report biphosphate
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report biphosphateTRANSCRIPT
DESIGN OF A PLANT FOR PRODUCTION OF TRIPLE SUPER PHOSPHATE AND
SINGLE SUPER PHOSPHATE FERTILIZER FROM PHOSPHORIC ACID, BY
HYDROCHLORIC ACID LEACHING PROCESS.
A Design Report Presented to
DEPARTMENT OF CHEMICAL AND PROCESS ENGINEERING
FACULTY OF TECHNOLOGY
MOI UNIVERSITY
In partial Fulfillment of Requirements
For the Degree of Bachelor of Technology (Honors)
In Chemical & Process Engineering
NAME: NYONJE ISAAC ODHIAMBO
REG NO.: CPE/10/99
SIGN:
NAME: BUSOLO JOY
REG NO.: CPE/21/99
SIGN:
SUPERVISOR: MR. KAGARA
SIGN:
DATE: AUGUST 12th, 2005
© Moi University
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ABSTRACT
The project was aimed at designing and documenting a plant which manufactures single
Superphosphate (SSP) and triple Superphosphate (TSP) types of fertilizer for the local
market. No plant of this type exist in the region and as a result the product’s market is
extended to the region reducing expenses of export and distribution. Application of
these fertilizers in the region will double the national yield of crops such as maize and
hence promote the achievement of one of the millennium goals (reduction of poverty).
To meet the demand, a plant capacity of 360000 tons/year operating at 300 days within
the year with 3 shifts per day is targeted. Most of the equipment have been designed to
operate at normal atmospheric pressure.
The acid leaching process will see the reduction of the lethal effects of lead. The
availability of raw materials, water, infrastructure and immediate market for the fertilizers
made the designated site of plant location to be in South Nyanza near the Tanzanian
border where large deposits of phosphate rock are found. Market price for the fertilizer
at the time of the design is Ksh 1100 while the projected price is Ksh 900. This is as a
result of reduced transport costs, export duties thus improving fertilizer usage.
About US $ 44 million as total capital investment will be invested. This capital is
recoverable within the first two years, at a discounted cash flow rate of return of 47%.
Accumulated cash flow of US $ 294 million after fifteen years of the total life of the
project is reported from the economic analysis.
Little adverse environmental effect experienced from the plant operation as seen due to
emission of hydrogen fluoride is reduced by adequate pollution control, this and others
are specified under environmental impact assessment.
The two-phase project was commissioned by the department of Chemical and Process
Engineering, Moi University, in pursuance of the curriculum requirement. The first phase
concerned, primarily the literature review, mass and energy balance which was
accomplished in the first semester. The second phase comprising equipment design
and economic analysis was accomplished in the last semester. Inadequacy of data on
the local actual fertilizer consumption, current cost index and cost of some equipment
posed as the major constraints.
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ACKNOWLEDGEMENT
We are grateful to our supervisor, Mr. Maina Kagara for his encouragement, technical
advice, co-operation and patience. Without him it would not have been possible. Not
leaving out our projects coordinator, Dr. Kirimi Kiriamiti for his professional
encouragement and on-time assistance that helped us complete the project.
We are thankful to our families for their support both financially and morally all through
the project design duration. Above all, all glory to The Almighty.
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TABLE OF CONTENTS
ABSTRACT ......................................................................................................................2
CHAPTER ONE................................................................................................................1
1.0 Introduction ............................................................................................................1
CHAPTER TWO ...............................................................................................................2
2.0 Project Justification .................................................................................................2 2.1 History Of Fertilizer Development. ..........................................................................4 2.2 History Of Acid Leaching Process...........................................................................5
CHAPTER THREE............................................................................................................6
3.0 Literature Review ....................................................................................................6
CHAPTER FOUR............................................................................................................19
4.0 Process Specification............................................................................................19 4.2 Process Description ..............................................................................................21 4.5 Mass Balance........................................................................................................28 4.6 Energy Balance.....................................................................................................47
CHAPTER FIVE..............................................................................................................56
5.0 Equipment Specification........................................................................................56
CHAPTER SIX................................................................................................................62
6.0 Equipment Design.................................................................................................62 6.1 Cyclone Design ......................................................................................................62 6.4 Rotary Dryer Design..............................................................................................69
CHAPTER SEVEN..........................................................................................................76
7.0 Process Control And Instrumentation ...................................................................76 7.1 Process Control......................................................................................................76
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CHAPTER EIGHT...........................................................................................................84
8.0 Economic Analysis ................................................................................................84 8.4 Profitability Analysis ..............................................................................................94
CHAPTER NINE .............................................................................................................95
9.0 Safety And Environmental Impact.........................................................................95 9.1 Safety .....................................................................................................................95 9.2 Environmental Impact ...........................................................................................98 9.2.5 Pollution Control..................................................................................................99
CHAPTER TEN.............................................................................................................101
10.0 Plant Location ...................................................................................................101
CONCLUSION AND RECOMMENDATION .................................................................102
APPENDIX....................................................................................................................103
Detailed Calculation For Mass And Heat Balance For Reactor ....................................103
Detailed Calculation For Mass And Heat Balance For Cone Mixer ..............................105
BIBLIOGRAPHY...........................................................................................................107
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CHAPTER ONE
1.0 INTRODUCTION This document addresses the production of triple super phosphate fertilizer and single
super phosphate fertilizer from phosphate rock using acid leaching process.
The term fertilizer refers to chemically synthesized (manufactured) plant nutrient
compounds. They are usually applied to soil to supplement its natural fertility, thus
fertilizer becomes one of the most important as well as expensive input in agriculture.
Fertilizer may contain one or more of essential nutrients required for plant growth, the
ones that contain only one nutrient are know as single, simple or straight fertilizers.
Fertilizers which contain two or more nutrients are classified as mixed or compound
fertilizers.
Phosphate fertilizers are produced by adding acid to ground or pulverized phosphate
rock. If sulfuric acid is used, single or normal, super phosphate (SSP) is produced, if
phosphoric acid is used to acidulate the phosphate rock, triple super phosphate (TSP) is
the result. Two processes are used to produce TSP fertilizers: run-of-pile and granular.
Phosphate rock is obtained from the ores of the earth. Regionally, phosphate mining can
be done in Tanzania, Uganda and Kenya to provide raw material for this project.
Acid leaching is used for the removal of metal impurities from the fertilizer after it’s
processed. Acetic acid and hydrochloric acid are commonly used to remove the
unwanted lead particles because they both form water-soluble salts.
This project uses hydrochloric acid for leaching out the lead and clearly outlines the
reasons.
Plant capacity is estimated at 50tons/hr for either of the products.
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CHAPTER TWO
2.0 PROJECT JUSTIFICATION The basis and development of this project was as a result of the reasons given below.
The project aims at coming up with a solution that will try to eliminate the problems
associated with the manufacture of phosphate fertilizers using a single process; these
included,
o Lead overexposure is a leading cause of work place illness. Lead poisoning is
the leading environmentally induced illness in children. At greatest risk are
children under the age of six because they are undergoing rapid neurological and
physical development. Once in the blood, lead is distributed primarily among
three compartments – blood, soft tissue(kidney, brain, bone marrow and liver)
and mineralizing tissue(bones and teeth).Most exposure occur with inorganic
lead which is not metabolized, but directly absorbed, distributed and excreted.
Lead’s presence affects wide range of reproductive system, nervous system,
gastrointestinal blood and kidney damage; learning disability in children; animal
carcinogen (US Department of labour: Occupational Safety and Health
Administration, 1999)
o The identified constrains in Fertilizer use are: Rapid increase in price and
unavailability of the fertilizer at the right time. The supply of the commodity was
not steady during the planting season and the farmers had to do with any
planting fertilizer they found in the market (KARI Annual Report 1991).
o Most of the nitrogen fertilizer is water soluble and, in time, much of it can be
leached from most soils, especially during non-growing seasons. Due to
nitrification and denitrification, elemental nitrogen and its oxides are volatilized
from the soil. Water soluble Phosphorus is quickly converted in the soil to less
soluble forms. These materials do not leach from most soils (Othmer, 1980).
o Experts have used a variety of methods for estimating the future demand for
fertilizer. The quantities forecast differ but there is an agreement that the need for
food, and therefore, the demand for fertilizer will continue to grow in the
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foreseeable future. The food- Fertilizer-Population linkage is the important under
laying basis supporting demand (Othmer, 1980).
o Chemical fertilizers have increased global food production and have thus helped
feed the expanding human population. For this reason, modern farmers all over
the world use fertilize in ever-increasing amounts (Turk, 1993).
o One of the Eight of September 2000 UN General Assembly Millennium
Development Goals by the year 2015, pledged by the 191 UN Member states
was to completely eradicate extreme poverty and hunger (IEK, 2005).
o Recent Maize shortage experienced by the country which led the Government to
request for Maize supply from Tanzania could have been avoided by the
application of fertilizer that promotes high yields. Since field data indicate that the
maize crop yields is proportional to the amount of the fertilizer applied as
compared to wheat crop (Uasin Gishu District Annual Report for 1992).
o Importation of fertilizers contributes to the country’s negative balance of trade.
Having considered the reasons mentioned above, we embarked on the process of
designing a process that manufactures single super phosphate and triple super
phosphate fertilizer from phosphoric acid, by hydrochloric acid leaching process. The
process involves the production of the fertilizer and then subjecting it to acid leaching
process which provides long –term effectiveness by recovering much of the lead and
reforming to commercial use; this also eliminates the effects of lead associated with the
production and use of fertilizer.
When lead contained in the fertilizer as result of it being contained in phosphate rock is
reduced, the delivered cost of the fertilizer will be tremendously reduced due to reduced
bulkiness. This also increases the P205 content per bag.
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2.1 HISTORY OF FERTILIZER DEVELOPMENT.
The history of the world fertilizer industry can be traced to the earliest agriculture when
man began cultivation of plants to produce food. The early farmers learned that some
soils were more productive than others; they also learned that continuous cultivation of
the same land resulted in reduced yields. Some learned that the addition of manures,
composts, fish, ashes and other substances would sometimes increase yields or restore
productivity to “worn out” fields.
Agriculture and the use of soil amendments started through independent developments
in Mesopotamia in the river basins of the Tigris and Euphrates, in the Nile valley, in the
Orient and other parts of the world.
Soil science and chemistry did not develop very far until late in the 18th century. Aristotle
believed that organic matter was the source of all plant nutrition. Empedocles thought
that everything, organic or inorganic was composed of four elements – earth, air, fire and
water. Some useful textbooks or agricultural practices were developed during the middle
ages by the roman, Arab scholars and others. Soil fertility and soil amendment practices
remained much same in the year 1800 as were described by the Greek scholars in 300
B.C. Major fertilizer materials were animal manures, compost, sewage, sea sand,
seaweed, fish, bones and liming materials, particularly marl.
One of the first true experiments with a living plant was conducted by Van Helmont, a
Flemish physician and chemist, in his classical “willow experiment.” His simple direct
approach and use of quantitative measurement paved the way for future
experimentation that led to an understanding of plant nutrition which led to a scientific
approach to fertilizer development.
Justus Von Liebig (1803-73) is generally considered to be father of the world fertilizer
industry. Von Liebig stressed the value of mineral elements derived from the soil in plant
nutrition and the necessity of replacing those elements to maintain soil fertility. He
recognized the value of nitrogen but believed that plants could derive their nitrogen from
the air. He envisioned a fertilizer industry with nutrients such as phosphate, lime,
magnesia and potash prepared in chemical factories. His philosophy was as follows:
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Perfect agriculture is the true foundation of all trade and industry – it is the
foundation of the riches of nations. But a rational system of agriculture
cannot be formed without the application of scientific principles for such a
system must be based on an exact acquaintance with the means of
vegetable nutrition. This knowledge we must seek through chemistry.
2.2 HISTORY OF ACID LEACHING PROCESS
A recently completed bench-scale study examined the ability of hydrochloric acid
leaching to reach clean up goals for lead in seven soils (Van Benschofer, 1997). The
soils were wet-sieved into two fractions: coarse sand (-4 + 20 mash) and fine sand (-20
+ 200 mash). The fine sand was processed by tabling and the coarse sand was
processed by jigging.
Leaching with HCl was effective in reducing the lead concentration for most soils, but
low pH was essential. The percentage of Lead removed by acid leaching ranged from
22% to 93% for the several tested soils. All of the leached tailings passed the TCLP test
criteria, indicating that HCl can successfully treat most lead species. [TCLP – Toxicity
Characteristics Leaching Procedure].
The bureau of mining (Wellington et al, 1992) and RSR Corporation (Prengama and
McDonald, 1990) are independently developing similar acid leaching processes to
recover lead from soils and battery wastes such as casing and sulfite – oxide sludge
from scrap batteries. The process converts lead sulfate and lead dioxide to lead
carbonate which is soluble in fluoro silicic acid. Lead is recovered by electro wining and
the acid is recycled back.
Several vendors including Cogwis, Inc (Terr), Earth Treatment Technologies, Inc, and
Bescorp have developed and commercialized acid leaching processes to recover lead
from soils.
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CHAPTER THREE
3.0 LITERATURE REVIEW Vegetation, like all living things requires food for its survival and growth. Fertilizers are
materials added to the soil and sometimes to foliage to supply nutrients to sustain plants
and promote their abundant and fruitful growth (Othmer, 1980). The main components of
fertilizer are nitrogen, phosphorus and potassium. Fertilizer is used to amend soil to
promote the growth of desirable plants.
The elements that constitute these plant foods are divided into three classes:
Primary – Nitrogen (N), Phosphorus (usually expressed as P2O5) and
Potassium (expressed as K20)
Secondary - Calcium (Ca), Magnesium (Mg), and sulfur (S); and
Micro nutrients- Iron (Fe), Manganese (Mn), Copper (Cu), Zinc (Zn), Boron
(B), and Molybdenum (Mo).
There are four distinct types of fertilizers:
• Ammonium nitrate
• Normal super phosphate (SSP)
• Triple super phosphate (TSP)
• Run of the pile (ROP) - Non-granular Triple super phosphate
• Granular Triple Super Phosphate (GTSP)
• Ammonium Phosphate
Phosphorus pentoxide (P2O5) is used to measure the phosphorus content of fertilizer.
Phosphate ores are of two major geological origins:–
• Igneous – found in Kola, South Africa, Brazil, etc. • Sedimentary – found in Morocco, Algeria, U.S.A., etc.
The phosphate minerals in both types of ore are of the apatite group, of which the most commonly encountered variants are:–
• Fluorapatite – Ca10(PO4)6(F,OH)2 • Francolite – Ca10(PO4)6–x(CO3)x(F,OH)2+x
Fluorapatite predominates in igneous phosphate rocks and francolite predominates in sedimentary phosphate rocks.
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Table 1 shows the variation in chemical analysis of various phosphate rocks.
TABLE 1
CEI S.AFRICA MOROCCO USA SENEGAL TOGO Russia* Phalaborwa* Khouribga Florida Grade (nominal) % BPL 84 80 73 75 80 80 Composition(%wt) P2O5 38.9 36.8 33.4 34.3 36.7 36.7
CaO 50.5 52.1 50.6 49.8 50 51.2 SiO2 1.1 2.6 1.9 3.7 5 4.5
F 3.3 2.2 4 3.9 3.7 3.8 CO2 0.2 3.5 4.5 3.1 1.8 1.6
Al2O3 0.4 0.2 0.4 1.1 1.1 1
Fe2O3 0.3 0.3 0.2 1.1 0.9 1
MgO 0.1 1.1 0.3 0.3 0.1 0.1 Na2O 0.4 0.1 0.7 0.5 0.3 0.2
K2O 0.5 0.1 0.1 0.1 0.1 0.1
Organics 0.1 0.3 0.5 Organ. C 0.1 0.2 0.4 0.1 SO3 0.1 0.2 1.6 0.1 0.3
Cl 0.1 0.1 SrO 2.9 0.3 0.1
Trace elements (ppm) Rare earth 6200 4800 900 600 metals U3O8 11 134 185 101 124
As 10 13 13 11 18 12 Cd 1.2 1.3 15 9 53 53 Cr 19 1 200 60 6
8
Hg 33 0.1 0.1 0.02 0.2 0.6 Pb 11 10 17 5 Ni 2 2 35 28 Zn 20 6 200-400 70 Cu 37 102 40 13
3.1 SOURCES OF PHOSPHATE ROCK IN EAST AFRICA
1. In Tanzania at a place called Minjingu mine. Up to 22 000 ton per year from flat-
laying soft phosphate beds about 1m thick. The purity of the rock is 20 – 25 %
P205 content used for making SSP in Kenya. It is transported by trucks to Arusha
(about 90 Km) and then by rail to a phosphoric acid /TSP plant at Tanga on
Coast until the plant closed in the late 1980s.
2. In Kenya even more pure phosphate rock with higher P205 content is found in
Homa-Bay district though in small quantity.
3. At Tororo in Uganda there is still deposit of rock though there is a higher content
of iron thus increasing the cost of production while tying to remove the iron.
3.2 EFFECTIVENESS OF FERTILIZERS
It is unfortunate that crops do not utilize applied fertilizers efficiently. On average, no
more than one half of applied fertilizer Nitrogen is used by crops (Othmer 1980). Most
of Nitrogen fertilizers are water soluble and in time much of it can be leached from most
soils, especially during non-growing seasons. Due to nitrification and denitrification,
elemental nitrogen and its oxides are volatilized from the soil. (Othmer,1980). Water
soluble phosphates are quickly converted in the soil to less soluble forms (Othmer
1980). These materials do not leach from most soils. Phosphate utilization is a function
of the nutrient status of the soil, the crop, the weather and other factors. Its uptake by
the first crop following its application ranges from about 6% to 30%. However, most of
the remaining phosphate stays in the soil and can be used by future crops but at a
reduced rate (Othmer, 1980).
Chemical fertilizers have increased global food production and have thus helped feed
the expanding human population. For this reason, modern farmers all over the world
use fertilizers in ever-increasing amounts (Turk 1993). Population growth is the
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dominant cause for increased demand on a world basis but another important cause is
the need to improve the food status of the world, especially in many developing nations
(Othmer 1980). Assuming a direct proportion between increased food production and
fertilizers demand, probable demand approaching 200 * 106 metric tons of fertilizer
nutrients by the year 2000 was realized (United Nations Data for world population
growth).
Nearly one half of the increased crop production in the US since 1940 is credited to the
increased use of fertilizers.
3.3 TOXICITY OF PHOSPHATE FERTILIZERS
Toxicity could be caused by the mode of action of the substance and of its breakdown
products or any contaminants and their persistence in areas of concentration in the
environment.
Mono calcium phosphate itself is considered generally non-toxic (Ramsey, 2000).
Fertilizer – grade triple super phosphate will form free acids and can release fluorides
(IMC, 1988).
Super phosphate will generally adsorb to clay and react with cations in the soil
depending on pH, cation exchange capacity and available cations.
Leaching of soluble or runoff super phosphate fertilizer bound to eroding soil is a source
of phosphate in rivers, lakes and streams although the amount and significance of the
contribution of fertilizer's source is questionable (Cooke and Williams, 1973).
3.4 EFFECT OF THE PHOSPHATE FRTILIZER ON THE ENVIRONMENT
The probability of environmental contamination could be during manufacture, use,
misuse or disposal of the substance.
The super phosphate manufacturing process generates air pollution (US EPA,
1966),effluent to streams (Gorecici, 1994), solid waste that can contain high levels of
toxic heavy metals (EPA, 1999a) and radioactive wastes (Bunns, 1994; EPA 1994) that
can potentially include hazardous components (EPA, 1998). Acidulation of apatite
produces hydrofluoric acid (HF), a very strong acid that is highly reactive (Gorecici,
1994). Liquid or vapour HF causes severe irritation of the eyes and eyelids and may
result in prolonged or permanent visual defects or total destruction of the eyes. Skin
contact may result in painful burns.
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The technology to remove and recover fluoride from the HF in both single and triple
super phosphate manufacturing has made great strides since the 1950s but has not
been installed in all manufacturing plants and still can be improved (Gorecici, 1994).
Phosphate fertilizer is known to contain varying levels of heavy metals such as
Cadnium, Lead, Nickel and Chromium (Charter et al, 1993, Mortradt, 1987). These
metals may originate in the phosphate rock (Mortradt and Giordano, 1987). The
Cadnium and other metals remain with the phosphate during processing (Wakefield,
1980, cited in center for Environmental Analysis, 1999).
3.5 EFFECT TO HUMAN HEALTH
The active calcium phosphate is not considered a human health risk. However
elemental contaminants of triple super phosphate with Arsenic, Cadnium, Fluorine and
Lead may be potential risks to human health (US EPA, 1999b).
3.6 NORMAL SUPER PHOSPHATE
It contains between 15% and 21% P2O5. It is maintained by reacting ground phosphate
rock with 65% to 75% Sulphuric acid.
This is produced by reacting phosphate rock with Sulphuric acid.
Reaction:
[Ca3 (PO4)2].CaF2 + 7H2SO4 +3H2O → 3CaH4 (PO4)2+2HF↑ +7CaSO4
3.6.1 PROPERTIES OF SSP 1 -2 % of free acid content as H2SO4
5 – 8% moisture content
20 – 22% citrate soluble P205 in neutral citrate solution
Hygroscopic at 30ºC
94% Relative humidity
Bulk density Non -Granular 800Kg/m3
Granular 970Kg/m3
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3.6.2 USES The chief uses of super phosphate are; for phosphate fertilizers, for enameling and in
construction material. Food and feed grade mono calcium phosphate is used as an
acidulant in baking powders and as a mineral supplement for various foods and
livestock feed.
3.6.3 MATERIAL REQUIREMENTS 1 ton of super phosphate fertilizer requires -
Phosphate Rock - 0.5 ton to 0.6 ton
Sulphuric acid - 0.5 ton to 0.6 ton (Shukta et al,1982)
While soluble, super phosphate rapidly becomes fixed to the soil particles (Barick,
1925), the primary interactions in the soil are free H2PO4, HPO4 and PO4 anion with
available cations. Heavy application of phosphate compounds enhances zinc
deficiency.
The enhanced solubility of super phosphate can be considered detrimental. Despite
being fixed in most situations, over a long time period, super phosphate will leach to a
certain extent. One experiment showed that fields that received farmyard manure and
super phosphate had twice as much soluble phosphate in the sub soils as fields that
received farmyard manure alone (Warren and Johnson, 1961, cited in Cooks and
Williams, 1973).
3.7 TRIPLE SUPER PHOSPHATE This is produced by an action of phosphoric acid on rock phosphate. The material is a
much more concentrated fertilizer than super phosphate containing about 45 – 50%
P2O5.
Reaction:
[Ca3 (PO4)2].CaF2 + 14H3PO4 → 10CaH4 (PO4)2 + HF
Material Requirement:
1 ton of triple super phosphates fertilizer requires -
Phosphate Rock - 0.45 tons
Phosphoric acid (50% P2O5) - 0.62 tons
Application:
It is applied at planting – drilled in about 2 inches below and 2 inches to the side of the
seed row.
Note
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Melting point of Phosphoric acid is 71.7 -73.6ºC
3.8 ANALYSIS:
3.8.1 TYPICAL CHEMICAL ANALYSIS: CaH4P2O8.H2O 63 – 73%
CaSO4 3 – 6%
CaHPO4,Fe and
AlPO4 13 – 18%
Free moisture 3 – 6%
Calcium 20%
Magnesium 0.7%
Sulphur 1.5%
Phosphorus
Total 20.7%
Available 20.0%
3.8.2 PHYSICAL PROPERTIES Sizing 95% in the 2mm – 4mm range
Bulk density Granular 1.10 – 1.20 t/m3
Non–Granular 879Kg/m3
Area or response 31°C - 33°C
Hygroscopic at 30ºC
Relative humidity 94%
3.9 COATING AGENTS These are materials that are applied uniformly onto the surface of the fertilizer particles.
Most coating agents are either finely divided inert powders (dusts) that adhere to the
particle surfaces or are liquids that are sprayed onto the surface e.g. Clays (Kaolin and
China), Diatomaceous earth and Talc (basic Magnesium Silicate).
Diatomaceous have a dry bulk density of 128 to 320 kg/m3 (8 to 20 lb/ft3), contain
particles mostly smaller than 50 mm, and produce a cake with porosity in the
range of 0.9 (volume of voids/total filter-cake volume). The high porosity (compared with
a porosity of 0.38 for randomly packed uniform spheres and 0.2 to 0.3 for a typical filter
cake) is indicative of its filter-aid ability.
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In this project, Diatomaceous earth is the coating agent to be applied since the same
material is used in dewatering as a filter aid. A 90% minus 20µm is recommended
(UNIDO)
3.10 EFFECT OF TSP ON PLANTS
When the soil needs phosphate the application of phosphatic manure has the following
results:
• Greatly assisted seedling growth. Crops make a better start. They show in
the rows sooner, grow faster and may be hoed and set out earlier.
• Improved root development and fibrous root growth.
• Cereals ripen earlier and give grain of better quality.
• Increased feeding value of grass, hay and fodder crop.
• Phosphate provides a constituent of genetic material, the nucleic acid, DNA
and RNA.
• Energy for respiration and photosynthesis is stored in phosphate bonds of
energy-rich compounds.
3.11 STORAGE AND HANDLING
• TSP has excellent physical qualities. It stores, handles and flows through all types
of equipment extremely well.
• Does not take up moisture in the storage area or in the fields
• Spreads very evenly
• TSP flows significantly quicker than other fertilizers, approximately 15% – 20%
faster than DAP so care must be taken in calibration before using.
3.12 ACID LEACHING PROCESS
After the physical separation of the course particulate metals have been removed from
the bulk fertilizer, Lead and other metals are still present in the fertilizer either as fine
particulates or as molecular or ionic species bound to the fertilizer. Fine particles could
consist of either elemental lead or precipitates of lead salts. Lead species could be
bound to the fertilizer by ion exchange, sorption or complexion with organic matter.
Acid leaching belongs to a group of techniques called soil washing, which tries to
mobilize the target metals from the soil into a solution. The solution is then treated to
recover the metals in a concentrated form for off-site disposal or recycling. Acid leaching
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aims to solubilize metals from the soil by changing the pH. Adding acid lowers the pH
and increases the supply of H+ ions. The H+ ions generated are consumed in a
multitude of reactions that increase soluble metal concentrations.
Fertilizer washing is a generic term for a group of techniques used to mobilize the Lead
from the fertilizer into solution by one or more of the following means.
• Change in pH (e.g. acid leaching)
• Changes in system ionic strength (by addition of a suitable salt)
• Changes in redox potential (by addition of a suitable reducing agent)
• Formation of complexes (by addition of a ligand such as ethylenediaminetetra
acetic acid [EDTA])
Acid leaching was conducted at Fort Polk as a continuous process involving the
following steps:
• Bringing acid and soil into contact in a leaching tank
• Separating the leached soil from the spent leachant
• Regenerating the spent leachant by precipitating the heavy metals.
The precipitated metals were dewatered and the resulting sludge was sent to an off-site
smelter for recycling of its lead content. Whereas physical separation is a fast operation
in which relatively small equipment is used to obtain high throughput, leaching is
relatively slow and requires larger equipment.
Depending on the amount of lead recovered by a series of leachants, the lead species
can be classified by this procedure as follows:
• Water soluble
• Ion exchangeable
• Silver displaceable
• Carbonate
• Easily reducible (bound to manganese oxides)
• Organically complexed
• Adsorbed on iron oxides
• Sulfide
• Residual.
Generally, the further down the list the metal occurs, the harder it is to remove by
leaching. Based on this classification, appropriate leachants can be selected and
15
optimized to achieve desired targets for the site. This sequential extraction procedure is
somewhat expensive and generally time consuming.
Soil washing was first used in the Netherlands in the early 1980s and is widely used in
Europe (Valenti 1992). Soil washing starts with physical separation techniques to
separate the course from the fine particles. The course fraction may be subjected to
density separation to remove particulate metals. The fine fraction is mixed with suitable
wash solution (e.g. acid) to remove the lead bound to the soil. The course soil may or
may not need washing depending on the amount of leachable lead associated with this
fraction.
One major objective of this project is to apply the soil washing principle to the fertilizer to
leach out specifically lead particles.
3.12.1 ACID LEACHING AND METAL CHEMISTRY Acid leaching helps to mobilize much of the fine particulate and fertilizer-bound lead into
solution by lowering the pH of the wash solution. Lowering the pH increases the supply
of Hydrogen ions which are consumed in a multitude of reactions that increase soluble
lead concentrations.
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Figure 4-6. Pb solubility diagram: calculations made assuming solid phase always to be present, with total chemical component concentrations [e.g., PbT, (SO4)T, (PO4)T, CT] varying depending on amount of solid phase that was dissolved (van Benschoten et al., 1997)
Acetic acid and hydrochloric acid have been commonly used to remove lead because
both acids produce water-soluble salts. Acetic acid is weak and is expected to be
effective at some sites where lead is mostly in the form of carbonate minerals (cerussite,
hydrocerrusite, etc.) In general solubilization rates are dependent on pH, liquid-to-solid
ratio, type of metal and contact time. Of these properties, pH and liquid-to-solid ratio are
the limiting factors for a given metal. PH determines the equilibrium solubility
concentration achievable and the liquid-to-solid ratio determines the total mass of metal
removed. As far as contact time is concerned, solubilization generally reaches a
maximum in a relative short time and then levels off (Wozniac and Huay, 1992). Metallic
lead dissolves very slowly and therefore, physical separation is desirable by leaching. A
contact time between 10 to 60 minutes should be economically acceptable for a field
leaching operation of the type concerned.
17
3.12.2 ACID ACTIVITY EFFECT ON LEACHING RATE Acid strength can be understood as the product of total acid concentration and
hydrogen ion “activity” that is the fraction of the available hydrogen ion that is not
already strongly bounded to something other than water (as “free” hydrogen or as H+
dissolved in water). Bounded H+ is not available to directly attack lead compounds to
leach the Pb2+ contained in them. Therefore as acid, HX, dissociates partially when
added to water to produce free H+ according to the following reversible reaction.
HX → H+ + X-
HCl (where X- = Cl-). When HCl is added to water and the resultant pH is less than 3.5,
100% of the HCl is ionized to form H+ and Cl- that is the reaction lies far to the right
hence
Ka (= [H+] [X-] / [HX]) is very large
3.12.3 LEAD ION CONCENTRATION (SOLUBILIZATION) CHEMISTRY OF HCL ACID Complexation reactions tend to solubilize metal ions in water. Chloride ions display
Pb2+ complexation capability.
Pb2+ + 2Cl- → PbCl2
PbCl2 solubility is only a little more than PbSO4 solubility. The low solubility limits the
total dissolved lead concentration to approximately 200parts per million. Higher Cl-
levels would depress this solubility still further.
18
Figure 4-8. Precipitation of heavy metals as hydroxides (Source: Lanouette, 1977)
19
CHAPTER FOUR
4.0 PROCESS SPECIFICATION 1. Two processes have been used to produce triple Superphosphate: run-of-the-pile
(ROP-TSP) and granular (GTSP).
GTSP yields larger, more uniform particles with improved storage and handling
properties. Most of this material is made with the Dorr-Oliver slurry granulation process.
In this process, ground phosphate rock is reacted with phosphoric acid in1 or 2 reactors
in series. The phosphoric acid used in this process is appreciably lower in concentration
(40 percent P2O5) than that used to manufacture ROP-TSP product. The lower strength
acid maintains the slurry in a fluid state during a mixing period of 1 to 2 hours.
2.Phosphate fertilizer are known to contain varying levels of heavy metals such as
Cadnium, Lead, Nickel and Chromium(Charter et al,1993;Mortredt,1987).The metals
may originate in the phosphate rock (Mortradt and Giordano,1987).The cadmium and
other metals remain with the phosphate during processing(Wakefield,1980,cited in the
center for Environmental Analysis,1999).
The choice of process is based on the certainty that, acid leaching process would be
able to remove about 93 – 97% of the lead and Cadnium metals contained in the rock
(Battelle, 1997a).
Acid leaching process may be carried out using either Acetic or Hydrochloric acid. The
project aims to utilize Hydrochloric acid as justified below:
1. A stronger acid such as Hydrochloric or Nitric acid is more economical when the
lead species requires much lower PH. A 0.1M solution of HCl, for example, has a
PH of 1 and is more aggressive. Nitric acid may generate toxic oxides of nitrogen
and difficult to handle. HCl is therefore preferred.
2. Generally speaking, HCl is an aggressive leachant that is a corrosive and low
cost acid, whereas Acetic acid (HOAC) is more selective, less corrosive, but
significantly higher in cost relative to HCl (Battelle, 1997a).
3. Based on the Fort Polk demonstration (Battelle, 1997a), acetic acid process will
require additional bench –and pilot-scale demonstration prior to completion.
However, HCl process is ready for implementation and does not require further
development and demonstration (Battelle1997a).
20
4.1 ACID LEACHING.
The functional requirements for acid leaching are to remove metals from the fertilizer to
total and leachable metal concentration requirements while producing the minimum
possible amount of process residuals.
For acid leaching to succeed, the leaching solution must be able to accomplish the
following.
o Remove metals to the required clean up level.
o Reach the required clean up level with minimum number of contracting cycles.
o Produce a minimum volume of waste leaching solution.
o Selectively dissolve the metals of concentration but not the matrix.
o Provide compatibility with moderate cost materials of construction.
The project aims that given the above goals of the acid leaching process when applied
to the fertilizer production process, will reduce the bulk weight thus reducing
transportation cost and at the same time increasing the P2O5 available for absorption by
plants.
21
4.2 PROCESS DESCRIPTION
The flow of the process of manufacturing the fertilizer to acid leaching is given below;
since the projects entails the incorporation of both processing of SSP and TSP, at the
discretion of production manager, who would plan which type between SSP and TSP to
be manufactured at a given time. The whole plant will operate on a continuous basis.
22
4.2.1 SINGLE SUPERPHOSPHATE (SSP) DESCRIPTION
Phosphate rock is graded in terms of percentage BPL1. The Rock received from the
mines is pulverized to 90% minus 100 mesh; this is fed by a weigher feeder into a
double-conical mixer where it is thoroughly mixed with metered quantities of Sulphuric
acid. The Sulphuric acid (98%) is diluted with water in the cone to a concentration of
75% (51°Be’),the heat of dilution servers to heat the Sulphuric acid to proper reaction
temperature and excess heat is dissipated by evaporation of extra water added. The
water and acid are fed into the cone mixer tangentially to provide the necessary mixing
with the phosphate rock. The fluid (fresh Superphosphate) material drops to a den,
which has a very low travel speed to allow about 1 hour for solidifying before reaching
the disintegrator. The disintegrator slices the solid mass of crude product so that it may
be conveyed to pile storage for `curing` or completion of the chemical reaction, which
takes 4 weeks to reach a P2O5 availability acceptable for plant food. The continuous den
is enclosed so that fumes do not escape into the working area. These fumes are
scrubbed with water sprays to remove acid and fluoride before being exhausted to the
atmosphere. The scrubber water is discharged to a limestone bed to neutralize the acid.
The SSP already formed in the storage pile is conveyed to the leaching tank for further
processing.
4.2.2 TRIPLE SUPERPHOSPHATE (TSP) DESCRIPTION.
The rock pulverized to 98% minus 100 mesh is mixed with phosphoric acid in a two
stage reactor. The resultant slurry is sprayed into the granulator. The granulator contains
recycled fines from the process. The product from the granulator is dried, screened, the
oversize crushed. The final product is conveyed to bulk storage where the material is
cured for 4 weeks during which time a further reaction of acid and rock occurs which
increases the availability of P2O5 as plant food. The free acid, moisture and unreacted
rock content decreases, and the available and water soluble P2O5 increases. The
exhaust gases from the granulator are scrubbed with water to remove silicofluorides.
The TSP already formed in the storage pile is conveyed to the leaching tank for further
processing.
1 BPL – Bone Phosphoric of Lime = 2.1852 × P2O5
23
4.2.3 DESCRIPTION OF ACID LEACHING OF SSP AND TSP.
Acid leaching is often performed as a continuous process and involves as least four
vessels. In the leaching tank the acid solution is mixed with the fertilizer to leach out the
metals. The contact time between the leachant and the fertilizer can be set by designing
the volume of the tank to achieve the required throughput rate. For a given volume of
the tank, slowing down the throughput is the only way of achieving long contact. Contact
time requirements vary depending on the type of fertilizer and of metal encountered.
The fertilizer slurry is pumped from the leach tank to the clarifier where the solids settle
out and are discharged from the bottom. A flocculant may be added to enhance settling.
The flocculant to be used for this project is Commercial Sodium Aluminate in solution; it
provides a strongly alkaline source of water-soluble Aluminium and more especially
when addition of sulfate ions is undesirable. The overflow from the clarifier is the
leachate containing the solubilized metals. This overflow goes to a metal recovery tank
where the solubilized metals usually are recovered by precipitation or sometimes electro
winning.
Precipitants used for metals recovery include OH-, phosphates, carbonates, sulfates and
sulfides. The pH maintained in the precipitation process is an important determinant of
the precipitation efficiency. The optimum pH is determined by the type of metal, type of
precipitant and presence of potential complexing agents such as NH3 or EDTA. As the
pH is raised, solubility decreases up to a certain point. Beyond a certain pH, solubility
starts increasing again. Therefore pH control during precipitation is important.
The treated leachate may then flow into a separate clarifier tank for settling of the
precipitates, mixing of precipitant and coagulant with the leachate is fairly fast (15 to
60min). Settling may require 2 to 4 hours at overflow rates of 300 to 700gal/ft2 of surface
area per day. Some of the initial precipitate formed may be recirculated to the mixing
tank, where the older precipitate can grow. In the clarifier, the precipitate floc often
settles down to form sludge with only 1 to 2% solids. This sludge has to be dewatered
before it is hauled away for disposal or recycling. The sludge can be dewatered in
centrifuges, rotary vacuum filters or plate-and-frame filters. Centrifuges require less floor
space but may not dewater to the extent that the filter can. Plate-and frame filters
provide a drier cake and occupy less floor space but require much operator attention
24
than do rotary vacuum filters. A filter aid such as diatomaceous earth may be required
to prevent clogging of the filter cloth with fine precipitate particles. The overflow from the
clarifier is recycled back to the leach tank after being refortified with acid.
4.2.4 GRINDING Grinding is done using ball mills and Bag house device is employed to trap dust particles
that will be leaving the ball mill. The particle emitted from the bag house is 0.1Kg/ton
(Othmer Vol 10).The power consumption during grinding is 10Kwh/t (UNIDO), this -
power is used in breaking down (size reduction) i.e. strain energy. Part of this energy is
converted to heat due to friction between the balls and rock and the rock themselves. In
this project it will be assumed that this energy converted to heat energy comprises 5% of
the total energy (10 Kwh/t).
4.2.5 SCREENING
The ground rock is passed via screen which separates the oversize particles from the
required size. The screen ( -200 mesh which is equivalent to < 74 µm) separates 60% of
the ground rock i.e. the right size of particles.
4.2.6 BAG HOUSE
The bag house traps the fine particles that leave the ball mill. About 0.1Kg/t of dust leave
the bag house.
4.2.7 CYCLONE AND SCUBBER The particles entrained in the air are reduced (partially removed) via a cyclone and a
venturi scrubber. Water is injected to the scrubber to dilute and/or dissolve the Hydrogen
Fluoride and fumes produced in the reactor.
4.3 TRIPLE SUPERPHOSPHATE 4.3.1 REACTOR CP Phosphoric acid =0.703Kcal/KgK (UNIDO)
CP Gypsum = 0.272 Kcal/KgK (UNIDO)
Some of the heat is lost by convection and conduction.
CP Fluoroapatite ( Ca10 (PO4)6F2 ) = 751.86J/degmol
CP = a + b T +c T -2 ,
a = 948.85, b = 113.77×10-3 , c = - 205.3×105 Temperature range 298 – 1600K
25
The reaction taking place in the reactor is given by this equation:
Ca10 (PO4)6F2 + 14H3PO4 +10H2O → 10CaH4P2O8.H2O + 2HF + 11.14GJ
The overall retention time is about 30 minutes. The thick slurry is fed into the rotary drum
granulator together with a high proportion of recycle (UNIDO).
4.3.2 GRANULATION Steam is spanged underneath the bed (and the temperature is about 90°C) to provide
wet granule material, all the steam added will condense and this increase the water
content. Water is then spayed onto the bed of material .The oversize granules are
crushed and recycled to the granulator along with fines to serve as nuclei for forming
more products-size granules.
The power consumption is 21KWh/t (75.6MJ/t) which is utilized to run a 300 hp motor at
10 rpm with peripheral speed of about 375 ft/min.It is proposed that the diameter of the
drum to be 14ft (Othmer).60Kg of steam and 65 Kg of water is required per tonne
(UNIDO).
4.3.3 DRYING Drying is controlled to yield a product of 6% moisture content (UNIDO).Drying is done
using Rotary Driers. A co-current flow of hot dry air is used for drying. The advantage of
this over counter current is that
i) The dried product will leave at a lower temperature than with the counter
ii) ii) Heat sensitive material can be handled satisfactorily.
It is proposed that a rotary drier of Diameter 3.0m, Length 6.0m with flights. About
2.5Kg/t of fines are carried away with the hot air
4.3.4 SCREENING The product leaving the granulator are the granules, they are in the size of 1-4mm.A
screen to separate those particles which are greater than these range is put in place.
Oversize granules are crushed and return to the granulator where they act as nuclei.
26
4.3.5 STORAGE The produced TSP is taken for storage for a period of four (4) weeks to complete the
reaction started in the reactor. At this point the fertilizer is assumed to will have attained
the 25ºC temperature required in the leaching tank.
4.4.0 SINGLE SUPERPHOSPHATE
Single super phosphate fertilizer contains between 15% and 21% P2O5. It is
manufactured by reacting ground phosphate rock with 75% sulfuric acid. This is
described by the following equation: (U.S. EPA, May 1979)
[Ca3 (PO4)2]3CaF2 + 7H2SO4 + 3H2O 3[CaH4 (PO4)2.H2O] + 7CaSO4 + 2HF
Fluorapate (phosphate rock) + sulfuric acid + water mono-calcium phosphate
monohydrate + Calcium sulfate + hydrogen fluoride
4.4.1 MIXER For production of single super phosphate, Sulphuric acid at a concentration of 75% is
required. To achieve this, the commercially available 98% concentrated Sulphuric acid is
mixed with water at room temperature. This reaction evolves a lot of heat from the heat
of dilution. This heat of dilution serves to heat the Sulphuric acid to proper reaction
temperature and excess heat is dissipated by evaporation of water added. The water
and acid are fed to the mixer tangentially to provide necessary mixing with the
phosphate rock.
4.4.2 CONE MIXER Finely ground phosphate rock (90% < 100 mesh) is thoroughly mixed with Sulphuric acid
in a double conical mixer. The rock containing 34% P2O5 content is mixed with Sulphuric
acid; about 0.6 ton of Sulphuric acid (75%) is required per tonne of rock. 30 tons of
ground rock are used to give a final result of 50 tons of Single super phosphate.
4.4.3 CONTINUOUS DEN The fluid material from the mixer drops onto the den which has a low travel speed to
facilitate solidification. Solidification results from continued reaction and crystallization of
monocalcium phosphate. The den is enclosed so that fumes do not escape into the
working area. The Superphosphate is removed from the den after 0.5 – 4 hours. At this
point it is still somewhat plastic and its temperature is about 100°C.
27
4.4.4 DRYING The product is then removed from the den and passed through rotary driers against a
counter current flow of hot dry air at a temperature of 120°C. This reduces the moisture
from 9% to 6% making it ready for storage.
4.4.5 STORAGE Storage takes about 2 – 6 weeks where the reaction approaches completion. The free
acid, moisture and unreacted rock contents decrease and the available and water –
soluble P2O5 contents decrease. This makes the material to harden and cool.
28
4.5 MASS BALANCE
4.5.1 MASS BALANCE FOR TSP 1. GRINDING To manufacture 1 ton of Triple super phosphate, 0.62 ton of phosphoric acid and 0.45
ton of phosphate rock is required (UNIDO).The plant operates on a continuous basis at
1200tons per day (50ton/hr), this will require 31 tons of the acid and 23 tons of the rock.
The ground rock and the acid are mixed together in the reactor tank.
Constant process during grinding is assumed with size reduction of up to 74µm
Bag filters operate at 95% efficiency i.e. can trap up to 1µm particle.
0.1Kg/t of solid is emitted from bag filters (Othmer Vol. 10)
Components Inlet(tons) Outlet(tons) Raw Rock 38 Ground Rock 38 Total 38 38
2. SCREENING 60% of the ground rock pass though the (-200 mesh) screen (UNIDO).
Component Inlet(tons) Outlet(tons) Ground Rock 38 Screened rock 23 Recycled stream 15 Total 38 38
M1 = 38 tons T =25°C H1 = 0 MJ
GRINDING M2 = 38 tons T =26.8°C H2 = 68.4 MJ
Q` = 10KWh/t = 36MJ/t Q =1368MJ
29
3. WEIGHING
Components Inlet(tons) Outlet(tons) Screened rock 23 Weighed Rock 23 Total 23 23
4. REACTOR
Component
Inlet(tons) Outlet(tons)
Phosphate Rock 23 Phosphoric acid 31 Slurry 1 54 Total 54 54
Phosphoric acid Cp = 2952.6J/KgK = 0.703Kcal/KgK Mp = 31 tons T = 25°C H3 =0MJ Rock
Cp = 751.86J/degmol M = 23 tons H2 = 68.4MJ T = 26.8°C
M` = 54 tons T = 57.6°C H4 = 70.9MJ
Q = 2475KJ = 2.5MJ
REACTOR
30
5. MIXER
Component Inlet(tons) Outlet(tons) slurry 54 Steam 3.2 Slurry 2 57.2 TOTAL 57.2 57.2 6. GRANULATION
Component Inlet(tons) Outlet(tons) Slurry 2 57.2 Water 3.5 Fresh TSP 60.7 Total 60.7 60.7
M` = 54 tons T = 57.6°C H4 = 70.9MJ
Steam MS = 3.2ton T = 100°C H =8.6GJ
M2 = 57.2 ton T = 90°C H = 8633460 KJ
MIXER
M2 = 57.2 ton T = 90°C H = 8633460 KJ
Water MW = 3500 Kg T = 25°C H =0KJ
Wet TSP M3 = 60.7 ton T = 86.3°C H = 8633460KJ
Q` = 75.6MJ/t Q = 4082.4GJ
GRANULATOR
31
7. DRYING Moisture content of fresh TSP is 21.7% which is to be dried to 6% using a rotary drier.
Component Inlet(tons) Outlet(tons) Wet TSP 60.7 Hot air 639 Entrained solids + Vapourised water
10.352
Cool air 639 Dried TSP 50.3 Total 699.7 699.7 8. SCREENING Component Inlet(tons) Outlet(tons) Dried TSP 50.3 To crusher 0.13 To storage 50.17 TOTAL 50.3 50.3
Wet TSP M3 = 60.7 ton T = 86.3°C H = 8633460KJ
Dried TSP M3 = 50.3 ton T = 86.3°C H2O 6% = 3ton H =6018180 KJ = 6.02GJ
Dry Hot Air T = 120°C Ma = 639ton Cp = 1.07 KJ/KgK
Cooled stream M4 = 649.352 ton Moisture Mw = 10.2 ton Solids = 152Kg Air = 639ton T = 86°C H = 25.86GJ
Heat for Drying Q = 23.25GJ
DRYER
32
9. STORAGE The produced TSP is taken for storage for a period of four (4) weeks to complete the
reaction started in the reactor. At this point the fertilizer is assumed to will have attained
the 25ºC temperature required in the leaching tank.
10. CRUSHER Granules whose sizes are greater than 4mm is screened out and taken to the crusher to
reduce the size further. The crushed granules are then returned into the granulator
where they act as seeds (nuclei) for granulation.
Screening 1- 4mm
Dried TSP M3 = 50.3 ton T = 86.3°C H2O 4% = 3ton H =6018180 KJ = 6.02GJ
To storage M4 = 50.17 tons H = 6.02GJ T = 86.3°C
To crusher M5 = 0.13 tons
To storage M4 = 50.17 tons H = 6.02GJ T = 86.3°C
To leaching tank M4 = 50.17 tons H = 0GJ T = 25ºC
Storage
33
11. CYCLONE 2.21 Kg/t of particle is collected by the cyclone and retuned to the Granulator
(0.134 ton)
Component Inlet(tons) Outlet(tons) Contents of cool air 649.352 Recycle stream 0.134 Exhaust 649.218 Total 649.352 649.352
12. SCRUBBER
To recycle 2.21Kg/t = 134 Kg T = 86ºC
To scrubber M = 649.218 ton T = 86ºC Air =639 ton Solid TSP = 18Kg Vapour = 10.2 ton
Cyclone
Cooled stream M4 = 649.352 ton Moisture Mw = 10.2 ton Solids = 152Kg Air = 639ton T = 86°C H = 25.86GJ
To crusher M5 = 0.13 tons Crusher
Recycle to Granulator M6 = 0.13ton
34
Water flow rate is 6 gal/ 1000ft3 of gas.
= 22.71× 10-3 m3 water/ 28.32m3 of gas
Using an average density of air as 1.149 Kg/m3 and density of water as 1000Kg /m3
Hence water flow rate is 22.71 Kg/ 32.54 Kg of gas
Thus amount of water needed for 649.218 ton of gas is given by
649.218 ×22.71 = 453.1 ton of water
32.54
Assuming
1. An efficiency of 94%, the amount of solid removed will be
= 0.94 ×18Kg = 16.92 Kg ~ 17 Kg
2. All the vapour condenses
3. No gas dissolves in the water
Hence the temperature at which the gas and sludge leaves is given by
453.1 ×4200 ×1000 [T -25] = 639 ×1.017 ×1000 [86 - T] + 10.217 × 4200 ×1000 [86 -T]
T = 26.4ºC
Component Inlet(tons) Outlet(tons) Air + Vapour + Solid TSP 649.218 Water 453.1 Sludge 463.317 Exit gas 639.001 TOTAL 1102.318 1102.318
35
4.5.2 MASS BALANCE FOR SSP
1. MIXER To prepare SSP, 75% Sulphuric acid is required. Water at room temperature of 25°C
is mixed with the 98% commercially obtained Sulphuric acid. 0.6 tons of Sulphuric
acid is required to manufacture one ton of SSP,hence, for 50 tons of SSP we require
30 tons of Sulphuric acid at 75% concentration. This is obtained by mixing 22.5 tons
98% Sulphuric acid with 7.041 tons of water.
H2O 2% H2O 25% H2O
98% H2SO4 75% H2SO4
Water M = 453.1 ton T = 25ºC
Air = 639 ton Solid TSP= 1Kg T = 26.4ºC
M = 649.218 ton T = 86ºC Air =639 ton Solid TSP = 18Kg Vapour = 10.2 ton
Sludge Ms = 463.317 ton Water = 463.3 ton Solid TSP = 17 Kg T = 26.4 ºC
Scrubber
36
For I mole of H2SO4 = 98g
Mass in = Mass out
H2SO4 in = H2SO4 out
22.5 tons = 22.5 tons
75% H2SO4 = 22.5 tons
98% H2SO4 = 22.5 tons
2% H2O = (2* 22.5)/ 98
= 0.459 tons
Total mass in = Total mass out
M (H2O) + 0.459 + 22.5 = 30tons
M (H2O) = 30 – 22.959
= 7.041 tons
Components Inlet(tons) Outlet(tons) Water 7.041 + 0.459 7.5 Sulphuric acid 22.5 22.5 Total 30 30
2. CONE MIXER 0.6 tons of ground rock is required per ton of SSP. For 50 tons/hr we require 30 tons
of ground rock mixing it with the 30 tons of Sulphuric acid (75%).
22.5 tons H2SO4
7.5 tons H2O 30 tons 60 tons
28.2 tons Rock 50.7 tons slurry 1.8 tons H2O 9.3 tons H2O
The rock contains 6% moisture and hence this accounts for the 1.8 tons of water in
the in feed to the cone mixer:
6 % (30) = 1.8 tons
Mass in = Mass out
(29.2 + 1.8 + 22.5 + 7.5) = (50.7 + 9.3)
60 tons = 60 tons
37
Component Inlet(tons) Outlet(tons) Ground Rock 30 Sulphuric acid 30 Slurry 60 Total 60 60
3. CONTINUOUS DEN
H2O (v) SiF4
Slurry 50.7 tons rock 4.5 tons H2O 9.3 tons H2O 49.5 tons SSP From literature, we find that there is 10% by mass evaporation of water vapour and
gases from the continuous den to the scrubber,
This accounts for the following mass:
Total mass into the continuous den = 60tons
10% of this mass = (10%)* 60
= 6 tons
Moisture content in the SSP = 4.5 tons
Mass balance for the moisture
Water in = Water out
9.3 tons = H2O (v) + 4.5 tons
Mass of H20 = (9.3 – 4.5) tons
= 4.8 tons
Mass of SiF4 = 1.2 tons (6 - 4.8)
Total mass balance
Mass in = Mass out
(50.7 + 9.3) tons = (1.2 + 4.8 + 4.5 + 49.5) tons
60 tons = 60 tons
Component Inlet(tons) Outlet(tons)
38
SSP 50.7 49.5 Water 9.3 4.5 Gases 6.0 Total 60 60
4. SCRUBBER
Water at 25°C 7.325 tons
13.325 tons
Water = 4.8 tons HF = 1.2 tons
Working with a spray scrubber, from literature, 6gal of water are essential to scrub
1000ft3 of gas
Converting to m3 = 22.71 x 10-3 m3 water / 28.32m3 gas
At 100°C
Density of water = 0.59817 kg/m3
Volume of water = [Mass of water]/ [Density of water]
= 4800/0.59817
= 8024.475m3
Density of Hydrogen Flouride = 1.08 kg/m3
Volume of Hydrogen Flouride = [Mass of water]/ [Density of water]
= [1200]/ [1.08]
= 1111.11m3
Total volume of gas = [1111.11+ 8024.475]
= 9135.586m3
If 28.32m3 gas requires = 22.71 x 10-3 m3 H2O
9135.586 m3 requires = [9135.586] * [22.71 x 10-3]/ [28.32]
= 7.325 m3 H2O
39
At 25°C density of water = 1000kg/m3
7.325 m3 volume in mass = 7325 kg
Component Inlet(tons) Outlet(tons) Slurry 13.325 Water 7.325 Gases (HF & H2O) 6.0 Total 13.325 13.325
5. DRYER
Hot dry air T = 120°C M = 250.093 tons
54 tons 52.365 tons 49.5 tons SSP SSP = 49.365 tons 4.5 tons H2O H2O = H2O = 3.0 tons 100°C Hot air
Vapour = 1.5 tons T = 105°C Solids = 0.135 tons M = 250.093 tons For every 1 ton of SSP, 2.5 kg of solids escape with the hot dry air used for drying
therefore
For 54 tons = 54 * 2.5
= 135kg = 0.135t
Using heat balance:
Heat energy = Mass * Enthalpy
Mass of water evaporated vapour (Mv) = 1.5tons
Enthalpy of steam at 100°C (λ) = 2676KJ/kg°
Q (Energy for Evaporation) MV * λ = 1.5 * 103 * 2676 = 4014MJ
M λ = Mair Cp ∆T
Mair = Mass of hot dry air
Cp of hot dry air at 100°C = 1.07KJ/Kg
Change in temperature (∆T) = 120°C – 105°C = 15°C
1.5 * 1000 * 2676 = Mair * 1.07 * 15
Mair = [1.5*1000*2676]/[1.07*15]
= 250.093 tons
40
Component Inlet(tons) Outlet(tons) SSP 49.5 49.365 Water (Moisture) 4.5 3.0 Air 250.093 250.093 Solids 0.135 Water (Vapour) 1.5 Total 304.093 304.093
6. SCRUBBER Water 25° C
205.625 tons
462.045 tons
250.093 tons air 1.5 tons Vapour 0.135 tons Solids
Working with the principle of a venturi scrubber,
For 28.32m3 gas = 22.71 x 10-3 m3 H2O is required
Volume of air = [Mass of air] / [Density of air]
= [250.093 * 1000] / [0.99]
= 252619.919 m3
Volume of vapour = [Mass of vapour] / [Density of water]
= [1.5* 1000] / [0.394639]
= 3800.942 m3
Volume of solids = [mass of solids] / [Density of SSP]
= [0.135 * 1000] / [1200]
= 0.1125m3
Total volume = [252619.919 + 3800.942 + 0.1125] m3
= 256420.246m3
If 28.32m3 gas requires = 22.71 x 10-3 m3 H2O
256420.246m3 = [256420.246 * 22.71 x 10-3] / [28.32]
= 205.625 m3
Density of water at 25°C = 1000kg/m3
Mass of water required = 205625 kg
Total solution out = [251.728 + 205.625]
41
= 457.353 tons
Component Inlet(tons) Outlet(tons) Slurry 457.353 Water 205.625 Air 250.093 Solids 0.135 Vapour 1.5 Total 457.353 457.353
4.5.3 MASS BALANCE FOR ACID LEACHING PROCESS
1. LEACHING TANK Taking an average of the composition of Lead content in Phosphate rock in Morocco,
Senegal and Togo i.e.
(10 + 17 + 3) / 3 = 10.6 ~ 11ppm
Hence the amount of lead contained in this rock is 0.85Kg
Using the data obtained from Battele arms Field. For 100 000 tons of soil, they used the
following data:
For 10 000 tons
For 50.17 ton
Component % composition Volume(gal) Mass (ton) Mass (ton) HCl 3 62 272 272.704 1.37 NaOH 4 70 060 404.395 2.03 Diatomaceous 0.5 50 ton 50 0.25 Flocculant 0.05 7200 36gal (1.04 ton)
42
2. CLARIFIER Assumption 97% of what is entering leaves down the clarifier.
2% of the overflow is composed of solids.
Component Inlet(tons) Outlet(tons) Solution 52.4 Leachate 1.2 Sludge 51.34 TOTAL 51.54 51.54 3. DEWATERING
M3 = 52.54 ton Pb = 0.85 Kg Solid = 44.29 ton Solution = 8.25 ton
Clarifier
M4 = 51.34 ton Pb = 0.03 Kg Solid = 44.24 ton Solution = 7.07ton
M5 = 1.2ton Pb = 0.82 Kg 2%Solid = 24Kg Solution = 1.17ton
Leachant – HCl M1 = 1.37 ton
Flocculant 1 ton
TSP/SSP M2 = 50.17 ton 6% moisture = 3.0 ton T = 25ºC Pb = 0.85Kg
M3 = 52.54 ton Pb = 0.85 Kg Solid = 44.29 ton Solution = 8.25 ton
Leaching Tank
43
Component Inlet(tons) Outlet(tons) Dewatered sludge 4.34 TSP/SSP 47 Sludge 51.34 TOTAL 51.34 51.34 4. COATING DRUM 6% of total weight of fertilizer is made of coating agent.
Component Inlet(tons) Outlet(tons) TSP/SSP 47 Coating agent 3 Final TSP/SSP 50 TOTAL 50 50
M6 = 51.34 ton Pb = 0.03 Kg Solid = 44.27 ton Solution = 7.07 ton
Dewatering
TSP/SSP M8 = 47 ton Pb = 0.03 Kg Solid = 44.18 ton 6%Moisture = 7 07ton
Dewatered sludge M7 = 4.34ton 2%Solid = 0.09ton Solution = 4.25ton
44
5. PRECIPITATION Assumptions:
82% of the Lead is precipitated.
92% of the inlet leaves at the bottom of the tank.
TSP/SSP M9 = 47 ton Pb = 0.03 Kg Solid = 44.18 ton 6%Moisture = 7.07ton
Coating Drum
TSP/SSP M11 = 50ton Pb = 0.03 Kg Solid = 47.18 ton 6%Moisture = 2.82ton
Coating agent M10 = 3 tons
M12 = M7 + M5 M12 = 5.54 ton Pb = 0.82 Kg Solid = 0.12 ton Solution = 5.42ton
PPT TANK
Bottom M13 = 6.65ton Pb = 0.67 Kg Solid = 2.17 ton Solution = 4.48ton
Overflow M14 = 0.91ton Pb = 0.15 Kg Solid = 0.02 ton Solution = 0.89ton
NaOH 2.03 ton
Flocculant 0.024 ton
45
Component Inlet(tons) Outlet(tons) NaOH 2.03 Flocculant 0.024 Solution 5.54 Overflow 0.91 Bottom 6.65 TOTAL 7.56 7.56 6. CLARIFIER 2
Component Inlet(tons) Outlet(tons) Overflow 1 0.91 Overflow 2 0.02 Bottom 0.89 TOTAL 0.91 0.91 7. DEWATERING 2
Overflow 1 M15 = 0.91ton Pb = 0.15 Kg Solid = 0.02 ton
Clarifier 2
Bottom M17 = 0.89ton Pb = 0.14 Kg Solid = 0.02ton Solution = 0.87ton
Overflow 2 M16 = 0.02ton 2%Solid = 0.4kg Solution = 0.0196ton Pb = 0.01kg
46
Component Inlet(tons) Outlet(tons) Diatomaceous earth 0.25 Dewatered sludge 2.60 Waste water 5.19 Inlet 7.54 TOTAL 7.54 7.54
M18 = 7.54 ton Pb = 0.81 Kg Solid = 2.19ton Solution = 5.35 ton
Dewatering
Dewatered sludge M19 = 2.60ton Pb = 0.81 Kg Solid = 2.39 ton 6%Moisture = 0.16ton
Waste water M20 = 5.19ton 2%Solid = 0.05ton Solution = 5.14ton
Diatomaceous M = 0.25 ton
47
4.6 ENERGY BALANCE
Basis Enthalpy at 25°C is taken to be Zero.
1. GRINDING
It is assumed that the temperature of in-coming rock is 25°C and that the enthalpy of the
rock at this temperature is taken to be 0KJ/Kg.It is also assumed that during grinding 5%
of the power required is lost due to friction in the form of heat energy
I.e. 5% of 1368MJ = 68.4MJ
This energy raises the temperature of the rock and the water it contains, thus
Q = 68.4MJ = MRCPR (T-25) + MWCPW (T-25)
Where MR –Mass of rock
CPR – specific heat capacity of rock (751.86KJ/Kmol degree)
T- Outlet temperature of rock
MW – Mass of moisture content in the rock (6% = 2.28 tons)
CPW- Specific heat capacity of water (4.2KJ/KgK)
H – is the enthalpy
Molecular weight of flouroapatite = 1008gmol, hence total number of moles
(38000/1.008) is 37 698 moles
68.4×1000000 = (T-25) [37698 ×751.86 + 2280× 4200]
T =26.8°C
H2 = H1+ Q = 0 + 68.4MJ
Component Enthalpy(MJ) Enthalpy(MJ) Phosphate Rock 0 Heat energy 68.4 Ground rock 68.4 TOTAL 68.4 68.4
M1 = 38 tons T =25°C H1 = 0 MJ
GRINDING M2 = 38 tons T =26.8°C H2 = 68.4 MJ
Q` = 10KWh/t = 36MJ/t Q =1368MJ
48
2. REACTOR
From the reaction equation in the reactor, it is seen that the heat of reaction is
172.58Kcal i.e.
Ca3(PO4)2 + 4H3PO4 + H2O →3Ca(H2PO4)2.H2O + 172.58 Kcal
And using the most appropriate reaction equation,
Ca10 (PO4)6F2 + 14H3PO4 +10H2O → 10CaH4P2O8.H2O + 2HF
Heat formation (HF) of the reaction components(UNIDO).
Ca10 (PO4)6F2 = 3267.2Kcal/gmol = 13.83GJ
H3PO4 = 308.25Kcal/gmol , hence 14H3PO4 =1.78GJ
H2O = 68.317 Kcal/gmol, hence 10H2O = 0.052GJ
10CaH4P2O8.H2O = 4.504GJ
HF= 75.56Kcal/gmol 2HF = 0.013GJ
Thus the heat of reaction is obtained as
13.83+ 1.78+ 0.052 - 4.504 – 0.013 = 11.14GJ
Component Inlet(GJ) Outlet(GJ) Rock 0.684 Heat of reaction 11.14 Phosphoric acid 0.0 TSP 11.824 TOTAL 11.824 11.824
Phosphoric acid Cp = 2952.6J/KgK = 0.703Kcal/KgK Mp = 31 tons T = 25°C H3 =0MJ Rock
Cp = 751.86J/degmol M = 23 tons H2 = 68.4MJ T = 26.8°C
TSP M` = 54 tons T = 57.6°C H4 = 11.824GJ
Q = 11.14GJ
REACTOR
49
3. MIXER The temperature after steam has been added (in the mixer) to fresh TSP is 90°C
(UNIDO)
Heat given out by steam is
Q/hr = mλ + mCp(100 - 90)
Where m is the mass of steam
= 3200 ×2256.7 + 3200 ×4.2 ×10
= 7355840KJ/hr
At (A) - CP of water is assumed since water is 12%(Cp H3PO4 = 0.703 Kcal/Kgdeg,
Cp Rock = 751.86J/degmol)
7355840 = 54 000 × 4.2 (90 - T)
T = 57.6°C
Components Enthalpy Inlet(GJ) Enthalpy Outlet(GJ) TSP 11.824 Steam 8.56 TSP Slurry 20.39 TOTAL 20.39 20.39
Steam m =3200Kg T = 100°C λ =2256.7 KJ/Kg hg =2675.8KJ/Kg H =8562560 KJ
M` = 54 tons T = 57.6°C H4 = 11.824GJ
M2 = 57.2 ton T = 90°C H = 20.39GJ
A
MIXER
50
4. GRANULATION M2CPW (90 - T) = MWCPW(T-25)
57200(90 -T) = 3500(T-25)
T = 86.3°C
Component Enthalpy(GJ) Enthalpy(GJ) TSP Slurry 20.39 Power for Granulation 4082.4 Water 0.00 Wet TSP 20.39 Motor & Peripheral Motion 4082.4 TOTAL 4102.79 4102.79 5. DRYING The amount of energy required to vaporize the water is Q = MW × λ =10200 ×2279 = 23.2GJ
Mass of air required to vapourize this water is given by
Q = Ma CPa( 120 - 86), CP air = 1.07KJ/Kg/K
Ma = 10200 ×2279000
1070 × 34
Ma = 639 ton/hr
Moisture Enthalpy = 10.2 ×1000 ×256.4 = 261280KJ = 2.61GJ
Since at 25°C the enthalpy was taken to be 0, enthalpy of moisture at 86.3°C is obtained
by deducting that of 25°C from 86.3°C i.e. (361.2 – 104.8KJ/Kg) = 256.4KJ/Kg
Enthalpy of wet TSP = 20.39GJ
M2 = 57.2 ton T = 90°C H = 20.39GJ
Water MW = 3500 Kg T = 25°C H =0KJ
Wet TSP M3 = 60.7 ton T = 86.3°C H = 20.39GJ
Q` = 75.6MJ/t Q = 4082.4GJ
51
Enthalpy of water it contains = 13.2 ×1000 ×256.4 = 3384480KJ = 3.38GJ
Enthalpy of dry TSP = (20.39*106 – 3384480) = 17005520KJ = 17.00GJ
Ratio before drying and after drying = 47.5: 47.3 ~ 1
After drying
Enthalpy of moisture content after drying = 3 × 256.4 ×1000 = 769200KJ = 0.77GJ
Total Enthalpy after drying = Enthalpy of dry TSP + Enthalpy of moisture it contains
= 17.00 + 0.77 = 17.77GJ
Component Enthalpy(GJ) Enthalpy(GJ) Wet TSP 20.39 Heat for Drying 23.25 Dried TSP 17.77 Cooled Stream 25.87 TOTAL 43.64 43.64
Wet TSP M3 = 60.7 ton T = 86.3°C H = 20.39GJ
Dried TSP M3 = 50.3 ton T = 86.3°C H2O 4% = 3ton H = 17.77GJ
Dry Hot Air T = 120°C Ma = 639ton Cp = 1.07 kJ/KgK
Cooled stream M4 = 649.352 ton Moisture Mw = 10.2 ton Solids = 152Kg Air = 639ton T = 86°C H = 25.86GJ
Heat for Drying Q = 23.25GJ
DRYER
52
4.6.2 ENERGY BALANCE FOR SSP
1. MIXER Normally when the acid is diluted a lot of heat is generated, to calculate this heat, we calculate the increase in enthalpy from 25°C to 70°C. Water 0 MJ 0 MJ 70° C
98% H2SO4 Q3 = 2.482 GJ Q5 = 2.482 GJ Heat of solution = MaCpa ( 70 – 25) + MwCpw (70 – 25) Ma = Mass of acid = 22.44 tons Cpa = Specific heat capacity of acid =1.4kJ/kg K Mw = Mass of water = 7.56 tons Cpw = Specific heat capacity of water = 4200kJ/kg K = 22.44 x 1000 x 1.4 x ( 70 – 25) + 7.56 x 1000 x 4.2 ( 70 – 25) = 2.842 GJ Q3 = 0 + 0 + 2.482 = 2.482 GJ Component Enthalpy(GJ) Enthalpy(GJ) H2SO4 0 Water 0 Heat of Dilution 2.48 Enthalpy of Solution 2.48 TOTAL 2.48 2.48 2. CONE MIXER Ca3 (PO4)2]3CaF2 + 7H2SO4 + 3H2O → 3[CaH4 (PO4)2.H2O] + 7CaSO4
Heat formation (HF) of the reaction components(UNIDO).
Ca10 (PO4)6F2 = 3267.2Kcal/gmol = 13.83GJ
H2SO4 = 193.91Kcal/gmol hence 7H2SO4 = 0.558GJ
CaSO4 = 483.06 Kcal/gmol hence 7CaSO4 = 1.93GJ
H2O = 68.317 Kcal/gmol, hence 3H2O = 0.0152GJ
3CaH4P2O8.H2O = 1.3512GJ
HF= 75.56Kcal/gmol 2HF = 0.013GJ
53
Heat of reaction is thus obtained,
13.83 + 0.559 + 0.0156 – 1.3512 – 1.93 – 0.013 = 11.11GJ
H2SO4 70°C Q5 = 2.482GJ Rock Slurry 100°C
Q6 = 13.646GJ Q3 =54 MJ QR Working backwards, Enthalpy of the slurry at 100°C is obtaining by using the enthalpy of water at 100°C QR = Heat of reaction QR = 11.11GJ Q6 = Q3 + Q5 + QR therefore = 0.054 + 2.482 + 11.11 = 13.646GJ Component Enthalpy(GJ) Enthalpy(GJ) Rock 0.05 Enthalpy of Solution 2.48 Slurry 13.65 Heat of reaction 11.11 TOTAL 13.65 13.65 3. CONTINOUS DEN 60 tons of fresh SSP Q6 Q8 H = 12.84GJ 100°C 100°C HF = 1.2 tons Water,M1 = 4.8 tons
Mw = 54 tons SSP Q7 Assuming the enthalpy of water Mw = Mass of water M1 = Mass of water Vapour λw = Enthalpy at 100°C (Saturated vapour) Q8 = 4800 x 2676 = 12.84 GJ
54
Q7 = Q6 –Q8 = 13.646 -12.84 = 0.806GJ Component Enthalpy(GJ) Enthalpy(GJ) Slurry 13.65 Water 12.84 Wet SSP 0.81 TOTAL 13.65 13.65 4. SCRUBBER 0MJ Water 25°C Q8 100°C Q10 HF = 1.2 t Solution Water = 4.8t As obtained earlier, Q8 = 12.84GJ Q10 = Q8 + Q9 = 12.84 + 0 = 12.84GJ Component Enthalpy(GJ) Enthalpy(GJ) Gases 12.84 Water 0 Solution 12.84 TOTAL 12.84 12.84 5. DRYER
Hot dry air
T = 120°C M = 250.093 tons
54 tons 52.365 tons 49.5 tons SSP SSP = 49.365 tons 4.5 tons H2O H2O 3.0 tons 100°C Hot air
Vapour = 1.5 tons Q = 4.014GJ T = 105°C Solids = 0.135 tons Heat energy = Mass * Enthalpy
55
Mass of evaporated vapour (Mv) = 1.5tons
Enthalpy of steam at 100°C (λ) = 2676KJ/kg°
Q (MV λ) = 1.5 * 103 * 2676 = 4014000KJ
Heat of Drying = 4.014GJ
MV λ = Mair Cp ∆T
Mair = Mass of hot dry air
Cp of hot dry air at 100°C = 1.07KJ/Kg
Change in temperature (∆T) = 120°C – 105°C = 15°C
1.5 * 1000 * 2676 = Mair * 1.07 * 15
Mair = [1.5*1000*2676]/[1.07*15] = 250.093 tons
Moisture Enthalpy at 25°C = 1.5 ×1000 ×335.474 = 503211KJ = 0.503GJ
Since at 25°C the enthalpy was taken to be 0, enthalpy of moisture at 105°C is obtained
by deducting that of 25°C from 105°C i.e.
(440.274 – 104.8KJ/Kg) = 335.474KJ/Kg
Enthalpy of wet TSP = 0.806GJ
After drying
Enthalpy of moisture content after drying = 3 × 335.474 ×1000 = 1006422KJ = 1.01GJ
Total Enthalpy after drying = Enthalpy of dry SSP + Enthalpy of moisture it contains
= 0.806 + 1.01 = 1.816 GJ Component Enthalpy(GJ) Enthalpy(GJ) Wet SSP 0.81 Heat for Drying 4.01 Dried SSP 1.82 Cooled Stream 3.00 TOTAL 4.82 4.82
56
CHAPTER FIVE
5.0 EQUIPMENT SPECIFICATION
1. Conveyor Belt This design requires six conveyor belts BC1 BC2 BC3 BC4 BC5 BC6
Diameter(m) 1 1 1 1 1 1
Length 46 49 47 45 48 50
Material Flexible rubber
Flexible rubber
Flexible rubber
Flexible rubber
Flexible rubber
Flexible rubber
2. Ball Mill Length - 4.25m
Diameter - 9.84ft
Power - 10kwh/ton
Balls diameter – 25 -125mm
Material - Carbon Steel
3. Cyclone Diameter - 1.1m
Length of cylinder - 2.2m
Length of cone - 2.2m
Height of entrance - 0.55m
Width of entrance - 0.275m
Diameter of exit cylinder - 0.55m
Diameter of dust exit - 0.275m
Number of revolutions - 6
Flow rate - 649.35 tons/hr
Material - Carbon Steel
4. Scrubber 1 Type – Circular spray tower
Gas flow rate – 365 399ft3/min
Water flow rate – 15792.5ft3/min
Material for construction – Carbon Steel & API
57
Pressure – Atmospheric pressure
Volume - 452m3
Diameter – 4m
Height – 36m
Mist eliminator – 33m height
5. Scrubber 2 Type – Circular spray tower
Gas flow rate – 5907.51ft3/min
Water flow rate – 7166.84ft3/min
Material for construction – Carbon Steel & API
Pressure – Atmospheric pressure
Volume – 204m3
Diameter – 3m
Height – 29m
Mist eliminator – 27m height
6. Leaching tank Flow rate – 52540kg/hr
Diameter – 3m
Height – 4m
Volume – 57m3
Material – Carbon Steel & API
Type - Vertical, cone roof and flat bottom
7. Agitator for leaching tank Type – Paddle with 4 arms
Power – 4.9Kw
Diameter – 1m
Rotation- 2.2rev/s
8. Storage tank Flow rate – 50170kg/hr
Diameter – 3m
58
Height – 6.83m
Volume – 48.30m3
Material – Carbon Steel & API
Type - Vertical, cone roof and flat bottom
9. Mixer 1 Flow rate – 30000kg/hr
Diameter – 3m
Height – 2.93m
Volume – 20.7m3
Material – Carbon Steel
Type - Jacketed and Non-agitated
10. Mixer 2 Flow rate – 60000kg/hr
Diameter – 3m
Height – 8.1m
Volume – 55.27m3
Material – Carbon Steel
Type - Mixer & Settler
11. Cone Mixer Flow rate – 30000kg/hr
Diameter – 3m
Height – 7m
Volume – 49.41m3
Material – Carbon Steel
Type - Mixer & Settler
12. Reactor Flow rate – 23000kg/hr
Diameter – 3m
Height – 4.5m
Volume – 32.20m3
59
Material – Carbon Steel
Type - Jacketed & Agitated
13. Agitator for Reactor Type – Paddle with 4 arms
Power – 6.3 Kw
Diameter – 1m
Rotation- 2.2rev/s
14. Continuous Den Flow rate – 60000kg/hr
Width – 3m
Length – 4m
Volume – 65m3
Material – Carbon Steel
Type - Mixer & Settler with screw conveyor
15. Vibrating screen Vibrations – 3600 vibrations/min
Screen diameter- 1.2m
Size of openings- 4mm
Feed rate – 50300kg/hr
Type – 1-deck
Deck area - 742ft2
Material - Carbon steel with light carbon steel wire
16. Coating drum Flow rate – 50000kg/hr
Diameter – 3m
Height – 8.3m
Volume – 59m3
Material – Carbon Steel
Type - Horizontal & round
17. Pump
60
Centrifugal pump
Type - Vertical turbine, 1-stage
Diameter - 6inches
Height - 22m
Length - 30m
Efficiency - 40%
Flow rate - 68.22m3/hr
Material - Cast Iron & API
Power - 20hp
18. Rotary Drier Design feed capacity 60700kg/hr
Volume flow rate of air 639M3/s
Slope of the shell 1in/ft
Diameter – 3m
Length – 6m
Type – Rotary, direct, Gas-fired with flights
Area – 55.65m2
19. Plate and Frame filter Plates – Rectangular and vertical
Plate area - 40cm x 40cm
Filter medium- Carbon Steel
Frame thickness – 5cm
Material – Cast Iron
Number of plates – 70
Area of filter – 121.25ft2
20. Precipitator Diameter – 3m
Area – 28.27m2
Height – 0.22m
Material – Carbon Steel
61
21. Agitator for Precipitator Type – Paddle with 4 arms
Power – 5.77Kw
Diameter – 1m
Rotation- 2.2rev/s
22. Rortification tank Flow rate – 20kg/hr
Diameter – 3m
Height – 3m
Volume – 57m3
Material – Carbon Steel & API
Type - Vertical, cone roof and flat bottom
23. Clarifier Flow rate – 12.3kg/s
Height – 0.49m
Area – 266.5m2
Material – Carbon Steel & API
Type - Vertical, cone roof and flat bottom
24. Agitator for clarifier Type – Paddle with 4 arms
Power – 5.3Kw
Diameter – 1m
Rotation- 2.2rev/s
25. Crusher Size range - 20 -200
26. Bag House Type – Fabric filter dust collector
Flow rate – 2ft/min
Particle size range – 74 – 1micrometer
27. Granulator Motor – 300hp
Feed – 57.2 tons
62
CHAPTER SIX
6.0 EQUIPMENT DESIGN
6.1 CYCLONE DESIGN
6.0 INTRODUCTION...................................................................................................62 6.1 CYCLONE DESIGN..................................................................................................62 6.2 CYCLONE LAYOUT .................................................................................................64 6.3 MECHANICAL DESIGN............................................................................................65 BY JOY BUSOLO CPE/21/99
63
6.1.1 INTRODUCTION A significant challenge in many fertilizer processing plants is to minimize air pollution
caused by dust fertilizer particles that could be carried in air. Dust separation mechanism
that offers effective pollution control is thus needed.
The available particulate control equipment available includes:
6.1.2 Gravity settling chambers Gravitational force is employed to remove particulate in settling chambers. Gravity
collectors are generally built in the form of long, empty, horizontal, rectangular chambers
with an inlet at one end and an outlet at the side or top of the other end. The difference
in densities between the solid particles and the transport gas acts as the driving force.
6.1.3 Wet collectors In a wet collector, a liquid, usually water is used to capture particulate dust or to increase
the size of aerosols. In either case the resulting increased size facilitates the removal of
the contaminant from the gas stream. Fine particulate, both liquid and solid ranging from
0.1 to 20 micrometers can be effectively removed from a gas stream by wet collectors.
6.1.4 Electrostatic precipitators When particles suspended in a gas are exposed to gas ions in an electrostatic field, they
will become charged and migrate under the action of the field. The functional
mechanisms of electrical precipitation may be listed as follows:
1. Gas ionization
2. Particle collection
a. Production of electrostatic field to cause charging and migration of dust
particles
b. Gas retention to permit particle migration to a collection surface
c. Prevention of re-entrainment of collected particles
d. Removal of collected particles from the equipment
There are two general classes of electrical precipitators:
(1) Single stage, in which ionization and collection are combined
(2) two-stage, in which ionization is achieved in one portion of the equipment, followed
by collection in another.
64
6.1.5 Impingement/Inertial separators Impingement separators are a class of inertial separators in which particles are
separated from the gas by inertial impingement on collecting bodies arrayed across the
path of the gas stream. Fibrous-pad inertial impingement separators for the collection of
wet particles are the main application in current technology. With the growing need for
very high performance dust collectors, there is little application anymore for impingement
collectors that catch large amounts of dry dust.
6.1.6 Centrifugal separators
6.2 CYCLONE DESIGN Cyclone separators are gas cleaning devices that employ a centrifugal force generated
by a spinning gas stream to separate the particulate matter from the carrier gas. In this
case air is used to separate TSP solid particles from the cooled stream from the dryer.
The solid particles are taken back to the process for recycle while the gas goes to the
scrubber for further cleaning.
There are two types of cyclones
The cyclone in question is a 2D2D single chamber rectangular inlet involute type.
6.2.1 Operation principle Once the gas is introduced into the cyclone through the rectangular inlet, the circular
motion of the gas is attained as a result of the tangential gas inlet. The rectangular
involute inlet passage has its inner wall tangent to the cylinder and the inlet blends
gradually with the cylinder over a 180° involute. The operation depends on the tendency
of the particles to move in a straight line when the direction of the gas stream is
changed. The particles then slide down the walls and into the storage hopper. The
gradually cleaned gas reverses its downward spiral motion and forms a smaller
ascending spiral.
6.2.2 Flow pattern In a cyclone the gas path involves a double vortex with the gas spiraling downward at
the outside and upward at the inside. When the gas enters the cyclone, its velocity
undergoes redistribution so that the tangential component of velocity increases with
decreasing radius. Tangential velocity approaches zero at the walls while radial velocity
65
is directed toward the center throughout most of the cyclone, except at the center, where
it is directed outward.
[v1/v2] = [r1/r2 ]0.7
The performance of a cyclone can be measured in terms of efficiency using
6.3 MECHANICAL DESIGN 1. Diameter of cyclone (Dc)
218
=
inC V
QD
Where
Q = volumetric flow rate of gas into the cyclone
Vin = velocity of inlet gas
Q = 639000 kg/hr
639000 / 4 = 159750 kg/hr
159750/1.149 = 139033.9 m3/hr
139033.9/3600 = 38.62 m3/s
Vin = Q/A
Where A = inlet area
= 38.62/0.15125
= 255.34 m/s
Dc = [(8 * 38.62)/255.34]1/2
= 1.1m
This diameter is used to determine several design parameters for the cyclone
according to the following correlations
66
Diameter - 1.1m
Length of cylinder, Lc - 2.2m
Length of cone, Zc - 2.2m
Height of entrance, Hc - 0.55m
Width of entrance, Bc - 0.275m
Diameter of exit cylinder, De - 0.55m
Diameter of dust exit, Jc - 0.275m
2. Number of revolutions (Ne)
[ ]2/1CCe ZLHN +=
= 1/0.55 [ 2.2 + 2.2/2]
= 6
3. Particle diameter (dp)
( )( )[ ]gpinep VNWd ρρµ −Π= /9
67
where
µ = viscosity of air at 86°c = 0.0002 Pa
Bc = inlet width = 0.275
ρp = density of particles = 1100kg/m3
ρg = density of air at 86°C = 1.149kg/m3
dp = √[9*0.00002*0.275/(3.142*6*255.34(1100 – 1.149))]
= 2.163 * 10-6m
4. Radial velocity of air
RVdV inpPr µρ 18/22=
= (1100*(2.163 * 10-6)2*(255.34)2)/(18*0.0002*0.55)
= 1.7m/s
5. Efficiency of a cyclone
η = [1 – (Amount of dust in the outlet stream/Amount of dust in the inlet stream)] * 100
= [ 1 – (18/152) ] * 100
= 88%
6. Pressure drop
( )[ ]{ }VerrKVP eting 21/221203/ 22+−+=∆ ρ
Where
K = function constant
rt = radius of which the centerline is tangential
re = radius of exit pipe
Ve = velocity of exit dust
To obtain K,
( )tsC AAF /=ϕ
Fc= friction factor which is taken as 0.005 for gases
As= surface area of cyclone exposed to the surface area of a cylinder with the
same diameter as the cyclone and length equal to the total height of the
cyclone (barrel and cone)
2πr (Zc + Lc)
= 2 * π * 0.55 (2.2 + 2.2)
= 15.20m2
A1 = area of inlet duct
= 0.55 * 0.275
68
= 0.15125m2
Φ = 0.005 * (15.20/0.15125)
= 0.5
rt/re = 0.275/0.1375
= 2
From tables, we obtain the cyclone pressure drop factor (K) using rt/re as 2 and φ
as 0.5.
K = 1
∆P = 1.149/203 {255.342 [1 + 2(1)2(2*2) – 1] + 2 * 1.72}
= 10.14 millibars
= 1014Pa
7. Cyclone thickness
( ) CPSEPDt YOm ++= 2/ where
P = Pressure
Do = Diameter of cyclone
C = corrosion allowance
E = Joint quality factor
S = maximum tensile strength
Y = coefficient having value in for ductile ferrous materials
= {(14.7 * 43.30) / 2[(60 000 * 0.85) + (14.7*0.6)]} + 0.1
= (636.6129/102017.64) + 0.1
= 0.10627inches
= 2.7mm
69
6.4 ROTARY DRYER DESIGN
BY NYONJE ISAAC ODHIAMBO CPE/10/99
TABLE OF CONTENTS
6.4 ROTARY DRYER DESIGN...................................................................................69 6.4.1 INTRODUCTION................................................................................................70 6.4.2 DYER CONSTRUCTION ....................................................................................70 6.6 MECHANICAL DESIGN........................................................................................73
70
6.4.1 INTRODUCTION
Drying theory When a surface is completely covered with water, the drying is fairly constant, and this
period is called the “constant-rate period”. The dry-bulb temperature minus the wet-bulb
temperature is the potential for heat transfer. The pressure at the wet bulb temperature
minus the pressure at the dew point is the potential for mass transfer.
The higher the temperature of the inlet gas stream, the higher the efficiency of the dryer
in general.
The equilibrium moisture content of any substance will depend upon temperature and
humidity of the surrounding and will vary according to the material. The temperature of
the material remains at the wet bulb temperature for as long as the moisture is being
removed, by which time the dry bulb temperature will have fallen to a point at which it
has no harmful effect on the product.
Types of Rotary Dryers The following are the types of dryers:
Drum dryers, Rotary dryers, Tunnel dryers, Spray dryer, Pneumatic dryers, Fluidized-
bed dryers, Turbo-shelf, Tray dryers -shelf, Disc dryers and Tumble Dryers.
Choice of Dryer More material is dried in rotary dryers than any other type of dryer. Lasts for years
without maintenance problems and their efficiency is also high.
Rotary Drying It is mounted at a modest angle with the horizontal so that any feed material introduced
at the upper end will travel to the lower or discharge end. The ratio of length to diameter
of the shell may vary widely from as high as 10 or 12 to 1 or as low as 2 to1.Most dryers
have flights or lifters placed spirally or parallel along the length of the shell. Heat is
usually supplied through the introduction of hot air. About 50-70% of he volume is filled
with the material to be dried and the internal pressure is between 1 -10Kpa.
6.4.2 DYER CONSTRUCTION Fabrication is done by carbon, stainless or other alloy with reinforced bands for fitting
and drive rings. Flight or lifters are welded or bolted internally to provide the required
degree of contact between the material and the drying air.
71
The drum rotates on cast iron or steel tyres, supported on forged or cast steel supported
rollers with shaft mounted. All rollers assemblies are fitted with safety guards and
lubrication where appropriate.
The dryer drum is rotated by an electric motor through V-belts, gear box pinion and
either heavy duty chain to a chain wheel. Integral low speed auxiliary drives can be
supplied for emergency or maintenance purposes.
6.4.3 Process Control Product moisture content can be controlled through control of exhaust air temperature.
This control is achieved by regulating the flow of fuel to the burner by means of a
temperature controller with a thermocouple located in the exhausted air duct.
The evaporation load may be controlled by measurement of inlet air temperature using a
second controller with temperature probe located in the inlet air duct and output signal to
a variable rate feeder.
6.4.5 Dryer Design 6.4.5.1 Design Consideration The general procedure for design of the rotary dryer is as outlined below.
1. Calculating the amount of heat required to achieve the desired reduction of moisture
at the design throughput.
2. The diameter of the dryer drum is therefore related to the quantity of air required for
drying.
3. The length of the dryer is related to the time required to the effect the transfer of heat
from the drying air stream to the material being processed and the time required to effect
the transfer of the masses of water evaporated from the material to the drying air stream.
4. Mechanical specifications (dryer drum plate thickness, tyre dimensions, support roller
loadings, shaft and bearing capacities as drive power requirements).
6.4.5.2 Heat Load Moisture content of fertilizer is reduced from 21.7 -6%.At T= 86.3°C,heat of evaporation,
λ = 2279KJ/Kg, it is assumed that this heat is used only for evaporation. The total
amount of moisture to evaporated is, m = 10.2 tons,
Thus QD = mλ = 102000kg × 2279KJ/Kg = 23.3GJ/hr
Where QD – is the amount of heat energy required to vaporize the water.
72
6.4.5.3 Amount Air required for Drying. Hot dry air enters at T1 = 120°C
Air leaves at T2 = 87°C
Hence ∆T = (T1-T2) = 33°C
Heat given out by dry air is given by
TCMQ PairAIR ∆=
Where CP – specific heat capacity of air = 1.07KJ/KgK
but QD = QAIR = 23.2GJ/hr = 22002880Btu/hr
thus Mair = G = (QAIR /Cp∆T) = (10200×2279)/(1070×33) = 658 ton /hr = 182.8 Kg/s
6.4.5.4 Diameter of the Dryer Drum Estimated diameter of the dryer is
D = 3.0m = 9.8424 ft, but ( ) 5.0/4 SGGD Π= where
G – gas flow rate Kg/s
GS – gas flow rate Kg/sm2
Thus GS = (4×182.8)/(π×9) = 25.85Kg/sm2 = 0.0235m3/sm2 = 19027 lb/hft2
Number of transfer units Nt is given by
( ) ( )PerrytmTTN t ∆−= /21
∆tm = logarithimic- mean temperature difference = (34 – 1.7)/(ln34/1.7) = 10.8K
∆t1 = 120 – 86 = 34K
∆t2 = 88 -86.3 = 1.7K
Hence Nt = (120-88)/10.8 = 2.96
The rate of heat transfer is given as
( )PerrytmLDGtmVGQq SDt ∆Π=∆== 67.067.0 125.05.0
where D – diameter of dryer(ft), L – dryer length(ft),V- dryer volume(ft3)
L = 22002880 /(0.125×9.8424×190270.67×10.8) = 715ft = 218m
But universally, 4< L/D <12 , hence 218/3 = 72
This requires more than i dryer to bring the ratio to acceptable level,
using 4 dryers instead of1, we get GS = (19027 / 4) = 4756.75 lb/hft2
qt= (22002880 / 4) = 5500720Btu/hr
hence L = 452.9ft = 138m , now L/D = 138/3 = 46 > 12, still more
for 5 dryers,
L = 420.8ft = 128m, L/D = 42.8 >12
73
For 6 dryers,
L = 396ft =120m, L/D = 40
Taking 6 dryers with L = 40m, D = 3m
The hold up which is given as percentage of dryer volume is obtained as
= DSNFX 9.07.25
Where D – Diameter,m – 3.0m
F - Feed rate m3/sm2(0.0235 / 6 = 0.0039m3/sm2)
S – slope of the dryer (m/m length = 0.083)
N – is the rate of rotation(HZ)
X – is the hold up, (50 -70%), taking 50%
) 9.017.25 FXSDN
=
= (0.5× 0.083× 9.8424 /25.7× 0.0039)1/0.9 = 0.246HZ = 12.6rpm
Which is within the acceptable value i.e 5 -35rpm
Summary of Chemical Dryer Design Dryer type : Rotary drum dryer
Diameter: 3m (9.8424ft)
Length : 40m (131.2ft)
Speed : 12.6 rpm
Operating Pressure: 11KN/m2
Material of Construction: Low Carbon steel
Flight: Radial with 90° lip
Inlet air temp. : 120°C
Hold up: 50%
Number of transfer units: 2.96
6.6 MECHANICAL DESIGN Material of construction is low carbon(mild) steel whose typical mechanical and physical
properties are given below(Lloyd,1986)
E – Young’s modulus of elasticity = 207 GN/m2
G – Shear modulus = 80GN/m2
бy – Elastic limit = 280MN/m2
٢y - Shear yield strength =175MN/m2
74
Tensile strength =480MN/m2
Ultimate strength in shear = 350MN/m2
Percentage elongation = 25%
Density = 7800Kg/m3
Linear coefficient of thermal expansion = 11.7×10-6
Design stress (f) at 100°C = 125N/mm2
6.6.1 Thickness of the Drum If Di – is the internal diameter, the minimum thickness, then, the mean diameter will be
(Di + t ).
Thickness, is given as (Coulson,1996)
( ) )
−=i
iiPf
DPt 2
where Pi(11KN/m2) – internal pressure , f(125N/mm2) – the design stress
= (0.011×3000) /(2×125 – 0.011)
= 0.132mm
A much thicker wall will be required at the column base to withstand dead weight loads.
The nominal thicker for a 3m diameter is 10mm (Coulson,1996).
Hence taking t = 10mm,
6.6.2 Dead weight of the vessel Coulson (1996) gives the formula
( ) 3108.0( −×+Π= tDHgDCW MVMMVV ρ
where Wv – total weight of the drum excluding the flights. CV (1.15) - a factor to account
for the weight flights and internal supports. HV – Length of dryer = 40m
t – wall thickness, ρm – density of material (7800Kg/m3) , Dm – mean diameter of
vessel(3 + 10×10-3) = 3.01m
Wv = π×7800×9.81×10-3×1.15×3.01(40 + 0.8×3.01)×10 = 352 KN
6.6.3 Analysis of stress (Hearn,1997) 6.6.3.1 Hoop or Circumferential stress,бH
tPDH 2/=σ where P – internal pressure, t- thickness, D- internal diameter
= (11×3000) / (2×10) = 1650 KN/m2
For a thin rotating cylinder, бH = ρω2r2 = 7800×1.542×1.52 = 27952N/m2
Since fΠ= 2ω = 1.54 rads/s
6.6.3.2 Longitudinal Stress бL
75
2/8254/ mKNtPDL ==σ
6.7 Design of Flat ends The minimum thickness required is given by
( )fpDCe eP /= = 0.55×3000×√(0.011/125) = 1.54mm
where
eP DC 55.0= ,De = D (nominal plate diameter)
6.8 Saddle Supports A vessel supported on two saddles, maximum stress occurs at the supports and at the
mid-span. The saddles supports will be located near the ends.
6.8.1 Stress in the vessel wall, бb1
( )tDLb 2/41 Π×= σσ = (4 × 825) /(π×9×10×10-3) = 11671KN/m2
76
CHAPTER SEVEN
7.0 PROCESS CONTROL AND INSTRUMENTATION
7.1 PROCESS CONTROL A process forms a set of production or processing functions executed in and by means
of process hardware such as tanks, pipes, fittings, motors, shafts, couplings, measuring
devices etc.
The performance of an industrial process is influenced by internal and external
conditions called process variables which include:
Energy variables temperature, pressure, electricity, sound and radiation.
Quantity and rate variables fluid flow, liquid level, weight, thickness and speed.
Chemical and physical characteristics density, humidity, moisture content, viscosity,
calorific value, colour, electrical and thermal conductivity, chemical absorption, refractive
index, x-ray diffraction, polarity, PH, oxidation-reduction potential.
7.1.1 CHARACTERISTICS OF INSTRUMENTATION SYSTEM. Measurement systems are designed to accurately detect changes in parameters
encountered in industrial process such as pressure, fluid flow, motion resistance,
voltage, current and power.
The information they generate facilitate the manual or automated control.
7.1.2 PROCESS CONTROL. In a processing plant, the above listed variables need to be controlled. One of the first
consideration is to categorize all the system inputs and outputs into those which can be
controlled, those which may be adjusted to achieve this control, and those which are
beyond the control of the designer.
The control of the process variables is achieved by the control instrument e.g.
electromagnetic valves, transformer trap positions etc. The process control is, therefore,
an engineering science of measuring one or more of these process variables and
automatically controlling them to the desired level called set points or reference points in spite of disturbance.
77
7.1.3 CLASSIFICATION OF CONTROLLERS The three types of controllers depending on the actuating medium are described below;
1. Pneumatic controllers’ i. Displacement sensing devices (pneumatic nozzle-
flapper); ii. Pneumatic relays
2. Hydraulic controllers. 3. Electrical controller.
7.1.4 MODES OF CONTROL ACTIONS A controller is used to eliminate or reduce error (difference between set point and the
measured output) by generating a correction signal to the final control element. Modern
industrial controllers are usually made to produce one or a combination of six basic
control actions i.e.
1. On –off or two position action
2. Proportional control action
3. Integral control action
4. Derivative control action
5. Proportional plus Integral (PI) control action
6. Proportional plus Integral plus Derivative (PID) control action
For this project, the system employed to control the process are;
• Automatic control which are electrically operated
• Direct digital (electronic) control which uses the PID.
7.1.5 CONTROL SEQUENCES The integrated system control will involve such operations as interlocking, timing and
recording. These are particularly important during such operation times such as start up,
shut down and change of operating capacity. Timers and relays should be used in these
operations.
Typical Control Of Unit Operation In all the unit operations to be performed, it requires the control of parameters such as;
• Pressure The pressure measurement method used in this project will be – Electrical pressure
transducers – which uses elastic primary sensing elements such as the Bourdon tube,
Bellows and Diaphragm’
78
These are mostly used pressure gauge because of their simplicity and rugged
construction. Covers ranges from 0-15psig to 0-100 000psig,as well as vacuum from 0 to
30 inches of mercury,
• Temperature Temperature controllers used for this project is thermostat and the instrument for
measuring the temperature would be thermocouple due their sensitivity.
• Flow rates concentrations of streams A number of measurements are used for determining the chemical composition. The
measurement of these variables is based on; Electromagnetic radiation, chemical
reactions, current, voltage or flux changes produced in energized electric and magnetic
circuits and the result of applying thermal or mechanical energy to a system.
• Level of liquids For the project, sight-glass and electrical method of measurement will be used.
• Alarms Alarms will be used to draw the attention of the operator to the process whenever
there is any disturbance /deviations caused by the change in one of the parameters to
be monitored in the equipment.
7.2 CONFIGURATION OF THE PROCESS CONTROLS 7.2.1 CONTROLS The main control parameters to be monitored in the plant would be pressure,
temperature,
composition, level and feed flows. Major equipment in the plant will be used to discuss
the controls.
1. Ball Mill It is used to grind the phosphate rock. There are a number of variables that can change
causing the operation to deviate from its desired value. Therefore, action must be taken
to control any deviation so as to maintain the outlet flow rate at its desired value F (t).
An automatic control can be achieved by measuring the flow rate using a flow sensor
comparing the value with the set point and the deviation corrected.
79
Flow Control in Ball Mill
2. Mixing Tank
This tank mixes the controlled flow of Sulphuric and water to produce dilute acid. A
desired flow rate of concentrated acid and diluting water is to be maintained. An
automatic control is achieved by measuring the flow rates using a flow sensor,
comparing the value with the set point and any deviation is corrected.
80
Control of the Mixer
3. Dryer The dryer receives granulated wet grains mixture from granulator and by hot gas, the
water content is lowered to an amount maintained at some desired level. This is
achieved automatically through utilization of a feed flow sensor to measure the flow rate.
Deviations are corrected by adjusting the inlet and outlet valves appropriately.
Control for Dryer
81
4. Reactor A desired flow rate of phosphoric acid rock products is to be maintained by opening or
closing the outlet valve. The automatic control is achieved by measuring the flow rate
using a flow sensor, comparing the value with the set point value and by deviation
adjusts the flow tare appropriately. A sight glass, pressure and temperature indicators,
lump are also fitted to enhance control.
Control for Reactor
6. Scrubber A desired concentration of exit gas is to be maintained. The automatic control can be a
achieved by measuring the concentration using a concentration sensor, comparing the
value with the desired (set point) value and adjusting the water inlet flow accordingly.
82
7. Leaching Tank A desired flow rate of hydrochloric acid, flocculant and the dry fertilizer is to be
maintained by opening or closing the inlet valve. When a disturbance such as change in
feed flow of inlets and concentration of acid occur, the automatic control can be
achieved by measuring the flow and concentration sensors, comparing the values with
the set points and adjusting the values appropriately.
FC
FC
Control for Leaching Tank
8. Pumps A desired flow rate is to be maintained by opening or closing the outlet valve. The disturbance may occur include flow changes. The automatic control may be achieved by
measuring the flow rate using a flow sensor, comparing the value with the set point
and adjusting the fluid outlet appropriately.
83
9. Plate and Filter Frame This is used to dewater the wet fertilizer. This is achieved by controlling feed flow of
fertilizer and the filter aid. The disturbance may include changes in flow .The automatic
control can be achieved by measuring the inlet flow rate. By putting a flow sensor and
comparing the value with the set points, adjustment of the values can be done
appropriately.
PF1
Control for Plate and Frame Filter
CC
84
CHAPTER EIGHT
8.0 ECONOMIC ANALYSIS
8.1 INTRODUCTION A design engineer, by analysis of costs and profits attempts to predict whether capital
should be invested in a particular project. This is done with the assumption that the
original cost predictions will agree with the facts obtained during implementation.
This chapter looks into the economic aspects of the plant. The viability of the project
would be tested by doing the profitability analysis. The equipment cost used is obtained
from www.matche.com giving costs as per year 2003 in relation to their physical
dimension.
8.2 PLANT SPECIFICATION Start of construction 2006
Completion is end of 2007
Commencement of operation 2008
Expected plant life is 15 years
Operation conditions are as follows:
• The plant operates in a 24 hour basis with 3 shifts of 8 hours each, 300 days a
year at 100 % capacity
• Production costs will increase at a rate of 4% per annum and selling price will
increase by 11% by the end of the 15th year.
• Salvage value is 12% of fixed capital investment
• Sum –of- the years digit method will be applied to calculate the depreciation
• An operation running at 100% capacity is equal to 50tons per hour and 1200 tons
per day.
• The cost index for 1990 is 356 while that for 2003 is 405.
8.3 ECONOMIC EVALUATION Consideration is given to the following factors while carrying out the economic
evaluation.
1. FIXED CAPITAL INVESTMENT [FCI] This is the capital needed to supply the necessary manufacturing and plant facilities.
Manufacturing FCI includes equipment with all auxiliary, piping, instrumentation,
85
insulation, foundation and site preparation. While the non-manufacturing FCI consists of
land, processing buildings, administrative offices, warehouse, laboratories,
transportation, shipping and receiving facilities.
2. WORKING CAPITAL [WC] This is the amount of money used to operate the plant. It consists of costs of raw
materials, finished products in stock , semi-finished products, accounts receivable, cash
kept at hand for salaries and wages, accounts and taxes payable.
3. TOTAL CAPITAL INVESTMENT [TCI] This is the sum value of working capital and fixed capital investment.
TCI = FCI + WC
Total product cost [TPC]
It consists of the following cost
i) Manufacturing cost
• Direct production costs
• Fixed charges
• Plant overhead costs
ii) General expenses
• Administrative expenses
• Distribution and marketing expenses
86
1. DELIVERED EQUIPMENT COST EQUIPMENT NUMBER COST (2003)
US $
TOTAL US $
(2003) Conveyor belt 6 90 800 544 800
Ball Mill 1 807 000 807 000
Cyclone 4 319 600 1 278 400
Scrubber 4 646 600 2 586 400
Scrubber 1 18 800 18 800
Agitator for scrubber 1 5 800 5 800
Leaching tank 2 19 900 39 800 Agitator for leaching tank 1 5 800 5 800
Storage tank 2 17 900 35 800
Mixer 1 1 21 000 21 000
Mixer 2 1 322 100 322 100
Cone mixer 1 306 400 306 400
Reactor 1 83 400 83 400
Agitator 1 5 600 5 600
Continuous den 1 9 900 9 900
Vibrating screen 2 125 000 250 000
Coating drum 1 25 300 25 300
Pump 8 3 100 24 800
Rotary drier 4 209 900 839 600
Plate & frame filter 4 47 700 190 800
Precipitator 1 123 900 123 900 Agitator for precipitator 1 6 200 6 200
Rortification tank 1 26 700 26 700
Clarifier 2 473 000 946 000
Agitator for Clarifier 2 6000 12 000
Crusher 1 792.8 793
Bag house 1 4001990 455
Granulator 1 792.8 793
Mortar (300hp) 1 18 0001990 20 478
TOTAL 3 747 385.6 8 538 819
87
2. FIXED CAPITAL INVESTMENT [FCI] FCI is based on percentage delivered equipment cost
ITEM % ON PURCHASED EQUIPMENT
COST (US $)
DIRECT COSTS 1. Purchased equipment 100 8 538 819
2. Equipment installation 36 3 073 975
3. Instrumentation and controls
28 2 390 869
4. Piping 32 2 732 422
5. Electrical installation 20 1 707 763
6. Buildings 20 1 707 763
7. Yard improvement 8 683 106
8. Service facilities 60 5 123 291
9. Land 4 341 553
TOTAL DIRECT COSTS 308 26 299 563 INDIRECT COSTS
1. Engineering and supervision
40 3 415 528
2. Construction expense 48 4 098 633
3. Contractor’s fee 8 683 106
4. Contingency 32 2 732 422
TOTAL INDIRECT COSTS 128 10 929 689 FCI (Indirect and direct) 436 37 229 252
3. TOTAL CAPITAL INVESTMENT [TCI] TCI = FCI + WC
Taking WC = 15% TCI
TCI = FCI + 0.15 TCI
TCI = FCI/0.85 = (37 229 252/ 0.85)
TCI = 43 799 120
WC = 6 569 868
88
4. LABOUR COSTS Department Title Number Unit Salary
Sh/Month
Total Amount US $
Per year Administration Chief Executive Officer 1 600000 94711.91792 Managing Directors 2 480000 151539.0687 General Managers 2 350000 110497.2376 Purchasing Agents 2 250000 78926.59826 Company Secretary 1 100000 15785.31965 Clerks 3 30000 14206.78769 Receptionists 2 25000 7892.659826 Messenger 2 25000 7892.659826Accounting Finance Manager 1 160000 25256.51144 Accountant 3 150000 71033.93844 Secretary 1 30000 4735.595896Sales Manager 1 190000 29992.10734 Sales men 4 100000 63141.27861 Secretary 1 20000 3157.063931Maintenance Superintendent 12 90000 170481.4522 Supervisors 12 80000 151539.0687 Technicians 12 45000 85240.72612Engineering Production Manager 1 350000 55248.61878 Mechanical Engineers 8 250000 315706.3931 Chemical Engineers 9 250000 355169.6922 Electrical Engineers 5 200000 197316.4957 Civil Engineers 2 200000 63141.27861 Draftsmen 6 40000 37884.76717Laboratory QC Manager 1 150000 23677.97948 Chief Chemist 1 70000 11049.72376 Chemists 6 30000 28413.57537Operation Supervisors 12 90000 170481.4522 Operators 50 60000 473559.5896Security Guards 15 12000 28413.57537Support Staff Drivers 7 19000 20994.47514 Cleaners 6 15000 14206.78769
89
Kitchen staff 6 15000 14206.78769TOTAL 197 2895501.18
5. TOTAL PRODUCTION COST ESTIMATION a) DIRECT PRODUCTION COSTS ITEM % COST
Raw materials 40% TPC 5 791 218
Operating labour 20% TPC 2 895 609
Operating supervision 25% OL(5%TPC) 723 902
Utilities 15% TPC 2 171 707
Maintenance and repair 6% FCI 2 233 755
Operating supplies 1% FCI 372 293
Laboratory charges 10% OL(2%TPC) 289 561
TOTAL TPC 14 478 044
b) FIXED CHARGES ITEM % COST Property taxes 4% FCI 1 489 170
Insurance 1% FCI 372 293
Depreciation 2 503 713
TOTAL FIXED CHARGES 4 365 176
c) PLANT OVERHEAD COST 60% of OL, supervision and maintenance 3 511 960
TOTAL MANUFACTURING COST 22 355 180
d) GENERAL EXPENSES ITEM % COST
Administrative 15% OL, supervision and maintenance
877 990
Distribution and marketing 11% TPC 1 592 585
Research and development 5% TPC 723 902
TOTAL GENERAL EXPENSES 3 194 477
90
TOTAL PRODUCTION COST 25 549 657
6. TOTAL SALES PRODUCT (SSP/TSP)
ANNUAL PRODUCTION BAGS
(Million)
COST PER BAG (KSH)
TOTAL SALES
US $ (Million)
1 4.32 900 51.14
2 4.68 900 55.14
3 5.04 920 61.00
4 5.04 920 61.00
5 5.18 940 64.05
6 5.18 940 64.05
7 5.40 950 67.48
8 5.40 960 68.19
9 5.76 960 72.74
10 5.76 970 73.50
11 6.12 970 78.09
12 6.12 980 78.09
13 6.48 980 83.34
14 6.84 1000 89.98
15 7.20 1000 94.71
1 bag = 50kg
The firm starts to operate at 60% maximum capacity and reaches 100% in the 15th year.
91
7. DEPRECIATION Salvage value (Vs) = 12 % of FCI
= US$ 2 731 323
Depreciation by sum –of - the year’s method
V = US $ 22 761 028
Depreciation = 20 029 705
Income tax is charged at 34% Gross profit
YEAR Depreciation YEAR Depreciation
1 2 503 713 8 1 335 314
2 2 336 799 9 1 168 399
3 2 169 885 10 1 001 485
4 2 002 971 11 834 571
5 1 836 056 12 667 657
6 1 669 142 13 500 743
7 1 502 228 14 333 828
15 166 914
92
8. ANNUAL CASH FLOW The year – to – year analysis will be based on the assumption that the plant starts operation at 60% capacity and projects to full
capacity in the subsequent years. (Values * 106)
ITEM 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
FCI 22.76
WC 4.02
TCI -43.80
Sales 51.14 55.41 59.67 61.00 64.05 64.05 67.48 68.19 72.74 73.50 78.09 78.90 83.54 89.98 94.71
TPC 25.55 26.57 27.63 28.74 29.88 31.08 32.32 33.62 34.96 36.36 37.81 39.33 40.90 42.54 44.24 Annual operating income
25.59 28.84 32.04 32.26 34.17 32.97 35.16 34.57 37.78 37.14 40.28 39.57 42.64 47.44 50.47
Depreciation 2.50 2.34 2.17 2.02 1.84 1.67 1.50 1.34 1.17 1.01 0.84 0.67 0.50 0.33 0.17 Profit before tax
23.09 26.50 29.87 30.24 32.33 31.30 23.66 33.23 36.61 36.13 39.44 38.90 42.14 47.11 50.30
Tax paid 7.85 9.01 10.16 10.28 10.99 10.64 11.44 11.30 12.45 12.28 13.41 13.23 14.33 16.02 17.01 Profit after tax
15.24 17.49 19.71 19.96 21.34 20.66 22.22 21.93 24.16 23.85 26.03 25.67 27.81 31.09 33.20
Annual cash income
17.74 19.83 21.88 21.98 23.18 22.33 23.72 23.27 25.33 24.86 26.87 26.34 28.31 31.42 33.37
Annual cash flow
-26.06 -6.23 15.65 37.63 60.81 83.14 106.86 130.13 155.46 180.32 207.19 233.53 261.84 293.26 326.63
9. GRAPH OF CUMULATIVE CASH FLOW
CUMULATIVE CASH FLOW
-50
0
50
100
150
200
250
300
350
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Years
Cas
h Fl
ow
94
8.4 PROFITABILITY ANALYSIS
1. DISCOUNTED CASH FLOW ON RETURN DCFROR is the minimum rate of return by which the capital investment is received at the
end of service life. It is equivalent to maximum interest rate at which money could be
borrowed to finance the project where the net cash flow of the project would be just
sufficient to pay the entire principle amount plus the interest.
i.e.
Initial TCI = Σ net present worth of cash flow for year 1 to 15 (US $)
= - 43 799 120
Year 1 = US $ 17 740 000
Year 2 = US $ 19 830 000
Year 3 = US $ 21 880 000
Hence
43 799 120 = {17 740 000/(1+i)} + {19 830 000/(1+i)2} + {21 880 000/(1+i)3}+
{21 980 000/(1+i)4}+ {23 180 000/(1+i)5}+ {23 330 000/(1+i)6}+
{23 720 000/(1+i)7}+ {23 270 000/(1+i)8}+ {23 330 000/(1+i)9}+
{24 860 000/(1+i)10}+ {26 870 000/(1+i)11}+ {26 340 000/(1+i)12}+
{28 310 000/(1+i)13}+ {31 420 000/(1+i)14}+ {33 370 000/(1+i)15}
i = 47%
2. PAY BACK PERIOD This is the period required after the start of the project to pay off the initial investment
from the income. From the graph showing the cumulative cash flow, it is the point where
the curve crosses the x – axis i.e. the pay back period is 2 years.
3. RATE OF RETURN R.O.R = {Average Net profit/ Total Capital Investment} * 100
Average net profit = US $ 24 695 333
R.O.R = {24 695 333/ 43 799 120} * 100
= 56%
95
CHAPTER NINE
9.0 SAFETY AND ENVIRONMENTAL IMPACT
9.1 SAFETY Any chemical industry has legal and moral obligation to safeguard the health and welfare
of its employees and the general public. The magnitude of safety factors are dictated by
the economic or market considerations, the accuracy of the design data and
calculations, potential changes in the operating performance and the background
information available. On the overall, process safety of the industry is considered under
the following titles:
• Identification and assessment of the hazards
• Control of the hazards
• Control of the process
• Limitation of any loss
The potential health hazard to an individual by material used in any chemical process is
a function of the inherent toxicity of the material and the frequency and duration of
exposure. The designer must therefore be aware of these hazards and ensure through
the application of sound engineering practice that the risks are reduced to acceptable
levels. The necessity to anticipate potential problems so as to avoid them or to reduce
their effect requires thorough appraisal of an environmentally significant action before it
is taken. The formalization of this concept is embodied in the environmental impact
assessment.
The main areas that involve safety considerations in this plant include:
• Vibration problems
• Spillage of acids and their effects
• Noise
• Corrosion
• Accidents
• Pressure buildup in continuous den, scrubbers and mixers
• Exposure to fumes and vapour and hydrogen fluoride
There are two ways of controlling such problems
• Engineering controls
• Administrative controls
96
9.1.2 ENGINEERING SAFETY CONTROLS Involves technical solutions within the design process to deal with the identified problem
1. ISOLATION Control by isolation or containment is used for highly volatile or toxic material. This will
apply to acids, alkalines and hydrogen fluoride.
2. VENTILATION Both forced and natural convection ventilation process will be required within the factory.
This will eliminate or reduce to minimal level exposure to fumes and dust
3. CONTROL VALVES There should be remote control valves to isolate equipment and areas of the plant in an
emergency.
4. ALARMS, SAFETY TRIPS AND INTERLOCKS Alarms are used to alert operations of the hazardous deviations in process conditions.
Key instruments are fitted with switches and relays to operate audible and visual alarms
on the control and communication panels.
Safety trips should be fitted in equipment where delay in action would cause serious
hazard e.g. the reactors, mixers
5. SPACING There should be a minimum distance between vessels (5m) between vessels and
buildings.
6. VENT For all pressure vessels including tanks and columns, a vent system must be installed to
protect the vessel from rupturing.
7. DETECTORS Detectors of fire should be placed all over the plant
8. MATERIALS Raw materials such as acids, rock, base and flocculant should be handled with care to
avoid spillage and its effect.
9. SPILLAGE Spillage should be avoided and whenever it happens, water system should be readily
available to wash out the spillage.
97
9.1.3 ADMINISTRATIVE CONTROLS 1. TECHNICAL FACILITIES It is required that all personnel working with technical facilities undergo introductory
training of all facilities as indicated below
• 45 hours initial instruction of site
• Day’s instruction on site
• An hour’s annual refresher training course
2. OPERATING PRACTISES
• Adequate training of personnel
• Provision of protective clothing
• Good house keeping and personnel hygiene
• Regular medical check-up of the employers
• Ensuring that all safety regulations are adhered to
• Conducting HAZOPS study
9.1.4 NOISE CONTROL Excessive noise is a hazard to health and safety. Long exposure to high noise levels
can cause permanent damage to hearing. At lower levels, noise is a distraction and
causes fatigue. In the plant, noise could be generated by vibration, ball mill and crusher.
To attain efficient, effective and practical noise control, it is necessary to understand the
individual equipment or process noise sources, their acoustic properties and
characteristics and how they interact to create the overall noise situation. Possible noise
control treatments may include acoustically lined fan covers, acoustic plenums, inline
silencers, vibration isolation and lagging.
98
9.2 ENVIRONMENTAL IMPACT
The concept of ecological sustainable industrial development motivates producers and
consumers to use products and operate industry using the best technologies to minimize
adverse environmental impact.
Fertilizer producers and users are faced with a number of potential points where adverse
impacts on the environment may occur. Fertilizer production processes may release
emissions containing potential pollutants that may have local environmental impact and
theoretically may contribute to global environmental problems.
The environmental issues related to use of fertilizer include:
9.2.1 ATMOSPHERIC EMISSIONS [SSP/TSP] Phosphate rock usually contains 3% to 4.5% of fluorine by weight. During the
acidulation of phosphate rock Hydrogen fluoride is released and converted into fluosilic
acid by silica in the rock most of which is retained in the TSP process but 25% is
released in the SSP process. Wet scrubbers are used in the production of SSP to trap
the 25% that is released to the atmosphere. Efficient scrubber designs allow recovering
of the H2SiF6 as a concentrated solution which could be processed to synthetic cryolite,
aluminium fluoride and various fluorosilicates. If there is no market for the acid or fluoride
derivatives, the fluosilic acid can be neutralized by liming. In addition, fluoride emission
continues during the curing process. Feedstock handling bins for phosphate rock must
be equipped with individual bag filters from which recovered dust is recycled.
9.2.2 PARTICULATE EMISSION Sources of particulate emissions include the reactor, granulator, dryer, screens, cooler,
mills and transfer conveyors. Additional emissions of particulate result from the
unloading, grinding, storage and transfer of ground phosphate rock. One facility uses
limestone, which is received in granulated form and does not require additional milling.
9.2.3 SOLID WASTE Solid wastes are not generally produced in finished fertilizer production process because
of the size of the required particles. Oversized particles are recycled to the process.
99
9.2.4 HAZARDOUS WASTE There are no hazardous wastes in fertilizer production other than the Cadnium contained
in fertilizer. The level of Cadnium content in fertilizer is limited to 50 mg Cd/kg of P2O5.
This level is increasingly causing concern. Fertilizer organic matter increases the
retention of Cadnium in the fertilizer.
Fluoride emissions cause damage to vegetation and are harmful to livestock that
consume that vegetation.
Phosphorus also contributes to the eutrophication process of the surface waters. Plant
residues contribute to the high phosphorus content of surface waters.
9.2.5 POLLUTION CONTROL At a typical plant, bag houses are used to control the fine rock particles generated by the
rock grinding and handling activities. These bag house - cloth filters have reported
efficiencies of over 99 percent.
Emissions from the reactor, den, and granulator are controlled by scrubbing the effluent
gas with recycled gypsum pond water in scrubbers.
Emissions from the dryer, cooler, screens, mills, product transfer systems, and storage
building are sent to a cyclone separator for removal of a portion of the dust before going
to wet scrubbers to remove fluorides. Collected solids are recycled to the process.
Emissions of SiF4, HF, and particulate from the production area and curing building
(storage vessel) are controlled by scrubbing the off-gases with recycled water. Gaseous
SiF4 in the presence of moisture reacts to form gelatinous silica, which has the tendency
to plug scrubber packings. Therefore, the use of conventional packed countercurrent
scrubbers and other contacting devices with small gas passages for emissions control is
not feasible. Most emissions of Fluoride into the atmosphere can be reduced by
selecting efficient absorption equipment.
Exhausts from the dryer, screens, mills, and curing building are sent first to a cyclone
separator and then to a wet scrubber. Wet scrubbers perform final cleanup of the plant
offgases.
100
Recycling and by-product recovery of all materials resulting from fertilizer production can
be recycled.
Use of acid leaching process is essential to curb the fatal effects of lead contained in
phosphate rock if exposed to human beings thorough the fertilizer. Acid leaching
process provides long – term effectiveness by recovering much of the lead and
reforming to commercial use; this also eliminates the effects of lead associated with the
production and use of fertilizer.
101
CHAPTER TEN
10.0 PLANT LOCATION
The following factors are to be put into consideration when determining the plant
location.
• Low nutrient containing fertilizers should be produced near the users’ area (e.g.
SSP, (NH4)CO3, (NH4)2SO4).
• High nutrient fertilizers, in particular phosphate fertilizers should be produced as
near as possible to the raw material source to minimize transportation costs.
• The availability of utilities such as water, steam and electricity near the selected
location presents an advantage.
• The establishment of the fertilizer complex near existing electricity power station
provides a better opportunity for process selection.
• Environmental protection units are cheaper when joint (industrial or communal)
water treatment stations are constructed or utilized. Waste from fertilizer provides
the feed for active bacteria in the treatment plant.
• 25 – 60 hectares of land surface are required.
• The soil’s characteristics and the underground water level are important factors.
• Existing transport infrastructure such as road, water, railway line is a necessity.
• Availability of both skilled and non skilled labour is a requirement.
With these factors in mind, the proposed plant location site is Migori District in South
Nyanza, Nyanza Province of Kenya. This is because of
• Availability of labour
• Infrastructure, the roads are well established
• Other neighbouring industries such as Sony Sugar
• Proximity of the major raw material being phosphate rock i.e. Homabay and
Minjingu in Tanzania
• Permanent river water i.e. River Kuja and River Migori
• Immediate market from the sugar cane, maize and tobacco farmers
• Power (Electricity) generated at Oyani power station.
102
CONCLUSION AND RECOMMENDATION The ever existing negative balance of trade is contributed by the importation of fertilizer.
The analysis carried out in this project establishes that by its implementation, this
negative balance of trade will reduce plus other benefits such as creation of
employment, reduction of poverty and elimination of diseases related to lead metal.
In the economic analysis, the cost index of 2003 was used and it is thus recommended
that during implementation, the cost of equipment to be adjusted appropriately.
It is our hope that this project or a similar one will be put into operation in the near future.
103
APPENDIX DETAILED CALCULATION FOR MASS AND HEAT BALANCE FOR REACTOR
Mass Balance
Mass of input material = Mass of output material (in tons) Mass of Rock +Mass of Phosphoric acid =Mass of the product(TSP) 23 + 31 = 54
Component
Inlet(tons) Outlet(tons)
Phosphate Rock 23 Phosphoric acid 31 Slurry 1 54 Total 54 54
Phosphoric acid Cp = 2952.6J/KgK = 0.703Kcal/KgK Mp = 31 tons T = 25°C H3 =0MJ Rock
Cp = 751.86J/degmol M = 23 tons H2 = 68.4MJ T = 26.8°C
M` = 54 tons T = 57.6°C H4 = 70.9MJ
Q = 2475KJ = 2.5MJ
REACTOR
104
Heat Balance
From the reaction equation in the reactor, it is seen that the heat of reaction is
172.58Kcal i.e.
Ca3(PO4)2 + 4H3PO4 + H2O →3Ca(H2PO4)2.H2O + 172.58 Kcal
And using the most appropriate reaction equation,
Ca10 (PO4)6F2 + 14H3PO4 +10H2O → 10CaH4P2O8.H2O + 2HF
Heat formation (HF) of the reaction components(UNIDO).
Ca10 (PO4)6F2 = 3267.2Kcal/gmol = 13.83GJ
H3PO4 = 308.25Kcal/gmol , hence 14H3PO4 =1.78GJ
H2O = 68.317 Kcal/gmol, hence 10H2O = 0.052GJ
10CaH4P2O8.H2O = 4.504GJ
HF= 75.56Kcal/gmol 2HF = 0.013GJ
Thus the heat of reaction is obtained as
13.83+ 1.78+ 0.052 - 4.504 – 0.013 = 11.14GJ
Component Inlet(GJ) Outlet(GJ) Rock 0.684 Heat of reaction 11.14 Phosphoric acid 0.0 TSP 11.824 TOTAL 11.824 11.824
Phosphoric acid Cp = 2952.6J/KgK = 0.703Kcal/KgK Mp = 31 tons T = 25°C H3 =0MJ Rock
Cp = 751.86J/degmol M = 23 tons H2 = 68.4MJ T = 26.8°C
TSP M` = 54 tons T = 57.6°C H4 = 11.824GJ
Q = 11.14GJ
REACTOR
105
DETAILED CALCULATION FOR MASS AND HEAT BALANCE FOR CONE MIXER
Mass Balance 0.6 tons of ground rock is required per ton of SSP. For 50 tons/hr we require 30 tons
of ground rock mixing it with the 30 tons of Sulphuric acid (75%).
22.5 tons H2SO4
7.5 tons H2O 30 tons 60 tons
28.2 tons Rock 50.7 tons slurry 1.8 tons H2O 9.3 tons H2O
The rock contains 6% moisture and hence this accounts for the 1.8 tons of water in
the in feed to the cone mixer:
6 % (30) = 1.8 tons
Mass in = Mass out
(29.2 + 1.8 + 22.5 + 7.5) = (50.7 + 9.3)
60 tons = 60 tons
Component Inlet(tons) Outlet(tons) Ground Rock 30 Sulphuric acid 30 Slurry 60 Total 60 60
Heat Balance [ ( ) ] )([ ] 472.24432342723243 CaSOOHPOCaHOHSOHCaFPOCa +→++
Heat formation (HF) of the reaction components(UNIDO).
Ca10 (PO4)6F2 = 3267.2Kcal/gmol = 13.83GJ
H2SO4 = 193.91Kcal/gmol hence 7H2SO4 = 0.558GJ
CaSO4 = 483.06 Kcal/gmol hence 7CaSO4 = 1.93GJ
H2O = 68.317 Kcal/gmol, hence 3H2O = 0.0152GJ
106
3CaH4P2O8.H2O = 1.3512GJ
HF= 75.56Kcal/gmol 2HF = 0.013GJ
Heat of reaction is thus obtained,
13.83 + 0.559 + 0.0156 – 1.3512 – 1.93 – 0.013 = 11.11GJ
H2SO4 70°C Q5 = 2.482GJ Rock Slurry 100°C
Q6 = 13.646GJ Q3 =54 MJ QR Working backwards, Enthalpy of the slurry at 100°C is obtaining by using the enthalpy of water at 100°C QR = Heat of reaction QR = 11.11GJ Q6 = Q3 + Q5 + QR therefore = 0.054 + 2.482 + 11.11 = 13.646GJ Component Enthalpy(GJ) Enthalpy(GJ) Rock 0.05 Enthalpy of Solution 2.48 Slurry 13.65 Heat of reaction 11.11 TOTAL 13.65 13.65
107
BIBLIOGRAPHY
1. Austin T. G, 1984, 5th edition Shreve's Chemical Process Industries. McGraw-Hill
book company, New York.
2. Battelle. 1997 a Technology Evaluation Report. Physical separation and acid
leaching. A demonstration of small – arms range remediation at Fort Polk, Lovsian.
Report prepared by Battelle Columbus, Ohio operations for the naval facilities
engineering service center and the U.S. Army environmental center.
3. Hearn, E. J. 3rd Ed. 1997, Mechanics of Materials, Linacre House, Jordan Hill,
Oxford, Boston.
4. Lloyd E. & Young E., 1986, Process Equipment Design, Mohinder Singh
Publishers, New Delhi, India.
5. http:// www.matche.com
6. Nriagu J. O and More P. B.(eds), 1984, Phosphate Minerals, Springer-verlag
Berline Heidberg, Germany
7. Othmer Kirk, 1980, 3rd edition, vol 10, Encyclopedia of Chemical Technology, John
Wiley & Sons, Incl, New York.
8. Perry, R. H. 6th edition 1984, Perry's handbook for chemical engineers McGraw Hill
book company, New York.
9. Shuka, S.D. Pandey G.N, 3rd edition, 1987, chemical Technology, Jughu offset,
shahdara, Delhi (India).
10. Sinnort,R.K, 1996, Chemical Engineering Design, Butterworth, Heinemann,
Oxford
11.TVA and US Department of Agriculture, 1964,Super phosphate: Its Chemistry and
Manufacture, Washington DC.
TVA – Tennessee Development Authority.
12.UNIDO and IFDC, 1998, Fertilizer manual, Kluwer Academics
Publishers, Netherlands.
UNIDO – United Industrial Development Organization Viena, Austria
IFDC – International Fertilizer Development centre, Alabama USA
13. US Environmental Protection Agency, office of pollution Prevention and Toxics
(US EPA) 1999. Background Report on Fertilizer use, contaminants and
regulation. Http://www.epa.gov/oppt/fertilizer.