Large-scale Chemical Plants Research Articles

Process Simulation Using a Distributed System

Simulation of large-scale chemical, mineral processing and nuclear plants is rapidly becoming a growth area. Benefits of such simulations are chiefly seen in the fields of operator training, and also increasingly in the fields of control system design and analysis.Plants, and the unit operations dictating plant response are often inherently modular. It appears sensible therefore to approach simulation design in a modular fashion. Once sufficient modules have been defined, and provided that the module interface is sufficiently general, it is argued that any process may be synthesised. This paper suggests that unit operations should form the basis for module selection. Once all unit operations occurring in the plant have been identified, modules may be selected. Modules comprise a unit operation, as applied to a number of physical units. They are selected to give acceptable response, while minimising hardware requirements of the simulation.Module interface design is considered important. This paper argues that a general interface applicable to any module, has certain advantages. The interface size is however constrained by inter-module communication time. The module should therefore only consist of primary variables, from which all other data may be inferred. A modular approach to simulation, and the fact that all modules have a high degree of autonomy, lends itself to distributed computing concepts. Thus, a simulation may be shared between several processors, yielding substantial time benefits. This allows an accurate simulation model, with diverse applications, to be developed. The proposed approach to simulation design is illustrated by means of an example. A small plant consisting of an autothermal reactor, with the product heating the feed, is decomposed, to illustrate the distributed approach to simulation design.

Implementation of self-tuning regulators with variable forgetting factors

A modified version of the self-tuning regulator having limited adaptability has been successfully implemented on a large-scale chemical pilot plant. The new algorithm uses a least-squares estimator with variable weighting of past data; at each step a weighting factor is chosen to maintain constant a scalar measure of the information content of the estimator. It is shown that, for nearly deterministic systems, such an approach enables the parameter estimates to follow both slow and sudden changes in the plant dynamics. Furthermore, the use of a variable forgetting factor with correct choice of information bound can avoid one of the major difficulties associated with constant exponential weighting of past data—namely, ‘blowing-up’ of the covariance matrix of the estimates and subsequent unstable control. Accordingly, the control algorithm described here may be well suited to the regulation of plants which would otherwise require periodic re-tuning of control constants.

Computer Control of Chemical Plants - Design Experience and Prospects

The problem of computer control system design for large scale chemical plants are studied from both the user's and designer's point of view. The compromise is a modifiable system. The designer's line is demonstrated on the algorithmic and aplication programming level together with the systems programing considerations. The authors experience is inn the field of centralized supervisory systems. Therefore those aspects may be of value. for future designs which are invariant with respect to changes of system arch1tecture towards decentralized control and distribued processing.

Some principles of design of a system for overall automation of large-scale chemical plant and the optimizing of this system

Some principles of design of a system for overall automation of large-scale chemical plant and the optimizing of this system

The Design and Working of Ammonia Stills

THREE hundred thousand tons of ammonium sulphate are produced annually in Great Britain by the direct distillation of the ammoniacal liquors arising from coal and shale products. Even from this consideration done, the publication of the first standard comprehensive book in English on the design and working of ammonium stills must be regarded as an event not only of scientific but also of economic importance. Many chemical manufacturers in the past for various reasons have endeavoured to keep their processes strictly secret, and improvements have come from internal experience on the plant rather than from general physico-chemical considerations or from a combined study of the theoretical and applied aspects of the problem or difficulty encountered. “Collaboration,” Dr. Charles Carpenter notes in the preface, “between those responsible for the design of large-scale chemical plant can only be a war-time measure.” Mr. Parrish will help to some extent to remove in one industry this individual outlook and veil of secrecy, for in his book he has collected together a great amount of novel information of a fundamental and authentic character on the subject of ammonia stills and accessory plant. This carefully-edited book, which includes 170 excellent illustrations and 70 technical tables, must benefit the industry generally and secure a common outlook for new developments on other than empirical lines. The Design and Working of Ammonia Stills. By P. Parrish. Pp. 300. (London: Ernest Benn, Ltd., 1924.) 40s. net.