CHAPTER ONE

INTRODUCTION

Chalk used in school classrooms comes in slender sticks approximately 9

mm in diameter and 80 mm long. Lessons are often presented to entire

classes on chalk-boards (or blackboards, as they were originally called)

using sticks of chalk because this method has proven cheap and easy.

As found in nature, chalk has been used for drawing since prehistoric times,

when, according to archaeologists, it helped to create some of the earliest

cave drawings. Later, artists of different countries and styles used chalk

mainly for sketches, and some such drawings, protected with shellac or a

similar substance, have survived. Chalk was first formed into sticks for the

convenience of artists. The method was to grind natural chalk to a fine

powder, then add water, clay as a binder, and various dry colors. The

resultant putty was then rolled into cylinders and dried. Although impurities

produce natural chalk in many colors, when artists made their own chalk

they usually added pigments to render these colors more vivid. Carbon, for

example, was used to enhance black, and ferric oxide (Fe2O3) was used to

create a more vivid red.

1

Chalk did not become standard in schoolrooms until the nineteenth century,

when class sizes began to increase and teachers needed a convenient way of

conveying information to many students at one time. Not only did

instructors use large blackboards, but students also worked with individual

chalkboards, complete with chalk sticks and a sponge or cloth to use as an

cleaner. These small chalkboards were used for practice, especially among

the younger students. Pens dipped in ink wells were the preferred tool for

writing final copy, but these were reserved for older students who could be

trusted not to make a mess: paper—made solely from rags at this time—was

expensive.

An important change in the nature of classroom chalk paralleled a change in

chalk-boards. Blackboards used to be black, because they were made from

true slate. While some experts advocated a change to yellow chalkboards

and dark blue or purple chalk to simulate writing on paper, when

manufacturers began to fashion chalkboards from synthetic materials during

the twentieth century, they chose the color green, arguing that it was easier

on the eyes. Yellow became the preferred color for chalk.

2

Almost all chalk produced today is dustless. Earlier, softer chalk tended to

produce a cloud of dust that some feared might contribute to respiratory

problems. Dustless chalk still produces dust; it's just that the dust settles

faster. Manufacturers accomplish this by baking their chalk longer to harden

it more. Another method, used by a French company, is to dip eighty percent

of each dustless chalk stick in shellac to prevent the chalk from rubbing off

onto the hands.

In Nigeria, Britannia school chalk, which is an imported brand of chalk, is

now on the decline with respect to its usage due to unfavorable foreign

exchange earnings. This has given rise to the need of sourcing available raw

materials to produce chalk, which is obviously in high demand in our

educational institutions. Blackboard chalk, which is used in facilitating

teaching and enhancing knowledge in our educational institution, is in high

demands. This is because of educational awareness recently taking place in

the country, leading to the establishment of additional educational

institutions at all levels i.e. primary, secondary and tertiary. Not only with

the intention of meeting educational demands, locally designed chalk plants

and the chalk production itself will boost the country’s technological

upliftment and foreign reserve when exportation is embarked upon. The

3

importance of chalk in Nigeria cannot be over emphasized, the tailors,

carpenters, road construction firms, etc, make use of chalk one way or the

other.

There are several raw materials used for the production of blackboard chalk

and these raw materials could be used separately or combined. The different

raw materials include Gypsum (CaSO4.2H2O), Calcium Carbonate (CaCO3),

cement, bones, kaolin (Al2O3.SO2H2O), and fertilizer. These raw materials

are available in great quantities in several parts of the country.

The objective of this project is to design a plant to produce sixty tons of

chalk per annum using locally available raw materials.

1.1 CALCIUM CARBONATE

Calcium carbonate is a chemical compound with the chemical formula

Ca C O 3. It is a common substance found as rock in all parts of the world, and

is the main component of shells of marine organisms, snails, and eggshells.

Calcium carbonate is the active ingredient in agricultural lime, and is usually

the principal cause of hard water. It is commonly used medicinally as a

4

calcium supplement or as an antacid, but high consumption can be

hazardous.

Calcium carbonate is found naturally as the following minerals and rocks:

Aragonite

Calcite

Vaterite or (μ-CaCO3)

Chalk(Blackboard chalk: CaSO4)

Limestone

Marble

Travertine

Table 1.1 Physical Properties of Calcium Carbonate

Other names Limestone; calcite; aragonite; chalk; marble

Identifiers

CAS number: [471-34-1]

Properties

Molecular formula: CaCO3

Molar mass: 100.087 g/mol

Appearance: White powder.

5

Density: 2.71 g/cm³ (calcite); 2.83 g/cm³ (aragonite)

Melting point: 825 °C Decomposes

Boiling point: Decomposes

Solubility in water: Insoluble

Structure

Molecular shape : Linear

Hazards

Main hazards: Not hazardous.

Flash point: Non-flammable.

(From Wikipedia, the free encyclopedia)

Note: Except where noted otherwise, data are given for materials in their

standard state (at 25 °C, 100 kPa)

2.1.1 Preparation

The vast majority of calcium carbonate used in industry is extracted by

mining or quarrying. Pure calcium carbonate (e.g. for industrial or

pharmaceutical use), can be produced from a pure quarried source (usually

marble).

Alternatively, calcium oxide is prepared by calcining crude calcium

carbonate. Water is added to give calcium hydroxide, and carbon dioxide is

6

passed through this solution to precipitate the desired calcium carbonate,

referred to in the industry as precipitated calcium carbonate (PCC):[3]

CaCO3 → CaO + CO2

CaO + H2O → Ca(OH)2

Ca(OH)2 + CO2 → CaCO3 + H2O

2.1.2 Uses

(a) Industrial applications

The main use of calcium carbonate is in the construction industry and in the

purification of iron from iron ore in a blast furnace

Calcium carbonate is also used in the oil industry in drilling fluids as a

formation bridging and filtercake sealing agent and may also be used as a

weighting material to increase the density of drilling fluids to control

downhole pressures.

Calcium carbonate is widely used as an extender in paints.[5]

Calcium carbonate is also widely used as filler in plastics.[3].

7

Fine ground calcium carbonate is an essential ingredient in the microporous

film used in babies' diapers and some building films as the pores are

nucleated around the calcium carbonate particles during the manufacture of

the film by biaxial stretching.

Calcium carbonate is known as whiting in ceramics/glazing applications,[3]

where it is used as a common ingredient for many glazes in its white

powdered form.

Used in swimming pools as a pH corrector for maintaining alkalinity

"buffer" to offset the acidic properties of the disinfectant agent.

It is commonly called chalk as it has been a major component of blackboard

chalk. Chalk may consist of either calcium carbonate or gypsum, hydrated

calcium sulfate CaSO4·2H2O.

8

CHARPTER TWO

LITERATUURE REVIEW

Despite the fact that school chalk can now be produced locally, there is need

to meet standard. A good quality chalk must be non-porous, non-toxic, non-

brittle, oil-free and must have the ability to give good inscription.

2.1 OTHER RAW MATERIALS FOR THE PRODUCTION OF

SCHOOL CHALK

The basic raw materials required in the manufacture of school chalk include,

limestone (Calcium Carbonate), gypsum, kaolin, pigments and water. These

materials are available in large quantities in Nigeria and could be easily

sourced for. Below are areas in Nigeria where these various raw materials

could be found;

KaolinKaolin is found in the following Nigerian states: Ogun, Kogi, Imo, Rivers,

Anambra, Bauchi, Kebbi, Ondo, Ekiti, Akwa Ibom, Katsina and Plateau

GypsumGypsum can be found in Yobe, Adamawa, Ogun, Gombe, Sokoto and Edo

9

States.

LimestoneLimestone can be found in Cross River, Ogun, Benue, Gombe, Ebonyi, Sokoto, Edo and Kogi States.

2.1.1 Gypsum

Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with

the chemical formula Ca S O 4·2H2O.[7]

Gypsum occurs in nature as flattened and often twinned crystals and

transparent cleavable masses called selenite. It may also occur silky and

fibrous, in which case it is commonly called satin spar. Finally it may also

be granular or quite compact. In hand-sized samples, it can be anywhere

from transparent to opaque. A very fine-grained white or lightly-tinted

variety of gypsum is called alabaster, which is prized for ornamental work of

various sorts. In arid areas, gypsum can occur in a flower-like form typically

opaque with embedded sand grains called desert rose. The most visually

striking variety, however, is the giant crystals from Naica Mine. Up to the

size of 11m long, these megacrystals are among the largest crystals found in

nature. A recent publication shows that these crystals are grown under

10

constant temperature such that large crystals can grow slowly but steadily

without excessive nucleation.[8]

Gypsum is a common mineral, with thick and extensive evaporite beds in

association with sedimentary rocks. Deposits are known to occur in strata

from as early as the Permian age.[9] Gypsum is deposited in lake and sea

water, as well as in hot springs.

The word gypsum is derived from the aorist form of the Greek verb

μαγειρεύω, "to cook", referring to the burnt or calcined mineral. Because the

gypsum from the quarries of the Montmartre district of Paris has long

furnished burnt gypsum used for various purposes, this material has been

called plaster of Paris. It is also used in foot creams, shampoos and many

other hair products. It is water-soluble.

Because gypsum dissolves over time in water, gypsum is rarely found in the

form of sand. However, the unique conditions of the White Sands National

Monument in the US state of New Mexico have created a 710 km² (275 sq

mile) expanse of white gypsum sand, enough to supply the construction

industry with drywall for 1,000 years.[10] Commercial exploitation of the

area, strongly opposed by area residents, was permanently prevented in 1933

11

when president Herbert Hoover declared the gypsum dunes a protected

national monument.

Table 2.1 Physical properties of Gypsum

General

Category: Mineral

Chemical formula: Calcium Sulfate CaSO4·2H2O

Identification

Color: White to grey, pinkish-red

Crystal habit: Massive, flat. Elongated and generally prismatic

crystals

Crystal system: Monoclinic 2/m

Twinning: common {110}

Cleavage: good (66° and 114°)

Fracture: Conchoidal, sometimes fibrous

Mohs Scale hardness: 1.5-2

Luster: Vitreous to silky, pearly, or waxy

Refractive index: α=1.520, β=1.523, γ=1.530

Optical Properties: 2V = 58° +

Pleochroism: None

Streak White

Specific gravity: 2.31 - 2.33

Fusibility: 3

Solubility: hot, dilute HCl

Diaphaneity: transparent to translucent

Major varieties

12

Satin Spar: Pearly, fibrous masses

Selenite: Transparent and bladed crystals

Alabaster: Fine-grained, slightly colored

(From Wikipedia, the free encyclopedia)

2.1.1.1 Uses of Gypsum

There are a large number of uses for gypsum throughout prehistory and

history. Some of these uses are:

Drywall

Plaster ingredient.

Fertilizer and soil conditioner. In the late eighteenth and early

nineteenth century, Nova Scotia gypsum, often referred to as plaister,

was a highly sought fertilizer for wheat fields in the United States.

Plaster of Paris (surgical splints; casting moulds; modeling).

A wood substitute in the ancient world; for example, when wood

became scarce due to deforestation on Bronze Age Crete, gypsum was

employed in building construction at locations where wood was

previously used.[11]

13

A tofu (soy bean curd) coagulant, making it ultimately a major source

of dietary calcium, especially in Asian cultures which traditionally use

few dairy products.

Adding hardness to water used for homebrewing.

Blackboard chalk.

A component of Portland cement used to prevent flash setting of

concrete.

Soil/water potential monitoring (soil moisture tension)

A medicinal agent in traditional Chinese medicine called Shi Gao.

2.1.2 CALCINED GYMPSUM

Calcinations of gypsum can take place either in kettle or rotary kilns. If the

gypsum is ground into powder, kettle is used. When calcinating at a

temperature between 120oC - 130oC, a hemihydrate of calcium sulphate is

known as plaster of paris (P.O.P)

CaSO4.2H2O Heat CaSO4.H2O + H2O

This is called the kettle. On heating up to a temperature of 1900C- 3000C, all

the water of hydration will be lost giving calcium sulphate (CaSO4)

14

CaSO4.2H2O Heat CaSO4.H2O + H2O

This is called second kettle. If heating continues at a very high temperature

above 11000C, gypsum decomposes to yield calcium oxide and sulphate.

CaSO4 CaO + SO2 + 1/2O2

For the rotary kiln process, the gypsum is crushed to pieces through a 40mm

screen.

Gypsum is used mainly during calcinations to obtain hemihydrates form and

anhydrite form at low temperatures (1200C- 3000C) and quicklime and

sulphate at higher temperature (11000C). Apart from its use in the

manufacture of chalk, calcined gypsum has some other wide industrial

applications such as in ceramics, wall and floor plastering, soil conditioning,

pottery mould, orthopedic and dental plaster, art and casting plasters,

suspended ceiling and fillers for paints.

2.1.3 Kaolinite

Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. It

is a layered silicate mineral, with one tetrahedral sheet linked through

15

2000C

MOUL Heat

oxygen atoms to one octahedral sheet of alumina octahedra (Deer and

others., 1992). Rocks that are rich in kaolinite are known as china clay or

kaolin.

The name is derived from Gaolin ("High Hill") in Jingdezhen, Jiangxi

province, China. Kaolinite was first described as a mineral species in 1867

for an occurrence in the Jari River basin of Brazil.[13]

Kaolinite is one of the most common minerals; it is mined, as kaolin, in

Brazil, France, United Kingdom, Germany, India, Australia, Korea , the

People's Republic of China, and the USA.

Kaolinite has a low shrink-swell capacity and a low cation exchange

capacity (1-15 meq/100g.) It is a soft, earthy, usually white mineral

(dioctahedral phyllosilicate clay), produced by the chemical weathering of

aluminium silicate minerals like feldspar. In many parts of the world, it is

colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter

concentrations yield white, yellow or light orange colours.

16

Kaolinite clay occurs in abundance in soils that have formed from the

chemical weathering of rocks in hot, moist climates - for example in tropical

rainforest areas. Comparing soils along a gradient towards progressively

cooler or drier climates, the proportion of kaolonite decreases, while the

proportion of other clay minerals such as illite (in cooler climates) or

smectite (in drier climates) increases. Such climatically-related differences

in clay mineral content are often used to infer changes in climates in the

geological past, where ancient soils have been buried and preserved. In

Nigeria, an estimated reserve of 3 billion tonnes of good kaolinific clays has

been identified (News letter, Embassy of Nigeria, 1995).

Table 2.2 Physical properties of Kaolin

GeneralCategory: MineralChemical formula: Al2Si2O5(OH)4

IdentificationColor: White, sometimes red, blue or brown tints from

impuritiesCrystal habit: EarthyCrystal system: triclinicCleavage: perfect on {001}Fracture: PerfectMohs Scale hardness: 2 - 2.5Luster: dull and earthyRefractive index: α 1.553 - 1.565, β 1.559 - 1.569, γ 1.569 - 1.570Streak: whiteSpecific gravity: 2.16 - 2.68

17

(From Wikipedia, the free encyclopedia)

2.1.3.1 Uses

Kaolin is used in ceramics, medicine, coated paper, making of school chalk,

as a food additive, in toothpaste, as a light diffusing material in white

incandescent light bulbs, and in cosmetics. It is also used in most paints and

inks. The largest use is in the production of paper, including ensuring the

gloss on some grades of paper.

A more recent, and more limited, use is as a specially formulated spray

applied to fruits, vegetables, and other vegetation to repel or deter insect

damage. A traditional use is to soothe an upset stomach, similar to the way

parrots (and later, humans) in South America originally used it.[16] Until the

early 1990s it was the active substance of anti-diarrhea medicine Kaopectate.

In April of 2008, the Naval Medical Research Center announced the

successful use of a Kaolinite-derived aluminosilicate nanoparticles infusion

in traditional gauze known commercially as QuikClot® Combat Gauze.[17]

[18].

18

Kaolinite can contain very small traces of uranium and thorium, and is

therefore useful in radiological dating. While a single magazine made using

kaolin does not contain enough radioactive material to be detected by a

security-oriented monitor, this does result in truckloads of high end glossy

paper occasionally tripping an overly-sensitive radiation monitor.

2.1.4 PIGMENTS AND DYES

School chalk are usually coloured as a result of the introduction of pigment

and dyes during the manufacturing process. True pigments are widespread in

plant and animal kindom, some have wide distribution while others are

restricted to a few species. One of the most widespread groups of pigments

is porphyries. They are represented by the chlorophylls of green plants and

myoglobin of red systems. Pigmentation resulting from structural color is

produced by physical surfaces which gives the effect of various colours

when light falls upon them in such a way as to split the spectrums. In other

words, colour production results from the pigments selective absorption of

visible light. Pigments are used in the paint industries where they act as

resistance to weatering or the protective film in paints.

19

Dyes are intensely coloured substances used for the colouration of various

substances including chalk, paper, leather, fur, lair, fabrics, etc. they are

retained in these substances or substrate by physical adsorption, salt or

metal-complex formation, solution, mechanical retention, or by the

formation of covalent chemical bons. The methods used for the application

of dyes to the substrate differ, depending upon the substrate and class of dye.

It is by application methods, rather than by chemical constitutions that dyes

are differentiated from pigments. During the application process, dyes lose

their crystal structures by dissolution or vapourization. The crystal structures

may in some cases be regained during a later stage of the dying process.

Pigments on the other hand retain crystal or particulate form throughout the

entire application procedure.

2.2 MECHANICAL PREPARATION OF RAW MATERIALS

Plasticity and castability are parameters used to determine the quality of

chalk. This this quality is determined by the particle size distribution of the

chalk.

Plasticity is a parameter used t determine the ability of the material to be

deformed or shaped without cracking or breaking when force is applied and

20

to retain its new shape when deformation force is reduced below certain

value. Castability on the other hand is dependent upon socculation, flow

characteristics and setting rate, which is interdependent and all depends upon

the particle size distribution in the chalk and determines the nature of the

cast to be formed. The smaller the size of the particles, the easier to form

their colloidal suspension and hence, the slower their rate of setting. As a

result, a more uniform and stronger cast is obtained when compared with

coarse particle size.

Removal of impurities from the raw materials is also necessary so that they

do not interfere with the production process/unit operations which includes,

grinding (size reduction), screening, mixing, moulding and drying.

2.3 TECHNOLOGY OF CHALK PRODUCTION

The main component of chalk is calcium carbonate (CaCO3), a form of

limestone. Limestone deposits develop as coccoliths(minute calcareous

plates created by the decomposition of plankton skeletons) accumulate,

forming sedimentary layers. Plankton, a tiny marine organism, concentrates

the calcium found naturally in seawater from .04 percent to 40 percent,

which is then precipitated when the plankton dies.

21

To make chalk, limestone is first quarried, generally by an open pit quarry

method. Next, the limestone must be crushed. Primary crushing, such as in a

jaw crusher, breaks down large boulders; secondary crushing pulverizes

smaller chunks into pebbles. The limestone is then wet-milled with water in

a ball mill—a rotating steel drum with steel balls inside to further pulverize

the chalk. This step washes away impurities and leaves a fine powder.

2.3.1 LIMESTONE (Calcium Carbonate)

Quarrying limestone

22

Approximately 95 percent of the limestone produced is quarried. After

a sufficient reserve (twenty-five years' worth is recommended) has

been prospected, the land that covers the deposit is removed with

bulldozers and scrapers. If the chalk is close to the surface, an open

shelf quarry method can be used; however, this is very rare. Usually

an open pit quarry method is used instead. In this method, holes are

drilled into the rock, explosives are placed inside, and the rock is

blown apart. Depending on the nature of the deposit, a pit can be

enlarged laterally or vertically.

Pulverizing the chalk

Once comparatively large chunks of limestone have been quarried,

they need to be transported to crushing machines, where they are

pulverized to meet the demands of the chalk industry. The first step is

primary crushing. Various crushers exist, but the principle is the same:

all compress the stone with jaws or a cone, or shatter it through

impact. Secondary crushing is accomplished by smaller crushers that

work at higher speeds, producing pebbles which are then ground and

pulverized.

23

The next phase, wet grinding, washes away impurities. It is used to

make the fine grade of limestone necessary to make chalk suitable for

writing purposes. Wet grinding is carried out in ball mills—rotating

steel drums with steel balls inside that pulverize the chalk until it is

very fine.

After grinding, the chalk particles are sifted over vibrating screens to

separate the finer particles. The particles are then mixed with water,

extruded through a die of the proper size, and cut to the proper length.

Finally, the chalk is cured in an oven for four days.

2.3.2 Gypsum

Dehydrating gypsum

24

Gypsum, like limestone, is also quarried and pulverized. The major

difference in processing gypsum is that it must be dehydrated to form

calcium sulfate, the major component of colored chalk. This is done in

a kettle, a large combustion chamber in which the gypsum is heated to

between 244 and 253 degrees Fahrenheit (116-121 degrees Celsius). It

is allowed to boil until it has been reduced by twelve to fifteen

percent, at which point its water content will have been reduced from

20.9 percent to between 5 and 6 percent. To further reduce the water,

the gypsum is reheated to about 402 degrees Fahrenheit (204 degrees

Celsius), at which point it is removed from the kettle. By now, almost

all of the water has evaporated, leaving calcium sulfate.

Sifting, cleaning, and shipping the chalk

The particles of chalk or calcium sulfate are now conveyed to

vibrating screens that sift out the finer material. The ensuing fine

chalk is then washed, dried, packed in bags, and shipped to the

manufacturer. Upon receiving chalk or calcium sulfate, the chalk

factory usually grinds the materials again to render them smooth and

uniformly fine.

25

2.3.3 Making white classroom chalk

To make white classroom chalk, the manufacturer adds water to form

a thick slurry with the consistency of clay. The slurry is then placed

into and extruded from a die—an orifice of the desired long, thin

shape. Cut into lengths of approximately 24.43 inches (62

centimeters), the sticks are next placed on a sheet that contains places

for five such sticks. The sheet is then placed in an oven, where the

chalk cures for four days at 188 degrees Fahrenheit (85 degrees

Celsius). After it has cured, the sticks are cut into 80 millimeters

lengths.

2.3.4 Making colored classroom chalk

Pigments (dry, natural, colored materials) are mixed in with the

calcium carbonate while both are dry (the procedure is similar to

sifting flour and baking powder together before adding liquid, as in a

cake recipe). Water is then added to the mixture, which is then baked

in the same manner as white classroom chalk.

2.3.5 Boxing the chalk

26

Placed in small boxes, the completed chalk sticks are stacked in large

boxes to be shipped to supply stores.

2.4 Quality Control

Chalk that is intended for the classroom must undergo stringent tests in order

to perform well and be labeled nontoxic. All incoming materials are tested

for purity before being used. After the chalk has been made into sticks, one

stick from each batch is selected for tests. The density and break strength of

the sample stick are determined. The sample is then used to write with, and

the quality of the mark is studied. Erasability is also studied. First, the chalk

mark is erased using a dry eraser, and the quality of erasure is examined.

Then, the chalkboard is washed, and again the amount of chalk left on the

board is examined. Furthermore, a sample from each batch is kept for five

years so that it can be inspected if in the future its quality is questioned.

Chalk for classroom use adheres to the American National Standards

Institute performance standards. Written specifications state the proper

length of the chalk stick, as well as how many sticks should go in a box. On

November 18, 1990, a Federal Act (Public Law 100-695) went into effect,

mandating that all art materials sold in the United States must be evaluated

27

by a qualified toxicologist who must then issue a label explaining their

toxicity. Toxicologists are concerned not with cost but with safety, and they

must consider many factors before granting approval. Each ingredient, the

quantity in which it is used, and its possible adverse reactions with other

ingredients are studied. The product's size and packaging, its potential harm

to humans, and its tendency to produce allergic reactions are also

considered. Toxicologists also take into account the products use and

potential mis-use, as well as all federal and state regulations. Formulas for

every color and every formula change must meet approval.

Classroom chalk is labeled "CP [certified product] nontoxic" if it meets the

standards of the Art and Craft Materials Institute, a nonprofit manufacturers'

association. This label certifies that art materials for children are nontoxic

and meet voluntary standards of quality and performance, and that the

toxicity of art materials for adults has been correctly labeled. The CP seal

also indicates that the product meets standards of material, workmanship,

working qualities, and color developed by the Art and Craft Materials

Institute and others such as the American National Standards Institute and

the American Society for Testing and Materials (ASTM). To ensure honesty,

most chalk manufacturers are tested at random by an independent

28

toxicologist, who checks to see that they are meeting nontoxic standards.

Most manufacturers conform to such exacting standards because

knowledgeable schools will not purchase chalk that is not properly labeled.

Various properties a standard school chalk must possess are:

1. Bulk Density: This is a measure of the mass of material occupied in a

unit volume. Range = 0.70 – 0.77g/cm3 .

2. The initial moisture content of produced chalk should not exceed 16%

3. The capillarity rate along a 10cm column of 15.2g mass should not be

less than 1.30.

4. The specific gravity ranges from 2.13 – 2.17.

2.5 PROPERTIES OF A STANDARD CHALK

1. Hard: School chalk must be hard or rather non-brittle. Brittleness is the

breakage of chalk into bits when in use. This could be as a result of using

a greater proportion of water than is required in mixing the materials and

also could be as a result of the porous nature of the chalk.

29

2. Non-porous: Porosity in chalk could be as a result of the diatortion for

the particle arrangement at drying when much water than necessary is

used during moulding. Porosity in chalk causes breakage.

3. Oil free: good quality chalk must be oil free. The presence of oil in chalk

affects the inscription and also difficulty in wiping out from the board as

the dust tends to be sticky to the duster.

4. Non-Toxic: good quality chalk must be safe for teachers and children

who make use of it. Toxic chalk is injurious to health thus should be

avoided.

5. Ability to give clear inscriptions: The presence of silica in chalk gives

rise to interruptions encountered during the use of chalk and also its

blurred nature on the board. Silica must be reduced or possibly removed

before moulding to give clear and a visible inscription.

2.6 UNIT OPERATIONS INVOLVED IN CHALK PRODUCTION

2.6.1 SIZE REDUCTION

30

Raw materials often occur in sizes that are too large to be used and,

therefore, they must be reduced in size. This size-reduction operation can be

divided into two major categories depending on whether the material is a

solid or a liquid. If it is solid, the operations are called grinding and cutting,

if it is liquid, emulsification or atomization. All depend on the reaction to

shearing forces within solids and liquids.

2.6.1.1 GRINDING AND CUTTING

Grinding and cutting reduce the size of solid materials by mechanical action,

dividing them into smaller particles. Cutting is used to break down large

pieces of materials into smaller pieces suitable for further processing, such

as in the preparation of calcium carbonate for the manufacture of chalk.

In the grinding process, materials are reduced in size by fracturing them. The

mechanism of fracture is not fully understood, but in the process, the

material is stressed by the action of mechanical moving parts in the grinding

machine and initially the stress is absorbed internally by the material as

strain energy. When the local strain energy exceeds a critical level, which is

a function of the material, fracture occurs along lines of weakness and the

stored energy is released. Some of the energy is taken up in the creation of

31

new surface, but the greater part of it is dissipated as heat. Time also plays a

part in the fracturing process and it appears that material will fracture at

lower stress concentrations if these can be maintained for longer periods.

Grinding is, therefore, achieved by mechanical stress followed by rupture

and the energy required depends upon the hardness of the material and also

upon the tendency of the material to crack - its friability.

The force applied may be compression, impact, or shear, and both the

magnitude of the force and the time of application affect the extent of

grinding achieved. For efficient grinding, the energy applied to the material

should exceed, by as small a margin as possible, the minimum energy

needed to rupture the material. Excess energy is lost as heat and this loss

should be kept as low as practicable.

The important factors to be studied in the grinding process are the amount of

energy used and the amount of new surface formed by grinding.

2.6.1.1.1 Grinding Equipment

Grinding equipment can be divided into two classes - crushers and grinders.

In the first class the major action is compressive, whereas grinders combine

32

shear and impact with compressive forces. Examples are Crushers, Hammer

mills, Fixed head mill, Plate mill, Roller mills, etc

2.6.1.2 SCREENING

The screening operation is usually done manually and this process is

employed to separate the oversized material from the desired undersized

which is fine powder.

SIEVING

In the final separation operation in this group, restraint is imposed on some

of the particles by mechanical screens that prevent their passage. This is

done successively, using increasingly smaller screens, to give a series of

particles classified into size ranges. The fluid, usually air, can effectively be

ignored in this operation which is called sieving. The material is shaken or

agitated above a mesh or cloth screen; particles of smaller size than the mesh

openings can pass through under the force of gravity.

Rates of throughput of sieves are dependent upon a number of factors:

nature and the shape of the particles,

frequency and the amplitude of the shaking,

33

methods used to prevent sticking or bridging of particles in the

apertures of the sieve and

tension and physical nature of the sieve material.

Standard sieve sizes have been evolved, covering a range from 25 mm

aperture down to about 0.6 mm aperture. The mesh was originally the

number of apertures per inch. A logical base for a sieve series would be that

each sieve size have some fixed relation to the next larger and to the next

smaller. A convenient ratio is 2:1 and this has been chosen for the standard

series of sieves in use in the United States, the Tyler sieve series. The mesh

numbers are expressed in terms of the numbers of opening to the inch (=

2.54 cm

By suitable choice of sizes for the wire from which the sieves are woven, the

ratio of opening sizes has been kept approximately constant in moving from

one sieve to the next. Actually, the ratio of 2:1 is rather large so that the

normal series progresses in the ratio of 2:1 and if still closer ratios are

required intermediate sieves are available to make the ratio between adjacent

sieves in the complete set 42:1. The standard British series of sieves has

been based on the available standard wire sizes, so that, although apertures

34

are generally of the same order as the Tyler series, aperture ratios are not

constant.

In the SI system, apertures are measured in mm. A table of sieve sizes has

been included in Appendix 1.

2.6.1.3 MIXING

Mixing is the dispersing of components, one throughout the other. It occurs

in innumerable instances in the chemical industry and is probably the most

commonly encountered of all process operations. Unfortunately, it is also

one of the least understood. There are, however, some aspects of mixing

which can be measured and which can be of help in the planning and

designing of mixing operations.

2.6.1.3.1 CHARACTERISTICS OF MIXTURES

Ideally, a mixing process begins with the components, grouped together in

some container, but still separate as pure components. Thus, if small samples

are taken throughout the container, almost all samples will consist of one

pure component. The frequency of occurrence of the components is

proportional to the fractions of these components in the whole container.

35

As mixing then proceeds, samples will increasingly contain more of the

components, in proportions approximating to the overall proportions of the

components in the whole container. Complete mixing could then be defined

as that state in which all samples are found to contain the components in the

same proportions as in the whole mixture.

Actually, this state of affairs would only be attained by some ordered

grouping of the components and would be a most improbable result from

any practical mixing process.

Another approach can then be made, defining the perfect mixture as one in

which the components in samples occur in proportions whose statistical

chance of occurrence is the same as that of a statistically random dispersion

of the original components. Such dispersion represents the best that random

mixing processes can do.

2.6.1.3.2 MIXING EQUIPMENT

Many forms of mixers have been produced from time to time but over the

years a considerable degree of standardization of mixing equipment has been

reached in different branches of the chemical industry. Possibly the easiest

way in which to classify mixers is to divide them according to whether they

36

mix liquids, dry powders, or thick pastes. examples are Liquid Mixers,

Powder and Particle Mixers

2.6.1.4 MOULDING

A mould is a hollow container with a particular shape, into which a soft or

liquid substance is poured to set or cool into that shape. This process is

known as moulding. It is achieved by pouring the homogenous mixture into

moulds immediately after mixing and allowing some time for the material to

set.

2.6.1.5 DRYING

Drying implies the removal of water from the material. In most cases, drying

is accomplished by vaporizing the water that is contained in the material,

and to do this the latent heat of vaporization must be supplied. There are,

thus, two important process-controlling factors that enter into the unit

operation of drying:

(a) transfer of heat to provide the necessary latent heat of vaporization,

(b) movement of water or water vapour through the material and then away

from it to effect separation of water from material.

37

Drying processes fall into three categories:

Air and contact drying under atmospheric pressure. In air and contact

drying, heat is transferred through the material either from heated air or from

heated surfaces. The water vapour is removed with the air.

Vacuum drying. In vacuum drying, advantage is taken of the fact that

evaporation of water occurs more readily at lower pressures than at higher

ones. Heat transfer in vacuum drying is generally by conduction, sometimes

by radiation.

Freeze drying. In freeze drying, the water vapour is sublimed off frozen

material. The structure is better maintained under these conditions. Suitable

temperatures and pressures must be established in the dryer to ensure that

sublimation occurs.

2.6.1.5.1 Heat Transfer in Drying

We have been discussing the heat energy requirements for the drying

process. The rates of drying are generally determined by the rates at which

heat energy can be transferred to the water or to the ice in order to provide

the latent heats, though under some circumstances the rate of mass transfer

(removal of the water) can be limiting. All three of the mechanisms by

38

which heat is transferred - conduction, radiation and convection - may enter

into drying. The relative importance of the mechanisms varies from one

drying process to another and very often one mode of heat transfer

predominates to such an extent that it governs the overall process.

As an example, in air drying the rate of heat transfer is given by:

q = hsA(Ta - Ts)                                                                              (2.14)

where q is the heat transfer rate in J s-1, hs is the surface heat-transfer

coefficient J m-2 s-1 °C-1, A is the area through which heat flow is taking

place, m2, Ta is the air temperature and Ts is the temperature of the surface

which is drying, °C.

To take another example, in a roller dryer where moist material is spread

over the surface of a heated drum, heat transfer occurs by conduction from

the drum to the material, so that the equation is

q = UA(Ti– Ts )

where U is the overall heat-transfer coefficient, Ti is the drum temperature

(usually very close to that of the steam), Ts is the surface temperature of the

39

material (boiling point of water or slightly above) and A is the area of drying

surface on the drum.

The value of U can be estimated from the conductivity of the drum material

and of the layer of material. Values of U have been quoted as high as 1800 J

m-2 s-1 °C-1 under very good conditions and down to about 60 J m-2 s-1 °C-1

under poor conditions.

2.6.1.5.2 MASS TRANSFER IN DRYING

In heat transfer, heat energy is transferred under the driving force provided

by a temperature difference, and the rate of heat transfer is proportional to

the potential (temperature) difference and to the properties of the transfer

system characterized by the heat-transfer coefficient. In the same way, mass

is transferred under the driving force provided by a partial pressure or

concentration difference. The rate of mass transfer is proportional to the

potential (pressure or concentration) difference and to the properties of the

transfer system characterized by a mass-transfer coefficient.

Writing these symbolically, analogous to q = UA T, we have

dw/dt = k'g A Y                                                      (2.16)

40

where w is the mass being transferred kg s-1, A is the area through which the

transfer is taking place, k'g is the mass-transfer coefficient in this case in

units kg m-2 s-1 , and Y is the humidity difference in kg kg-1.

2.6.1.5.3 DRYING EQUIPMENT

In an industry so diversified and extensive, it would be expected that a great

number of different types of dryer would be in use. This is the case and the

total range of equipment is much too wide to be described. The principles of

drying may be applied to any type of dryer. Examples are Tray Dryers,

Tunnel Dryers, Roller or Drum Dryers, Fluidized Bed Dryers, Spray Dryers,

Pneumatic Dryers, Rotary Dryers, Trough Dryers, Bin Dryers, Belt Dryers,

Vacuum Dryers, Freeze Dryers.

41

CHAPTER THREE

METHODOLOGY AND PROCESS DESCRIPTION

Chalk can be made from different raw materials or their combinations in

different proportion. The various raw materials used in chalk production are,

calcium carbonate, kaolin calcined gypsum and water. Pigments or dyes are

also used in the case of making coloured chalk.

The raw material (calcium carbonate, kaolin or calcined gypsum) is first

crushed in a crusher to obtain a homogenous fine powder. It is then mixed

with water in the volume proportion of 4:5 in the mixer or homogenizer. The

slurry is then passed through an extruder where a setting time of ten (10)

minutes is allowed. The set chalk is sent to the dryer where ten percent

(10%) of its water content is retained and the chalk is ready for use.

Fig 3.1 Flow chart of process

42

TANK

SOURCE(CaCO3)

CRUSHER

MIXER MOULDDRYER

3.1 DESIGN PROCESS DESCRIPTION

The type of process employed in this design is a semi continuous process.

The raw material after crushing is sent to the mixer through a conveying belt

where it is mixed with water from a tank. The slurry produced is then sent to

a vibrating extruder with holes moving at a particular velocity. A set time of

ten minutes is provided for. The vibration of the extruder is to ensure

adequate compatibility. The set chalk drops into a tray and is taken to the

dryer chamber where is to be heated to a particular temperature and the

moisture is removed to give a ten percent (10%) moisture content

specification.

3.2 PRODUCTION DATA

The objective of this design project is to design a plant that will produce

sixty (60) tons of chalk per annum.

Total no of days in a year (x1) = 365 days

No of days for unforeseen shutdown (x2) = 40 days

Expected production days (x3) = x1 – x2

x3 = 365 - 40 = 325days

Quantity of chalk produced per year = 6000 tons

43

= 6,000,000Kg

Quantity of chalk to be produced per day = 6,000,000 325

= 18,461.53Kg/day

Quantity of chalk to be produced per hour = 60,000,000 326 x 24

= 769.231Kg/hr

Standard School Chalk Specification

Mass of 1 piece of Chalk (g) = 4g = 0.004Kg

Diameter of 1 piece of chalk (cm) = 0.9cm = 0.009m

Length of 1 piece of chalk (cm) = 8cm = 0.08m

No of Chalk produced per hour = 769.231 = 192,307.75chalks/hr 0.004

Chalk Composition

CaCO3.6H2O - 70%

H2O - 30%

It is assumed that CaCO3.6H2O has no impurity.

Note: the mass of school chalk is not related to its volume. This is because

of a lot of pore spaces found in chalk which brings about its compatibility

property.

44

Density of Raw Material

Hydrated Calcium carbonate = 1.771g/cm3 = 2710Kg/m3

Water = 1 g/cm3 = 1000 Kg/m3

To calculate the mass and volume ratio of CaCO3.6H2O and H2O

mixture

For 1 piece of chalk;

Volume of 1 piece of chalk = π x 0.9 2 x 8 = 5.09cm3

4

Mass of 1 piece of chalk = 4g

Mass of CaCO3.6H2O = 0.7 x 4 = 2.8g

Mass of H2O = 0.3 x 4 = 1.2g

Density of CaCO3.6H2O = 1.771g/cm3

Density of H2O = 1g/cm3

Volume of CaCO3.6H2O = mass = 2.8 = 1.581cm3 Density 1.771

Volume of H2O = 1.2 = 1.2cm3 1

Total volume = 1.581 + 1.2 = 2.781cm3

Volume occupied by air = 5.09 – 2.781 = 2.309cm3

Knowing that this volume was initially occupied by water.

45

Volume of H2O initially mixed with CaCO3.6H2O

= 2.309 + 1.2 = 3.509cm3

Mass of H2O initially mixed = density x volume

= 1 x 3.3.509 = 3.509g

Volume mixture ratio H2O : CaCO3.6H2O = 3.509/1.581 = 2.22:1

Mass mixture ratio H2O : CaCO3.6H2O = 3.509/2.8 = 1.25:1

3.3 MATERIAL BALANCE

Material balance is the basis or starting point of any chemical process

design. The quantities or raw materials required and product produced can

be determined by carrying out a material balance over the entire process.

The process stream flow and composition are obtained by balances over

individual process units. The study of plant operation and trouble shooting

can be adequately carried out with knowledge of the material balances.

Material balances can also serve to check sources of loss of material and

instrument calibrations. In carrying out a material balance on a system, a

boundary is created around the system. This boundary separates the system

from the universe and is called a control volume.

46

Material balances obey the law of conservation of mass which states that,

matter can neither be created nor destroyed but the total quantity of matter

remains constant throughout the process. This can be represented

mathematically as shown below:

Accumulation = Mass in – Mass out + Generation – consumption

In cases where no chemical reaction takes place, the steady state balance

reduces to:

Mass in = Mass out

In other to carryout a proper material balance calculation, the following are

some of the parameters required:

1. Mass of stream leaving or entering and present in the system

2. composition of streams leaving or entering the system

Also, to simplify the material balance process, certain assumptions can be

made. Below are some of such assumptions:

1. the process is at steady state

2. the process is continuous

A summary of material balance of this project is given below:

47

3.3.1 Mixer Material Balance Calculation

From the production data

Mass of Chalk produced per hour = 769.23075Kg/hr

CaCO3.6H2O mass feed rate = 769.231 x 0.70 = 538.4617Kg/hr

H2O mass feed rate= 3.509 x 615.385 = 674.8079Kg/hr 2.8

Mass of mixture Out =538.4617 + 674.8079 = 1213.2696Kg/hr

Mass composition of CaCO3.6H2O Out = 538.4617 x 100 = 44.38%1213.2696 1

Mass composition of H2O = 674.8079 x 100 = 55.62%1213.2696 1

Table 3.1 Mixer Material Balance Summary

Component 1 (Kg/hr) 2 (Kg/hr) 3 (Kg/hr)

CaCO3 538.4617 0 538.4617

H2O 0 674.8079 674.8079

48

538.4617Kg/hr 1

1213.2696Kg/hr 3

674.8079Kg/hr 2

CaCO3.6H2O: 100%

H3O: 100%

CaCO3.6H2O: 44.38% H3O: 55.62%MIXER

Total 538.4617 674.8079 1213.2696

3.3.2 Material Balance For Extruder

About twenty five percent (25%) by mass of the mixture is lost to the

atmosphere during setting of the chalk in the mould due to extruder

compression.

Mass feed rate of mixture = 1213.2696Kg/hr

Mass composition of feed components

CaCO3.6H2O: 44.38%

H3O: 55.62%

Mass flow rate of H2O in the mixture

= 0.5562 x 1213.2696 = 674.8079Kg/hr

Mass flow rate of H2O lost during setting

= 1213.2696 x 0.25 = 303.3174Kg/hr

Mass flow rate of H2O left in the mixture

= 674.8079 - 303.3174 = 371.4905Kg/hr

Mass flow rate of CaCO3.6H2O Out

= 1213.2696 - 674.8079 = 538.4617Kg/hr

49

Mass flow rate of mixture from Out stream

= 538.4617 + 371.4905 = 909.9522Kg/hr

MASS FRACTION

Mass fraction of CaCO3.6H2O in the Out stream

= 538.4617 x 100 909.9522 1 = 59.17%

Mass fraction of H2O in the Out stream

= 3714905 x 100 909.9522 1 = 40.83%

Table 3.2 Extruder Material Balance Summary

Component 3 (Kg/hr) 4 (Kg/hr) 5 (Kg/hr)

CaCO3.6H2O 538.4617 0 538.4617

50

1213.2696Kg/hr 3

909.9522Kg /hr 5

303.3174Kg/hr 4

CaCO3.6H2O: 44.38% H3O: 55.62%

H2O: 100%

CaCO3.6H2O: 59.17% H2O: 40.83%MOULD

H2O 674.8079 303.3174 371.4905

Total 1213.2696 303.3174 909.9522

3.3.3 Material balance calculation of dryer

The end product after drying is suppose to leave with a product mass flow

rate of 769.231Kg/hr with mass composition of the components as 70%

CaCO3.6H2O and 30% H2O. Note that CaCO3.6H2O and impurities are

assumed together.

Mass feed rate of mixture = 909.9522Kg/hr

Mass flow rate of chalk (Out) = 769.231Kg/hr

Mass of H2O given off = 909.9522 – 769.231 = 140.7212Kg/hr

Mass flow rate of CaCO3.6H2O (In) (S)= 0.5917 x 909.9522

= 538.4617Kg/hr

Mass flow rate of H2O (In) = 0.4083 x 909.9522 = 371.4905Kg/hr

Mass flow rate of H2O (Out) = 0.3 x 769.231 = 230.7693Kg/hr

51

DRYER

CaCO3: 80% H3O: 20%

7. 769.231Kg /hr909.9522Kg /hr 5

140.7212Kg /hr 6

CaCO3.6H2O: 59.17% H2O: 40.83%

H2O: 100%

Table 3.3 Dryer Material Balance Summary

Component 5 (Kg/hr) 6 (Kg/hr) 7 (Kg/hr)

CaCO3 538.4617 0 538.4617

H2O 371.4905 140.7212 230.7693

Total 909.9522 140.7212 769.231

CHAPTER FOUR

ENERGY BALANCE

52

In process design, energy balances are carried out to evaluate the energy

requirement of the process i.e. heating, cooling and power requirements. In

plant operation, an energy balance on the plant will show the pattern of

energy usage and suggest areas for conservation and savings.

The cost of energy required for a process often represents a substantial

function of the operating cost. However, economic consideration show that a

lot of equipment is employed to conserve energy in the process plant.

4.1 CONSERVATION OF ENERGY

Energy can exist in several forms-heats, mechanical, electrical, etc. in order

to conserve energy, certain laws are obeyed. Most important of them all is

the first law of thermodynamics which is represented mathematically below:

Accumulation = Energy in – Energy out + Generation – Consumption

In the absence of any chemical reaction and at steady state,

Energy in = Energy out

4.2 HEAT (Q) AND ENTHALPY

53

Heat is the energy transfer that occurs between a system and its surroundings

by virtue of a temperature gradient. It is equal to zero for an adiabatic

process.

The energy balance is usually carried out in terms of enthalpy. This is an

integral balance written for the whole system. The various terms deserve

discussion. The enthalpies are relative to some reference temperature, Tref.

Standard tabulations of thermodynamic data make it convenient to choose

Tref = 298K, but choices of Tref 0K or Tref = 0oC are also common. The

enthalpy terms will normally be replaced by temperature using

H = Cp (T- Tref)

Where Cp is the specific heat capacity of the substance.

An additional term, e.g., a heat of vaporization, must be added to enthalpy

equation above if any of the components undergo a phase change.

For a flow diagram in Fig 4.1, the energy balance is thus,

GHG2 + SHS1 = GHG1 + SHS2 + Q

HG = CS(tG-t0) + Hƒ0

CS = 1.005 + 1.88H

Hs = CpS(ts - t0) + XCpA(ts - t0)

Where G = air flow rate

54

S = CaCO3 flow rate

H = humidity of air

CS = humid heat in KJ/Kg

CpS = heat capacity of CaCO3

CpA = heat capacity of liquid H2O

ƒ0 = latent heat of water

t = temperature

t0 = ref temperature

Q = heat transferred

ASSUMPTIONS

1. Process operation at steady state conditions.

2. Negligible heat losses i.e. adiabatic process.

3. Outlet stream temperature is at process unit temperature

55

Q

H1, tG1 G, H2, tG2

X2, tS2

S, X1, tS1

Below are some of the thermodynamic properties of some compounds in this

project.

Table 4.1 Thermodynamic properties of compounds

Component Tc Cp (KJ/Kg) Vapour pressure

Boiling point (0C)

Melting point (0C)

Density (Kg/m3)

Mol. Wt (g/mol)

Specific gravity

Tp

CaCO3 9.848KJ/Kg 2710 100 2.71H2O 4.187 100 0 1000 18 1

Dryer

In this project, only the dryer has an energy input.

Energy balance calculation of dryer

Change in enthalpy H = Q = MCPT

H solid in + Q = H vap.water + H solid out

H solid in = (MCPT)solid + (MCPT)water

= [538.4617 x 9.848 x (25 – 0)] + [371.4905 x 4.187 x (25 – 0)]

= 171455.0386KJ/Kg

H solid out = [538.4617 x 9.848 x (100 – 0)] + [230.7693 x 4.187 x (100 – 0)]

= 626900.1881KJ/Kg

H vap.water = Mƒ0

ƒ0 = heat of vaporization of water at 1000C

H vap.water = 140.7212 x 2501 = 351943.7212KJ/Kg

56

Q = (351943.7212 + 626900.1881) - 171455.0386

Q = 807,388.8707KJ/Kg

Table4.2 Summary of Energy balance

Input

(KJ/Kg)

Output

(KJ/Kg)

H5 171455.0386

Q 807,388.8707

H6 351943.7212

H7 626900.1881

Total 978843.9093 978843.9093

57

CHAPTER FIVE

EQUIPMENT DESIGN

5.1 CHEMICAL ENGINEERING DESIGN

In a process design, equipment design involves a system of choosing,

specifying and designing of equipment required to operate a process plant or

unit. It also includes selection of appropriate materials of construction,

specification and fabrication

The equipment used in the chemical industries includes proprietary and non-

proprietary equipment. Proprietary equipments are those manufactured by

proprietary firms or specialists, who have patent right to such equipment.

Equipment like pumps, compressors, filters, dryers, heat exchangers,

reactors, distillation columns etc are proprietary equipment, while

conventional vessels are non- proprietary equipment.

In this project, the equipments to design are a mixer, extruder, and a dryer.

5.2 SCOPE OF DESIGN

The scope of this design include determination of:

1. total heat transfer surface area

2. diameter of equipment

3. length/height of equipment

58

4. wall thickness of equipment

5. material for construction

5.3 INSTRUMENTATION AND CONTROL

In the chemical industry, instruments are used to measure process variables

such as temperature, pressure, density, viscosity, specific heat, conductivity,

pH, humidity, dew point, liquid level, flow rate, chemical composition and

moisture content. By use of necessary instruments, the values these variables

can be recorded continuously and controlled within narrow limits.

Automatic control can also be adopted. This in turn will save labour cost and

improves plant operation efficiency.

The aims of instrumentation scheme are as follows

1. It provides information for production route

2. It provides information for quality products

3. It enhances plant operation at minimum production cost and

optimum output

4. It ensures safe plant operation

5. It prevents and minimizes process plant accidents.

59

5.4 SPECIFICATION SHEET OF MIXER

MATERIAL FOR CONTRUCTION STAINLESS STEEL

MASS FLOW RATE (Q) 1213.26Kg/hr

VOLUME 3.1416m3

HEIGHT 4m

DIAMETER 1m

SURFACE AREA OF VESSEL 12.5664m2

OPERATING TEMPERATURE 250C

PRESSURE 1atm

TENSILE STRESS 145N/m

THICKNESS OF VESSEL 0.1656mm

MOTOR POWER 1.5-2.0 KW/m3

BLADE Ribbon blade

60

5.5 SPECIFICATION SHEET OF EXTRUDER

MATERIAL FOR CONTRUCTION STAINLESS STEEL

MASS FLOW RATE 1213.26Kg /hr

VOLUME OF EXTRUDER LINE 152.6928cm3

LENGTH OF LINE 240.0179cm

DIAMETER OF LINE 0.9cm

SURFACE AREA OF LINE 678.6346cm2

NO OF EXTUDER LINE 534.1880

OPERATING TEMPERATURE 250C

61

5.6 SPECIFICATION SHEET OF DRYER

MATERIAL FOR CONTRUCTION STAINLESS STEEL

MASS FLOW RATE (Q) 909.9522Kg/hr

VOLUME 2.2m3

HEIGHT 1m

LENGTH 2.2m

WIDTH 1M

DRYING SURFACE AREA 10m2 /hr

OPERATING TEMPERATURE 1000C

PRESSURE 1atm

TENSILE STRESS 145N/m

THICKNESS OF VESSEL 0.1656mm

NO OF DRYER TRAY 20

62

5.7 CAPACITY SIZING CALCULATIONS

MIXER

From the production data:

Mass feed rate of CaCO3 = 538.4617Kg/hr

Mass feed rate of H2O = 674.8079Kg/hr

Density of CaCO3 + impurities = 1.771g/cm3 = 1771Kg/m3

Density of H2O = 1g/cm3 = 1000Kg/m3

Volumetric flow rate of CaCO3 = 538.4617 1771

= 0.304 m3/hr

Volumetric flow rate of H2O = 674.8079 1000

= 0.771 m3/hr

Volumetric flow rate of the mixture =0.304+ 0.6748

= 0.9788 m3/hr

Assume a retention time (t) =5mins = 5/60hr

Mixture volume = Retention time x Volumetric flow rate of mixture

= 5 x 0.9788 60

= 0.08157 m3

Actual size of vessel = mixture volume + 40% mixture volume

63

= 0.08157 + (40% 0.08157)

= 0.11419m3

Taking height to diameter ratio of 3/2

Height (H) = 3 x Diameter ---------------------------------12

Volume of a cylinder = πD 2 H ---------------------------------2 4

Substituting equation 1 into 2 and equating to the size of vessel

22 x D 2 x 3D = 0.114197 4 2

D =

D = 0.459m aprox to 1m

H = 3 x 0.459m2

H = 0.689m approx to 4m

Surface area of mixer = 2πDH 2

= 2 x 22 x 1 x 4 7 2

= 12.5664m2

Auxiliary equipment needed for the mixer are motor and blades.

64

0.11419 x 7 x 4 x 2 22 x 33

From Coulson & Richardson, 1999, Vol 6, 3rd Edition

Type of equipment is a Horizontal trough mixer, with ribbon blades, paddles

of beaters. This is because it’s rotating element produces contra flow

movement of materials necessary for moist powders

Motor Power Requirement;

The power requirement is 1.5 – 2.0 KW/m3 because it is suitable for slurry

suspension.

EXTRUDER

Chalk/hole specification

Diameter (D) = 0.9cm = 0.009m

Length (L) = 8cm = 0.08m

Volume of a chalk/hole (Vc) = πD 2 L 4

= 22 x 0.009 2 x 0.08 7 4

= 5.0894 x 10-6cm3

Setting time of chalk = 10mins = 1 hr6

From the production data:

Mass feed rate of CaCO3 = 538.4617Kg/hr

65

Mass feed rate of H2O = 674.8079Kg/hr

Density of CaCO3 + impurities = 1.771g/cm3 = 1771Kg/m3

Density of H2O = 1g/cm3 = 1000Kg/m3

Volumetric flow rate of CaCO3 = 538.4617 1771

= 0.304 m3/hr

Volumetric flow rate of H2O = 674.8079 1000

= 0.6748 m3/hr

Volumetric flow rate of the mixture =0.304+ 0.6748

= 0.9788 m3/hr

No of chalk/hole per hr = volume feed rate/hr Volume of a piece of chalk

= 0.97885.0894 x 10-6cm3

No of chalk /hole per hr = 192307.6923 pieces

Let each line of extruder produce 1 piece of chalk every 10 seconds

Therefore, every 1hour, it will produce = 60 x 60 = 360 10

No of extruder line 192307.6923 = 534.18803lines 360

66

Taking setting time of 5mins

Volume flow rate = 0.9788 x 5 = 0.08156667m3 = 81566.6667cm3

60

Diameter of pipe/chalk = 0.9cm

Volume flow for each extruder line = 81566.6667 = 152.6928cm3

534.1880

Length of extruder line

Vol = πD2L 4

152.6928 = π x 0.92 x L 4

L = 152.6928 x 4 π x 0.92

L = 240.0179cm = 2.4m

Surface area = 2 π D L 2

= 2 π x 0.9 x 240..0179 2

= 678.6346cm2

NOTE: The volume of chalk is calculated before twenty percent (20%) by

mass of water goes off. This is because the volume will still be the volume

of the chalk even after the water has gone off. This effect rather leaves pore

67

spaces within the structure of the chalk which ensures its compatibility

specification.

DRYER

Going by an approximation of 20,000 pieces of chalk per hour, a tray

measuring 1m x 1m takes about 1000pieces. Therefore, the dryer shold

contain 20 trays, 10 trays at each side to accommodate 20,000 pieces.

Assuming a dryer chamber height of 8cm,

Height of dryer = (8 x 10) + 25% of (8 x 10) = 100cm = 1m

(25% is an allowance for the dryer cap and standing)

Width of dryer = 1m

Length of dryer = 1m + 1m = 2m

Taking demarcation allowance of 10% length;

Actual length of dryer = 2 + (10% of 2) = 2.2m

Height of dryer = 1m

Drying surface area of dryer = 10m2

DETERMINATION OF WALL THICKNESS

68

The wall thickness e is given by the expression

e = PiDi

2f-Pi

Where Pi = internal pressure, N/m2

F = design stress, N/m2

Di = internal diameter, m

e = minimum thickness, m

MIXER

Pi = 1atm = 0.1N/m2

F = 145N/m

Di = 0.48 x 103mm

e = 0.1 x 0.48 x 10 3 (2 x 145) - 0.1

e = 0.1656mm

EXTRUDER

Pi = 1atm = 0.1N/m2

F = 145N/m

Di = 0.09968 x 103mm

e = 0.1 x 0.09968 x 10 3 mm (2 x 145) - 0.1

69

e = 0.00307mm

CHAPTER SIX

ECONOMIC ANALYSIS

70

When a chemical plant is built, profit output is expected from it therefore an

estimation of the investment required and the cost of production are needed

before the profitability of any project can be assessed.

The knowledge of economic analysis helps to determine the relationship of

income and expenses that should be applicable for such venture to lead to a

break even point and the rate of return on the investment.

6.1 ACCURACY AND PURPOSE OF CAPITAL ESTIMATION

The accuracy of an estimate depends on the amount of design details

available, the cost data available and the time spent on preparing the

estimate, (Coulson & Richardson’s, 2002). In the early stages of a project

only an appropriate estimate will be required.

6.2 FIXED AND WORKING CAPITAL

Fixed capital is the total cost of the plant ready for start up (Coulson &

Richardson’s, 2002). It is the cost paid to the contractor and includes:

(a) Design and other engineering and construction supervision

(b) All items of equipment and their installation

(c) All piping instrument and control

(d) Building and structure

71

(e) Auxiliary facility is the additional investment needed, over

and above the fixed capital to start the plant up and operate

it to the point when income is earned. The total investment

needed for project is the sum of the fixed and working

capital.

6.3 ECONOMIC EVALUATION CALCULATION

Purchase Cost of Equipments

From (2002), Coulson & Richardson, 2002,

Ce = CSn

Ce = purchase equipment cost ($)

S = characteristic size parameter (m)

N = index for that type of equipment

MIXER

C = 15000

S = 0.130

n = 0.4

Ce = 15000 x 0.1300.4

= $6,632.37

EXTRUDER

72

C = 960

S = 2.3

n = 1.0

Ce = 960 x 2.31

= $2208

DRYER

C = 7700

S = 1.9

n = 0.55

Ce = 7700 x 1.90.55

= $10,959.87

Conversion factor from dollars to naira = 118

Mixer $6,632.37 N 782,619.66

Extruder $2208 N 260,544.00

Dryer $10,959.87 N 1,293,264.66

Total $19,800.24 N 2,336,428.32

Total of Purchase Cost of Equipments, PCE is $19,800.24/ N 2,336,428.32

ƒ1 Equipment erection 0.50

73

ƒ2 Piping 0.20

ƒ3 Instrumentation 0.10

ƒ4 Electrical 0.10

ƒ5 Buildings ----

ƒ6 Utilities ----

ƒ7 Storages 0.25

ƒ8 Site development ----

ƒ9 Ancillary buildings ---

Total physical plant cost (PPC) = PCE(1+ƒ2 +ƒ3+ƒ4+ƒ5 +ƒ6 +ƒ7 +ƒ8 )

PPC = 19,800 (1+0.5+0.2+0.1+0.1+0.25) = 19,800(2.15)

= $42,570/ N5,023,260.00

ƒ10 Design and Engineering 0.20

ƒ11 Contractors fee ----

ƒ12 Contingency 0.10

Fixed Capital(FC) = PPC(1+ ƒ10 + ƒ11 + ƒ12 )

FC = 425570(1+ 0.2 + 0.1) = 42570(1.3) = $55,341/ N 6,530,238.00

Working capital = 5% of Fixed capital = N326,511.90

Total Investment Cost = WC + FC = N 6,856,749.90

Annual Operating Costs

74

Operating time = 325days

Variable Costs:

Raw material = N5,000/ton = N30,000,000.00/6000tons

Utilities cost = N18,000.00/year

Shipping and packaging = 1% of Raw material = N300,000.00

Variable Cost = N 30,318,000.00

Fixed Costs:

Maintenance = 5% of FC = N326,511.90

Labour(two shifts with 0ne extra per shift ) 2 at mixer and 3 at dryer plus 1

extra man multiplied by two = 12men

With annual salary of N960, 000 = N11, 520,000.00

Capital charges (10% of FC) = N653,023.80

Fixed Cost = N 12, 499,535.70

Annual Operating Cost = N30,318,000.00 + N12,499,535.70

= N 42,817, 535.70

Assume a project life of 20 years. Also assume a profit of N 500,000.00 for

the first year and an increase of N 250,000.00 for subsequent years .

Also assume that the first 12 years is best year for profit making.

Table 6.1: Cost estimate of Production of 769.231Kg/hr of Chalk

75

EQUIPMENTS AMOUNT(N)

MIXER 782,619.66

EXTRUDER 260,544.00

DRYER 1,293,264.66

PURCHASE COST OF EQUIPMENTS 2,336,428.32

PHYSICAL PLANT COST 5,023,260.00

FIXED CAPITAL 6,530,238.00

TOTAL INVESTMENT COST 6,856,749.90

VARIABLE COST 30,318,000.00

FIXED COST 12, 499,535.70

ANNUAL OPERATING COST 42,817, 535.70

ACCUMULATIVE CASH FLOW

76

Accumulative Cash Flow = P1 (I1 + I2 + I3 + ……+ I12 )

Where P = profit in the 1st year = N 500,000.00

Profit in 2nd year = 500000 + 250000 = N 750,000.00

I2 = ratio of the 2nd year to the 1st year

I2 = 750000 500000

= 1.5

The common difference = 1.5 – 1 = 0.5

I3 = I2 + 0.5 = 1.5 + 0.5 = 2.0

I4 = I3 + 0.5 = 2.0 + 0.5 = 2.5

I5 = I4 + 0.5 = 2.5 + 0.5 = 3.0

I6 = I5 + 0.5 = 3.0 + 0.5 = 3.5

I7 = I6 + 0.5 = 3.5 + 0.5 = 4.0

I8 = I7 + 0.5 = 4.0 + 0.5 = 4.5

I9 = I8 + 0.5 = 4.5 + 0.5 = 5.0

I10 = I9 + 0.5 = 5.0 + 0.5 = 5.5

I11 = I10 + 0.5 = 5.5 + 0.5 = 6.0

I12 = I12 + 0.5 = 6.0 + 0.5 = 6.5

Cumulative Cash Flow = 500,000(45) = N 22,500,000.00

RATE OF RETURN

77

Rate of return is given as

ROR = cumulative cash flow attend of project x 100 Life of project x original investment

ROR = F - C x 100 C x G

F = cumulative cash flow

C = investment

G = life of project

ROR = 22,500,000 - 6,856,749.90 x 1006,856,749.90 x 12

= 19.01%

PAYBACK TIME

Since the annual saving is constant

The payback time is the reciprocal of rate of return

Payback time = 1ROR

= 100 19.01

= 5.26years

BREAK-EVEN POINT

78

Flow rate of chalk produced = 6000Kg/yr

Capacity of plant in 4.36 years (Payback Tme)

= 6000 x 5.26 = 31560tons

Capacity in 12 years

= 6000 x 12 = 72000tons

Break even point = capacity at 4.36 years capacity at 12 years

= 31560 72000

= 0.4383 = 43.83%

CHAPTER SEVEN

79

PROCESS SAFETY

Concern for accidents dates back to the industrial revolution of the 18 th

century. This is when machines were invented and factories were built and

were installed with these machines.

Several accidents occurred in the factories resulting in injuries, maiming,

incapacitation, and death. All these are due to poor safety management.

Accidents are caused by unsafe act and unsafe condition.

Unsafe acts includes

- working on moving or dangerous equipment unnecessary

- failure to wear personal protective equipment wearing

- by passing safety devices

- unsafe position or posture

- unsafe placing or mixing

Unsafe conditions includes

- unsafe clothing

- unkempt environment

- hazardous method of operation

- public hazard

80

In other to tackle hazards associated with work place, process called HEMP

(Hazard and Effect Management Process. It is a process for identifying the

hazards in an activity and the effect, with a view to eliminating them or

controlling them to reduce the effect to ALARP (As Low As Reasonably

Practicable)

The is achieved by

1. identify

2. access

3. control

4. recover

81

REFERENCE

1. Kirk and Othimer (1982). Encyclopedia of Chemical Technology.

Vol. 6, 3rd Ed., John Wiley And Sons, Pg. 645-649

2. Kirk and Othimer (1982). Encyclopedia of Chemical Technology.

Vol. 4, 3rd Ed., John Wiley And Sons, Pg. 290

3. "Solvay Precipitated Calcium Carbonate: Production". Solvay S.

A. (2007-03-09). Retrieved On 2007-12-30.

4. ^ "Blast Furnace". Science Aid. Retrieved On 2007-12-30.

5. ^ A B C D "Calcium Carbonate Powder". Reade Advanced Materials

(2006-02-04). Retrieved On 2007-12-30.

6. ^ "Selected Solubility Products and Formation Constants at 25

°C". California State University, Dominguez Hills.

7. ^ Cornelis Klein And Cornelius S. Hurlbut, Jr., 1985, Manual Of

Mineralogy, John Wiley, 20th Ed., Pp. 352-353, ISBN 0-471-

80580-7

8. ^ Juan Manuel García-Ruiz, Roberto Villasuso, Carlos Ayora,

Angels Canals, and Fermín Otálora (2007). "Formation of Natural

82

Gypsum Megacrystals In Naica, Mexico". Geology 35 (4): 327–

330. Doi:10.1130/G23393A.1.

9. ^ Barry F. Beck, Felicity M. Pearson, P.E. Lamoreaux &

Associates, National Groundwater Association (U.S.), Karst

Geohazards: Engineering And Environmental Problems In Karst

Terrane, 1995, Taylor & Francis, 581 Pages ISBN:9054105356

10. ^ Abarr, James. "Sea Of Sand", The Albuquerque Journal, 1999-

02-07. Retrieved On 2007-01-27.

11. ^ C. Michael Hogan, Knossos Fieldnotes , Modern Antiquarian

(2007)

12. Douglas, A. S. (1990). “Analytical Chemistry”. Harcourt Brace

Jovanovich College Publishers, Pg 300

13. Breck, D.W. (1984)Zeolite Molecular Sieves, Robert E. Brieger

Publishing Company: Malabar, FL, Pp. 314-315, ISBN 0-89874-

648-5.

14. Deer, W.A., Howie, R.A., and Zussman, J. (1992) an Introduction

to the Rock-Forming Minerals (2nd Ed.). Harlow: Longman ISBN

0-582-30094-0.

83

15. Hurlbut, Cornelius S., Klein, Cornelis (1985) Manual Of

Mineralogy - After J. D. Dana, 20th Ed., Wiley, Pp. 428 - 429,

ISBN 0-471-80580-7.

16. Bellotto, M., Gualtieri, A., Artioli, G., And Clark, S.M. (1995)

Kinetic Study Of The Kaolinite-Mullite Reaction Sequence. Part I:

Kaolinite Dehydroxylation', Phys. Chem. Minerals, Vol 22, 207-

214.

17. The Mineral KAOLINITE - Mineral Galleries

18. MSDS: Incandescent Light Bulb - GE

19. Snell. Ethre (1969). Encyclopedia of Industrial Chemical

Additives. Inter Science Publishers, Pg80 – 100

20. Boynton, Robert. Chemistry and Technology of Lime and

Limestone. John Wiley & Sons, 1980.

21. Cobb, Vicki. The Secret Life of School Supplies. J. B. Lippincott,

1981.

22. Institution of Civil Engineers Staff, Eds. Chalk. American Society

of Civil Engineers, 1990.

23. Toth, Beth. "Jeanne Otis: A Color Dialogue," Ceramics Monthly.

January, 1988, P. 40.

84

24. Authors: R.L. Earle With M.D. Earle., Unit Operations In Food

Processing, Web Edition, 2004. The New Zealand Institute Of

Food Science & Technology (Inc.)

25. ASHRAE Guide and Data Books, American Society of Heating,

Refrigerating and Air Conditioning Engineers, New York.

26. Bird, R. B., Stewart, W. E. And Lightfoot, E. N. (1960) Transport

Phenomena, Wiley, New York.

27. Bond, F. C. (1952) Min. Engng. 4, 484; Chem. Engng. 59, 169.

28. Coulson, J. M. And Richardson, J. F. (1977, 1978) Chemical

Engineering, Vol.1, 3rd Edition. Vol.2, 3rd Edition, Pergamon,

Oxford.

29. Dk V Arbeitsblatt 2-02 (1950), C. F. Muller, Karlsruhe.

30. Ede, A. J. (1949) Mod. Refrig. 52, 52.

31. International Critical Tables (1930), Mcgraw-Hill, New York.

32. Jason, A. C. (1958) In Fundamental Aspects of The Dehydration

Of Foodstuffs, Society Of Chemical Industry, London.

33. Mccabe, W. L.,Smith, J. C.And Harriott, P.(1975) Unit Operations

Of Chemical Engineering, 3rd Edition, Mcgraw-Hill, New York.

85

34. Mccabe, W. L. And Thiele, E. W. (1925) Industr. Eng. Chem. 17,

605.

35. Manheim, H. C., Steinberg, M. P., Nelson, A. I. And Kendall, T.

W. (1957) Food Technol. 11, 384.

36. Moody, L. F. (1944) Trans. Am. Soc. Mech. Engrs. 66, 671.

37. Perry, J. H.And Others (1997) Chemical Engineers' Handbook, 7th

Edition, Mcgraw-Hill, New York.

38. Plank, R. (1913) Z. Ges. Kalteind., 20, S. 109; (1941) Ibid., Beih.

Reihe 3, H.10.

39. Rushton, J. N., Costich, E. W. And Everett, H. 5. (1950) Chem.

Engng. Prog. 46,395.

40. Treybal, R. E. (1987) Mass Transfer, 3rd Edition, Mcgraw-Hill,

New York.

41. Trowbrldge, M. E. O'k. (1962) Chem. Engng. (U.K.) No.162,

A.73.

42. Whitman, W. G. (1923) Chem. and Met. Engng. 29, 147.

43. Nigerian Institute of Safety Professional, Contractor Employee

HSE Training Manual

86

44. Sinnot, R. (2002), Coulson & Richardson’s Chemical Engineering,

Vol 6, Butterworth Heinemann

45. 1995,News letter, Embassy of Nigeria

87