EPA-600/2-76-295
December 1976
Environmental Protection Technology Series
GRANULATION OF COMPLEX FERTILIZERS
CONTAINING AMMONIUM SULFATE BY
MELT TECHNOLOGY
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Athens, Georgia 30601
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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 five series. These five 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 five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-295
December 1976
GRANULATION OF COMPLEX FERTILIZERS CONTAINING
AMMONIUM SULFATE BY MELT TECHNOLOGY
by
Juan Lanier
Robert MacDonald
Ferguson Industries
Dallas, Texas 75220
Contract No. 68-01-0754
Project 13020 HMV
Project Officer
Robert R. Swank, Jr.
Technology Development and Applications Branch
Environmental Research Laboratory
Athens, Georgia 30601
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30601
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DISCLAIMER
This report has been reviewed by the Environmental Research
Laboratory, Athens, Georgia, U. S. Environmental Protection Agency, and
approved for publication. 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.
11
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ABSTRACT
A novel process was developed for production of high analysis
fertilizers in which large portions of the nutrients are derived from
by-product and waste ammonium sulfate. The materials produced exhibit
good physical and storage characteristics and are similar in grades to
those now being consumed in large quantities.
Phosphoric acid and anhydrous ammonia are reacted to form the
liquid bonding agent. Solid ammonium sulfate, potassium chloride and
recycled fines are added to the melt in a pug mill. Emission of
pollutants is less than from conventional plants and is readily
contained.
The process was developed and tested on a laboratory scale and in a
small pilot plant and was verified in a 454 kilogram per hour (1000
pound per hour) demonstration unit.
Capital and operating cost estimates are presented. The operating
cost is sensitive to the assumed value of waste ammonium sulfate. In
comparison to similar grade products, cost savings of 10 to 20% can be
realized if true waste values can be assumed. The financial estimates
did not attempt to evaluate the indirect benefit to society, in terms of
dollars and of energy, of recovering waste ammonium compounds and sulfur
dioxide — which often are discarded into aquifers or into the
atmosphere and thus constitute major pollutant threats — and of
converting these chemicals into useful products.
This report was submitted in fulfillment of Project No. 13020 HMV,
Contract No. 68-01-0754 by Ferguson Industries under the sponsorship of
the Environmental Protection Agency. Work was completed as of June 1975.
111
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CONTENTS
Page
Abstract ill
List of Figures vi
List of Tables vii
Glossary of Abbreviations and Symbols ix
Acknowledgements x
Sections
I Introduction 1
II Conclusions 9
III Recommendations 10
IV Laboratory Investigation 11
V Pilot Plants 34
VI Scale-Up Prototype and Full Size Plant 49
VII Market Analysis 67
VIII Bibliography 79
IX Appendix 82
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FIGURES
No. Page
1. Flow sheet of conventional fertilizer plant. 4
2. Polyphosphate concentrations vs. reaction tube temperature 14
3. Alternate II and III flow sheet for 227 Mt/d (250 st/d) 35
pilot plant producing grade 13-13-13-13.
4. Tee reactor design. 37
5. Pug mill designs for pilot plant designs. 38
6. Isometric drawing of 227 Mt/d (250 st/d) plant - 51
Alternate III.
7. Energy balance for 227 Mt/d (250 st/d) prototype plant 57
8. Fertilizer consumption in the U.S. 68
9. Average nutrient content of fertilizer. 68
10. Consumption of mixed fertilizers. 69
11. Soil areas in the U.S. known or suspected to be 74
sulfur deficient.
12. Soil areas in the U.S. where acidification probably 75
would benefit crop production or which contain coarse
textured soils which readily could become sulfur
deficient.
A-l. Vacuum line for measuring critical relative humidities 86
of fertilizers.
A-2. Alternate I flow sheet for 907 Mt/d (1000 st/d) pilot 89
plant producing grade 13-13-13-13.
VI
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TABLES
No. Page
1. Material Ratios of Potassium Chloride, Melt 18
(Ammonium Phosphate) and Ammonium Sulfate to Produce
Various Fertilizer Grades
2. Polyphosphate Concentration in Product and Granulation 20
Quality
3. Screen Analysis of Sources of Ammonium Sulfate 23
4. Mixing Temperature/Recycle Effect on Granulation 24
5. Particle Size Effect of Ammonium Sulfate and 26
Potassium Chloride on Granulation
6. Recycle Effect on Granulation at Optimum Temperature 28
7. Hygroscopicity 29
8. Critical Relative Humidity at 30°C (86°F) 30
9. Relative Rates of Solution 31
10. Rate of Hydrolysis 33
11. Chemical Analysis of Pug Mill Exhaust 39
12. Optimum Operating Parameters for the 45.6 kg/hr 42
(100 lb/hr) and 454 kg/hr (1000 kg/hr) Pilot Plants
13. Data From Five Day Run in 454 kg/hr (1000 lb/hr) Plant 44
14. Major Components of 227 Mt/d (250 st/d) Plant 52
15. 227 Mt/d (250 st/d) Fertilizer Plant Costs Using 58
Alternate III Flow Sheet for 13-13-13-13 Grade
Fertilizer
VII
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No.
16. New Plant Cost Comparison - Alternate I and III 60
Producing 907 Mt/d (1000 st/d) of 13-13-13-13 Grade
Fertilizer
17. Modified 907 Mt/d (1000 st/d) Fertilizer Plant Costs Per 64
Alternate III Flow Sheet for Grade 13-13-13-13
18. Consumption of Fertilizer in U.S. by Grade for 1970, 1971 70
19. Consumption Percentages of Fertilizers by Regions & 72
Grades, 1971
20. Consumption of Sulfur-Containing Fertilizers in the 76
Continental U. S.
21. Sulfur Requirements and Fertilizer Sulfur Applications 78
A-l. Laboratory Formulations 83
A-2. Energy Balance Calculations 90
A-3. Pilot Plant Operation in 45 kg/hr (100 Ib/hr) Plant 94
vi 11
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GLOSSARY OF ABBREVIATIONS AND SYMBOLS
kilogram
pound
metric
ton
per
day
short ton
nitrogen
phosphorus
sulfur
Tennessee Valley
Authority
degrees
Centigrade
kg
Ib
M
t
/
d
st
N
P
S
TVA
o
C
Fahrenheit
percent
phosphorus penoxide
kilogram
square
centimeter
pounds per square inch
hydrogen ion concentration
potassium oxide
gram
weight
millimeter
milliliter
ammonia
F
*
P2°!
k
sq
cm
psi
pH
K20
gm
wt
mm
ml
NH-,
IX
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ACKNOWLEDGMENTS
Facilities and personnel were furnished by Ferguson Industries.
Sponsorship and guidance were supplied by the Office of Research and
Development, Environmental Protection Agency.
Dr. Robert Swank, Jr., served as project officer and provided
valuable guidance and assistance throughout this project.
The authors are indebted to Pope Laboratory for their analyses of
the fertilizers produced and to all persons who spent many uncounted
hours of dedicated support.
Thanks are given to J. L. Overfield of Pollution Abatement
Research for his important contributions to this project.
The authors are particularly indebted to Mr. Robert Killer, Envi-
ronmental Protection Agency, Region VI, Dallas, Texas, who provided
local support and encouragement.
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SECTION I
INTRODUCTION
PURPOSE AND SCOPE
When the Environmental Protection Agency began to give serious
consideration to removal of sulfur dioxide from stack gases by the use
of ammonia scrubbing, it was considered essential that suitable
processing methods be found which would permit the power companies to
sell their by-product ammonium sulfate to the fertilizer industry in
order to recover the cost of the ammonia which they used.
During the decade of the 1960's, the advent of granular diammonium
phosphate, granular potash, bulk blending marketing stations and the
introduction of polyphosphate liquids resulted in the closing of most
conventional fertilizer granulation plants. In previous years, most of
the by-product ammonium sulfate generated in dispersed chemical and
steel plants had been sold to these local granulation plants and reached
the market in the form of nitrogen-phosphorus-potash-sulfur (N-P-K-S)
mixtures. The shutdown of granulation facilities caused the price of
by-product ammonium sulfate to drop to very low levels. The ammonium
sulfate market was completely demoralized.
Thus, the purpose of this investigation was to devise a method of
modifying the melt granulation process to permit maximum incorporation
of ammonium sulfate.
It was considered essential that a new economic process be
developed for production of a high nutrient N-P-K-S fertilizer which
would be capable of utilizing waste and by-product ammonium sulfate from
steel and plastic industries and projected power plant scrubbers. It
was most desirable that the new process not be damaging to the
environment.
In 1971 and 1972, it seemed to Ferguson Industries that a granu-
lation process in which an ammonium phosphate - polyphosphate melt is
produced offered an attractive prospect for the accomplishment of these
objectives. Despite the fact that there were no plants in existence in
which this was being done, there did not appear to be any inherent
reasons for not adopting this melt technology.
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If the melt granulation process could be modified to increase the
ratio of solid constituents to melt, and to use ammonium sulfate rather
than low-melting nitrogenous compounds such as ammonium nitrate or urea,
then it would be superior to processes which require the use of aqueous
solutions. The melt granulation process would be preferable because its
equipment and energy requirements are lower and because its pollution
emission is more readily controllable. The use of ammonium nitrate or
urea would be incompatible with the objectives of this concept, because
they would partially or completely displace the ammonium sulfate in the
formulations.
Before initiating laboratory work, it was deemed important to
review all literature pertaining to melt and aqueous processes and
fertilizer products; to evaluate the status and potential market for
sulfur bearing fertilizers; and to review fertilizer usage to determine
which grades offer potential for large volume outlets of ammonium
sulfate in granular formulation.
Following the literature review, the most promising process and raw
materials would be selected. An extensive laboratory evaluation would
be made to verify the feasibility of the process and to solve any
operating problems which might be found. This laboratory work would
incorporate studies of the effects of changes of chemical formulation,
of changes of operating conditions and of physical and chemical
properties of the materials which would be produced.
The results of the laboratory investigation would be evaluated in
a small and a large pilot plant. The small pilot plant would be
designed for a capacity of 45 kg/hr. Most of the pilot plant testing
would be conducted in this unit. The large pilot plant would be
designed for a capacity of 454 kg/hr. It would be used to verify the
results of the work in the small unit and to demonstrate the operability
of the process by running it continuously for five days.
The data obtained from the laboratory and pilot plant work would be
used to design a 227 Mt/d and a 907 Mt/d plant. Capital and operating
cost estimates would be prepared for both plant sizes.
At the conclusion of all the work described above, the feasibility
of the process would be reviewed. As warranted by the results obtained
in this study, recommendations would be developed for further investi-
gation by field tests or by engineering research and development.
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BACKGROUND AND THEORETICAL APPROACH
The conventional method of producing granulated fertilizer is by an
aqueous process. A flow sheet of a conventional ammoniation-granulation
plant is shown in Figure 1. As seen in this figure, the conventional
process requires the following major pieces of equipment and steps:
1. Preneutralizer - Phosphoric and sulfuric acids are
partially neutralized with ammonia. This step
produces much heat and water vapor.
2. Ammoniator-granulator - Partially neutralized acids
are ammoniated to the end point. Materials such as
potassium chloride and micronutrients can be added
at this point. In this step/ water vapor and excess
ammonia must be recovered or removed.
3. Dryer - Product from the ammoniator-granulator is
dried. This step produces much dust and requires a
considerable input of heat.
4. Cooler - Product from the dryer is cooled so that it
can be handled and stored.
5. Screen - The screening unit separates the dryer
product into three fractions: oversize, which is sent
to the crusher and recycled; market size, which is
sent to the storage bins; and fines, which are
recycled back to the ammoniator-granulator.
A conventional granulation plant emits both air and water
pollutants. The problem areas and types of pollutants emitted are:
1. Ammoniator-granulator - Dust, ammonia and water vapor,
and fine particulate aerosols, e.g. ammonium chloride
and fluorides.
2. Product dryer - Dust, water vapor.
3. Product cooler - Dust.
4. Liquid scrubber - Aqueous fertilizer solutions.
In most cases, to control these effluents in existing plants is
costly; for older plants it is perhaps prohibitively so.
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SULFURIC ACID
AMMONIA
POTASH
PHQSPBDRIC
ACID
-»~WA.TER VAPOR
SCRUBBER
EXHAUST CONTAINING
AMMONIA & WATER VAPOR
GRANULAR
FERTILIZER
Figure 1. Flow sheet of conventional fertilizer plant.
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In the new manufacturing process ammonium phosphate - polyphosphate
melt was to be made from proper combination of ammonia and wet process
phosphoric acid. This melt was to be mixed with ammonium sulfate and
other ingredients, such as potassium chloride, as required by market
demand. Ammonium sulfate might comprise up to 55% of the raw material
used in the new mixed fertilizer.
The key to the process was considered to be its capability to
produce an ammonium phosphate - polyphosphate melt from conventional,
merchant grade, wet process phosphoric acid. It was necessary to
produce a melt combining two characteristics which had been considered
mutually exclusive: polyphosphate content sufficient to provide good
temperature and flow characteristics, and the capability to solidify and
granulate readily in combination with ammonium sulfate at low recycle
rates. This melt was to be produced by reacting ammonia with phosphoric
acid under conditions similar to those used in anhydrous productions.
The sensible heat of the feedstock plus the exothermic heat of reaction
would be utilized to evaporate all the free water and a controlled
portion of the chemically combined water.
Ammonium polyphosphate melt, water, ammonium sulfate and potassium
chloride were to be combined in a pan-type granulator, a Tennessee
Valley Authority (TVA) ammoniator, or a pug mill — as was used in this
investigation — to form hard, round fertilizer granules. It was hoped
that it would prove possible to produce medium and high analysis ferti-
lizer grades when the ammonium phosphate - polyphosphate melt was
concentrated and the total mixture had a low water content. (The low
nitrogen content of ammonium sulfate naturally limits the total
nutrient content of the N-P-K mixtures which can be produced. However,
when sulfur is required by the crop and the soil, ammonium sulfate
becomes a high nutrient carrier.)
Two basic processes were developed. A discussion of the selection
criteria for each of the major process steps is presented in Section V
of this report.
DESCRIPTION OF PROJECT PHASES
A description of each phase and a brief description of the tasks
involved is presented below.
Phase I - Laboratory Optimization
The laboratory optimization consisted of the tasks outlined below.
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Task 1. Literature Review - A search was conducted of all Ferguson
Industries' ammonium phosphate and ammonium polyphosphate process and
product information, of technical information from the TVA and
universities, and of industrial research and development literature.
The compiled information was used to select the most promising
production process and raw materials for laboratory evaluation and pilot
plant design.
Task 2. Selection of Fertilizer Compositions and Processes - A market
analysis was undertaken to determine the types and quantities of ferti-
lizers currently used in each region of the United States. This was
done to determine desired chemical compositions of the new fertilizer
products, the standard processes used to make the various fertilizer
grades and fertilizer plant pollution sources and control techniques.
Task 3. Laboratory Testing - A program was carried out to establish the
effects of ammonium polyphosphate concentration, ammonium sulfate grade
and potassium chloride concentration on the fertilizer product quality.
Process steps evaluated in the laboratory included mixing techniques,
thermal treating and atmospheric control.
Task 4. Measure Fertilizer Quality - Fertilizer quality was determined
by laboratory tests of nutrient analysis, solubility, storability and
granule quality. Agronomic testing was not a goal of this effort, but
was left for future evaluation.
Phase II - Pilot Plant Design and Construction
Two pilot plants were designed and constructed. The smaller plant,
in which most of the experiments were conducted, had a capacity of
45 kg/hr (100 Ib/hr). Process information and product quality data
obtained by operation of this unit were used as the basis for design of
the larger 454 kg/hr (1000 Ib/hr) pilot plant. Tasks outlined below
were essentially similar for both plants.
Task 1. Preliminary Design and Instrumentation - Results obtained in
the Phase I work were used to establish chemical process steps, raw
materials and handling operations to be tested in the pilot plants.
Equipment sizing and a tentative process flow sheet for the plant were
established. This preliminary process design was used as the basis for
the mechanical design and equipment selection of Task 2. Instrumen-
tation required for process control and monitoring of plant operations
was defined.
Task 2. Mechanical Design and Equipment Selection - The pilot plant was
designed and drawings were made. Equipment and instruments were
selected.
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Task 3. Release of Purchase Orders for Equipment and Components -
Purchase orders for equipment, components, instruments and supplies
were issued. Manufacturing instructions for subsystems fabricated by
Ferguson Industries were provided. Raw materials for the pilot plant
were ordered.
Task 4. Receipt of Parts, Equipment and Components - Purchased parts,
equipment, instruments, components and in-house fabricated subsystems
were received. Raw materials for pilot plant operation were received
and stored.
Task 5. Construction and Assembly of Pilot Plant - The pilot plants
were constructed.
Phase III - Pilot Plant Operations and Analysis
For each pilot plant operation, the tasks were:
Task 1. Pilot Plant System Check - All subsystems of the pilot plant
were checked separately and in combination for proper operation and
function. Debugging and redesigning were performed as required.
Task 2. Pilot Plant Start-Up - The pilot plant was put in operation and
individual plant process steps were checked for proper operation.
Task 3. Pilot Plant Operations - The pilot plant was operated at
various production rates and with various combinations of raw materials.
Parameters significantly affecting production costs and fertilizer
product quality, as well as plant effluent and emission levels, were
used. Plant modifications were made as required. The small pilot plant
was operated for four months, and the large one for about sixty days.
Task 4. Analysis of Pilot Plant Products, Operation and Effluents - The
fertilizers produced at various operating modes of the plants were
analyzed for the following characteristics:
1. Polymerization Levels (Non-orthophosphate concentration)
2. Feed Stock Ratios
3. Feed Stock Grades
4. Solubility
5. Storability
6. Granule Quality
The effluents and emissions from various sources were sampled and
analyzed.
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PHASE IV - Best Chemicals - Process Selection and Scale-Up to Full Sized
Plant
This phase consisted of three tasks, outlined below:
Task 1. Best Chemicals - Process Selection and Flow Diagram - Results
from the laboratory and pilot plant phases were analyzed in terms of
project goals. The optimum process flow sheet and raw materials were
selected on the basis of this analysis.
Task 2. Scale-Up to Full Scale Plant - All previous work results were
used to perform the scale-up to full scale plant design. Final flow
sheets were generated. Plant components, instrumentation and subsystems
were sized. Drawings of the plant layout were made. This full scale
plant design was used in the cost-effectiveness analysis of Task 3.
Task 3. Cost-Effectiveness Analysis - The prices of raw materials,
plant capital investment, labor, overhead and other financial factors
were analyzed. Costs were compared for production of the new fertilizer
in new plants and in typical remodeled plants. Costs were compared for
melt and aqueous produced granular fertilizer of the same grade.
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SECTION II
CONCLUSIONS
1. A process was developed in which ammonium phosphate - polyphosphate
melt technology was utilized to produce a high concentration granular
fertilizer containing a major proportion of waste or by-product ammonium
sulfate. The process was successfully tested in a continuously operated
454 kg/hr demonstration unit.
2. The type of pollutants generated by the process can be readily
contained by the utilization of known technology; the quantity of
pollutants is significantly less than would be produced in a plant using
an aqueous process to produce the same fertilizer grades.
3. This new technology offers lower capital and operating costs than
other procedures for incorporating large quantities of solid ammonium
sulfate into mixed fertilizer granules.
4. The process can be readily adopted by existing granulation plants.
5. Utilization of the process would tend to enhance the market for by-
product and waste ammonium sulfate.
6. Most of the processes now recommended for scrubbing sulfur dioxide
from power plant stacks do not recover sulfur in a form which can be
used for agricultural purposes. If an ammonia scrubbing process were
adopted, then sulfur dioxide would be converted into ammonium sulfate.
As indicated above, the ammonium sulfate could readily be incorporated
into a granular fertilizer.
7. Agriculture in the United States is operating on a negative sulfur
balance. The addition of sulfates to mixed granular fertilizers will be
helpful, particularly in those areas in which soil sulfur deficiencies
have been reported.
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SECTION III
RECOMMENDATIONS
Based on competitive price structure and pollution benefits to be
derived from the proposed manufacturing process and the demonstrated
capability of the pilot plant to produce quality products, it is recom-
mended that:
1. A 227 metric ton per day (250 short ton per day) prototype plant be
built and operated to demonstrate the process on a large scale and to
establish the most cost-effective method of operation.
2. Agronomic tests be made to determine field response to the use of
the fertilizers. Such tests should be made particularly in areas where
examination of soil or of plant tissues has shown the soil to be
deficient in sulfur. Crop responses should be studied to determine
whether there are any trace elements in the by-product or waste product
ammonium sulfate which affect plant growth adversely-
3. Laboratory tests be initiated to determine the possibility
of modifying the newly developed fertilizers to impart slow release
properties to them. It may be possible to accomplish this by incorpo-
rating certain materials within the fertilizer or by using such
materials as coating agents. Products which have been suggested as
suitable for this purpose include wax, sulfur and plastic substances.
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SECTION IV
LABORATORY INVESTIGATION
PREVIOUS WORK
All previous work performed by Ferguson Industries in ammonium
phosphate and ammonium polyphosphate processing, technical information
from TVA, the Environmental Protection Agency and universities, and
industrial research and development were searched to avoid any dupli-
cation of effort. The search was expanded to include all studies which
utilized ammonium sulfate, ammonium polyphosphate, potassium chloride
and admixtures of these. Conclusions drawn from this research provided
a basis for tentative selection of the most promising production
process and raw materials. At the same time, tentative selection was
made of plant process steps and raw materials which would minimize
environmental pollution. Current knowledge of processes, chemical
mixtures and production techniques is summarized below.
Ferguson Industries and others have noted that a melt of ammonium
polyphosphate can be mixed directly with ammonium sulfate and potash
to avoid several manufacturing steps which consume energy, require
capital investment and are major sources of pollutants. This consider-
ation led to the conclusion that ammonium phosphate - polyphosphate is
the best material, on balance, to use for direct combination with
ammonium sulfate to produce a good, mixed fertilizer. A further
advantage of such granulated phosphatic fertilizers is their lack of low
melting constituents. This characteristic enables them to be'coated
with water-insoluble substances such as waxes, asphalt and sulfur for
conversion into slow release substances.
The technology of polyphosphates has been developed primarily for
the production of fertilizer liquids. The range of polyphosphates in
liquid fertilizers is usually 70% or higher.
It has been found that solid fertilizers which contain large
concentrations of polyphosphates are primarily amorphous in nature and
exhibit cold flow characteristics. They have poor manufacturing,
handling and storage properties. Up to this time, no acceptable solid
11
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product containing over 50 percent (50%) polyphosphates has been found.
TVA has produced solid products containing up to 50% polyphosphates in
commercial demonstration plants. Most commercially acceptable ferti-
lizers contain less than 25% polyphosphates.
High order, single species potassium polyphosphates with slow
release properties have been produced. While these compounds are
available commercially, there is no reported method for their direct
production by reaction of anhydrous ammonia and phosphoric acid. '
High fugacity of ammonia appears to be the impediment to development of
a commercial process.
Liquid fertilizers generally are produced from anhydrous ammonia
and superphosphoric acid containing appreciable quantities of
polyphosphates. Direct reaction of these two materials produces
temperatures over 300 degrees Centigrade (570 degrees Fahrenheit).
Merchant grade wet process phosphoric acid containing 52 to 55%
phosphorus pentoxide (P2O5) also can be reacted directly with anhydrous
ammonia to produce fertilizers containing 15 to 55% polyphosphates.
Reaction temperatures will be above 200° C (390° F). Fertilizers with a
wide range of polyphosphate content can be produced by manipulation of
process variables such as temperature, pressure, retention time and free
water content of the reactants.4'5'6'7 Several variations of this
process are noted below.
1. A process test was described which produced
polyphosphates at an ammonia:phosphoric acid ratio
of 1.6:1.0, a pressure of 0.70 kilograms per square
centimeter (10 pounds per square inch), temperatures
of 293 to 315° C (560 to 600° F), and residence
time of less than one second.
2. Another test produced an ammonium potassium
hydrogen phosphate in a bench scale reactor with
the following parameter ranges: potassium:
phosphorus ratio of 0.5:1.0, temperatures of 200
to 210° C (390 to 410° F), pressures greater than
2.81 kg/sq cm (40 psi) and retention time greater
than four minutes. The product contained a poly-
merized product up to the tripolyphosphate level.
Effects of temperature, pressure and retention
time were studied.
3. Similar processes are described in which urea is
reacted and/or mixed with polyphosphates. Upon
being heated, urea will either break down to
ammonia and carbon dioxide or react with acid to
produce urea - phosphates and ureapolyphosphate. 10,11,12
-------
A process has been patented in which urea is mixed
with ammonium polyphosphate. The range of
ammonium polyphosphate content was 25 to 98% of
the total ?2°5' an<* the urea to ammonium phosphate
weight ratio range varied from 85:15 to 25:75.
4. TVA and others have reacted ammonia and phosphoric
acid in various concentrations. Ammonium sulfate,
urea and potassium salts have been incorporated
into the reaction product to form a variety of
fertilizers. '•LJfl^'lb'16 None of these
fertilizers was considered to have slow release
properties.
5. An accidental water loss during the operation of
one of Ferguson Industries' super-acid fertilizer
plants in Georgia resulted in the plugging of the
reactor column with an ammonium phosphate solid
containing substantially more polyphosphates than
the feed acid. In September 1968, this observation
led Ferguson Industries to build a crude pipe
reactor to test the theory of direct ammoniation
of phosphoric acid to produce polyphosphates.
The reactor consisted of a 2.54 cm (1 inch)
diameter pipe approximately 1.8 M (6 feet) long
with an aspirator jet attached to one end. The
motive power for the aspirator was 427° C (800° F)
ammonia at 7 kg/sq cm (100 psi). Boiling ortho
acid was introduced into the jet by aspiration
only. The ammonium phosphate - polyphosphate melt
was discharged into a container of water. This
first attempt at direct ammoniation netted a
product containing 9% nitrogen and 62% ^2°$ witn a
polyphosphate content of 75.77%. In order to
aspirate 0.5 kg (1 pound) of acid in this crude
system, it was necessary to use 3.0 kg (6 pounds)
of heated ammonia.
Many pilot plant modifications were made in late
1968 to develop an efficient and controllable
operation. In February 1969, a series of pilot
plant test runs was made to establish the
parameters affecting formation of polyphosphates.
It was concluded that polyphosphate formation was
highly dependent upon reaction temperatures and
feedstock concentrations, as shown in Figure 2.
13
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80
-H
0>
-P
IT)
•a
co
o
-p
c
-------
Analysis of the product melt showed particular
consistency in the 12% N and 58% P2°5 ran9e.
Several product characteristics were observed.
The polyphosphate hydrolyzed rapidly unless the
melt was cooled below 125° C (255° F) within five
to fifteen minutes. Also, hydrolysis would occur
upon addition of very small quantities of water.
The polyphosphate concentration of the melt was
critical to successful crystallization. If the
polyphosphate concentration was above 40% the
melt would remain plastic, sticky and soft rather
than crystallize.
6. The use of ammonium polyphosphate as a carrier for
micronutrients is well documented by TVA and
1 7 18 1 Q
others. '-LO/J-:* Ammonium sulfate has been mixed
with ammonium polyphosphate to produce a high
sulfur content material.20,21,22
7. Much data have been produced on the comparative
effects of ammonium polyphosphate and ammonium
phosphates on plant growth and production. All
reports show that ammonium polyphosphates are
effective to an equal or greater extent than the
orthophosphates. Economic comparisons of the two
fertilizers show that the polyphosphates are
preferred for their higher concentration of plant
nutrients per unit volume.
LABORATORY STUDY
A laboratory scale granulation and product quality study was
performed to determine various chemical and physical parameters of
production and product quality. Raw materials were combined in various
proportions under different mixing conditions to determine the optimum
set of variables for production of the fertilizer grades and qualities
shown most desirable in market analysis.
Critical Process Factors
As both laboratory and plant experience have demonstrated, it is
impossible to retain ammonia in ammonia to phosphoric acid mole ratios
greater than one in the melt granulation system. Mole ratios less than
one result in products which contain free acid and exhibit poor storage
and handling characteristics. Therefore, for any nutrient formulation,
the amounts of ammonia and phosphoric acid are fixed by the desired
content. Thereafter, ammonium sulfate may be added to bring the
15
-------
nitrogen content of the fertilizer to a desired level; potassium
chloride may be added to bring the potassium to a desired level; and an
inert filler may be used to complete the fertilizer analysis. Thus, the
amount of nutrients required for any given analysis is fixed.
One of the most important considerations in the melt granulation
process is the necessity of having a sufficient quantity of melt to
serve as a bonding agent for the solid ingredients in order to form a
hard, stable granule. In low melt formulations, those containing high
concentrations of ammonium sulfate or potash, it is absolutely essential
that the mixing action produce a high yield of product-size granules so
that the recycle ratio is held to a manageable level, because the
recycled material acts, in essence, like any other solid material. If
the ratio of melt to recycle becomes too low, there will be an
insufficient amount of bonding agent to form granules and the process
will become inoperable.
In this regard, the melt process, with its fixed amount of
nutrients for any given fertilizer analysis, is less flexible than the
aqueous process. In the latter process, it is possible to add more
water when necessary, thereby increasing the quantity of the bonding
agent.
Laboratory work was directed to the development of melt processes
by which phosphoric acid, ammonia, ammonium sulfate, potash and filler,
if needed, could be formed into a commercially acceptable granular
product. The variables which were studied included:
1. Concentration and impurity level of phosphoric
acid.
2. Temperature of phosphoric acid and of ammonia
piped to the reactor.
3. Reaction temperature.
4. Melt (reaction product) solidification temperature.
5. Temperature of undersize recycled to granulator.
6. Temperature of ammonium sulfate, potassium
chloride and filler added to the granulator.
7. Particle size of ammonium sulfate and potassium
chloride added to the granulator.
8. Granulator holding time.
16
-------
Laboratory Procedures
The solids-melt combinations were produced by two techniques:
1. Ammonium phosphate - polyphosphate particles
were remelted in the laboratory and granulated
with the solids in a Hamilton-Beach mixer.
2. Melt was produced in a small tee reactor and
directed onto the agitating bed of solids in the
Hamilton-Beach mixer.
Although these test data were reported separately, the results were
similar and only one set of conclusions was reached.
Test Results
The results of selected tests are reported in the Appendix, Section
IX, in Table A-l and text. The laboratory work indicated that the
proposed process was technically feasible.
The conclusions of the laboratory work may be summarized as follows.
Grade of Fertilizer - The concentration of ammonium phosphate melt in
the mixed product was varied. Eight different concentrations of melt,
ranging from 11.00 to 54.73% by weight of mix, were combined with dry
solid ammonium sulfate and potassium chloride. Table 1 shows the
material ratios for the various fertilizer grades which were produced.
The laboratory work was concentrated on the 13-13-13-13 grade for
the following reasons:
1. The 1-1-1 ratio is one of the major grade ratios
used by the farmer.
2. By inspection of Table 1, it is apparent that this
grade contains the highest concentration of
ammonium sulfate, more than 50%.
3. Because the ratio of dry solids to melt in this
grade is the highest of all major fertilizer
ratios, it is the most difficult to produce by
the melt granulation process.
17
-------
Table 1. MATERIAL RATIOS OF POTASSIUM CHLORIDE, MELT (AMMONIUM
PHOSPHATE) AND AMMONIUM SULFATE TO PRODUCE
VARIOUS FERTILIZER GRADES
Grade
16-31-0-11
14-42-0-6
14-24-12-9
14-24-10-12
14-24-8-11
13-13-13-13
13-30-10-8
12-24-12-13
kg/Mta
544
451
737
246
193
420
387
161
420
387
130
420
387
210
225
489
161
525
319
420
330
194
lb/ta
1088
902
1474
492
386
840
774
320
840
774
260
840
774
420
460
980
332
1050
638
840
840
388
Ingredients
Meltb
Sulfate0
Melt
Sulfate
Potashd
Melt
Sulfate
Potash
Melt
Sulfate
Potash
Melt
Sulfate
Potash
Melt
Sulfate
Potash
Melt
Sulfate
Melt
Sulfate
Potash
Solid/Melt
0.84
0.35
1.37
1.37
1.39
3.34
0.92
1.98
Difference between 1000 kg and/or 2000 Ib adjusted by addition
of filler, where necessary.
Ammonium phosphate melt, 12-57-0.
cAmmonium sulfate, 21% nitrogen.
dPotassium chloride, 62% (K20).
18
-------
Concentration of Polyphosphates in the Melt - Early studies indicated
that degrees of polymerization of phosphates in the melt might have an
effect on granulation. Therefore, different melt phosphate
concentrations, varying from 12.5 to 55.6% polyphosphate based on the
total phosphate content, were tested. Summarizing data are shown in
Table 2.
It was found that good granulation, evidenced by the production of
hard granules, was obtained repeatedly with up to 35.6% poly
concentration when fine mesh (-40) ammonium sulfate was used. However,
when coarse mesh (-14 to +40) ammonium sulfate and/or potassium chloride
was mixed with high polyphosphate content melt, more irregular
fertilizer granules were produced. It was concluded that the optimum
concentration for obtaining consistently good granulation is
approximately 25% polyphosphate.
Concentrations of Ammonium Sulfate in the Mixed Product - The initial
tests utilized a low ratio of solids to melt and, therefore, low
concentrations of ammonium sulfate. Successful granulation was achieved
although" granule quality was unsatisfactory. Other investigators have
reported similar results. ''
As noted previously, the objective of this investigation was to
develop a process that would offer large market outlets for by-product
ammonium sulfate and would produce popular fertilizer grades with high
nitrogen ratios. The fertilizer grade which contains the most ammonium
sulfate, approximately 54%, is 13-13-13-13. The first laboratory tests
designed to adapt the melt technology to the granulation of this grade
were not successful. It was found necessary to apply standard aqueous
technology to produce satisfactory granules.
Various polyphosphate concentrations were tried. The polyphosphate
levels of the melt were attained either by heating an intermediate
concentration of phosphoric acid and ammonia prior to reaction, or by
using a more concentrated phosphoric acid. Reaction temperature is a
function of product polyphosphate content. It was observed that
polyphsphate melt tended to agglomerate within itself and not to
incorporate any of its solid constituents into the granules.
As polyphosphate content was lowered, melt viscosity decreased.
The melt dispersed more readily. The effect was the same as if the
melt-to-solids ratio had been increased. However, although the
polyphosphate level was dropped progressively to zero, it still was
impossible to obtain satisfactory granulation.
It was found necessary to utilize an aqueous solution to achieve
successful granulation. Such granules had to be dried to attain
satisfactory storage and handling properties.
19
-------
Table 2. POLYPHOSPHATE CONCENTRATION IN PRODUCT AND GRANULATION QUALITY
K)
o
Sample
Number
Tl-17
11-16
12-15
10-31
12-15
10-31
11-21
12-12
12-13
11-03
11-15
11-21
11-22
11-22
11-16
12-14
11-14
02-21
Analysis. %
Melt
24.55
24.55
19.60
23.0
24.55
23.00
24.55
24.55
46.85
24.70
24.70
24.55
24.55
24.55
24.55
24.55
24.55
24.55
KC1
22.55
22.55
18.00
24.00
22.55
24.00
22.55
22.55
43.04
22.10
22.09
22.55
22.55
22.55
22.55
22.37
22.55
22.55
AS
52.89
52.89
42.40
52.00
52.89
52.00
53.00
52.29
10.09
53.20
53.21
53.00
53.00
53.00
52.89
53.46
52.89
52.89
Fine
52.89
52.89
20.00
-
52.87
-
75.55
52.89
53.13
53.20
53.21
22.55
53.00
None
52.89
75.83
31.20
52.89
Temp., °C
Solid
260
177
-
177
163
121
204
163
163
163
163
-
204
177
177
163
163
177
Melt
191
232
-
-
218
-
204
191
204
246
246
-
204
204
260
204
246
204
Phosphate. %
Total
13.4
15.5
20.49
21.14
17.37
13.45
13.90
16.71
16.12
16.41
18.48
15.34
14.49
13.60
14.64
15.88
15.97
26.03
Poly
20.4
25.3
31.2
30.8
35.0
34.0
37.2
38.1
41.3
42.3
43.2
45.2
45.9
51.1
52.5
53.3
55.6
12.5
Granu-
lation
good
good
-
good
good
-
good
fair
good
good
v. poor
poor
good
poor
good
poor
v. good
good
Comments
Hard, melt conditioned with NH^OH, then heated.
Very hard melt; conditioned with NH4OH.
Low attrition, pH 2.7.
Good sample.
Attrition m.
Added melt to dry elements, bad mixing.
Attrition 3.93.
Without NH4OH.
Ammonium sulfate ground.
Mixed melt with NH4OH - heated.
Excessive melt.
Slow cooling, 21.08% attrition.
Mixed melt with NH4OH, then heated.
Soft.
KC1 -14 to 40, 88.3%.
High pH, very hard.
-------
Table 2. (Continued) POLYPHOSPHATE CONCENTRATION IN PRODUCT AND GRANULATION QUALITY
K)
Sample
Number
02-21
02-08
02-22
02-22
02-24
02-24
02-27
02-28
03-19
02-21
02-24
03-05
02-28
02-28
03-05
02-24
03-19
03-19
Analysis, %
Melt
24.55
24.55
24.55
24.55
24.87
24.55
24.55
24.55
24.55
24.44
24.87
24.55
24.55
24.55
24.55
24.87
24.55
24.55
KC1
22.55
22.55
22.55
22.55
23.24
22.55
22.55
22.55
22.55
22.55
23.24
22.55
22.55
22.55
22.55
23.24
22.55
22.55
AS
52.89
52.89
52.89
52.89
49.64
52.89
52.89
52.89
52.89
52.89
49.64
52.89
52.89
52.89
52.89
49.64
52.89
52.89
Fine
52.89
52.89
52.89
-
-
52.89
-
-
-
52.89
49.64
26.45
52.89
52.89
13.22
49.64
26.45
13.72
Temp., °C
Solid
177
191
177
191
177
191
191
163
160
204
191
191
199
-
191
204
193
193
Melt
204
204
213
218
210
204
216
204
246
204
199
210
216
-
216
204
246
246
Phosphate, %
Total
19.42
22.18
20.61
20.81
17.83
20.00
14.49
14.19
15.37
12.84
22.77
14.19
14.49
14.49
14.34
12.78
15.66
15.08
Poly
13.0
14.0
14.5
20.7
20.8
21.5
23.7
24.2
24.8
25.6
25.9
26.3
28.9
28.0
29.2
36.0
38.3
29.8
Granu-
lation
good
-
-
v. good
-
v. good
-
-
-
none
-
good
good
-
good
-
-
-
Comments
Better granulation.
Many fines, mainly KC1, agglomerate
melt, pH 2.8.
Melt at 250 cooled too fast; temp, of melt 350°.
High pH.
Temp, of melt 350°, over-agglomeration, pH 4.3.
Over-agglomeration, 9.02 attrition, pH 4.7.
KC1 +20 mesh, pH 4.2.
KC1 +20 mesh, pH 4.0; irregular, angular
granules.
pH 3.1.
pH 4.5.
Over-agglomeration, pH 4.0, 2.25% urea.
Agglomerate of AS and KC1 , KC1 not completely
wetted; pH 4.8.
Solid too hot, much oversized particles 36.6%.
pH 4.5.
Solid too hot or too much melt, pH 4.4.
Too hot, pH 4.5, 2.25% urea.
pH 3.4.
pH 3.5.
-------
At this point, it may be desirable to point out that at atmospheric
pressure the ammonia-phosphoric acid-water system behaves differently
than either the ammonium nitrate-water or the urea-water system. The
latter two systems maintain a single liquid phase as they are heated,
and the water content of the solution is decreased from 100% down to 0%.
The ammonia-phosphoric acid-water system, at a one-to-one mole ratio of
ammonia to phosphoric acid, is discontinuous from about 40 or 45% down
to 0% water. In this discontinuous range, a two phase system is formed,
consisting of a liquid plus solid mono-ammonium phosphate. Therefore,
when an aqueous solution is employed in a granulation process, the
liquid binder always contains approximately 40% water. The removal of
this water would require additional processing steps and the expenditure
of energy. Such costs were considered inconsistent with project goals.
Heating of the solid ingredients was tried next. It was found that
heating these materials above the crystallization point of the melt
brought about a remarkable transformation. At this temperature, the
particles were wetted by the melt. Upon subsequent cooling and
crystallization, hard, stable granules were formed.
Some flexibility is needed in plant operations to compensate for
the amount of recycle or for other operating contingencies. This can be
attained by changing the polyphosphate content of the melt, utilizing
either of the two methods mentioned above. The result would be the
same as if the ratio of melt-to-solids had been changed.
Source Grades of Ammonium Sulfate Used - Samples of by-product ammonium
sulfate were obtained from four suppliers. Physical characteristics are
listed in Table 3. Coarse and fine mesh particles from both the
chemical and steel industries were used. Fine mesh ammonium sulfate
generally is the most difficult to market by these industries. Chemical
characteristics of the by-product ammonium sulfate obtained from various
sources differed only slightly and required no concentration adjustments
to produce the same fertilizer grades.
Concentration of Potassium Chloride in the Mixed Product - Six potassium
(chloride) gases were made, as indicated in-Table 1. It was observed
that the behavior of potassium chloride in the melt system was very
similar to that of ammonium sulfate. As before, it was found necessary
to heat the potassium chloride crystals to obtain satisfactory wetting
by the ammonium phosphate melt and to produce good granules.
Granulator Mixing Temperature - Each grade has an optimum range of
granulation temperatures. For example, the best temperature range for
granulation of grade 13-13-13-13 is 175 to 200° C (345 to 390° F), as
shown in Table 4, whereas grade 13-30-10-8 can be granulated sucessfully
at 100 to 160° C (210 to 320° F).
22
-------
Table 3. SCREEN ANALYSIS OF SOURCES OF AMMONIUM SULFATE
(Cumulative percent by weight)
Mesh No.
(U.S. Std.)
12
14
20
30
40
50
70
100
-100
International
Minerals &
Chemicals Corp.
—
-
1.7
-
40.0
-
-
95.0
5.0
Weirton Div.
Of National Steel
Company
12.4
30.3
83.0
-
96.6
-
-
-
-
Jones and
Laughlin
Steel Company
20.1
_
77.5
97.0
-
99.4
99.4
-
-
Dow-Badishe Company
13.8
58.0
_
88.0
_
_
99.0
-
-------
Table 4. MIXING TEMPERATURE/RECYCLE EFFECT ON GRANULATION
(Grade 13-13-13-13)
Sample
Symbol
11-15-2
11-16-2
11-17-2
11-14-2
01-04-3
01-09-3
01-12-3
01-15-3
02-07-3
02-24-0
Analysis, % Temperature, °F
N-P205-K20
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
--
n-60-o
11-60-0
12-57-0
—
--
12-57-0
12-57-0
--
—
Melt
24.7
24.6
24.6
24.6
24.6
—
18.7
18.7
19.6
24.6
24.6
12.3
12.6
24.8
24.8
KC1
22.1
22.6
22.6
22.6
22.6
—
17.3
17.3
18.0
22.6
22.6
11.3
11.3
23.2
23.2
AS
53.2
52.9
52.9
52.9
52.9
—
40.3
40.3
42.2
52.9
52.9
26.5
26.5
49.6
49.6
- 14
Mesh
53.2
75.4
52.9
52.9
52.3
—
40.3
40.3
42.2
52.9
52.9
26.5
26.5
0.0
49.6
Solid
325
325
350
350
500
325
300
275
250
—
375
225
225
--
400
Melt
475
450
350
450
375
400
425
325
425
—
250
425
425
410
400
Granulation
Quality
v. poor
v. poor
good
good
good
—
good
good
good
rubbery
good
v. good
none
—
—
P, as
PP, %
43.2
—
52.5
25.3
20.2
—
—
—
—
—
—
—
—
—
—
Comments
Mixed melt with NH4OH; heated.
Mixed melt with NH4OH; heated,
solid not wet.
Mixed melt with NH40H; heated,
58% marketable.
Melt conditioned with NH4OH,
very hard.
Melt conditioned with NH4OH,
heated; hard, 53% marketable.
Ammoniated a sample that was
very sticky, stayed sticky.
pH 5.0 - 5.5; ammoniated after
granulation.
pH 3.5; ammoniated during
granulation.
pH 4.5; ammoniated.
Lab melt, acid + NH4OH.
Lab melt, acid + NH4OH.
Added acid to melt before
granulation.
Added acid to solids before
heated.
pH 4.3, over agglomeration,
much fines, 36% marketable.
pH 4.5, too hot, some granu-
lation achieved by crushing hot.
-------
As a general rule, the higher the solids-to-melt ratio, the higher
the required granulation temperature. The ratio of recycled material to
product also affects the granulation temperature. As the recycle ratio
is increased at a high solids-to-melt ratio, it becomes necessary to
increase the granulation temperature. This is not true when the solids-
to-melt ratio is low. In this case, the optimum granulation temperature
may be either high or low, and the operator must observe the process to
make the proper adjustment. When insufficient granulation is noticed,
the process is corrected by increasing the granulation temperature; when
excess fluidity is noticed, the process is corrected by decreasing the
temperature.
Granulator Mixing and Crystallization Technique - The granulator has two
functions: to mix the melt with the solid constituents, and to effect a
phase change of the melt.
Thorough mixing of the melt with the solid ingredients with which
it is to be incorporated occurs while the materials are still hot.
Heat must be removed before crystallization can occur. Normally,
this is done by air cooling. However, in the course of these
experiments it was found that heat could be removed more advantageously
by adding cold raw materials to the mixture of melt and recycle. Most
of the raw materials do not agglomerate at this time, but they do remove
the heat of crystallization of the mixture. The unagglomerated
materials are separated on the product screen and returned as recycle.
The advantage of this procedure is that the cost of air blowing is
reduced significantly; the energy and equipment needed to heat the raw
materials is decreased or eliminated; and the requirement for pollution
control is signally reduced.
Particle Size Effects of Ammonium Sulfate and Potassium Chloride on
Granulation - Because the size of dry mix materials used in the process
cannot always be specified, the effect of variations of particle size of
the ammonium sulfate and potassium chloride dry mix materials on the
granulation quality and marketable fraction of the product was
investigated. Only a 13-13-13-13 grade, with the lowest melt-to-solid
ratio, was studied; the melt must wet more solids for this formulation
than for any other. Formulation "fines" are defined as that portion of
the mixed chemicals passing the No. 14 screen. Test results indicated
that for a high quality granule and a high percent marketable product,
optimum fines, at the mixed temperatures utilized, are about 50% by
weight of the total amounts added. Efficiency decreases at more or less
than this figure. Summary data are presented in Table 5.
-------
Table 5. PARTICLE SIZE EFFECT OF AMMONIUM SULFATE AND POTASSIUM CHLORIDE ON GRANULATION
(Grade 13-13-13-13)
tsi
Sample
Symbol
10-24-2
11-14-2
12-13-2
11-21-2
11-21-2
11-22-2
11-22-2
12-12-2
12-13-2
12-14-2
12-14-2
12-15-2
01-12-3
01-15-3
01-15-3
Analysis, %
Melt
N-P205-K20
12-57-0
11.5-61-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
—
--
12-57-0
Melt
24.2
24.6
46.9
24.6
24.6
24.6
24.6
24.6
46.9
24.4
24.3
24.6
24.6
24.6
24.6
KC1
22.4
22.6
53.0
22.6
22.6
22.6
22.6
22.6
43.0
22.4
22.4
22.6
22.6
22.6
22.6
AS
52.5
52.9
10.0
53.0
53.0
53.0
53.0
52.9
10.1
53.5
53.5
52.9
53.0
53.0
53.0
- 14
Mesh
52.5
31.2
43.0
75.6
22.6
53.0
none
52.9
53.1
75.8
75.8
52.8
53.0
53.0
—
Temperature, °F
Solid
75
325
325
400
—
400
350
325
325
325
325
325
~
375
--
Melt
—
475
300
400
—
400
400
275
400
400
40
425
—
250
—
Granulation
Qual i ty
poor
v. good
good
good
poor
good
poor
fair
good
soft
poor
good
none
good
--
% Marketable
—
55.7
59.1
43.7
41.7
64.4
45.2
54.4
59.1
33.1
—
31.0
—
—
--
Comments
Over agglomeration and
unagglomerated material.
KC1 88% -14 +40.
—
Granulation 30 seconds.
Excessive melt.
—
Slow cooling; 21% (-14 mesh).
—
—
Rounded particles; KC1 and AS
added for heat transfer.
Very sticky.
19% attrition.
Rubber-like product melt
produced in lab.
pH high; melt produced in lab.
—
-------
Recycle Effects on Granulation - Table 6 summarizes data on recycle
effect for grade 13-13-13-13 product at approximately the optimum
granulation temperature. The data indicate that the recycle rates for
good granulation generally are less than 30%. The marketable portions
of the product reported in Table 6 are representative of the complete
data set.
Pertinent Physical Characteristics - Several laboratory tests investi-
gating reaction to moisture were performed. These tests included:
Hygroscopicity - Table 7 shows the results of hygroscopicity tests on
on two general grades of product. The Ferguson research product shows
higher moisture absorption than the conventional Olin product. However,
these results may not be as truly indicative of caking sensitivity as
they purport to show. Samples of Ferguson product made in the research
pilot plant, having been stored at warehouse conditions for over a year,
are still free flowing and show no evidence of caking.
A possible explanation of this behavior may be that the
polyphosphate in the research product acts as an internal dessicant.
Water absorbed from the atmosphere will first convert the polyphosphate
to the orthophosphate. It is only when additional amounts of water have
been absorbed that the granules become subject to caking. The Olin
product does not contain any polyphosphates.
As supporting evidence for this supposition, one may cite the
fact that some granular ammonium nitrate is marketed on this basis.
Imperial Chemical Industries mixes ammonium nitrate with magnesium
nitrate. The latter is an extremely hygroscopic substance which forms a
hydrate with six water molecules. When added to the granulated ammonium
nitrate, it acts as an internal dessicant.
Critical relative humidity at 30° C (86° F) - Table 8 presents test data
attempting to quantify moisture sensitivity of the product by vapor
pressure measurements. Results are erratic and do not correlate well
with the hygroscopicity results. Thus, it appears that the two
different fertilizer products will require different test limits to
indicate caking susceptibility.
Relative rates of solution - Table 9 presents comparative data on
nutrient solubility. These data indicate that the solubility rates of
the Ferguson research products and the Olin products are similar.
27
-------
Table 6. RECYCLE EFFECT ON GRANULATION AT OPTIMUM TEMPERATURE
(Grade 13-13-13-13)
NJ
00
Sample
Symbol
12-12-2
12-14-2
12-19-2
01-04-3
01-04-3
01-09-3
01-09-3
01-10-3
01-19-3
02-06-3
02-07-3
Analysis, %
Melt
NP205-K20
12-52-0
12-52-0
12-57-0
11-60-0
11-60-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
12-57-0
Melt
17.3
12.3
14.7
18.7
18.7
19.6
21.8
19.6
12.3
12.3
12.3
KC1
15.9
11.3
13.5
17.9
17.3
18.0
20.0
18.0
11.3
11.3
11.3
AS
38.1
36.0
31.7
40.3
40.3
42.2
47.1
42.2
26.5
26.5
26.5
Recycl e
26.7
50.0
39.9
23.8
23.8
20.0
11.1
20.0
49.9
50.0
50.0
- 14
Mesh
38.1
37.8
31.7
40.3
40.3
42.2
47.1
42.2
26.5
26.5
26.5
Temperature, °F
Solid
325
325
375
300
275
250
250
350
290
225
275
!
Melt
400
400
375
425
325
425
425
425
450
425
450
Granulation
Quality
good
poor
poor
good
good
good
good
--
—
v. poor
v. poor
Mesh -5
+14, %
44.4
51.7
35.2
43.6
38.3
43.0
45.8
—
37.9
30.3
--
Comments
--
Very sticky, (hi-poly).
pH 2.8; part of recycle not wetted.
pH 5.0 - 5.5; ammoniated with vapors
after granulation.
pH 3.5; ammoniated during granulation.
pH 4.5; NH4OH added.
Tried to increase yield.
Balanced the recycle product.
Insufficient wetting of solids.
Granules angular.
--
-------
Table 7. HYGROSCOPICITY
(Weight gained, based on dry weight, %)
Fertil
(Sampl
izer grade
e number)
Days
1
in chamber
2
3
6
35% RH, 30°C (86°F)
14-24-8
(12-21-73)
12-24-12
01 in sample
12-24-12
(1-3-73)
12-24-12
(1-5-73)
16-31-0
(1-3-73)
14-14-14
(12-19-73)
12-12-12
01 in sample
12-24-12
(12-28-73)
1.8
1.3
2.9
2.6
1.1
2.9
0.7
0.7
1.6
1.1
2.8
2.7
1.0
2.6
0.5
0.5
1.7
1.1
2.7
2.8
1.0
2.7
0.6
0.6
1.7
1.2
2.8
2.8
1.2
2.7
0.6
0.7
40% RH, 30°C (86°F)
14-24-8
(12-21-73)
14-14-14
(12-21-73)
12-24-12
(12-28-73)
12-24-12
(1-3-73)
5.3
4.0
4.8
0.9
5.7
4.6
5.5
1.6
6.5
4.4
5.9
2.4
8.7
5.5
7.0
3.9
29
-------
Table 7 (continued). HYGROSCOPICITY
(Weight gained, based on dry weight, %)
Fertilizer grade
(Sample number)
Days in
1
2
chamber
1 3
6
40% RH, 30°C (86°F)
12-24-12
(1-5-73)
16-31-0
(1-3-73)
12-12-12
01 in sample
12-24-12
01 in sample
4.9
4.3
1.8
1.7
4.9
4.8
1.3
1.4
5.4
4.7
1.2
1.6
6.0
4.5
1.2
1.4
Table 8. CRITICAL RELATIVE HUMIDITY AT 30°C (86°F)
Fertilizer grades
(Sample number)
14-24-8
(12-20-73)
14-14-14
(12-19-73)
12-24-12
(12-28-73)
16-31-0
(1-3-73)
12-12-12
01 in sample
12-24-12
01 in sample
Critical relative
Humidity, %
26.9
65.1
32.5
29.4
79.1
32.6
Sample size, gm
1.1
1.2
1.0
1.2
1.1
1.1
30
-------
Table 9. RELATIVE RATES OF SOLUTION
(Sample dissolved in 10 minutes, %)
Grade
Sample
14-14-14
12-15-72
12-12-12
01 in Sample
12-24-12
12-29-72
14-14-08
12-21-72
12-24-12
01 in Sample
12-24-12
12-29-72
Solution Rate
N
3.0
2.4
3.0
2.8
2.3
0.0
Total P205
4.2
5.2
6.5
5.4
3.5
1.1
K
2.5
1.2
2.0
1.5
1.4
0.5
pH
2.5
3.5
3.1
2.5
3.5
3.5
Total
Solids, %
21.6
14.5
21.9
20.3
15.2
--
31
-------
Rate of moisture pick-up - Table 10 presents comparative data for
several fertilizer grades and two product sources. The Olin products
again show somewhat less sensitivity to moisture in storage. However,
the acceptable limits should be defined differently for the Ferguson and
the Olin products in view of the observed favorable, warehouse storage of
the Ferguson product for more than one year.
Conclusions
The results obtained in the laboratory investigation were used to
select flow sheets and equipment for the pilot plant phase. The data
defined many parametric windows within which a good quality fertilizer
could be produced. These tests also eliminated much preliminary work
towards defining the operating parameters needed to produce the various
grades of fertilizer desired.
32
-------
Table 10. RATE OF HYDROLYSIS
Fertilizer Grade
Sample number
14-14-14
12-15-72
12-12-12
Olin
14-24-8
16-31-0
12-28-72
12-24-12
12-28-72
12-24-12
Olin
Week in Chamber
82%, RH
1
2
3
_
1
2
3
_
1
2
3
_
1
2
3
_
1
2
3
_
1
2
3
Moisture, %
1.7
9.2
19.7
29.7
1.6
5.2
5.2
16.8
1.7
16.2
23.3
25.7
0.6
9.4
20.2
21.3
0.4
11.1
22.8
29.8
1.0
7.1
11.8
20.3
Total
P205, %
20.8
19.4
19.9
20.2
14.6
14.3
14.3
11.5
30.5
29.4
29.5
28.8
29.6
30.1
32.2
32.1
30.5
29.6
29.8
32.3
24.4
24.1
24.6
25.7
P as PP
% of Total
31.7
24.2
28.6
37.4
1.2
1.3
13.2
7.8
25.0
19.6
0
14.8
20.1
14.3
15.9
14.2
41.5
36,4
38.6
44.0
0.6
0.5
7.4
3.6
N, %
13.1
_
14.1
13.5
11.5
11.1
11.7
12.1
13.0
_
13.4
13.4
14.8
14.9
15.0
15.3
11.8
12.6
12.3
12.5
12.2
12.1
12.4
12.5
K20, %
12.6
-
19.3
13.1
12.6
11.7
-
12.6
6.3
-
6.8
-
0.1
0
_
-
10.5
11.8
_
11.5
11.6
11.5
_
11.5
pH
2.7
-
2.5
2.6
3.4
3.5
3.8
3.9
2.6
-
2.3
2.5
2.8
2.5
2.5
2.6
3.3
3.0
3.1
3.1
3.4
3.4
3.6
3.5
-------
SECTION V
PILOT PLANTS
INTRODUCTION
Two pilot plants were constructed and operated. One had a capacity
of 45 kg/hr (100 Ibs/hr) and the other, a capacity of 454 kg/hr
(1000 Ibs/hr). The information obtained on operating parameters and
equipment behavior in the small unit was applied to the design of the
larger plant. Equipment design and operating data obtained during pilot
operations were used to formulate the design of the scale-up commercial
plants described in Section VI.
DESIGNS
Of the many preliminary designs considered, three were chosen for
detailed consideration: Alternates I, II and III. Material and energy
balances were developed for these alternates based upon the laboratory
optimization study results. It became apparent that Alternate I, with
its higher equipment and energy requirements, would not be as desirable
as. Alternate II or III. Therefore, Alternate I was not investigated
beyond the computation state.
Alternates II and III were quite similar. Therefore, only minor
changes of pilot plant equipment were needed to test both designs.
Alternate I flow sheet and equipment are presented in the Appendix,
Section IX. Energy balances for all alternates are also included in the
Appendix. Only Alternates II and III are discussed in this section.
The flow sheets for Alternates II and III are shown in Figure 3.
To prevent excessive duplication of figures to be presented, Figure 3
also includes data developed for the 227 Mt/d scale-up which is
discussed in the next section. The basic process concepts and equipment
are described below. The results and conclusions of the pilot plant
operations are presented separately for each plant size.
34
-------
STREAM N2.
-------
ALTERNATE II
Basic process and equipment were:
Ammonium Polyphosphate Melt Production - Phosphoric acid was mixed with
ammonia in a tee reactor chamber to produce ammonium phosphate and
ammonium polyphosphate. A drawing of this is shown in Figure 4. An
acid scrubber in the phosphoric acid feedline captured ammonia lost
from the steam disengagement chamber which separated water vapor and
ammonia from the melt, plus that in the pug mill vent.
Mixing the Melt with Solid Material - A pug mill was chosen as the
granulation mill. This was done because laboratory experiments had
shown that vigorous pugging is required to mix the viscous ammonium
polyphosphate melt with the dry ammonium sulfate, potassium chloride,
recycle solids and other materials. Two pug mill designs for the pilot
plant are shown in Figure 5. Preheating of the solids was required for
the dry materials stream. This preheating enabled the melt to be mixed
with the solids before crystallization occurred. In the small pilot
plant, the solids were heated as they were fed from the bins. The
sensible heat of the hot product was wasted. In the large pilot plant,
and in the 227 Mt/d scale-up plant, the raw materials were added to the
product from the pug mill in order to utilize the product heat and to
control crystallization.
Sizing, Recycle, and Storage Steps - Material from the granulation
process was screened. Oversize material was sent to the crusher and was
resieved. Fine material, which in the large pilot plant and in the 227
Mt/d flow chart contained heated raw solids, was recycled. The
intermediate, market size was cooled and sent to storage.
Pollution Control - The steam and ammonia separated in the steam
disengagement chamber was scrubbed by incoming phosphoric acid in the
ammonium scrubbing unit. Pug mill vapors and particulate matter were
also piped to this scrubber. Effluent vapors from the scrubber which
contain ammonium chloride were removed and sent to an electrostatic
precipitator. The gaseous effluent from the precipitator was vented to
the atmosphere. The solids collected from the scrubbing operation and
the precipitator were recycled. Table 11 presents representative data
for this operation.
In the pilot plants, no effort was made to control dust from the
dry handling equipment. In the scale-up plants, this material was
cleaned by cyclones and bag filters and was recycled.
36
-------
20X PIPE
DIAMETERS
H3P04
INLET
MELT
TO
PUGMILL
VAPOR
NH3 INLET
NOTE:
ALL PIPING 316 STAINLESS-
TEFLON LINED.
SIZES'. M"^ FOR 45 KG/HR, PILOT
!/£"<)) FOR 454 KG./HR, PILOT
2"(j>FOR 227 M TON DAY
ALL PIPE AND FITTINGS SCH.40
Figure 4. Tee reactor design.
37
-------
45.4 KG.PER HR.PUG MILL
454 KG.PER HR. PUG MILL
00
1MILL
'SHAFTS
PLAN VIEW
. I'"7".
h1
•-•£
— f
t
r
,_.
t" 9'" J " *\
LDISCHARGE
OUTLET
R^1^ , T rH
;mum . '-'" - g
i-Ull If/ \ 4
, -,. ,
\ \
£
[M
. l'-8".
3
3
/<
* \
V
ATERIALS \
INLET \
-kl"x34"X2"E BAR
2. EQUALLY SPACED
ROTATION «C3 FLOW-
93 RPM
RPM
-GEAR BOX
*
DRIVE TRAIN
\-SPARGE
LINE
(I5)/8"(|)DIA HOLES
PUGMILL
|
NH3 SPARGE
LINE
4"SCH 80
PIPE
ROTATION -eS-FLOW
58 RPM
Figure 5. Pug mill designs for pilot plants.
-------
Table 11. CHEMICAL ANALYSIS OF PUG MILL EXHAUST
(Percent total stream)
Sample
NH3 - N
Sulfate
Chloride
P2°5
H20
A
6.84a
0.01
0.23
0.01
93.27
B
2.13a
0.01
0.55
0.01
97.30
C
1.02b
0.01
0.41
0.01
98.55
D
0.71b
0.01
0.68
0.01
98.59
E
0.82b'c
0.01
0.04
0.01
99.01
aExcess ammonia added in pug mill.
bSample D before, and Sample E after, a Gothard "Fulgor"
multistage electrostatic precipitator.
GEquivalent to 10 milligrams per cubic meter (mg/m).
Notes:
Solids collected off first stage plates: Nitrogen 15.00%
Sulfate 15.40%, P205 27.80%, Potash 7.44%, Chloride 9.02%,
Ammonium Chloride 3.40%.
Accuracy limits of analytical methods - 0.01%.
39
-------
ALTERNATE III
Basic processes and equipment were:
Ammonium Polyphosphate Melt Production - The process was the same as in
Alternate II, except that some ammonia was diverted to the downstream
end of the pug mill. This produced a more acidic melt with desirable
wetting and viscosity properties.
Mixing the Melt with Solid Materials - The process was the same as in
Alternate II, except that diverted ammonia was sparged into the lower
end of the pug mill. In the cases of the prototype and commercial
plants, part of the diverted ammonia was sparged into a separate mixing
drum to insure attainment of a one-to-one ratio of ammonia to phosphoric
acid and to insure non-hydroscopic product quality.
Sizing, Recycle and Storage - Same as in Alternate II.
Pollution Control - Same as in Alternate II.
OPERATION OF THE 45 kg/hr PILOT PLANT
Upon completion of construction of the Alternate II design plant,
an operational checkout was conducted to determine the effectiveness of
mechanical configurations and equipment sizing in producing fertilizer
grades 13-13-13-13 and 12-24-12-13. Work was concentrated on these two
grades because they represent two segments of a spectrum of granular
materials which can be made by the methods proposed 'in this report.
Grade 12-24-12-13, which has a solids-to-melt ratio slightly less than
2, was easy to handle and to form into a marketable product. Grade
13-13-13-13, which has a solids to melt ratio of slightly higher than 3,
was difficult to process. However, grade 13-13-13-13 was the most
desirable since increasing its use would increase the amount of ammonium
sulfate waste product that could be utilized. Test results are
presented in Table A-3 of the Appendix. This table also includes
pertinent physical and chemical conclusions from each run. In the pilot
plant and the laboratory work, the chemical content of the product was
relatively closely fixed by the nature of the raw materials and recycle.
Indeed, at steady state operation, the chemical content of the recycled
material did not affect the output stream. In the pilot plants, as in
the laboratory, it was the granular quality which was the dependent
variable and was controlled by the acid-to-ammonia ratio in the tee
reactor, reaction temperature, pug mill temperature and the ratio of
recycled material to product.
40
-------
Pug mills, of necessity, are ruggedly built. The shafts must be
non-deflecting, as they transmit relatively large amounts of horsepower.
As a result, small pug mills are built with close clearance and have
relatively small flow areas. For example, as shown in Figure 5, the
smaller pug mill had a 1-1/4 inch shaft and 3/4 inch blades; the larger
mill had a 4 inch shaft, 4 inch blades and a correspondingly larger flow
area. This relationship is even more pronounced in a commercial mill,
in which the blade length may be two or three times the shaft diameter.
The purpose of using a pug mill was to cause intimate mixing of the
melt and solids to promote crystallization, or granulation. Ideally,
this phenomenon would occur within the mixture that was being processed
as it was cooled and mixed. However, the mechanical equipment
constituted a heat transfer surface which also affected the granulation
process. When the equipment surface temperature was above the
temperature of the mixture being processed, excessive fluidity tended to
occur. In such instances, when crystallization finally was achieved,
there was a tendency for the mixture to form large lumps rather than
granules. These lumps adhered to the mechanism and tended to plug it,
thus effectively destroying the mixing action. Alternatively, when the
equipment surface was below the mixture temperature, the melt tended to
crystallize on the equipment surface, again resulting in plugging of the
equipment. For this reason, the performance of the pilot plant pug mill
was not completely indicative of the performance of large scale pug
mills. This factor was taken into consideration in the test evaluations.
It very soon became apparent that Alternate II produced a melt too
viscous to wet the solids in the pilot plant pug mill, and good
granulation could not be obtained. The plant configuration was changed
to Alternate III, which entails the two step generation of a melt. In
the first step, part of the ammonia and all of the phosphoric acid were
mixed in a tee reactor. This mixture produced an acidic, low viscosity
melt. This melt was piped to a pug mill where it was mixed with solids.
Thereafter, ammoniation was completed.
From the test data, it was concluded that optimum material and
operating parameters for product grades 13-13-13-13 and 12-24-12-13 are
in the ranges presented in Table 12.
OPERATION OF 454 kg/hr PLANT
Reconfiguration of the 45 kg/hr plant into the 454 kg/hr plant for
design Alternate III was based upon the results obtained from operation
of the 45 kg/hr plant. Prior experience with smaller unit configuration
enabled the start-up of the 454 kg/hr unit to be accomplished with a
minimum of trouble. Only minor adjustments were required.
41
-------
Table 12. OPTIMUM OPERATING PARAMETERS FOR THE 45.6 kg/hr
(100 Ib/hr) AND 454 kg/hr (1000 lb/hr)a PILOT PLANTS
(13-13-13-13 Grade)
Materials
Phosphoric acid 52% ?2®5
Ammonia
Potash
Ammonium sulfate
Filler
Recycle-variable up to
kg/hr
10.5
1.6
9.7
22.1
31.3
13.6
Ib/hr
23.7
3.5
21.1
48.5
69.0
30.0
(12-24-12-12 Grade)
Materials
Phosphoric acid 52% P205
Ammonia
Potash
Ammonium sulfate
Filler
Recycle-variable up to
kg/hr
38.2
5.7
18.1
29.7
2.4
75.0
Ib/hr
84.2
12.5
40.0
65.4
5.3
165.0
afor 454 kg/hr plant, multiply all values above
by 10.
OPTIMUM OPERATING PARAMETERS FOR BOTH GRADES
Tee reactor temperature
Recycle temperature
Ammonium sulfate and potassium
chloride particle sizes
Recycle/product ratio
13-13-13-13
12-24-12-13
110-130° C
82° C
60% (-20 + 100)
0.3/1.0
0.8/1.0
42
-------
Operation of the 454 kg/hr pilot plant proceeded rapidly due to •
previous identification of the significant operating parameters. Some
of the operational problems encountered with the 45 kg/hr plant,
primarily mixing effectiveness and temperature control, were eliminated
in the 454 kg/hr pilot plant. The larger unit size smoothed out some of
the fluctuations encountered in the 45 kg/hr plant. Because of some
difficulty with output sizing from the previously used crusher, a chain
mill was installed to reduce oversized products in this plant.
Product grades 13-13-13-13 and 12-24-12-13 were produced in this
test operation. From these results, optimum material and operating
parameters were found to be essentially the same as for the 45 kg/hr
plant. The optimum parameter ranges presented in Table 12 apply to the
454 kg/hr plant also.
To test the durability of the equipment and process, a five day
continuous run was made producing 454 kg/hr of mixed fertilizer. Grades
13-13-13-13, 12-23-12-13 and 18-18-0-0 were produced with satisfactory
granulation. Data and comments on each sample are presented in Table 13.
Results show this process can be varied to produce several grades, and
the production is stable.
GENERAL PROCESS AND OPERATION CONCLUSIONS
The following comments and observations made during the laboratory
and pilot plant studies are relevant to this fertilizer production
process.
1. The process depends upon the melt to agglomerate
the solids. Therefore, the solid-to-melt ratio
and the properties of the melt, i.e. its viscosity
and wetting ability, affect granulation.
2. It is apparent that in steady state operation a
change in the recycle rate will have no affect on
the chemical composition of the product. However,
changing this ratio will result in a significant
change of the solids-to-melt ratio in the mixing
zone.
3. The ability of the melt to coat and bind the
particles is affected by changes in the raw
material, in the recycle fines and in the relative
surface per unit volume of the dry ingredients.
43
-------
Table 13. DATA FROM FIVE DAY RUN IN 454 kg/hr (100 Ib/hr) PLANT
Sample
Number
Chemical Analysis %
M
P
PP
K
H20 { pH
Comments
Grade 13-13-13-13
Nov. 21-1 ; 13.2
2
3
4
Nov. 22-1
i
13.0
13.1
11.2
11.1
11.9
j
13.1
13.7
12.1
11.8
2.7
6.6
3.7
4.9
5.0
"15.8
16.9
16.1
15.7
15.1
0.6
0.7
0.7
0.6
0.5
3.4 | 121°C (250°F) in re-
2.9
3.1
3.5
3.5
actor. Granulation
fair but useable.
Tee Reactor problem,
granulation fair and
somewhat steady.
Granulation fair, Pug
Mill got too wet and
caused some problems.
Fair granulation,
stable.
Fair granulation, but
variable, too much
recycle.
Grade 18-18-0-13
Nov. 22-2
3
4
Nov. 23-1
18.1
18.5
18.7
18.1
12.4
12.1
13.0
12.7
4.8
4.7
5.7
4.3
0.99
-
-
_
0.3
0.2
0.7
0.4
3.7
3.5
4.3
4.9
Granulation question-
able. Reactor 143°C
(250°F)
Good granulation-stable
Good granulation, acid
pump problems, resumed
good granulation and
stable.
Reactor Temp. 106 C
(250 F) good granula-
tion. Pug Mill wet at
one time. Very good
granulation.
Grade 12-24-12-13
Nov. 23-1
Nov. 24-1
2
12.8
12.4
14.0
20.6
20.3
22.1
7.2
9.6
6.1
13.8
12.9
9.1
0.8
0.4
0.5
3.7
3.7
7.1
Fair granulation,
Exhaust fan trouble,
very good granulation
after repair
Repair Pug Mill trans-
mission poor to good
granulation.
Stable and good granu-
lation. Reactor Temp.
99°C (210°F)
44
-------
Table 13. (Continued) DATA FROM FIVE DAY RUN IN
454 kg/hr (100 Ib/hr) PLANT
Sample
Number
3
Nov. 25-1
Chemical Analysis %
M
13.0
13.5
P
22.7
20.6
PP
4.6
2.9
K
11.3
11.1
H20
0.5
0.7
PH
3.6
3.7
Comments
Reactor 99°C (210°F)
good and stable granu-
lation.
Pug Mill very sensitive
to over agglomeration.
Grade 13-13-13-13
2
3
13.8
14.8
12.7
12.0
8.2
11.3
14.3
13.1
0.9
0.4
4.2
4.8
Granulation varied,
usually good.
Granulation fair to
good periods of Pug
Mill wetness. Tee
Reactor 99°C (210°F).
Grade 12-24-12-13
4
12.2
18.7
9.6
16.7
0.7
4.8
Tee Reactor 110°C
(230°F) good granula-
tion. Acid line
plugged which caused
some problems.
45
-------
4. As the grade formulation is fixed by the
composition of the raw materials which are to be
used, each grade has a fixed raw material solids-
to-melt ratio. However, the total solids-to-melt
ratio will vary, depending upon the amount of
fines which are recycled. Two illustrations of
the increase of solids-to-melt ratio with fines
recycle are shown below for the grades that were
investigated.
Total Solids-to-Melt Ratio
With 300 Parts of Fines
Raw Material Solids-to- Recycled per 1000 Parts of
Grade Melt With No Recycle Product
13-13-13-13 3.1 to 1 4.2 to 1
12-24-12-13 1.9 to 1 2.8 to 1
5. It is important that solids and melt initially are
mixed at temperatures above the melt crystal-
lization point to attain satisfactory wetting and
agglomeration. Normally, this would be
accomplished by heating the raw materials.
However, it was found that satisfactory mixing
could be attained without supplemental heating by
adding the unheated raw materials downstream of
the point at which melt and recycle materials are
mixed.
6. For high solids-to-melt ratios, it is very
desirable to control the melt viscosity by
diverting some of the ammonia from the reactor to
the pug mill for final ammoniation near the end
of the granulation step.
7. The larger pug mill which was used in the 454
kg/hr pilot plant, with its greater free volume,
proved much more effective and exhibited a greater
granulation efficiency, i.e. produced a greater
yield of market size granules per pass, than did
smaller pug mills which were used in the 45 kg/hr
pilot plant.
46
-------
POLLUTION CONTROL CONSIDERATIONS
A major objective of this project was to utilize process steps
which avoid or minimize polluting effluents. This will reduce adverse
impacts of future fertilizer plants on the environment and, possibly,
will provide a means whereby existing plants may be converted to reduce
pollution as an alternative to the installation of expensive pollution
control devices. The following discussion identifies the pollution
characteristics of conventional and melt process fertilizer production.
In the typical ammonium phosphate sulfate plant, concentrated
sulfuric acid, "filter strength" phosphoric acid and ammonia are
combined in the tank preneutralizer to produce a slurry. Solubility
properties require the operator to maintain relatively low pH and high
temperature. Vapors from these conditions tend to have a high fluoride
concentration. The partially ammoniated slurry flows to the ammoniator
granulator where it is combined with more ammonia, potash, filler and
recycle. Fumes of ammonium chloride and ammonium fluoride escape from
this process and are sent to an acid scrubber. A conflict involved in
the scrubber operation is that when pH levels are above 5.3,
non-scrubbable ammonium fluoride aerosols form and ammonia losses occur;
when pH levels are below 2.0 fluoride losses occur. Therefore, pH
levels must be carefully maintained between these limits.
Although approximately the same total amounts of fluorine must be
treated regardless of the process, it is much more efficient and
economical to treat the fumes from acid production at a large, central
facility than to scrub process off-gases at a number of regional
granulation plants.
Thus, the advantages of the melt process are:
1. No free sulfuric acid is used, therefore reducing
the heat, steam and fluorine involved.
2. The melt process uses high concentration
phosphoric acid rather than "filter strength" in
order to produce minimum water and fluoride
emissions.
3. The tee reactor, with a higher nitrogen-to-
phosphate ratio, retains fluorine in the melt.
4. Low water evolution produces less fluorine loss.
(To monitor the potential fluorine problem in the
melt process, a number of measurements was made
of the fluorine-to-P2Og ratios in the feed and in
the product. There was no detectable change in
47
-------
these ratios, indicating a minimum problem from
this process as compared to the conventional
production method.)
5. The melt process requires a smaller addition of
ammonia to the granulator. Therefore, the volume
of gaseous effluent which must be handled and
treated is reduced.
6. Only a small quantity of ammonium chloride
aerosol is generated.
48
-------
SECTION VI
X
SCALE-UP PROTOTYPE AND FULL SIZE PLANT
OBJECTIVES
The objectives of this section were to prepare detailed design and
cost figures for the best technical manufacturing process plants to
produce 227 Mt/d and 907 Mt/d of the common grades of fertilizer from
the raw materials previously discussed. The plants were to utilize a
melt technique and were to be based upon the laboratory and pilot plant
studies of the previous sections. Adequate pollution controls were to
be included.
The 227 Mt/d size is recommended for a prototype plant because it
has been most commonly used in regional granulation facilities. The
907 Mt/d size is suggested for large commercial installations in which
most of the economies of scale can be realized.
BASIC DESIGN CONSIDERATIONS
In order to be sure that the proposed plant would be commercially
and technically sound and comparable with a plant based on current
aqueous methods, additional consideration was given to the three
factors listed below before the final plant design was established.
1. Did the market analysis indicate that the design
N-P-K-S fertilizer product was being used in
significant quantities?
2. Would the plant design incorporate enough
flexibility to permit production of fertilizer
grades other than that for which the plant had
been designed?
3. Did the laboratory study indicate that a critical
N-P-K-S grade had been selected as the basis for
the plant design?
49
-------
Based on these considerations, an N-P-K-S ratio of 1-1-1-1 was
chosen for the study. The market analysis showed that a 1-1-1 ratio, or
very near a 1-1-1 ratio, accounted for approximately 11 to 12% of the
total mixed fertilizer market. The laboratory study had shown that a
1-1-1 ratio was the most difficult to produce. This ratio has the
lowest concentration of ammonium phosphate - polyphosphate melt.
Therefore, it is most difficult for the melt to satisfactorily wet the
dry raw products to produce good granulation. From the various process
flow sheets considered, it was concluded that the plant could produce
the other significant grades shown in the market analysis if the plant
had the process steps necessary to produce a 1-1-1-1 ratio N-P-K-S
fertilizer.
PROTOTYPE 227 Mt/d PLANT
The plant design was based on Alternate III because it has lower
capital and operating requirements than the other two Alternates.
Details of capital and operating requirements are discussed later in
this section.
An isometric drawing of the proposed plant is shown in Figure 6.
Equipment Design
Details of the major plant components are given in Table 14.
Comments pertaining to the most significant equipment and its
operation are detailed below.
1. Tee Reactor - The phosphoric acid and ammonia are
mixed and reacted to produce the ammonium
phosphate - polyphosphate melt. Temperature
control of the melt is important in producing
optimum mixing with solid recycled material in the
pug mill. Tee reactor details are shown in Figure
4. Separation of water from the melt is necessary
to produce good melt and good granulation. The
steam disengagement chamber, an integral part of
the tee reactor, also separates excess ammonia
vapor from the melt. The ammonia vapor is
returned to the acid scrubber.
2. Pug Mill - This equipment is used to mix the
recycled product fines and the melt. Granulation
occurs following mixing. The temperature of the
pug mill is important for proper granulation of
the product. When the temperature of the incoming
50
-------
Figure 6. Isometric drawing of 227 Mt/d (250 st/d) plant - Alternate III.
-------
Table 14. MAJOR COMPONENTS OF 227 Mt/d (250 st/d) PLANT
Item
1.
2
3.
4.
9
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
0.91m x 9.4m (36 in x 30 ft )
Pug Mill
4.54 ton (5 ton) Rotary Drum Mixer
1.8m dia. x 12m (6 ft. x 40 ft OAL)
Rotary Drum Prod. Cooler
1.2m x 1.5m (48 in x 60 in )
Chain Mill
3.7m x 1.8m (12 ft x 6 ft ) Deck
3 Deck totally enclosed vi. screen
17,000 CFM Blower @ 15.24cm
(6 in ) H20 Pressure
37.9 1/min. (10 GPM) Acid Pump
5.0cm (2 in ) Teflon lined Tee
Reactor, and Steam Disengagement
Chamber.
0.7m dia. x 1.8m (30 in x 6 ft )
Cascade Steam - NHj Vapor Scrubber
1.2m dia. x 3.1m (4 ft dia. x 10 ft
OAL) Dust Cyclone
#130 S-8-20 Micro-Pulsaire Bag
Filter 113.8 square m. (1225 sq ft )
Recycle Splitter Valve
0.3 x 3.66m (12 in x 12 ft )
Screw Conveyor
0.23 x 6.2m (9 in x 20 ft )
Screw Conveyor
0.3 x 7.32m (12 in x 24 ft )
Screw Conveyor
Motor Size, (HP)
150
25
25
30
20
25
3
_
_
_
_
1
5
3
5
Quantity
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
52
-------
Table 14. (Continued) MAJOR COMPONENTS OF 227 Mt/d (250 st/d) PLANT
Item
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
0.36 x 7.32 (14 in x 24 ft )
Product Loadout Screw Conveyor
27.2 Mt/hr (30 st/hr)
Elevator 22.9m (75 ft ) Lift
45.4 Mt/hr (50 st/hr) Bucket
Elevator 24.4m (80 ft ) Lift
68.0 Mt/hr (75 st/hr) Bucket
Elevator 18.3 (60 ft ) Lift
4.54 Mt/hr (5 st/hr)
Weigh Belt
9.08 Mt/hr (10 st/hr)
Weigh Belt
18.16 Mt (20 st) Ingredient
Holding Bin
52.2 Mt (60 st) Finished Product
Surge Bin
Electrostatic Preci pita tor
Ratio Controller (Anmonia &
Phosphoric Acid)
Temperature Recorder - 1 Pen &
Monitor
Recorder - 3 pen
Recorder - 4 Station Monitor
Motor Size, (HP)
10
10
15
15
1
1 1/2
_
_
-
-
-
-
-
Quantity
1
1
1
1
2
1
3
1
1
1
1
1
1
53
-------
solids is not within a specified range, the result
is poor granulation or no granulation. When
cooling occurs too rapidly, melt crystallizes
without mixing with solids.
3. Vibrating Screen Unit - This unit separates market
size product (-5 to +14 mesh) from oversize
product (+5 mesh) and from fines (-14 mesh).
Improper separation will give either a lumpy or a
dusty product.
4. Oversize Product Crusher - This takes the oversize
materials separated in the vibrating screen unit
and crushes them to a market size product.
Careful operation is necessary to avoid a buildup
of fines or of oversize material.
5. Mixing Chamber and Product Handling Equipment -
In the pilot plant operation, raw materials were
added to the latter part of the pug mill to
conserve heat and to improve granulation. In the
full size plant, this is done in a separate rotary
mixer downstream of the pug mill.
6. Product Cooler - The hot, market size product is
cooled to approximately 171° C (160° F) or lower
before being transported to storage. Ambient air
is used as the coolant. This air must be cleaned
of particulate matter before being discharged to
the atmosphere.
7. Pollution Control Equipment - Steam and ammonia
separated by the steam disengagement chamber, as
well as vapors from the pug mill and mixer, are
scrubbed by phosphoric acid in the ammonia
scrubbing unit. An electrostatic precipitator is
used to remove particulate ammonium chloride from
acid-scrubbed vapors. This effluent stream
quality is discussed in Section V.
Cleaning of the cooler air is performed in two
stages. The first stage employs a cyclone to
remove the larger solids. The second stage
consists of a pulsed-air bag filter in which the
tubes are periodically back-flushed with air.
54
-------
By using the melt production process and the
specified control devices, it is possible to
practically eliminate granular fertilizer plant
pollution. Solids collected from both cleaning
operations are returned to the recycle bin.
Process Control and Monitoring Instrumentation -
The process instrumentation consists mainly of
temperature monitors, temperature controllers,
solids feeder controllers and feed ratio
controllers.
The temperature in the tee reactor is monitored
and recorded. It is important that this
temperature be controlled carefully to insure
optimum temperature of the melt being fed to the
granulator. Temperature control is achieved by
regulating the amount of ammonia which is added at
the tee reactor. To insure the proper proportion
of ammonia and phosphoric acid, the flows of these
materials are ratio-controlled. The small amount
of ammonia which is not sent to the reactor is
added to the granulator.
The raw material hoppers have built-in level
monitoring devices. Monitoring of the weigh belts
is done with a 3-pen recorder, one pen for each
raw material: potassium chloride, ammonium sulfate
and any other material, such as filler. Monitoring
insures that the desired mixed fertilizer analysis
is being produced.
Temperature monitoring and alarming at key points
in the process can indicate any operational
problem before it can produce a significant
quantity of off-specification product. The points
to be monitored are the phosphoric acid downstream
of the ammonia scrubber, the product from the pug
mill, the product and raw material mixture from
the rotary drum mixer, and the recycle material
from the vibrating screen.
Environmentally sensitive plant emissions include
particulate matter, ammonia vapors and phosphoric
acid vapors. Particulate matter from sieves,
conveyors and the pug mill is trapped by the
cyclone and bag filter. All vapors and aerosols
-------
are passed through the acid scrubber and
precipitator before being vented. Dust traps are
monitored intermittently with portable equipment.
Exhaust from the precipitator is monitored
continuously by automatic instruments equipped
with alarm points.
Material and Energy Balance
The flow of materials through various components of the 227 Mt/d
plant is shown across the top of Figure 3. These figures indicate
amounts of materials to be handled by each component or process flow
stream, assuming twenty-two hours of operation per day. Optimum
temperatures of materials at various points in the flow sheet also are
shown in Figure 3.
The material balance is for a 13-13-13-13 grade fertilizer. When
other grades are produced, phosphoric acid, ammonia, filler, potassium
chloride and ammonium sulfate flow rates are changed. The total
quantity flow of materials through the various process steps will vary
because of the recycle. Provision has been made in the equipment
selection to handle the maximum quantities which may be required.
The energy balance for the 227 Mt/d prototype plant is shown in
Figure 7. No allowance has been made for heat losses. The heat
requirement shown in the flow sheet for Alternate III is satisfied by
the reaction of ammonia with phosphoric acid. By using the unique
Alternate III process of mixing raw materials with the hot product after
granulation, heat is transferred directly to the raw materials, as
described in Section V. Thus, the Alternate III process uses no
additional fuel to heat incoming raw materials. Thermal loss is
minimized, and power requirements are reduced.
Investment Requirements and Manufacturing Costs
Analysis of the plant capital and manufacturing costs was
completed. Details of this analysis are presented in Table 15. These
cost estimates were prepared on the same basis as those for the
commercial plant, as described below.
COMMERCIAL 907 Mt/d PLANT
Investment and manufacturing cost estimates were prepared for a
new 907 Mt/d plant utilizing the technology described above, and for
converting an existing 907 Mt/d aqueous process plant to this melt
process.
56
-------
01
-J
Alternate III Producing a 13-13-13-13 Grade Fertilizer
398 kg ( 795 Ib)
Ammonia
2,631 kg (5,261 Ib)
Phosphoric Acid
RKACTOR
Heat of Reaction 670,630 kcal (2,443,395 BTU)
Heat of Polymerization 19,050 kcal ( 33,000 BTU)
Net Heat Produced 661,580 kcal (2,410,000 BTU)
PUG MILL
-407,943 kcal
-(1,466,102 BTU)
PRODUCT TO STORAGE
-38,717 kcal
(-173,188 BTU)
-398 kg (795 Ib)
Steam __
-214,920 kcal
(771,150 BTU)
Note: No allowance has been made for ambient heat loss.
Figure 7. Energy balance for a 227 Mt/d (250 st/d) prototype plant.
-------
Table 15. 227 Mt/d (250 st/d) FERTILIZER PLANT COSTS USING ALTERNATE III
FLOW SHEET FOR 13-13-13-13 GRADE FERTILIZER
Plant operates 330 d/yr to produce 74,828 Mt (82,500 st)
PLANT, EQUIPMENT. CONTROLS, BUILDINGS, ERECTION AND OFFSITES
Ul
Co
1. Equipment
2. Buildings
Total Plant Investment
MANUFACTURING COSTS
1. Depreciation/t @ 6-2/3% per annum on plant cost
0.666 x 2,450,000 (.067) (2,450,000/82,500)
74,828
2. Raw Material Cost/t of 14-14-14-14
3. Direct Labor (0.46 man hr/t @ $4.00/hr)
4. Overhead (100% of direct labor)
5. Interest, 9% of 1/2 of plant costs
6. Interest in Inventory
7. Maintenance (20% of plant costs)
8. Supplies (20% of maintenance)
9. Electricity, 50 kwh @ $.02/kwh
10. Analysis (20% of labor)
11. Insurance and Taxes (2% of plant cost)
12. Overformulation (2% of raw material costs)
13. 20% Return on Total Investment
Plant Cost $ 2,450,000
Inventory 2,500,000
(20% x Total $ 4,950,000/82,500 t)
$ 1,925,000
525,000
$ 2,450,000
Cost/Mt, $
2.16
99.18
3.05
3.05
1.47
3.01
1.64
0.33
1.10
.61
.66
1.98
13.23
Cost/st, $
( 1-96)
(90.00)
( 2.77)
( 2.77)
( 1.34)
( 2.73)
( 1.49)
( .30)
( 1.00)
( .55)
( .60)
( 1.80)
(12.00)
14. Dealer Mark-Up (9% of total)
Total Cost $ 131.47 ($ 119.31)
11.83 ( 10.74)
Selling Price $ 143.30/Mt ($ 130.05/st)
-------
As before, the estimates are based on the use of the Alternate III
design to produce grade 13-13-13-13.
New Plant
The process flow sheet for Alternate I is shown in Figure A-2. The
material balance assumes twenty-two hours of operation per day- The
process flow sheet for Alternate II and III are shown in Figure 3(flows x 4)
A comparison of capital and manufacturing costs for a new plant, as
of June 1975, is shown in Table 15 for Alternates I and III. Alternate
II is a less efficient minor modification of Alternate III; therefore,
it is not included. The cost analysis clearly shows the advantage of
using the Alternate III design. The total plant equipment investment is
smaller; consequently, the cost per ton of fertilizer is lower.
Most of the services which form part of the overhead and utility
costs of the plant were assumed to be a selected percentage of either
plant capital or labor costs. These estimates were based upon many
years of experience in fertilizer plant manufacturing. The assumptions
made here are not to be considered absolute, but merely as a guide in
comparing one process flow sheet with another and to assist in
selecting the most economical, practical plant size and design.
Transportation costs to ship the fertilizer to the user were
eliminated from the study by making both costs free on board the plant.
In order to compare one process flow sheet against the other,
costs of transporting raw materials to the plant were considered equal
and were included in the estimated prices of the raw materials. The
prices of raw materials were based upon costs as of the date of this
study. Ammonium sulfate was priced at $60.00/Mt, delivered, equivalent
to the approximate market price of the contained ammonia. (It is
recognized that this price may not be valid under present market
conditions.) At this price, the manufacturer who produced ammonium
sulfate as a by-product or in a waste stream would recover at least the
cost of the ammonia used. For example, the cost of the ammonia used to
scrub sulfur oxide radicals (SOX) from the flue gases would be recovered
from the sale of by-product ammonium sulfate produced.
CONVERTED PLANT
In order to determine the cost per ton of fertilizer in a 907 Mt/d
plant which has been modified from present aqueous fertilizer
technology, a five year old plant was used as a model. The plant cost
approximately $3,200,000 five years ago. The price of the equipment
59
-------
Table 16. NEW PLANT COST COMPARISON - ALTERNATES I AND III
PRODUCING 907 Mt/d (1000 st/d) OF 13-13-13-13 GRADE FERTILIZER
PLANT EQUIPMENT, CONTROLS, BUILDING, ERECTION AND OFFSETS
All equipment cpsts below Include necessary structures, foundations, distribution equipment,
downspouts and instrumentation.
Item
•••^•MIMBHMVMBIBIaMH
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Alternate I
Description jQuan.
45 Mt/hr (50 st/hr) Bucket Elevators 2
91 Mt/hr (100 st/hr) Bucket Elevators 2
136 Mt/hr (150 st/hr) Bucket Elevators
91 Mt/hr (100 st/hr) Pug Mill 1
41 Mt/hr (45 st/hr) Product Cooler with 1
Air System
73 Mt/hr (80 st/hr) Preheater with Furnace 1
91 Mt/hr (100 st/hr) Partial Cooler With 1
Air System
2,832 cu m/min (100,000 cu f/min) Dust Col- 1
lector and Scrubber
1,982 cu m/min (70,000 cu f/min) Dust Col-
lector and Scrubber
91 Mt/hr (100 st/hr) 3-Screen Tyler Hummer 1
136 Mt/hr (150 st/hr) 3-Screen Tyler Hummer
9 Mt/hr (10 st/hr) Chain Mill 1
Miscellaneous Lot Screw Conveyors 1
18 Mt Ing. (20 st Ing.) Bins with 4
Vibrating Feeders
Truck Dump Hopper Feeder 1
Acid Scrubber 1
Ammonium Polyphosphate Tee Reactor and 1
Disengagement System
Total Price. $
56,000
98,000
_
140,000
280,000
360,000
360,000
840,000
-
140,000
-
70,000
112,000
224,000
42,000
42,000
112,000
Alternate III
Quan.
1
2
1
1
1
_
-
-
1
-
1
1
1
4
1
1
1
Total Price. $
28,000
98,000
42,000
140,000
280,000
_
-
-
270,000
_
210,000
70,000
112,000
224,000
42,000
42,000
112,000
-------
Table 16. (Continued) NEW PLANT COST COMPARISON - ALTERNATES I AND III
PRODUCING 907 Mt/d (1000 st/d) OF 13-13-13-13 GRADE FERTILIZER
Item
18.
19.
20.
21.
22.
23.
24.
Alternate I
Description Quan.
136 Mt/hr (150 st/hr) Rotary Mixer
Electrostatic Precipitator 1
Total Equipment Cost
Controls & Electrical System (20% of Equipt.) -
Erection of Equipment (30% of Equipment)
Building 929 sq m (10,000 sq ft)
G> $161.46/sq m
Total Battery Limits, Items 1-22
Off site + 25% of Battery Limits
90.718 Mt (100,000 st) of storage @ $16.53/t -
Total Battery Limits, Off sites and Storage
Total Price, $
110,000
600,000
900,000
210,000
4,696,000
1,174,000
2,100,000
7,970,000
Alternate III
Quan.
1
1
-
-
Total Price, $
280,000
110,000
412,000
618,000
210,000
3,300,000
825,000
2,100,000
6,225,000
TOTAL MANUFACTURING COST
1. Depreciation @ 6-2/3 % per annum
of Plant Capital Investment,
0.067 x plant cost/299,310 Mt,
or (330,000 st)
2. Raw Material Cost
3. Direct Labor
4. Overhead = 100% of Direct Labor
Alternate I
Alternate III
Cost/Mt, $
= 1.78
= 99.19
1.92
1.92
Cost/st,
$ Cost/Mt, $
( 1.62) 1.40
(90.00
( 1.74
( 1.74
99.18
1.92
1.92
Cost/st,
( 1.26)
(90.00)
( 1.74)
1.74
$
-------
Table 16. (Continued) NEW PLANT COST COMPARISON - ALTERNATES I AND III
PRODUCING 907 Mt/d (1000 st/d) OF 13-13-13-13 GRADE FERTILIZER
TOTAL MANUFACTURING COST
Alternate I
Alternate III
Cost/Mt, $
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Interest = 9% of 1/2 Plant Cost
0.09 x plant cost/299,310 Mt,
or (330,000 st)
Interest on Inventory =
Maintenance = 5% of Plant Cost =
0.05 x plant cost/299,310 Mt
or (330,000 st)
Supplies = 20% of Maintenance =
Electricity - 50 kwh @ $.01/kwh
5.1 kw @ $.005/kw
Water (1,460 gal @ $.20/1,000 gal) =
Analysis 20% Labor
Insurance and Taxes = 2% of Plant
Cost
Overformulation = 2% of Raw =
Material Cost
Sub Totals 1
20% Return on Total Investment
Alternate I Alternate III
Plant Costs 7,970,000 6,225,000
Inventory 10,000,000 10,000,000
Total 17,970,000 16,225,000
Above total, per ton
Dealer Mark-Up = 9% of Total
1.20
3.01
1.33
.26
1.10
.03
.38
.53
1.98
14.62
12.08
11.40
Cost/st, $
( 1.09)
( 2.73)
( 1.21)
( .24)
( 1.00)
( .03)
( .35)
( .48)
( 1.80)
(104.03)
( 10.95)
( 10.35)
Cost/Mt, 3
.94
3.01
.89
.18
1.10
--
.38
.35
1.98
113.49
10.84
11.19
i Cost/st, $
( .72)
( 2.73)
( .81)
( .16)
( 1.00)
--
( .35)
( .32)
( 1.80)
(102.75)
( 9.83)
( 10.17)
Selling Price (per ton)
138.10
(125.33)
135.52
(122.75)
-------
to modify the plant to produce fertilizer in accordance with the
Alternate III design was added to the original cost. Depreciation was
predicated on a useful life of ten years, the remaining estimated life
of the original equipment. It was assumed that the added equipment
would not be usable when the original equipment had reached the end of
its useful life. This was considered to be a reasonable approach to
depreciation and to be more conservative, i.e. to result in a higher
depreciation cost, than any other approach which might be considered.
Table 17 lists the estimated capital and manufacturing costs for
producing grade 13-13-13-13 fertilizer in a modified 907 Mt/d plant.
CONCLUSIONS
At the start of this project, ammonium sulfate was a by-product or
a waste product of several industries. It could be obtained at little
or no cost and, indeed, presented a disposal problem. Calculations at
that time indicated that the melt process had a favorable cost advantage
over the conventional aqueous process for producing grade 13-13-13.
The fertilizer market recently has undergone a significant change.
Most products, including ammonia, sulfuric acid and mixed fertilizer are
in short supply and are very costly. Ammonium sulfate is extremely
difficult to obtain, and its price fluctuates rapidly and erratically.
In an attempt to compare the cost of the fertilizer to be produced
by ammonium sulfate, ammonium phosphate - polyphosphate melt and
potassium chloride with the cost of other products, a price quotation
was requested for 13-13-13 grade fertilizer. Listed below are the
prices obtained.
PRODUCT FERTILIZER PRICE AT SHIPPING POINT
Agrico Chemical Co. 15-15-15 $178 per Short Tona
(Mississippi)
Agrico Chemical Co. 13-13-13 $148 per Short Tona
(Arkansas)
aPhone quote June 30, 1975. Dealer delivered bulk price.
The total cost of producing grade 13-13-13-13 was smaller than the
prices indicated above, as demonstrated in Tables 15, 16 and 17. These
evaluations are not altogether comparable, however. Currently,
ammonium sulfate prices are so erratic that it is not possible to
obtain a reasonable cost estimate. The melt process which has been
developed has always been intended for use as a method of recovering
and recycling chemicals with values that might otherwise be wasted.
63
-------
Table 17. MODIFIED 907 Mt/d (1000 st/d) FERTILIZER PLANT COSTS PER
ALTERNATE III FLOW SHEET FOR GRADE 13-13-13-13
An existing plant having an original cost of $3,200,000, five years old, is modified to the
process flow sheet of Alternate III. The cost of fertilizer is then estimated based upon 10
years of plant depreciation rather than 15 years. This assumption is used since the
improvements to the plant will be useful as long as the original parts are useful. This is
considered to be the most reasonable, conservative approach.
Plant operates 330 days/year to produce 299,360 Mt (330,000 st)
PLANT EQUIPMENT, CONTROLS. BUILDING, ERECTION AND OFFSITES
The following equipment will be added to the original plant equipment:
1. 907 Mt/d (1000 st/d) Pug Mill $ 158,000
2. 1982 cu m/min (70,000 cu f/min) Dust Collector 200,000
and Scrubber
3. Acid Scrubber 42,000
4. Tee Reactor and Steam Disengagement Section 112,000
5. NH4C1 Electrostatic Precipitator 110,000
Total Equipment Added 622,000
6. Controls and Electrical Systems 102,000
(16% of added plant equipment)
7. Equipment Erection (25% of added plant equipment) 154,000
8. Additional Building Requirements (48,000 f2 @ $15/f^) 72.000
Total Modification Cost 950,000
Original Plant Cost (5 years old) 3,200,000
Total Original Plus Modification Cost $ 4,150,000
-------
Table 17. (Continued) MODIFIED 907 Mt/d (1000 st/d) FERTILIZER PLANT COSTS PER
ALTERNATE III FLOW SHEET FOR GRADE 13-13-13-13
TOTAL MANUFACTURING COSTS Cost/Mt. $ Cost/st, $
1. Depreciation per t @ 10% per annum on plant cost = 1.39 ( 1.20)
(0.10) (3,875,000)/299.310 Mt
2. Raw Materials costs/t = 99.18 (90.00)
3. Direct Labor (0.32 man hr/Mt @ $6.62/hr) = 1.92
(0.29 man hr/st @ $6.62/hr) = ( 1.74)
4. Overhead (100% of Direct Labor) = 1.92 (1.74)
5. Interest on Plant and Inventory, 9% = 4.21 ( 3.82
o 6. Maintenance (5% of plant costs) ' = .69 ( .63
01 0.05 x 3,875,000/299,310
8. Electricity, 50 kwh @ $.02/kwh = 1.10 ( 1.00)
9. Analysis = .38 ( .35)
10. Insurance and Taxes (2% of plant cost) = .28 ( .23)
11. Overformulation (2% raw material cost) = 1.9.8 ( 1.80)
12. 20% Return on Total Investment = 9.47 ( 8.58)
Plant Costs: $ 4,150,000
Inventory: $ 10,000,000
Total Manufacturing Costs: $ 122.66 ($ 111.30)
-------
As previously indicated, the costs of raw materials shown in
Tables 15, 16 and 17 reflect the assumption that ammonium sulfate is
priced at its ammonia value only, while recognizing that this price
also is very high at the present time. If the cost of ammonium sulfate
was to be included at any approximation of its current market price,
then the cost of producing grade 13-13-13 by the melt process and the
cost of its production by the aqueous process probably would be very
close to the same amount.
The prices of many raw materials and of all mixed fertilizers
behave in a manner which is very similar to that of commodities. Their
prices are determined in large measure by the supply-demand relationship
in the marketplace. It is quite likely that in the future the price of
ammonium sulfate will fall much lower, and that waste and by-product
ammonium sulfate will again be sold at the cost of their contained
ammonia. Each metric ton of ammonium sulfate will contain $19.00 worth
of sulfuric acid (at current market prices). This is equivalent to a
savings of $10/Mt for grade 13-13-13 which can be realized when the melt
process is employed.
As noted previously, the capital and energy charges for the melt
process will be lower than for the aqueous process because the dryer
and its ancillary equipment are not needed, pollution control
requirements are less and the melt process operates with a lower
recycle ratio.
The overall effect of these factors is that the melt process
constitutes an attractive granulation technique, particularly whenever
by-product or waste ammonium sulfate is priced solely on the basis of
its contained ammonia.
66
-------
SECTION VII
MARKET ANALYSIS
INTRODUCTION
A market analysis was made to determine national and regional
consumption patterns of mixed fertilizer usage. Fertilizer ratios
chosen for study in the project were selected for their ready acceptance
by the farmer, as demonstrated in the results of market analysis.
ANALYSIS OF NATIONAL USE OF MIXED FERTILIZERS
The annual use of fertilizers for farm crop production in the
United States has almost doubled over the period from the 1950's to the
1970's, increasing from about 22 million tons to 38 million tons.
During the same years, the annual volume of mixed fertilizers increased
from about 15 million tons to 22 million tons. Annual consumption is
shown in Figure 8.
In these two decades, the average nutrient content of the ferti-
lizer consumed in the United States also doubled^, increasing from
about 23 to 42%. These data are shown in Figure 9.
The combination of increase in volume of fertilizer used and in
plant nutrient concentration of the fertilizer has increased farm
nutrient consumption by a factor of four.
Figure 10 shows that the largest volumes of mixed fertilizers are
used in three regions: the South Atlantic, the East North Central and
the West North Central. In 1971, for example, these three regions (17
states) consumed 12.29 million metric tons (13.55 million short tons) of
mixed fertilizer, or over half of the total volume consumed in the U.S.
that year.
Table 18 shows grades of mixed fertilizers and the market share for
each grade in 1970 and 1971. The columns are arranged in decreasing
order with the highest demand grade of fertilizer listed at the top.
67
-------
-------
South Atlantic
E. North Central
W. North Central
E. South Central
W. South Central
(1961) 62 63 64 65 66 67 68 69 70 (1971)
Figure 10. Consumption of mixed fertilizers.
69
-------
The nutrient ratios of the fertilizers are also shown. Inspection of
these data indicates that perhaps 25% of the mixed fertilizer grade
ratios presently being used could offer a vehicle for the disposition of
by-product or waste ammonium sulfate.
ANALYSIS OF REGIONAL USE OF MIXED FERTILIZERS
Table 19 shows the major grades of mixed fertilizer and the percent
market share of each fertilizer in the significant agricultural regions
in the U.S.A.
DEPLETION OF SULFUR IN SOILS
Sulfur is needed by plants and must be available in relatively
large amounts for good crop growth. It is essential for synthesis of
certain amino acids, for formation of chlorophyll and of some essential
oils, and for formation or activation of several enzymes. In addition
to satisfying these basic nutritional needs, sulfur sources may increase
the availability of other essential nutrients and may be helpful in the
reclamation of alkali and saline/alkali soils when applied to soils
which are calcareous or which have high concentrations of hydrogen ions
(high pH soils).24
Plants utilize sulfur in differing amounts according to species.
For example, corn, sorghum and vegetables have relatively high sulfur
requirements; legumes generally have intermediate requirements; most
small grains and grasses need less sulfur. Crop sulfur requirements
increase as higher yields are obtained. On soils which are both
nitrogen and sulfur, or phosphorus and sulfur, deficient, and where the
amounts of fertilizers being applied are on the order of the crop's
normal requirements, fertilizer treatments of five to seven pounds of
nitrogen for every pound of sulfur, or three pounds of ?® ^or everY
pound of sulfur, will be satisfactory for most cropping situations.
Plants obtain their sulfur requirements from "soils, crop residues,
and manure; from irrigation waters; from rainfall and atmosphere; and
from fertilizers and soil amendments . "
Soils which are deficient in sulfur are found most often in humid
regions of the country. Some humid soils contain large amounts of
organic matter or hydrated oxides of aluminum or iron in which sulfates
may have been absorbed. Such soils have relatively higher sulfur
contents. In coarse-textured sandy soils, sulfates are lost readily by
leaching. Most arid region soils contain large amounts of sulfate
sulfur. However, such soils may provide poor water penetration or micro-
nutrient availability. It may be possible to overcome such problems by
the use of acid-forming sulfur materials."
70
-------
Table 18. CONSUMPTION OF FERTILIZER IN U.S. BY GRADE
FOR 1970, 1971
(Percent of total)
Grade
18-46-0
6-24-20
5-10-15
10-10-16
5-10-10
12-12-12
8-32-16
10-20-20
10-20-10
13-13-15
6-12-12
1970
7.31
5.81
4.39
4.00
3.70
3.02
2.17
1.98
2.85
1.69
2.41
1971
8.03
5.94
3.86
3.79
3.27
2.86
2.18
2.17
2.00
1.90
1.84
71
-------
Table 19. CONSUMPTION PERCENTAGES OF FERTILIZERS BY REGIONS AND GRADES, 1971
Region*
% of Totals
North E.
48.8%a
N. Atlantic
45.1%
S. Atlantic
48.9%
E. N. Central
42.7%
W. N. Central
39.6%
E. S. Central
67.9%
W. S. Central
42.7%
Mountain St.
49.1%
Pacific St.
16.3%
Grades and Percent of Total Mixed Fertilizer Use
18-
48-
0
1.9
2.9
-
8.7
20.5
1.7
8.9
42.2
3.9
16-
16-
16
—
-
-
2.1
—
2.4
—
—
3.6
15-
15-
15
11.9
3.8
—
1.1
—
2.2
—
—
13-
13-
13
—
—
—
—
-
12.4
3.8
—
—
12-
12-
12
2.1
-
—
5.7
3.7
—
6.0
—
4.5
10-
34-
0
_
-
-
1.6
3.3
-
1.6
6.9
3.0
10-
20-
20
1.8
10.5
2.2
—
—
2.0
1.8
—
10-
20-
10
2.3
3.0
-
—
—
—
14.4
—
10-
15-
15
16.1
-
-
—
—
—
-
—
10-
10-
10
8.1
11.9
7.7
—
—
6.4
—
1.3
8-
32-
16
-
-
5.3
5.1
—
-
—
8-
24-
24
—
-
-
-
-
8.2
1.5
—
6-
24-
24
_
2.0
—
18.2
7.0
2.8
3.1
—
6-
12-
12
—
—
2.0
-
—
12.3
—
—
b-
10-
15
—
—
12.6
—
-
6.6
—
—
b-
10-
10
4.6
11.0
8.6
—
—
—
—
—
4-
12-
15
—
—
4.0
-
-
6.5
—
—
3-
9-
18
_
-
5.0
—
—
—
—
—
3-
9-
9
—
—
6.8
-
—
—
—
—
0-
20-
20
_
—
-
—
—
4.4
1.6
—
to
aPercent of total use accounted for U.S. 43.90%
-------
Many soil areas in the United States are known or suspected to be
sulfur deficient. Such areas occur in twenty states within the conti-
nental United States, as shown in Figure 11, as well as in Alaska and
Hawaii. Almost all states contain areas which have a pH value exceeding
7. In these areas crop production would probably benefit from acidifi-
cation in fertilizer bands or a more general downward adjustment of pH.
Areas which contain coarse textured soils not presently considered sulfur
deficient could readily become so. Such areas are shown in Figure 12.
Crop residues and manure are sources of sulfur. However, the use
of manure has decreased dramatically except near feedlot operations.
Irrigation water which is derived from glaciers contains very small
amounts of dissolved solids. Many inland water supplies are somewhat
brackish, particularly in the Middle West and West, and may contain
several hundred parts per million of sulfates. Sulfur emitted from
the stacks of fossil-fuel burning power plants and industrial plants
constitutes a potentially important sulfur source. However, most of
this sulfur is deposited near the source of the emission rather than
evenly throughout the country. Furthermore, as the requirements of the
Clean Air Act become effective, less sulfur will be discharged into the
atmosphere.^ ^
The other major sources of sulfur are fertilizers and soil
amendments. Until about 1950, normal superphosphate and ammonium
sulfate were used in large quantities. These fertilizers contain 12 to
24% sulfur, respectively. When their use was supplanted by the
introduction of concentrated fertilizers, which are less costly to
transport and to apply to the soil, the use of sulfur-containing
materials decreased sharply. As shown in Table 20, the total amount of
sulfur contained in all applied fertilizers fell from 1.8 million tons
in the 1949-50 crop year to 1.1 million tons in the 1972-73 crop year;
at the same time the ratio of sulfur to the total of Nitrogen +
Phosphorus Pentoxide + Potassium Oxide + Sulfur (N + P2°s + K2O + S) is
estimated to have fallen from 0.31 in the 1949-50 crop year to 0.06 in
the 1972-73 crop year.25
There is no generally recognized or accepted method for calculating
the amount of sulfur that should be applied to crop lands. Two methods
may be considered. These are:
1. Sulfur Replacement - An estimate is made of the
total amount of sulfur removed by various crops.
This is multiplied by a factor (estimated at 1.75
for sulfur) to correct for losses caused by
leaching and for elements which limit efficiency
of utilization for fertilizer applications.
73
-------
Figure 11. Soil areas in the U.S. known or suspected to be sulfur deficient.
-------
Figure 12. Soil areas in the U.S. where acidification probably would benefit crop production
or which contain coarse textured soils which readily could become sulfur deficient.
-------
Table 20. CONSUMPTION OF SULFUR-CONTAINING
FERTILIZERS IN THE CONTINENTAL U.S.
Fertilizer Corns umpti on
N+P205+K20
Total Contained Sulfur
Total Sulfur as Percent
of N+P205+K20+S
Ratio of N:S in Ferti-
lizers
Ratio of P20g in Ferti-
1 i zers
Crop Year
1949/50
1959/50
1969/70
1972/73
1000 Short Tons
3,995
1,803
31.3
0.5
1.1
7,350
1,486
16.8
1.8
1.7
15,947
1,272
7.4
5.8
3.6
17,822
1,088
5.8
7.6
4.6
76
-------
2. Recommended application Rates - Recommended
application rates may be projected for specific
areas based on factors such as crop sulfur
requirements, crop yields, soil conditions and
application rates of other nutrients.
The results of estimates of sulfur requirements based on these two
methods are shown in Table 21. Estimates of requirements based on
sulfur replacement values were calculated from data on the three crop
years of 1970-72. Estimates of requirements based on crop and soil
conditions were calculated from data obtained prior to 1968. Table 21
also shows the total amount of sulfur in all fertilizer which was
applied during the 1972-73 crop year.
The data presented in this table "indicate that the amount of
sulfur added to crops in the United States in the form of fertilizer is
insufficient to meet the requirements of the crops for this element. The
balance of the crop's sulfur requirement is provided chiefly by soil
sulfur reserves and by sulfur in the rain and atmosphere. Soil surface
reserves are finite and exhaustible, and increasingly strict air
pollution regulations are limiting the amount of sulfur oxides emitted
to the atmosphere. Thus, the United State agriculture is operating on
a negative sulfur balance."
77
-------
Table 21. SULFUR REQUIREMENTS AND FERTILIZER SULFUR APPLICATIONS
(Thousand short tons)
00
Estimated Sulfur
Requirements By:
1 . Crop sulfur
replacement
(1970-72)
Field crops
Hay and pasture
Total
2. Recommended
application
rates (prior to
1968)
Field crops
Hay and pasture
Total
Total Sulfur in
Applied Fertilizers
(1972-73)
Field crops
Hay and pasture
Total
Cont'l
U.S.
1298
2775
4073
1246
1248
2494
927
160
1087
New
England
14
19
33
8
15
23
7
1
10
Middle
Atlantic
67
112
179
56
54
no
49
_9
58
South
Atlantic
84
169
253
111
98
209
148
35
183
E. North
Central
313
352
665
302
87
389
164
14
178
E. South
Central
55
245
300
65
68
133
49
12
79
W. North
Central
471
683
1154
437
313
750
167
20
187
W. South
Central
177
628
745
150
195
345
90
li
124
Mountains
86
398
484
29
86
115
74
_9
83
Pacific
91
170
261
88
332
420
179
7
186
-------
SECTION VIII
REFERENCES
1. Lee, R.,G., R. S. Meline, and R. D. Young. Pilot Plant Studies of
an Anhydrous Melt Granulation Process for Ammonium Phosphate-Based
Fertilizer. Proceedings of the International Superphosphate
Manufacturers Association Technical Conference (Sandfjord, Norway).
September 1970. Paper No. 5.
2. Kubasova, L. V., T. D. Pozlarskaya, and H. M. El Shinnawy-
Potassium Polyphosphates. Vestnik Moskovskogo Universiteta,
Khimiya. 11/6):680-685, 1970.
3. Moore, W. P. and W. C. Sierichs. Potassium Polyphosphates. U. S.
Patent No. 3,607,018. Issued September 21, 1971.
4. Legal, C. C. Apparatus for Producing Ammonia Phosphate Fertilizers.
U. S. Patent No. 3,482,945. Issued April 10, 1968.
5. Cariou, J. and 0. Foubert. Ammonium Polyphosphates from Orthophos-
phoric Acid. French Patent No. 1,553,120. Issued January 10, 1969.
6. Carroll, R. L., J. H. Sims, B. L. Owens, and V. Reynolds, Jr.
Ammonium Polyphosphates. German Patent No. 909,438. Issued
November 13, 1969.
7. Farr, T. D. and H. K. Walters. Ammonium Polyphosphates Produced At
Atmospheric Pressure. U- S. Patent No. 3,537,815. Issued November
3, 1970.
8. Kearns, T. C. Polyphosphate Fertilizers Made Via Simplified Route.
Chemical Engineering. 76_(27):94-96, 1969.
9. Hodge, C. A. Bench Scale Production of Ammonium Potassium Poly-
phosphates. Industrial and Engineering Chemistry, Product Research
and Development. 10 (4):437-441, 1971.
79
-------
10. Knapsack, A. G. and G. M. B. H. Benckiser-Knapsack. Preparation of
Ammonium Polyphosphates. French Patent No. 2,006,107. Issued
December 19, 1969.
11. Vol'fkovich, S. I., L. V. Kubasova, O. R. Norchaeva, and L. S.
Kulikova. Synthesis of Nitrogen-Phosphorus Fertilizer Based on the
Intermediate Product of Urea and Phosphoric Acid Reaction. Zhurnal
Prikladnoi Khmii. 42^5):979-984, 1969.
12. Vol'fkovich, S. I. and I. I. Checkovskikh. Urea Polyphosphates.
U. S. S. R. Patent No. 296,743. Issued March 2, 1971.
13. Fleming, J. D. Polyphsophates Are Revolutionizing Fertilizers.
Part I, What Polyphosphates Are. Farm Chemicals. 132(8);30-36,
1969.
14. Siegel, M. R. and R. D. Young. Polyphosphates Are Revolutionizing
Fertilizers. Part II, Base Materials. Farm Chemicals. 132 (9);41-
47, 1969.
15. Achorn, F. p. and J. S. Lewis. Uses for Solid Ammonium
Polyphosphates in Bulk Blending, Granulation and Fluid Fertilizers.
Fertilizer Industry Round Table, Proceedings No. 18. 123-127.
16. Beglov, B. M., V. A. Budkov, and F. P. Chumakov. Physicochemical
Properties of Granulated Fertilizer Mixtures Based on Ammonium
Polyphosphates. Uzbekskii Khimicheskii Zhurnal. 15_(2):76-78, 1971.
17. Achorn, F. P. and W. C. Scott. Polyphosphates Are Revolutionizing
Fertilizers. Part III, Polyphosphates in Mixtures. Farm Chemicals.
132_(12):46,48,50,51,192, 1969.
18. Slack, A. V., J. M. Potts, and H. B. Shaffer, Jr. Effect of Poly-
phosphates Content on Properties and Use of Liquid Fertilizers.
Journal of Agricultural and Food Chemistry. L3_(2): 165-171, 1965.
19. Thiokol Chemical Corporation. Sulfur Encapsulates Fertilizer
Pellets. British Patent No. 1,171,255. Issued November 19, 1969.
20. Fleming, P. S. Coating Fertilizers With Sulfur to Control Disso-
lution. U. S. Patent No. 3,576,613. Issued April 27, 1971.
21. Olson, R. A. (ed.). Fertilizer Technology and Use. Soil Science
Society of America, Inc. Madison, Wisconsin. 1971.
22. U. S. Department of Agriculture. Commercial Fertilizers. Statis-
tical Bulletin No. 472. Government Printing Office. Washington,
D. C.
80
-------
23. National Fertilizer Development Annual Reports, 1966-1974.
24. Bixby, D. W. and J. D. Beaton. Sulphur Containing Fertilizers.
Technical Bulletin No. 17. The Sulphur Institute. Washington, D.C.
December 1970.
25. Beaton, J. D., D. W. Bixby, S. L. Tisdale, and J. S. Platou. Ferti-
lizer Sulphur. Technical Bulletin No. 21. The Sulphur Institute.
Washington, D. C. August 1974.
26. Beaton, J. D., S. L. Tisdale, and J. Platou. Crop Responses to
Sulphur in North America. Technical Bulletin No. 18. The Sulphur
Institute. Washington, D. C. December 1971.
27. Esso Research and Engineering Company, Esso Research Agricultural
Products Laboratory. Paper by Paul R. Geissler. Determination of
the Critical Relative Humidity of Multi-Component Systems. 1966.
ADDITIONAL REFERENCES
Bauwens, R. and R. Julou. Preparation of Water-Soluble Ammonium Poly-
phosphates. German Patent No. 1,923,246. Issued November 20, 1969.
Bottai, G. A. and J. M. Stinson. Method For Urea-Ammonium Polyphosphate
Production. U. S. Patent No. 3,578,433. Issued May 11, 1971.
Rohlfs, H. A. and H. Schmidt. Ammonium Polyphosphates. U. S. Patent No.
3,419,349. Issued December 31, 1968.
Siegel, M. R., R. S. Meline, and T. M. Kelso. High-Analysis Fertilizers
From Phosphoric Acid and Conventional Ammoniating Materials. Journal of
Agricultural and Food Chemistry. 1£(5):350-361, 1962.
Vol'fkovich, S. I., A. I. Chekhovskikh, and T. K. Mikhaleva. Preparation
of Urea Phosphates. Khimicheskaya Promyshlennost. 46_(9):676-678, 1970.
Young, R. D., G. C. Hicks, and C. H. Davis. TVA Process for Production
of Granular Diammonium Phosphate. Journal of Agricultural and Food
Chemistry. 10(6):442-447, 1962.
81
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SECTION IX
APPENDIX
LABORATORY INVESTIGATION
Table A-l presents selected results of laboratory tests which were
performed.
The following pages describe the procedures which were used to
determine the moisture sensitivity of the product.
These data and techniques are discussed in Section IV.
Hygroscopicity Test 30° C (86° F)
Application - To determine the rate of water vapor absorption of product
fertilizer granules.
Apparatus and Reagents -
Balance Concentrated sulfuric acid
Constant temperature chamber 40% (by weight) sulfuric acid
Container to hold 15 grams (gms) 35% (by wt.) sulfuric acid
of fertilizer in a monolayer. One to three dessicators
For example/ a 100 x 15 milli-
meter (mm) Petri dish.
Procedure -
1. Condition approximately 15 gms of fertilizer for one week in a
desiccator containing concentrated sulfuric acid at 30° c (86° F)
2. Weigh container and fertilizer accurately within 0.01 gm.
82
-------
Table A-l. LABORATORY FORMULATIONS
00
Sample
Number
10-31-72
11 -02-72
11-08-72
11-07-72
11-16-72
11-17-72
11-18-72
12-07-72
12-12-72
12-13-72
12-15-72
12-15-72
12-21-72
Sample
Symbol &
Grade
12-24-12
14-14-14
12-24-12
14-14-14
14-14-14
14-14-14
14-14-14
12-24-12
14-14-14
14-14-14
14-14-14
14-14-14
14-24-08
Melt
12-57-0
48.6
11.5-61-0
11.5-61-0
12-57-0
12-57-0
12-57-0
12-57-0
12-52-0
12-52-0
12-57-0
12-57-0
12-57-0
Mix Formulation
Percent
Melt
37.3
24.7
44.5
24.6
24.6
24.6
22.6
14.5
46.8
17.3
24.6
19.6
32.0
KC1
23.7
22.1
20.6
22.6
22.6
22.6
24.6
6.5
43.0
15.9
22.6
18.0
9.8
Recycle
_
.
.
0.0
0.0
0.0
0.0
33.8
0.0
26.7
0.0
20.0
25.4
AS
39.2
53.2
35.0
52.9
52.9
52.9
53.0
11.4
10.1
38.0
52.9
42.2
32.7
Fines
_
_
44.3
33.9
75.4
75.4
0.0
11.4
53.1
38.0
52.9
42.2
42.6
Temperature ,°C
Solids
163
163
163
163
177
260
204
177
163
163
163
-
121
Reactor
Melt
177
246
247
247
260
190
204
218
204
204
218
-
190
Lab Analysis
Percent
N
12.7
13.5
12.2
13.6
13.7
13.9
13.7
8.7
13.6
13.4
13.4
12.9
12.9
P2<>5
18.6
16.4
23.7
16.0
14.6
13.4
13.9
20.0
16.1
16.4
17.4
20.4
28.4
PP
32
42
40
55
52
20
37
24
41
36
35
31
22
K20
14.4
14.0
12.7
14.5
13.7
14.2
15.4
24.8
13.0
13.2
12.6
12.4
7.4
Marketable
Prod. -5/
+14 Mesh,*
„
31.2
48.3
55.7
58.1
53.4
43.7
51.2
59.1
44.4
31.0
37.8
62.7
Hard-
ness, kg
_
"5.0
5.6
.
.
hard
6.3
-
-
-
8.4
10.4
.
Granu-
lation
Quality
good
good
good
v. good
good
good
good
poor
good
good
good
v. good
Comments
Mixed 1n two stages.
AS used; -40 mesh.
Mixed melt with aqua NHj
heated to 260°C.
Melt conditioned with aqua
NH3.
Granulation 30 seconds.
Improper wetting of solids,
pH 3.6.
Very sticky hi poly content
Attrition 19? (-14 mesh).
Low attrition, pH 2.7.
Solids and melt mixed till
crystallization started,
then granulation started.
(With tee reactor)
02-22-72
02-24-72
02-24-72
02-27-72
03-05-72
03-05-72
03-4-72
03-19-72
14-14-14
14-14-14
14-14-14
14-14-14
14-14-14
14-14-14
14-14-14
14-14-14
Lab. Re.
Lab. Re.
Lab. Re.
Lab. Re.
Lab. Re.
Lab. Re.
Lab. Re.
Lab. Re.
24.6
24.9
24.5
24.6
24.6
24.6
24.6
24.6
22.5
23.2
22.5
22.5
22.6
22.6
22.6
22.6
0.0
0.0
0.0
0.0
-
-
-
-
52.9
49.6
52.9
52.9
52.9
52.9
52.9
52.9
0.0
49.6
52.9
0.0
26.5
13.2
none
13.2
190
204
200
200
200
200
200
~
219
204
204
216
210
216
247
"
14.0
13.2
14.2
13.6
14.1
14.2
-
14.1
20.8
12.8
20.0
14.5
14.2
14.3
-
15.1
20
36
21
23
26
29
59
39
9.9
17.1
8.7
14.5
13.0
13.6
59.0
14il6
61.2
41.0
51.9
50.5
41.5
68.7
-
-
.
-
5.0
.
-
-
81.0
-
v. good
-
v. good
good
good
good
good
-
Reactor 219°C, pH high.
Urea crystal 2*. pH 4.5,
too hot; by crushing hot
some granulation occurred.
Initial pH 4.7, lab analysis
pH 4.2, KC1 +20 mesh.
pH 4.8, KC1 not completely
wetted.
pH 4.4, too much melt or
solids too hot.
Concentrated add, stltky
product cooled slowly.
pH 3.5.
-------
3. Place weighed container with fertilizer in a desiccator containing
40% sulfuric acid in a 30° C (86° F) constant temperature chamber.
4. Weigh container each day for five to seven days to establish
moisture pick-up rate.
5. Repeat test using 35% sulfuric acid.
Calculations -
(Wt. after being in chamber - initial dry wt.) X 100/initial dry wt.
= % moisture absorbed.
Rate of Solution Test for Granular Fertilizers
Application - To determine the solubility rate of fertilizers at
controlled conditions.
Apparatus and Reagents -
Long stem glass funnel
100 milliliter (ml) graduated cylinder
Thermometer
Constant temperature bath
Procedure -
1. Select 50 gms of fertilizer passing through a 5 mesh but retained
on a 14 mesh screen (U.S. Standard).
2. Place the fertilizer in the funnel; pour through 100 ml of
distilled water at 10° C (50° F).
3. Recirculate this 100 ml of water at two-minute intervals for ten
minutes for a total of six passes.
4. Analyze liquid for N, P, K and pH.*
*pH measurement used to make approximation of mole ratio NH,/P205
Calculations -
Present data as %N, %P20, %K in liquid.
84
-------
Rate of Hydrolysis Test
Application - To determine the reversion rate of polyphosphates to the
ortho form.
Apparatus and Reagents -
25% (by wt.) sulfuric acid solution
Four containers that hold approximately 15 gm of fertilizer
in a monolayer
One or more desiccators
One constant temperature chamber
Procedure -
1. Place approximately 15 gms of fertilizer in three different
containers in the desiccator after recording the total weight of
each container of fertilizer.
2. Place desiccator in chamber at 30° C (86° F).
3. After one week, remove one container and analyze for N, total
P2O5, non-ortho P2°5' K an(^ water content,
4. Repeat Step 3 after two and three weeks.
Hygroscopicity of Complex Fertilizers
Application - A vacuum line technique is described for the measurement
of the equilibrium relative humidity of complex fertilizers. It
consists of determining the vapor pressure of the saturated solution
that is formed on the surface of such fertilizers by the absorption of
small amounts of water, vapor. Application of this method to systems of
binary mixtures, reciprocal salt pairs and commercial fertilizers
containing several components is discussed. The main advantage of this
method is that it can measure critical relative humidities of samples
over a wide range of measurable water concentrations even at the low
concentrations usually found under storage conditions. '
Procedure - The pertinent parts of the glass vacuum line used in this
method are shown schematically in Figure A-l. The line consists of a
water reservoir and thermostat sample containers that can be filled
with water vapor, isolated by means of a stopcock from the rest of the
vacuum line, and mamometers to measure the vapor pressure inside the
sample containers. The vacuum line is wrapped with nicrome heating wire
to prevent the condensation of water vapor on cold spots.
-------
To
Vacuum
Pump
H2O
Reservoir
To
Manometer
Thermostated
Sample
Container
Figure A-l.
Vacuum line for measuring critical relative humidities
of fertilizers.
-------
The critical relative humidity of a fertilizer is determined by
placing a 1 to 5 gm sample in a 25 ml round bottom flask which is
attached to the vacuum line by means of a greased standard tapered joint,
Figure A-l. The sample is then allowed to come to thermal equilibrium
at the desired temperature. With Stopcocks A and C open and B closed,
the system is evacuated to a pressure of less than 0.001 mm of mercury.
Stopcock A is then closed and B opened, filling the sample containers
with water vapor. The temperature of the water reservoir must be at
least as high as that of the thermostated sample to ensure that water
vapor fills the sample containers to pressures greater than the vapor
pressure of the saturated solution. The water in the reservoir must be
previously degassed so that the pressure of water vapor alone is being
measured in the sample containers. Stopcock C is closed at any time
after B is opened, and the decrease in vapor pressure is recorded as a
function of time as the sample absorbs water. The pressure at
equilibrium is taken to be the vapor pressure of the saturated solution
of the sample, and its critical relative humidity is equal to that
pressure divided by the vapor pressure of pure water at the temperature
of the sample.
The amount of water absorbed can be varied by changing the time
interval during which the sample is exposed to the water reservoir. By
weighing the sample before and after a determination and knowing the
absolute water concentration of the original sample, the amount of water
absorbed can be measured. Thus, the critical relative humidity of a
fertilizer can easily be studied as a function of % water over a wide
range of water concentrations.
Equilibrium can also be approached by the absorption of water vapor
from wet fertilizers. This is done by allowing the fertilizer sample to
absorb water as above. Stopcock B is then closed and, with C open,
Stopcock A is opened for a short time so as to evacuate the water vapor
from the sample container. The sample is then isolated by closing
Stopcock C. The increase of vapor pressure as water evaporates from the
wet surface is recorded as a function of time until equilibrium is
reached.
The two methods of approach to equilibrium have been found to give
identical results in all of the systems investigated, although the
attainment of equilbrium by absorption of water vapor is the method used
in the majority of the cases studied. At a given temperature, the rate
at which equilibrium is approached depends on many factors, such as
surface area, particle size and water content of the sample. In actual
practice, using 5 gm samples ground to pass through 80 mesh, equilibrium
is reached at room temperature in less than one hour when the amount of
water absorbed is about 1% of the total sample Weight. Use of unground
samples does not change the equilibrium values obtained, but does
require longer time.
87
-------
PILOT PLANT INVESTIGATIONS
Alternate I Design
Figure A-2 presents a flow sheet and material balance for a plant
utilizing the Alternate I design referred to in Section V. It is
included only in the Appendix because the cost analyses of Section VI
showed that Alternate I is not as economical as Alternates II and III.
No pilot plant work was done on this design.
The Alternate I design contains the following steps:
1. Melt production - The method of producing the
ammonium polyphosphate melt is similar to that
of Alternate II.
2. Mixing the melt with solid material - A
preheated mix of dry materials, ammonium sulfate,
potassium chloride, filler and recycle is intro-
duced and mixed with the melt.
3. Sizing, recycle and storage - The mixed product
is used to exchange heat with the raw feed. It
is sieved for recycle, crushed and marketed or
stored.
Thus, it may be seen that the Alternate I design embodies the same
process concepts as Alternates II and III, which are reviewed in detail
in Section V, but with the following key differences:
1. In Alternates II and III, a series of preheaters
and partial coolers is added to more efficiently
utilize heat which normally would be wasted.
2. In Alternate I, all mixing of dry product with
raw materials occurs prior to the single point
injection into the pug mill.
3. In Alternate I, no means are provided for
sparging ammonia into the pug mill.
Alternates II and III Design
Table A-2 presents a summary of the calculations of the energy
balances for the production of 13-13-13-13 and 12-24-12-13 grade
fertilizers in the 454 kg/hr pilot plant using the melt process. This
energy balance is applicable to both design alternates.
-------
00
to
STREAM N2
DESCRIPTION
FLOW (TPH) METRIC
TEMP °C
H3PQ,
1.2
NH,
1.45
H20
VAP
3.18
STM
3.36 41.3
REC-
YCLE
AS
22
KCL
9.5
FILL
MIX
72.8
MELT
9.9
21 21 149 265 115 21 21 — 132 265 171 115 115 115 115 71 115 115
PROD
82.5
+ 5
8.2
41.3
PROD PROD
22.2
-14
19
41.3
REC-
PRODlYCLE
41.3
MIX
90.7
MELT TEE
DISENGAGE- REACTOR
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXI MENT
n
ELECTROSTATIC
1 PRECIPITATOR
TTY
L5
II'X 60'
PRODUCT COOLER
^
CONVEYOR
~P
INGR.
TO
RECYCLE
BIN
HOPPER
Figure A-2. Alternate I flow sheet for 907 Mt/d (1000 st/d)
pilot plant producing grade 13-13-13-13.
-------
Table A-2. ENERGY BALANCE CALCULATIONS FOR 454 kg/hr
(1000 Ib/hr) PILOT PLANT
FOR 13-13-13-13 GRADE PRODUCT
Ingredients Kg/t of product (Lb/t of product)
Phosphoric acid 56% 232 (wet) (463) (wet)
197 (dry) (395) (dry)
Ammonia, anhydrous 35 ( 70)
Ammonium sulfate 485 (970)
Potassium chloride (61.5% K) 212 (423)
From the reactor:
NH3 (gas) + H3P04 (liquid) _^L ^ NH3H2P04 (crystalline)
Hf -11.04 -305.6 -345.28 kcal/g-mole
(21°C) HR = 28.64* kcal released/g-mole
*Heat absorbed in polyphosphate formation included (2900 BTU/t
equivalent).
Heat released based upon NH3:
28.64 kcal/g-mole/17 gm/g-mole = 1.85 kcal/g, or 1685 kcal/kg NH3
28.64 (kcal/g-mo1e)/17 g-mole x 1800 (conversion factor)
= 3032 BTU/lb NH3
The heat released (total heat generated):
35 kg NH3/t product x 1685 kcal/kg NH3 = 58,975 kcal/t product
(70 Ib NH3/t product x 3032 BTU/lb NH3 = 212,240 BTU/t product)
Assume a melt temperature in the tee reactor of 121°C (250°F). If
ambient acid and ammonia gas feed temperature is 21°C (70°F), then the
sensible heat required becomes:
232 kg acld/t product x (121° - 21°C) x 0.53 (specific heat)
= 12,296 kcal/t product.
(463 Ib acid/t product x |250° - 70°FJ x 0.53 specific heat
= 44,170 BTU/t product).
90
-------
Table A-2 (continued). ENERGY BALANCE CALCULATIONS FOR
454 kg/hr (1000 Ib/hr) PILOT PLANT
30 kg NH3/t product x (121° - 21°C) x 1.1 (specific heat)
= 3,850 kcal/t product.
(70 Ib NH3/t product x \250° - 70°F| x 1.1 ["specific heat]
•— -1 - 1-3 csn RTII
= 13,860 BTU/t product).
Total sensible heat = 16,146 kcal/t product
(58,030 BTU/t product)
Evaporation of water at 100°C (212°F) assumes 540 kcal/km (970 BTU/lb).
35 kg H20/t product x 540 kcal/kg = 18,900 kcal/t product
(68 Ib H20/t product x 970 BTU/lb = 65,960 BTU/t product)
Solid ingredients:* (Assume heated to 130°C by reactor heat)
707 kg/t product (130° - 21°C) x 0.26 (specific heat)
= 19,753 kcal/t product.
(1393 Ib/t product [266° - 70°F~] x 0.26 [specific heat]
*- J u 70,987 BTU/t product).
*Alternate I - Sensible heat of solid ingredients is furnished by an
external heat source. This added heat must then be removed during
cooling.
Heat utilized:
Sensible heat
Water (latent heat)
Solids
Total
Heat remaining in product:
Total heat generated
Heat consumed
Heat remaining
kcal/t
16,146
18,800
19,753
54,799
kcal/t
68,975
54,799
4,176
(BTU/t)
( 58,030)
( 65,960)
( 70,987)
(194,977)
(BTU/t)
(212,240)
(194,977)
( 17,263)
Estimated ambient heat losses: 4,176.
91
-------
Table A-2 (continued). ENERGY BALANCE CALCULATIONS FOR
454 kg/hr (1000 Ib/hr) PILOT PLANT
FOR 12-24-12-13 GRADE PRODUCT
Ingredients
Phosphoric acid 54%
Ammonia, anhydrous
Ammonium sulfate
Potassium chloride (61.5%)
Kg/t of product
428 (wet)
365 (dry)
60
336
196
(Lb/t of product)
(855) (wet)
(730 (dry)
(120)
(672)
(392)
Heat released by chemical reaction:
101,100 kcal/t product
(363,840 BTU/t product)
Melt temperature in the tee reactor: 121°C (250°F)
Ambient temperature: 21°C (70°F)
Heat consumed:
Sensible heat
kcal/t
29,284
34,020
15,354
78,658
kcal/t
Solids
Total
Heat remaining in product:
Total heat generated
Heat consumed
Heat remaining
Estimated ambient heat losses: 10,760
(BTU/t)
105,327
121,250
74,693
301,270
(BTU/t)
101,100
78,658
22,442
(363,840
(301,270
( 62,570
( 30,000)
92
-------
Alternates II and III Pilot Plant Test Data
Table A-3 presents selected results of the 45 kg/hr pilot plant
tests. This data is discussed in Section V.
-------
Table A-3. PILOT PLANT OPERATION IN 45 kg/hr (100 Ib/hr) PLANT
Sample
5/29
6/15
6/25
6/28
7/11
7/14
7/16
7/18
7/1 9a
7/1 9b
7/25
7/27
7/27
7/30
7/31
8/09
9/06
9/11
9/1 4a
9/14b
Analysis, %
N
12.72
9.46
2.80
2.77
11.91
11.56
13.56
12.94
12.27
12.35
14.20
14.84
14.84
14.93
13.92
13.58
14.97
15.52
14.17
14.54
P2°5
23.43
16.10
9.37
9.66
17.93
13.00
13.89
17.48
22.11
20.92
18.37
19.22
19.22
13.90
15.33
14.34
11.24
11.95
19.37
15.23
Poly P
29.4
17.3
29.7
28.8
56.7
28.1
29.0
37.6
25.7
30.0
36.6
28.5
28.5
33.0
25.7
40.6
30.3
31.3
36.6
31.1
K?0
10.22
23.64
47.09
48.09
19.8
20.8
15.3
14.83
15.03
14.03
11.22
8.21
8.21
10.82
14.02
15.13
11.42
9.92
11.70
11.9
pH
3.7
3.4
6.0
5.6
4.6
5.4
5.4
5.1
4.8
4.7
4.4
4.7
4.7
5.4
5.4
4.7
5.1
5.1
4.7
4.9
Marketable
Product -5/
+14 Flesh, %
-
-
-
-
-
83.9
82.8
-
82.2
98.8
-
91.7
91.7
90.2
88.2
"
-
-
-
-
Reactor
Temp. . °C
218
-
218
228
225
218
218-232
-
-
-
238
238
238
232
238
275
246
-
222
223
Comments
Heated add, heated solid to 149° C, crystal-
lization of melt on pug mill.
Heated add, sensitive to liquid and over-
agglomeration followed by under-agglomer-
atlon.
Add KC1 and ammonium sulfate 1n pug mill
to force crystallization recycle minimum.
54% phosphoric add.
Raw materials added at center, recycle
sulfate, amx>n1at1on 1n tee reactor and
pug mill.
Fine ammonium sulfate, ammonlatlon tee
reactor, pug mill, 9% attrition.
Ammonlated In tee reactor and pug mill,
good granulation, low attrition.
Ammonlatlon In pug mill and tee reactor,
recycle temperature 107° C, very uniform
granulation, 1 Ib/hr ammonium In pug mill.
Recycle 107° C, melt added upstream,
ammonlatlon In pug mill.
Recycle 107° C, ammonlatlon In pug mill
Increased the liquid phase, 8.4%
attrition.
Heated sol Ids, excess fluidity in pug
mill.
Heated recycle, recycle balanced 3% attrition.
Heated recycle, recycle balanced, 3%
attrition.
Heated recycle, 4% attrition.
Reactor temperature of 204° C caused tee
reactor to start plugging 7.3% attrition.
Heated add and recycle to 149° C,
granules had a "wet" appearance, large
particles produced, granules very tacky.
Recycled all recycle material.
Heated recycle, good mixing, solids took on
cohesive appearance prior to melt addition.
Heated recycle, problem of buildup 1n pug
mill.
Heated recycle, clean section of shaft 1n
pug mill assisted operation.
94
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-76-295
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
GRANULATION OF COMPLEX FERTILIZERS CONTAINING
AMMONIUM SULFATE BY MELT TECHNOLOGY
5. REPORT DATE
December 1976 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Juan Lanier and Robert MacDonald
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Ferguson Industries
1900 North Northwest Highway
Dallas, Texas 75220
10. PROGRAM ELEMENT NO.
1BB036
11. CONTRACT/GRANT NO.
68-01-0754
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory - Athens, GA
Office of Research and Development
US Environmental Protection Agency
Athens, Georgia 30601
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/01
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A novel process was developed for production of high analysis fertilizers in
which large portions of the nutrients are derived from by-product and waste ammonium
sulfate. The materials produced exhibit good physical and storage characteristics
and are similar in grades to those now being consumed in large quantities.
Phosphoric acid and anhydrous ammonia are reacted to form the liquid bonding
agent. Solid ammonium sulfate, potassium chloride and recycled fined are added to
the melt in a pug mill. Emissions of pollutants is less than from conventional
plants and is readily contained.
The process was developed and tested on a laboratory scale and in a small pilot
plant and was verified in a 454 kilogram per hour (1000 pound per hour) demonstra-
tion unit.
Capital and operating cost estimates are presented. The operating cost is
sensitive to the assumed value of waste ammonium sulfate. In comparison to similar
grade products, cost savings of 10 to 20% can be realized if true waste values can
be assumed. The financial estimates did not attempt to evaluate the indirect berrefit
to society, in terms of dollars and of energy, of recovering waste ammonium compounds
and sulfur dioxide—which often are discarded into aquifers or into the atmosphere
and thus constitute major pollutant threats and of converting these chemicals into
useful products.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
Fertilizers, Water Pollution Sources,
Ammonium Compounds, Phosphates, Waste
Treatment, Recycling, Ultimate Disposal
Nutrient Conservation,
Wastes Into Products,
Fertilizer Production,
Melt Process, Minimum
Emissions
COSATl Field/Group
02 A
13. DISTRIBUTION STATEMEN1
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
105
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
95
.S. GOVERNMENT PRINTING OFFICE: 1977-757-056/5530 Region Mo. 5-11
------- |