Page 53 - Plant design and economics for chemical engineers

36 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

is required, and control of the equipment and grade of final product is
simplified. Whereas batch operation was common in the early days of the
chemical industry, most processes have been switched completely or partially to
continuous operation. The advent of many new types of control instruments has
made this transition possible, and the design engineer should be aware of the
advantages inherent in any type of continuous operation.

EQUIPMENT DESIGN AND SPECIFICATIONS

The goal of a “plant design” is to develop and present a complete plant that can
operate on an effective industrial basis. To achieve this goal, the chemical
engineer must be able to combine many separate units or pieces of equipment
into one smoothly operating plant. If the final plant is to be successful, each
piece of equipment must be capable of performing its necessary function. The
design of equipment, therefore, is an essential part of a plant design.
The engineer developing a process design must accept the responsibility of
preparing the specifications for individual pieces of equipment and should be
acquainted with methods for fabricating different types of equipment. The
importance of choosing appropriate materials of construction in this fabrication
must be recognized. Design data must be developed, giving sixes, operating
conditions, number and location of openings, types of flanges and heads, codes,
variation allowances, and other information. Many of the machine-design de-
tails are handled by the fabricators, but the chemical engineer must supply the
basic design information.

SCALE-UPINDESIGN
When accurate data are not available in the literature or when past experience
does not give an adequate design basis, pilot-plant tests may be necessary in
order to design effective plant equipment. The results of these tests must be
scaled up to the plant capacity. A chemical engineer, therefore, should be
acquainted with the limitations of scale-up methods and should know how to
select the essential design variables.
Pilot-plant data are almost always required for the design of filters unless
specific information is already available for the type of materials and conditions
involved. Heat exchangers, distillation columns, pumps, and many other types of
conventional equipment can usually be designed adequately without using
pilot-plant data.
Table 6 presents an analysis of important factors in the design of different
types of equipment.? This table shows the major variables that characterize the

tAdapted from Johnstone, R. E., and M. W. Thring, “Pilot Plants, Models, and Scale-up Methods,”
McGraw-Hill Book Company, New York, 1957. See also Bisio, A., and R. L Kabel, ,“Scaleup of d
Chemical Processes,” J. Wiley & Sons, New York, 1985.