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The chemical engineering profession includes a wide variety of activities in a number of institutions including industry, research, government, and academia. Chemical engineering mainly deals with industrial processes in which raw materials are changed into useful products. The chemical engineers develop, design, and engineer both complete processes and the equipment used; choose the proper raw material; operate the plants efficiently, safely, and economically; and see to it that the products meet the requirements set by the customers. Chemical engineering is both an art and a science. The variety of processes and industries that call for the services of a chemical engineer is enormous. Chemical engineers work in numerous areas besides petroleum refining and the petrochemical industries because their background and experience are easily portable and found useful. Products of concern to chemical engineers range from commodity chemicals like sulphuric acid and chlorine to high-tech items like lithographic support for electronic industry ( Silicon chips, microprocessors ) and genetically modified biochemical agents. The number of chemical engineers working throughout the world is enormous. These engineers are employed by both private and public enterprises. They work in a variety of fields besides process and designing. The wide spectrum of application of chemical engineers shows that chemical engineers must be trained to function in any phase of chemical manufacturing. A chemical engineer during his career performs various activities. From plant design to successful plant operation he has to face many tasks and challenges. To have a better understanding of the work of a chemical engineer let us consider the important activities undertaken by him.
The selection of a process is one of the most hectic and time consuming activities undertaken by a chemical engineer. One process may be energy efficient than the other but the other may be less polluting or may have its raw materials readily available. For example, in selecting a process for an ammonia plant we can use many raw materials such as natural gas, fuel oil, wood, lignite, coal, and even water ( by electrolysis ). Then there are a number of processes available such as steam reforming of natural gas and Partial oxidation process. Selecting a process out of these is no easy job because each process has certain advantages and certain disadvantages. In addition to these they have certain limitations and require certain conditions. To select a process many constraints have to be faced such as time, available data, investment, and economics. As all industries are mainly concerned with profits, hence out of all the constraints economics always remains the chief concern and is always the main factor in selecting a process. While selecting a process, the following factors are always considered:
Selecting a process to be in batches or to be continuous is another important task. Early chemical processing was usually done in batches and much continues to be done in that way. Batches can be measured most concisely and are much suitable for small scale production. However, the temperature and pressure control can be troublesome. Furthermore time and resources lost in attaining the required conditions such as temperature and pressure, limits the use of batch processes. On the other hand, continuous processes require far smaller and less expensive equipment, have much less material in process, have less chance to ruin large quantities, have more uniform operating conditions, and give more uniform products than batch processes. Continuous processes are very suitable for large scale productions. However, these require concise control of flow-rates and conditions, which is impossible without quality instrumentation. The reduction in plant cost per unit of production is often the major force in selecting a process to continuous or in batches.
Operation of a plant is another important activity carried out by a chemical engineer. Chemical processing of a raw material into the desired product can only be achieved by operating the chemical plant. The quality and quantity of the product is directly dependent on the efficient operation of a plant. The smooth operation of a plant is a very difficult task and requires close attention of the engineer at all times. Many problems like temperature and pressure control, maintenance, and safety continue to arise during the plant operation. Experience and application of engineering principles is always needed to shoot out these problems. Negligence of a small problem can often lead to bigger, more complex problems and can cause unnecessary halts in production. In order to be able to handle plant operation smoothly, a chemical engineer should start early to become familiar with the industrial equipment such as pumps, compressors, distillation columns, filter presses, and heat exchangers, etc. Almost every industry wants its engineers to be intimately familiar with every pipe & gauge of that industry. That is why every industry makes its new engineers spend their earlier time in tracing pipelines, an activity known as line tracing. The reason behind this practice is to intimately familiarize the engineers with all the pipelines, gauges, valves, and equipment of that industry so that whenever there is any fault in any section he should be able to identify the location and problem immediately to work out its solution immediately. In fact trouble shooting is the core of plant operation. Successful plant operation of a chemical plant does not only depend upon the original strength of the materials of construction but also upon the affects of corrosion. Constant check-ups and watch must be kept to avoid corrosion. Mechanical failures are seldom experienced unless there has been previous corrosion or weakening by chemical attack. Chemical manufacturing process can be divide into the following steps
The initial physical treatment steps include feed preparation methods such as mixing. Some purification and preparation of the raw materials is usually necessary before sending them to the chemical treatment or chemical reaction step. Liquids may be purified by filtration or gravity settling. Sometimes they need to be vapourized. Gases may be purified by adsorption or absorption. Solids may need crushing, grinding, and screening. Initial physical treatment steps are also called feed preparation stage. After the initial physical treatment the raw materials are sent to the chemical reaction step. The reaction step is the heart of a chemical manufacturing process. This step is carried out in a reactor. After the reaction step the feed is sent for the final physical treatments. These treatments are carried out for product separation. After the product separation, the unreacted materials are sent back to the initial physical steps and the product is further purified to the required degree. This product is then sent for storage.
In large scale continuous operations the function of the workers and the supervising chemical engineer is to maintain the plant in proper running conditions. Maintaining required temperature, pressure, flow-rates, and other conditions is a very difficult task. Quality instrumentation is a must for maintaining these conditions. Instruments are the essential tool for modern processing. A chemical engineer must have the proper knowledge of the instruments involved for controlling and measuring process variables. He should have adequate ability to design control systems for processes and workout problems faced in controlling process operations. Batch operation requires few instruments and hence more supervision on the part of the workers and the chemical engineer because the conditions and procedures differ from the start to the finish. Even these problems can be solved by programmed instruments if the expense can be justified. Instrument costs, once a trivial part of the total plant investment, have risen up to 25% of the total investment. The use of computers has reduced this cost to some extent. Earlier plants used mechanical control instruments. These were replaced by pneumatic control systems which were replaced by electronic control systems. Nowadays plant-control is being done by DCS ( Distributed Control System ) using computers. DCS incorporates the use of electronic control devices but it utilizes computers to monitor and control process conditions. Even though many industries continue to use pneumatic and electronic control systems, however, the global trend is towards DCS because of its ability to handle plant operation more smoothly. Instrumentation has been forced into this position of eminence by the increase in continuous processes, increase in labour and supervision costs, the relative unreliability of human actions, and by the availability of many types of instruments at decreasing price and increasing reliability. Instrument types include indicating instruments, recording instruments, and controlling instruments. Two types of instruments are generally used: analog and digital. Analog instruments such as pressure spring thermometer and Bourdon pressure gauges, show results by mechanical movement of some type of device ( e.g. spring or Bourdon tube ), which is proportional to the quantity being measured. Digital devices generally utilize a transducer, a device which converts the measured signal into some other type of signal usually electronic or pneumatic. These devices also use electronic circuits which convert the signal to readable numerical figures ( digits ) which are then displayed and may be recorded.
Economics is a vital part of an engineers work. Engineers are distinguished from scientists by their consciousness of costs and profits. Economics plays a vital role in the operation, design, and maintenance of every chemical plant. A good chemical engineer always gives economics top priority in his every effort. Every engineering decision involves cost considerations. Engineers must continue to keep up with the economic changes that may affect their products. The primary objective of an engineer's endeavours must be to deliver safely the best product or the most efficient services at the lowest cost to the employer and the consumer. Since change is an outstanding characteristic of the chemical procedures, hence potential alteration of a process is of importance not only when the plant is being designed but continuously. Judgements based on comparative facts must be exerted in most of the important discussions of a chemical engineer. Careful calculations using local parameters generally lead to clear and just decisions. Yield and conversions of the chemical process form the basis for the material and energy balances which in turn are the foundation for the cost determination. Primary stress must be laid on these balances to keep the plant operation economical and profitable. Economic conditions and limitations are one of the most important factors of any plant design activity. The engineer must consider costs and profits constantly throughout his work. Cost per unit product always turns out to be the key issue for any business enterprise and an engineer should always work to keep it as economical as possible. Its almost always better to sell many units of product at a low profit per unit than a few units at a high cost. An engineer must take into account the volume for production when determining costs and total profits for various types of designs, keeping in view customer needs and demands.
Whenever a new product is under appraisal, market evaluation for that product becomes essential. The job of a chemical engineer then leads to the market evaluation of that product. The factors generally considered in the market evaluation are the present and future supply and demand, present and future uses, new uses, present buying habits, price range for products and by-products, character, location, and number of possible customers. The marketing of a product does not only depend upon its advertisement but also on the quality of the product, its physical conditions, and its packing. Good firms rarely compromise on quality. Proper instrumentation, uniform plant conditions, good operators, and careful supervision leads to quality production. The physical conditions of the products have a very strong impact on the marketability. The physical conditions involve crystal structure, particle size and shape, colours, and moisture content. For example, gasoline is dyed in various colours to provide distinctive trademark, but also to conceal a colour which is often objectionable to the customer but otherwise has no affect on the performance. Here it is cheaper to dye the product than to remove the undesirable colour. Packaging of the product also plays an important role in the marketing of a product, especially the consumer products. However, packaging is often expensive. The most economical containers are refillable bulk ones such as tanks, tank-ships, tank-cars. But these cannot be used for the consumer products since the container appearance is very important to the customers. For consumer products quality packing with attractive colours, designs, and materials has to be used. Price of a product is the real concern for a customer. Prices should be maintained within the affordable range of a large number of people, since bigger markets lead to larger profits. To enhance the marketing of a product, an engineer should listen to the suggestions and the information brought to him by the salesperson, since he is the link between the company and the customer. The suggestion and ideas of the salesperson are very important, for he is the eyes, ears, and nose of a company, bringing in information to aid in economic forecasting and help increase marketing of products.
Chemical engineer also has to work as a safety engineer. Nothing is more dangerous to a plant than fire. Precautions to prevent fire and to fight fire must be taken. Employees must be protected against toxic chemicals. Safety measures not only keep the employees out of danger but also save money and time by reducing accidents and any unnecessary halts in the production. Even though every human being is apt to err sometime, but at times he gets careless too. Sometimes too much familiarity with chemicals breeds carelessness, hence well-run plants have safety devices and continuing programmes for alerting those working with a given process to its hazards. Adequate safety and fire protection measures require expert guidance. There is considerable difference of opinion in rating certain chemicals as hazardous and their degree of toxicity. For example, particular attention is given to carcinogens ( substances causing cancer ) and teratogens ( substances causing fatal malfunction ), but there is considerable difference of opinion about just how much dangerous many of these materials are. There are different standards for many toxic and harmful substances, however nowadays the governments decide these standards and are very severe on their implementation.
The construction ( erection ) of a plant is another important activity carried out by a chemical engineer. The presence of the chemical engineer is essential during the erection of the plant in order to implement the design standards and interpret technical and design data whenever needed. The chemical engineer should always work closely with the construction team during the final stages of construction and purchasing designs. In this way, the design sequence can be arranged to make certain important factors that might delay construction, first priority. Construction of the plant may be started before the final design is completed. During plant erection, the chemical engineer should visit the plant site to assist in the interpretation of plans and learn methods for improving future designs. The engineer should also be available during the initial start-up of the plant and early phases of operation. During the erection of a plant the engineer becomes intimately connected with the plant and hence learns the internal structure of the plant. He becomes involved with the installation of every pipe and gauge of the plant and this helps him greatly while running the plant and eliminating problems faced during operation. He learns methods and techniques which are very helpful to him in the maintenance of the plant and provide him knowledge and information for making the maintenance and check-up plans in future.
Adequate and skilled research with patent protection is necessary for future profits. The chemical process industry has certain outstanding characteristics such as rapidly changing procedures, new processes, new raw materials and new markets. Research creates or utilizes these changes. Without forward-looking investigation or research a company would be left behind in the competitive progress of its industry. Development is the adaptation of research ideas to the realities of production and industry. The progress of industry opens up new markets for even the most fundamental, established products. The advantages of research can be summed up as
Due to the dramatic rise in productivity and the recent technological changes in the chemical process industries, this industry has become very complex. The complexity of this industry has made it very difficult for business graduates, who do not have any knowledge of chemicals and equipments, to handle it. Now the chemical companies like to have chemical engineers as their mangers. Management is a very important aspect of plant operation. Handling the personnel, most importantly the workers is one of the most difficult jobs but a chemical engineer is always in contact with his workers and most of the time has to rely on them. Dealing the personnel is often called Human Engineering. The job of a chemical engineer is to control and run machines effectively and efficiently, and there is no machine better or more complex than human being. Controlling this machine is perhaps the most difficult task, a man has to perform. But as an engineer is in constant interaction with his workers and personnel so he has to perform it effectively. Hence, a good engineer must be a good manager as well. He has to listen to their opinions and understand their attitude. He has to listen to their problems they are facing in the plant operation, since they are the one who are more closely in contact with the plant and its units. He has to them feel part of the team and boost up their morale. Keeping the personnel in high spirits and high morale is very important.
More and more engineers are realizing that they can no longer think of a process plant as a collection of individually designed operations and processes. It is becoming increasingly evident that each separate unit of a plant influences all others in subtle ways. It is also true that the plant is a part of an ecological system extending well beyond its boundaries. The general availability of the computers has made it possible to study the dynamic behaviour of plants as well as their static or steady-state behaviour. Such intense studies have shown new possibilities for plant operation not previously conceived. Instead of measuring and attempting to maintain rigid temperature, pressure, and general conditions ( feedback control ), chemical engineers are trying to adjust system variables so that the output is satisfactory even though the inputs very widely and are not fixed ( feed-forward control ). Attempts at optimizing control are also being made. The next generation of engineers will be studying, analyzing, and optimizing such interacting and complex systems. This is a major improvement over envisioning design as involving simple, non-interacting, static systems that use only operations and unit processes.
Role of a chemical engineer in controlling pollution and waste generation can hardly be over emphasized. More and more chemical engineers are concentrating in the area of environmental engineering to develop new methods and techniques to treat wastes generated by the process industries, minimize waste generation trends, and develop renewable sources of material and energy. These engineers are working towards developing sustainable and renewable technologies. Their role in the earlier design phases of process industries has now led to new practically fume-less chemical plants.
Design of a chemical process plant is the one activity unique to chemical engineering and is the strongest reason justifying the existence of chemical engineering as a distinct branch of engineering. Design is a creative activity and is perhaps the most satisfying and rewarding activities undertaken by a chemical engineer. It is the synthesis, the putting together of ideas to achieve a desired purpose. It is perhaps the most important task undertaken by a chemical engineer. The design does not exist at the commencement of a project. The designer starts with a specific objective in mind, a need, and by developing and evaluating possible designs, arrives at what he considers best way of achieving that objective. A principle responsibility of the chemical engineer is the design, construction, and operation of chemical plants. In this modern world age of industrial competition, a successful chemical engineer needs more than a knowledge and understanding of the fundamentals sciences and related engineering subjects such as thermodynamics, reaction kinetics, and computer technology. The engineer must also have the ability to apply this knowledge to practical situations for the purpose of accomplishing something that will be beneficial to society. However, in making these applications, the chemical engineer must recognize the economic implications which are involved and proceed accordingly. Plant design includes all engineering aspects involved in the development of either a new, modified, or expanded industrial plant. In this development the chemical engineer makes economic evaluations of new processes, designs individual pieces of equipment for the proposed new venture, or develops a plant layout for coordination of the overall operation. Because of these design duties, the chemical engineer is many times referred to as design engineer. On the other hand, a chemical engineer specializing in the economic aspects of the design is often referred to as cost engineer. Chemical engineering design of new chemical plants and the expansion or revision of the existing ones require the use of engineering principles and theories combined with a practical realization of the limits imposed by individual conditions. Development of a new plant or process from concept evaluation to profitable reality is often an enormously complex problem. A plant design project moves to completion through a series of stages, which involve each and every activity explained in the preceding pages. The main stages in a plant-design project are:
These steps clearly show that the plant-design project involves a wide variety of skills. Among these research, market analysis, design of individual pieces of equipment, cost estimation, computer programming, and plant location surveys. In other words plant design involves every aspect of chemical engineering and allows a chemical engineer to use not only his knowledge but also his experience, skill, and innovation. The first step in preparing design is to establish the bases for design. In addition to the known specifications for the product and availability for raw materials, the design can be controlled by such items as the expected energy requirements, fuel used, and the value of by-products, etc. The next step consists of preparing a simplified flow diagram showing the processes that are involved and deciding upon the unit operations which will be required. After preparing diagram material balance is carried out, which is followed by energy balance, a knowledge of raw material and product specifications, yields, reaction rates, and time cycles. The temperature, pressure, and composition of every process stream is determined. Design of individual pieces of equipment comes next. Use of unit process principles is incorporated here. Volume, length, diameter, wall thickness, head thickness and type of head, number of plates for columns, type of packing or plates, catalyst type, heat interchange facilities, power requirement and pressure heads for pumps and compressors, and materials of construction, etc. are determined. After this design step the instrumentation and control required for the process is determined, which is followed by utilities and labour requirements tabulation. Estimates of the total capital investment and the total product cost complete this plant-design sequence. The general approach in any plant design involves a carefully balanced combination of theory, practice, originality, and plain common sense. In original design work, the engineer must deal with many different types of experimental and empirical data. The engineer may be able to obtain accurate values of heat capacity, density, vapour-liquid equilibrium data, or other physical properties from the literature. In many cases, however, exact values for necessary physical properties are not available and the engineer is forced to use approximate estimates of these values. Many approximations also must be made in carrying out theoretical design calculations. In the engineer's approach to any design problem, it is necessary to be prepared to make various assumptions. Sometimes these assumptions are made because no absolutely accurate values or methods of calculations are available. At other times, methods involving close approximations are used because exact treatments would require long and labourious calculations giving little gain in accuracy. The good chemical engineer recognizes the need for making certain assumptions but also knows that this type of approach introduces some uncertainties into the final results. Therefore, assumptions are made only when they are necessary and essentially correct.
