. PRODUCTION PROCESS CHANGES
All processes used commercially to make wet process phosphoric
acid, superphosphoric acid, diammonium phosphate, and triple super-
phosphate are summarized in Sections 3.1 through 3.5, below. Changes of
production process application since NSPS publication in August 1975,
are identified and discussed in Section 3.6. The status of potential
regulation of radioactive emissions from phosphate plants is given in
Section 3.7.
3.1 WET PROCESS PHOSPHORIC ACID
3.1.1 Pi hydrate Processes
Wet process phosphoric acid (WPPA) is made by reacting sulfuric
acid (H2S04) with fluorapatite (Ca10(P04)6F2) in PnosPnate rock- In tne
dihydrate processes, calcium sulfate, as the dihydrate, gypsum (CaS04
2H20), is also formed. The overall reaction is described by the following
equation:
3 Ca1Q (P04)6 F2 + 30H2S04 + Si02 + 58H20 - 30CaS04 ' 2 H20 + 18H3P04 + H
Calcium sulfate precipitates, and the liquid phosphoric acid is separated
by filtration. A modern dihydrate, WPPA plant flow diagram is shown in
Figure 3-1.
Finely ground phosphate rock is continuously metered into the
reactor and sulfuric acid is added. The single-tank reactor (Dorr-
Oliver design) illustrated in Figure 3-1 consists of two concentric
cylinders. Reactants are added to the annul us and digestion occurs in
this outer compartment. The second (central) compartment provides
retention time for gypsum crystal growth and prevents short-circuiting
of rock.
3-1
-------
GO
I
ro
WASH .
WATER
GYPSUM
POND WATER
GROUND
PHOSPHATE
ROCK
'HEATER
SI
FAN
SUCK
DRY
SL9.TH CAKE., I SUCK 3 WASH
WASH REMOVE I PR
I 1 WASH I
2 WASH 1 WASH I LIQUOR
-». VACUUM
.TO VACUUM
"*• AND HOT WELL
Si ft.
PARTICULATE.
SO,. ODOR
GYPSUM SLURRY,
TO POND
•TO SCRUBBER ,
HYDROFLUOSILICIC ACID
Fiqure 3-1. Flow diaqram illustratinq dihydrate wet-process phosphoric acid process.
-------
Concentrated sulfuric acid is usually fed to the reactor. The only
other water entering the reactor is the filter-wash water.
Considerable heat of reaction is generated in the reactor and must
be removed. This heat removal is done in modern plants by vacuum-flash-
cooling part of the slurry and sending it back into the reactor.
The reaction slurry is held in the reactor for up to 8 hours before
being sent to the.filter. The most common filter design is the rotary
horizontal tilting-pan vacuum filter denoted in Figure 3-1. It consists
of a series of individual filter cells mounted on a revolving annular
frame.
Product slurry from the reactor is introduced into a filter cell
and vacuum is applied. After a dewatering period, the filter cake
/
undergoes two or three stages of washing with progressively weaker
solutions of phosphoric acid. The wash-water flow is countercurrent to
the rotation of the filter cake with heated fresh water, or barometric
condenser water, used for the last wash; the filtrate from this step is
used as the washing liquor for the preceding stage, etc.
After the last washing, the cell is subjected to a cake dewatering
step and then inverted to discharge the gypsum. Cleaning of the filter
media occurs at this time. The cell is then returned to its upright
position and begins a new cycle.
The 32 percent P205 acid obtained from the filter generally is
concentrated to 54$ in a two- or three-stage vacuum evaporator system.
In the evaporator, illustrated 1n Figure 3-1, provision is made for
recovery of fluoride as fluosilicic acid. Inclusion of this recovery
feature depends on economics. Many evaporation plants do not have this
device.
3-3
-------
3.1.2 Hemihydrate (Henrid1 hydrate) Processes
Commercial hemihydrate, or hemidihydrate (HDH), processes for
making phosphoric acid are distinguished from dihydrate processes by
inclusion of two main stages - the hemihydrate stage, or first stage;
and the dihydrate stage, or second stage. Fluoride recovery can be co-
2
installed with the HDH process.
Hemihydrate Stage
In the hemihydrate stage, phosphate rock is reacted with a mixture
of 98% sulfuric acid and return phosphoric acid (from the hemihydrate
2
filter) to yield phosphoric acid and calcium sulfate hemihydrate. The
overall reaction is represented by the equation:
3Ca1Q(P04)6F2 + 30H2S04 + Si02 + 13H20 -> 30CaS04 ' 1/2H20 + 18H3P04 + H
Relatively high temperatures and P205 concentrations are required to
obtain calcium sulfate as hemihydrate, instead of dihydrate, in the
reaction of fluorapatite with H2S04.
The resulting slurry is filtered to obtain the hemihydrate residue
and phosphoric acid filtrate. Hemihydrate crystallization permits
easier filtration, compared with dihydrate crystallization, requiring
less water to dilute the acid for satisfactory filtration. Therefore,
the acid obtained directly from filtration in the hemihydrate stage
contains 40 to 54% P205, and is suitable as the finished product WPPA,
2 '
without further concentration by evaporation.
3-4
-------
Pi hydrate Stage
In the di hydrate stage, with further H^SO- addition, the hemi hydrate
is recrys tali zed as the dihydrate. Co-precipitated lattice P205 is
released from the hemihydrate precipitate during recrystallization. The
dihydrate slurry is filtered with one or two wash stages. Filtrate,
from the first wash stage, is recycled to the hemihydrate filter to
2
recover the released PoOq-
Fluoride Recovery
Fluorides are evolved from the reactors in both the hemihydrate and
dihydrate stages, and from the flash cooler, in the hemihydrate stage.
These fluorides can be recovered by means of a co- ins tailed scrubbing
2
system as byproduct
3.2 SUPERPHOSPHORIC ACID
Superphosphoric acid (SPA) is produced by submerged combustion or
vacuum evaporation of clarified WPPA (containing 54% PoOc) to a p?°5
concentration between 72 and 76%. Vacuum evaporation is, commercially,
much the more important method.
There are two commercial processes for the production of super-
phosphoric acid by vacuum evaporation:
1. The falling film evaporation process (Stauffer Chemical Co.)
2. The forced circulation evaporation process (Swenson Evaporator Co.)
Feed acid clarification in both processes is usually accomplished by
settling or by a combination of aging and settling. In general, both
processes are also similar in other operations.
3-5
-------
Figure 3-2 shows the Stauffer process. Feed acid is added to the
evaporator recycle tank, where it mixes with concentrated product acid to
maintain a highly concentrated process acid for lower corrosion rates.
This mixture is pumped to the top of the evaporator and distributed to
the inside wall of the evaporator tubes. The acid film moves down along
the inside wall of the tubes receiving heat from the steam on the outside.
Evaporation occurs and the concentrated acid is separated from the water
vapor in a flash chamber located at the bottom of the evaporator.
Product acid flows to the evaporator recycle tank and vapors to the
barometric condenser. To minimize P205 loss, the separator section
contains a mist eliminator to reduce carryover to the condenser.
3.3 DIAMMONIUM PHOSPHATE
Diammonium phosphate (DAP) is made in the reaction:
2 NH3 + H3P04 * (NH4)2 HP04
/
It contains 18 percent nitrogen and 46 percent available 1>2®5' Tlie ™
process for DAP production is the one in widest use, and there are
several variations of the original now in use. A flow diagram of the
5
basic process is shown in Figure 3-3.
Anhydrous ammonia and phosphoric acid (about 40 percent PJ^S^ are
reacted in the preneutralizer using a NH3 / H3P04 mole ratio of 1.35,
which allows evaporation to a water content of 18 to 22 percent without
thickening the DAP slurry to a nonflowing state. The slurry flows into
the ammoniator-granulator and is distributed over a bed of recycled
3-6
-------
steam from
package boiler FALLING-FILM
EVAPORATOR
Condensole, „
to package
Steam boiler
:Wct -pro cess
(phosphoric Concent
locid(54%P2Oj)
FE
; CO
EO TANK
EVAPORATOR
RECYCLE
TANK
f *
rated
ocid
1
\. ,
p*
i
i
. ./
Vapors
Freih
end
recycle
acid
Hr-
c
— T~" ^ L. •
r
d
.OOLIN:
TAN*
f~
C03i<
To ejectors
BAROMETRIC
CONDENSER
?SiF4, HF
Hot V.CH
r^iF/i. HF
«~» i Water
= C_| — . i coolant.
C ci'
ml Superphosphoric
Superphosphoric discharge
ocid (68-72%P2OsJ
Ftqure 3-2. Stauffer Superphosphoric acid process.
3-7
-------
CO
I
CO
PHOSPHORIC
ACID-
J PR
AMMHK.T- CT UP TO AIR POLLUTION
_ AMMONIA.JjF^, _H£ „ CONTROL SYSTEM
AMMONIA, PARTICULATE, SiF^ HF ^
GRANULATOR
DRYER
CYCLONES
COOLER
CYCLONES
rVf
_N
! 1 "
DRYER
I 1
4J>
AMMONIA PRENEUTRALIZER
FEED -^
PARTICULATE
OVERSIZE
MILL
. t
COOLER
PRODUCT
Figure 3-3. TVA diammonium phosphate process.
-------
fines. Ammoniation to the required mole ratio of 2.0 takes place in the
granulator by injecting ammonia under the rolling bed of solids. It is
necessary to feed excess ammonia to the granulator to achieve a 2.0 mole
ratio. Excess ammonia and water vapor driven off by the heat of reaction
are directed to a scrubber, which uses phosphoric acid as the scrubbing
liquid. The ammonia is almost completely recovered by the phosphoric
acid scrubbing liquid and is recycled to the preneutralizer. Solidification
occurs rapidly once the mole ratio has reached 2.0, making a low solids
recycle ratio feasible.
Granulated DAP is next sent to the drier, then screened. Undersized
and crushed oversized material are recycled to the granulator. Product
sized material is cooled and sent to storage.
r
3.4 TRIPLE SUPERPHOSPHATE (TSP)
3.4.1 TSP from Phosphate Rock Treatment
Triple superphosphate (TSP), also called concentrated superphosphate,
is made from phosphate rock in the reaction:
Ca]0 (P04)6 F2 + 14H3P04 + 10H20 •* 10 CaH4(P04)2 ' H20 + 2HF
The product contains from 44-47 percent available 1*2®$'
3.4.1.1 Run-of-Pile Triple Superphosphate - Figure 3-4 is a schematic
diagram of the den process for the manufacture of run-of-pile (ROP) TSP
Phosphoric acid containing 52 - 54 percent P205 is mixed at ambient
temperature with ground phosphate rock, usually in a TVA cone mixer.
Mixing is accomplished by the swirling action of rock and acid streams
introduced simultaneously into the cone. The chemical reaction begins
during mixing.
3-9
-------
PHOSPHATE
ROCK—?
_V
PHOSPHORIC
ACIO
O CONTROLS
to
I
SIP,. PARTICULATE
Finure 3-4. Run-of-pilc triple superphosphate production and storaqe.
-------
After mixing, the slurry goes to a "den," where solidification
occurs. One of the most popular den designs is the Broadfield,
a linear horizontal slat belt conveyor mounted on rollers with a long
stationary box mounted over it and a revolving cutter at the end. The
sides of the stationary box serve as retainers for the slurry until it
sets.
The solidified slurry from the den must be cured - usually for 3
weeks or more - to allow the reactions to approach completion. Final
curing occurs during sheltered storage, illustrated in Figure 3-4.
3.4.1.2 Granular Triple Superphosphate - Granular triple superphosphate
(GTSP) is made from cured ROP TSP by treatment with water and steam in a
rotary drum, then drying and screening.
The TVA one-step granular process, shown in Figure 3-5, makes GTSP
directly. Ground phosphate rock and recycled process fines are fed into
the acidulation drum along with concentrated phosphoric acid and steam.
The use of steam helps accelerate the reaction and ensure an even distri-
bution of moisture in the mix. The mixture is discharged into the
granulator, where it solidifies, passes through a rotary cooler, and is
screened. Over-sized material is crushed and returned with undersized
material to the process.
3-11
-------
A
1
. . | RECYCLED
»nr.K — «-T
N/V;
STEAM-J
PHOSPHORIC ME/I
AGIO 1
udjb
METER I
1 *{
r
>fl
' L
1 -
1 *c
TER
I— CONO.
KD
UMP
S
r
r «
^
iom ATIO
DHUM
u
WEENS
>TEAM
C
X.
1
FINES I
1
1
1
nr
)
RANULATOR
COOLER ||
1"
^7 i
--"-•
FINE
OVERSIZE
] 1
1 ^
S _L M
ROLL
CRUSHER
r
i
•i
AGE
ILL
1
_
1
PARTICULATE
»SiFA, PARTICULATE
_ >SiF4> PARTICULATE
PRODUCT
STORA6K
Figure 3-5. TVA one-step process for qranular triple superphosphate,
3-12
-------
The Dorr-Oliver slurry granulation process also produces GTSP
directly. Ground phosphate rock is mixed with phosphoric acid (39%
PpOc) in a series of mixing tanks. A thin slurry is continuously
removed, mixed with a large quantity of dried, recycled fines in a
pugmill mixer (blunger), where it coats out on the granule surfaces and
builds up the granule size. The granules are dried, screened, and
mostly (about 80 percent) recycled back into the process. Emissions
from the drier and screening operations are sent to separate cyclones
for dust removal and collected material is returned to the process.
After manufacture, GTSP is stored for a short curing period. After
storage of usually 3 to 5 days, during which some fluorides evolve from
the storage pile, the product is .considered cured. Front-end loaders
move the GTSP to elevators or hoppers, where it is conveyed to screens
for size separation. Oversize material is rejected, pulverized, and
returned to the screen. Undersize material is returned to the GTSP
production plant. Material within specification is shipped as product.
3-13
-------
3.4.2 GTSP from Limestone Treatment
GTSP is made from limestone in the reaction
2 H3P04 + CaC03 -»• CaH4(P04)2 ' H20 + C02
The product contains 45 to 50% available P2°5-
Dilute, 22-38% P205 phosphoric acid and limestone are reacted in
an agitated vessel system. Fines from the granulation circuit can be
added, and reacted slurry can be recycled to disperse the reactants.
The final slurry goes to a granulator, where pellets are formed and then
dried and screened. The reaction appears complete in the liquid phase,
and the resultant stable granulator product does not continue to emit
fluorides. The only fluoride entering this process is that contained
in the WPPA fed.
3.5 PHOSPHATE ROCK DRYING AND GRINDING
/
Wet rock from mining and beneficiation contains from 7 to 20 percent
moisture. Some customer contracts require 3 percent maximum moisture.
Rock is dried to comply with that requirement. The two types of dryers
used in the field are rotary and fluid bed dryers. The rotary dryers
are inclined parallel flow units equipped with steel lifting flights,
and are 2.1 or 2.4 meters (7 or 8 feet) in diameter. The fluid bed
dryers operate by passing hot gases up through a perforated grating,
which agitates and dries the rock. The dryers are primarily fired by
oil, but use natural gas on standby service. The rock is discharged
from the dryers at a temperature range of 100°C (212°F) to 140°C (284°F)
o
onto conveyor belts feeding dry storage bins.
3-14
-------
Some phosphate rock is pulverized at the mines and shipped to the
customer ready for acidulation. To accomplish this, the rock is conveyed
to the grinder after it has been dried. There, it is ground, then
conveyed to the storage bin or loaded directly into the car. Some
phosphate rock is also pulverized for direct soil application, to a
fineness of 85 percent less than 0.07 millimeter (0.003 inch) particle
size. This rock is bulk-loaded into cars, or is conveyed to a machine
o
where it is bagged, normally in 45-kilogram (100-pound) bags.
Drying is often eliminated. Rock, containing 6 to 20% moisture, is
transported from the beneficiation plant to the chemical plant where it
910
is ground and chemically processed wet. '
3.6 PRODUCTION PROCESS CHANGES SINCE NSPS PUBLICATION
.-
3.6.1 Production Processes in Use at Time of NSPS Publication
When the present NSPS was published in August 1975, WPPA was made
by dihydrate processes, SPA by submerged combustion or vacuum evaporation,
DAP by the TVA and similar processes, run-of-pile TSP by phosphate rock
treatment with phosphoric acid in the den process, and GTSP by treatment
of run-of-p1le TSP and by phosphate rock treatments with phosphoric acid
that produce GTSP directly.12
3.6.2 Production Process Changes in the U.S.
In the U.S., there has been no substantial change in commercial
production of WPPA, SPA, DAP, and run-of-pile TSP since NSPS
publication.13"30
The production of GTSP by treating limestone with phosphoric acid
is a new process introduced by the J.R. Simplot Co. at its Pocatello,
Idaho plant.
3-15
-------
The elimination of phosphate rock drying by wet-rock grinding,
prior to chemical processing is an important change of production
practice. Wet-rock grinding facilities are in full-scale operation in
phosphoric acid plants at the Plant City complex of C.F. Industries
(Florida)» at Agrico Chemical's Faustina (Louisiana) facility, and at
Q
both the old and new plants of W.R. Grace's Bartow complex (Florida).
IMC is also converting its dry-rock grinding operations to wet grinding
32
at its New Wales phosphate chemicals complex (Florida).
There have been no reports of commercial WPPA production by hemihydrate
or hemidihydrate (HDH) processes in the United States; however, the
Heyward-Robinson Company of New York is now marketing the hemihydrate
33
process developed by Nisson Chemicals of Japan. Occidental Research
Corporation claims development of a proprietary method to make WPPA by
the hemihydrate process. Also, TVA has demonstrated pilot plant
4
35
production of WPPA by its "hemihydrate foam" process.
3.6.3 Production Process Changes Outside the U.S.
A commercial plant using the HDH process, developed by Fisons Ltd.
in the United Kingdom (UK), is now producing WPPA in Trepca, Yugoslavia.
The plant was designed and built by Lurgi Chemie and Huettentechnik GmbH
of West Germany. A similar plant for Albright & Wilson at Whitehaven,
2
UK, is under construction. HDH plants are also in commercial use in
oo oc
Japan. The HDH process has been used commercially since 1974. '
3-16
-------
3.6.4 Discussion of Limestone Treatment (Simplot) Process for GTSP Production
In the Simplot process, when H-PO, in WPPA is reacted with CaCO^ to
make GTSP, fluorides are present only in the WPPA. Thus the only fluorides
that might be emitted are the residual fluorides (H2SiF6 or HF and SiF4)
in the WPPA.
In the old GTSP process, when fluorapatite (Ca(P04)gF2) in phosphate
rock is reacted with H^PO,, the fluorides present are comprised of both
the fluorapatite fluoride content and the WPPA residual fluorides.
It follows from the above that the new Simplot process would emit
much less fluoride (uncontrolled) than the old GTSP process, for each
mole of monocalcium phosphate (CaHJPOJg ' H20) in GTSP produced.
However, the phosphate content of each CaH4(P04)2 * 2H20 molecule,
produced in either process, is derived, ultimately, from fluorapatite.
Therefore, the emittable fluorides from the total processing of fluorapa-
tite to make one mole of CaH.(P(h)2 ' H20 is the same regardless of
whether the old process or the Simplot process is used. Potential
fluoride emissions from the Simplot process are lower only in the
absence of the WPPA plant.
The Simplot process provides a means of reducing local fluoride
emissions at the plant where it is applied. Fluorapatite is not used as
a feed material, so this fluoride source is eliminated. Excess limestone
can also be fed to precipitate the fluoride in the WPPA as insoluble
calcium fluoride (CaF«). In contrast, the old process emits more fluorides
which require more scrubbing water and therefore larger pond areas. The
amount and complexity of emission control equipment is reduced by the
Simplot process. The company has found that the only gas cleaning
3-17
-------
devices necessary are a scrubber on the dryer and conventional (uncoated)
38
baghouses on other system components, e.g. screens and elevators.
Results of the NSPS compliance test at the Simplot plant showed
31
average emissions of 0.187 Ib F (fluoride)/ton P205 fed. The require-
ment for NSPS compliance in GTSP production is 0.20 Ib F/ton P205 fed.
3.6.5 Discussion of Wet-Rock Grinding
Drying and grinding of phosphate rock can cause particulate emissions
to the atmosphere. The particles can escape as dust if dryer gases are
uncontrolled, as well as during grinding, especially if the materials
are very dry. Dust can also be a significant problem at each point of
transfer of the materials. The size of the dry, ground phosphate rock
39
particle is less than 0.07 millimeter (0.003 inch).
The world's primary phosphate occurrences are of sedimentary origin
and contain radioactive materials, predominantly uranium and its decay
/
products. Uranium, along with a very small amount of thorium, is thought
to have been deposited contemporaneously with the phosphate. Phosphate
rock in central Florida contains uranium concentrations of between 0.01
and 0.02 percent; despite the fact that uranium ore mined in the western
United States solely for its uranium content contains 10 to 20 times
this concentration, the phosphate industry currently mines slightly more
40
total uranium than does the uranium industry.
3-18
-------
Under the Environmental Impact Statement for the Central Florida
Phosphate Industry, proposed action will eliminate rock drying with
certain exceptions where approved dryers will be used. This will decrease
sulfur dioxide (SCL) and dust emissions in Polk County caused by drying,
grinding, and transportation as mines in that county are depleted and
new mines are opened elsewhere. Since the new mines will ship wet rock,
an estimated 1140 metric (1250 short) tons per year of dust and 7090
metric (7800 short) tons per year of S0? emissions from dryers in Polk
County will not migrate into adjoining areas. The emissions from existing
41
rock drying will decrease as the dryers are phased out.
Reduction in radiation levels will occur as dry-rock grinding is
replaced with wet-rock grinding and dryers are eliminated. This will
lower fugitive dust levels, thus lowering escaping radionuclides, and
also result in lower radiation levels in the immediate vicinity of the
41
grinders and the eliminated dryers.
Wet-rock grinding has four advantages:
(1) Reduces by about half the capital expense - from receipt of
unground wet rock through the point of feeding it into the
42
acid processing system.
42
(2) Eliminates dry-rock dust pollution.
(3) Improves fuel economy by 2.5 gallons per ton of phosphate rock
ground, which combines with electrical power savings'to reduce
4?
operating costs by $3.00-$4.25 per ton of Po°5'
(4) Improves reliability, thus, reducing the required amount of
surge of ground rock. If a plant is located near a mine, a rock
slurry can be pumped directly to the plant from the mine,
42
eliminating rail transportation and belt conveyors.
3-19
-------
By converting from dry to wet grinding, IMC expects to save 8
million gallons of fuel oil and 18 million kWh of electricity per year
in producing WPPA at its New Wales complex. Conversion will cost about
$11.3 million.32
3.6.6 Discussion of Hemihydrate (Hemidihydrate) Processes for WPPA Production
Solutions to three WPPA production problems are claimed for the
two-stage HDH process: (1) energy consumption, (2) gypsum disposal, and
2
(3) fluoride emission.
Energy consumption is reduced by avoiding the need for evaporative
2
concentration of product acid.
The gypsum produced is reported to be of sufficient purity for use
2
in building material. Gypsum from conventional dihydrate processes
cannot be so used because of its radioactivity level.
Fluoride emissions are controlled by recovery reported to be greater
/
than 99% in a co-installed, on-line system. The recovered fluorides may
be concentrated to 20 to 24% H2SiFg.2
Capital cost savings are reported for the HDH process (compared
with the dihydrate process) in rock grinding, steam used for acid concen-
tration, weak acid intermediate storage, and product acid clarification.
These savings are partially offset by a larger reaction volume and
filter area requirement. The capital cost for recrystallization and
dihydrate filtration approximately equals that for acid concentration in
dihydrate processes. An overall 5 to 10% capital cost reduction for the
HDH process, compared with dihydrate processes, has been reported.
Operating costs are also reported lower for the HDH process, mainly
2
because of P205 recovery exceeding 98%, and low steam consumption.
3-20
-------
In the HDH process, recrystallization depends largely on phosphate
rock composition. Morocco rock is used at the Trepco, Yugoslavia,
plant. The planned Whitehaven, UK, plant is designed to use Morocco
rock, but is reported capable of processing other rocks such as Florida
2
rock.
Reasons given for not using HDH processes in the U.S. include:
1. Uranium recovery is practiced by many plants in the U.S.,
and is reported to be greater from the more dilute phosphoric
acid produced in dihydrate processes. About 1 Ib uranium/ton
P^Og is recoverable. At about $40 per pound of uranium, it
is more economical to use the current dihydrate process,
recover the uranium, and finally concentrate the acid from
28 percent.43
2. Florida rock is not of sufficiently high quality to allow its
use.36
3. Problems are encountered in the filtration operation when using
Florida rock.
4. The relatively large amount of clay fines and other impurities
36
make this process difficult to control.
3.7 STATUS OF POTENTIAL REGULATION OF RADIOACTIVE EMISSIONS FROM PHOSPHATE
PLANTS UNDER THE CLEAN AIR ACT
The Office of Radiation Programs (ORP) of EPA has been assigned the
responsibility for potential standards for radioactive emissions. ORP
has furnished the following information regarding the status of that
45
work as it relates to phosphate plants.
3-21
-------
"Phosphate ore deposits contain radioactive materials primarily in
the form of uranium-238 and its decay products. The concentrations of
these radioactive materials in phosphate ores range up to 100 times
greater than the concentrations of these materials in normal soils and
rocks. Therefore, the mining and processing of phosphate ore has the
potential for releasing quantities of radioactive materials into the
atmosphere which may be of public health concern.
"The Environmental Protection Agency, as required by Section 122 of
the Clean Air Act as amended in 1977, is presently reviewing available
information to determine whether emissions of radioactive materials into
the environment will cause or contribute to air pollution which may
reasonably be anticipated to endanger public health. If the Agency makes
a positive determination, then radioactive materials most probably will
be listed as hazardous pollutants under Section 112 of the Clean Air Act
and emission standards established for sources emitting important
quantities of radioactive materials.
"Studies are now in progress to assess the health impact from
emissions of radioactive materials from phosphate processing activities.
These studies include development of information on the emission levels,
pathways of human exposure and health risks to the exposed populations.
The results of these studies will be evaluated to determine if a need
exists to establish standards under Section 112 of the Clean Air Act for
phosphate processing plants. Some preliminary results of these studies
have already been published in the following EPA reports:
(1) "Radiation Dose Estimates Due to Air Particulates
Emissions from Selected Phosphate Industry Operations,"
Technical Note, ORP/EERF-78-1, June 1978.
3-22
-------
(2) Radiological Surveys of Idaho Phosphate Ore Processing
the Thermal Process Plant, Technical Note, ORP/LV-73-3,
November 1977.
(3) Radiological Surveys of Idaho Phosphate Ore Processing
the Wet Process Plant - Technical Note, ORP/LV-78-1,
April 1978."
3-23
-------
3.8 REFERENCES FOR SECTION 3.
1. Final Guidelines Document: Control of Fluoride Emissions from
Existing Phosphate Fertilizer Plants. U.S. EPA. Research Triangle Park, N.C.
Publication No. EPA-450/2-77-005. March 1977. pp. 4-3 to 4-10.
2. Blumrich, W.E., H.J. Koening, and E.W. Schwehr. The Fisons HDH
Phosphoric Acid Process. Chemical Engineering Progress. 74_: 58-61. Nov. 1978.
3. Slack, A.V. Fertilizers. Kirk-Othmer Encyclopedia of Chemical
Technology, 2nd edition, Vol. 9, Stanton A. ed. New York, John Wiley
& Sons. 1966. p. 93.
4. Reference 1. pp. 4-11 to 4-17.
5. Reference 1. pp. 4-17 to 4-20.
6. Reference 1. pp. 4-21 to 4-28.
7. U.S. Patent. Direct Granulation Process for Triple Superphosphate.
Assignee: J.R. Simplot Co. No. 4,101,637. July 18, 1978.
8. Central Floride Phosphate Industry Areawide Impact Assessment Program,
Vol. 1: Description of Program and Industry. U.S. EPA Region 4. Atlanta, GA.
Project No. 08-01-4196. Sept. 1978. pp. 25-26.
9. Environmental Impact Statement, Central Florida Phosphate Industry,
Vol. 1. U.S. EPA Region 4. Atlanta, GA. Publication No. EPA 904/9-78-026a.
Nov. 1978. p. 2.1.
10. Environmental Impact Statement, Central Florida Phosphate Industry,
Vol. 2. U.S. EPA Region 4. Atlanta, GA. Publication No. EPA 904/9-78-026b.
Nov. 1978. p. 2.21
11. Federal Register. Volume 40, p. 33152.
12. Reference 1. pp. 4-1 to 4-30.
13. Telecon. W. Herring, U.S. EPA OAQPS, to W. Aronson, U.S. EPA
Region 4. April 17, 1979. Subject: Phosphate Industry in Region 4.
14. Letter from K.T. Johnson, The Fertilizer Institute, to W.O. Herring,
U.S. EPA. April 18, 1979. Subject: Phosphate Industry in U.S.
15. Telecon. W. Herring to G. McNeil!, U.-S. EPA Region 4.
April 18, 1979. Subject: Phosphate Industry in Region 4.
16. Telecon. W. Herring to Derr Leonhardt, State of N.C.
April 20, 1979. Subject: Phosphate Industry in N.C.
17. Telecon. J. Rom, U.S. EPA Region 4, to W. Herring. April 23, 1979.
Subject: Phosphate Industry in Region 4.
3-2'4
-------
18. Telecon. W. Herring to J. Symes, State of Florida.
April 23, 1979. Subject: Phosphate Industry in Florida.
19. Telecon. W. Herring to J. Pfander, U.S. EPA Region 10.
May 21, 1979. Subject: Phosphate Industry in Region 10.
20. Telecon. W. Herring to R. Stenner, State of Idaho.
April 19, 1979. Subject: Phosphate Industry in Idaho.
21. Telecon. W. Herring to B. Varner, U.S. EPA Region 5.
April 24, 1979. Subject: Phosphate Industry in Region 5.
22. Telecon. W. Herring to L. Szempruch, U.S. EPA Region 5.
April 24, 1979. Subject: Phosphate Industry in Region 5.
23. Telecon. W. Herring to J. Reed, State of Illinois.
April 24, 1979. Subject: Phosphate Industry in Illinois.
24. Telecon. W. Herring to J. Hepola, U.S. EPA Region 6.
May 21, 1979. Subject: Phosphate Industry in Region 6.
25. Telecon. W. Herring to S. Spruiell, U.S. EPA Region 6.
June 5, 1979. Subject: Phosphate Industry in Region 6.
/
26. Telecon. G. Wallin, State of Texas, to W. Herring.
April 30, 1979. Subject: Phosphate Industry in Texas.
27. Telecon. W. Herring to 0. Tanner, State of Louisiana.
May 1, 1979. Subject: Phosphate Industry in Louisiana.
28. Telecon. W. Herring to F. Collins, U.S. EPA Region 4.
May 21, 1979. Subject: Phosphate Industry in Region 4.
29. Telecon. W. Herring to B. Swan, U.S. EPA Region 10.
May 21, 1979. Subject: Phosphate Industry in Region 10.
30. Telecon. M. Johnson, U.S. EPA Region 10. May 22, 1979.
Subject: Phosphate Industry in Region 10.
31. Letter and attachments from J.F. Cochrane, J.R. Simplot Co.,
to D.P. Dubois, EPA Region 10. Dec. 30, 1977. Subject: TSP Performance Test.
32. Phosphate Process Saves on Energy. Chemical Marketing Reporter.
pp. 4,27. Sept. 11, 1978.
33. Phosphoric Acid Process Cuts Costs. The Journal of Commerce.
p. 5. Dec. 22, 1978.
34. Farm Chemicals, p. 138. Jan. 1979.
3-25
-------
35. TVA Displays Energy-Saving Phosphoric Acid Process. Chemical
& Engineering News. pp. 32, 38-41. Nov. 13, 1978.
36. Linero, A.A. and R. A. Baker. Evaluation of Emissions and
Control Techniques for Reducing Fluoride Emissions from Gypsum Ponds in
the Phosphoric Acid Industry. U.S. EPA. Washington, D.C. Publication No.
EPA-600/2-78-124. June 1978. pp. 193-200.
37. ' Memo from G.B. Crane, EPA OAQPS, to S.T. Cuffe, EPA OAQPS. April 30,
1979. Subject: Phosphate Fertilizer NSPS Review. New Low Emission
Process for GTSP.
38. Telecon. W. Herring to J. Smith, J.R. Simplot Co.
April 25, 1979. Subject: Simplot GTSP process.
39. Reference 8. p. 35.
40. Reference 10. pp. 1.48-1.50.
41. Reference 9. pp. 21., 3.1, 3.8.
42. Reference 10. p. 2.21.
43. Telecon. G.B. Crane, U.S. EPA OAQPS, to E. Wyatt and
D. Leyshon, Jacobs Engineering Group. April 17, 1979. Subject: Phosphate
Fertilizer Industry.
44. Telecon. W. Herring to A. Richardson, EPA Office of Radiation
Programs. June 6, 1979. Subject: Radioactive Emissions.
45. Memo from P.J. Magno, EPA (ORP) to G.B. Crane, EPA (OAQPS).
June 20, 1979. Subject: Regulation of Radioactive Emissions from
Phosphate Plants.
3-26
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4. FLUORIDE EMISSION CONTROL CHANGES
4.1 CONTROL SYSTEMS PREVIOUSLY AVAILABLE
Systems available to control fluoride emissions (hydrogen fluoride
(HF) and silicon tetrafluoride (SiFj), when the NSPS for phosphate
plants was published in August 1975, consisted of scrubbers. Gypsum
pond or coolinq pond water was used as scrubbing media. Spent scrubbing
water was returned to the plant pond system without chemical treatment.
The spray-crossflow packed bed scrubber, shown in Figure 4-1, was
generally used in the more effective scrubbing systems. A venturi
scrubber was used in series with and before the spray-crossflow packed
bed unit for gas streams having high solids content, and where solids
might precipitate from scrubbing solution, as in granulated triple
superphosphate (GTSP) and diammonium phosphate (DAP) processes.
r
The spray-crossflow packed bed scrubber consists of two sections -
a spray chamber and a packed bed - separated by a series of irrigated
baffles. Both the spray and the packed sections are equipped with a gas
inlet. Effluent streams with relatively high fluoride concentrations -
particularly those rich in SiF^ - are treated in the spray chamber
before entering the packing. This preliminary scrubbing removes SiF^
thereby reducing the danger of plugging the bed. At the same time, it
reduces the loading on the packed stage and provides some solids handling
capacity. Gases low in SiF^ can be introduced directly to the packed
section.
The spray section accounts for approximately 40 to 50 percent of
the total length of the scrubber. It consists of a series of counter-
current spray manifolds with each pair of spray manifolds followed by a
system of irrigated baffles. The irrigated baffles remove precipitated
silica and prevent the formation of scale in the spray chamber.
4-1
-------
GAS INLET
ro
POND WATER
to
LJJ
CD
Q
LU
SECONDARY
GAS INLET
GAS FLOW
FIGURE 4-1. SPRAY-CROSSFLOH PACKED BED SCRUBBER.
-------
In spray-crossflow packed bed scrubbers the gas stream moves hori-
zontally through the bed while the scrubbing liquid flows vertically
through the packing. Solids tend to deposit near the front of the bed
where they can be washed off by a cleaning spray. This design also
allows the use of a higher, irrigation rate at the front of the bed to
aid in solids removal. The back portion of the bed is usually operated
dry to provide mist elimination.
Pressure loss through the scrubber is usually 4 to 6 inches of
water. Filters in the water lines ahead of the spray nozzles prevent
/
plugging by suspended solids. The ratio of scrubbing liquid to gas
ranges from 0.02 to 0.07 gpm/acfm depending upon the fluoride content -
especially the SiF^ content - of the gas stream. Approximately one
third of this water is used in the spray section while the remaining
two thirds is used in the packing.
The packed bed is designed for a scrubbing liquid inlet pressure of
about 4 or 5 pounds per square inch (gauge). Water at this pressure is
available from the pond water recycle system. The spray section requires
an inlet pressure of 20 to 30 pounds per square inch (gauge). This
normally requires the use of a booster pump. Spent scrubbing water is
collected in a sump at the bottom of the scrubber and pumped to a
pond.
4.2 NEW CONTROL SYSTEMS
Since NSPS publication, scrubbers have remained the principal means
of controlling fluoride emissions from phosphate plants. A few
modifications of scrubbing system design have been introduced. These
involve scrubbing to recover fluorides as saleable fluosilisic acid
) byproduct, and removing the remaining fluorides from the gas
4-3
-------
by scrubbing with water that is cooled in closed-loop, cooling tower
14-19
systems. In some of these systems, scrubbing water is caustic
treated, and a slip stream is limed to precipitate the fluoride as CaF2
and regenerate the caustic.
One phosphate production process modification has been introduced
since NSPS publication, as a means of controlling fluoride emissions.
That modification consists of making GTSP by treating limestone, instead
of phosphate rock, with wet process phosphoric acid (WPPA). This process
and its emissions were described in Section 3, PRODUCTION PROCESS
CHANGES.
A modification of phosphate rock processing has been introduced.
Emissions, including radioactive constituents, evolved during rock
drying and grinding, are reduced by eliminating drying and by grinding
the rock wet. This modification was also described in Section 3.
4.2.1 Modified Scrubbing Systems for WPPA and TSP Production
A modified scrubbing system is used at one plant complex in Mississippi
to control fluoride emissions from WPPA and triple superphosphate (TSP)
production.
In the WPPA process at this plant complex, gases from the phosphate
rock acidulation reactor are treated in a spray-crossflow packed bed
scrubber to collect fluorides. Water from gypsum pond overflow is used
as the scrubbing medium. Gases from the reactor vacuum cooler and from
four vacuum evaporators used for acid concentration go to a series of
low-pressure-drop cascade scrubbers. Each cascade scrubber receives gas
from one vacuum cooler or evaporator. The scrubbing water from the
reactor scrubber is used in the cascade scrubbers, removing additional
4-4
-------
fluoride from the gases in each, finally leaving the scrubber train as
byproduct 23% H2SiFg. To avoid deposition of gelatinous Si(OH)4, which
might plug equipment, the arrangement of gas and liquid streams flowing
to each cascade scrubber must be in an order that effects a satisfactory
F/Si ratio in the scrubbing liquid. This system is reported to recover
99% of the gaseous fluorides emitted during acidulation and acid concen-
tration as saleable H2$iF6.14"18
Gases from each cascade scrubber go to one of the series of plant
barometric condensers where the remaining fluorides are collected. The
water from the barometric condensers, at pH 3-3.5 and 120°F, goes to a
cooling tower where sodium hydroxide (NaOH) is added to the stream to
increase its pH to greater than 4, reduce fluoride vapor pressure, and
prevent fluoride emissions from the tower. Make-up water is also added.
The resulting liquid stream leaves the cooling tower at 90°F, then
returns to the barometric condensers, forming a closed loop. A slip
stream from the cooling tower is treated with calcium hydroxide (CaCOH^)
to obtain pH 11.5-12 and precipitate the fluorides in a crystalline
product composed of fluoride and silicate salts of calcium. This product
is presently landfilled but has potential use as glass raw material.
Fluorides emitted from TSP production and storage facilities at
the above plant complex are also collected in scrubbers. The TSP
scrubbing system is incorporated as a portion of the WPPA closed-loop
20
cooling tower system. Quantities of fluoride emissions from TSP
production are smaller than those from WPPA production; and emissions
from production of both products can be handled compatably since they
are derived from the same basic raw materials and therefore, consist of
similar constituents.
4-5
-------
In addition to the use of cooling towers with caustic treatment of
water, as just described, cooling towers are used or planned for use at
several other phosphate plants in closed-loop water handling systems,
but without any reported water treatment to reduce fluoride vapor pressure.
In some of these systems, process gas is treated in Swift spray-chamber
19
scrubbers' to recover fluoride as byproduct HSiF. In the usual plant
arrangement, the Swift scrubbers are positioned between the acid-concen-
tration vacuum evaporators and the barometric condensers, and provide 65
18 19
to 90% fluoride recovery. ' In at least one plant, the process gas
is not treated to recover fluorides prior to final scrubbing; and the
resulting scrubbing water is cooled in a closed-loop cooling tower
21
without caustic treatment.
4.2.2 Modified Scrubbing System for DAP Production
A modified scrubbing system is used to control fluoride emissions
from DAP production at three NPK (nitrogen, phosphorous, potassium mixed
15
fertilizer) plants at the previously mentioned Mississippi plant complex.
Gases from the preneutralizer and granulator first go to a venturi
scrubber where most of the ammonia (NH3) in the gas is absorbed in
dilute phosphoric acid. Residual ammonia leaves the venturi, in the
outlet gas, as gaseous NH3 or as submicron particulate ammonium fluoride
(NH4F) or ammonium bi fluoride (NH4F*HF). Phosphoric acid might be
•I r -i p
contained in the venturi outlet gas in entrained liquid particles.
The gas from the venturi goes to the first stage (nitrogen-phosphorous
removal section) of a two-stage spray-crossflow packed bed scrubber
where residual ammonia and phosphates are removed in additional dilute
phosphoric acid scrubbing liquid. '
4-6
-------
The scrubbing solution leaving the venturi and the spray-crossflow
packed bed first stage goes to the sump of the venturi scrubber. It is
treated with make-up dilute phosphoric acid and then recycled to both the
venturi and the spray-crossflow packed bed first-stage scrubbers.
Another stream from the venturi sump returns part of the solution to the
DAP process in the preneutralizer feed stream, to recover the NH3 and
phosphates.16'17
The remaining fluorides in the exit gas from the spray-crossflow
packed bed scrubber first stage are removed in the second stage of that
scrubber. The scrubbing water for the second stage is cooled in a
cooling tower and treated with NaOH in a closed-loop system to increase
its pH and limit fluoride emissions from the tower. A slip stream of
water from the tower is limed to precipitate the fluoride and regenerate
the NaOH.15'16'17
Gases from the DAP dryer are treated in a scrubbing system similar
to that just described for the DAP preneutralizer and granulator gases.
Gases from the cooler may also be similarly treated or might be sent to
the inlet of the spray-crossflow packed bed scrubber treating the DAP
dryer gas, thus being treated as a part of that gas stream.
The system for handling gas from DAP production, including the
cooling tower, is segregated from that used for WPPA and TSP process
20
gases to keep nitrogen compounds out of the WPPA-TSP system.
4.2.3 Discussion of the Modified Scrubbing Systems
By employing NaOH to increase the pH of scrubbing solution and
reduce fluoride vapor pressure, modified scrubbing systems provide for a
potential fluoride emission reduction estimated as much as 75% below
18
present achievement levels. Maintenance problems, however, are reported
4-7
-------
to restrict scrubbing efficiency. Applicable standards are met when
packed beds are in good order, but maintaining that condition is reported
to be difficult.20
A plant representative states that the system has not yet been
perfected. Refinements are still being made, and more time is needed to
develop improved utilization of the system. Packed beds become clogged.
Various types of packing and washing techniques are being tried to over-
come clogging. Deterioration of rubber scrubber lining has necessitated
relining in less than one year of usage. Some lined components have had
to be replaced with stainless steel. Maintaining service is generally
20
difficult because of corrosion of steel parts.
The closed-loop scrubbing system, employing cooling towers and
alkali water treatment, was installed mainly to improve water utilization
and prevent water pollution. This purpose has been met satisfactorily.
Because of high rainfall in its Mississippi location, the plant complex
cannot use all of the water that falls on its property. The plant
gypsum pond system collects the rain water, and pond overflow feeds all
20
plant processes. Any excess water must be treated before release.
The plant land area is too limited to .provide for cooling ponds of
sufficient size to accept the cooling duty for the WPPA and TSP processes.
The closed-loop system avoids the unacceptable alternative of taking
water into the plant from the nearby bayou, using it for scrubbing, then
20
returning it to the bayou. It also reduces the total amount of plant
water that must be treated before leaving the plant.
By eliminating the cooling pond, the closed-loop scrubbing system
with alkali treatment is estimated to reduce plant pond area and fluoride
emissions from the ponds by at least 50%.14'17'18
4-8
-------
Phosphate plants converting from cooling ponds to cooling towers
are located in Louisiana. As in the Mississippi plant complex just
discussed, rain added to water from plant processes causes water levels
in ponds to increase. Therefore, water must be recycled for disposal.
Cooling towers effect evaporative cooling, while pond cooling is largely
19
by convection. Thus, cooling towers appear advantageous for reducing
quantities of water that must be handled in recycling and disposal.
They seem, therefore, to be coming into increased use in states with
high rainfall.
4-9
-------
4.3 REFERENCES FOR SECTION 4.
1. Final Guidelines Document: Control of Fluoride Emissions from
Existing Phosphate Fertilizer Plants. U.S. EPA. Research Triangle Park,
N.C. Publication No. EPA-450/2-77-005. March 1977. pp. 6-1 to 6-87.
2. Pflaum, C.A. Practical Design of Cross-flow Scrubbers in the
Phosphate Industry. International Minerals & Chemical Corp. Tampa, FL.
(The Fertilizer Institute Environmental Symposium. Washington.
March 8, 1978.) 11 p.
3. Letter from K.T. Johnson, The Fertilizer Institute, to W.O. Herring,
U.S. EPA. April 18, 1979. Subject: Phosphate Industry in U.S.
4. Telecon. G.B. Crane, U.S. EPA OAQPS, to E. Wyatt and D.Leyshon,
Jacobs Engineering Group. April 17, 1979. Subject: Phosphate Fertilizer
Industry.
5. Telecon. W. Herring, U.S. EPA OAQPS, to W. Aronson, U.S. EPA
Region 4. April 17, 1979. Subject: Phosphate Industry in Region 4.
6. Telecon. W. Herring to G. McNeill, U.S. EPA Region 4.
April 18, 1979. Subject: Phosphate Industry in Region 4.
7. Telecon. W. Herring to Derr Leonhardt, State of N.C.
April 20, 1979. Subject: Phosphate Industry in N.C.
8. Telecon. J. Rom, U.S. EPA Region 4, to W. Herring.
April 23, 1979. Subject: Phosphate Industry in Region 4.
9. Telecon. W. Herring to J. Symes, State of Florida.
April 23, 1979. Subject: Phosphate Industry in Florida.
10. Telecon. W. Herring to R. Stenner, State of Idaho.
April 19, 1979. Subject: Phosphate Industry in Idaho.
11. Telecon. W. Herring to J. Reed, State of Illinois.
April 24, 1979. Subject: Phosphate Industry in Illinois.
12. Telecon. G. Wall in, State of Texas, to W. Herring.
April 30, 1979. Subject: Phosphate Industry in Texas.
13. Telecon. W. Herring to 0. Tanner, State of Louisiana.
May 1, 1979. Subject: Phosphate Industry in Louisiana.
14. Telecon. G.B. Crane and W. Herring to A.J. Teller, Teller
Environmental Systems, Inc., May 14, 1979. Subject: Review of Phosphate
Fertilizer NSPS.
15. Plant Closes Loop on its Wastewater Treatment. Environmental
Science & Technology. ]2: 260-263. March 1978.
4-10
-------
16. Teller, A.J. New Technologies in Fertilizer Emission Control.
Teller Environmental Systems, Inc. Worcester, MA. (Meeting, Central
Florida Section, American Institute of Chemical Engineers. Daytona.
May 14-16, 1976.) 11 p.
17. Teller, A.J. New Technologies in Control of Fertilizer Plant
Emissions, Pond Control - Fluoride Products. (Meeting, Fertilizer
Round Table. Nov. 1975.) 25 p.
18. Teller, A.J. Scrubbers in the Fertilizer Industry, Their
Success, Near Future, And Eventual Replacement. (Meeting, Fertilizer
Round Table. Washington. Nov. 1973.) pp. 150-158.
19. Telecon. J. Dehn, EPA Region 6, to W. Herring. April 27. 1979.
Subject: Phosphate Industry in Region 6.
20. Telecon. W. Herring to A. Gentry, Mississippi Chemicals Co.,
May 16, 1979. Subject: Emission Control at Pascagoula Plant.
21. Telecon. W. Herring to J. Murray, 01 in Co. July 27, 1979.
Subject: Emission Control at 01 in Co. Plant.
4-11
-------
5. ADVANCES IN GYPSUM POND FLUORIDE CONTROL
5.1 PREVIOUS OPERATION AND CONSTRUCTION OF POND SYSTEMS
When the phosphate industry NSPS was published in August 1975,
liquids entering gypsum ponds at plants in the U.S. consisted princi-
pally of rainfall plus the process streams listed below. These process
streams were formed from recycled gypsum pond water plus fluorides and
other substances generated in the processes.
5.1.1. Discharge streams from dihydrate processes making wet process
phosphoric acid (WPPA).
1. Gypsum slurry (filter cake slurried with pond water).
Approximately 2.5 pounds of gypsum are produced per pound of pure phos-
2 3
phoric acid , or 1.2 pounds of gypsum per pound of 30% phosphoric acid.
2. Liquid from barometric condensers that treat gas from (a)
the reactor vacuum cooler, and (b) the vacuum evaporators that concen-
trate the WPPA. At some plants, the gas from the WPPA evaporators might
have been treated in scrubbers for flousilisic acid (H2SiFg) recovery
prior to entering the barometric condensers.
3. Liquid discharged from the scrubber that treats gases from
the acidulation reactor, filters, hot wells, and filtrate seal tanks.
5.1.2 Superphosphoric acid (SPA) process discharge streams.
1. Liquid from the barometric condenser that treats gas from
the vacuum evaporator.
2. Liquid from heat-exchanger cooling tank.
.5-1
-------
5.1.3 Diammonium phosphate (DAP) process discharge streams.
1. Liquid from the scrubbers that treat gases from the reactor,
granulator, dryer, and cooler.
5.1.4 Run-of-pile (ROP) triple superphosphate (TSP) process discharge
streams.
1. Liquid discharged from the scrubbers that treat gases from
the mixer, den, and storage building.
5.1.5 Granular triple superphosphate (GTSP) process discharge streams.
1. Liquid discharged from the scrubbers that treat gas from
the reactor, granulator, dryer, cooler, and screens.
4
Gypsum ponds are generally dyked areas. In the past, they have
3
usually not been lined to prevent seepage. The gypsum pond serves two
purposes: (1) as a settling and storage area for waste gypsum, and (2)
as an area for cooling process water prior to reuse.
Figure 5-1 is a simplified representation of a typical gypsum pond
serving a 1000-ton/day-P205 WPPA plant. This pond, handling
both slurry and process water, would have about 350 acres of wet area.
Water depth would be about 10 feet. Most likely it would be located
adjacent to the plant and surrounded by mined-out land of sparse vegeta-
tion or swamp. Assuming that the pond is used for both gypsum settling
and cooling, there is a region where the stream from the sluicing
operation joins the pond. This area, known as the gypsum flats, is
where the gypsum settles. It is constantly worked by draglines, which
remove settled wet gypsum and transfer it onto an active gypsum pile
5-2
-------
GYPSUM PILE
rgROCESS HATEB.g-1151E.
i
en
i
CO
/
I
I
I
\
FERTILIZER
PROCESSES
f
Jp_PROCESS_
0 9~5~07
FRESH
~ MAKE-UP
WATER
DOUBLE
LIMING
t
EFFLUENT
figure 5-1. Typical gypsum pond servicing a 1000-ton/day PJD(- plant.
2U5
-------
to dry. The gypsum pile would be about 80 feet high on about 150 acres
adjacent to the wet pond.
Table 5-1 shows a fluoride material balance for WPPA production.
TABLE 5-1
TYPICAL MATERIAL BALANCE OF FLUORIDE IN MANUFACTURE
OF WET-PROCESS PHOSPHORIC ACID
BASIS: 100 LB PHOSPHATE ROCK
Fluoride-bearing
material or source Fluoride, Ib
Phosphate rock 3.9
Product wet process acid 1.0
Gypsum 1.2
Barometric condensers 1.67
Air 0.03
Total fluoride output 3.9
Fluorides in the gypsum slurry and in the water from the barometric
condensers and the scrubber that treats process emissions to air go to
the gypsum pond. It therefore follows from Table 5-1 that over 70
percent of the fluorine content of the rock used in the wet-acid process
may pass to that pond. If the same plant also produces DAP or TSP, a
large part of the fluorine content of the phosphoric acid will also pass
to the gypsum pond through the water scrubbers in these additional processes
5-4
-------
Thus, 85 percent or more of the fluorine originally present in the
phosphate rock may find its way to the gypsum pond. Fluoride associated
with the gypsum is, however, in insoluble form, probably as calcium
fluoride (CaF2), before being sent to the pond.6'7 It is believed that
fluorides from the barometric condensers are the primary source of pond
. . 8
emissions.
In gypsum ponds, approximately one acre foot of disposal volume is
4
required per year for each daily ton of PpOg produced by the plant.
Based on wet process phosphoric acid production, plants have gypsum ponds
of surface areas in the range of 0.1-0.4 acre per daily ton of P2°5-
Thus a large plant may have a gypsum pond with a surface area of 200 acres or
more.
The water of pond systems is normally acid, having a pH around 1.5.
This acidity is probably due mainly to inclusion of phosphoric acid in
the washed gypsum from the gypsum filter.
Gypsum pond water can be expected to contain from 0.2 to 1.5 percent
fluosilicic acid (2000-12,500 ppm F) or most often, 5000-6000 ppm F.
The fluosilicic acid decomposes to silicon tetrafluoride and hydrogen
fluoride, resulting in a vapor-liquid equilibrium. The fluoride concentra-
tion of a given pond does not continue rising as fluorides are added,
but tends to stabilize. This action may be due to precipitation of complex
calcium silicofluorides in the pond water.
5-5
-------
Published emission factors from gypsum ponds range from 0.2 to 10
Ib F/acre-day. Table 5-2 shows the emission factors obtained from one
comprehensive investigation.
Table 5-2 FLUORIDE EMISSION FACTORS FOR SELECTED GYPSUM PONDS AT
90°F (Ib/acre-day)
Wind velocity
at 16 ft elevation,
m/sec
Pond 10
(6,400 ppm F)
Pond 20
(12,000 ppm F)
1
0.8
0.8
2
1.3
1.3
4
2.3
2.3
6
-
3.2
The most recent measurements of fluoride emissions from gypsum
ponds indicated fluoride concentration above the pond of 18 to 46 parts
per billion (ppb), consisting almost entirely of hydrogen fluoride (HF),
as measured by the Remote Optical Sensing of Emissions (ROSE) system.
Emission rates of 0.2 to 7.3 Ib F/acre-day were indicated by concurrent
12
wet sampling and analysis.
13
Gypsum ponds also contain radioactive material. Dried areas of
14
ponds are a possible source of radioactive emissions to the atmosphere.
Radioactive emissions from phosphate plants are being investigated by
15
the Office of Radiation Programs, EPA, for possible regulation. The
status of this investigation is reported in Section 3, "PRODUCTION
PROCESS CHANGES."
5-6
-------
5.2 PRESENT OPERATION AND CONSTRUCTION OF POND SYSTEMS
Since NSPS publication, infprmation on ponds not previously reported,
including a few changes in gypsum pond operation and construction, has
been published. This information is shown below. Apart from the changes
noted, present pond operation and construction is the same as described
above.
5.2.1 Treatment of Pond Water for Discharge
When rainfall exceeds evaporation, water is discharged from the
5
pond. This water has been treated prior to entering a natural water course.
Successful treatment of discharges has been demonstrated by the use of a
two-stage process; in the first stage the discharge passes through
limestone (calcium carbonate), which effectively increases the pH to
approximately 4.5 and in the second stage hydrated lime in used to
increase the pH to more than 7. This process reduces fluoride to less
than 10 milligrams per liter, phosphate to approximately 30 milligrams
o
per liter and radium to less than 1 picocurie per liter.
5.2.2 Pond Lining
The Environmental Impact Statement (EIS) for the Central Florida
Phosphate Industry includes the proposed requirement:
"Line gypsum ponds with an impervious material unless it can be
demonstrated in the site-specific EIS that such lining is unnecessary in
protecting ground water from chemical and radiological contamination."
Since Florida plants account for most WPPA production capacity in
the U.S., and would, therefore, have the majority of gypsum ponds, most
new ponds constructed in the U.S. will probably have impervious linings.
5-7
-------
5.2.3 Pond Area Reduction by Cooling Towers and Fluoride Recovery
Phosphoric acid plants utilize a wide variety of gypsum cooling
pond arrangements. In most cases process and gypsum sluicing waters are
transported to a common pond allowing these waters - which are vastly
different in properties to mix, with the ultimate result that both
process and gypsum pond waters become highly contaminated with phos-
phoric acid, h^SCL, and hLSiF,-.
In some cases, separate cooling and gypsum ponds are utilized. All
process waters except gypsum sluicing water are sent to cooling ponds.
Gypsum slurry is pumped from the filtration operation to a gypsum pile
where the gypsum settles. The supernatant water is subsequently re-
cycled through the cooling pond, thus contaminating it with phosphoric
acid, HLSO,, and fluorides from the filtered gypsum.
The required size of the gypsum slurry pond is small (about 5
acres) since no area is required for cooling. This water would be the
most contaminated and acidic water in the plant because of the presence
of phosphoric acid, H^SO,, iron and aluminum complexes, and fluorides
from the filtration operation.
The pond area required for the barometric condensers is determined
by the cooling duty requirements. This area is estimated to be 0.1
acre per ton of P205 per day.
Since the cooling pond receives condensed vapors from the flash
cooler and evaporators, entrained phosphoric acid could be present as a
contaminant. This, nowever, can be minimized by entrainment separators
so that the main contaminant entering the cooling pond could be limited
to fluorides.
5-8
-------
Since NSPS publication, cooling towers have been introduced, in
place of cooling pond area, at phosphate plants as described in Section
4, "FLUORIDE EMISSION CONTROL CHANGES." In these applications, fluorides
in the gases from the WPPA vacuum cooler and vacuum evaporators are
scrubbed to recover the fluorides as H2SiFg prior to final scrubbing in
the process barometric condensers. Water from the WPPA-reactor scrubber
is used to scrub the vacuum cooler/evaporator gases, thus effecting
further fluoride recovery. Recovery efficiencies as high as 99% are
reported. The water from the barometric condensers is cooled in closed-
loop cooling tower systems. In some of these systems, the scrubbing
water in the closed loop is caustic treated and a slip stream is limed
to precipitate the fluorides for disposal, and to regenerate the caustic.
With cooling pond area thus mostly eliminated, pond systems are reduced
18
to the principal function of handling gypsum slurry.
From /Table 5-1, most of the soluble (potentially emittable) fluorides
are contained in the gases routed to the barometric condensers. Additional
fluorides are contained in the gases from the WPPA reactor. Since the
fluorides from both of these sources are efficiently recovered and
converted to the saleable H2SiFg byproduct, and since pond area is
reduced by removal of pond thermal load by cooling towers, pond area and
1R
pond fluoride emissions can be reduced at least one-half.
5.2.4 Gypsum Pond Emission Reduction by Fluoride Recovery from WPPA
Evaporator Gas
Fluoride emissions from the pond system at the W.R. Grace WPPA
plant are reduced by the process described in the following excerpt from
a letter to the EPA:
5-9
-------
"The fluoride recovery system in the W.R. Grace phosphoric acid
plant is the Swift & Co. process licensed to Grace by Swift.
Fluorides are recovered in the form of hydrofluosilicic acid
(HLSiFg) of approximate 25 percent strength. The process recovers
approximately 65 percent of the fluorine in these vapors as 25
percent hydrofluosilicic acid, which calculates to approximately
25 percent fluorine recovery from the total coming in with the
phosphate rock. The vapors leaving the phosphoric acid vacuum
evaporators are scrubbed under vacuum with a recirculating solution
of hydrofluosilicic acid whose temperature is approximately that of
the vapors. Little or no water is condensed while the SiF. and HF
are absorbed in the fluosilicic acid solution. The lean vapors
from the fluorine scrubber are then passed to the usual barometric
condenser for total condensation. A specific gravity controller
activates a valve which discharges the H«SiFg to storage when up to
the desired strength. Makeup water then flows into the hot well
13
through a float control valve."
Pertaining to fluoride recovery as a means of reducing pond emissions,
the Central Florida EIS includes the proposed requirement:
"Provide for recovery of fluorine compounds from phosphoric-acid
evaporators unless it is determined at the time of permit applica-
tion that market conditions are such that the cost of operation
(not including amortization of initial capital cost) of the re-
covery process exceeds the market value of the product. If there
is an exception, the site-specific EIS is to contain an estimate of
pond-water fluoride concentrations to be attained and levels of
5-10
-------
fluorine emission. Estimated fluorine emissions from new-
source gyp ponds should not cause the plant complex to exceed
the total allowable point-source fluorine emissions within the
plant complex if a permit is to be issued."
Also, from the Central Florida EIS, "Reported costs of fluoride
recovery operations exceed prices by 25 to 36 percent. Fluoride is
marketed for the fluoridation of water supplies and for use as an
industrial chemical."13
5.2.5 Gyspum Pond Emission Reduction by Fluoride Recovery from WPPA
Process Water
Fluoride emissions from the pond system at the USS Agri-Chemicals
WPPA plant are reduced by the process described in the following excerpt
from a letter to the EPA:
"As a result of development engineering in the late 1960s to
generate a means of diluting concentrated sulfuric acid with wet-
process phosphoric acid pond water and thereby eliminate production
problems with respect to conventional sulfuric acid dilution coolers
and simultaneously create a negative water balance in the phosphoric
acid pond water system, an offshoot of this work was devised and a
process resulted which would recover fluosilicic acid (FSA) from
phosphoric acid.
"Our (USS Agri-Chemicals) process uses 22 percent of P205 recycle
phosphoric acid from the filtration wash steps as a diluent for
diluting 98 percent sulfuric acid. The heat of dilution drives off
silica (sic) tetrafluoride (SiF.) from the 22 percent recycle
stream, along with water vapor. The hydration product is a 25
5-11
-------
percent H^SiFg fluosilicic acid of extremely low P^Oc content.
Conventional processes for stripping FSA during phosphoric acid
evaporation produce FSA containing between 0.5 and 2 percent PO^C-
Our process consistently produces FSA with a content well below 0.3
and frequently under 0.1 percent POr (100 percent H^SiF basis).
"We installed a commercial unit which became operational in May 1970
as a first of its kind at a total capital cost of $1.5MM. In
addition to reclaiming FSA through the recycle acid dilution route,
we built certain flexibilities in the commercial plant to innovate
recovery of FSA from fluorine scrubber systems from the triple
super phosphate (TSP) manufacture and from steam stripping of the
final concentrated phosphoric acid. The latter two process adjuncts
did not prove satisfactory and have since been abandoned. I cannot
project accurately the capital costs of a unit designed and built
for recycle acid service only on today's cost basis but would guess
at least $2.5MM.
"Since this was an entirely new concept and the process conditions
were extremely severe, the operating costs and profit benefits have
been considerable less than satisfactory. Mechanical and corrosion
problems resulting from the stringent operating conditions have led
to prohibitive maintenance costs. The process deals with high-
temperature mixes of sulfuric acid and phosphoric acid in an atmosphere
of fluoride compounds, all of which contain abrasive, precipitated
SiO« and calcium sulphate (gypsum). The high temperatures tend to
promote the anhydride formation of calcium sulphate, and scaling is
5-12
-------
a serious problem. We have learned to live with the process and,
19
though it now performs well, it is a costly operation."
5.2.6 Gypsum Pond Reduction by Hemihydrate WPPA Production
As discussed in Section 3, "PRODUCTION PROCESS CHANGES", gypsum
produced in the hemihydrate (hemidihydrate or HDH) process for WPPA is
reported suitable as building material. Sale of this material would
20
greatly reduce its accumulation in the gypsum pile and in ponds.
The HDH process has not, however, been commercially demonstrated in
20
the U.S.; commercial plants in Europe and Japan have been reported.
5-13
-------
5.3 REFERENCES FOR SECTION 5.
1. Final Guidelines Document: Control of Fluoride Emissions from
Existing Phosphate Fertilizer Plants. U.S. EPA. Research Triangle Park,
N.C. Pulbication No. EPA-450/2-77-005. March 1977. pp. 5-15 to 6-82.
2. Linero, A.A. and R.A. Baker. Evaluation of Emissions and
Control Techniques for Reducing Fluoride Emissions from Gypsum Ponds
in the Phosphoric Acid Industry. U.S. EPA. Washington, D.C. Publication
No. EPA-600/2-78-124. June 1978. p. 3.
3. Central Florida Phosphate Industry Areawide Impact Assessment
Program, Vol. 1: Description of Program and Industry. U.S. EPA Region 4.
Atlanta, GA. Project No. 08-01-4196. Sept. 1978. p. 37.
4. Reference 2. pp. 6-7.
5. Reference 2. pp. 143-6.
6. Reference 1. pp. 5-6, 5-15.
7- Reference 2. p. 184.
8. Reference 2. p. 159.
9. Reference 1. p. 5-16.
10. Reference 1. p. 5-15.
11. Reference 1. pp. 5-16, 5-17.
12. Boscak, V.G., N.E. Browne, and N. Ostojic. Measurement of
Fluoride Emissions from Gypsum Ponds, Draft Final Report. U.S. E.P.A.
Washington, D.C. Contract 69-01-4145, Task 10. Sept. 1978.
13. Environmental Impact Statement, Central Florida Phosphate
Industry, Vol. 2. U.S. EPA Region 4. Atlanta, GA. Publication No.
EPA 904/9-78-026b. Nov. 1978. p. 2.25.
14. Telecon. W. Herring, EPA (OAQPS) to P.J. Magno, EPA (ORP).
June 7, 1979. Subject: Radioactive Emissions from Phosphate Plants.
15. Memo from P.J. Magno, EPA (ORP) to G.B. Crane, EPA (OAQPS).
June 20, 1979. Subject: Regulation of Radioactive Emissions from
Phosphate Plants.
16. Environmental Impact Statement, Central Florida Phosphate
Industry, Vol. 1. U.^. EPA Region 4. Atlanta, GA. Publication No.
EPA 904/9-78-026a. Nov. 1978. p. 2.3.
5-14
-------
17. Reference 2. pp. 154-5.
18. Telecon. G.B. Crane and W. Herring to A.J. Teller, Teller
Environmental Systems, Inc., May 14, 1979. Subject: Review of
Phosphate Fertilizer NSPS.
19. Reference 13. p. 2.24.
20. Blumrich, W.E., H.J. Koening, and E.W. Schwehr. The Fisons
HDH Phosphoric Acid Process. Chemical Engineering Progress. 74: 58-61
Nov. 1978.
5-15
-------
6. NSPS ENFORCEMENT PROBLEMS AND COMPLAINTS
6.1 NEW SOURCES SINCE NSPS PUBLICATION
Based on inquiries to EPA Regions 4, 5, 6, and 10, and the States
of Florida, North Carolina, Illinois, Texas, Louisiana, and Idaho, only
one phosphate production plant was identified as a new, modified, or
reconstructed source. That source is the J.R. Simplot Co. plant at
Pocatello, Idaho, that makes granular triple superphosphate (GTSP).
That plant began production of GTSP in March 1977, using a process
modification that consists of treating limestone with wet process phos-
phoric acid (WPPA). This modified process is described in Section
3, "PRODUCTION PROCESS CHANGES."
Results of the NSPS compliance test at the Simplot plant, submitted
to the EPA Regional Administrator on Dec. 30, 1977, show average fluoride
21
emissions of 1.11 Ib/hr, or 0.187 Ib/ton P2°5- Tne requirement for
NSPS compliance in GTSP production is 0.20 Ib F (fluoride)/ton P205.
According to a State of Idaho estimate, the above emission rate
compares with fluoride emissions from the old process as great as 43
Ib/hr. The State also notes that the old process utilized the ROP/GTSP
method where run-of-pile triple superphosphate (ROP) was manufactured
and cured, and then GTSP was made from the cured ROP. The State notes
further that the new process eliminates the ROP step and the new GTSP
product thus goes to storage in the final cured state. High
19
fugitive emissions are therefore eliminated in the storage area.
6-1
-------
6.2 COMPLAINTS OF PHOSPHATE PLANT EMISSIONS AND SUGGESTED IMPROVEMENTS
OF REGULATIONS
Inquiries about complaints were made to representatives of EPA
Regions 4, 5, 6, and 10, the states of Florida and North Carolina in
Region 4, Illinois in Region 5, Texas and Louisiana in Region 6, and
Idaho in Region 10. Responses indicated that public complaints applying
to emissions from phosphate production facilities were limited to those
1-18
summarized below.
6.2.1 Florida
Region 4 has had recent complaints about phosphate plants in
central Florida:
1. Heavy emissions are alleged to occur at night. The complaints
indicate that control equipment is not maintained satisfactorily and not
operated continuously.
2. Excursions above allowable limitations of Florida regulations
are alleged to affect blooms on orange trees.
3. Plant neighbors report heavy fugitive emissions from GTSP
storage facilities. These emissions have not occurred during Region 4
1 22
visits, but Region 4 representatives have seen pictures of them. '
The complaints on the central Florida plants were received from a
total of five individuals during 1974 to 1979. They included five
22
complaints from one individual in 1977.
A Region 4 representative commented that there is currently no way
of checking whether or when control equipment has been on or off. He
suggested that NSPS should include continuous monitoring of controls
6-2
-------
to show when equipment has been in service and operated per design
specifications, and when not in service.
The following public comments recorded in Volume III of the
Environmental Impact Statement (EIS) for the Central Florida Phosphate
Industry also appear pertinent:
1. "With respect to fluoride and uranium, recovery of these two
compounds, based solely on economic consideration ... is totally
unacceptable in view of the documented damage caused by these compounds.
"They should be removed from the waste water as a simple matter of
health protection. If a profit results, so much the better for the
industry. But placing such an emphasis on profit is neither justifiable
23
nor desirable from the public or environmental health standpoint."
2. "We suggest you include the information that Florida has the
highest rate of lung cancer in the United States, the statistics weighted
so incidences are not attributable to age.
"It does not seem unreasonable to assume, based on studies by
Goffman and others, that these lung cancers are related to the high
levels of radioactivity in our region. Additionally, statistics readily
available from the Department of MRS for last year show that Florida led
24.
the nation in deaths from cancer."
3. "Without adequate, proper and timely monitoring by the federal
and state environmental agencies, all proposed actions and existing
rules, regulations and requirements are worthless and ineffective.
"Therefore, we request that adequate surveillance programs be
instigated with an appropriate funding level in order to accomplish
those goals which should be of the highest priority."25
6-3
-------
Pertaining to the above comments on uranium and radioactivity,
radioactive emissions from phosphate plants are being investigated by
the Office of Radiation Programs, EPA, for possible regulation. The
status of this investigation is reported in Section 3, "PRODUCTION
PROCESS CHANGES."
6.2.2 Idaho
A State of Idaho representative stated that farmers have complained
about contamination of cattle feed by fluoride emissions from the
Simplot plant, mentioned above. He also said that private legal action
against the company was taken by the farmers, and that the company has
since reduced the emissions. Since the aforementioned legal action was
taken privately, the State was not involved, and has not retained a file
on this matter. The representative of the State commented, however,
that it is too soon to know whether the emission reduction has been
18 19
sufficient to stop harm to the cattle. '
6.3 STATUS OF DEVELOPMENT OF FLUORIDE MONITORING
Pertaining to the Region 4 suggestion that emission control systems
be monitored, information was obtained on the current status of systems
for monitoring fluoride emissions.
A continuous monitor for fluoride emissions was recently evaluated
by the EPA Environmental Sciences Research Laboratory, which furnished
the following comment:
The monitor is designed to detect HF gas. Fluoride particulate
is not included in the measurement. Should any particulate get
6-4
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into the analyzer past the particulate thimble filter, the water-
soluble portion of the particulate fluoride will be included in the
27
selective ion electrode measurement.
Pertaining to the same investigation, the EPA Emission Measurement
Branch commented:
These instruments have been around since initial promulgation [of
the phosphate plant NSPS] and have not proven to be adequate for
continuously monitoring total fluoride emissions. The instrument
is designed to measure only gaseous fluoride and in field appli-
cations, has proven to be unreliable and produce erratic results.
28
John Nader's report also points out these problems.
6.4 STATE PLANS FOR REGULATING EXISTING PHOSPHATE PLANTS
The status of state plans for controlling fluoride emissions from
existing phosphate plants, as of October 1979, under Section lll(d) of
the Clean Air Act, is summarized as follows:
A. EPA Region 4
1. Negative declarations (no phosphate plants in state) were
29
received from Alabama, Kentucky, Tennessee, South Carolina, and Georgia.
2. North Carolina. Plan not yet submitted. State has one
phosphate plant. State held a public hearing June 1978, and intends
to submit lll(d) plan about December 1979. Requirements of plan are expected to
be less stringent than lll(d) guidelines regarding granulated triple
OQ
superphosphate (GTSP) storage.
3. Mississippi. Plan not yet submitted. State has one
phosphate plant. State requested extension to July 1979. 29
6-5
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4. Florida. Plan has been submitted. It is less stringent
than lll(d) guidelines. State must have public hearings before Region
can act on plan. State plans to hold and certify hearings in FY 80.
pQ
State has 9 or 10 plants in 2 counties.
B. EPA Region 6
on
1. Negative declaration received from New Mexico.
plants.
2. Texas. Plan not submitted. State has several phosphate
30
3. Oklahoma. Plan not submitted. Region does not have
30
information on whether State has phosphate plants.
4. Arkansas. Draft plan submitted in July 1979. Goes to
30
hearing in November 1979.
5. Louisiana. Plan has been submitted. Plan generally met
lll(d) guidelines except would allow emissions about 100 times guideline
requirements for triple superphosphate (TSP). The reason given for
allowing the higher TSP-plant emissions is that, because of hot weather,
pond temperature is too high for more effective fluoride removal in
scrubbers. The Region is considering suggesting that the State employ
a contractor to study the claim that guidelines cannot be met, but has
30
not yet acted.
C. EPA Region 10
1. Idaho. Plan not submitted. An extension to July 1979 had
31
been discussed, but was not formally requested.
6-6
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2. Idaho 1s the only state 1n Region 10 that has phosphate
plants.
32
D. No state plan has yet been approved by EPA.
EPA guidelines for development of State emission standards are
specified 1n the publication, "Final Guidelines Document: Control of
Fluoride Emissions from Existing Phosphate Fertilizer Plants," U.S. EPA,
Research Triangle Park, N.C., EPA-450/2-77-005, March 1977.
6-7
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6.C, REFERENCES FOR SECTION 6.
1. Telecon. W. Herring, U.S. EPA OAQPS, to W. Aronson, U.S. EPA
Region 4. April 17, 1979. Subject: Phosphate Industry in Region 4.
2. Telecon. W. Herring to G. McNeil!, U.S. EPA Region 4.
April 18, 1979. Subject: Phosphate Industry in Region 4.
3. Telecon. J. Rom, U.S. EPA Region 4, to W. Herring.
April 23, 1979. Subject: Phosphate Industry in Region 4.
4. Telecon. W. Herring to J. Hund, EPA Region 4. May 3, 1979.
Subject: Phosphate Industry in Region 4.
5. Telecon. W. Herring to F. Collins, U.S. EPA Region 4.
May 21, 1979. Subject: Phosphate Industry in Region 4.
6. Telecon. W. Herring to B. Varner, U.S. EPA Region 5.
April 24, 1979. Subject: Phosphate Industry in Region 5.
7. Telecon. W. Herring to L. Szempruch, U.S. EPA Region 5.
April 24, 1979. Subject: Phosphate Industry in Region 5.
8. Telecon. W. Herring to J. Hepola, U.S. EPA Region 6.
May 21, 1979. Subject: Phosphate Industry in Region 6.
9. Telecon. W. Herring to S. Spruiell, U.S. EPA Region 6.
June 5, 1979. Subject: Phosphate Industry in Region 6.
10. Telecon. W. Herring to J. Pfander, U.S. EPA Region 10.
May 21, 1979. Subject: Phosphate Industry in Region 10.
11. Telecon. W. Herring to B. Swan, U.S. EPA Region 10.
May 21, 1979. Subject: Phosphate Industry in Region 10.
12. Telecon. M. Johnson, U.S. EPA Region 10. May 22, 1979.
Subject: Phosphate Industry in Region 10.
13. Telecon. W. Herring to J. Symes, State of Florida.
April 23, 1979. Subject: Phosphate Industry in Florida.
14. Telecon. W. Herring to Derr Leonhardt, State of N.C.
April 20, 1979. Subject: Phosphate Industry in N.C.
15. Telecon. W. Herring to J. Reed, State of Illinois.
April 24, 1979. Subject: Phosphate Industry in Illinois.
16. Telecon. G. Wallin, State of Texas, to W. Herring.
April 30, 1979. Subject: Phosphate Industry in Texas.
6-8
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17. Telecon. W. Herring to 0. Tanner, State of Louisiana.
May 1, 1979. Subject: Phosphate Industry in Louisiana.
18. Telecon. W. Herring to R. Stenner, State of Idaho.
April 19, 1979. Subject: Phosphate Industry in Idaho.
19. Letter and attachments from R. Stenner, State of Idaho, to
W. Herring. April 20, 1979. Subject: Phosphate Industry in Idaho.
20. U.S. Patent. Direct Granulation Process for Triple Superphosphate.
Assignee: J.R. Simplot Co. No. 4,101,637. July 18, 1978.
21. Letter and attachments from J.F. Cochrane, J.R. Simplot Co.,
to D.P. Dubois, EPA Region 10. December 30, 1977. Subject: TSP
Performance Test.
22. Telecon. W. Herring, U.S. EPA OAQPS, to W. Aronson, U.S. EPA
Region 4. April 18, 1979. Subject: Phosphate Industry in Region 4.
23. Environmental Impact Statement, Central Florida Phosphate
Industry, Vol. 3. U.S. EPA Region 4. Atlanta, GA. Publication No.
EPA 904/9-78-026C. Nov. 1978. p. 1-63.
24. Reference 23. p. 1-46.
25. Reference 23. p. 1-222.
26. Telecon. W. Herring to R. Stenner, State of Idaho.
April 25, 1979. Subject: Phosphate Industry in Idaho.
27. Memo from J.S. Nader, EPA Environmental Sciences Research
Laboratory, to G.B. Crane, EPA Emission Standards and Engineering
Division. June 25, 1979. Subject: Status of Development of Continuous
Monitor for Fluoride Emissions.
28. Memo from E. McCarley, EPA Emission Measurement Branch, to
G.B. Crane. June 26, 1979. Subject: Report, Continuous Monitoring
System for Fluoride Emissions from Stationary Sources.
29. Telecon. W. Bishop, EPA Region 4, to W. Herring.
October 10, 1979. Subject: State Plans for Existing Phosphate Plants.
30. Telecon. W. Herring to J. Stubberfield, EPA Region 6.
October 9, 1979. Subject: State Plans for Existing Phosphate Plants.
31. Telecon. K. Lepic, EPA Region 10, to W. Herring.
October 11, 1979. Subject: State Plans for Existing Phosphate Plants.
32. Discussion. W. Herring with R. Shell, EPA Control Programs
Development Division. October 9, 1979. Subject: State Plans for
Existing Phosphate Plants.
6-9
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7. CONCLUSIONS
7.1 HEMIHYDRATE PROCESS FOR WET PROCESS PHOSPHORIC ACID (WPPA)
The hemihydrate (hemidihydrate or HDH) process for WPPA production
appears to have certain potential advantages for reducing fluoride air
pollutant emissions, compared with the conventional dihydrate processes.
Fluorides evolved in process gases are recovered as byproduct
fluosilicic acid (H^SiFg) at an efficiency reported to be greater than
99%. (Possible fluoride recovery between 65 and 99% is reported for the
dihydrate process). Also, P205 recovery is reported to exceed 98%,
which is alleged to be greater than in the dihydrate process. Greater
P«0c recovery would reduce the amount of phosphoric acid entering pond
water. This reduction would tend to increase pond pH, and thereby
further reduce fluoride emissions from ponds and improve scrubber efficiency.
Gypsum produced in the HDH process is reported to be of sufficient
purity to be used in building material. This indicates that the gypsum
may be substantially free of radioactive constituents and saleable.
This is in contrast to dihydrate-process gypsum, which has radioactive
constituents, and therefore is not saleable and must be retained at the
plant in gypsum piles. The HDH process therefore might reduce gypsum
piles and the attendant radioactive emissions and fugitive dust generated
in handling the piles.
7-1
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Possible disadvantages of the HDH process are that radioactive
constituents removed from the gypsum would apparently go into the
product WPPA or pond water. Also, recovery of valuable uranium from HDH
product WPPA is reported less satisfactory than recovery from the more
dilute WPPA produced in the dihydrate processes.
The HDH process has been used commercially in Europe and Japan but
not in the U.S.
7.2 SIMPLOT PROCESS FOR GRANULATED TRIPLE SUPERPHOSPHATE (GTSP)
The new Simplot process, in which GTSP is made by treating lime-
stone with WPPA, provides a means for reducing local fluoride emissions
at the plant where it is applied. However, the fluoride emissions from
the Simplot process added to those from the production of the WPPA, used
in the Simplot process, might not be less than the corresponding total
for the old process.
Emission test results for the Simplot process (0.187 Ib F/ton P2°5)
indicate that fluoride emissions comply with - but are not substantially
less than - requirements of the present NSPS (0.20 Ib F/ton P2°5)-
The Simplot process appears to reduce or eliminate fugitive emissions
and evolved fluorides during storage by eliminating the curing period
required when GTSP is made from run-of-pile triple superphosphate (ROP).
7.3 WET GRINDING OF PHOSPHATE ROCK
Emissions of sulfur dioxide (S0«) and dust with radioactive content,
that occur during drying, grinding, and transport of phosphate rock, can
be substantially reduced by eliminating rock drying prior to grinding
and chemical processing.
7-2
-------
Companies are converting from dry to wet grinding of phosphate rock
to save energy.
7.4 SCRUBBING SYSTEMS, COOLING TOWERS, AND GYPSUM PONDS
Scrubbing systems remain the principal means of controlling fluoride
emissions from phosphate plants. A few modifications have been introduced
since NSPS publication.
7.4.1 Fluoride Recovery
Scrubbers that recover fluorides as saleable H2S1Fg have been
incorporated at a substantial number of WPPA plants. These scrubbers
are reported to recover between 65 and 99% of the gaseous fluorides
emitted during acidulation and acid concentration. Fluoride removal by
this means substantially reduces the fluorides emitted from plant pond
systems or cooling towers. Costs of fluoride recovery as H2SiFg might
exceed H2SiFg market prices, but not to an extent that precludes its
commercial applicability for reducing emissions.
7.4.2 Cooling Towers
Cooling towers are being used at a substantial number of plants in
place of cooling ponds, or instead of the gypsum pond area required to
cool water for scrubbers and barometric condensers. The cooling towers
are used in closed-loop systems. Here, water from the scrubbers or
barometric condensers goes to the cooling tower, where it is cooled -
mainly by evaporation - to the required scrubbing temperature. The
water is then returned to the scrubbers or barometric condensers, thus
closing the cool ing-tower loop. Make-up water is added to the closed
loop from the gypsum pond water overflow caused by rainfall, or from the
plant storm water collection system. Four variations of this cooling-
tower closed-loop system were identified in this investigation:
7-3
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1. Cooling Tower without Fluoride Recovery and without Caustic
Treatment
In a WPPA plant system, process gases are scrubbed, without prior
removal of fluorides as byproduct hLSiF,.. The resulting scrubbing water
is cooled in a cooling tower, then returned to the scrubbers. The water
in this closed loop is not caustic treated to increase its pH and limit
fluoride emissions from the tower. Substantial fluoride emissions from
the cooling tower probably occur in this system.
2. Cooling Tower with Fluoride Recovery but without Caustic
Treatment
In a WPPA plant system, process gases are first scrubbed in a
scrubber designed to recover fluorides as byproduct hLSiFg. The gases
are then scrubbed again in the plant barometric condensers. The water
from the barometric condensers is cooled in a cooling tower and returned
to those condensers. This water is not caustic treated to limit fluoride
emissions from the tower. Fluoride emissions from the cooling tower
would be less in this system than in the system described in paragraph
1, above.
3. Cooling Towers with Fluoride Recovery and Caustic Treatment
A WPPA plant system that employs a cooling tower with fluoride
recovery and caustic treatment is similar to that described in paragraph
2, above, except that the water in the cooling tower is treated with
sodium hydroxide (NaOH) to increase its pH and limit fluoride emissions
from the tower. Also, a slip stream of water from the tower is limed to
precipitate the fluoride and regenerate the NaOH. Fluoride emissions
7-4
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from the cooling tower would be less in this system than in either of
the systems described in paragraphs 1 or 2, above.
4. Cooling Tower with Nitrogen and Phosphorous Recovery and with
Caustic Treatment
In a diammounium phosphate (DAP) plant system, process gases are
first scrubbed with dilute phosphoric acid to recover ammonia and phos-
phorous compounds. To remove fluorides, the gases are then scrubbed
again with water that is treated with NaOH in a cooling-tower closed-
loop system. A slip stream of water from the tower is limed to preci-
pitate the fluoride and regenerate the NaOH. Fluoride emissions from
the cooling tower would be reduced to a very low rate in this system.
7.5 FLUORIDE EMISSION MONITORING
A system that would satisfactorily monitor fluoride emissions has
not been developed. However, the present NSPS for phosphate plants
requires continuous monitoring of total pressure drop across the process
scrubbing system. It is thus required that records be kept of when
emission control systems are operated and not operated.
7.6 RADIOACTIVE EMISSIONS
The health impact of radioactive emissions from phosphate plants is
being studied by the EPA Office of Radiation Programs (ORP). Results of
this study will determine whether those emissions will be listed as
hazardous pollutants under Section 112 of the Clean Air Act. If these
emissions are so listed, standards for their control will be developed
by ORP, under Section 112.
7-5
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1.1 AREAS FOR RESEARCH AND DEVELOPMENT
As noted above, phosphate plant pond area and pond fluoride emissions
may bo reduced by a WPPA plant system that Includes: fluoride recovery
ar, byproduct H^MFg, and a closed-loop cooling tower system where scrubbing
water \c> caustic treated and a slip stream 1s Hmed to recover the
caustic and precipitate the fluorides. This system 1s used, however, at
only one plant, and Its user reports difficulties, which that company 1s
working to overcome. Furthermore, the developer of this system,
Dr. Aaron Teller, advocates a different system for future application.
Dr. Teller's preferred system would use a baghouse with continuous
injection of a dry additive that would remove fluorides by adsorption
and filtration. Advantages claimed for this dry system Include reduced
pond area, reduced pond emissions, reduced plumbing costs, and reduced
corrosion. Dr. Teller estimates pond cost at $2000 to $2500 per acre
vear and plumbing costs at *1000 per foot of piping.
Tl'f? dry Teller system has not yet been used at a commercial phosphate
plant. Two such units are being furnished to the IMC New Wales, Fla.,
plant. These units will be applied to GTSP and DAP processes. They are
expected to be on line by 1980.
The dry continuous-Injection baghouse described above might provide
an Improved emission control system for phosphate plants, compared with scrubbing
systems now 1n use.
7.8 INDUSTRY GROWTH
Some processes are being modified and there 1s some new construction
*t phosphate plants 1n the U.S. Particularly notable are (1) conversions
7-6
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from processing dry phosphate rock to processing wet rock and (2)
conversions from process cooling water ponds to cooling towers. These
modifications and new construction do not apply to the affected facilities
as defined In the present NSPS.
The responses obtained In this Investigation to enquiries to EPA
Regional offices and State agencies Indicate that the extent of new and
modified source construction 1s small. Furthermore, there 1s negligible
projected Industry growth to 1985.
7.9 REGULATION OF EXISTING SOURCES
Only two states - Florida and Louisiana - have submitted formal
Section lll(d) plans for controlling fluoride emissions from existing
phosphate plants. Both of these plans have less stringent requirements
than those of the EPA guidelines. One state - Arkansas - has submitted
a Section 111(d) draft plan. No state plan has been approved by EPA.
7.10 REFERENCES FOR SECTION 7.
1. Memo from G.B. Crane, EPA Emission Standards and Engineering
Division, to File. 5/15/79. Subject: Review of Phosphate Fertilizer
NSPS: Conversation with Dr. Aaron Teller.
7-7
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8. RECOMMENDATIONS
8.1 HEMIHYDRATE PROCESS FOR WET PROCESS PHOSPHORIC ACID (WPPA)
The henrihydrate (HDH) process is not recommended for study as a possible
basis for NSPS revision because there are no commercial HDH plants in the
U.S. and because no data showing reduced emissions were found in this
investigation. However, reported reduced energy consumption and reduced
capital cost might lead to commercial use of this process in the U.S.
In the event of commercial adoption, this matter should be reconsidered.
8.2 SIMPLOT PROCESS FOR GRANULATED TRIPLE SUPERPHOSPHATE (GTSP)
The Simplot process is not recommended for study as a possible
basis for NSPS revision because available data do not show that it
effects a substantial reduction of process emissions below the present
NSPS requirement. This process should, however, be included in any future
study concerned with regulating evolved-fluoride or fugitive emissions from
GTSP storage facilities.
8.3 WET GRINDING OF PHOSPHATE ROCK
Wet grinding is not recommended for study as a possible basis for
NSPS revision because the energy-saving advantage of this process modification
is presently inducing companies to adopt it.
8.4 SCRUBBING SYSTEMS, COOLING TOWERS, AND GYPSUM PONDS
8.4.1 Fluoride Recovery
Fluoride recovery, as byproduct H2SiFg, is recommended for inclusion if
a study is undertaken to determine a basis for NSPS revision.
8.4.2 Cooling Towers
Cooling towers are recommended for inclusion if a study is undertaken
to determine a basis for NSPS revision.
8-1
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8.5 RADIOACTIVE EMISSIONS
Findings of the Office of Radiation Programs study of radioactive
phosphate plant emissions should be obtained if a study is undertaken
to determine a basis for NSPS revision. This information would be needed to
show impacts of proposed NSPS revisions on radioactive emissions.
8.6 RECOMMENDATION ON NSPS REVISION STUDY
In view of the low projected growth of this industry, a study to
establish a basis for NSPS revision is not recommended now. Possible
revision should be reconsidered in four years.
8-2
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
EPA-450/3-79-038
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Review of New Source Performance Standards for
Phosphate Fertilizer Industry
5. REPORT DATE
November 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
William Herring
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
EPA, Office of Air Quality Planning and Standards
Emission Standards and Engineering Division
Research Triangle Park, N.C. 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA 200/04
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Since promulgation of new source performance standards (NSPS) for the
"phosphate fertilizer industry, in 1975, commercial applications of a few new systems
that reduce air pollution from phosphate plants have been reported. These include
scrubbing system modifications that reduce the size of ponds used to cool process
water, and reduce pond fluoride emissions. Also, a proprietary new process produces
a stable granular triple superphosphate (GTSP) directly. This process reduces or
eliminates the emissions of fluorides and fugitive particulate during the curing,
storage period. The new GTSP process also eliminates the scrubbing of certain
process gas, thus reducing required cooling pond area and pond fluoride emissions.
Wet grinding of phosphate rock, in place of dry grinding, has been introduced, which
eliminates dryers and reduces emissions that include particulate with radioactive
content. NSPS revision, however, would probably not have significant impact now
because the extent of new and modified source construction in this industry is small,
and because industry growth projected to 1985 is negligible. The recommendation
is, therefore, made not to develop NSPS revisions now, but to assess additional
developments in this industry in four years, and then reconsider possible revision.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Air Pollution
Phosphate Industry
Fluorides
Air Pollution Control
Stationary Sources
Particulate
New Source Peformance
Standards
Industry Study
13B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
81
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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