[3 D A U.S. Environmental Protection Agency Industrial Environmental Research CDA 1/7 7C
dr M Office of Research and Development Laboratory
Cincinnati. Ohio 45268 December 1976
ENVIRONMENTAL
CONSIDERATIONS OF
SELECTED ENERGY
CONSERVING MANUFACTURING
PROCESS OPTIONS:
Vol. XIII. Phosphorus/
Phosphoric Acid Industry Report
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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EPA-600/7-76-034m
December 1976
ENVIRONMENTAL CONSIDERATIONS OF SELECTED
ENERGY CONSERVING MANUFACTURING PROCESS OPTIONS
Volume XIII
ELEMENTAL PHOSPHORUS AND PHOSPHORIC ACID INDUSTRY REPORT
EPA Contract No. 68-03-2198
Project Officer
Herbert S. Skovronek
Industrial Pollution Control Division
Industrial Environmental Research Laboratory - Cincinnati
Edison, New Jersey 08817
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
For sale by the Superintendent or Documents, U.S. Government Printing Office, Washington, D.C. 30*03
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (lERL-Ci) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and
economically.
This study, consisting of 15 reports, identifies promising industrial
processes and practices in 13 energy-intensive industries which, if imple-
mented over the coming 10 to 15 years, could result in more effective uti-
lization of energy resources. The study was carried out to assess the po-
tential environmental/energy impacts of such changes and the adequacy of
existing control technology in order to identify potential conflicts with
environmental regulations and to alert the Agency to areas where its activi-
ties and policies could influence the future choice of alternatives. The
results will be used by the EPA's Office of Research and Development to de-
fine those areas where existing pollution control technology suffices, where
current and anticipated programs adequately address the areas identified by
the contractor, and where selected program reorientation seems necessary.
Specific data will also be of considerable value to individual researchers
as industry background and in decision-making concerning project selection
and direction. The Power Technology and Conservation Branch of the Energy
Systems-Environmental Control Division should be contacted for additional
information on the program.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
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EXECUTIVE SUMMARY
PHOSPHORUS/PHOSPHORIC ACID
Phosphate rock is mined in Florida, Tennessee and North Carolina, and
in the mountain states of the West. It is converted to commercial end pro-
ducts by digestion with sulfuric acid (the "wet process") or by reduction to
elemental phosphorus in an electric furnace. Most of the phosphorus is sub-
sequently converted to phosphoric acid. Although phosphoric acid is the
principal commerical product of either method, there is an important differ-
ence in the purity of the acid obtained. Furnace acid is essentially a pure
chemical that is suitable for detergent, food, and fine chemical uses.
Wet-process acid is not pure; it is suitable for fertilizer manufacture but
not for most other purposes without cleanup.
The electric furnace process has very high energy requirements, 13,000
kWh as electricity is required per ton of phosphorus produced. This rate
is almost as high as that for aluminum and much higher than that of any other
significant electroprocessing industry. Wet-process energy requirements
are modest, about one-fifth of the electric furnace method on a total energy
basis. The total energy requirement of the industry is about 1 x 10-" Btu/
year; this is a significant requirement.
Pollution problems are related to the impurities in the ore, which for
either method must eventually be disposed of as sludge to landfill. Fluorine
is an integral part of the ore and its safe containment is vital. Because
of the nature of the processes, pollution control is more manageable in the
wet process than in the electric furnace method.
More than 80% of the phosphate mined is converted to phosphoric acid by
the wet process, and this acid is used for fertilizer materials. A number
of proprietary process variations can be expected to compete for new wet
process plants, but there are no pollution or energy effects of interest to
our study. Uranium has been produced as a wet process system byproduct and
interest may be revived. If significant processing for uranium occurs there
are pollution problems which must be controlled. Elemental phosphorus once
was produced by the blast-furnace process. However, this method requires
more total energy, has more severe pollution problems than the electric
furnace method, and has poorer economics. Consequently, there is little
chance that it will be revived.
IV
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Phosphoric acid for detergent manufacture is made from elemental phos-
phorus; a purity better than that of current wet-process acid is required
and furnace acid easily meets these specifications. The detergent market is
likely to grow at a rate which will soon outstrip the available supply of
phosphorus from the existing electric furnace plants, and cleanup of wet-
process acid will be of interest as an alternative to expansion of the elec-
tric furnace industry. A chemical method for cleanup has been commercially
demonstrated; it appears to be economic and the establishment of several
such plants — each with a capacity of about 50,000 tons of P2C>5 per year —
is likely in the next 5-10 years. Pollution control would not be much differ-
ent from that required in the conventional wet-process system. Energy sav-
ings over the elemental phosphorus route are substantial.
A solvent extraction system for making clean wet-process acid has been
operated commercially outside the United States, but is not well established.
It has economic interest under special circumstances and on an energy basis
is equivalent to the chemical cleanup option.
The adoption of this system would depend upon the availability of
byproduct hydrochloric acid and a satisfactory solution of the environmental
problems inherent in the disposal of a calcium chloride brine. In certain
locations, for example, where disposal of calcium chloride solutions into
underground strata, into large rivers or by ocean dumping might be permitted,
the problems of calcium chloride disposal might be less than the problems of
disposing of byproduct hydrochloric acid, thereby effecting a more environ-
mentally acceptable solution for a difficult disposal problem.
If the projected expansion in the detergent market is by the wet-process
chemical cleanup route six 50,000-ton per-year P205 plants would be required.
At present arinual production rates for the entire United States industry
(and without consideration of the energy contributions of coke or sulfur)
production of 1.4 x 10*> tons of ?2°5 as furnace acid requires 0.09 quads of
energy, and 9.0 x 10^ tons of ^2^5 as wet-process acid requires only 0.03
quads. Expansion by 300,000 tons P205 per year would add 0.019 quads by the
electrothermal route but only 0.001 by the wet-process alternate. Net energy
saved would be 0.018 quads per year. Moreover, pollution control in these
new plants would be attained by established methods that are more easily
managed than those necessary at the electric furnace if that industry were
expanded.
.This report was submitted in partial fulfillment of contract 68-03-2198
by Arthur D. Little, Inc. under sponsorship of the U.S. Environmental Protec-
tion Agency. This report covers a period from June 9, 1975 to January 21, 1976.
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TABLE OF CONTENTS
FOREWORD ill
EXECUTIVE SUMMARY iv
List of Figures x
List of Tables xi
Acknowledgments xiii
Conversion Table ^
I. INTRODUCTION 1
A. BACKGROUND 1
B. CRITERIA FOR INDUSTRY SELECTION 1
C. CRITERIA FOR PROCESS SELECTION 3
D. SELECTION OF PHOPHORUS/PHOSPHORIC ACID INDUSTRY
PROCESS OPTIONS 4
II. FINDINGS AND CONCLUSIONS 6
A. PRODUCT TRENDS 6
B. PHOSPHORIC ACID: ELECTROTHERMAL VS WET PROCESS 6
C. CLEAN WET-PROCESS PHOSPHORIC ACID OPTIONS 7
1. Economics 8
2. Energy 9
3. Environmental 9
D. USE OF BYPRODUCT SULFURIC ACID 12
E. STRONG ACID PROCESSES 12
F. SECONDARY OPTIONS 13
1. Blast Furnace Phosphorus 13
2. Other Options 13
III. PHOSPHATE INDUSTRY OVERVIEW 14
A. INDUSTRY STRUCTURE ' 14
B. OUTLOOK FOR THE INDUSTRY 21
vix
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TABLE OF CONTENTS (Cont.)
IV. CURRENT TECHNOLOGY 22
A. PROCESS CONSIDERATIONS 22
B. BASE LINE: FURNACE ACID-ELECTRIC FURNACE PRODUCTION OF
PHOSPHORUS AND CONVERSION OF PHOSPHORUS TO PHOSPHORIC
ACID 23
1. Process Description 23
2. Effluents 25
3. Energy Requirements 32
4. Economic Factors 33
C. BASE LINE - WET-PROCESS PRODUCTION OF PHOSPHORIC ACID 35
1. Process Description 35
2. Effluents 37
3. Energy Requirements 41
4. Economic Factors 42
D. PROBLEMS RELATED TO PROCESS CHANGE AND INDUSTRY GROWTH 43
1. Pollution Control 43
2. Shortage and Escalating Cost of Electricity 44
3. High Capital Cost of Incremental Capacity 44
4. Economic Availability of Suitable Ore 44
V. PROCESS OPTIONS 46
A. OPTIONS TO BE ANALYZED IN DEPTH 46
1. Solvent Extraction Cleanup of Wet-Process
Phosphoric Acid 47
2. Byproduct Sulfuric Acid for Wet-Process
Phosphoric Acid 47
3. Strong Phosphoric Acid Processes 48
B. CHEMICAL CLEANUP OF WET PROCESS PHOSPHORIC ACID 48
1. Process Description 48
2. Current Status 52
3. Effluents 52
4. Energy 54
5. Economics 56
6. Assessment 56
C. SOLVENT EXTRACTION CLEANUP OF WET-PROCESS PHOSPHORIC ACID 60
1. Process Description 60
2. Current Status 63
3. Effluents 63
4. Energy Requirements 67
5. Economics 69
6. Assessment 71
viii
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TABLE OF CONTENTS (Cont.)
D. THE USE OF BYPRODUCT SULFURIC ACID 72
E. STRONG PHOSPHORIC ACID PROCESSES 73
F. SECONDARY OPTIONS 76
1. Variations of Basic Wet-Process Technology 76
2. Blast-Furnace Phosphorus 76
3. Uranium Extraction 77
4. Exploitation of Low Grade Phosphate Reserves 77
REFERENCES 78
ix
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LIST OF FIGURES
Number Page
II-l Phosphate Rock Price Analysis - Midwest Production of
Clean Phosphoric Acid 8
III-l Wet-Process Phosphoric Acid Plants in the United States 16
III-2 Phosphorus Furnaces and Furnace Phosphoric Acid Plants
in the United States 19
IV-1 Elemental Phosphorus Production 24
IV-2 Process Effluents - Electric Furnace Phosphorus 26
IV-3 Phosphoric Acid - Wet Process 36
IV-4 Fluorine Material Balance - Wet-Process Phosphoric Acid 41
V-l Flow Sheet Chemical Cleanup of Wet-Process Phosphoric Acid 51
V-2 Energy Comparison for Wet-Process and Electric Furnace
Methods of Cleaning Phosphoric Acid 59
V-3 Solvent Extraction Process for Phosphoric Acid -
The IMI Process 61
V-4 Emission Problems Found in Solvent Extraction Process
for Wet-Process Phosphoric Acid Cleanup 64
V-5 Phase Diagram CaSO, Precipitation 74
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LIST OF TABLES
Number Page
1-1 Summary of 1971 Energy Purchased in Selected Industry Sectors 2
II-l Summary of Costs/Energy/Environmental Considerations of
Process Options in Phosphorus/Phosphoric Acid Production 7
II-2 Alternative Routes to Phosphoric Acid-Comparison of Treated
Wastewater Characteristics 11
II-3 Alternative Routes to Phosphoric Acid-Comparison of Wastewater
Treatment Costs 11
II-4 Summary of Costs/Energy/Environmental Considerations of
Secondary Process Options in Phosphorus/Phosphoric Acid
Industry 13
III-l Phosphoric Acid Plant Capacity 15
III-2 Phosphorus Producers 17
III-3 Location of Furnace Acid Plants 18
IV-1 Characteristics of Raw Process Wastewater From Phosphorus
Manufacture 28
IV-2 Electric Furnace Production of Phosphoric Acid Wastewater
Characteristics ' 29
IV-3 Electric Furnace Production of Phosphorus and Phosphoric
Acid Wastewater Treatment Costs 30
IV-4 Important Electrochemical Operations 32
IV-5 Estimated Cost of Elemental Phosphorus Manufacture 34
IV-6 Estimated Cost of Phosphoric Acid Manufacture 36
IV-7 Wet-Process Phosphoric Acid Wastewater Characteristics 39
IV-8 Wet-Process Phosphoric Acid Wastewater Treatment Costs 40
xx
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LIST OF TABLES (Cont.)
Number Page
IV-9 Estimated Cost of Phosphoric Acid Manufacture 43
V-l Industrial Phosphate Demand 46
V-2 Process Effluents Chemical Cleanup of Wet-Process Phosphoric
Acid 53
V-3 Wet-Process Phosphoric Acid Plus Chemical Cleanup Wastewater
Characteristics 55
V-4 Wet-Process Phosphoric Acid Plus Chemical Cleanup Wastewater
Treatment Costs 55
V-5 Operating Cost of Chemical Cleanup 57
V-6 Pollution Trade-Offs 60
V-7 Wet-Process Production of Phosphoric Acid With Solvent
Extraction-Purification Wastewater Characteristics 66
V-8 Wet-Process Phosphoric Acid Plus Solvent Extraction-
Purification Wastewater Treatment Costs 68
V-9 Estimated Cost of Phosphoric Acid Manufacture Solvent
Extraction Cleanup - IMI Process 70
V-10 Phosphoric Acid-Fisons Strong Acid Process 75
xii
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ACKNOWLEDGMENTS
This study could not have been accomplished without the support of a
great number of people in government agencies, industry, trade associations
and universities. Although it would be impossible to mention each individual
by name, we would like to take this opportunity to acknowledge the particular
support of a few such people.
Dr. Herbert S. Skovronek, Project Officer, was a valuable resource to us
throughout the study. He not only supplied us with in format--inn on work
presently being done in other branches of EPA and other government agencies,
but served as an indefatigable guide and critic as the study progressed. His
advisors within EPA, FEA, DOC, and NBS also provided us with insights and
perspectives valuable for the shaping of the study.
During the course of the study we also had occasion to contact many
individuals within industry and trade associations. Where appropriate we
have made reference to these contacts within the various reports. Frequently,
however, because of the study's emphasis on future developments with compara-
tive assessments of new technology, information given to us was of a confiden-
tial nature or was supplied to us with the understanding that it was not to be
credited. Therefore, we extend a general thanks to all those whose comments
were valuable to us for their interest in and contribution to this study.
Finally, because of the broad range of industries covered in this study,
we are indebted to many people within Arthur D. Little, Inc. for their parti-
cipation. Responsible for the guidance and completion of the overall study were
Mr. Henry E. Haley, Project Manager; Dr. Charles L. Kusik, Technical Director;
Mr. James I. Stevens, Environmental Coordinator; and Ms. Anne B. Littlefield,
Administrative Coordinator.
Members of the environmental team were Dr. Indrakumar L. Jashnani,
Mr. Edmund H. Dohnert and Dr. Richard Stephens (consultant).
Within the individual industry studies we would like to acknowledge the
contributions of the following people.
Iron and Steel; Dr. Michel R. Mounier, Principal Investigator
Dr. Krishna Parameswaran
Petroleum Refining; Mr. R. Peter Stickles, Principal Investigator
Mr. Edward Interess
Mr. Stephen A. Reber
Dr. James Kittrell (consultant)
Dr. Leigh Short (consultant)
Kill
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Pulp and Paper:
Olefins:
Ammonia:
Aluminum:
Textiles:
Cement:
Glass:
Chlor-Alkali:
Phosphorus/
Phosphoric Acid;
Mr. Fred D. lannazzi, Principal Investigator
Mr. Donald B. Sparrow
Mr. Edward Myskowski (consultant)
Mr. Karl P. Fagans
Mr. G. E. Wong
Mr. Stanley E. Dale, Principal Investigator
Mr. R. Peter Stickles
Mr. J. Kevin O'Neill
Mr. George B. Hegeman
Mr. John L. Sherff, Principal Investigator
Ms. Nancy J. Cunningham
Mr. Harry W. Lambe
Mr. Richard W. Hyde, Principal Investigator
Ms. Anne B. Littlefield
Dr. Charles L. Kusik
Mr, Edward L. Pepper
Mr. Edwin L. Field
Mr* John W, Rafferty
Dr. Douglas Shooter, Principal Investigator
Mr* Robert M. Green (consultant)
Mr* Edward S, Shanley
Dr* John Willard (consultant)
Dr., Richard F* Heitmiller
Dr, Paul A. Huska, Principal Investigator
Ms. Anne B. Littlefield
Mr* J.. Kevin O'Neill
Dr. D. William Lee, Principal Investigator
Mr* Michael Rossetti
Mr* R, Peter Stickles
Mr* Edward Interess
Dr* Ravindra M. Nadkarni
Mr. Roger E. Shamel, Principal Investigator
Mr, Harry W. Lambe
Mry Richard P. Schneider
Mr. William V. Keary, Principal Investigator
Mr. Harry W. Lambe
Mr. George C. Sweeney
Dr., Krishna Parameswaran
Primary Copper:
Fertilizers:
Dr. Ravindra M. Nadkarni, Principal Investigator
Dr, Michel R. Mounier
Dr, Krishna Parameswaran
Mr. John L. Sherff, Principal Investigator
Mr. Roger Shamel
Dr. Indrakumar L. Jashnani
xiv
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ENGLISH-METRIC (SI) CONVERSION FACTORS
To Convert From
Acre
Atmosphere (normal)
Barrel (42 gal)
British Thermal Unit
Centipoise
Degree Fahrenheit
Degree Rankine
Foot
Foot /minute
3
Foot
Foot2
Foot/sec
2
Foot /hr
Gallon (U.S. liquid)
Horsepower (550 ft-lbf/sec)
-Horsepower (electric)
Horsepower (metric)
Inch
Kilowatt-hour
Litre
Micron
Mil
Mile (U.S. statute)
Poise
Pound force (avdp)
Pound mass (avdp) ,
Ton (assay)
Ton (long)
Ton (metric)
Ton (short)
Tonne
To
2
Metre
Pascal
3
Metre
Joule
Pascal-second
Degree Celsius
Degree Kelvin
Metre
3
Metre /sec
3
Metre
2
Metre
Metre/sec
2
Metre /sec
3
Metre
Watt
Watt
Watt
Metre
Joule
Metre3
Metre
Metre
Metre
Pascal-second
Newton
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Kilogram
Multiply By
4,046
101,325
0.1589
1,055
0.001
t° = (tj -32)/1.8
tj - tj/1.8
0.3048
0.0004719
0.02831
0.09290
0.3048
0.00002580
0.003785
745.7
746.0
735.5
0.02540
3.60 x 106
1.000 x 10~3
1.000 x 10~6
0.00002540
1,609
0.1000
4.448
0.4536
0.02916
1,016
1,000
907.1
1,000
Source: American National Standards Institute, "Standard Metric Practice
Guide," March 15, 1973. (ANS72101-1973) (ASTM Designation E380-72)
xv
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I. INTRODUCTION
A. BACKGROUND
Industry in the United States purchases about 27 quads* annually, approxi-
mately 40% of total national energy usage.** This energy is used for chemical
processing, raising steam, drying, space cooling and heating, process stream
heating, and miscellaneous other purposes.
In many industrial sectors energy consumption can be reduced significantly
by better "housekeeping" '(i.e., shutting off standby furnaces, better thermo-
stat control, elimination of steam and heat leaks, etc.) and greater emphasis
on optimization of energy.usage. In addition, however, industry can be
expected to introduce new industrial practices or processes either to con-
serve energy or to take advantage of a more readily available or less costly
fuel. Such changes in industrial practices may result in changes in air,
water or solid waste discharges. The EPA is interested in identifying the
pollution loads of such new energy-conserving industrial practices or proc-
esses and in determining where additional research, development, or demonstra-
tion is needed to characterize and control the effluent streams.
B. CRITERIA FOR INDUSTRY SELECTION
In the first phase of this study we identified industry sectors that have
a potential for change* emphasizing those changes which have an environmental/
energy impact.
Industries were eliminated from further consideration within this assign-
ment if the only changes that could be envisioned were:
• energy conservation as a result of better policing or "housekeeping,"
• better waste heat utilization,
• fuel switching in steam raising, or
• power generation. '
*1 quad = 1015 Btu
**Purchased electricity valued at an approximate fossil fuel equivalence of
10,500 Btu/kWh
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After discussions with the EPA Project Officer and his advisors,
industry sectors were selected for further consideration and ranked using;
• Quantitative criteria based on the gross amount of energy (fossil
fuel and electric) -purchased by industry sector as found in U.S.
Census figures and from information provided from industry sources.
The phosphorus/phosphoric acid industry purchased 0.12 quads out of
the 12.14 quads purchased in 1971 by the 13 industries selected for
study, or 0.4% of the 27 quads purchased by all industry (see Table 1-1)
• Qualitative criteria relating to probability and potential for
process change, and the energy and effluenf consequences of such
changes.
In order to allow for as broad a coverage of technologies as possible, we
then reviewed the ranking, eliminating some industries in which the process
changes to be studied were similar to those in another industry planned for
study. We believe the final ranking resulting from these considerations identi-
fies those industry sectors which show the greatest possibility of energy con-
servation via process change. Further details on this selection process can be
found in the Industry Priority Report prepared under this contract (Volume II).
On the basis of this ranking method, the phosphorus/phosphoric acid industry
appeared in 12th place among the 13 industrial sectors listed.
TABLE 1-1
SUMMARY OF 1971 ENERGY PURCHASED IN SELECTED INDUSTRY SECTORS
SIC Code
, - In Which
Industry Sector 10 Btu/Yr Industry Found
1. Blast furnaces and steel mills 3.49 3312
2. Petroleum refining 2.96 2911
3. Paper and allied products 1.59 26
4. Olefins 0.984 ^ 2818
5. Ammonia 0.63^ 287
6. Aluminum 0.59 3334
7. Textiles 0.54 22
8. Cement 0.52 3241
9- Glass 0.31 3211, 3221, 3229
10. Alkalies and chlorine 0.24 2812
11. Phosphorus and phosphoric
acid production 0.12 2819
12. Primary copper 0.081 3331
13. Fertilizers (excluding ammonia) 0.078 287
Estimate for 1967 reported by FEA Project Independence Blueprint,
p. 6-2, USGPO, November 1974.
(2)
Includes captive consumption of energy from process byproducts
(FEA Project Independence Blueprint)
Olefins only, includes energy of feedstocks: ADL estimates
(4)
Amonla feedstock energy included: ADL estimates
(5^ADL estimates
Source: 1972 Census of Manufactures, FEA Project Independence Blueprint,
USGPO, November 1974, and ADL estimates.
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C. CRITERIA FOR PROCESS SELECTION
In this study we have focused on identifying changes in the primary
production processes which have clearly defined pollution consequences. In
selecting those to be included in this study, we have considered the needs
and limitations of the EPA as discussed more completely in the Industry
Priority Report mentioned above. Specifically, energy conservation has been
defined broadly to include, in addition to process changes, conservation of
energy or energy form (gas, oil, coal) by a process or feedstock change.
Natural gas has been considered as having the highest energy form value
followed in descending order by oil, electric power, and coal. Thus, a
switch from gas to electric power would be considered energy conservation
because electric power could be generated from coal, existing in abundant
reserves in the United States in comparison to natural gas. Moreover, pollu-
tion control methods resulting in energy conservation have been included
within the scope of this study. Finally, emphasis has been placed on process
changes with near-term rather than long-term potential within the 15-year
span of time of this study.
In the phosphorus/phosphoric acid industry, an unusual energy/process
option consideration exists. In some phosphate markets, phosphorus produced
at the expense of electric energy competes with wet-process phosphoric acid
produced by digestion with sulfuric acid, with sulfur serving as both a
reagent and an energy source. This consideration turned out to be important
to our study.
'In addition to excluding from consideration better waste heat utilization,
"housekeeping," power generation, and fuel switching, as mentioned above,
certain options have been excluded to avoid duplicating work being funded
under other contracts and to focus this study more strictly on "process
changes." Consequently, the following have also not been considered to be
within the scope of work:
• Carbon monoxide boilers (however, unique process vent streams
yielding recoverable energy could be mentioned),
• Fuel substitution in fired process heaters;
• Mining and milling, agriculture, and animal husbandry,
• Substitution of scrap (such as reclaimed textiles, iron, aluminum,
glass, and paper) for virgin materials.
• Production of synthetic fuels from coal (low-and high-Btu gas,
synthetic crude, synthetic fuel oil, etc.); and
• All aspects of industry-related transportation (such as trans-
portation of raw material).
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D. SELECTION OF PHOSPHORUS/PHOSPHORIC ACID INDUSTRY PROCESS OPTIONS
Within each industry, the magnitude of energy use was an important
criterion in judging where the most significant energy savings might be
realized, since reduction in energy use reduces the amount of pollution
generated in the energy production step. Guided by this consideration,
candidate options for in-depth analysis were identified from the major energy
consuming process steps with known or potential environmental problems.
After developing a list of candidate process options, we assessed sub-
jectively
• pollution or environmental consequences of the process change,
• probability or potential for the change, and
• energy conservation consequences of the change.
Even though all of the candidate process options were large energy users,
there was wide variation in energy use and estimated pollution loads between
options at the top and bottom of the list. A modest process change in a major
energy consuming process step could have more dramatic energy consequences
than a more technically -significant process change in a process step whose
energy consumption is rather modest. For the lesser energy-using process
steps process options were selected for in-depth analysis only if a high
probability for process change and pollution consequences was perceived.
Because of the time and scope limitations for this study, we have not
attempted to prepare a comprehensive list of process options or to consider
all economic, technological, institutional, legal or other factors affecting
implementation of these changes. Instead we have relied on our own background
experience, industry contacts, and the guidance of the Project Officer and
EPA advisors to choose promising process options (with an emphasis on near-
term potential) for study.
Reconciling such difficulties with the desire to cover as wide a spectrum
as possible of the consequences of process change, the following candidates
were considered:
• Chemical Cleanup of Wet-Process Phosphoric Acid
• Solvent Extraction Process for Wet-Process Phosphoric Acid
• Byproduct Sulfuric Acid for Wet-Process Phosphoric Acid
• "Strong Acid" Systems for Wet-Process Phosphoric Acid
• Blast-Furnace Production of Phosphorus
• Minor Variations of the Conventional Wet-Process Phosphoric Acid
System
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After discussion with the EPA Project Officer, his advisors, and
industry representatives, we chose the first four from this list for analysis
because:
• It is not likely that the Blast-Furnace Phosphorus Method will be
economically acceptable.
• No pollution or energy considerations of importance are involved in
the proprietary process variations offered to the industry by
contractors and process licensors.
These last two options are only qualitatively discussed based on readily avail-
able information. As it turns out, the byproduct sulfuric acid and the "strong
acid" process are also of less interest and are treated with less detaj.1 than
the "clean-up" processes.
In this study, the phosphorus/phosphoric- acid industry description is
based on 1973, the latest representative year for the industry for which we
had good statistical information. Recognizing that capital investments and
energy costs have escalated rapidly in the past few years and have greatly
distorted the traditional basis for making cost comparisons, we developed
costs representative of the first half of 1975, using constant 1975 dollars
for our comparative analysis of new and current processes.
5,
-------
II. FINDINGS AND CONCLUSIONS
A. PRODUCT TRENDS
Phosphorus and its compounds are important requirements for many
industries, and the establishment of new plants to support the growth of
phosphate products is assured. The principal requirements are in fertilizers,
food chemicals, industrial phosphates, and detergents. The fertilizer
requirement will continue to be supplied in the conventional manner by diges-
tion of phosphate rock with sulfuric acid in the so-called wet-process route.
Elemental phosphorus, food grade "chemicals, and industrial phosphates where
high purity is required will be derived from elemental phosphorus produced in
an electric furnace as at present. Immediate expansion of the electric
furnace industry is not foreseen because of the high capital costs required,
the shortage and cost escalation of electric power, and the uncertainty of
costs for pollution control. As requirements for detergent phosphates
increase, the total potential demand for elemental phosphorus will exceed
furnace capacity. It is likely that the opportunity for production of deter-
gents from wet-process acid will then be exploited.
B. PHOSPHORIC ACID: ELECTROTHERMAL VS WET PROCESS
Expansion of the production of phosphoric acid for industrial phosphates
will require a choice between an elemental phosphorus basis and a wet-process
system with the addition of a cleanup method.
From an overall energy standpoint the wet process is much more efficient
than the electric furnace process. It requires about 16 x 10^ Btu per ton
of ?2®5 Pro
-------
component of the phosphate rock and which have been removed from gaseous
streams by scrubbing. The removal and management of the fluorides are more
easily carried out in the wet process plants. However, the long-term con-
tainment of the fluoride-containing gypsum solids is a problem analogous
to that facing the steam-electric generating industry in its disposal of
sludges from flue gas desulfurization, and it is an area where research and
development is needed to delineate the disposal methods most acceptable to
regulatory agencies.
In the electric furnace plants, coke must be handled in large quantities
and at high temperatures and its control is difficult. In general, the opera-
tions of the feed preparation sections and of the electric furnace require ex-
tensive solids-handling systems at high temperatures and create rock and carbon
dust which is difficult to contain. Problems of quenching hot slag and handl-
ing ferrophosphorus (byproduct of electric furnace) also contribute to this
dust control problem.
Fluorine is a component of phosphate rock and its disposal is a problem
faced by each process. It eventually appears as HF or SiF^ gas in vent
streams from the process and is recovered by scrubbing. These scrubber
effluents can be managed more easily in the wet process plants. Finally,
the product of the electric furnace is elemental phosphorus and there is an
inherent hazard in storing, handling, and shipping this material. Contact
with process water is required, and small amounts of entrained phosphorus
create problems with cleanup of this "phossy" water.
C. CLEAN WET-PROCESS PHOSPHORIC ACID OPTIONS
There are two methods of modifying the wet-process system so that the
phosphoric acid produced is clean enough for production of detergent phosphate:
the chemical cleanup and the solvent extraction systems. Economic, energy, and
pollution factors significant for these options are summarized in Table II-l.
TABLE II-l
SUMMARY OF COSTS/ENERGY/ENVIRONMENTAL CONSIDERATIONS
OF PROCESS OPTIONS IN PHOSPHORUS/PHOSPHORIC ACID PRODUCTION
Base line process: Electrothermal Phosphoric Acid
Process Options
B
COSTS
ENERGY
ENVIRONMENTAL
Chemical Cleanup
Competitive for detergent-grade
phosphates.,
Less sensitive to escalating
electricity, capital costs.
Clean wet-process acid -
$294.12/ton P20c.
Furnace acid = $337.82/ton ?2°5-
Total energy required is
16 x 106 Btu/ton P205 instead
of 79 x 106 for base line.
Gypsum disposal at 4 tons/ton
P2t>5 is required.
Cost = $15.13/ton ?205
Difficult dust and fume problems
at electric furnace avoided.
"Phossy" water problem eliminated.
Transport of P^ eliminated.
Cost = $24.11/ton
Solvent Extraction
Likely to be more expensive
than option A.
Depends upon cheap HC1
Same as A.
t
Calcium chloride brine at 2.6
tons/ton P205 must be disposed
of, but problem of disposal of
HC1 is avoided.
Same as A.
-------
1. Economics
The economic viability of incorporating one of these methods with a wet-
proc^ess plant, instead of production from elemental phosphorus, depends to a
large extent on the price at which phosphate rock, sulfur, or hydrochloric
acid can be made available to the producer. These prices will vary greatly
with plant location and among companies; an integration to phosphate rock
production is a great asset. We have illustrated this point in Figure II-l
which compares the price at which rock available to an electric furnace pro-
ducer in the West is competitive with rock prices delivered to a midwestern
wet-process plant. A delivered price of suitable rock at $30 per ton to a
midwest plant would be competitive with rock at $15 per ton delivered to a
western electric furnace plant. At these rock prices the cost of detergent-
grade acid from either source would be about $240/ton ^2^5- These methods of
supplying clean wet-process acid have been commercially demonstrated, and the
adoption of one or the other for expanded detergent phosphate production is
likely.
S
"•To
i*
°t
g"
30
25
20
15
COST OF Fl
OF CLEAN
SI 4.85 -"^
JRNACEACID
/VET-PROCESS
/J
= COST
ACID S
/
SULFUR S>
COKE@40
FURNACE
/
/
45.00/TON
00/TON
>OWER @6MI
/
/
.LS/KWH
25
30
4S
FLORIDA ROCK - DELIVERED MIDWEST
(S/TON (§> 30% P205)
Figure II-l.
Phosphate Rock Price Analysis
of Clean Phosphoric Acid
- Midwest Production
8
-------
2. Energy
A summary of the energy trade-off associated with these options is
tabulated below. The electricity consumed in the furnace is the dominant
factor, with the result that furnace acid requires 79 x 10^ Btu/ton ?2Q5>
chemical cleanup 16 x 106, and solvent extraction 13 x 106. When sulfur is
considered as a fuel, its energy contribution is significant (13 x 106 Btu)
but less than that of the coke charged to the electric furnace. The analogous
energy contribution in the solvent extraction system is hydrochloric acid, but
we have not attempted to trace its energy content to first sources. It is a
byproduct material and its manufacture will not be influenced by use for
phosphoric acid.
TOTAL ENERGY REQUIRED (Btu Equivalent)
(106 Btu/Ton P205)
Goke
Fuel
Sulfur
HC1
Steam
Electricity
TOTAL
Furnace Acid
16
3
60_
79
Wet-Process plus
Chemical Cleanup
13
16
Byproduct HC1 and
Solvent Extraction
No Charge
10
_3
13
3. Environmental
a. Effluent Quality
Each of the three* alternate routes to phosphoric acid generate wastewater
streams which must be treated prior to discharge. Some of the pollutants pre-
sent in the treated effluent are common to all three alternatives, while others
are characteristic of specific alternatives. In general terms:
• All three alternatives produce treated effluents which contain
low (but not insignificant) amounts of soluble phosphates and
. fluorides.
i
• The treated effluents from the elemental phosphorus alternative and
the chemical cleanup alternative both contain moderately high con-
centrations of sulfates.
• The treated effluent from the wet process-solvent extraction alter-
native is generally devoid of sulfates, but contains an extremely
large quantity of calcium chloride. The wastewater also contains
a moderate amount of n-butanol solvent.
*Electrothermal phosphoric acid, wet-process plus chemical cleanup, wet-
process with solvent extraction.
-------
In our assessment, the high concentration (13.6%) of calcium chloride
present in the treated effluent from the wet process-solvent extraction
alternative will render it unsuitable for discharge into most receiving
streams. For estimation of pollution control costs, we assumed that the
most feasible disposal method for this waste stream is deep-well injection
(where permitted).
A summary of wastewater flow rates, concentrations, and waste loadings
is presented in Table II-2.
We conclude that, from a water pollution standpoint, the wet process-
neutralization/precipitation alternative is the most favorable. The wet
process-solvent extraction is the least favorable", solely due to the serious
calcium chloride brine disposal problem.
b. Wastewater Treatment Cost and Energy Consumption
\
Economically feasible wastewater treatment control technology is available
for. each of the three alternatives. Estimates of comparative treatment costs
are presented in Table II-3. As shown, the elemental phosphorus alternative
is the most expensive, while the wet process (chemical cleanup) alternative
is the least costly. The costs are very close to each other; and plant-to-
plant variations and site-specific factors could easily upset the relative
cost ratios. In general, it can be concluded that no one process has a very
significant treatment cost advantage over the other. (It should be noted that
deep-well disposal, although perhaps economically feasible, is only a viable
option in regions where geological formations are favorable. If the calcium
chloride brines were required to be converted to calcium chloride salt, the
operation would be energy-intensive. Furthermore, the major markets for
calcium chloride are for road deicing, especially in the northern tier of
states and Canada, as well as in the cement industry for removal of sodium
and potassium as the chloride. In either instance the potential for high
concentrations of chlorides entering ground or surface waters has not been
decreased from the potential that exists at the plant. In fact, road deicing
would result in a much wider potential distribution with probably greater
impact on drinking and surface waters. Obviously, the disposal of brines is
a significant problem.) The cost of wastewater treatment (as arrived at
within the bases of this study) is a relatively small percentage of the total
production cost.
None of the wastewater treatment processes is highly energy-intensive,
and even the highest wastewater treatment energy consumption is a very small
fraction of the total process energy consumption.
10
-------
TABLE II-2
ALTERNATIVE ROUTES TO PHOSPHORIC ACID-
COMPARISON OF TREATED WASTEWATER CHARACTERISTICS
(Basis: 50,000 tpd P205)
Wastewater Characteristics
Total Suspended Solids
Phosphorus (P,)
Phosphate (PO^"3)
Sulfate (S04~2)
Fluoride (F~)
Calcium Chloride (CaCl2)
n-Butanol
Total Acidity (as CaCOj)
Wastewater Flow Rate
Electrothermal
Elemental
Phosphorus
(mg/1) (Ib/day)
20
145
Wet Process
Chemical Clean-Up
(mg/1) (Ib/day
20
36
Wet Process
Solvent Extrac-
tion Purification
(mg/1) (Ib/day)
20
132
5
2020
15
0
0.88
37
14,830
110
0
mgd
20 36
2000 3600
15 27
0 0
0.216 mgd
5.4
4.1
136,400
180
no data
0.792
36
27
901,300
1,200
no data
mgd
Source: Arthur D. Little, Inc., estimates, based on Development Document for
Phosphorus Derived Chemicals . . . U.S. Environmental Protection Agency,
EPA 440/1 - 73/006, 1973.
TABLE II-3
ALTERNATIVE ROUTES TO PHOSPHORIC ACID-
COMPARISON OF WASTEWATER TREATMENT COSTS
(Basis: 50,000 tpy
Wee Process Wet Process
Elemental Neutral./Precip. Solvent Extraction
Phosphorus Purification Purification
Capital Investment $930,200
Direct Operating Costs
Labor
Maintenance (Labor & Materials)
Chemicals .
Electricity (<3 0.006/kWh)
Sludge Disposal
Total Direct Operating Costs $313,050
Indirect Costs
$292,000
$ 48,700
11,700
87,800
13,300
161,400
$322,900
Energy Consumption -
(Fuel Equivalents -
106 Btu/ton P2<>s)
Source: Arthur D. Little, Inc., estimates
$636,000
$395,600
Depreciation (@ 9Z)
Return on Investment (@ 20%)
Taxes and Insurance (@ 22)
Total Indirect Cost
Annual Total Cost
Unit Cost ($/ton PjOj)
Wastewater Treatment
$ 83,700
186,100
18,700
$288,500
$601,550
$12.03
0.0578
' $ 26,300
58,400
5,800
$90,500
$413,400
$8.27
0.140
$ 57,200
127,200
12,700
$197,100
$592,700
$11.85
0.850
11
-------
c. Solid Waste Related to Wastewater Treatment
All three systems process significant amounts of wastewater treatment
sludge. In each case, the sludge contains large amounts of calcium fluoride
and calcium phosphates and cannot be disposed of indiscriminately. Estimated
quantities of wastewater treatment sludge are given below.
Quantity of Sludge
. Alternative (tpy wet basis)
I. Elemental phosphorus 84,750
II. Wet process - neutralization/
precipitation 80,700
III. Wet process - solvent extraction 45,500
Although the mass of sludge from the solvent extraction alternative
is about one half that of the other alternatives, it is more environmentally
objectionable due to the high concentration of soluble chemicals which could
rapidly leach from the sludge.
D. USE OF BYPRODUCT SULFURIC ACID
The wet-process industry has the option to operate with purchased
byproduct sulfuric acid rather than with sulfur. It is likely that the price
of sulfuric acid to such an operation would be negotiated with the result
that the cost of phosphoric acid product would be competitive with that from
an ordinary wet-process acid system. In addition to purchasing sulfuric acid,
a plant independent of a sulfuric acid plant would require steam at about
3 million Btu/ton P205- This steam might be generated with an on-site steam
boiler, or could be purchased from a utility if the plants are adjacent.
Pollution problems directly associated with phosphoric acid would be the
same; the pollution problems normally part of the sulfuric acid plant would •
be eliminated.
E. STRONG ACID PROCESSES
Another alternative system for wet-process phosphoric acid production is
to operate the digestion system at phosphoric acid concentrations of about 50%
P205. Evaporation of the product acid is not required under these conditions.
The digestion system must be operated at a temperature of about 100°C and the
calcium sulfate is separated as the hemihydrate. The process is claimed to be
competitive with the standard wet-process system and would be particularly
attractive at .an integrated fertilizer production site where additional process
units can use the steam no longer required for evaporation. Evolution of
fluorides from the digester can be expected to be more severe than with the
standard wet-acid system, but the evaporator vent stream is eliminated. On
an overall basis, about the same pollution control problems as experienced with
the standard wet-process system can be expected.
The adoption of a strong acid process with the use of byproduct sulfuric
acid would be attractive on an energy basis.
12
-------
F. SECONDARY OPTIONS
1. Blast Furnace Phosphorus
Elemental phosphorus can be produced in a blast furnace which utilizes
coke as a fuel rather than energy from electricity. There were commercial
furnaces of this type, but they were abandoned with the advent of cheap
electricity. Capital costs are about 60% higher than for an electric furnace
system and the quantity of coke required is more than doubled. The high
electric load of the electric furnace is eliminated at the expense of burning
fuel in the form of coke. In addition, coke equivalent to that consumed in
the electric furnace must be used to achieve the reduction of ?2®5" Pollution
problems associated with dust and furnace ventilation are likely to be more
severe than with the electric furnace system because the quantity of furnace
gas is greatly increased.
2. Other Options
There are a number of variations of the conventional wet-process system
which have only minor interest for our study. We have also reviewed and dis-
cussed briefly extraction of uranium from wet-process acid and the exploitation
of tailings and low-grade reserves.
Economic, energy, and environmental considerations of use of byproducts
H^SO^, the "strong-acid" process, and blast-furnace phosphorus are summarized
in Table II-4.
TABLE II-4
SUMMARY OF COSTS/ENERGY/ENVIRONMENTAL CONSIDERATIONS
OF SECONDARY PROCESS OPTIONS IN PHOSPHORUS/PHOSPHORIC ACID INDUSTRY
Process Options
For mfg of wet-process
fo'r fertilizerjis
For elemental
phosphorus^
Baseline
Process
Economics
Energy
Environmental
C
Byproduct H-SO^
Wet-Process P
Investment
Reduced
Operating costs
depend on price
of,H2SOi
Steam required f
equivalent to 2x
Sulfurlc acid
plant pollution;
Control costs
eliminated
D
Strong Acid
losphorlc Acid
Competitive
>r evaporation*
0<> Btu/con ?20j
No Change
E
Blast Furnace Pt
Electric Furnace
Probably not
Competitive
Flectrlcifv
eliminated, 130
x 106 BTU/ton P4
caved but equiv-
alent coke muse
be burned.
Utilization of
fuel value of
CO doubtful -
CO must be vente
13
-------
III. PHOSPHATE INDUSTRY OVERVIEW
A. INDUSTRY STRUCTURE
Commercial mining of phosphate rock occurs in several areas of the
United States. The most important area by far is Central Florida, but major
deposits are also being worked in North Carolina, Tennessee, and the Mountain
States.
Approximately 83% of the phosphate rock mined (apart from that exported
as such) is used in the production of phosphate fertilizers. These are
mostly for domestic use, but substantial quantities are exported. The
remaining 17% is used in the manufacture of various industrial phosphate
materials.
Two processing methods are used to transform phosphate rock into commer-
cial products. The most widely used process produces so-called wet-process
phosphoric acid by the acidulation of phosphate rock with sulfuric acid.
Phosphoric acid produced by this method is used almost entirely in the pro-
duction of phosphate fertilizers, although one plant uses this process for
industrial phosphates.
The second process consists of the treatment of phosphate rock in an
electric furnace to produce elemental phosphorus. Most of this is then used
to produce a purer grade of phosphoric acid than that available from the
wet-process, although small quantities of phosphorus are used directly in the
synthesis of phosphorus-based chemicals. Small quantities of furnace phos-
phoric acid occasionally find markets in the fertilizer area, but for the
most part phosphorus-derived acid is restricted to the industrial phosphate
area.
The wet-process phosphoric acid plants are located for the most part
adjacent to phosphate rock mines in Florida, North Carolina, and to a small
degree in the Mountain States. The production of phosphorus is concentrated
in the Tennessee area close to mines, and in the western Mountain States also
close to phosphate rock mining activities. There are, however, a number of
wet-process phosphoric acid plants located close to fertilizer markets but
distant from the phosphate rock mining operations. We have listed wet-process
phosphoric acid plants by company and location in Table III-l and illustrated
them in Figure III-l.. These include plants currently in operation and those
under construction.
14
-------
TABLE III-l
PHOSPHORIC ACID PLANT CAPACITY
(000 metric tons P00C)
Company
Agrico
it
Allied Chemical
Beker Industries
Borden Chemical
CF Industries
Collier Carbon
Conserve
Duval
Farmland Industries
First Mississippi Corp.
Freeport Minerals
Gardinier
Location
Florida
Louisiana
Louisiana
Idaho
Illinois
Louisiana
Florida
Florida
Calfornia
Florida
California
Florida
Iowa
Louisiana
Florida
Arkansas
Florida
Idaho
W.R. Grace & Company
Gulf Resources
Int'l.Minerals & Chemical Florida
Mississippi Chemical Corp.Mississippi
Mobil Chemical
N.Carolina Phosphates
Occidental Petroleum
11
Olin Corporation
ti
Phosphate Chemicals
Royster
Simplet
Stauffer Chemical
Texasgulf
USS Agrichemicals (
Valley Nitrogen
TOTAL U.S.
Illinois
North Carolina
Florida
California
Texas
Illinois
Texas
Florida
Idaho
Utah
North Carolina
Florida
California
Phosphoric Acid
Capacity
306
362
145
231
94
187
158
1,136
13
136
13
412
172
680
493
45
297
29
680
181
113
362
525
28
270
115
45
122
217
90
621
240
126
9,006
Source: TVA publications.
15
-------
Wet-Process Phosphoric Acid Plants
Source: National Fertilizer Development Center, Tennessee Valley Authority,
Muscle Shoals, Alabama.
Figure III-l. Wet-Process Phosphoric Acid Plants in the United States
-------
There are some 28 phosphorus furnaces in operation in the United States,
operated by six producing companies and the U.S. Government. These are
listed in Table III-2.
TABLE III-2
PHOSPHORUS PRODUCERS
Company
Holmes Company
FMC Corporation
Mobil Chemical
Monsanto Company
Hooker Chemical
Stauffer Chemical
Location
Number
Operating Furnaces
Pierce, Florida
Pocatello, Idaho
Nichols, Florida
Soda Springs, Idaho
Columbia, Tennessee
Columbia, Tennessee
Silver Bow, Montana
Tarpon Springs, Florida
Mt. Pleasant, Tennessee
Muscle Shoals, Alabama
2
4
1
3
6
3
2
1
3
3
Operating Furnace
Capacity (tons P )
20,000
145,000
5,000
110,000
135,000
60,000
42,000
23,000
45,000
40,000
658,000
Source: National Fertilizer Development Center, Tennessee Valley Authority,
Muscle Shoals, Alabama.
The production of furnace phosphoric acid from elemental phosphorus is
generally located close to market locations because of the economies of ship-
ping concentrated phosphorus instead of the finished acid. There are some
23 furnace phosphoric acid plants in operation in the United States, and
these are listed in Table III-3. Figure III-2 shows the geographical loca-
tions of the phosphorus furnaces and furnace phosphoric acid plants in the
United States.
As mentioned above, most wet-process acid is used in the manufacture of
various phosphate fertilizers. However there is one plant, operated by the
Olin Corporation, Joliet, Illinois, that produces phosphoric acid solely for
the production of industrial phosphates. The principal phosphate fertilizers
produced from wet-process acid include triple superphosphate, monoammonium
phosphate, diammonium phosphate, and various compounds of fertilizers con-
taining all three plant nutrients - nitrogen, phosphate, and potash. Small
but significant quantities of phosphoric acid are also used in the production
of liquid mixed fertilizers, either solution or suspension.
17
-------
TABLE III-3
LOCATION OF FURNACE ACID PLANTS
Producers
Plant Location
Grouped Company
Capacity
(tons ?0*
FMC Corporation
Mobil Oil Corporation
Monsanto Company
"Occidental Petroleum Corp.
Stauffer Chemical Company
TVA
Goodpasture, Inc.
Total
Carteret, New Jersey
Lawrence, Kansas
Newark, California
Green River, Wyoming
Carteret, New Jersey
Fernald, Ohio
Augusta, Georgia
Carondolet, Missouri
Kearny, New Jersey
Long Beach, California
Trenton, Michigan
Dallas, Texas
Jeffersonville, Indiana
Columbia, Tennessee
Chicago, Illinois
Chicago Heights, Illinois
Morrisville, Pennsylvania
Nashville, Tennessee
Richmond, California
Silver Bow, Montana
South Gate, California
Muscle Shoals, Alabama
Brownfield, Texas
340,000
115,000
455,000
85,000
250,000
75,000
45,000
1,365,000
Source: National Fertilizer Development Center, Tennessee Valley Authority,
Muscle Shoals, Alabama.
18
-------
****
I 3 '^rr —
Iv /
/fl /
/ ^ /
/ °«W — 4
'
^
s
0^-7--. /
/ ^^-,
i
>
\
s
S»-
V.
Irj*i5^\l
•°AHo .
i
-J8/
1 "TAff-l I
N. DAKOTA
S. DAKOTA
<
irtuiA i
\
NEBR;
i
.
*SKA^~^\ VilL!
\ f
XMISSOURI \
KANSAS v. \
CONN.
(NO. \
OHIO
WMEvEvV"—I—J—•
TE-JSTI °KLAHOMA
v
V..
• Location of Furnace Acid
Plants
v Phosphorus Producers
Source: National Fertilizer Development Center, Tennessee Valley Authority,
Muscle Shoals, Alabama.
Figure III-2. Phosphorus Furnaces and Furnace Phosphoric Acid Plants in the United States
-------
There also are substantial exports of solid phosphate fertilizer,
principally diammonium phosphate and triple superphosphate. Exports have
run as high as 1.5 million tons of P205 Per year compared to the domestic
consumption of about 5.0 million tons of P2C>5 in fertilizers.
Industrial phosphate consumption amounts to approximately 1.2 million
tons of P205- The approximate distribution of industrial phosphate demand in
1972 is shown in Table III-4.
TABLE III-4
INDUSTRIAL PHOSPHATE DEMAND
(000 tons P2°5)
Elemental phosphorus 165
and non-acid derivatives
Phosphoric acid derivatives
Sodium tripolyphosphate (STPP) 600
All others 240
Furnace phosphoric acid
Direct use 120
Fertilizer 115
Phosphorus exports 45
Miscellaneous 100
TOTAL 1,385
The importance of sodium tripolyphosphate used primarily as a builder
in the formulation of detergents is obvious from this table. It accounts for
almost 50% of total industrial phosphate demand.
As can be seen from Tables III-2 and III-3, the industrial phosphate
industry is highly integrated, most of the manufacture of furnace phosphoric
acid being undertaken by basic phosphorus producers.* The production of
derivatives of furnace phosphoric acid is also largely undertaken by the same
companies that produce phosphorus and furnace acid.
*It should be noted that the Hooker Chemical Company is a subsidiary of
Occidental Petroleum.
20
-------
B. OUTLOOK FOR THE INDUSTRY
The fertilizer segment of the phosphate industry is currently facing a
substantial overcapacity due to a number of new plants that have either come
on-stream recently or are expected within the next year or two. This together
with a short-term outlook for reduced growth in fertilizer usage should lead
to some downward pressure on phosphate fertilizer prices. However, this is
sufficiently distinct from the industrial phosphate fertilizer industry that
it should have little effect on the latter area.
Much of the future growth in demand for industrial phosphates will depend
on the outlook for sodium tripolyphosphate. It is believed that most of the
reduction in usage of this compound in detergent formulations because of
environmental considerations has already taken place, and future growth in
demand for the product would continue at a fairly normal rate - expected to
be in the neighborhood of 2%-3% per year. Our market demand forecast thus
represents a moderate position. It is about 20% less than if environmental
restraints were removed. On this basis, additional plant capacity would
probably be needed toward 1980. As discussed elsewhere in this report, this
is likely to take the form of new production units, based on clean wet-process
phosphoric acid, rather than from the construction of additional phosphorus
furnaces. '
21
-------
IV. CURRENT TECHNOLOGY
A. PROCESS CONSIDERATIONS
Phosphate ore is an important mineral resource of the United States;
important deposits are located in Florida, Tennessee and North Carolina in
the East, and in the western Mountain States. This mineral is a complex
of the phosphate and fluoride salts of calcium. It is known as fluorapatite
and is commonly represented by the formula 3Ca3(PO^)2*CaF2» Fluorine is
usually present in the ore at a ratio of about 10% of the phosphate.
A number of circumstances will probably have important effects upon
the development of the technology of the industry. For example, phosphate
(P20s) accounts for about 30% of the ore processed; the other 70% includes
silica, fluorine compounds, calcium minerals, and a number of metallic con-
stituents. In one way or another this latter group of materials, plus any
reagents, such as sulfuric acid or coke, must be disposed of as plant
effluents. With the strict standards that must now be considered, the dis-
posal problem has become especially important to the industry. A second
important circumstance is the end-use markets for phosphorus and its com-
pounds and the growth of these markets, because the phosphoric acid produced
from the wet process must be used primarily in fertilizers, whereas the
phosphoric acid that is derived from electric-furnace phosphorus must be
used primarily in detergent and phosphate chemical manufacture. Since
phosphoric acid is the principal product of each of these processes, one
would suppose that there is considerable opportunity to use phosphoric acid
from each process interchangeably. Technically, this supposition is
correct. Wet-process acid has indeed been used for detergent phosphates
and phosphorus from the electric furnace could be converted to phosphoric
acid and the acid used in fertilizers. Economically, however, the supposi-
tion is false. Purification of the wet-process acid to the degree required
for detergent phosphate is difficult and the process has been slow to be
adopted commercially. Conversely, the economics of the cleaner electric
furnace acid generally have not favored use of this acid in fertilizers.
The importance of this constraint lies in the difference in energy
consumption between the wet process and the electric furnace methods. The
electric furnace process yields elemental phosphorus (?4) at an expenditure
of about 13,000 kWh/ton of P^. Coke is also burned as a reductant in the
electric furnace and represents an additional major fuel requirement. A
considerable part of this energy is released as heat of reaction when the phos-
phorus is burned to phosphoric acid, but it is not practical to recover it
22
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because the elemental phosphorus is not usually converted to phosphoric acid
at the electric furnace facility. Instead.it is shipped to scattered sites
and the acid produced on a much smaller scale. In the wet process, sulfur is
shipped to the point of phosphoric acid manufacture, 'and converted there to
the sulfuric acid needed to digest the phosphate rock in efficient plants.
Because the sulfur is being converted to sulfuric acid at just one site, the
plant can be made efficient enough to recover the heat of combustion from the
conversion reaction and use this heat to generate steam for the phosphoric acid
plant. The net result is that the heat of combustion of the sulfur is utilized
as an important energy input in the wet process for phosphoric acid.
B. BASE LINE: FURNACE ACID-ELECTRIC FURNACE PRODUCTION OF PHOSPHORUS AND
CONVERSION OF PHOSPHORUS TO PHOSPHORIC ACID
1. Process Description*
An electric furnace system for the conversion of phosphate rock to ele-
mental phosphorus is shown in Figure IV-l. The primary reaction in the
electric furnace is the reduction of ?2®5 to ^4 ^y the use of carbon. Elements
such as calcium react with silica to form a slag.
Each of the three furnace feed materials—the phosphate ore, the coke,
and the silica—must be carefully prepared to allow proper operation of the
furnace. The diagram shows one method of preparing a suitable phosphate
burden. Phosphate rock is fed to a direct-fired rotary kiln where it is
heated to a temperature of incipient fusion (about 2500°F). It is then pro-
cessed through a screening operation to a suitable size range (1/4 to 1 inch).
Oversized material is crushed and recycled to the kiln along with the under-
size fraction; the kiln gases must be scrubbed to remove dust and fluorides.
Carbon monoxide produced in the electric furnace is used for part of the kiln
fuel requirements. The coke and silica streams must also be carefully dried
and of a proper size before they are fed to the electric furnace. In addi-
tion to being of- proper and uniform size, the charge materials must be free
from fines in order to feed properly into the electric furnace. The solid
furnace burden floats on top of the molten materials in the furnace. The
phosphorus is produced in gaseous form as P^. Carbon monoxide is the prin-
cipal byproduct and is removed along with the phosphorus. Before condensing
the phosphorus it is necessary to operate an electrostatic precipitator on
this gas stream to remove and recover dust carried out of the furnace. The
phosphorus is then liquified in a water-cooled condenser and the carbon
monoxide piped away for use as fuel in the kiln.
There are currently two major sites in the United States for electric
furnace phosphorus production. One is in Tennessee where furnaces are oper-
ated by Monsanto, Hooker, and Stauffer. The TVA also operates a large
furnace system there, but has announced that is will be shut down. In the
Mountain States, Monsanto and FMC operate furnaces in Idaho and Stauffer
*(Waggaman et al, 1952), (Van Wazer, Jr», 1961)
23
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NODULIZING
FINES SCREENING
TO SCRUBBER
TO STORAGE
ELECTRIC FURNACE OPERATION
STORAGE BINS
PHOSPHATE SILICA COKE
PHOSPHORUS SEPARATION
ELECTROSTATIC
PRECIPITATORS
GAS PUMP & FURNACE
PRESSURE CONTROL
WEIGH FEEDER
FERROPHOSPHORUS
TO KILN FUEL
PHOSPHOROUS TO
STORAGE TANKS
COLLECTION SUMP
Figure IV-1.. Elemental Phosphorus Production
24
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operates one in Montana. There is little important use of elemental phospho-
rus by itself. The majority of it is converted by burning in air and absorp-
tion of the oxide in water to make pure phosphoric acid suitable for deter-
gent, food grade, and fine chemical end-uses. There is some production of
phosphoric acid in this manner at the site of phosphorus production, but the
practice generally is to ship the phosphorus to the point of end-use and run
a smaller phosphoric acid plant at that site. It is believed that most
phosphorus burning plants operate at a rate of 50,000 tons of P205» or less,
annually.
2. Effluents
There are severe pollution control problems associated with elemental
phosphorus production. Principal effluents and their source are indicated in
Figure IV-2.
a. Water Pollution
There are three major wastewater streams generated by the electric fur-
nace production of elemental phosphorus:
• Nodulizer scrubber water blowdown - Gaseous emissions from the
phosphate rock nodulizer are dusty and contain fluorides (such as
HF or SiF*); therefore, they must be controlled by means of a wet
scrubber. The scrubber water is recycled. The necessary purge
stream from the recycle system is acidic, contains phosphates, sul-
fates, fluorides, and suspended solids, and must be treated prior
to discharge.
• Slag quench water - Furnace slag .is cooled by means of quenching
with a water stream. The slag quench water is slightly alkaline,
contains phosphates, sulfates, fluorides, and suspended solids,
and also must be treated prior to discharge.
• "Phossy" water - A notoriously difficult stream is the so-called
"phpssy" water. This stream results from the necessary contact of
liquid phosphorus with water in the condenser and in the transfer
lines for phosphorus. Water is also used as a seal in storage and
transport to prevent exposure of the phosphorus to air. The result
is that water discharged from these operations contains a small
amount of very finely/divided phosphorus in suspension. The
"phossy" water also contains significant amounts of phosphates and
fluorides.
The volume and pollutional loadings of the various wastewater streams
can vary considerably from plant to plant, depending on process configuration
and other site specific conditions. In some plants there is a high degree
of wastewater recycle; in other plants there is none. In any event, waste-
water discharged from elemental phosphorus plants will have to be treated to
remove phosphorus, phosphates, and fluorides, and to neutralize acidity.
25
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PHOSPHATE
ROCK
, COKE
, SILICA
, ELECTRICITY
, WATER
PHOSPHATE ROCK
NODULIZING
2500°F
COKE
DRYING
SILICA
DRYING
FERROPHOS
STACK GASES, DUST, FLUORIDES
DUST
DUST
ELECTRIC FURNACE
VENTILATION FOR FUME CONTROL
ELECTROSTATIC
PRECIPITATOR
DUST RECOVERY
PHOSPHORUS
CONDENSER
SLAG QUENCH
"PHOSSY" WATER
DUST, QUENCH WATER
SLAG
FUME, DUST
FERROPHOSPHORUS
BYPRODUCT
PHOSPHORUS PRODUCT
Figure IV-2. Process Effluents - Electric Furnace Phosphorus
26
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Metallic elements, originating in phosphate rock, can be present in the
wastewater. A typical analysis is presented below:
MINOR CONSTITUENT ANALYSIS
ELECTRIC FURNACE PHOSPHORUS OPERATION*
Constituent P Si Ca Fe Al Cr V Ni Mn
Slag 0.5 18 34 0.1 3.1
Ferrophosphorus 27 0.15 59 4.5 5.4 0.7 0.5
Water pollution regulatory constraints imposed upon the phosphorus
industry are mainly the results of the applicable effluent limitations guide-
lines published by the Environmental Protection Agency (Effluent Guidelines,
1974). The effluent limitations guidelines are based on a technical study
commonly referred to as the EPA Development Document (Development Document...
Phosphorus-Derived Chemicals, 1973). The function of the Development Docu-
ment is to characterize the industry, describe the sources of water pollution,
the wastewater characteristics, control technology currently in use, suggested
permissible effluent levels, recommended technology for their attainment, and
cost estimates for the implementation of such technology. For this study,
much of the data on wastewater characteristics and type of treatment tech-
nology required have been taken from the Development Document. However, the
industry has taken exception, through legal action, to the use of these data
by the EPA in developing effluent limitation guidelines. These objections
apply especially to the industry-wide application of data which, it contends,
are both site and time specific. Without attempting to make a judgment on
the validity of these, claims, we have chosen to utilize the data as it was
reported rather than attempt an independent modification which would be apt
to create additional confusion.
Characteristics of the various raw wastewater streams generated from an
elemental phosphorus plant of the size used in this study are presented in
Table IV-1.
There are a number of treatment alternatives that are currently being
employed or are potentially applicable. The most general treatment method
is as follows:
1, Combine the nodulizer scrubber liquor blowdown with the slag quench
water and treat with lime (in a clarifier or settling pond) to
precipitate fluorides and phosphates as calcium salts. In addition,
the lime treatment removes suspended solids and neutralizes acidity.
*(VanWazer, Jr., 1961)
27
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TABLE IV-1
CHARACTERISTICS OF RAW PROCESS WASTEWATER FROM PHOSPHORUS MANUFACTURE
Basis: 100,000 tpy phosphorus production (230,000 tpy as P^^
Wastewater
Characteristic
*.
Total Suspended Solids
Phosphorus (P/)
-3
Phosphate (P04 )
Sulfate (SO ~2)
Fluoride (F~)
Total Acidity (as CaCO )
Wastewater Flow Rate
Combined Raw
Wastewater
(mg/1) (Ib/day)
525
56
2,020
480
990
17,550
1,880
67,390
16,010
33,040
4.0 mgd
Total Treated
Effluent
(mg/1) (Ib/day)
20
5
2,020
15
0
670
167
67,390
500
0
4.0 mgd
Source: Arthur D. Little, Inc., estimates, based on "... Develop-
ment Document for Phosphorus Derived Chemicals . . .", EPA.
2. Treat the phossy water with lime or other coagulants to remove
colloidal phosphorus and to precipitate soluble fluoride and phos-
phates. The entire phossy water stream is then recycled back to
the process. The result is that there is zero discharge of phossy
water.
Based on the characteristic wastewater flow rates, pollutional loadings and
characteristic removal efficiencies, an estimate of the treated wastewater
composition is presented in Table IV-2.
The plant for conversion of phosphorus to phosphoric acid must include
a scrubbing system to remove acid fumes from the furnace effluent, but this
is a conventional unit and adequate control is not difficult or expensive.
.The treatment system required to achieve the effluent levels (shown in
Table IV-2) consists of:
1. Combined nodulizer scrubber liquor and slag quench water effluent
treatment -
• clarifiers (2 units),
• chemical feed system,
• sludge thickener,
28
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TABLE IV-2
ELECTRIC FURNACE PRODUCTION OF PHOSPHORIC ACID
WASTEWATER CHARACTERISTICS
100,000 tpy production (as P )
330 operating days/year
Nodullzer
Wastewater • Scrubber
Characteristic Liquor*
Total Suspended Solids
Phosphorus (P^)
Phosphate (PO^)
Sulfate (S04)
Fluoride (F~)
Total Acidity (as CaCO )
Total Alkalinity (as CaC03>
Wastewater Flow Rate
i
(mg/1)
280
70
1,200
730
2,000
(Ib/day)
5,100
1,270
21,830
13,280
36,380
2.18 mgd
Phosphorus
Condenser Plus Other
Phossy Water
(mg/1)
135
90
220
270
(Ib/day)
8,190
5,460
13,350
16,380
7.27 mgd
Slag I
Quenching Combined
Water
(mg/1)
820
40
(Ib/day)
12,450
610
3,000 1 45,560
|
180 | 2,730
220
3,340
1.82 mgd
Wastewater
(mg/1) i (Ib/day)
273 i 25,740
58 ! 5,460
t
162 ! 15,230
i
717 ! 67,390
344 32,390
351 i 33,040
11.27 mgd
^Assumes scrubber liquor is recirculated with a 10% blowdown.
Source: "...Development Document for the Phosphorus Derived Chemicals..."
U.S. Environmental Protection Agency, EPA 440/1-73/006, 1973.
• vacuum filtration (for sludge dewatering),
• all necessary pumps, piping, and auxiliary equipment.
2. Phossy water treatment and recycle -
• clarifiers (2 units),
• chemical feed system,
• sludge thickener,
• vacuum filtration (for sludge dewatering),
• all necessary pumps, recycle piping, and auxiliary equipment.
Capital and operating cost estimates along with the quantities of chem-
icals, energy, and sludge associated with the treatment system are presented
in Table IV-3.
It should be noted that the costs presented in Table IV-3 are for the
specific size plant used in this study and have been developed mainly for
comparative purposes; they in no way .are intended to represent industry-wide
treatment costs. The estimate is for a consolidated P^/H3P04 plant, such as
those in the west.
'29
-------
TABLE IV-3
ELECTRIC FURNACE PRODUCTION OF PHOSPHORUS AND PHOSPHORIC ACID
WASTEWATER TREATMENT COSTS
Basis: 100,000 tpy phosphorus production (230,000 tpy as P2°5)
TOTAL PLANT
CAPITAL INVESTMENT $4,279,000
DIRECT OPERATING COST
Labor 194,000
Maintenance (Labor and Materials) 171,000
Chemicals 677,000
Electricity (@ $0.006/kWh) 7,600
Sludge Disposal 390,000
TOTAL DIRECT OPERATING COST $1,439,600
INDIRECT COSTS
Depreciation (@ 9%) 385,000
Return on Investment (@ 20%) 856,000
Taxes and Insurance (@ 2%) 86,000
TOTAL INDIRECT COST $1,327,000
TOTAL ANNUAL COST $2,766,600
UNIT COST: ($/ton as P^) $ 27.67
($/ton as P0) $ 12.03
Notes:
1. Treatment consists of:
a) Lime treatment and clarification of combined nodulizer
scrubber liquor blowdown and slag quench water;
b) Lime treatment and clarification of phossy water, with
total recycle of treated phossy water stream.
2. Capital investment adjusted to March 1975 level (ENR=2126).
Source: Arthur D. Little, Inc. estimates.
30
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Even though the treatment described is capable of producing a liquid
effluent of relatively low fluoride and phosphate content, there is still a
serious solid-waste disposal problem. Since furnace slag is usually sold to
contractors, the major source of solid waste destined for ultimate disposal
is wastewater treatment sludge. The sludge volume is large (84,750 tpy @ 30%
solids) and contains very high concentrations of calcium fluoride, calcium-
phosphate salts, sulfates, and elemental phosphorus.
b. Solids Disposal
The land disposal of sludges from phosphorus manufacture requires con-
siderable acreage with the concomitant problems of surface runoff and seepage
into groundwaters. Because slight variations in process operating conditions
for all wet chemistry methods can cause wide variations in the nature of the
sludges, e.g.., these may vary from high-solid content cakes to. slurries, the
magnitude of the solids waste disposal problem can also vary widely. In
addition, elemental phosphorus and arsenic compounds can result in low-level
occurence of volatile species, such as the phosphorus oxides and arsine. The
latter is known to occur from natural sources as part of the environment's
arsenic cycle; however, local concentrations of these substances, which may
be of concern in certain disposal areas, are usually the results of leaching
from solids disposal. The prevention of groundwater seepage and the control
of surface runoff by a variety of methods - such as lining of disposal areas,
maintenance of water cover during operational periods and perhaps, ultimately,
covering of disposal areas - will probably require increasing attention.
Because the costs of these controls are highly site-specific, we have made
no attempt to detail probable costs.
c. Air Pollution
Air pollution control is a significant problem in the phosphorus plant.
The process importance of handling dusty streams in the phosphorus plant is
illustrated by the need to remove dust generated from processing raw mate-
rials (phosphate rock, coke, and silica) at a rate more than 10 times that
of the product. These particulates are produced particularly in the high-
temperature rotating equipment, but also escape from conveyors, etc. They
are usually -finely divided and contain carbon and fluorides. However,
removal of particulates can be carried out in conventional air pollution
control equipment such as cyclones, fabric filters, or electrostatic
precipitators.
i
Although dry air pollution control systems are widely used, one air
stream that requires scrubbing is the emission from the phosphate nodulizer
because it contains fluorides, such as HF or SiF^. As mentioned earlier,
this wastewater stream is combined with other wastewater streams for treat-
ment in a common facility. Similarly, the plant for conversion of phosphorus
to phosphoric acid must utilize water scrubbing to remove acid fumes from
the effluent and, again, the wastewater stream is recycled to process or
combined with others for treatment.
31
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Air pollution control systems of the type described are normal features
of present plants. Because the capital investments associated with air pol-
lution control systems are intimately involved with the manufacturing process
and, consequently, are highly dependent upon specific site conditions, it
was felt that estimates would have little meaning for comparative purposes.
Although their costs are not separately estimated, they are included in the
capital and operating costs presented for the electric furnace system.
3, Energy Requirements
Electric furnace production of phosphorus is a very energy-intensive
operation ,. As illustrated in Table IV-4, it consumes 13,000 kWh/ton of phos-
phorus, a rate second only to aluminum among the selected electric furnace-
based commercial operations included in the scope of this study. The process
is inherently wasteful because phosphorus itself is not the major commercial
product; in the subsequent combustion operation the heat released upon oxidiz-
ing the phosphorus to ?2®5 ^s l°st to t*16 atmosphere and to cooling water.
TABLE IV-4
IMPORTANT ELECTROCHEMICAL OPERATIONS
Process Electricity Required
kWh/ton product
Aluminum 15 , 600
Phosphorus 13,000
Ferro- manganese (75%) 4,600
Zinc 3,000
Calcium carbide 2,800
Copper ( electrowinning) 2,400
Coke charged to the furnace is a significant fuel requirement, but is
burned only to carbon monoxide; it must be recovered and piped to the burden
preparation unit for full use of its fuel value. Energy requirements as
auxiliary fuel for the nodulizer and as electricity for pumping operations
amount to about 10% of the electricity requirement of the electric furnace
itself.
32
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TOTAL EQUIVALENT ENERGY - SUMMARY
As Electricity 13,000 kWh = 137 x 106 Btu/ton ?4 = 60 x 106 Btu/ton ?20
As Coke 1.9 tons C = 36 x 10 Btu/ton P, = 16 x 106 Btu/ton f 0
As Supplementary 6 x 10 Btu/ton P, = 3 x 10 Btu/ton P 0
Fuel 4 2 5
179 x 10 Btu/ton P, = 79 x 10 Btu/ton P^
4. Economic Factors
The costs of conversion of phosphate rock to elemental phosphorus by the
electrothermal reduction process are detailed in Table IV-5. This estimate
is based on 1975 construction costs of a new plant in the Mountain States to
produce phosphorus at a rate of 100,000 tpy. A more realistic event would
probably be the expansion of one of the existing three plants in the region
by the addition of a furnace at about half that capacity. However, we have
no way of estimating the cost of such incremental production on a realistic
basis. Because of economies of scale in the larger plant, the unit cost of
P^, as estimated, is probably not far from that of incremental production in
an expanded plant. The result is that a producer considering expansion of
his phosphorus business by the electrothermal route must look at a production
cost of about $540/ton of phosphorus. Raw materials account for a major
fraction of this cost at $290/ton. Phosphate rock and coke are the major raw
materials and since the 1973 "energy crisis," prices have been volatile. The
prices ($20/ and $40/ton respectively) represent our best judgment of current
values, but may be quite different from an actual local circumstance. Phosphate
rock costs, are, to a certain extent, fuel-rdependent, but as captive opera-
tions of the phosphorus producer can be kept under better cost control than
coke or electricity.
Electricity is the major energy cost and amounts to'$78/ton of phosphorus.
The current price of electricity is 6 mils/kWh and its future is quite
uncertain. It is likely that the price of power in the West will increase by
a factor of 50-100% in the next decade. The price of electricity for electric
furnace phosphorus use is negotiated and subject to contract with the power
company. The high base load at a good power factor commands a favorable
price. (
A large labor force is required for operation of an elemental phosphorus
plant. About 220 men are employed in the direct' operating staff, and more
than 100 additional people in the maintenance force. The result is a total
labor cost Cincluding labor overhead) of about $75/tbn of phosphorus. Fixed
costs for plant overhead, taxes, insurance, and depreciation bring the total
estimated cost to $543.31. The depreciation cost is $28.80 and is based on
an 11-year depreciation of the plant.
33
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TABLE IV-5
ESTIMATED COST OF ELEMENTAL PHOSPHORUS MANUFACTURE
Product: Elemental Phosphorus
Annual/Deslgn • 100,000 tons P4
Capacity
Annual Productioni100.000 tons P4
Process: Electrothermal Reduction
Fixed Investment: $64,000,000
Location: Western States
Variable Costs
Raw Materials
Phosphate rock
Silica
Coke
Electrodes
Energy
Electricity
Fuel
Water
Labor.
Direct operating labor
Direct supervisory wages
Maintenance labor
Maintenance supervision
Maintenance material
Labor overhead
Operating Supplies
Ferrophosphorus credit
Slag credit
Total variable cost
Fixed Costs
Plant overhead
Local taxes & ins.
Depreciation
Total cost of manufacture
20% return on investment (pre-tax)
Pollution control (Table IV-3)
Units Used in
Costing or
Annual Cost
Basis
tons
tons
tons
Ibs
kWh
106 Btu
Man-hrs
15% Op. Lbr
Man-hrs
15% Mnt, Lbr
'3% of Cl
30% of Wages
tons
tons
60% of Wages
2% CI
9% CI
$/unit
20.00
1.40
40.00
0.24
0.006
0.80
6.00
6.50
47.00
0.85
Units/ton P^
10.0
1.25
1.9
53.0
13,000
11.0
5.15
3.0
0.14
7.2
$/ton P^
200.00
1.75
76.00
12.72
290.47
78.00
8.80
86.80
2.00
30.90
4.64
19.50
2.93
20.00
17.39
5.00
<6.58>
<6.12>
466.93
34.78
12.80
28.80
543.31
128.00
27.67
698.98
Source: Arthur D. Little, Inc. estimates
34
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An additional economic factor in the phosphorus business is the deple-
tion credit. This credit should not be considered a part of the usual cost
structure because it depends on profit. If there is no profit, there is no
depletion credit allowed. It is really a credit against income tax; the
depletion is applied as a reduction of profit before tax is calculated. Its
actual calculation follows a complex formula that depends upon the transfer
of the elements of the cost of mining and beneficiation of the phosphate rock
as part of the total cost of the operation of a phosphorus furnace plant.
In Table IV-6 we have estimated the cost of manufacture of phosphoric
acid from elemental phosphorus. This estimate is based upon a plant in the
midwest with an annual capacity of 50,000 tpy of ?205' Capital investment
for such a facility as of 1975 would be $1,700,000. Phosphorus delivered to
midwest locations would cost about $570/ton. At a conversion efficiency of
0.44 ton of phosphorus /ton of P2^5> tne phosphorus represents $250/ton cost
to. phosphoric acid. Conversion costs amount to about $12/ton for a total
cost at the plant site of $262.67/ton of
C. BASE LINE - WET-PROCESS PRODUCTION OF PHOSPHORIC ACID
1. Process Description*
Figure IV-3 is a block flow diagram which shows the method for converting
phosphate rock to phosphoric acid by digestion with sulfuric acid. The sul-
furic acid is manufactured from sulfur. The primary product of the digestion
and filtration section is 32% phosphoric acid which is concentrated by evap-
oration to the 54% P205 product.
On an overall basis, sulfuric acid reacts with tricalcium phosphate to
precipitate gypsum and form phosphoric acid in solution:
2 + 3H2S04 + 3CaS04 + 2H3P0
Conditions in the digestion system must be carefully controlled to dis
perse and dissolve all of the phosphate rock, and to precipitate gypsum
without co-precipitation of unreacted rock and in the form in which it can
be readily filtered and washed. The system is arranged so that phosphate
rock can first react with a recycled stream of phosphoric acid forming
Ca0(PO.)0 + 4H-PO. -»- 3Ca(H.PO.)
3
42 34 _»wa\"2'- 4'2
*(Waggaman, 1952; Van Wazer, Jr., 1961)'
35
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TABLE IV-6
ESTIMATED COST OF PHOSPHORIC ACID MANUFACTURE
Product: Phosphoric Acid
Annual/°eslg" : 50.000 tons P?0s
Capacity z <~~^
Annual Productioni 50,000 tons P205
Process: via Elemental Phosphorus
Fixed Investment: $1,700,000
Location: Midwest
Variable Costs
Phosphorus
Energy
Water
Labor
Maintenance
Labor Overhead
Total Variable Costs
Fixed Costs
Plant Overhead
Local taxes & ins.
Depreciation
Total
20% Return on investment (pretax)
Phosphorus plant
Phosphoric acid plant
Pollution control
,
Units
tons
2% of CI
9% of CI
$/unit
570.00
Units/ton
P2°5
0.44
$/ton
P2°5
250.80
1.00
1.00
3.50
1.50
1.00
258.87
2.00
0.34
1.53
262.67
56.32
6.80
12.03
337.82
AIR
i SULFUR -
SULFUR
BURNER
1
SULFURIC
ACID
PLAOT
STACK GAS
•HOSPHATE HOCK
HjS04
GYPSUM SLURRY
PRODUCT PHOSPHORIC ACID
S4XPj06
Figure IV-3. Phosphoric Acid - Wet Process
36
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monocalcium phosphate in solution. In a subsequent digestion tank, the sul-
furic acid is then mixed at a controlled rate with the slurry:
3Ca(H2P04)2 + 3H2S04 ~" 3CaS04 4- + 6H3P04.
The temperature, strength of the phosphoric solution, and degree of free sul-
furic acid present are controlled at conditions to give the optimum digestion
efficiency, and the best form of gypsum for filtration. Total residence time
in the digestion system is about 6 hours. The reaction is strongly exothermic
and cooling is required to maintain the desired temperature. Cooling is
accomplished in some plants by sparging with air and evaporation in the
digesters. Another common system is to pump the recycled slurry through a
flash cooler. The recirculation rate is high enough so that the temperature
rise through the digestion system is not excessive before cooling is accom-
plished in the flash cooler. Impurities in the phosphate rock include silica,
fluorine, iron, aluminum, sulfate, and minor constituents such as magnesium,
sodium, potassium, manganese, copper, zinc, lead, titanium, chromium, molyb-
denum, nickel, arsenic, vanadium, and uranium. Carbon in the form of organic
matter is particularly troublesome because it promotes foam in the digestion
system. This foam can often be controlled by adding anti-foam agents, but
with some rocks calcination to burn off the organic matter is necessary
before it can be used in wet process systems.
The slurry from the digestion system is processed on a rotary vacuum
filter to separate the gypsum,for disposal. It is necessary to wash gypsum
cake carefully to get full recovery of phosphate, and the washing conditions
must be carefully controlled to prevent blinding of the filter medium. All
of the washwater used appears as water of dilution, and the product acid and
the water balance must be carefully managed from this standpoint.
Acid from the filter has a phosphoric acid concentration of about 30-32%
P205- This material is next concentrated to 54% ?205 in an evaporation
system. The crude acid is always saturated in calcium sulfate and precipita-
tion upon concentration is a major problem. A recirculation system is used
to help minimize scaling of the evaporator surface.
2. Effluents
a. Water Pollution ,
The major waste stream from the phosphoric acid plant is the gypsum
slurry from the filtration step. The gypsum cake is slurried in recirculated
water and pumped to a settling basin. The phosphoric acid plants are usually
located close to the phosphate mines and it is not difficult to form a satis-
factory settling pond in a mined out area. A substantial fraction of the
fluorine originally present in the phosphate rock is discharged along with
the gypsum as sodium silico fluoride. This stream also contains free phos-
phoric acid and is slightly acidic.
37
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Although there is no inherent wastewater stream from the sulfuric acid
plant, tube leaks in the cooling system can result in intermittent discharges
of sulfuric acid.
The characteristics of the gypsum pond water have been reported in the
Development Document (Development Document...Basic Fertilizer Chemicals, 1974)
for Effluent Limitation Guidelines. The Document also provides data on the
type of treatment required and the anticipated treated effluent characteristics.
The main pollutants of concern present in the gypsum pond water are sol-
uble phosphates and fluoride, both of which may be typically present in the
8,000 to 15,000 mg/1 concentration range. As long as this water is contained
within the pond, there is no water pollution problem. At some plants rain-
fall during the dry season is low enough to approach this condition for many
consecutive days. Zero discharge has been proposed as an ultimate standard,
but its practice by solar evaporation at any location and the cost of forced
evaporation are currently part of the litigation now in the courts. For this
report we are interested in a midwest location where rainfall is normally in
the 30 to 40 in/yr range. Our pollution control estimates are therefore
based on treatment of overflow from the pond after settling and containment
of the gypsum and other settleable solids. Due to the high phosphate and
fluoride concentrations in the gypsum pond water, overflow cannot be dis-
charged without treatment.
In general terms, the Development Document recommends three treatment
measures for the operation of wet process phosphoric acid plants:
1. Collection, containment, and neutralization of the intermittent
leaks from the sulfuric acid plant;
2. Lime treatment and clarification of the gypsum pond overflow to
precipitate phosphates and fluorides as their calcium salts;
3. Installation of a seepage control system. The seepage control
system is intended to collect seepage from the perimeter of the
pond and to then return it to the pond. Seepage control in itself
does not result in a wastewater stream, but by adding to the over-
all pond water inventory, can cause the overflow stream to increase
in size.
Based on an assumed gypsum pond overflow rate (as delineated in the
Development Document), an estimation of the volume and characteristics of
both the raw gypsum pond water and the treated overflow effluent is presented
in Table IV-7-
The wastewater treatment system will produce a waste sludge containing
calcium fluoride and calcium phosphate salts.
38
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TABLE IV-7
WET-PROCESS PHOSPHORIC ACID WASTEWATER CHARACTERISTICS
Basis: 50,000 tpy (P2°5)
Wastewater
Characteristics
Total Suspended solids
Phosphorus (P.)
Phosphate (PO ~3)
Sulfate (S04~2)
Fluoride (F~)
Total acidity (as CaCO )
Wastewater Flow Rate
Gypsum Pond
Raw Wastewater
(mg/1)
No Data
15,000
^2,000
8,500
No Data
(Ib/day)
No Data
27,600
3,600
15,300
No Data
0.216 mgd
Treated Effluent
(mg/1)
20
20
^2,000
15
0
(Ib/day)
36
36
3,600
27
0
0.216 mgd
Note; The above wastewater flow rates and waste loadings are based on the
assumption that there will be a gypsum pond overflow.
Source: Arthur D. Little, Inc., estimates, based on
Document -for Phosphorus Derived Chemicals .
. Development
US EPA.
It is estimated that wastewater treatment sludge will be generated at
the rate of 45,500 tpy @ 10% solids. Since the gypsum pond is available for
storage, in most cases it would be feasible to pump the wastewater treatment
sludge into the pond. The resultant sludge-disposal costs would be lower
than if the sludge had to be hauled to an offsite disposal area.
Wastewater treatment cost estimates, based on the previously described
treatment system, are presented in Table IV-8.
I
b. Air Pollution
Both the digestion system and the evaporation system produce vent gas
streams which contain both T?2®5 Particulates and fluorine. The fluorine dis-
tribution in the system is illustrated by the material balance presented in
Figure IV-4. The normal fluorine content of phosphate rock is about 3-1/2%.
Of this fluorine, 30% appears as part of the product acid at a rate of about
60-70 Ib of fluorine/ton of P2C>5, About the same quantity is discharged,
along with, the gypsum filter cake, to the settling pond. Some 16% of the
original fluorine is evolved in the digesters and 24% in the evaporator
stack. It is not difficult to recover this fluorine by wet scrubbing,
39
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TABLE IV-8
WET-PROCESS PHOSPHORIC ACID WASTEWATER TREATMENT COSTS
Basis: 50,000 tpy P20-
TOTAL PLANT
CAPITAL INVESTMENT $292,000
DIRECT OPERATING COST
Labor (including overhead) 48,700
Maintenance (labor and materials) 11,700
Chemicals 87,800
Electricity (@ $0.020/kwh) 13,300
Sludge Disposal 91,000
TOTAL DIRECT OPERATING COST $252,500
INDIRECT COSTS
Depreciation (@ 9%) 26,300
Return on Investment (@ 20%) 58,400
Taxes and Insurance (@ 2%) 5,800
TOTAL INDIRECT COST $ 90,500
TOTAL ANNUAL COST $343,000
UNIT COST ($/ton as P^) $6.86
Notes:
1. Treatment consists of:
a) Sulfuric acid plant leakage containment system.
b) Gypsum pond seepage control, and
c) Lime treatment and clarification of gypsum pond
overflow water.
2. Capital investment adjusted to March 1975 level (ENR=2126).
3. Quantities:
• Labor - 3960 man hour/yr @ $12.30/man hour (with OHD),
• Chemicals - 2700 tpy hydrated lime @ $32.50/ton,
• Electricity - 666,000 kWh/yr @ $0.020/kWh,
• Sludge - wastewater treatment sludge - 45,500 tpy (wet basis)
(sludge disposal on-site @ $2.00/wet ton)
Source: Arthur D. Little, Inc., estimates.
40
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F=100 /PHOSPHATE ROCKS
V@ 3.5% F )
F-30
PRODUCT PHOSPHORIC ACID
^ F=16
DIGESTER VENT GAS
F=24
EVAPORATION VENT GAS
F-30
GYPSUM FILTER CAKE
Figure IV-4. Fluorine Material Balance - Wet-Process Phosphoric Acid
although the chemistry is complicated by the presence of silica. In the vent
gases fluorine exists as hydrogen fluoride and silicon tetrafluoride gas. The
hydrogen fluoride dissolves readily in the scrubber water to make hydroflu-
oric acid solution and the silicon tetrafluoride reacts with water to form
fluosilicic acid and precipitate silica:
(3S1F
4(g)
2H2°
H20
2H0SiF,, .,
2 6(sol)
The equipment must be shut down and cleaned at rather frequent intervals to
control this formation of silica. At some plants the fluosilicic acid can
be recovered either as the acid or as the sodium or potassium salt. In a
majority of plants, however, this stream is pumped to the settling pond and
contained there.
3., Energy Requirement
I
Purchased electricity is the major energy requirement for the wet process
phosphoric acid system and is required at about 250 kWh/ton of ^2^5' Ifc ^s
used to drive pumps, agitators, filters, and similar machinery, including for
the circulation of cooling water. If the plant were not integrated with an
onsite sulfuric acid plant, it would be necessary to use fuel to raise sub-
stantial amounts of steam, primarily for concentration of the acid from 32%
filtrate to 54% as product. The recoverable energy in the sulfur burned
amounts to about 13 million Btu/ton of P205. About half of the steam equiv-
alent of this heat is used for turbine drives in the sulfuric acid plant and
the other half for evaporation and other needs in the phosphoric acid plant.
41
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4. Economic Factors
Table IV-9 presents the capital and operating costs of a wet process
plant for production of phosphoric acid. The plant is assumed to be located
in the midwest and operate at a capacity of 50,000 tpy of ^2^5- This is a
small capacity compared to new units located at phosphate centers, such as
Florida, where plants larger than 200,000 tpy are common. The smaller size
has been chosen because it does have economic viability, and is a good match
for onsite use of phosphoric acid in a system to produce purified phosphate
for the detergent industry.
Capital costs for this plant are estimated at $10,200,000. This figure
includes processing facilities necessary for grinding phosphate rock to the
size desirable for the digestion system, and the digestion, filtration, and
evaporation sections of the phosphoric acid facility. The cost of the unit
for converting sulfur to sulfuric acid is also included. The investment of
$10,200,000 includes the battery limits plant and necessary site development
and auxiliary and storage facilities. It is based on 1975 construction costs.
Raw materials required are phosphate rock and sulfur. Dry Florida rock
at 30% ?205 is used and the price of $30/ton includes shipping to the midwest
plant site. This price represents our best judgment in today's volatile
market. Recovery of ?2Q5 as aci(i amounts to better than 95% of the phosphate
in the raw material. Sulfur is assumed to be obtained from the Gulf Coast
and delivered at about $45/ton. These raw materials are the most significant
cost elements.
Electric power consumption amounts to 250 kWh/ton of 1*2^5 » ab°ut one-
third of this being required for grinding of phosphate rock. This is a large
power requirement, but not an unusually heavy industrial load and the plant
can be expected to pay about the average price for electricity which was
about 20/kWh in 1975.
There is a small process water requirement for manufacture of sulfuric
acid and an additional water requirement for phosphoric acid. Together these
stoichiometric requirements amount to about 0.6 thousand gal/ton of £2^5
product. The total water requirement of 4.3 thousand gal/ton also includes
recycled water required for slurrying and disposal of the gypsum, and for
makeup streams to the scrubbing towers for the digestion and evaporation
systems. Labor requirements have been calculated on the basis of a, staff of
about eight operators /shift, plus one shift supervisor. The maintenance
labor staff is a little smaller. Maintenance labor and materials together
are estimated at an annual cost equal to 6% of the capital investment. The
depreciation cost of about $18/ton of P205 has been estimated on the basis
of an 11 year life of the facility. Total cost of manufacture is about
$213/ton of
42
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TABLE IV-9
ESTIMATED COST OF PHOSPHORIC ACID MANUFACTURE
Product: Phosphoric Acid
Annual/°esig" ; 50,000 tons P205
Capacity •*•
Annual Production)50,OOP tons P20s
Wet-Process
Process: (Phosphate Rock + H2S04)
Fixed Investment: $10,200,000
Location:
Midwest
Variable Costs
Raw Materials
Phosphate rock (30% P20s)
Sulfur
Energy
Electricity
Water
Labor
Direct operating labor
Direct supervision
Maintenance
Maintenance Material
Labor Overhead
Total variable costs
Fixed Costs
Plant overhead
Local taxes & ins.
Depreciation
Total cost of manufacture
20% return on investment (pretax)
Pollution control
Units
tons
tons
kWh
mgal
Man-yr
Man-yr
3% CI
3% CI,
30% Labor
70% Labor
2% CI
9% CI
Price
($/unit)
30.00
45.00
0.020
0.03
15,000
20,000
Requirement
(Units/ton P^)
3.49
0.84
250.0
4.3
7xlO~/
IxlO'4
Cost
($/ton P205)
104.70
37.80
5.00
0.13
10.50
2.00
6.12
6.12
5.59
177.96
13.04
4.08
18.36
213.44
40.80
6.86
261.10
D. PROBLEMS RELATED TO PROCESS CHANGE AND INDUSTRY GROWTH
1. Pollution Control
I
The problems of pollution control in the elemental phosphorus and the
wet process phosphoric acid systems have been the subjects of extensive studies
in the EPA guidelines work. This work is most detailed in the case of aqueous
effluents, but considerable attention has also been given to air pollution
and to sludge disposal problems. The major air pollution problems, common to
both processes, concern elimination of fluorine and dust. In the case of the
wet process plants, aqueous streams, including waste scrubber liquor, can
usually be handled in containment basins. The location of the electric
furnace plants on the other hand, particularly in the western states, is such
that the handling of aqueous effluents represents a difficult problem.
43
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2. Shortage and Escalating Cost of Electricity
The electric furnace process for conversion of phosphate rock to elemen-
tal phosphorus requires a power input of about 13,000 kWh/ton of phosphorus
which makes it one of the most intensive users of electricity among the elec-
tric furnace industrial operations. In addition, the industry has progressed
to the point where the size of single furnace installations is now at least
40,000 kW. This industry grew in Tennessee at about the same time as the
rapid development of the TVA, and to a large extent these growths were syner-
gistic. Phosphorus requires power in large blocks, and thus a commitment to
use the power provided the utility with an assured outlet for a major part
of each increment of expansion. The electrical characteristics of the phos-
phorus furnace are such that it can be interrupted for relatively long periods
without any damage other than the loss of the phosphorus production. TVA
utilized this feature to offer interruptible power contracts at favorable
rates, thus, in effect, utilizing the phosphorus customer as a peak-shaving
facility. In a similar manner, the electric furnace operations in Idaho and
Montana were developed on the basis that electricity would be available in
abundant supply and at economical rates, largely derived from hydroelectric
power. In recent years the availability of this electricity has markedly
diminished and the expansion of the electric furnace industry has been held
back largely because of a fear that sufficient power would not be available.
This has been dramatically illustrated by the fact that the Stauffer plant in
Montana has not been able to run at more than a fraction of its capacity
because of the allotment of Bonneville power.
3. High Capital Cost of Incremental Capacity
An additional deterrent to expansion of electric furnace phosphorus is
the capital cost of a single furnace required for such an expansion. If such
an expansion were to occur today, it would probably be based on a furnace with
a capacity of 60,000 kW and a capital investment of about $25 million. Such
an investment is extremely risky in view of the doubtful availability and
uncertain price of the electricity required to operate the furnace.
4. Economic Availability of Suitable Ore
The analysis and physical characteristics of available deposits of phos-
phate rock, to a degree, have influenced the type of conversion practiced.
The wet process requires rock in a state of subdivision which will disperse
readily in the digestion slurry and have good reactivity with the acid. A
number of impurities are present in phosphate minerals, such as iron and
aluminum salts, carbonates, and organic matter, which cause difficulty in the
wet-process system. The carbonate evolves C02, and the organic matter creates
foam and makes a dark colored acid. The presence of impurities of this type
increases the size of the digestion system, and requires expensive special
measures for their control. The presence of iron and aluminum makes filtra-
tion of the resultant gypsum slurry difficult. A relatively fine rock is
desired to increase the surface area available for reaction. The phosphate
content of the rock varies among deposits. A relatively high grade at 30-35%
44
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?2®5 has been economically available and most phosphate rock for wet-process
acid has been based on this type of material. Deposits of this type of phos-
phate rock are abundant in central Florida and have been the basis for the
growth of the industry in that state. In addition to production of phosphoric
acid and derivatives in Florida, the rock is exported through the Port of
Tampa for shipment elsewhere in the United States notably throughout the mid-
west on the Mississippi River system. There is also a very large and vital
trade of phosphate rock for export to foreign countries.
In Tennessee, deposits of this grade of phosphate rock have largely been
mined out and the remaining deposits are of lower grade and cannot compete with
the Florida rock for wet-process systems. Over the years a sizeable electric
furnace phosphorus industry has grown in Tennessee based on the availability
of cheap electric power from the TVA. This industry utilizes the Tennessee
rock which must first be processed by calcining and agglomeration to a size
suitable for feed to the phosphorus electric furnace. Escalating costs of
both rock and electricity make expansion of the industry in Tennessee doubtful
for either process.
The other major U.S. deposit is in the Mountain States in the West, pre-
dominantly in Idaho, Montana, Wyoming, and Utah. Two types of deposits exist.
One is a rich high-grade deposit existing in thick seams, but at depths suit-
able only for underground methods, and the second consists of deposits which
exist in relatively thin seams at shallow depths, uplifted at fairly steep
angles which can be exploited by strip mining. An extensive strip mining
industry exists at present in southeastern Idaho and western Wyoming and is
the source of most of the western rock currently in use. The western rock is
of a grade which can be used directly in the electric furnaces without benefi-
ciation. A smaller percentage of the western rock, perhaps 25% to 33%, is
currently used in wet process plants in the western states. The higher grade
and more suitable eastern rock cannot compete in this location because of the
cost of shipment.
45
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V. PROCESS OPTIONS
A. OPTIONS TO BE ANALYZED IN DEPTH
The use of phosphate and phosphorus compounds for fertilizers, deter-
gents, and industrial chemicals is increasing and expansion of production
appears to be certain. For a number of reasons, as detailed earlier, there
are strong .pressures to bring about this expansion without the commitment
to additional electric furnace capacity. A significant part of the expan-
sion may be via wet-process acid, purified to the degree necessary for use
in some of the furnace-grade outlets.
An estimate of current and future markets for products important to
this analysis is presented in Table V-l. Current use of phosphoric acid
in detergents is estimated to be 600,000 tpy of P^OS* or about 40% of the
total use of clean phosphoric acid. In .10 years this application is
expected to increase to about 900,000 tpy and maintain its share of the
total demand. Thus, it is apparent that there is ample opportunity for
adoption of a clean wet-process acid even though that process does not
purify the acid to food-grade specifications.
TABLE V-l
INDUSTRIAL PHOSPHATE DEMAND
(000 tons P205)
1975 1985
Phosphoric Acid Derivatives
Detergents 600 900
Food and fine chem. 240 400
Phosphoric acid (furnace)
Direct use 120 200
Fertilizer 115 0
Elemental phosphorus and
non-acid uses 165 200
Phosphorus exports 45 40
Unaccounted for 100 100
1385 1840
Nominal Phosphorus capacity 1354
Source: Arthur D. Little, Inc., estimates.
46
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Two methods of cleanup have been demonstrated commercially. One is
a chemical method which involves neutralization and precipitation of the
impurities; the second is a solvent extraction system. These options, as
they pertain to detergent grade phosphates, are summarized below and des-
cribed in detail in Sections V-B and V-C.
Purification to food-grade specification is possible and has been
demonstrated, but it is quite complicated and expensive. Sufficient
furnace acid will be available for food-grade products if some detergent
production is switched to wet-process acid. The results of this work are
reported in a later section of this report.
We feel that there is a strong likelihood that several such units will
be built in the near future.
1. Solvent Extraction Cleanup of Wet-Process Phosphoric Acid
The solvent extraction system begins with conventional digestion of
phosphate rock with mineral acid to produce an aqueous solution of HjPO^.
An immiscible organic solvent is used to extract ^2^5' anc* a clean aqueous
phosphoric acid is regenerated by contacting with water. Such a system was
proposed on a number of occasions, and we believe several companies have
pursued research on the method. It was developed, patented, and commercial-
ized by Israeli Mining Industries, Ltd. (Baniel et al, 1962; I.M.I., 1963;
"Hydro-chloric-Based Route .—," 1962). The IMI process employs hydro-
chloric acid as a digestion agent and butyl alcohol as the solvent. A
small plant was built at Haifa and commercial units built and operated in
Japan and .Mexico. In North America, Kaiser proposed such a unit in
Louisiana ("Hydrochloric-Based Rotate ...", 1962), and Dow at Sarnia in
Ontario ("Dow to Test ... ", 1963). Kaiser's plant was never built. Dow's
unit was a pilot plant and Dow has not pursued this opportunity to our
knowledge. Interest in this unit has been based on possible improvement in
economics, and on operation 'in conjunction with a plant producing hydro-
chloric acid as a waste material. These incentives remain and are strength-
ened by pressing needs for additional phosphate capacity and the dwindling
availability and rising cost of electric power.
2. Byproduct Sulfuric Acid for Wet-Process Phosphoric Acid
In the conventional wet process for phosphoric acid, sulfur is a raw
material and is converted to sulfuric acid at the site of the phosphoric
acid plant. The emphasis on S02 control in utility plant stacks presents
the opportunity to manufacture sulfuric acid as a byproduct at the electric
power station. A possible outlet for this sulfuric acid would be a phos-
phoric acid plant which could be located at the utility site to convert
phosphate rock shipped from the phosphate mine. One such location is Tampa,
Florida, where there is strong pressure for better S02 control, and which is
only 50 miles from the phosphate source in Polk County. As currently
practiced, burning sulfur at the phosphoric acid plant results in byproduct
steam at a rate ample for the needs of the phosphoric acid unit. If sulfuric
,47
-------
acid is substituted for sulfur, this energy would have to be made up by
the independent generation of steam. A major fraction of this steam
requirement is devoted to concentration of the 30% Po^5 phosphoric acid
produced in the digestion system to the 54% strength required for shipment
or use as fertilizer acid.
3. Strong Phosphoric Acid Processes
There are now at least two processes for modification of the wet
process system so that acid of 50% strength may be produced directly without
the need for evaporation, thus eliminating the need for steam. One such
system has been developed by Fisons (Crerar, 1973; Blumrich) and commercial
units have been built and are operating in Holland and in Yugoslavia. The
opportunity for practice of this strong acid system either in conjunction
with a conventional sulfur-based plant or in a plant supplied with by-
product sulfuric acid has been analyzed in a later section of this report.
B. CHEMICAL CLEANUP OF WET-PROCESS PHOSPHORIC ACID
1. Process Description
As stated in Chapter IV, there are a number of impurities in wet-
process phosphoric acid which make it unsuitable for uses such as detergent
phosphate. These impurities include calcium chloride, iron and aluminum
salts, carbon and organic- matter, and small quantities of a number of
heavy metals, such as magnesium, chromium, titanium, manganese, copper,
zinc, arsenic, vanadium, and uranium. The acid is saturated in calcium
sulfate and has a high content of fine suspended solids. It is difficult
to remove these impurities to the degree necessary to meet specifications
for food-grade or fine-chemical phosphate use. A major outlet for phos-
phoric acid, however, is in the form of sodium tripolyphosate (STPP).
Wet-process acid can be purified to the degree necessary for this product
by a two-stage neutralization (Van Wazer, Jr., 1961). A major impurity
which precipitates upon neutralization is sodium silicofluoride and, if the
first step of neutralization is stopped at a pH of about 2, the precipitate
is relatively pure and can be readily separated by filtration. The second
stage neutralization completes the reaction to the stoichiometric equiva-
lent of monosodium phosphate at a pH of about 5. Iron and aluminum phos-
phates are insoluble under these conditions and precipitate, along with the
remaining sodium silicofluoride. The use of chemical dosing agents, such
as barium carbonate and sodium sulfide, at this stage can eliminate the
sulfate as barium sulfate, and the heavy metals as the sulfides. This
dosing may not be required with some phosphate rock raw materials. The
process has been described in a qualitative way in a number of literature
references, but there is little quantitative data on its application. For
purposes of this report, we have prepared the process outline as illustrated
in the accompanying flowsheet and a material and energy balance to permit
evaluation of the system.
48
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STPP is made by drying and calcining a solution stoichiometrically
equivalent to a mixture of one mole of monosodium phosphate and two moles
of disodium phosphate. The objective is to supply sodium phosphate solu-
tions at about 50% concentration in the purity required for STPP manufacture,
A simplified diagram of this process is illustrated below.
3H3P04
5/2 Na2C03
6NaH2P04
3Na2HP04
5NaH2PO4
2Na2H2 and,
in the early stages of reaction!, a danger of carrying off an acidic mist
with undesirable loss of fluorine as HF or SiF^. In the latter stages of
neutralization, a highly alkaline local concentration would result if
sodium carbonate were added directly, and would produce gelatinous precipi-
tates very difficult to separate by filtration. With the method diagrammed
above, neutralization is accomplished after the impurities have been
removed and without any precipitation during neutralization.
49
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The flowsheet presented in Figure V-l is based upon production of
sodium salts equivalent to 50,000 tpy of Po^S' ^ an °Peratin8 factor of
330 stream days/year, the feed rate is about 40,000 Ib/hr of 32% P205 crude
phosphoric acid from the wet-process system. This stream is mixed with
recycled disodium phosphate solution at about 14,000 Ib/hr in the primary
neutralizer. The crude acid is stoichiometrically deficient in silica to
precipitate the fluorine, and additional silica at the rate of 130 Ib/hr
is added to the primary neutralizer. This unit is about 500 gallons in
capacity and provides a residence time of 5 minutes. Separation of the
sodium silicofluoride takes place in the primary crystallizer where we
estimate that a residence time is required for proper crystal growth.
These crystals are separated from the partially neutralized phosphoric
acid in a rotary vacuum filter where about 1600 Ib/hr of filter cake are
obtained. This sludge contains about 475 Ib/hr of sodium silicofluoride
and accounts for about 75% of the fluorine in the crude acid.
Literature references recommend that the pH of the solution at this
point be about 2 for- proper precipitation and separation of the sodium sili-
cofluoride cake. At this pH; about 30% of the initial phosphoric acid will
be neutralized. This value is based' upon calculations using the dissocia-
tion constants for phosphoric acid in dilute solutions. At the ionic
strengths employed in the commercial process, there is undoubtedly some
error in this calculation, but the error affects only the split of neu-
tralizing agent between the first and second stages and not the overall
results. A rough laboratory check has confirmed that the neutralization
will proceed to the extent of 30-40% of the initial phosphoric acid.
Prior to completion of the neutralization, barium carbonate is added
in a secondary dosing tank to react with sulfate in solution to form and
precipitate barium sulfate. In the material balance as presented, a total
of 1135 Ib/hr of barium sulfate is obtained and this material is the major
constituent of this second filter cake. The treated slurry is then pumped
to the second neutralizer where it reacts with about 33,000 Ib/hr of
disodium phosphate solution. At this point, the phosphoric acid has been
entirely neutralized to monosodium phosphate and the pH is stated to be
about 5. Under these conditions, heavy metals can be precipitated as the
sulfides and removed with the second stage filter cake. As in the first
stage, a residence time of about 5 minutes is provided in the neutralizer
and about 60 minutes in the crystallizer. These conditions require a
nominal volume of about 1000 gallons for the neutralizer and about 10,000
gallons for the crystallizer. Sludge from the second-stage filter amounts
to about 7300 Ib/hr and contains about 2200 Ib.of solids on a dry basis.
Characteristics and disposal of these and other effluent streams is dis-
cussed below. After filtration, the monosodium phosphate solution is
divided, and 83.3% of it is treated with soda ash. We estimate that a
residence time of 30 minutes is required here and a volume of 3000 gallons
is needed. Sodium carbonate at a rate of about 14,000 Ib/hr is added to
this tank and carbon dlxoide at about 6000 Ib/hr is vented to the stack.
-------
Ul
Figure V-I. Flow Sheet-Chemical Cleanup of Wet-Process Phosphoric Acid
-------
2. Current Status
Commercial installations utilizing the method as described were oper-
ated in the United States prior to World War II. As the availability of
elemental phosphorus and clean electric furnace acid grew under the impetus
of the program of the TVA, these plants were abandoned in favor of pro-
duction based on clean furnace acid.
At the present time in the United States, there is one commercial plant
utilizing a process of this type. It is operated by Olin Corporation at
Joliet, Illinois, and was originally built and operated by the Blockson
Chemical Corporation. To our knowledge, it has not been described in the
literature. Nevertheless, in a gross sense, we believe that the evaluation
of the chemical method for cleanup of wet-process acid as presented in this
report is not importantly different from the Olin operation. A midwest
location has been chosen as the basis for our estimate because it is an
Important center of detergent manufacture and is the site of the Olin plant.
3. Effluents
There are three vapor streams and two filter cakes which are effluents,
and these must be controlled to prevent environmental contamination. The
quantities and characteristics of these materials are detailed in Table V-2.
The gas streams consist of two vacuum pump exhausts and a neutralizer vent.
The vacuum pumps pull air through the filter cake to displace the liquor
which it contains. This air is disengaged from the filtrate in the seal
tank and discharged to the stack by the vacuum pump. The quantity of air
is small, but it will become saturated with water vapor by contact with the
filtrate and it is likely to entrain small quantities of the filtrate as a
mist. Small quantities of lubricating oil from the pump are also likely to
be carried off with the vapor. These exhaust streams can be handled at low
cost in a conventional mist eliminator which is washed with a small quantity
of recirculated liquor.
About 5900 Ib/hr of carbon dioxide are formed as a gaseous byproduct
in the DSP neutralizer. This gas will be vented to a stack under draft
control so that it is diluted with a small amount of air. It will be
saturated with water vapor at the temperature of operation of the neutralizer
which should be about 100°F. A small quantity of mist consisting of the
solution in the neutralizer will be carried off with the gas stream. This
mist can be recovered in an irrigated mist eliminator. The liquor from the
mist eliminator can be returned to the neutralizer.
The filter cakes from the first- and second-stage neutralization contain
the impurities separated from the crude acid. The first stage cake contains
about 75% of the fluorine present in the crude acid, and amounts to about
475 Ib/hr of sodium silicofluoride on a dry basis. This salt will be rela-
tively pure material and does have some commercial uses, principally for '
water treating or for synthetic cryolite•. It is doubtful, however, that it
•.52
-------
TABLE V-2
PROCESS EFFLUENTS CHEMICAL CLEANUP OF WET-PROCESS PHOSPHORIC ACID
Operating Rate: 50,000 tpy P90C.
Gas Streams
Vacuum Pump Exhaust - Primary Filter
Rate; 200 scfm Temperature: 100°F
Composition; Air
H?0 Vapor - saturated
Mist - from contact with 24% H PO , 21% NaH PO at: pH=2
Vacuum Pump Exhaust - Second Stage Filter
Rate;'' 200 scfm Temperature; 100°F
Composition; Air
H20 Vapor - saturated
Mist - from contact with 49% NaH PO,, pH=5
Neutralizer Vent
Rate: 900 scfm Temperature: 100°F
Composition: C0_2 ~ 5917 Ib/hr
Air - Minor
H?0 Vapor - saturated
Mist - from contact with 50% Na HPO , pH=5
Liquid Streams None
Solid Streams (Sludge)
First Neutralization Cake
Solids Content; 30%
Rate; 475 Ib/hr (dry basis)
Composition; Na.SiF,,
/ o
Minor Impurities - H^PO^ NaR^PO^, CaS04, FeP04, A1P04
Trace Impurities - Mg, Mn, K, CR, Ti, U, V, As
Second Neutralization Cake
Solids Content: 30%
Rate; 2195 Ib/hr (dry basis)
Composition; Na^SiFg - .158 Ib/hr
FeP04 - '607
A1PO, - 67
BaS04 - 1135
Other - 228
2195 Ib/hr
Trace Impurities - Mg. Mn, K, CR, Ti, U, V, As
Source: Arthur D. Little, Inc.., estimates.
53
-------
could be economically marketed from this plant, and it is more likely that the
sludge will be pumped to a settling pond and treated along with the gypsum
slurry and scrubber effluents from the wet-process acid plant. There are
one or two plants processing these fluids for recovery of fluorine com-
pounds for use in aluminum manufacture, but alternate sources of fluorides,
such as old "pot-linings," are much cheaper.
The second-stage cake contains less sodium silicofluoride, and its
major constituents are the iron and aluminum and other impurities precipi-
tated from the acid at this stage. In our material balance, we have shown
a large quantity (1135 Ib/hr) of barium sulfate in this cake. In some wet-
process plants, the quantity of sulfate present in the crude acid is less
than shown here, and the requirement for barium can be reduced or even
eliminated. Barium is nominally used at its stoichiometric requirement,
and the solubility of barium is low. The possibility of barium ion in the
effluent must, nevertheless, be recognized. The metallic elements listed
as trace impurities are derived from phosphate rock. They occur in similar
small amounts in the effluent streams from the wet-process system and in
the slag from elemental phosphorus production. In these processes, they
have not been cited as harmful pollutants. We do not anticipate that any
special measures for their control will be necessary in this process.
a. Water Pollution .Control
Aside from the previously described neutralization filter cakes (which
are really considered a waste sludge rather than a wastewater stream),
there are no major wastewater streams discharged from the chemical cleanup
step. The volume and characteristics of the treated effluent from the
entire phosphoric acid production and purification unit are essentially the
same as the base line wet process plant described in Chapter IV. The efflu-
ent characteristics are shown in Table V-3.
For the purpose of cost comparison, it is assumed that the neutraliza-
tion filter cakes will be deposited in the gypsum pond and that the cost
will be accounted for under sludge disposal. Wastewater treatment cost
estimates are presented in Table V-4. The treatment costs are essentially
the same as without the cleanup step, with the exception of the additional
sludge disposal cost due to the neutralization cake.
4. Energy
Electricity is the only energy requirement for this process. We have
summarized the major motors and drives required by the process; about
103 connected horsepower are required. We estimate that an electric load
of 100 kW would result; this would be equivalent to 16 kWh/ton of P_0,.
processed.
No steam and no energy for heating or cooling are required. The process
operates at ambient temperature and the heats of reaction are small.
54
-------
TABLE V-3
WET-PROCESS PHOSPHORIC ACID PLUS CHEMICAL CLEANUP
WASTEWATER CHARACTERISTICS
Waste water
Characteris tics
Total suspended solids
Phosphorous (P.)
Phosphate (P<>4~3)
Sulfate (S04~2)
Fluoride (F~)
Total acidity (as CaC03>
Wastewater Flow Rate
Gypsum Pond
Raw Wastewater
(rag/1)
No data
15,300
"2,000
8,500
No data
(Ib/day)
No data
27,600
3,600
15 , 300
No data
0.216 mgd
Treated Effluent
(mg/1)
20
20
'2,000
15
0
(Ib/day)
36
36
3,600
27
0
0.216 mgd
Note: The above wastewater flow rates and waste loadings are based
on the assumption that there will be
• Sludge - a. Uastewatar treatment sludge - 45,500 tpy (wat basia)
b. Purification sludge - 35,200 tpy (wet basil)
(Sludge disposal on-alte 8 $2.00/vet ton)
55
-------
5. Economics
Cost of chemical cleanup of wet-process phosphoric acid has been
estimated on the basis of the flowsheet and material balance previously
described. On the basis of this equipment list, we have estimated the
capital investment at $1,200,000. The estimate includes a process
building at $100,000 and an allowance for offsite facilities at 20% of
the battery limits cost.
In Table V-5 we present an estimate of the operating cost for the
chemical cleanup method. The resulting cost of manufacture is $240/ton
of P2°5 as t*ie m*xed sodium salt. This cost is $30 for more than the cost
of ?2®5 as c^e cru<*e acid and represents the cost of operating the cleanup
section. .For this estimate we have used the cost of crude acid manufactured
at 54% P2°5 strength, less about $3 allowance for the qost of the evapora-
tion step which would not be required. A requirement of about 1.1 tons of
soda ash/ton of P^OS ^-s shown in the table, but with no charge for the
soda ash. The estimate has been prepared in this manner to permit com-
parison of a clean acid cost with comparable material by the electric
furnace route; the cost of the soda ash is a cost element in the conversion
of acid to STPP. The chemical treatment and the cost of the chemicals for
cleanup of the acid have been based on complete removal of the sulfate as
barium sulfate. The result is a charge for barium carbonate which amounts
to $18/ton of ?205 and is almost two-thirds of the total cost of cleanup
of the acid. . The necessity for this step depends both upon the nature of
the crude acid and the phosphate rock from which it is made and upon the
specifications for the detergent end-use. The precipitation of barium
sulfate at this step helps to make the precipitate more readily filterable,
but cheaper filter aids could probably be utilized. The results of this
calculation illustrate the sensitivity of the economics to the chemical
dosing actually required for adequate cleanup. Other chemical costs for
silica and sulfide are minor. Electricity and water are also insignificant
costs.
The plant is operated with two men/shift and with one man for direct
supervision. The labor charge, including maintenance labor, is about
$4.2D/ton of P£05. Major items of fixed cost are plant overhead, which at
70% labor is about $2.50, and depreciation at an 11-year life with a charge
of a little over $2.00/ton of P2°5'
6. Assessment
The estimates presented in this report indicate a cost of about
$240/ton of ^2^5 as purified wet-process acid, as compared to a cost of
about $213/ton of acid derived from elemental phosphorus. The difference
between these figures is well within the accuracy of the estimating methods
employed, and we believe that the methods are economically competitive.
Actual sales on fair transfer value must include an allowance for return on
investment; the capital cost of the electric furnace is so high that this
return reverses the economics and makes the price of furnace acid more than
that of clean wet-process acid.
56
-------
TABLE V-5
OPERATING COST OF CHEMICAL CLEANUP
Annual/
,Design
Capacity'
50,000 tons P,0
Fixed Investment: $1,200,000
, _ . . 50,000 tons P_0,
Annual Production i 2_ 5
Location:
Midwes t
VARIABLE COSTS
Raw Materials & Chemicals
32% P205 acid
Na2C03
Si02
BaC03
Na2S
Energy
Electricity
Water
Labor
Direct Operating Labor
Direct Supervision
Maintenance Labor
Maintenance Material
Labor Overhead
TOTAL VARIABLE COST
FIXED COSTS'
Plant Overhead
Local Taxes & Ins.
Depreciation
TOTAL COST OF MANUFACTURE
Return on Investment (pretax)
Wet-Acid Plant'
Cleanup System
POLLUTION CONTROL
TOTAL
Units
tons P205
tons
Ib
Ib
Ib
kWh
103 gal
man-yr
man-yr
man-yr
2% of CI
30% Labor
70% Labor
2% of CI
9% of CI
1
Price
$/Unit
210(D
N.C.C2)
0.008
0.12
0.15
0.020
0.03
15,000
20,000
15,000
Units/
ton P205
1.0
1.13
22.7
152
2.5
16
1
2 x 10~4
2 x 10~5
6 x 10-5
Cost
$/ton P205
210.00
N.C.C2)
0.18
18.24
0.38
0.32
0.03
3.00
0.30
0.90
0.48
1.13
234.96
2.65
0.48
2.16
240.25
40.80
4.80
8.27
294.12
(1)
(2)
At cost of 54% P205 acid less $3
Soda ash is chargeable to STPP operation.
Source: Arthur D. Little, Inc., estimates.
57
-------
The cost also includes conversion of the ?2^5 to *-^e s°dium salts in
the proper stoichiometric mixture for STPP. The capital and operating
costs for such a step should really be added to the cost of electrothermal
acid to make the economics directly comparable.
A major uncertainty with either process is the escalating cost of
energy, particularly electricity. We believe that this threat, plus the
fact that large increments of investment at high risk are necessary for
electric furnace phosphorus, will cause producers to consider seriously
the cleanup of wet-process acid as a viable alternate for necessary expan-
sion of supplies of detergent-grade phosphate.
Figure V-2 shows the overall energy consideration in the choice between
the wet-process and electrothermal routes to clean phosphoric acid. It is
assumed that the energy required for supplying phosphate rock is the same
for each process, and that each method produces sodium phosphates in the
proper ratio for STPP. The electrothermal route suffers from the major
disadvantage that thermally expensive electric energy is expended to reduce
phosphate rock to elemental phosphorus, but that the energy of reconversion
to P2°5 is not recovered, but is lost as low-level heat in the phosphorus
burner-and acid plant. Another significant difference in the two methods,
amounting to 3 x 10^ Btu/ton of P20e, *s rePresented by the use of sulfur
(13 x 106 Btu) as an overall chemical reagent in the wet process, as con-
trasted to carbon as fuel (16 x 106 Btu) in the electrothermal process.
The electric furnace process was originally adopted to exploit cheap hydro-
electric power, but today it must depend on thermal power. It inherently
is penalized by the loss of almost 70% of the thermal energy in its fuel
cycle producing electricity. This loss amounts to about 40 x 10^ Btu/ton
P205. Even without this penalty, however, 39 x 106 Btu/ton P205 are
required at the electric furnace, and the method consumes 23 x 10^ Btu/ton
P20ij more than the wet-process system.
On a total energy basis, the wet-process system can be operated at a
fraction of the total energy required for the electrothermal process, and
this saving is in electric energy where conservation is most urgently
required.
The trade-offs to be considered from a pollution standpoint in choosing
between the two methods are illustrated in Table V-6. Because a substantial
amount of energy is saved as electrical energy, the equivalent pollution
as stack effluent associated with that energy production is saved. From a
process standpoint, we would be building a new wet—process unit and the
required sulfuric acid unit to support production of 50,000 tpy of ?2°5'
It would be necessary to establish the necessary cooling pond and settling
basins to accommodate the sludge, gypsum, and scrubber effluents from this
system. The comparable units for a western electrothermal system would be
larger, more expensive, and more difficult to operate. Rainfall is highly
variable in the Mountain States, and problems of flash-flooding, and unde-
pendable water flow in small streams must be considered. Scrubbers would
involve handling some very dusty materials such as carbon and silica, par-
ticularly from the phosphate nodulizing and handling systems. The electro-
thermal route also involves hazards with exposure to vent streams from the
phosphorus furnace and £o the notorious problems with "phossy" water which
are not present in the wet-process sytems.
58
-------
WET PROCESS
ELECTRIC FURNACE
3S (13 x 10 Btu/ton
5C (16 x 10 Btu)
Electricity '(3 x 10 Btu)
3H20
+
3CaSO,
Fuel (3 x 106 Btu)
Electricity (60 x 106 Btu)
1/2 P,. + SCO
( H20)
2H3P04
3CaO
TOTAL ENERGY 16 x 106 Btu/t
on
79 x 106 Btu/ton
Source: Arthur D. Little, Inc. estimates.
Figure V-2. Energy Comparison for Wet-Process and Electric Furnace
Methods of Cleaning Phosphoric Acid
59
-------
TABLE V-6
POLLUTION TRADE-OFFS
Wastewater Treatment Costs
Capital Investment
Unit Cost ($/ton P°)
Elemental Phosphorus
$930,000
$12.03
Wet-Process with
Chemical Cleanup
$292,000
$8.27
Air Pollution Control
Same, but dust load-
ing is much heavier
and includes carbon
dust
Wet scrubber control
dust, SiF4, and HF
Source: Arthur D. Little, Inc. estimates.
Although the choice will be strongly influenced by a company's access
to phosphate rock and economical electricity we believe that economic con-
siderations influence adoption of the chemical cleanup option. The effect
on both energy and the environment is likely to be favorable.
C. SOLVENT EXTRACTION CLEANUP OF WET-PROCESS PHOSPHORIC ACID
1. Process Description
Cleanup of wet-process phosphoric acid is based upon the fact that
phosphoric acid can be transferred from solution in an aqueous phase to
solution in an organic phase, such as normal butanol, and leave behind
undesirable impurities, such as calcium chloride, in the aqueous layer.
The organic phase can then be contacted in a separate unit with fresh water
to yield a pure solution of phosphoric acid.
The process is illustrated in greatly simplified form in Figure V-3.
After digestion of the phosphate rock, phosphoric acid extraction is
achieved in countercurrent vertical columns. In the first of these, the
calcium chloride brine containing crude phosphoric acid is pumped to the
top of the column, and the waste brine is discharged from the bottom. The
recirculated solvent stream, which has been stripped of phosphoric acid, is
fed to the bottom of the column and flows out of the top after having
60
-------
PHOSPHATE ROCK
WATER
WATER
CT>
HYDROCHLORIC ACID
f
DIGESTION
J
r~!
CRUDE
PHOSPHORIC
ACID
WASTE
SLUDGE
(-
z
UJ
>
_]
WITH SO
O
j-
oc
i-
X
UJ
1
1
1 1 SOLVENT | SOLVENT, HC1 LOSS
. | H2O, HC1 1
Lu-
1
1
1
L— ^
1
t
z
O
EXTRACT
WATER
a: J
1- g
z
8
••^•a
CONCENTRATED
WEAK
PHOSPHORIC
ACID
| SOLVENT. HC1 LOSS
1
^ STE°AM fc
WASTE BRINE STRIPPER WASTE CaCl2 BRINE
Figure V-3. Solvent Extraction Process for Phosphoric Acid - The IMI Process
-------
extracted the phosphoric acid from the crude aqueous stream. Recovery of
phosphate from the brine can be practiced at any degree desired if a suf-
ficently large extraction unit is employed. The phosphate-carrying solvent
stream is next contacted in the second extraction column. Fresh water is
used as the stripping agent. The aqueous phase is the product acid, and
the organic phase is recycled as solvent to the first extraction column.
There are a number of complications which require special handling;
these are not illustrated in full detail on the flowsheet. The first of
these complications is the presence of HC1 in the crude acid. Although a
wet-process system employing solvent extraction for cleanup may be practiced
in the conventional manner with sulfuric acid, (Wasselle et al., 1966), there
are a number of advantages in using hydrochloric acid as the digestion
medium. One important advantage is economic. The process permits the use
of waste HC1 instead of requiring generation of sulfuric acid from sulfur.
The calcium chloride produced in the digestion system improves the effi-
ciency of the extraction system, reduces the solubility of solvent in the
aqueous phase, and simplifies the problems of solvent recovery. The crude
acid contains an appreciable excess of HC1 to eliminate or reduce the con-
centration of monocalcium phosphate present in solution. This salt
[Ca(H2P04)2l is extracted to the organic phase, along with phosphoric acid,
and must be eliminated by special provisions in the extraction circuit.
The solvent stream from the first column contains hydrochloric acid,
extracted along with phosphoric acid. The HC1 is stripped from the solvent
and appears as part of the clean aqueous phosphoric acid stream. Unlike
the calcium salt, however, it can be boiled off during evaporation of the
product acid. This evaporation step also serves to separate and recover
any solvent dissolved in the aqueous product acid.
The calcium chloride brine initially separated from the.extraction step
also contains hydrochloric acid and solvent which must be recovered. This
recovery is accomplished in a steam-stripping step and the acid and solvent
are recycled to the solvent stream.
There are many opportunities for improvement of this system through
the development of solvents with better extraction efficiency, and through
the use of both chemical and physical methods to improve the separation of
the pure phosphoric acid at lower cost. Credit for aggressive development
of this system belongs to Israeli Mining Industries, Ltd., which first
demonstrated the method in the early 1960*s.*
*A recent paper presented to the Fertilizer Society of London in November of
1975 discusses some of the newer technology and the opportunities for its
commercial exploitation. The reader is advised to consult this paper and
Wasselle et al. for further details of the process.
62
-------
2. Current Status
A demonstration unit with a 1 tpd of ^2^5 capacity was established at
Haifa in 1961 (Baniel et al., 1962). On the basis of this design, a 7-tpd
unit was installed by Toyo Soda Manufacturing Company, Ltd., in Japan
("Hydrochloric-Based Route ...," 1962), and started up in 1962. About 1965,
a similar unit was installed by FFM in Mexico.
In the United States, the Kaiser Aluminum and Chemical Company announced
in 1962 its intention to build a $2,000,000 unit at Gramercy, Louisiana.
Kaiser abandoned plans for this unit after design studies.* In 1963, Dow
Chemical Company of Canada announced plans for a pilot plant at Sarnia,
Ontario ("Dow to Test ...," 1963). The unit was stated to have a capacity
of 35 tpd and was scheduled to start operating in 1965. Again, no public
announcement has been made of the outcome of the project.
Both the Kaiser and the Dow efforts were aimed at exploiting the poten-
tial outlet for waste hydrochloric acid. It is likely that detailed design
studies revealed that the system was quite a bit more complex than initially
believed and the investment correspondingly high. Another possible economic
problem lies in the need to keep solvent losses at a very low level. On a
theoretical basis, there 'is no inherent loss of solvent, but the recircula-
tion rate and the opportunity for inadvertent loss is high. Severe corro-
sion problems can be expected in this environment which include hydrochloric
acid, phosphoric acid, calcium chloride, and wet solvent.
3. Effluents
On the' basis of available information, it is difficult to make quanti-
tative estimates of the pollution control problems associated with the
solvent extraction process. The problems likely to be encountered are
illustrated in qualitative fashion in Figure V-4. Most of the problems
encountered ;Ln the sulfuric acid digestion system are also present in the
hydrochloric acid-based solvent extraction system. Major differences include
substitution of waste calcium chloride brine, instead of solid gypsum, the
problem of acidic fumes compounded by the presence of hydrochloric acid,
and the presence of solvent which adds a new dimension to the control of both
aqueous and gaseous emissions.
Because of the high rate of reaction with hydrochloric acid and the
volatility of this agent, it is ,desirable that the phosphate rock be calcined
prior to digestion. This step is carried out in high-temperature rotary
kilns. The operation is dusty. Large quantities of C02 are evolved if the
rock contains much carbonate, and fluoride gases and particulate matter
must be controlled.
*("Hydrochloric-Based Route ...", 1962; Wasselle, et al., 1966)
63
-------
PHOSPHATE ROCK
CALCINING
DUST, CO2, FLUORIDE
DIGESTION IN
HYDROCHLORIC
ACID
FLUORIDE FUME
HYDROCHLORIC ACID FUME
UNDERFLOW TO SEDIMENTATION BASIN
SOLVENT
EXTRACTION
AQUEOUS CALCIUM CHLORIDE BRINE
CONTAMINATED WITH SOLVENT,
HC1, AND FLUORIDES
EVAPORATION
SOLVENT FUME
HYDROCHLORIC ACID FUME
Figure V-4.
Emission Problems Found in Solvent Extraction Process
for Wet-Process Phosphoric Acid Cleanup
In the digestion step, the fluoride in the rock will be liberated as
HF and SiF4 vapor in the same manner as with digestion in sulfuric acid.
The heat of reaction is considerably less than with sulfuric acid, but
evaporative cooling is still required to control the temperature.
The major waste stream from the solvent extraction system is the cal-
cium chloride brine after it has been stripped of phosphoric acid. HC1
and solvent are vaporized from this brine before it is discharged. This
operation is likely to produce an acid fume. The product acid is concen-
trated in an evaporator. Solvent vapors and hydrochloric acid vapors
from the evaporator are condensed and recycled. Careful control of all
vent streams from these operations is necessary to avoid losses of the
volatile solvent and HC1.
a. Water Pollution
As in the case of the sulfuric acid-based, wet-process phosphoric acid
process, undissolved inorganic solids separated from the digester liquor
must be impounded in large ponds. Because of the high solubility of calcium
chloride and the general absence of sulfates, the volume of solids will be
less than that of the sulfuric acid process, as there will be no calcium
sulfate (gypsum) precipitate. The pond will therefore be somewhat smaller.
As in the case of the base line sulfuric acid wet-process, overflow and pond
water seepage must be controlled.
64
-------
Phosphates and fluorides can be removed from the overflow water by
means of lime treatment, as described under the base line wet-process in
Chapter IV.
By far, the most significant wastewater stream from this process is the
highly concentrated calcium chloride brine from the solvent extraction step.
This stream also contains significant amounts of the n-butanol solvent. As
can be seen from the estimated wastewater characteristics presented in
Table V-7, the quantity of calcium chloride generated is very large -
amounting to approximately 1.65 tons per ton of phosphorus. The problems
that would be encountered with disposal of this brine are analogous to those
encountered from soda ash plants using the Solvay process. These disposal
problems have accelerated the closing of a number of U.S. Solvay plants,
except where located on streams with large flows. If disposal of large
amounts of calcium chloride brines into streams is prohibited, an assumption
we believe is necessary for a plant of economic size, the only remaining
disposal methods are:
1. Ocean dumping,
2. Deep-well disposal,
3. Evaporation to produce calcium chloride for sale, and
4. Solar evaporation.
The problems with each of these disposal methods are discussed below:
1. Ocean disposal of wastes .is being discouraged as an official U.S.
policy. Although these waste brines might be proven to have little
ecological hazard when ocean-dumped, the costs of transport to an
approved ocean-dumping site would probably be prohibitively expen-
sive for plants located any distance from the ocean. For ocean
disposal from plants located on the sea coasts, we estimate that
the disposal costs for these brines would be in the range of $5 to
$20/ton of phosphorous.
2. It appears that deep-well disposal of this brine would probably
not be permitted, except at sites where unique geological condi-
tions (an extensive saline aquifier) exist. While we have con-
siderable doubts that approval would be given for deep-well
disposal, we have chosen this method for developing pollution
control cost estimates.
3. The production of CaCl2 for sale would have to compete with CaCl2
from Solvay Na2C03 plants and this market is already limited -
one of its largest uses being as a deicing chemical. We do not
believe that the CaCl2 product could compete with CaCl2 that
comes from present sources.
65
-------
TABLE V-7
WET-PROCESS PRODUCTION OF PHOSPHORIC ACID WITH SOLVENT EXTRACTION
PURIFICATION WASTEWATER CHARACTERISTICS
Was tewater
Characteris tic
Total suspended solids"
Phosphorus (^A)
_3
Phosphate (PO, )
Sulfate (S04~2)
Fluoride (F~)
Calcium chloride (CaCl_)
n -Butanol
Total acidity (asCaCO.,)
Was tewater Flowrate
Treated Pond
Water Overflow
(mg/1 (Ib/day)
20
20
15
100,000*
-
No data
36
36
27
180,300
-
No data
0.216 mgd
Solvent Extraction
Brine
(mg/1) Qlb/day)
~20
-
-
150,000
250
No data
96
-
-
721,000
1,200
No data
0.576 mgd
Total Was tewater
Stream
(mg/1) (Ib/day)
20
5.4
4.1
136,400
180
No data
132
36
27
)01,300
1,200
No data
0.792 mgd
It is assumed that the pond liquor will contain 10% CaCl.. The actual
concentration will depend on the HC1 concentration used in the digestion step,
Source: Arthur D. Little, Inc. estimates.
-------
4. Solar evaporation would only be possible in extremely arid
regions, and even there the CaCl£ concentration would only rise
to about 35 to 40 percent because of the stability of the
hydrates. At these concentrations, the concentrated lagoons
would represent a latent hazard should a violent rainfall wash
out supporting dikes. Therefore, no estimates of costs were
prepared for this moc*e of disposal.
As mentioned earlier, the treatment system chosen for cost estimation
is envisioned to consist of:
1. Pond water-seepage control,
2. Lime treatment of pond water overflow to remove phosphates and
fluorides, and
3. Deep-well injection of the combined treated pond overflow water
and calcium chloride brine.
Cost estimates for such a system are presented in Table V-8.
Sludge from the lime treatment step could be disposed of on-site by
pumping it back into the impoundment pond. As in the base line wet process,
this sludge will contain high concentrations of phosphates and fluorides.
In considering the water pollution problems associated with this
process, it should be remembered that the actual volume of wastewater dis-
charge depends on the overall water balance of the plant, which in turn
depends on the specific process configuration and local climatic conditions.
Moreover, deep-well injection has recently been viewed, in general, as an
environmentally unacceptable disposal method, and the ability to use it
depends heavily on the local geological conditions.
4. Energy Requirements
A major difference between the energy requirements of the solvent
extraction system and those of the conventional sulfuric acid wet-process
plant is that in'the former steam requirements are much higher and by-
product steam is not available from acid manufacture. Clean acid produced
by the extraction section is at about 15% phosphoric acid concentration.
It must be evaporated to a concentration of about 60% ?2°5' T*118 evapora-
tion requirement amounts to about 5 Ib of water evaporated per Ib of
produced. In the sulfuric acid route, concentration from 32% ?2°5 to
product requires only 1.3 Ib of water evaporation per Ib of P205- The use
of a multiple effect evaporator will help to minimize the steam requirement
associated with this evaporation load, but an energy supply of about
10 x 106 Btu/ton of P205 product will still be required. Electricity
requirements will be about 300 kWh/ton of P205, a little higher than for
the conventional sulfur-based process.
67
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TABLE V-8
WET-PROCESS PHOSPHORIC ACID PLUS SOLVENT EXTRACTION PURIFICATION
WASTEWATER TREATMENT COSTS
(Basis: 50,000 tpy P2°5)
CAPITAL INVESTMENT
DIRECT OPERATING COST
Labor
Maintenance (labor and materials)
Chemicals
Electricity C@ $0.020/kHh)
Sludge disposal
TOTAL DIRECT OPERATING COST
INDIRECT COSTS
Depreciation (@ 9%)
Return on investment (@ 20%)
Taxes and insurance (@ 2%)
TOTAL INDIRECT COST
TOTAL ANNUAL COST
UNIT COST ($/ton as P205 )
$636,000
110,400
25,400
87,800
81,000
91,000
$395,600
57,200
127,200
12,700
$197,100
$592,700
$ 11.85
Notes: 1. Treatment consists of:
a. Solid pond seepage control
b. Lime treatment of pond water overflow
c. Deep well injection of combined treated pond water
overflow and solvent extraction brine.
2. Capital investment adjusted to March 1975 level (ENR=2126)
3, Quantities:
• Labor - 8975 man-hr/yr @ $12.30/hr (with OHD)
• Chemicals - 2700 tpy hydrated lime @ $32.50/ton
• Electricity - 4,047,000 kWh/yr <§ $0.020/kWh
• Sludge - 45,500 tpy (wet basis) (sludge disposal on-site
@ $2.00/wet ton)
Source: Arthur D. Little, Inc., estimates.
68
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5. Economics
The cost of production of clean phosphoric acid by the IMI process at
a rate of 50,000 tpy of ?205 is detailed in Table V-9. Capital investment
is estimated at $7,400,000 for construction of a plant in 1975. This figure
is based on a study published by Kaiser and IMI in 1966 (Wasselle, et al.,
1966). A minor modification has been made in the substitution of calcined
rock to permit elimination of the carbon decolorization step. Kaiser's 1966
estimates for battery limits and offsite facilities amounted to $3,500,000;
updating this figure to the 1975 basis brings it to $5,900,000. Sludge
ponds and scrubbers and other pollution control devices not included as part
of the wastewater system would require an additional $1,500,000, bringing the
total to $7,400,000. Depreciation at an 11-year plant life and local taxes
and insurance at 2% of capital investment per year contribute more than
$16/ton to the cost of product.
Phosphate rock and hydrochloric acid are the raw materials required for
the system. A high grade of dry, ground, calcined phosphate rock at 34%
]?2^5 is charged at a price of $35/ton. Our cost estimate is based upon an
overall recovery of 95% of the T?2®5 *n tn^s rock. This efficiency is less
than that claimed in IMI and Kaiser studies, but commercial experience with
the method is limited and opportunities for loss of phosphate are high.
(The loss could be soluble ?2^5» adding to the effluent problem.) Rock costs
amount to about $108/ton of ?2^5 product. The hydrochloric acid requirement
at 2.1 tons per ton of ?2®5 ^s ab°ut 20% in excess of the theoretical require-
ment for reaction with the apatite in the rock. Some of this acid is
required for reaction with acid-consuming constituents of the ore other than
apatite, but a large part of it represents physical losses from the system.
The price of acid at $30/ton represents a reasonable transfer value for
this material, but the charge is arbitrary. The.system is only economically
practical when byproduct hydrochloric acid is available, and a fair charge
for the acid depends upon alternative uses for it at the site of its pro-
duction, or on the costs of its disposal. At $30/ton, the cost is equiva-
lent to $63/ton of product, and is considerably more expensive than the
sulfur cost for the conventional process. Hydrochloric acid would have to
be priced at $18/ton to make its cost equivalent to that of sulfur at
$45/ton.
The solvent makeup requirements are estimated at 8 Ib/ton of product;
a rate which is equivalent to the loss of about 50 Ib/hr of solvent. The
resulting charge to product is about $2/ton of P2°5' Inadequate control of
potential points of solvent loss could result in losses much higher than
this figure, and would overload the pollution control system.
69
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TABLE V-9
ESTIMATED COST OF PHOSPHORIC ACID MANUFACTURE SOLVENT EXTRACTION
CLEANUP - IMI PROCESS
= 50'000 ton
Capacity
50,000 ton P-0,
Annual Production ) _ £_•>
Fixed Investment: $7,400,000
Location: Midwest
VARIABLE COSTS
Raw Materials & Reagent
Phosphate Rock
(34% P205)
HC1 (100% Basis)
Solvent
Energy
Electricity
Steam
Water
Labor
Direct Operating Labor
Direct Supervision
Maintenance Labor
Maintenance Material
Labor Overhead
TOTAL VARIABLE COST
FIXED COST
Plant Overhead
Local Taxes & Ins.
Depreciation
TOTAL COST OF MANUFACTURE
Units
tons
tons
Ib
kWh
103 Ib
103 gal
man-yr
man-yr
4% of CI
4% of CI
30% Labor
70% Labor
2% of CI
9% of CI
Price
$/Unit
35.00
30.00
0.25
0.020
1.00
0.03
15,000
20,000
Requirement
Units/ton
P2°5
3.1
2.0
8
300
10
45
8 x 10-4
1 x 10-4
Cost
$/ton P205
108.50
63.00
2.00
6.00
10.00
1.35
12.00
2.00
5.92
• 5.92
5.98
222.67
13.94
2.96
13.32
252.89
Source: Arthur D. Little, Inc., estimates.
70
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Requirements for electricity and steam have been discussed above.
The resulting charges total about $16/ton of product. The labor costs of
about $14/ton are based on an operating 'staff of 40 men; maintenance
requirements are estimated at about 8% of capital investment per year and
are equally divided between maintenance labor and maintenance material.
Total cost is about $12/ton of product. The total annual maintenance bill
is about $600,000 per year. This figure is not unduly pessimistic in view
of the extremely corrosive nature of the acidic process streams.
Total cost of manufacture of clean phosphoric acid by this method is
indicated to be about $253 per ton of P90t..
£ J
6. Assessment
At $253/ton of P2^5» clean phosphoric acid by the solvent extraction
process would b'e competitive with the chemical cleanup system and not much
different from the cost of acid derived from elemental phosphorus. The
likelihood of achieving these economies requires several favorable circum-
stances. Most important is that the producer must have access to a source
of byproduct hydrochloric acid at $30/ton or less. The plant will be
located at the place where the acid is available and costs for disposing of
the byproduct calcium chloride must be manageable. This probably means that
deep-well injection has to be permitted, or that the plant site must be
adjacent to a major waterway, so that direct disposal of the neutralized
brine is permissible. Under these circumstances the adoption of this method
would probably be acceptable from an environmental standpoint, because
problems of disposal of the calcium chloride brine replace equally difficult
pollution problems with byproduct hydrochloric acid.
An unknown factor, however, is the severity of the solvent control
problem. At the solvent loss rate claimed (50 Ib/hr of butanol) control
costs are not severe. Failure to achieve this solvent efficiency, however,
in addition to being a severe economic penalty could result in unmanageable
BOD problems.
From the point of view of plant operations, this system must be classed
as very difficult. Hydrochloric acid by itself is one of the more corrosive
chemicals. When mixed with saline solutions and with phosphoric acid, and
with the added complication of the acidic mixed aqueous and organic phases,
the potential for extreme corrosion exists.
In view of these process uncertainties, there appears to be less likeli-
hood that this option will be chosen than will the chemical cleanup method
as an alternative to expanded electrothermal production. It would probably
require an integration with a byproduct HC1 disposal problem.
71
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D. THE USE OF BYPRODUCT SULFURIC ACID
A conventional wet-process plant for phosphoric acid consists of two
distinct process units. In the first, sulfur is converted to sulfuric
acid; in the second, sulfuric acid is used as a reagent to convert phos-
phate rock to phosphoric acid. Byproduct steam from the sulfuric acid unit
is used to advantage in the phosphoric acid unit, principally for the
evaporation of dilute phosphoric acid from the filtration system. Sulfur
is a major element of the production cost of phosphoric acid amounting to
about $38/ton of P2°5- At tlie ri§nt price, the phosphoric acid producer
would be tempted to use byproduct sulfuric acid in place of the sulfur.
One site where favorable circumstances might exist is at Tampa, Florida,
where there is a large electric utility. Tampa is also the principal
transit point for shipment of phosphate rock from the Florida fields, and
is already the site of substantial phosphoric acid production. The Tampa
Electric Company operates four generating units at a capacity of 400 MW
each. It has been estimated that when operating on 3.5 percent sulfur
coal, each of these units could produce 100 x 10" Ib/yr of SOoJ this esti-
mate was based upon a 60% load factor for the generator. The byproduct
sulfuric acid from all four units would support a phosphoric acid production.
of only 112,000 tpy of P2(-)5' a rate which is very small in comparison to
units now operating in Florida. Byproduct sulfuric acid can be considered
only as a supplemental supply rather than a primary source of sulfur for
the phosphoric acid plant. Even if the load factor were increased to 100%,
the unit could not support a full size phosphoric acid plant.
Under these circumstances, it is likely that the utility would have
to offer sulfuric acid at a price under $20/ton to interest the phosphoric
acid manufacturer to contract for its supply. Steam to replace that lost
by captive manufacture of sulfuric acid would also have to be part of the
commercial arrangement. The phosphoric acid producer would be reluctant to
engage in a firm, long-term contract, because the potential profits do.not
appear to justify the risk of dependence on the utility for a reliable
supply of acid. The phosphoric acid producer would probably elect to install
sufficient sulfuric acid manufacturing capacity for his entire needs in the
event that supply of the fraction from the utility were interrupted.
Although realizing no savings on capital investment for his plant, the
arrangement would save the energy associated with production of the equiva-
lent sulfur and its shipment to the plant site and conversion to sulfuric
acid. Associated polution problems would also be eliminated. These benefits
are marginal, however, and we do not believe it would influence the decision
in any material way.
72
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E. STRONG PHOSPHORIC ACID PROCESSES
The success of a process for digestion of phosphate rock and sulfuric
acid depends upon management of the step in which calcium sulf ate is pre-
cipitated. Calcium sulf ate can exist as the dihydrate or as the hemihydrate
The stable form depends upon both the acid concentration and the temperature
of precipitation in a manner described in Figure V-5, attributed to
Nordengren (Van Wazer, Jr., 1961). An understanding of this phase phenom-
enon has been the work of many years . It has been established that if the
concentration is about 50% P2°5» an5> as stated above, are
relatively simple, there is considerable expertise in making the process
work on a practical basis, and this information is closely guarded by the
process licensors.
The cost of manufacture by the Fisons strong acid process is estimated
in Table V-10. At $209/ton of P205» the cost of manufacture is about $4/ton
less than by the conventional wet-process method. Capital investment for
the two methods is quite similar - $10,100,000 by Fisons and $10,200,000 by
the conventional sulfuric acid system. The difference is well within the
accuracy of the estimates. As originally proposed, the Fisons system was a
little simpler, but the ?2<->5 recovery has been increased by the addition of
a unit for slurrying, washing, and refiltering the calcium sulf ate as the
dihydrate. This step improves the yield from 96% to almost 99%. The added
investment from this step about compensates for the saving and elimination
of the evaporation step.
The opportunity for even small savings by the stronger acid process is
of interest to companies in this competitive business, but as long as the
plant includes a sulfuric acid unit, there are no appreciable energy or
pollution effects of interest to our study. The method does offer the
opportunity to operate with purchased sulfuric acid without incurring the
penalty of having to purchase steam. But as outlined in paragraph D, no
appreciable use of byproduct sulfuric acid can be expected in the industry.
73
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140
FILTERABLE HEMIHYDRATE
IS PRECIPITATED
BOILING POINT OF
PHOSPHORIC ACID
UNFILTERABLE HEMIHYDRATE
IS PRECIPITATED
DIHYDRATE IS
PRECIPITATED
20
10
20
30
40
50
60
ACID CONCENTRATION,
Source: Van Wazer, p. 1049.
Figure V-5. Phase Diagram, CaSO, Precipitation
74
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TABLE V-10
PHOSPHORIC ACID - FISONS STRONG ACID PROCESS
Location; Midwest
Annual/?6818" . 50.000 tons P 0
Capacity fc—l
, _ , , 50,000 tons P00C
Annual Productioni ' 2 5
Fixed Investment: $10.100.000
»
VARIABLE COSTS
Raw Materials & Chemicals
Phosphate Rock ,
Sulfur
Energy
Electricity
Water
Labor
Direct Operating Labor
Direct Supervision
Maintenance Labor
Maintenance Material
Labor Overhead,
TOTAL VARIABLE COST
FIXED COSTS
Plant Overhead
Local Taxes & Ins.
Depreciation
TOTAL COST OF MANUFACTURE
RETURN ON INVESTMENT (Pretax)
POLLUTION CONTROL
TOTAL
Units
tons
tons
kWh
103 gal
man-yr
man-yr
2% of CI
3% of CI
30% Labor
70% Labor
2% of CI
9% of CI
1
Price
$/Unit
30.00
45.00
0.020
0.03
15,000
20,000
Units/
ton P20g
3.40
0.84
215
3.0
7 x 10~4
1 x 10~4
Cost
$/ton P205
102.00
37.80
4.30
0.09
10.50
2.00
4.04
6.06
5.57
172.36
13.04
4.04
18.18
207.62
40.40
6.86
254.88
Source: Arthur D. Little, Inc., estimates.
75
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F. SECONDARY OPTIONS
1. Variations of Basic Wet-Process Technology
Modern processes for production of phosphoric acid by a reaction of phos-
phate rock with sulfuric acid are the result of many years of invention and
improvement. This work has involved all three major steps: digestion, filtra-
tion, and evaporation. Both process conditions and processing machinery have
been refined to a high state of efficiency and economy. A number of oper-
ating and construction companies own these processes, and most of them are
available for license. Each has its proponents, but within the scope of this
study we believe differences among them are not important in assessing pollu-
tion control problems, energy efficiency, or process economics.
2. Blast-Furnace Phosphorus
The essential requirements of the process for reduction of phosphate rock
to elemental phosphorus are to supply the energy required for tne endojthermic
reaction and to supply an acceptor for the oxygen released. The electric fur-
nace supplies the energy by passing an electric current through the charge.
The same result (Waggaman, 1961, Waggaman, 1950) can be achieved by supplying
heat from gas blown through the furnace from the bottom, as in blast-furnace
production of pig iron. In addition to the coke required for reaction with
the phosphate rock, coke must be burned with air at about 130 x 10 Btu/ton
phosphorus.
The result is a furnace much larger, more complex, and more costly than
the electric furnace. It operates at a gas volumetric rate about seven times
that of the electric furnace.
Despite these handicaps, a few blast furnaces were built and operated
commercially in the days before TVA made electricity cheap and abundant near
the phosphate fields. It is not likely that the demand for elemental phos-
phorus and shortage of electricity will again make the blast furnace attrac-
tive, but industry analysts should be aware of the availability of the process.
A comparison of significant factors is tabulated below:
Electric Furnace Blast Furnace
Investment factor 1.0 1-6
P4 efficiency 92% 88%
Coke, tons/ton P^ 1.9 5.5
Heat recovery factor 1.0 0.7
Furnace gas volume factor 1 7
76
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Pollution control problems would be magnified as a function of the much
higher volume of hot furnace gas. In view of the severe economic disadvan-
tage implied by this comparison, we believe it unlikely that interest in blast
furnace phosphorus will be revived.
3. Uranium Extraction
There is a small amount of uranium in phosphate rock, and it is dissolved
as part of the 32% acid in the wet-process system. In the 1950's there were
three plants where solvent extraction units were,operated commercially to
supply this uranium to the AEG. All were plagued with operating difficulties,
both in the uranium plant and in its effect on the phosphoric acid plant.
None was economically successful and all were shut down in favor of more con-
ventional methods of uranium processing.
There is a current revival of interest in this source of uranium (Ross,
1975); several development programs are underway and one plant is under con-
struction. The processes have been refined on the basis of new solvent sys-
tems and will be watched with interest. The scale of phosphate rock processing
is such that it represents a substantial uranium resource. Problems of pollu-
tion control are substantial and are similar to those encountered in the
solvent extraction process for cleanup of wet-process acid. The EPA should
perhaps monitor this development, and perhaps, at an appropriate time, assist
in solving these problems.
4. Exploitation of Low-Grade Phosphate Reserves
There are two sources of phosphate which are not currently being exploited.
One is in strata which are left in the ground in favor of richer material; the
second consists of phosphate slimes produced as tailings from beneficiation.
Consideration of exploitation of these reserves is outside the scope of this
study by the specific exclusion of mining and milling processes, but their
importance at least demands mention.
Mining of low-grade material, either underground hard rock in the West or
Florida overburden now rejected, will be necessary when the higher grades are
exhausted. It will be more expensive, require more energy, and produce more
waste than the current system.
Recovery of phosphate from tailings of current operations may come about
if the technology can be developed. But it has been a research effort for many
years without real success. Operating costs and energy requirements would be
high, but phosphate-free tailing would be more ecologically acceptable.
7:7
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REFERENCES
Baniel, A., Blumberg, R., Alon, Al, El-Roy, M., Gondiaski, K., "The I.M.I.
Phosphoric Acid Process," Chemical Engineering Progress, Volume 58, No. 11,
November 1962, pp. 100-104.
Beveridge, G.S.G., and Hill, R.G., "Phosphoric Acid," Chemical and Process
Engineering, July 1968, Process Survey - Part 1, pp. 61-66, 73.
Blumberg, R., "Newer Developments in Cleaning Wet Process Phosphoric Acid,"
presented to the Fertiliser Society of London, November 13 ,1975.
Blumrich, W.A., (Lurgie Chemie), and Crerar, J.D., Quinton, G.N., (Fisons
Limited), "The Fisons Hemi-Dihydrate (HDH) Phosphate Acid Process."
Chelminski, R., and Somerville, R.L., "New Process for Phosphoric Acid,"
Chemical Engineering Progress, Vol. 62, No. 5, May 1966, pp. 108-111.
Crerar, J.D., Fisons Limited, "H»PO, Route Cuts Costs," Chemical Engineering,
April 30, 1973, pp. 62-63.
Hignett, T.P., and Striplin, M.M., "Elemental Phosphorus in Fertilizer Manu-
facture," Chemical Engineering Progress, Vol. 63, No. 5, May 1967, pp. 85-92.
Huang, T.H., "Making Strong Phosphoric Acid by ... Modified Wet-Process Using
Solvent Extraction," Industrial and Engineering Chemistry, Vol. 53, No. 1, -
January 1961, pp. 31-32.
I.M.I., "Phosphoric Acid Process," Technical Bulletin, The Laboratories Haifa,
November 1963.
Ross, Richard C., "Uranium Recovery from Phosphoric Acid Nears Reality as a
Commercial Uranium Source," Engineering and Mining Journal, December 1975,
pp. 80-85.
Rushton, W.E., "Isothermal Reactor Improves Phosphoric Acid Wet-Process,"
Chemical Engineering, February 23, 1970, pp. 80.
Singmaster and Breyer, "S.A. Heurtey Develops a New Hemihydrate Route to
Phosphoric Acid," January/February 1973 issue of Phosphorus & Potassium.
Singmaster and Breyer, "Dihydrate Process Description."
Specht, R.C., and Calaceto, R.R., Gaseous Fluoride Emissions from Stationary
Sources," Chemical Engineering Progress. Vol. 63, No. 5, May 1967, pp. 77-84*
Van Wazer, Johl Jr., "Phosphorus and its Compounds," Volume II, Interscience
Publishers. 1961.
78
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Waggaman, W.H., "Phosphoric Acid, Phosphates, and Phosphatic Fertilizers,"
Reinhold, Second Edition, 1952
Waggaman, W.H., and Bell, R.E., "Western Phosphates ... Comparison of Sulfuric
Acid and Thermal Reduction Processing," Industrial and Engineering Chemistry,
Vol. 42, No. 2, February 1950, pp. 282.
Wasselle, L.A., Lasseter, E.F., and Brosh, R.A., "Pure Phosphoric Acid From
Hydrochloric or Sulfuric Acidulated Rock - The I.M.I. Process," Society of
Mining Engineers of A.I.M.E., October 13-15, 1966.
"Development Document for Effluent Limitations Guidelines and New Source
Performance Standards for the Basic Fertilizer Chemicals Segment of the Fer-
tilizer Manufacturing Point Source Category," U.S. Environmental Protection
Agency, EPA-440/l-74-011-a, March 1974.
"Development Document for Proposed Effluent Limitations Guidelines and New
Source Performance Standards for the Phosphorus Derived Chemicals Segment of
the Phosphate Manufacturing Point Source Category," Environmental Protection
Agency, EPA-440/1-73/006, August 1973.
"Dow to Test Phosphoric Acid Process in Canada," Chemical Engineering News,
Vol. 41, No. 41, October 14, 1963, pp. 35.
Effluent Guidelines and Standards, Phosphate Manufacturing. 40 CFR422, Federal
Register, February 20, 1974.
"Hydrochloric-Based Route to Pure Phosphoric Acid," Chemical Engineering,
December 24, 1962, pp. 34-36.
"New Plants and Facilities ... CE Construction Alert," Chemical Engineering,
April 2, 1973, pp. 69-78.
"New Plants and Facilities ... CE Construction Alert," Chemical Engineering,
March 31, 1975, pp. 110-120.
"Making Phosphate Fit to Eat," Chemical & Engineering News, September 30, 1974,
pp. 90.
79
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-76-034m
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
ENVIRONMENTAL CONSIDERATIONS OF SELECTED ENERGY CON-
SERVING MANUFACTURING PROCESS OPTIONS. Vol. XIII.
Phosphorus/Phosphoric Acid Industry Report
5. REPORT DATE
December J&16 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Arthur D. Little, Inc.
Acorn Park
Cambridge, Massachusetts 02140
10. PROGRAM ELEMENT NO.
EHE624B
11. CONTRACT/GRANT NO.
68-03-2198
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
is. SUPPLEMENTARY NOTES Vol, III-XII, EPA-$00/7-76-Q34c through EPA-600/7-76-034g, and XIV-
XV, EPA-600/7-76-034n through EPA-600/7-76-034o, refer to studies of other industries
as noted below; Vol. I, EPA-600/7-76-334a is .the Industry Summary "Report .ana Vol. II.
16. ABSTRACT
Vol. II, jiPA-60G/7-7b-U34b is the Industry Priority Report.
This study assesses the likelihood of new process technology and new practices being
introduced by energy intensive industries and explores the environmental impacts of
such changes.
k
Specifically, Vol. XIII deals with the phosphorus and phosphoric acid industry and
examines four alternatives: (1) chemical cleanup of wet-process phosphoric acid,
(2) solvent extraction process for wet-process phosphoric acid, (3) byproduct sul-
furic acid for wet-process phosphoric acid, and (4) "strong acid" system for wet-
process phosphoric acid in terms of relative process economics and environmental/
energy consequences. Vol. III-XII and Vol. XIV-XV deal with the following industries:
iron and steel, petroleum refining, pulp and paper, olefins, ammonia, aluminum,
textiles, cement, glass, chlor-alkali, copper, and fertilizers. Vol. I presents the
overall summation and identification of research needs and areas of highest overall
priority. Vol. II, prepared early in the study, presents and describes the overview
of the industries considered and presents the methodology used to select industries.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Energy
Pollution
Industrial Wastes
Phosphorus
Phosphoric Acid
Manufacturing Processes;
Energy Conservation;
Phosphate Products;
Phosphate Detergents
13B
18. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report/'
unclassified
21. NO. OF PAGES
96
20. SECURITY CLASS (Thispage)
unclassified
22. PRICE
EPA Form 2220-1 (9-73)
80
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