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The study of the composition of substances and their effects upon one another. Chemistry is the basic science on which the chemical industries rest. Whether it be organic, inorganic, physical or bio, chemistry is always very helpful for a chemical engineer. The function of the chemical engineer is to apply the chemistry of a particular process through the use of coordinated scientific and engineering principles. To do this effectively, the engineer must develop the research laboratory results of the chemist into an economical chemical process. The most important single factor in cost is usually the yield, which must be carefully differentiated from conversion. Yield is that fraction of raw material which is recovered as the main ( or desired ) product, while conversion is the fraction which is changed from the original raw material to some other form including products and by-products. The goal of a chemical engineer, always concerned with the cost, is to have the conversion equal the yield. Because of low conversions some plants such as, methanol and ammonia synthesis plants are 4 to 5 times as large as would be expected if conversion equaled yield. With the proper knowledge of the chemistry of a process conversion can be increased and process conditions can be appropriately controlled. By changing the operating conditions, the equilibrium can be shifted and the conversion enhanced. Raising operating pressure, sometimes, improves yields, but at the same time increases the operating and equipment costs. Increased reaction time allows closer approach to equilibrium but requires larger, more expensive equipment. Improved catalysts can shorten reaction time, but equilibrium remains unaffected.
The chemistry of carbon compounds excluding metal carbonates, carbides, and carbonyls is called organic chemistry. Originally, it was the chemistry of the substance produced by living organisms. Until the early nineteenth century chemical substances of animal or plant origin were designated as organic and held to differ fundamentally from inorganic substances of mineral origin in that a vital force was required for their production. The vital force theory was discredited in 1828 but the term organic has remained. Organic chemistry is now the study of the compounds of carbon, whether they be isolated from natural sources or synthesized in the laboratory. Most, but not all, organic compounds contain hydrogen as well as carbon, while other common elements are oxygen, nitrogen, sulphur, phosphorous, and the halogens. These and other elements are usually bound to carbon by covalent bonds as distinct from the ionic links typical of inorganic compounds. A few very simple carbon compounds, e.g. metallic carbonates, are considered as inorganic, and the large class of organo-metallic compounds is studied both in organic and inorganic chemistry.
It is the branch of chemistry dealing with all the elements other than carbon. Simple carbon compounds e.g. carbides, carbonates, and carbonyls are often regarded as inorganic.
It is the study of the physical changes associated with chemical reactions and the dependence of physical properties on chemical composition.
Bio chemistry is the study of the living matter. It includes the chemistry involved in humans, animals, plants, and micro-organisms.
Chemical reaction engineering is a very important activity in chemical engineering. It is mainly concerned with the exploitation of chemical reactions on a commercial scale. Its goal is the successful design and operation of chemical reactors. This activity, probably more than any other, sets chemical engineering apart as a distinct branch of engineering profession. Design of equipment for the physical treatment steps is studied in the unit operations. The chemical treatment step of a process are studied in chemical reaction engineering. The chemical treatment step is the heart of a process and the very thing that makes or breaks the process economically. Reactor design uses information, knowledge, and experience from a variety of areas such as thermodynamics, chemical kinetics, fluid mechanics, heat transfer, mass transfer, and economics. Chemical reaction engineering is the synthesis of all these factors with the aim of properly designing a chemical reactor. The design of chemical reactors is probably the one activity which is unique to chemical engineering and it is probably this function more than anything else which justifies the existence of chemical engineering as a distinct branch of engineering. In chemical reactor design two aspects must always be kept in view
The first aspect concerns thermodynamics, while the second concerns various rate processes such as chemical kinetics, heat transfer, etc. Thermodynamics gives two important pieces of information needed in design; the heat liberated or absorbed during reaction and the maximum possible extent of reaction. Chemical kinetics deal with the rate of the reaction. It searches for the factors that influence the rate of reaction. It measures this rate and proposes explanations for the values found. Its study is important for a number of reasons, some of which are For gaining insight into the nature of reacting systems, understanding how chemical bonds are made and broken, and for estimating their energies and stability. For determining the structure of compounds so that the relative strength of chemical bonds and their molecular structure can be investigated. Chemical kinetics is the basis for important theories in combustion and dissolution. It provides a method to study heat and mass transfer, thus providing different techniques to tackle the ever complex rate phenomena. Kinetics of a reaction are very important in the designing of equipments. The kinetics provide the necessary knowledge to apply the reactions, involved to manufacture a product, on a technical scale.
Material balance is the study showing the origin and ultimate disposition of all the materials used in a process while energy balance is the study concerned with the use and distribution of energy. Professor Himmelblau defines material balance as an accounting for material flows and changes in inventory of material for a system. Both material and energy balance calculations are based upon the conservation laws according to which mass and energy can neither be created nor destroyed but can only be transformed from one form to another. Since costs are most strongly affected by material uses and distribution, the material balance is an essential first step in any processing study and is almost invariably a pre-requisite to all other calculations in the solution of both simple and complex chemical engineering problems. Material balance calculations are always followed by energy balance calculations. With today's high energy costs the energy conservation has taken up a new vital role. Chemical processing is a high energy consuming industry and recently much efforts are being spent on reducing the energy costs. For this purpose extensive use of thermodynamics and heat transfer is being made. Material balances are the fundamental of process design. A material balance taken over the complete process determines the quantities of raw materials required and products obtained. Balance over individual process units set the process stream-flows and compositions. Material balances are very useful tools for the study of plant operations and trouble shooting. They can be used to check the performance of the plant or an individual unit against the designed value. Material balances are often used to check instrument calibrations, to extend the data available from the plant instrumentation, and to locate sources of material loss. The general equation for material balance can be written as
Material in = Material out + Accumulation + Consumption - Generation
For a steady-state process the accumulation term becomes zero. When there is no chemical reaction taking place the accumulation and generation terms also become zero. Hence for a steady state process in which no reaction is taking place, the material balance equation becomes
Material in = Material out
Einstein showed that mass and energy are equivalent and are inter-convertible with his famous equation
E = m C2
However, in chemical reactions mass and energy are considered to be separately conserved. The conservation of energy differs from the mass since it can be generated or consumed in a chemical process. Material may change form, new molecular species may be formed by chemical reactions, but the total mass flow into a process unit must be equal to the mass flow-out at steady state. The same is not true for energy. The total enthalpy of the outlet streams will not equal that of the inlet streams if energy is generated or consumed in the process such as that due to heat of reaction. Energy can exists in several forms such as heat, mechanical energy, and electrical energy, it is always the total energy that is conserved. In process design, energy balances are made to determine the energy requirements of the process: the heating, cooling, and the power required. Similar to material balance the general equation for energy balance is written as
Energy in = Energy out + Accumulation + Consumption - Generation
Mathematics is no doubt the basic science of all engineerings. By definition, it is a science of space, number, and quantity. Its importance for engineers is unlimited. Many mathematical operations such as geometry, algebra, integration, Laplace transform, numerical analysis, progression and regression, differentiation, dimensional analysis, and optimization are used by the engineers, all the time. The use of mathematical operations greatly facilitates the tackling of a complex engineering problem. Whether it comes to the determination of the volume of vessels, strengths of material, wall thickness, energy and material balances, the angles of vessel heads, or the cost of an equipment, every time mathematics is involved. The mathematical treatment of engineering problems involves four basic steps: (1) formulation (2) solution (3) interpretation (4) refinement. Formulation is the expression of the problems in mathematical language. The translation is based on suitable physical laws governing the process. The formulation step generally results in the form of algebraic equations, difference equations, differential equations, integral equations, or a combination of any of these. Solution of a problem involves the accomplishment of proper mathematical operations so that logical deductions may be drawn from the mathematical model. Interpretation means the development of relations between the mathematical results and their meaning in physical world. Refinement means the purification or improvement of the procedures, by repeating them again and again, to obtain better predictions as indicated by experimental checks. In engineering, the most widely used form of mathematics is calculus. It is the mathematics of motion and change. Where there is motion or growth, where variables forces are at work, calculus is the right mathematics to apply. Integration and differentiation are two major methods of calculus.
Differentiation is the inverse of integration. It is a mathematical operation which deals with continuously changing quantities. It is used to determine the derivative of a quantity. In chemical engineering differentiation is used to describe diffusion, measure the rate of reactions, effect of forces, and the motion of fluids. The natural laws in any scientific or technological fields are not regarded as precise and definitive until they have been expressed in mathematical form e.g. an equation. Such a form is a relation between the quantity of interest such as yield, and independent variables such as time and temperature upon which yield depends. Whenever this equation involves one or more functions besides itself, it is called a differential equation. When the function involved in the equation depends upon only one variable, its derivatives are ordinary derivatives and the differential equation is called ordinary differential equation. When the function depends upon several independent variables, then the equation is called partial differential equation.
Integration is a summation process. It is the inverse of differentiation. This method provides a method of finding the rate of change of a process, position of moving bodies, the lengths of curved paths, cross-sectional areas of vessels, the area enclosed by curves, and solutions to other problems involving summation of infinitesimals ( very small quantities or quantities decreasing indefinitely without actually becoming zero ). Integration is widely used in finding out the volume of reactors, the rate of reactions, and the total conversion in a process. The integration of function may either be definite or indefinite, depending upon the interval or region over which it is taking place. For a specified interval the integration will be definite and for unspecified interval it will be indefinite.
The difference equation is a relation between the differences and the independent variables. In a variety of situations, the independent variable does not vary continuously but has meaning only for discrete values. Such situations occur widely in the stage-wise processes such as distillation, extraction, and absorption. In each of these cases the operation is characterized by a finite between-stage change of the dependent variable in which the independent variable is the integral number of the stage.
Laplace transform provides a procedure of solving differential and difference equations by which the boundary or initial conditions are automatically satisfied in the course of the solutions. This method is very useful in finding the solutions for complex variables. Laplace transform is used in a variety of mass transfer and heat transfer applications.
The purpose of using numerical analysis is to provide convenient techniques for obtaining useful information from mathematical formulations of physical problems. The mathematical formulations are not usually solvable by analytical means or sometimes even if analytical means are available they are too complex for direct numerical interpretation. In the first case it is necessary either to attempt to approximate the problem satisfactorily, or obtain an approximate solution form which a solution of the original problem can be obtained by numerical means, or use a combination of both techniques. Gauss reduction method, Simpson's rule, Runge Kuta's method, Gaussian integration, and Newton's method are some of the numerical analysis techniques.
Dimensional analysis is an algebraic treatment of the symbols for the units, considered independently of the magnitude. This method greatly simplifies the task of fitting experimental data of design equation. It is also useful in checking the consistency of the units in equations and in converting units. Dimensional analysis is based upon the fact that if a theoretical equation exists among the variables affecting a physical process, that process must be dimensionally homogeneous. Because of this requirement and due to the fact that the physical quantities can be expressed in terms of fundamentals such as mass, length, time, and temperature, it is possible to group many factors into a smaller number of dimensionless groups of variables. The groups rather than separate factors appear in the final equations. Many engineering problems, especially in heat transfer, mass transfer, and fluid flow, cannot be solved by theoretical or empirical methods because of the presence of too many parameters affecting these processes. Dimensional analysis greatly facilitates the treatment of these problems by grouping these variables into small groups. The grouping of these variables in dimensionless groups is very important for a chemical engineer since chemical engineering analysis requires the formulation of relationships which will apply over a wide range of individual items of a plant and can be used in a variety of situations. The requirement of dimensional consistency places a number of constraints on the form of the functional relation between variables in a problem and forms the basis of the technique of dimensional analysis which enables the variables in a problem to be grouped into the form of dimensionless groups. Since the dimensions of the physical quantities can be expressed in terms of a number of fundamentals such as mass, length, time, and temperature, the requirement of dimensional consistency must be satisfied in respect of each of the fundamentals. Dimensional analysis is simply a mathematical tool. It enables engineers to save considerable time in planning experiments and correlating results of an experiment. In order to apply dimensional analysis to a situation only the variables believed to be involved and their dimensions must be known. The use of these dimensions and fundamental algebra saves time, trouble, and expense involved in the experimental investigation or correlation of a problem. In some cases, from dimensional analysis alone, it is possible to tell whether a suspected variable is really involved in a particular problem. In all cases, dimensional analysis reduces the number of experimental variables to be correlated, and often point outs the best experimental approach to the problem. However, it does not provide quantitative information such as a numerical equation, and experiments must be conducted to complete the solution of the problem. Some of the mostly used dimensionless groups ( also called dimensionless numbers ) along with their applications are :
The physical operations necessary for manufacturing chemicals are called unit operations. It is a method of organizing much of the subject matter of chemical engineering. Unit operations can be, no doubt, called the core of chemical engineering. The unit operations concept is based on the fact that by systematically studying the operations ( such as heat transfer, mass transfer, fluid flow, drying, distillation, evaporation, absorption, extraction, and mixing ) involved in chemical industry, the treatment of all processes is unified and simplified. The unit operations are largely used to conduct the primary physical steps of preparing the reactants, separating and purifying the products, recycling unconverted reactants, and controlling the energy transfer into or out of the chemical reactors. The design of the equipment involved for these operations are also studied in unit operations. Because of the complexity and variety of the modern chemical manufacturing processes the need for arranging the different processes systematically has become undeniable.
As a chemical engineer has to handle these processes all the time, so it will be very convenient for him if the operations or methods involved in these processes can be arranged in a pattern such that the operations and their principles can be studied step by step rather than processes. The unit operations concept provides a method of arranging these operations. It is based on two facts although a lot of individual processes are involved in chemical engineering, however each one can be broken down in a series of steps called operations, each of which in turn appears in process after process. the individual operations have common techniques and are based on the same scientific principles. For example, in most of the processes solids and fluids have to be moved, heat has to be transferred from one substance to another, fluids have to be mixed together, materials have to dried, and fluids have to be separated. So instead of studying the whole manufacturing processes involved for every chemical, the main operations involved in them are classified as unit operations and are studied under this heading, since the type of chemical to be manufactured might be different, and the sequence and number of operations required may vary but the operations involved will be the same ( i.e. either be distillation, or extraction, or absorption, or any of the unit operations ) and so will be the principles governing these operations. A number of scientific principles and techniques are basic to the treatment of the unit operations. Some are elementary physical and chemical laws such as the conservation of mass and energy, physical equilibria, kinetics, and certain properties of matter. The concept of unit operations is based both on science and experience. Theory and practice must combine to yield designs for equipment that can be fabricated, assembled, operated, and maintained. The unit operations are applicable to many physical processes as to chemical ones. For example, the process used to manufacture common salt consists of the following sequence of unit operations: transportation of solids and liquids, transfer of heat, evaporation, crystallization, drying, and screening. No chemical reaction appears in these steps. On the other hand, the cracking of petroleum with or without the aid of a catalyst, is a typical chemical reaction conducted on an enormous scale. Here the unit operations involved ( i.e. transportation of fluids and solids, distillation, and various mechanical separations ) are vital and cracking reaction cannot take place without them. The chemical steps themselves are conducted by controlling the flow of material and energy to and from the reaction zone. The study of unit operations can be divided into four basic groups.
The branch of engineering that deals with the behaviour of fluids is called fluid mechanics. It is a part of larger branch of engineering called continuum mechanics which deals with the behaviour of fluids as well as stressed solids. A fluid is a substance that does not permanently resist distortion. An attempt to change the shape of a mass of fluid results in layers of fluids sliding over one an another until a new shape is attained. During the change in shape, shear stresses exist depending upon the viscosity of the fluid and the rate of sliding, but when the final shape is achieved all the shear stresses disappear. A fluid in equilibrium is free from shear stresses. Fluids may be compressible or incompressible. If the density of a fluid changes slightly with the changes in temperature and pressure then such a fluid is called incompressible and if the density changes significantly then such a fluid is said to be compressible. Gases are generally considered to be compressible while liquids are considered incompressible. The behaviour of fluids is very important in chemical engineering. It is a major part of unit operations principle. Understanding of fluids is essential not only for accurately treating problems in the movement of fluids through pipes, compressors, pumps, and all kinds of process equipment but also for the study of heat flow and many separation principles that depend on diffusion and mass transfer. Design and study of measuring devices ( such as flow meters, area meters, pressure gauges ), transportation equipment ( such as compressors and pumps ), and mixing and agitation equipment ( such as mixers and agitators ) are considered in fluid mechanics. Fluid mechanics can be divided into two branches
Fluid statics deals with the fluids at rest or in equilibrium state with no shear stress. It is concerned with the properties and behaviour of fluids. In the case of liquids this subject is called hydrostatics and in the case of gases it is called pneumatics. Fluid dynamics, also called fluid flow, deals with the flowing fluids or with fluids when portions of the fluid are in motion relative to the other parts. The flow of a fluid may be laminar or turbulent. The flow in which the layers of the fluid are flowing parallel to the axis of the pipe or conduit is called laminar flow. The flow in which the layers of the moving fluids are not parallel to the axis of the pipe and the fluid is disturbed from point to point, is called turbulent flow. Chemical engineers continuously deal with the flow of fluids. Most of the time they have to transport fluids from one place to another through pipes or open ducts which requires the determination of pressure drops in the system, selection of a proper type of pump or compressor, power required for pumping or compression, and measurement of flow rates. All these aspects are studied in fluid flow. A major portion of fluid flow deals with the transportation, metering, and mixing & agitation of fluids. Fluids are usually transported in pipes or tubing by using pumps or compressors. Valves such as gate valves, ball valves, globe valves, plug cock valves, and butterfly valves are used for controlling the flowrates of the fluids. To measure and monitor flowrates and pressure drops certain metering devices such as venturi meters, orifice meters, pitot tubes, rota meters, target meters, and turbine meters are used. For the transportation of fluids pumps, compressors, fans, and blowers are used. Pumps are the devices generally used for liquid transportation. They are of two types (1) positive displacement pumps (2) centrifugal pumps. The positive displacement pumps displace a liquid by applying pressure directly on it. They are divided into two sub-classes (i) those in which direct pressure is applied to the fluid by using a piston. Such pumps are called reciprocating pumps e.g. plunger pump, diaphragm pump. (ii) those in which direct pressure is applied by rotating pressure members. Such pumps are called rotary pumps e.g. spur-gear pump, internal gear pump, screw pump. The centrifugal pumps use torque to generate rotation, increasing the mechanical energy of the liquid by centrifugal action, for liquid displacement. High speed rotary parts called impellers are used to produce this motion. The compressors are the devices used for the transportation of gases. Compressors work in a similar fashion to the pumps and have the same types. Mixing is the random distribution, into one another, of two or more initially separate phases. Agitation, however, refers to the induced motion of a material in a specified way, usually in a circulatory pattern inside some sort of a container. e.g. a single homogeneous material such as a tank full of water can only be agitated and cannot be mixed until some other material such as salt or powder is added to it. Mixing is one of the most common operations carried out in the chemical processing industries. The term mixing is applied to the processes used to reduce the degree of non-uniformity, or gradient of a property in a system such as concentration, viscosity, temperature and so on. Mixing is achieved by moving the material from one region to another. Mixing is also used to promote heat and mass transfer in a system.
Heat transfer is the branch of engineering science that deals with the rates of heat exchange between hot and cold bodies. The driving force for heat transfer is the temperature difference per unit area or temperature gradient. In majority of chemical processes heat is either given out or absorbed. Most of the times the fluids must be heated or cooled in a variety of equipment such as boilers, heaters, condensers, furnaces, dryers, evaporators, and reactors. In all of these cases the primary problem faced is the transferring of heat at the desired rate. Some times it is necessary to prevent the loss of heat from vessels or pipes. The control of flow of heat at the desired rate is one of the most important areas of chemical engineering. The principles and laws governing the rates of heat flow are studied under the heading of heat transfer. Even though the transfer of heat is involved in every unit operation, however, in evaporation, drying, and combustion the primary concern is the transfer of heat rather than transfer of mass and these operations are governed by the rate of transfer of heat. Laws and equations of heat transfer are used for the designing of the equipment required for these processes. Evaporation, is the process used to concentrate a solution consisting of a non-volatile solute and volatile solvent. In majority of evaporations the solvent is water . Drying is the removal of relatively small amounts of water or other liquid from the solid material to reduce the content of residual liquid to a low value. In addition to these the heat exchangers, coolers, condensers, reboilers, and boilers are also studied in this subject. Provided that a temperature difference exists between two parts of a system, heat transfer can take place through the following three modes of heat transfer (1) Conduction (2) Convection (3) Radiation. However, most of the processes are a combination of two or more modes of heat transfer. Conduction is the transfer of heat through fixed material such as stationary walls. In a solid, the flow of heat is the result of the transfer vibrational energy from one molecule to another, and in fluids it occurs in addition as a result of the transfer of kinetic energy. Heat transfer through conduction may also arise from the movement of free electrons. Convection is the heat transfer occurring due to the mixing of relatively hot and cold portions of a fluid. If this mixing takes place due to density differences, then such a process is called natural or free convection e.g. when a pool of liquid is heated from below. However, if the mixing takes place due to the eddies produced by mechanical agitation then such a process is called forced convection. It is important to note that convection requires mixing of fluid elements and is not governed by just the temperature difference as in conduction and radiation. Radiation is the transfer of radiant energy from body to another. All materials radiate thermal energy in the form of electromagnetic waves. When radiation falls on a second body it may be partially reflected, transmitted, or absorbed. It is only the fraction that is absorbed that appears as heat in the body. While heat transfer deals with the transfer of heat between hot and cold bodies independently , Process heat transfer deals with the rates of heat exchange as they occur in the heat-transfer equipment of the engineering and chemical processes.
Mass transfer is the transfer of a component in a mixture from a region in which it has a high concentration to a region in which its concentration is lower. This process can take place in a gas, liquid, or vapour. It can result from the random velocities of the molecules ( molecular diffusion ) or form the circulating or eddy currents present in a turbulent fluid ( eddy diffusion ). Like temperature gradient is the driving force for heat transfer, the driving force for mass transfer is the concentration gradient. Many unit operations such as distillation, absorption, extraction, leaching, membrane separation, dehumidification, crystallization, ion exchange, and adsorption are considered as mass transfer operations. Even though transfer of heat is also involved in these operations but the rate of mass transfer governs the rate phenomena in these processes. Unlike purely mechanical separation processes which utilize density difference and particle size, these methods make use of differences in vapour pressure, solubility, or diffusivity. The function of distillation is to separate, by vaporization, a liquid mixture of miscible and volatile substances into individual components or, in some cases into groups of components. In absorption a soluble vapour is absorbed by means of a liquid in which the solute gas is more or less soluble, from its mixture with an inert gas. The solute is subsequently recovered from the liquid by distillation, and the absorbing liquid can either be discarded or reused. When a solute is transferred from the solvent liquid to the gas phase, the operation is known as stripping or desorption. In dehumidification a pure liquid is partially removed from an inert or carrier gas by condensation. Usually the carrier gas is virtually insoluble in the liquid. In membrane separations, including gas separations, reverse osmosis, and ultrafiltration, one component of a liquid or gaseous mixture passes through a selective membrane more readily than the other components. In adsorption a solute is removed from either a liquid or a gas through contact with a solid adsorbent, the surface of which has a special affinity for the solute. In liquid extraction also called solvent extraction, a mixture of two components is treated by a solvent that preferentially dissolves one or more of the components in the mixture. The mixture so treated is called the raffinate and the solvent-rich phase is called extract. In extraction of solids, or leaching, soluble material is dissolved from its mixture from an inert solid by means of a liquid solvent. Crystallization is used to obtain materials in attractive and uniform crystals of good purity, separating a solute from a melt or a solution and leaving impurities behind.
Also called particle technology. This branch of unit operations deals with the solid handling and is mainly concerned with the mixing, size reduction, and mechanical separation of solids. Solids in general are more difficult to handle than fluids. In processing solids appear in a variety of forms such as angular pieces, continuous sheets, finely divided powders. They may be hard and abrasive, tough and rubbery, soft or fragile, dusty, cohesive, free-flowing, or sticky. Whatever their form, means must be found to handle these solids. Mixing of solids resembles to some extent with the mixing of low-viscosity liquids, however, mixing of solids requires much more power. In mixing two or more separate components are intermingled to obtain a uniform product. Some of the mixers and blenders used for liquids are also used for solids. Solid mixers mainly used are kneaders, dispersers, masticators, mixer-extruders, mixing rolls, pug mills, ribbon blenders, screw mixers, tumbling mixers, and impact wheel. Size reduction, sometimes also called communition, is a term applied to the methods and ways used to cut or break-down solid particles in smaller pieces. Reduction of particle size is usually carried in four ways (1) compression (2) impact (3) attrition or rubbing (4) cutting. A nutcracker, a hammer, a file, and a pair of shears exemplifies these four types of action. In general, compression is used for coarse reduction of hard solids, giving a few fines; impact gives coarse, medium, or fine products; attrition yields fine products form soft, nonabrasive materials; cutting provides a definite particle size and sometimes a definite shape. The principle types of size-reduction machines are: Crushers ( jaw crushers, gyratory crushers, crushing rolls ), Grinders ( hammer mills or impactors, rolling compression mills, attrition mills, tumbling mills including ball mills, pebble mills, rod mills, and tube mills ), Ultrafine grinders ( hammer mills, fluid-energy mills, agitated mills ), Cutting machines ( knife cutters, dicers, slitters ). Crushers use compression, grinders use impact and attrition sometimes combined with compression, ultrafine grinders use attrition, while cutting machines use cutting action. Separations can be divided into two classes. One class, known as diffusional operations, involves the transfer of material between phases e.g. absorption, distillation, adsorption etc. Another class, known as mechanical separations, is used for heterogeneous mixtures. This class of separation processes consists of techniques based on physical differences between the particles such as size, shape, or density. They are applicable to separating solids from gases, liquid drops from gases, solids from solids, and solids from liquids. Two general methods are: (i) the use of a sieve, or membrane such as a screen or a filter, which retains one component and allows the other to pass. (ii) the utilization of differences in the rate of sedimentation of particles or drops as they move through a liquid or a gas. The operations included in mechanical separations are screening, filtration, and gravity and centrifugal settling. Screening is a method of separating particles according to size alone. In industrial screening the solids are dropped or thrown against a screening surface. The undersize ( also called fines ) pass through the screen openings leaving behind oversize ( also called tails ) particles. Industrial screens are made from woven wire, silk, plastic cloth, metal, and perforated or slotted metal plates. Stationary screens, grizzlies, gyrating screens, vibrating screens, and centrifugal sifters are used for this purpose. Filtration is the removal of solid particles from a fluid by passing the fluid through a filtering medium ( also called septum ) through which the solids are deposited. Industrial filtrations range from simple straining to highly complex separations. The fluid may be a liquid or a gas; the valuable stream from the filter may be fluid, solid, or both. Filters are divided into three main groups cake filters, clarifying filters, and cross-flow filters. Cake filters separate relatively large amounts of solids as a cake of crystals or sludge. Filter press, shell and leaf filter, belt filter, rotary drum filter, batch centrifuge filters are used for this purpose. Clarifying filters remove small amounts of solids to produce a clean gas or a sparkling clear liquid by trapping the solid particles inside the filter medium. Gravity bed filters, cartridge filters, edge filters, tank filters, pad filters, bag filters, and granular bed filters are used for this purpose. Cross flow filters are used for very fine particles or for micro-filtration. In a cross-flow filter the feed suspension flows under pressure at a fairly high velocity across the filter medium. Some of the liquid passes through the medium as a clear filtrate, leaving behind a more concentrated suspension. For these filters different types of membranes are used. Settling processes are used for mechanical separations, utilizing the movement of solid particles or liquid drops through a fluid. Gravity settling processes are based on the fact that particles heavier than the suspended fluid can be removed from a gas or liquid in a large settling tank in which the fluid velocity is low and the particles are allowed a sufficient time to settle out. A settler that removes virtually all the particles from a liquid is known as a clarifier, whereas a device that separates the solid into two fractions is called a classifier. Centrifugal settling processes are efficient than gravity settling processes. A given particle in a given fluid settles under gravitational force at a fixed maximum rate. To increase the settling rate the force of gravity acting on the particle may be replaced by a much stronger centrifugal force. Centrifugal separators, to certain extent, have replaced the gravity separators because of their greater effectiveness with fine drops and particles and their much smaller size for a given capacity. The most widely used type of centrifugal separators is the cyclone separators. Other types mostly used are centrifugal decanters, tubular centrifuges, disk centrifuge, nozzle discharge centrifuge, and centrifugal classifiers.
The chemical operations involved in the manufacture of chemicals is called unit processes. Such processes include chlorination, esterification, nitration, oxidation, hydrogenation, sulphonation, etc. The concept of unit processes was introduced by P. H. Groggins in 1930. This concept has not proved as useful as the unit operations idea nor have its concept been reduced to mathematical procedures, however, it is frequently useful. This concept deals with the processes involved in the manufacture of a chemical on the basis of the main group to be attached with a substance to form the desired product. For example the addition of nitro group to benzene for nitro-benzene manufacture is treated as nitration process, since the main group to be attached with benzene is nitro group. Chlorination is the introduction of a chlorine atom into a compound by substitution or by an addition reaction e.g. chlorobenzene, chloroethane, chlorophenol, etc. Esterification is the process of formation of an organic compound by the combination of an acid and an alcohol with the elimination of a water molecule. The compound formed is called an ester e.g. polyesters, ethyl acetate, poly vinylchloride etc. Esterification process is widely used in the polyester, solvents, paints, and artificial flavours industries. Nitration is the addition of the nitro group ( -NO2 ) into organic compounds by the use of nitric acid. Nitration is of particular importance in the production of fertilizers and explosives. Usually the nitro derivatives of organic compounds are chemically unstable. Oxidation is the process of addition of oxygen to a substance or the removal of hydrogen from it. Hydrogenation is the addition of hydrogen. This process is of particular importance in the manufacture of artificial mineral oil from coal, and the artificial hardening of liquid animal and vegetable oils to produce cooking oil and margarine. Sulphonation is the addition of sulphonic group ( -SO3H ). Sulphonation process is widely used in the production of sulpha drugs and dyestuff.
The transformation of heat energy into some other form of energy or the transformation of some other form of energy into heat energy is called thermodynamics. Thermodynamics is a very useful branch of engineering science and is very helpful in the treatment of such processes as refrigeration, flashing, and the development of boilers and , steam and gas turbines. Sometimes heat transfer is mixed up with thermodynamics. To understand the difference between heat transfer and thermodynamics we should always remember that Heat transfer is the science which deals with the rates of exchange of heat between hot and cold bodies while Thermodynamics deals with the quantitative transitions and re-arrangements of energy as heat in bodies of matter. The word thermodynamics means heat in motion. However, this was only an earlier concept of thermodynamics. Now thermodynamics has become a very broad branch of science and it deals with the transformations of all kinds of energy from one form to another. Thermodynamics is governed by two rules called the first and second law of thermodynamics. First law of thermodynamics states that Energy can neither be created nor destroyed, however it can be transferred from one form to another. Or Although energy assumes many forms but the total energy remains constant and whenever energy disappears in one form it appears simultaneously in other forms. This law is also known as law of conservation of energy. In thermodynamic sense, heat and work refer to energy in transit across the boundary between the system and surroundings. These forms of energy can never be stored. It is incorrect to speak of heat or work as being contained in a body or system. Energy is stored in its potential, kinetic, and internal forms. These forms reside with material objects and exist because of position, configuration, and motion of matter. The transformations of energy from one form to another and transfer of energy from one place to another often occur through the mechanisms of heat and work. The second law of thermodynamics states that It is impossible to transfer heat from a cold body to a hot body unless external work is done on the system. Or No heat engine operating continuously in a cycle can extract heat from a hot reservoir and convert it into useful work without having a sink. The value of thermodynamics lies in the fact that these laws and certain accompanying definitions have been given mathematical expression. This has led to the development of a consistent network of equations from which a wide range of practical results and conclusions may be deduced. The universal applicability of this science is shown by the fact that it is employed by physicists, chemists, and engineers. In each case the basic principles are the same but the applications differ. Thermodynamics enables a chemical engineer to cope with a wide variety of problems. Among the most important of these are the determination of heat and work requirements for many physical and chemical processes, and the determination of equilibrium conditions for chemical reactions and for the transfer of chemical species between phases.
Economics is the science of production and distribution of wealth. Or Economics is the science concerned with the dealing of money, trade, and commerce. Most of the times economics is considered to be an allied subject of engineering curriculum and is not stressed upon. However, economics plays a vital role in feasibility of any project undertaken by an engineer. Whether it comes to designing an individual piece of equipment, construction of a plant, production of a new chemical, change in production, or modification of a plant, in every step economics is concerned. Infact the ability of engineers to evaluate every project on the basis of its economics and their cost and investment consciousness distinguishes them from other scientists. Even though the need of chemicals every phase of life is undeniable and their requirement can be the single factor for the production of various chemical-products, however, the main concern of a process plant, like any other business enterprise, is profit. Chemical engineering is critically concerned with running an industry in profit, since without profit a business cannot operate. The chemical process industry processes raw materials into useful and profitable products. These products are used both as consumer goods and as intermediates for further chemical and physical processing to yield consumer products. About one-quarter of the total chemical output is utilized in the manufacture of other chemicals, so the chemical industry is unique in being its single best customer. A chemical engineer, by analyses of costs and profits involved in a process, attempts to maintain a plant in profit. This analysis is made by maintaining record of all the transactions and financial results of these transactions. So a chemical engineer must be aware of the cost and accounting procedures in order to fully understand these records. Costs also play a major role in the design of a plant and only those processes are considered which are economical and profitable. In addition to this the total investment required for a plant, cost of different equipment, cost of raw materials, and the cash flow for different industrial operations also have to be determined. None of which can be determined without proper knowledge of various methods of cost estimation and economics.
