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The Control of Chemical Processes

March 10th, 1975

Invited paper (13g) to the 5th National Convention of Industrial Engineers, Quimica, Barcelona, 10th-12th March 1975.

S F Bush, ICI Europa.

An addendum – “A necessary condition for effective control in business systems” – was added in January 1979.  


Control of processes is conducted on a number of levels, from control of plant to the planning of projects. These levels are distinguished principally by their different working time-scales. The main means of dealing with control problems in the process itself has been to design them out. In situations where process and commercial time-scales are too long to rely for control on feedback alone, on-line computers have a unique role in predictive control. Current examples are taken to illustrate these points.


The object of this paper is to expound basic control ideas relevant to the design and operation of chemical processes. No attempt has been made to include detailed performance figures of specific applications as would be required by control system designers. It is hoped, nevertheless, that even for them the presentation of principles may be relevant to the matching of the equipment specifications to the characteristics of the many different processes and industrial systems encountered in practice.

The control of processes can be seen narrowly as the provision of equipment for essentially regulation and scheduling, or very broadly as the design of complete business systems (including processes and managerial systems) to optimise some criterion (usually financial) over a period of time.

While the first view is too narrow to obtain full practical benefit from the available control ideas, these ideas do not as yet comprehend enough of the practical factors of process operations, factory constraints and commercial realities to make more than a relatively small contribution to the engineering and management skills deployed in design, and running a complex of factory processes.