report biphosphate

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


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


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


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



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


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



H2SO4 = 193.91Kcal/gmol hence 7H2SO4 = 0.558GJ

CaSO4 = 483.06 Kcal/gmol hence 7CaSO4 = 1.93GJ


3CaH4P2O8.H2O = 1.3512GJ


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



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


Type - Mixer & Settler

11. Cone Mixer Flow rate – 30000kg/hr

Diameter – 3m

Height – 7m

Volume – 49.41m3


Type - Mixer & Settler

12. Reactor Flow rate – 23000kg/hr

Diameter – 3m

Height – 4.5m

Volume – 32.20m3

59


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


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


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


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



23. Clarifier Flow rate – 12.3kg/s

Height – 0.49m

Area – 266.5m2



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

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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.

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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.

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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

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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

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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

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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

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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.

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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’

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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.

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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.

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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

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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.

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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.

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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

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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,

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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

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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

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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

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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

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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

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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.

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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

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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

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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



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



H3PO4 = 308.25Kcal/gmol , hence 14H3PO4 =1.78GJ


10CaH4P2O8.H2O = 4.504GJ


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



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 +→++



H2SO4 = 193.91Kcal/gmol hence 7H2SO4 = 0.558GJ

CaSO4 = 483.06 Kcal/gmol hence 7CaSO4 = 1.93GJ


106

3CaH4P2O8.H2O = 1.3512GJ


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.

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