project chalk correction

June 10, 2018 | Author: Emeka Nicholas Ibekwe | Category: Gypsum, Mill (Grinding), Heat Transfer, Chemistry, Materials


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CHAPTER ONEINTRODUCTION 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 CaCO3. 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 aragonite. 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 Physical Properties of Calcium Carbonate Table 1. marble [471-34-1] CaCO3 100. chalk. 5 . calcite.1 Other names Identifiers CAS number: Properties Molecular formula: Molar mass: Appearance: Limestone.087 g/mol White powder.calcium supplement or as an antacid. the free encyclopedia) Note: Except where noted otherwise.71 g/cm³ (calcite). data are given for materials in their standard state (at 25 °C. can be produced from a pure quarried source (usually marble). for industrial or pharmaceutical use).83 g/cm³ (aragonite) 825 °C Decomposes Decomposes Insoluble Linear Not hazardous.1 Preparation The vast majority of calcium carbonate used in industry is extracted by mining or quarrying. Non-flammable. Pure calcium carbonate (e.Density: Melting point: Boiling point: Solubility in water: Structure Molecular shape : Hazards Main hazards: Flash point: 2.g. 100 kPa) 2. Water is added to give calcium hydroxide. calcium oxide is prepared by calcining crude calcium carbonate. 2. and carbon dioxide is 6 .1. (From Wikipedia. Alternatively. 7 .passed through this solution to precipitate the desired calcium carbonate.[3]. Calcium carbonate is widely used as an extender in paints. 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 2.2 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.1.[5] Calcium carbonate is also widely used as filler in plastics. hydrated calcium sulfate CaSO4·2H2O.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. 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.[3] where it is used as a common ingredient for many glazes in its white powdered form. 8 . Calcium carbonate is known as whiting in ceramics/glazing applications. Rivers. pigments and water. Bauchi. Ogun. Ondo. 2. gypsum. nonbrittle. Gombe. Ekiti. These materials are available in large quantities in Nigeria and could be easily sourced for. Katsina and Plateau Gypsum Gypsum can be found in Yobe. Kogi. Kaolin Kaolin is found in the following Nigerian states: Ogun. Imo. kaolin. A good quality chalk must be non-porous.1 OTHER RAW MATERIALS FOR THE PRODUCTION OF SCHOOL CHALK The basic raw materials required in the manufacture of school chalk include. Adamawa. there is need to meet standard. Anambra.CHARPTER TWO LITERATUURE REVIEW Despite the fact that school chalk can now be produced locally. Below are areas in Nigeria where these various raw materials could be found. non-toxic. Sokoto and Edo 9 . Kebbi. Akwa Ibom. oil-free and must have the ability to give good inscription. limestone (Calcium Carbonate). gypsum can occur in a flower-like form typically opaque with embedded sand grains called desert rose.States. 2.1 Gypsum Gypsum is a very soft mineral composed of calcium sulfate dihydrate. A very fine-grained white or lightly-tinted variety of gypsum is called alabaster. The most visually striking variety. Ebonyi. A recent publication shows that these crystals are grown under 10 . is the giant crystals from Naica Mine.[7] Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. Benue. Finally it may also be granular or quite compact. however. In arid areas.1. in which case it is commonly called satin spar. Up to the size of 11m long. it can be anywhere from transparent to opaque. these megacrystals are among the largest crystals found in nature. Ogun. It may also occur silky and fibrous. which is prized for ornamental work of various sorts. Edo and Kogi States. In hand-sized samples. Gombe. Limestone Limestone can be found in Cross River. Sokoto. with the chemical formula CaSO4·2H2O. 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. with thick and extensive evaporite beds in association with sedimentary rocks. enough to supply the construction industry with drywall for 1. referring to the burnt or calcined mineral. this material has been called plaster of Paris.[10] Commercial exploitation of the area. was permanently prevented in 1933 11 . shampoos and many other hair products.000 years. strongly opposed by area residents.[8] Gypsum is a common mineral. as well as in hot springs. It is also used in foot creams. Because gypsum dissolves over time in water. It is water-soluble. "to cook". Deposits are known to occur in strata from as early as the Permian age.[9] Gypsum is deposited in lake and sea water. Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes. However. gypsum is rarely found in the form of sand. The word gypsum is derived from the aorist form of the Greek verb μαγειρεύω.constant temperature such that large crystals can grow slowly but steadily without excessive nucleation. 2. flat.33 3 hot. or waxy α=1.523. γ=1.31 .5-2 Vitreous to silky. dilute HCl transparent to translucent Mineral Calcium Sulfate CaSO4·2H2O Physical properties of Gypsum 12 . Table 2.when president Herbert Hoover declared the gypsum dunes a protected national monument. pearly. sometimes fibrous 1. β=1.520.1 General Category: Chemical formula: Identification Color: Crystal habit: Crystal system: Twinning: Cleavage: Fracture: Mohs Scale hardness: Luster: Refractive index: Optical Properties: Pleochroism: Streak Specific gravity: Fusibility: Solubility: Diaphaneity: Major varieties White to grey. pinkish-red Massive.530 2V = 58° + None White 2. Elongated and generally prismatic crystals Monoclinic 2/m common {110} good (66° and 114°) Conchoidal. when wood became scarce due to deforestation on Bronze Age Crete. Some of these uses are: • • • Drywall Plaster ingredient. gypsum was employed in building construction at locations where wood was previously used. In the late eighteenth and early nineteenth century. for example. modeling).1. • • Plaster of Paris (surgical splints. casting moulds. slightly colored (From Wikipedia. fibrous masses Transparent and bladed crystals Fine-grained.Satin Spar: Selenite: Alabaster: Pearly. was a highly sought fertilizer for wheat fields in the United States. often referred to as plaister.1 Uses of Gypsum There are a large number of uses for gypsum throughout prehistory and history.[11] 13 . Fertilizer and soil conditioner.1. the free encyclopedia) 2. Nova Scotia gypsum. A wood substitute in the ancient world. a hemihydrate of calcium sulphate is known as plaster of paris (P. When calcinating at a temperature between 120oC . making it ultimately a major source of dietary calcium. 2. Blackboard chalk.O.P) CaSO4.130oC.2 CALCINED GYMPSUM Calcinations of gypsum can take place either in kettle or rotary kilns. If the gypsum is ground into powder. • • • Adding hardness to water used for homebrewing. kettle is used.1.3000C.H2O + H2O This is called the kettle. On heating up to a temperature of 1900C.• A tofu (soy bean curd) coagulant. all the water of hydration will be lost giving calcium sulphate (CaSO4) 14 . 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.2H2O Heat CaSO4. especially in Asian cultures which traditionally use few dairy products. 1.3000C) and quicklime and sulphate at higher temperature (11000C).2H2O Heat CaSO4.2000C CaSO4. gypsum decomposes to yield calcium oxide and sulphate. soil conditioning. CaSO4 MOULD Heat CaO + SO2 + 1/2O2 For the rotary kiln process. 2. calcined gypsum has some other wide industrial applications such as in ceramics. Apart from its use in the manufacture of chalk. Gypsum is used mainly during calcinations to obtain hemihydrates form and anhydrite form at low temperatures (1200C. the gypsum is crushed to pieces through a 40mm screen.3 Kaolinite Kaolinite is a clay mineral with the chemical composition Al2Si2O5(OH)4. art and casting plasters. orthopedic and dental plaster. It is a layered silicate mineral. pottery mould. wall and floor plastering. If heating continues at a very high temperature above 11000C. suspended ceiling and fillers for paints.H2O + H2O This is called second kettle. with one tetrahedral sheet linked through 15 . 16 . Germany. United Kingdom. Lighter concentrations yield white.oxygen atoms to one octahedral sheet of alumina octahedra (Deer and others. giving it a distinct rust hue. usually white mineral (dioctahedral phyllosilicate clay). it is colored pink-orange-red by iron oxide. Australia. Jiangxi province. 1992). The name is derived from Gaolin ("High Hill") in Jingdezhen. China. in Brazil. earthy. produced by the chemical weathering of aluminium silicate minerals like feldspar. the People's Republic of China.) It is a soft. Rocks that are rich in kaolinite are known as china clay or kaolin. it is mined. In many parts of the world. India. Kaolinite was first described as a mineral species in 1867 for an occurrence in the Jari River basin of Brazil. and the USA.[13] Kaolinite is one of the most common minerals. France. yellow or light orange colours. as kaolin. Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g. Korea .. β 1.for example in tropical rainforest areas.2.565.570 white 2. Embassy of Nigeria.1. In Nigeria. 1995).Kaolinite clay occurs in abundance in soils that have formed from the chemical weathering of rocks in hot. γ 1.569. Table 2. where ancient soils have been buried and preserved.569 .559 .1. sometimes red. the proportion of kaolonite decreases.2 Physical properties of Kaolin Mineral Al2Si2O5(OH)4 White.2.553 . Such climatically-related differences in clay mineral content are often used to infer changes in climates in the geological past.5 dull and earthy α 1.68 17 General Category: Chemical formula: Identification Color: Crystal habit: Crystal system: Cleavage: Fracture: Mohs Scale hardness: Luster: Refractive index: Streak: Specific gravity: . an estimated reserve of 3 billion tonnes of good kaolinific clays has been identified (News letter.1. while the proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. Comparing soils along a gradient towards progressively cooler or drier climates. blue or brown tints from impurities Earthy triclinic perfect on {001} Perfect 2 . moist climates .16 . A more recent.(From Wikipedia. In April of 2008.[17] [18] . and more limited. in toothpaste. It is also used in most paints and inks. as a light diffusing material in white incandescent light bulbs. and other vegetation to repel or deter insect damage.[16] Until the early 1990s it was the active substance of anti-diarrhea medicine Kaopectate. The largest use is in the production of paper. medicine. making of school chalk. including ensuring the gloss on some grades of paper.3. as a food additive. the free encyclopedia) 2. and in cosmetics. 18 . 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.1 Uses Kaolin is used in ceramics. vegetables. use is as a specially formulated spray applied to fruits.1. coated paper. humans) in South America originally used it. similar to the way parrots (and later. A traditional use is to soothe an upset stomach. One of the most widespread groups of pigments is porphyries. While a single magazine made using kaolin does not contain enough radioactive material to be detected by a security-oriented monitor. In other words. True pigments are widespread in plant and animal kindom. 19 . They are represented by the chlorophylls of green plants and myoglobin of red systems.Kaolinite can contain very small traces of uranium and thorium. 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.1. and is therefore useful in radiological dating.4 PIGMENTS AND DYES School chalk are usually coloured as a result of the introduction of pigment and dyes during the manufacturing process. this does result in truckloads of high end glossy paper occasionally tripping an overly-sensitive radiation monitor. Pigments are used in the paint industries where they act as resistance to weatering or the protective film in paints. colour production results from the pigments selective absorption of visible light. some have wide distribution while others are restricted to a few species. 2. fur. mechanical retention. rather than by chemical constitutions that dyes are differentiated from pigments.Dyes are intensely coloured substances used for the colouration of various substances including chalk. fabrics.2 MECHANICAL PREPARATION OF RAW MATERIALS Plasticity and castability are parameters used to determine the quality of chalk. Pigments on the other hand retain crystal or particulate form throughout the entire application procedure. lair. leather. The crystal structures may in some cases be regained during a later stage of the dying process. paper. It is by application methods. This this quality is determined by the particle size distribution of the chalk. or by the formation of covalent chemical bons. they are retained in these substances or substrate by physical adsorption. etc. dyes lose their crystal structures by dissolution or vapourization. solution. depending upon the substrate and class of dye. The methods used for the application of dyes to the substrate differ. During the application process. 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 . 2. salt or metal-complex formation. 04 percent to 40 percent.to retain its new shape when deformation force is reduced below certain value. a tiny marine organism. concentrates the calcium found naturally in seawater from . Removal of impurities from the raw materials is also necessary so that they do not interfere with the production process/unit operations which includes. 21 . screening. moulding and drying. The smaller the size of the particles.3 TECHNOLOGY OF CHALK PRODUCTION The main component of chalk is calcium carbonate (CaCO3). Limestone deposits develop as coccoliths(minute calcareous plates created by the decomposition of plankton skeletons) accumulate. Plankton. 2. forming sedimentary layers. 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 easier to form their colloidal suspension and hence. Castability on the other hand is dependent upon socculation. grinding (size reduction). a more uniform and stronger cast is obtained when compared with coarse particle size. flow characteristics and setting rate. mixing. the slower their rate of setting. a form of limestone. which is then precipitated when the plankton dies. As a result. This step washes away impurities and leaves a fine powder. 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. the limestone must be crushed. limestone is first quarried. generally by an open pit quarry method. such as in a jaw crusher. breaks down large boulders.To make chalk.1 LIMESTONE (Calcium Carbonate) Quarrying limestone 22 . 2. secondary crushing pulverizes smaller chunks into pebbles.3. Primary crushing. Next. explosives are placed inside. Pulverizing the chalk • Once comparatively large chunks of limestone have been quarried. but the principle is the same: all compress the stone with jaws or a cone. producing pebbles which are then ground and pulverized. Various crushers exist. In this method. where they are pulverized to meet the demands of the chalk industry. After a sufficient reserve (twenty-five years' worth is recommended) has been prospected. Depending on the nature of the deposit. an open shelf quarry method can be used. 23 . this is very rare. and the rock is blown apart. holes are drilled into the rock. Usually an open pit quarry method is used instead. Secondary crushing is accomplished by smaller crushers that work at higher speeds. If the chalk is close to the surface. The first step is primary crushing. or shatter it through impact. they need to be transported to crushing machines. however. the land that covers the deposit is removed with bulldozers and scrapers. a pit can be enlarged laterally or vertically.• Approximately 95 percent of the limestone produced is quarried. wet grinding. The particles are then mixed with water.3. Finally. and cut to the proper length. 2. washes away impurities. extruded through a die of the proper size. Wet grinding is carried out in ball mills—rotating steel drums with steel balls inside that pulverize the chalk until it is very fine. It is used to make the fine grade of limestone necessary to make chalk suitable for writing purposes.2 Gypsum Dehydrating gypsum 24 . After grinding. the chalk is cured in an oven for four days.• The next phase. the chalk particles are sifted over vibrating screens to separate the finer particles. is also quarried and pulverized. almost all of the water has evaporated.9 percent to between 5 and 6 percent. 25 . The major difference in processing gypsum is that it must be dehydrated to form calcium sulfate. at which point its water content will have been reduced from 20. 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. Sifting. Upon receiving chalk or calcium sulfate. packed in bags. like limestone. the chalk factory usually grinds the materials again to render them smooth and uniformly fine. By now. The ensuing fine chalk is then washed. cleaning. the major component of colored chalk. dried. It is allowed to boil until it has been reduced by twelve to fifteen percent. This is done in a kettle.• Gypsum. and shipping the chalk • The particles of chalk or calcium sulfate are now conveyed to vibrating screens that sift out the finer material. and shipped to the manufacturer. a large combustion chamber in which the gypsum is heated to between 244 and 253 degrees Fahrenheit (116-121 degrees Celsius). leaving calcium sulfate. 5 Boxing the chalk 26 . thin shape. which is then baked in the same manner as white classroom chalk. natural.2.43 inches (62 centimeters). as in a cake recipe). the sticks are next placed on a sheet that contains places for five such sticks. After it has cured.4 Making colored classroom chalk • Pigments (dry. the manufacturer adds water to form a thick slurry with the consistency of clay. 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. where the chalk cures for four days at 188 degrees Fahrenheit (85 degrees Celsius).3. The slurry is then placed into and extruded from a die—an orifice of the desired long. the sticks are cut into 80 millimeters lengths. 2. Cut into lengths of approximately 24. 2.3. The sheet is then placed in an oven. Water is then added to the mixture.3 Making white classroom chalk • To make white classroom chalk.3. Furthermore. the chalkboard is washed. and the quality of the mark is studied. Written specifications state the proper length of the chalk stick. the chalk mark is erased using a dry eraser. a sample from each batch is kept for five years so that it can be inspected if in the future its quality is questioned. a Federal Act (Public Law 100-695) went into effect. All incoming materials are tested for purity before being used.4 Quality Control Chalk that is intended for the classroom must undergo stringent tests in order to perform well and be labeled nontoxic. On November 18. Erasability is also studied. the completed chalk sticks are stacked in large boxes to be shipped to supply stores. 1990. The density and break strength of the sample stick are determined. and the quality of erasure is examined. Then.• Placed in small boxes. and again the amount of chalk left on the board is examined. The sample is then used to write with. mandating that all art materials sold in the United States must be evaluated 27 . First. one stick from each batch is selected for tests. Chalk for classroom use adheres to the American National Standards Institute performance standards. 2. as well as how many sticks should go in a box. After the chalk has been made into sticks. the quantity in which it is used. The product's size and packaging. The CP seal also indicates that the product meets standards of material. and its possible adverse reactions with other ingredients are studied. as well as all federal and state regulations. workmanship. working qualities. and they must consider many factors before granting approval. 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). a nonprofit manufacturers' association. and its tendency to produce allergic reactions are also considered. most chalk manufacturers are tested at random by an independent 28 . Toxicologists are concerned not with cost but with safety. Formulas for every color and every formula change must meet approval.by a qualified toxicologist who must then issue a label explaining their toxicity. Classroom chalk is labeled "CP [certified product] nontoxic" if it meets the standards of the Art and Craft Materials Institute. its potential harm to humans. To ensure honesty. and that the toxicity of art materials for adults has been correctly labeled. Toxicologists also take into account the products use and potential mis-use. This label certifies that art materials for children are nontoxic and meet voluntary standards of quality and performance. Each ingredient. 29 .toxicologist. Bulk Density: This is a measure of the mass of material occupied in a unit volume. Most manufacturers conform to such exacting standards because knowledgeable schools will not purchase chalk that is not properly labeled. Brittleness is the breakage of chalk into bits when in use. The initial moisture content of produced chalk should not exceed 16% The capillarity rate along a 10cm column of 15.77g/cm3 . Hard: School chalk must be hard or rather non-brittle. PROPERTIES OF A STANDARD CHALK 1.17.13 – 2.5 The specific gravity ranges from 2. who checks to see that they are meeting nontoxic standards. 2. 4. Various properties a standard school chalk must possess are: 1. 2. 3. Range = 0.2g mass should not be less than 1.70 – 0. 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.30. Silica must be reduced or possibly removed before moulding to give clear and a visible inscription.1 SIZE REDUCTION 30 . Porosity in chalk causes breakage. 3. Toxic chalk is injurious to health thus should be avoided. 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. 2.2. 4. 5.6. Oil free: good quality chalk must be oil free. 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.6 UNIT OPERATIONS INVOLVED IN CHALK PRODUCTION 2. 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. Non-Toxic: good quality chalk must be safe for teachers and children who make use of it. Some of the energy is taken up in the creation of 31 . emulsification or atomization. dividing them into smaller particles.1. the operations are called grinding and cutting. which is a function of the material. they must be reduced in size. materials are reduced in size by fracturing them. In the grinding process.6. If it is solid. This size-reduction operation can be divided into two major categories depending on whether the material is a solid or a liquid.1 GRINDING AND CUTTING Grinding and cutting reduce the size of solid materials by mechanical action. Cutting is used to break down large pieces of materials into smaller pieces suitable for further processing. but in the process. All depend on the reaction to shearing forces within solids and liquids. 2.Raw materials often occur in sizes that are too large to be used and. therefore. When the local strain energy exceeds a critical level. 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. if it is liquid. such as in the preparation of calcium carbonate for the manufacture of chalk. The mechanism of fracture is not fully understood. fracture occurs along lines of weakness and the stored energy is released. the energy applied to the material should exceed. In the first class the major action is compressive. but the greater part of it is dissipated as heat. Grinding is.6. therefore. and both the magnitude of the force and the time of application affect the extent of grinding achieved.1. by as small a margin as possible.1 Grinding Equipment Grinding equipment can be divided into two classes . impact. 2.crushers and grinders. The force applied may be compression. the minimum energy needed to rupture the material. 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. or shear.its friability.1. 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 .new surface. Excess energy is lost as heat and this loss should be kept as low as practicable. For efficient grinding. whereas grinders combine 32 . 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. shear and impact with compressive forces. This is done successively.6.1. etc 2.  frequency and the amplitude of the shaking. Fixed head mill.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. 33 . usually air. The fluid. Roller mills. SIEVING In the final separation operation in this group. using increasingly smaller screens. particles of smaller size than the mesh openings can pass through under the force of gravity. restraint is imposed on some of the particles by mechanical screens that prevent their passage. can effectively be ignored in this operation which is called sieving. to give a series of particles classified into size ranges. Plate mill. The material is shaken or agitated above a mesh or cloth screen. Rates of throughput of sieves are dependent upon a number of factors:  nature and the shape of the particles. Hammer mills. Examples are Crushers. Actually. Standard sieve sizes have been evolved. covering a range from 25 mm aperture down to about 0. A convenient ratio is 2:1 and this has been chosen for the standard series of sieves in use in the United States. The standard British series of sieves has been based on the available standard wire sizes.6 mm aperture. the Tyler sieve series. 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 4√2:1.54 cm By suitable choice of sizes for the wire from which the sieves are woven. The mesh was originally the number of apertures per inch. methods used to prevent sticking or bridging of particles in the apertures of the sieve and  tension and physical nature of the sieve material. 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. the ratio of opening sizes has been kept approximately constant in moving from one sieve to the next. The mesh numbers are expressed in terms of the numbers of opening to the inch (= 2. although apertures 34 . so that. almost all samples will consist of one pure component. apertures are measured in mm. one throughout the other. Thus. 35 .3.1. In the SI system. There are.1 CHARACTERISTICS OF MIXTURES Ideally. Unfortunately. some aspects of mixing which can be measured and which can be of help in the planning and designing of mixing operations. grouped together in some container. It occurs in innumerable instances in the chemical industry and is probably the most commonly encountered of all process operations. but still separate as pure components.1.3 MIXING Mixing is the dispersing of components. if small samples are taken throughout the container. 2. 2. The frequency of occurrence of the components is proportional to the fractions of these components in the whole container. A table of sieve sizes has been included in Appendix 1.are generally of the same order as the Tyler series.6.6. aperture ratios are not constant. a mixing process begins with the components. however. it is also one of the least understood. 6. Another approach can then be made.As mixing then proceeds. Such dispersion represents the best that random mixing processes can do. 2.1.3. Actually. 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. 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. 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. Possibly the easiest way in which to classify mixers is to divide them according to whether they 36 .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. samples will increasingly contain more of the components. 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 40 41 . The principles of drying may be applied to any type of dryer.3 DRYING EQUIPMENT In an industry so diversified and extensive.1. Examples are Tray Dryers. Roller or Drum Dryers.5. Vacuum Dryers. Pneumatic Dryers. Bin Dryers. and Y is the humidity difference in kg kg-1. Freeze Dryers.16) where w is the mass being transferred kg s-1. Trough Dryers. Fluidized Bed Dryers. Tunnel Dryers. This is the case and the total range of equipment is much too wide to be described. Belt Dryers. Spray Dryers. it would be expected that a great number of different types of dryer would be in use. Rotary Dryers. A is the area through which the transfer is taking place.dw/dt = k'g A ∆ Y (2. 2.6. k'g is the mass-transfer coefficient in this case in units kg m-2 s-1 . 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.CHAPTER THREE METHODOLOGY AND PROCESS DESCRIPTION Chalk can be made from different raw materials or their combinations in different proportion. kaolin calcined gypsum and water. The raw material (calcium carbonate. TANK SOURCE (CaCO3) CRUSHER MIXER MOULD DRYER 42 . kaolin or calcined gypsum) is first crushed in a crusher to obtain a homogenous fine powder. The slurry is then passed through an extruder where a setting time of ten (10) minutes is allowed. Pigments or dyes are also used in the case of making coloured chalk. The various raw materials used in chalk production are. It is then mixed with water in the volume proportion of 4:5 in the mixer or homogenizer. calcium carbonate. The slurry produced is then sent to a vibrating extruder with holes moving at a particular velocity. The vibration of the extruder is to ensure adequate compatibility.2 PRODUCTION DATA The objective of this design project is to design a plant that will produce sixty (60) tons of chalk per annum.Fig 3. The raw material after crushing is sent to the mixer through a conveying belt where it is mixed with water from a tank.1 DESIGN PROCESS DESCRIPTION The type of process employed in this design is a semi continuous process. 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. Total no of days in a year (x1) No of days for unforeseen shutdown (x2) = = 365 days 40 days 43 . A set time of ten minutes is provided for. 3.1 Flow chart of process 3. 44 .40 = x1 – x2 = 325days Quantity of chalk produced per year = 6000 tons = 6.000Kg Quantity of chalk to be produced per day = 6.6H2O has no impurity.307.231Kg/hr Standard School Chalk Specification Mass of 1 piece of Chalk (g) = 4g = = = = 0.000.Expected production days (x3) x3 = 365 .231 = 192.461.08m 769.004Kg Diameter of 1 piece of chalk (cm) Length of 1 piece of chalk (cm) No of Chalk produced per hour Chalk Composition CaCO3.000 325 = 18.9cm = 0.004 It is assumed that CaCO3.009m 8cm = 0.6H2O H2O 70% 30% 0.53Kg/day Quantity of chalk to be produced per hour = 60.000.000 326 x 24 = 769.000.75chalks/hr 0. 7 x 4 0.2g π x 0.92 x 8 4 = 5. This is because of a lot of pore spaces found in chalk which brings about its compatibility property.6H2O = Density of H2O = Volume of CaCO3.3 x 4 1.8g 1.581cm3 = = 2.6H2O and H2O mixture For 1 piece of chalk.2 1 = 2.8 = 1.Note: the mass of school chalk is not related to its volume.771g/cm3 1g/cm3 mass = Density 1.771g/cm3 = 2710Kg/m3 1 g/cm3 = 1000 Kg/m3 To calculate the mass and volume ratio of CaCO3.09cm3 Density of CaCO3.2cm3 1.6H2O Mass of H2O = = = 4g 0.6H2O = Volume of H2O = 45 .771 1. Volume of 1 piece of chalk Mass of 1 piece of chalk = Mass of CaCO3. Density of Raw Material Hydrated Calcium carbonate Water = = 1. 8 = 1.509cm3 Mass of H2O initially mixed = = density x volume 1 x 3.6H2O Mass mixture ratio H2O : CaCO3.2 = 3.581 + 1.581 = 2. In carrying out a material balance on a system. The quantities or raw materials required and product produced can be determined by carrying out a material balance over the entire process.3 MATERIAL BALANCE Material balance is the basis or starting point of any chemical process design.6H2O = 2.509 = 3.Total volume = 1. Material balances can also serve to check sources of loss of material and instrument calibrations. a 46 .25:1 3.781cm3 2. The process stream flow and composition are obtained by balances over individual process units.309cm3 Volume occupied by air = 5. The study of plant operation and trouble shooting can be adequately carried out with knowledge of the material balances.781 = Knowing that this volume was initially occupied by water.22:1 = 3.09 – 2.309 + 1. Volume of H2O initially mixed with CaCO3.6H2O = 3.3.509g Volume mixture ratio H2O : CaCO3.2 = 2.509/1.509/2. This boundary separates the system from the universe and is called a control volume. This can be represented mathematically as shown below: Accumulation = Mass in – Mass out + Generation – consumption In cases where no chemical reaction takes place. to simplify the material balance process. 2. Mass of stream leaving or entering and present in the system composition of streams leaving or entering the system Also. the process is at steady state the process is continuous A summary of material balance of this project is given below: 47 .boundary is created around the system. certain assumptions can be made. Below are some of such assumptions: 1. 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. the following are some of the parameters required: 1. the steady state balance reduces to: Mass in = Mass out In other to carryout a proper material balance calculation. 2. 231 x 0.2696Kg/hr Mass composition of CaCO3.8079 x 100 = 55.8079 = 1213.62% .8079Kg/hr 2.509 x 615.70 = 3.385 = 674.2696 1 674.2696Kg/hr CaCO 3 2 MIXER 48 H3O: 55.4617Kg/hr 769.23075Kg/hr 538.3.6H2O Out = 538.2696 1 Mass composition of H2O = 674.38% 3 1213.38% 1213.1 Mixer Material Balance Summary .4617Kg/hr 1 CaCO3.62% 1213.4617 x 100 = 44.6H2O: 100% Table 3.1 Mixer Material Balance Calculation From the production data Mass of Chalk produced per hour CaCO3.8 =538.8079Kg/hr H3O: 100% 2 538.3.4617 + 674.6H2O mass feed rate H2O mass feed rate= Mass of mixture Out = = 769.6H O: 44. 8079 3 (Kg/hr) 538.8079 1213.5562 x 1213.38% 55.3174 = 371.6H2O: H3O: 44.8079 303.4617 2 (Kg/hr) 0 674.4617Kg/hr 49 .3174Kg/hr Mass flow rate of H2O left in the mixture = 674.3.8079 = 538.2696 x 0.25 = 303.Component CaCO3 H2O Total 1 (Kg/hr) 538. Mass feed rate of mixture = 1213.2696 = 674.62% Mass flow rate of H2O in the mixture = 0.2696Kg/hr Mass composition of feed components CaCO3.2696 674.2 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.6H2O Out = 1213.8079 674.2696 3.8079Kg/hr Mass flow rate of H2O lost during setting = 1213.4617 674.4905Kg/hr Mass flow rate of CaCO3.4617 0 538. Mass flow rate of mixture from Out stream = 538.83% Table 3.3174 5 (Kg/hr) 538.6H2O: 44.6H2O: 59.4905 Component CaCO3.83% 303.9522 x 100 1 = 59.9522Kg /hr 5 CaCO3.9522Kg/hr Mass fraction of H2O in the Out stream = 3714905 909.2696Kg/hr 3 CaCO3.4617 371.9522 x 100 1 4 = 40.38% H3O: 55.4617 + MASS FRACTION Mass fraction of CaCO3.6H2O H2O 50 .4617 909.6H2O in the Out stream = 538.8079 4 (Kg/hr) 0 303.4905 = 909.17% 371.17% H2O: 40.4617 674.2 Extruder Material Balance Summary 3 (Kg/hr) 538.3174Kg/hr H2O: 100% 1213.62% MOULD 909. 17% H2O: 40.9522 = 371.3174 909.3 Material balance calculation of dryer The end product after drying is suppose to leave with a product mass flow rate of 769.6H2O: 59.6H2O and impurities are assumed together.83% DRYER 51 5 6 7.9522Kg /hr CaCO3.2696 303.4617Kg/hr Mass flow rate of CaCO3.9522 – 769.4905Kg/hr 0.6H2O (In) (S)= Mass flow rate of H2O (In) Mass flow rate of H2O (Out) = = 0. 769.231Kg /hr CaCO3: 80% H3O: 20% .231Kg/hr with mass composition of the components as 70% CaCO3.231 = 230.3 x 769. Mass feed rate of mixture = 909.4083 x 909.9522 3.7212Kg /hr H2O: 100% 909.6H2O and 30% H2O.231 = 140.7212Kg/hr 0.Total 1213.7693Kg/hr 140.231Kg/hr Mass flow rate of chalk (Out) = Mass of H2O given off = 909. Note that CaCO3.5917 x 909.9522Kg/hr 769.3.9522 = 538. 7693 769. In plant operation.231 CHAPTER FOUR ENERGY BALANCE In process design.4617 371.7212 7 (Kg/hr) 538.4617 230.3 Component CaCO3 H2O Total Dryer Material Balance Summary 5 (Kg/hr) 538.9522 6 (Kg/hr) 0 140. an energy balance on the plant will show the pattern of energy usage and suggest areas for conservation and savings.7212 140. energy balances are carried out to evaluate the energy requirement of the process i.e. heating.Table 3. 52 . cooling and power requirements.4905 909. electrical. economic consideration show that a lot of equipment is employed to conserve energy in the process plant.1 CONSERVATION OF ENERGY Energy can exist in several forms-heats. 4. Energy in = Energy out 4.2 HEAT (Q) AND ENTHALPY Heat is the energy transfer that occurs between a system and its surroundings by virtue of a temperature gradient. However. in order to conserve energy. This is an integral balance written for the whole system. It is equal to zero for an adiabatic process. mechanical. certain laws are obeyed. The energy balance is usually carried out in terms of enthalpy. The various terms deserve 53 . 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.The cost of energy required for a process often represents a substantial function of the operating cost. etc. Tref. but choices of Tref 0K or Tref = 0oC are also common. the energy balance is thus. The enthalpies are relative to some reference temperature.88H Hs = CpS(ts . must be added to enthalpy equation above if any of the components undergo a phase change. Standard tabulations of thermodynamic data make it convenient to choose Tref = 298K. An additional term.t0) Where G = air flow rate 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 54 .. For a flow diagram in Fig 4.g.discussion.1.t0) + XCpA(ts .005 + 1. a heat of vaporization. The enthalpy terms will normally be replaced by temperature using H = Cp (T.Tref) Where Cp is the specific heat capacity of the substance. GHG2 + SHS1 = GHG1 + SHS2 + Q HG = CS(tG-t0) + Hƒ0 CS = 1. e. adiabatic process.ƒ0 = latent heat of water t = temperature t0 = ref temperature Q = heat transferred Q H1.848KJ/Kg 2710 100 4.1 Thermodynamic properties of compounds Vapour Boiling Melting Density Mol. tG1 S.71 1 Component Tc Cp (KJ/Kg) CaCO3 H2O 55 . Outlet stream temperature is at process unit temperature Below are some of the thermodynamic properties of some compounds in this project. X1. pressure point point (Kg/m3) Wt 0 0 ( C) ( C) (g/mol ) 9. 2.187 100 0 1000 18 Specific Tp gravity 2. Negligible heat losses i. tG2 X2. H2. tS1 G.e. tS2 ASSUMPTIONS 1. Table 4. Process operation at steady state conditions. 3. 388.8707KJ/Kg Table4.171455.4617 x 9. Energy balance calculation of dryer Change in enthalpy H = Q = MCPT H solid in + Q = H vap.7212 + 626900.7693 x 4. only the dryer has an energy input.848 x (100 – 0)] + [230.848 x (25 – 0)] + [371.0386 Q = 807.0386KJ/Kg H solid out = [538.4617 x 9.4905 x 4.water = 140.1881KJ/Kg H vap.187 x (25 – 0)] = 171455.2 Summary of Energy balance Input Output 56 .7212KJ/Kg Q = (351943.1881) .7212 x 2501 = 351943.187 x (100 – 0)] = 626900.Dryer In this project.water = Mƒ0 ƒ0 = heat of vaporization of water at 1000C H vap.water + H solid out H solid in = (MCPT)solid + (MCPT)water = [538. specification and fabrication 57 .0386 807. equipment design involves a system of choosing.388.1 CHEMICAL ENGINEERING DESIGN In a process design. It also includes selection of appropriate materials of construction.9093 CHAPTER FIVE EQUIPMENT DESIGN 5.1881 978843.9093 (KJ/Kg) 351943.7212 626900.870 7 978843. specifying and designing of equipment required to operate a process plant or unit.H5 Q H6 H7 Total (KJ/Kg) 171455. conductivity.2 SCOPE OF DESIGN The scope of this design include determination of: 1. 5. compressors. flow rate. heat exchangers. In this project. distillation columns etc are proprietary equipment. liquid level. and a dryer. pressure. extruder. the equipments to design are a mixer. density. dew point. 5. instruments are used to measure process variables such as temperature. viscosity.3 INSTRUMENTATION AND CONTROL In the chemical industry. 2. pH. 3. chemical composition and 58 . reactors. Equipment like pumps. while conventional vessels are non. filters. humidity.The equipment used in the chemical industries includes proprietary and nonproprietary equipment. specific heat. Proprietary equipments are those manufactured by proprietary firms or specialists. 5.proprietary equipment. total heat transfer surface area diameter of equipment length/height of equipment wall thickness of equipment material for construction 4. who have patent right to such equipment. dryers. It ensures safe plant operation It prevents and minimizes process plant accidents. 5. It provides information for production route It provides information for quality products It enhances plant operation at minimum production cost and optimum output 3. Automatic control can also be adopted. the values these variables can be recorded continuously and controlled within narrow limits.5664m2 MATERIAL FOR CONTRUCTION MASS FLOW RATE (Q) VOLUME HEIGHT DIAMETER SURFACE AREA OF VESSEL 59 . The aims of instrumentation scheme are as follows 1. By use of necessary instruments.26Kg/hr 3. 2.moisture content. This in turn will save labour cost and improves plant operation efficiency.1416m3 4m 1m 12. 5.4 SPECIFICATION SHEET OF MIXER STAINLESS STEEL 1213. 4. 0179cm 0.1656mm 1.6928cm3 240.26Kg /hr 152.1880 250C MATERIAL FOR CONTRUCTION MASS FLOW RATE VOLUME OF EXTRUDER LINE LENGTH OF LINE DIAMETER OF LINE SURFACE AREA OF LINE NO OF EXTUDER LINE OPERATING TEMPERATURE 60 .0 KW/m3 Ribbon blade 5.5 SPECIFICATION SHEET OF EXTRUDER STAINLESS STEEL 1213.OPERATING TEMPERATURE PRESSURE TENSILE STRESS THICKNESS OF VESSEL MOTOR POWER BLADE 250C 1atm 145N/m 0.5-2.9cm 678.6346cm2 534. 2m3 1m 2.1656mm 20 MATERIAL FOR CONTRUCTION MASS FLOW RATE (Q) VOLUME HEIGHT LENGTH WIDTH DRYING SURFACE AREA OPERATING TEMPERATURE PRESSURE TENSILE STRESS THICKNESS OF VESSEL NO OF DRYER TRAY 5.5.9522Kg/hr 2.7 CAPACITY SIZING CALCULATIONS MIXER 61 .2m 1M 10m2 /hr 1000C 1atm 145N/m 0.6 SPECIFICATION SHEET OF DRYER STAINLESS STEEL 909. 8079Kg/hr 1771Kg/m3 1000Kg/m3 1.08157 m3 = mixture volume + 40% mixture volume 0.08157 + (40% 0.11419m3 62 .From the production data: Mass feed rate of CaCO3 Mass feed rate of H2O Density of CaCO3 + impurities Density of H2O Volumetric flow rate of CaCO3 = = = = Volumetric flow rate of H2O = = Volumetric flow rate of the mixture = = 538.304+ 0.9788 m3/hr = 5/60hr Assume a retention time (t) Mixture volume = = = Actual size of vessel = = =5mins Retention time x Volumetric flow rate of mixture 5 60 x 0.771g/cm3 = 1g/cm3 538.4617Kg/hr 674.08157) 0.304 m3/hr 674.6748 = 0.4617 1771 0.9788 0.771 m3/hr = =0.8079 1000 0. 11419 0. From Coulson & Richardson.5664m2 Auxiliary equipment needed for the mixer are motor and blades. 1999. 3rd Edition 63 .459m 2 0.11419 x 7 x 4 x 2 22 x 3 D H H = = = 0.689m approx to 4m = 2πDH 2 Surface area of mixer = = 2 x 22 x 1 x 4 7 2 12.Taking height to diameter ratio of 3/2 Height (H) = 3 2 x Diameter = πD2H 4 ---------------------------------1 ---------------------------------2 Volume of a cylinder Substituting equation 1 into 2 and equating to the size of vessel 22 x D2 x 3D 7 4 2 D = 3 = 0.459m aprox to 1m 3 x 0. Vol 6. with ribbon blades.08 7 4 5.0 KW/m3 because it is suitable for slurry suspension. EXTRUDER Chalk/hole specification Diameter (D) Length (L) = = 0. paddles of beaters. This is because it’s rotating element produces contra flow movement of materials necessary for moist powders Motor Power Requirement.8079Kg/hr .9cm 8cm = = = Setting time of chalk = = = πD2L 4 22 x 0.5 – 2.4617Kg/hr 674.0092 x 0. The power requirement is 1.08m Volume of a chalk/hole (Vc) 10mins From the production data: Mass feed rate of CaCO3 Mass feed rate of H2O 64 = = 538.0894 x 10-6cm3 = 1 hr 6 0.Type of equipment is a Horizontal trough mixer.009m 0. 9788 m3/hr No of chalk/hole per hr = = volume feed rate/hr Volume of a piece of chalk 0.6923 pieces No of chalk /hole per hr = Let each line of extruder produce 1 piece of chalk every 10 seconds Therefore. it will produce No of extruder line Taking setting time of 5mins = = 60 x 60 = 360 10 534.0894 x 10-6cm3 192307.6748 m3/hr = 1771Kg/m3 1000Kg/m3 Volumetric flow rate of H2O = = Volumetric flow rate of the mixture =0.Density of CaCO3 + impurities Density of H2O Volumetric flow rate of CaCO3 = = = = 1.304 m3/hr 674.8079 1000 0.6923 360 65 .771g/cm3 = 1g/cm3 538.4617 1771 0.18803lines 192307.6748 = 0. every 1hour.304+ 0.9788 5. 0179cm = 2.9cm = 0.6928cm3 NOTE: The volume of chalk is calculated before twenty percent (20%) by mass of water goes off.08156667m3 = 81566.4m Surface area = 2 π D L 2 = 2 π x 0. This effect rather leaves pore 66 .1880 Length of extruder line Vol = πD2L 4 152.92 x L 4 L = 152..6928 x 4 π x 0.Volume flow rate = 0.6928 = π x 0.9788 x 5 60 Diameter of pipe/chalk = 0.6346cm2 = 152.9 x 240.92 L = 240.0179 2 = 678.6667cm3 Volume flow for each extruder line = 81566.6667 534. This is because the volume will still be the volume of the chalk even after the water has gone off. 000 pieces.2m Drying surface area of dryer DETERMINATION OF WALL THICKNESS 67 . Assuming a dryer chamber height of 8cm. DRYER Going by an approximation of 20.000 pieces of chalk per hour.spaces within the structure of the chalk which ensures its compatibility specification. Therefore. 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 Length of dryer = = 1m 1m + 1m = 2m Taking demarcation allowance of 10% length. the dryer shold contain 20 trays. 10 trays at each side to accommodate 20. Actual length of dryer Height of dryer = = 2 + (10% of 2) 1m = 10m2 = 2. a tray measuring 1m x 1m takes about 1000pieces. 1 68 0.1N/m2 PiDi 2f-Pi = = = = internal pressure.1N/m2 .0.0.1 x 0.09968 x 103mm 0.1 0.The wall thickness e is given by the expression e Where = Pi F Di e MIXER Pi F Di e e = = = = = 1atm = 145N/m 0. N/m2 design stress. m EXTRUDER Pi F Di e = = = = 1atm = 145N/m 0. m minimum thickness.48 x 103mm 0.48 x 103 (2 x 145) . N/m2 internal diameter.1656mm 0.1 x 0.09968 x 103mm (2 x 145) . 00307mm CHAPTER SIX ECONOMIC ANALYSIS 69 .e = 0. the cost data available and the time spent on preparing the estimate. 2002).2 FIXED AND WORKING CAPITAL Fixed capital is the total cost of the plant ready for start up (Coulson & Richardson’s. It is the cost paid to the contractor and includes: (a) (b) (c) (d) Design and other engineering and construction supervision All items of equipment and their installation All piping instrument and control Building and structure 70 .When a chemical plant is built.1 ACCURACY AND PURPOSE OF CAPITAL ESTIMATION The accuracy of an estimate depends on the amount of design details available. (Coulson & Richardson’s. 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. 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. 2002). In the early stages of a project only an appropriate estimate will be required. 6. 6. (e) Auxiliary facility is the additional investment needed. Coulson & Richardson.1300. The total investment needed for project is the sum of the fixed and working capital.4 = $6.3 ECONOMIC EVALUATION CALCULATION Purchase Cost of Equipments From (2002).632. over and above the fixed capital to start the plant up and operate it to the point when income is earned.130 n = 0. 2002. Ce = CSn Ce = purchase equipment cost ($) S = characteristic size parameter (m) N = index for that type of equipment MIXER C = 15000 S = 0. 6.4 Ce = 15000 x 0.37 EXTRUDER 71 . 959.32 Total of Purchase Cost of Equipments.31 = $2208 DRYER C = 7700 S = 1.800.87 $19.544.37 $2208 $10.336.428.32 ƒ1 Equipment erection 0.87 Conversion factor from dollars to naira = 118 Mixer Extruder Dryer Total $6.0 Ce = 960 x 2.632.24/ N 2.66 N 260.50 72 .66 N 2. PCE is $19.3 n = 1.336.90.264.293.959.00 N 1.428.55 = $10.55 Ce = 7700 x 1.C = 960 S = 2.619.9 n = 0.800.24 N 782. 10 0.15) = $42.530.341/ N 6.1+0.1+0.238.260.3) = $55.800 (1+0.00 ƒ10 Design and Engineering ƒ11 Contractors fee ƒ12 Contingency 0.570/ N5.00 Working capital = 5% of Fixed capital = N326.90 Total Investment Cost = WC + FC = N 6.511.20 ---0.20 0.10 ------0.25 ------ Total physical plant cost (PPC) = PCE(1+ƒ2 +ƒ3+ƒ4+ƒ5 +ƒ6 +ƒ7 +ƒ8 ) PPC = 19.10 Fixed Capital(FC) = PPC(1+ ƒ10 + ƒ11 + ƒ12 ) FC = 425570(1+ 0.749.1) = 42570(1.2+0.5+0.800(2.856.2 + 0.ƒ2 Piping ƒ3 Instrumentation ƒ4 Electrical ƒ5 Buildings ƒ6 Utilities ƒ7 Storages ƒ8 Site development ƒ9 Ancillary buildings 0.023.25) = 19.90 Annual Operating Costs 73 . 000/ton = = N30. 520.499.000.00 for the first year and an increase of N 250.000.70 N30. Also assume that the first 12 years is best year for profit making.90 = N30.70 Assume a project life of 20 years.00/6000tons N18. Also assume a profit of N 500. 535.000. Table 6.70 N653.1: Cost estimate of Production of 769.817. 000 Capital charges (10% of FC) Fixed Cost = Annual Operating Cost = = N 42.00 Variable Cost Fixed Costs: Maintenance = 5% of FC = N326.00 for subsequent years .000.231Kg/hr of Chalk 74 .000.00 Labour(two shifts with 0ne extra per shift ) 2 at mixer and 3 at dryer plus 1 extra man multiplied by two = 12men = N11.000.535.000.00 = N12.023.511. 499.Operating time = 325days Variable Costs: Raw material = Utilities cost N5.80 With annual salary of N960.000.318.00 + N12.318.535.00/year Shipping and packaging = 1% of Raw material = N300.000. 260.00 6.EQUIPMENTS MIXER EXTRUDER DRYER PURCHASE COST OF EQUIPMENTS PHYSICAL PLANT COST FIXED CAPITAL TOTAL INVESTMENT COST VARIABLE COST FIXED COST ANNUAL OPERATING COST AMOUNT(N) 782.856.66 2.00 I2 = ratio of the 2nd year to the 1st year I2 = 750000 500000 75 .023.000.238.66 260.544.619.530.535. 535.00 Profit in 2nd year = 500000 + 250000 = N 750.00 1.817. 499.70 ACCUMULATIVE CASH FLOW Accumulative Cash Flow = P1 (I1 + I2 + I3 + ……+ I12 ) Where P = profit in the 1st year = N 500.264.00 6.318.70 42.90 30.336.428.293.000.749.000.32 5.00 12. 5 + 0.0 = I12 + 0.5 The common difference = 1.5 + 0.5 = 4.C x 100 C x G F = cumulative cash flow 76 .5 Cumulative Cash Flow = 500.5 = 2.0 + 0.5 = 2.0 + 0.5 = 5.500.5 = 5.5 = 6.5 I3 I4 I5 I6 I7 I8 I9 I10 I11 I12 = = = = = = = I2 + 0.000(45) = N 22.0 + 0.5 + 0.0 + 0.5 = 3.5 + 0.5 = 3.5 = 6.0 I7 + 0.5 = 5.5 + 0.0 + 0.5 = 4.5 = 1.5 I4 + 0.0 I3 + 0.5 = 4.000.5 = 3.0 I5 + 0.5 I8 + 0.0 = I9 + 0.5 = 2.5 = 6.5 – 1 = 0.= 1.5 = 3.5 = 5.5 I6 + 0.5 = 4.5 = I10 + 0.00 RATE OF RETURN Rate of return is given as ROR = cumulative cash flow attend of project x 100 Life of project x original investment ROR = F .5 = 2. 26 = 31560tons Capacity in 12 years = 6000 x 12 = 72000tons 77 .6.90 6.26years BREAK-EVEN POINT Flow rate of chalk produced = 6000Kg/yr Capacity of plant in 4.500.01% x 100 PAYBACK TIME Since the annual saving is constant The payback time is the reciprocal of rate of return Payback time = 1 ROR = = 100 19.01 5.749.C = investment G = life of project ROR = 22.90 x 12 = 19.856.000 .749.36 years (Payback Tme) = 6000 x 5.856. 36 years capacity at 12 years = 31560 72000 = 0.4383 = 43. 78 .83% CHAPTER SEVEN PROCESS SAFETY Concern for accidents dates back to the industrial revolution of the 18th century.Break even point = capacity at 4. This is when machines were invented and factories were built and were installed with these machines. with a view to eliminating them or controlling them to reduce the effect to ALARP (As Low As Reasonably Practicable) 79 . and death. maiming. All these are due to poor safety management. Accidents are caused by unsafe act and unsafe condition. It is a process for identifying the hazards in an activity and the effect. incapacitation.Several accidents occurred in the factories resulting in injuries. 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 In other to tackle hazards associated with work place. process called HEMP (Hazard and Effect Management Process. identify access control recover REFERENCE 1. 6. 4. 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