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CHEMICAL. PLANT DESIGN: A CHEMICAL. ENGINEERING COURSE* C. L. MANTELL, P u r r INSTITUTE, BROOKLYN, N. Y.
Chemical plant design as part of the chemical engineering curriculum is given in only a very small percentage of institutions which presumably train men for the chemical and allied industries. Its value as a summation and correlative course can be equalled by very few engineering subjects. Its emphasis on the practical side closely connects the student with industry. The viewpoint from the financial and economic phases causes the subject to be ever alive, progressive, and necessarily up-to-date. Practically all of our engineering teaching is done from text-books. All of us are familiar with the statement that it takes ten years to get facts and practices into text-books and twenty years to get them out again. Far too often is this criticism true. Seldom in his engineering course does the student come in contact with the printed matter which is up to the minute-manufactmels' catalogs, reports of industrial lesearch, and experimental work by equipment makers, etc.-the huge mass of information termed "trade literature." The work of chemical plant design forces the student into useful acquaintance with this source of industrial practice. The previous training of the student has given him a grounding in physics, mathematics, electrical engineering, industrial chemistry, mechanics, power, metallur.gy, and chemical engineering unit processes. These subjects are but little correlated in their presentation. Their specific a~plicationt o specific problems are but slightly touched in connection with the economic side of actual industry. Chemical plant design converts them into a coordinate whole for the chemical engineeras expressed by one student, all of the rest of the engineering course was just preparation for this one. The language of chemical plant design is a universal one-that of engineering drafting. It is assumed that the student is sufficiently apt in the use of this mechanism of expression of ideas and directions. Previous training in drawing is presumed. Chemical plant design is not a drafting course any more than industrial chemistry is a course in English; the vehicle or means of expression is entirely subordinate. Design courses, in general, may be divided into three diierent types. The broadest and most useful variety employs the industry as a unit. The second type is a subdivision of the first and employs a specific plant as a unit. The third type is a subdivision of the second and employs a specific unit process or a single piece of equipment as the unit. In the first type, of course, the survey of the specific industry (either 'Paper read before the Division of Chemical Education of the A. C. S. at Philadelphia, Pa.. September 7, 1926.
selected by a group of students and approved by the instructor, or assigned by the instructor) is the starting point. The economics of the industrythe annual production, consumption, imports and exports, sources of raw material, location for existing plants, the history of the industry, its economic importance, product distribution, the effect of a new plant on the industry, the disposal and utilization (if possible) of by-products, etc.are first investigated. Governmental reports of the Department of Commerce, the Federal Trade Commission, the Tariff Commission, along with data available from the work of various trade organizations furnish the sources of material for this part of the work. The majority of students have had little need to come in contact with these fields of information previously. Those who have, perhaps thought it dry as dust for they could not see a specific application to their own work. The student's attitude should be that of an engineer connected with a group of men and capital desirous of entering some established industry or organizing a new one. The specific industries for which plants are to he designed are either selected by groups of students working together, and approved by the instructor, or else assigned by the instructor to these groups. After the survey of the industry has been completed and reported, the plant size, expressed in terms of quantity of product, is determined. From economic studies, sources of raw material, availability of labor, disposal of product, freight rates, etc., the plant location is determined. Capital to the extent required is assumed to be available. The problem then resolves itself down to the design of a specific plant of definite size in a definite location. The type of plant, the completeness or incompleteness of its mechanically handled operations, the type of process used, the equipment specified, the k i d of power used, etc., will be determined by availability, original investment costs, operating costs, location of raw materials, and the plant location. It is interesting to note, as an example, that even a t large hydroelectric power centers, where power is "inexpensive," that it is cheaper to employ coal as a fuel for low-temperature heating than it is to use electrical energy for the same purpose. It is understood that this first type of course can only be applied in the case of men with exceptional preparation in chemical engineering. It is believed that only one engineering school gives this type of course. That school is connected with a large eastern university. The engineering course there is of six years' duration. The design of a specific plant, definitely located, of determined size, to make some definite product or products, is employed as the unit of the second type of plant design course. The problem involves the selection and layout of equipment from the chemical, engineering, and financial phases of the situation. In chemical plants, knowledge of the chemical
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resistance of engineering materials of construction becomes of great importance. The emphasis should be placed on the dollars and cents aspect a t all times. After a short while the student may suddenly realize that the equipment he had seen in plants he visited and thought clumsy and stupid, was, from the dollars and cents viewpoint, exactly suited to the job. Conversely he may find that apparatus in other plants that he thought clever, was economically unsound. Shortly there will come the comprehension that he is working not only with apparatus built of engineering materials, but with dollars which he is condemning to grow or to die. As a subdivision of the unit plant, there is a third variety of course still more limited in scope. The individual piece of equipment or a single unit process is chosen as the unit. The problem is either to select the apparatus in all its details or to design the same. Provision must be made for its setting up in the plant in its appointed place. Determination is made of its physical tying-in with the rest of the plant, its piping, driving mechanism, control, operation, etc. Familiarity with the catalogs of manufacturers and ability to use trade literature becomes important. Complete acquaintance with the details of the process, its conditions, corrosion phenomena, physical characteristics of the materials handled, must all be learned before equipment can be selected or designed. Often, in industrial work, considerable preliminary experimentation on the material, process, and equipment is necessary. The approach to the entire course, no matter which type or subdivision is employed, must necessarily be through the avenue of unit processes. Fundamentally filtration is the same whether encountered in the manufacture of heavy chemicals, pigments, or dyes. Evaporation, as a process, is the same, irrespective of the product made in a particular plant. Of course, it is understood that the specific equipment for the unit process may be quite different a t times. The differenceis in details, not in fuudamentals. The "flow sheet" or chart of operations affords a starting point for the plant. Obviously the student must acquaint himself with the industrial chemistry of the process, with all its twists and turns. Visits to plants in operation will be found very helpful. A tonnage flow sheet, showing the amounts of materials to be handled a t each step of manufacture, is prepared. An equipment flow sheet showing the type, variety, and size and number of pieces of apparatus for each portion of the process, carries the work still further. Detailed selection of equipment, with complete specification for accessories follows in natural order, as do the bills of material for construction. The selected apparatus then has to be coordinated into an operating group. The physical dimensions of the machines, etc., are known and the layout of the plant can be prepared. The large number
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of conditions to be met in making a layout can be appreciated only after considerable experience. A good engineering instructor can point out and observing students can usually see the obvious desirability of providing sufficient space to work, free flow of materials, proper ventilation, observance of the building laws and fue department ordinances of the municipality, agreement with the underwriter's rules, etc. The most economic layont, however, can not be so readily seen. From the viewpoint of operating cost, one of a number of layouts will be better than the others. It is very likely that the student may produce half a dozen layouts before satisfaction is reached. Machines must be driven, power transportation and transmission have to be taken care of, and sources of energy provided. Liquids and gases may need to be moved from place to place; piping systems must be calculated and located most e5ciently. Solids must be transported in the plant and conveyed from place to place through the various stages of plant operation. Heat energy, or its removal, must be provided where desired for use. Raw material has to be gotten into the plant and finished product shipped out for disposal. Waste and by-products bring along their own problems as to the best ways of handling them. The layout concluded, detail design and assembly drawings follow. These are started only after the layout, if both plan and elevation have been satisfactorily completed. Provision is made for the erection of the plant and its control in actual operation. Administrative control, control of labor, time, material, temperature, moisture, light, power, sanitation, waste disposal, and hazards are carefully planned. The whole mass of data is then coordinated into the finished plant design. At first glance it would appear that the design of chemical engineering plants, owing to the multiplicity of the processes involved and the apparent highly specific nature of almost every case, is a subject impossible to treat as a coordinated whole. Certainly at first glance it does not look like a teachable subject unless given by a "professor of th'mgs in general." But a closer view of the field will disclose a remarkable simplicity of the underlying structure, obscured it is true by an infinity of detail, but everywhere yielding to a common system of analysis. The plant embodying truly unique features is rare indeed. Ordinary structural design is in the last analysis a question of protection from the elements; ordinary machine design is a question of pure mechanics, but plant design is a problem in coijrdination. There must be no loose ends, no bliid alleys.
Summary An attempt has been made to show the value of courses in chemical plant design in the chemical engineering curriculum as a useful mechanism for coordination and correlation of the students' engineering training in
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seemingly loosely connected fields. Types of courses now in use have been briefly outlined. The incorporation of courses in chemical plant design in our engineering schools and their intense utilization would not only connect the student more closely with industry but cause him to realize that the only reason men enter business and industry is to cause money to earn more money. Plants are, after all only mechanismsfor the growth of capital. Chemical plant design causes engineering students, as does no other course, to select and constantly maintain a definite point of view-the first duty of an engineer. I n the institutions in which the course, in one of its varieties, has been given, it has producedgratifying results, satisfactory in its entirety to both the students and the instructor.
