Article published in Cybernet News, Issue 80, March/April 1978.

S F Bush with G Schwarz and E P B Jongen.

Introduction

APEX III mathematical programming system and PDS/MaGen matrix and report gnerator from CYBERNET Data Services help ICI Europa analyze complex business plans.

ICI, or Imperial Chemical Industries Limited, is a British-based international group of companies with 1977 sales of 4.6 billion pounds ($9 billion) in chemicals, petrochemicals, plastics, fibers, dyes, paints, pharmaceuticals, agrichemicals and nonferrous products.

Since its incorporation in 1926, ICI has provided the world with many new products including:

• Polyethylene
• Polyester fiber
• An important group of cardiovascular drugs
• Remedies for tropical diseases and epilepsy
• Animal feed from methanol

 
Outside the United Kingdom, ICI has almost 300 subsidiary companies and a considerable number of associated companies engaged in manufacturing and selling.

ICI Europa, with headquartes near Brussels, Belgium, coordinates the activities of the manfacturing and selling companies located in continental Europe. ICI Europa also works closely with nine product group divisions in the UK and ICI headquarters in London.

ICI’s use of APEX III in combination with PDS/MaGen began when a member of the polyurethane business area asked for assistance in analyzing investment plans. The Systems Technology Group of ICI Europa began to work on a solution.

Paper to European Branch of the Institution of Chemical Engineers One-day Conference on Polymer Processing.

Published in The Chemical Engineer of March 1978, Issue no 330.
S F Bush with additional papers by G Schwarz, R Caloine and C Clayton

Introduction

For a number of reasons the mechanical and thermal processing of polymeric materials has developed in a largely empirical fashion over the last 30 years. One probable reason is that equipment manufacturers have not concerned themselves with the detailed properties of polymers, while until recently polymer manufacturers have relied on a few in-house specifications to characterise their materials.

In recent years, however, an effort to decrease processing times and improve quality in the manufacture of fibres, mouldings and films has led to a steady demand for improved quality and especially uniformity of polymer as supplied to the processor. Correspondingly there is now a greater interest in defining the limiting factors in the total polmer plus processing equipment system.

As its first technical venture the recently formed European Branch of the IChemE organised in conjunction with the Dutch engineering and chemistry societies a one-day conference to discuss the application of the basic principles of mass, momentum and energy transport to polymer processing. Accordingly, six of the seven contributions were oriented to specific operations, such as the drying and transport of polymer granules, injection moulding and the formation of laces (thick fibres) and foamed plastics, while the remaining paper, on bubble formation, dealt with phenomena of acute relevance to two of the others.

The basic lesson of the conference papers is that application of quite simple principles pays off at least as well on the polymer processing side as in the polymer manufacturing side. In particular, precision in mechanical layout, temperature control and setting is more important than in most mainstream chemical engineering operations. Both requirements are well illustrated by the paper on lace-forming. The individual components of a lace-casting line are relatively simple, but they must be precisely sized and positioned by being part of a larger system (e.g. to make granules and then fibres, films or mouldings), they can cause interruptions and out-of-specification production which can propagate through to the final customer. Temperatures at extrusion must be uniform within a few degrees on all co-extruded laces to avoid breakage and the excessive degree of line supervision then entailed, but once known, the required standard is readily obtainable in practical cases.

Two papers considered the drying, storage and pneumatic conveying of granules. Again the key sep in each case was the relating of well-understood theoretical ideas of momentum mass and thermal transport to equipment designed largely on a quite different basis. Three papers, however, touched on the less well understood phenomenon of bubble formation in polymer liquids and its crucial importance for foamed plastics. The final paper analysed the filling process in injection moulding and the relationships needed to maintain close control in practical cases.

Overall, the papers indicated the great scope for chemical engineering in the design of systems and equipment for polymer processing of all types.

Invited paper to the Norwegian Institute of Technology Conference on Steam Cracking, Trondheim, 16th-17th August 1977.

S F Bush

Summary

What follows is an approximate mechanism and derived rate expressions determined by the need to see broadly what is going on in a very complex system. For a detailed prediction of the cracking pattern of any of dozens of feedstocks, the computer based methods described in Bush and Dyer (Ref 9) are required. In the following, some necessarily approximate generalisations have been made in the interests of understanding the meaning of the overall activation energy and pre-exponential parameters of carbon formation found experimentally.

References

Ref 9: S F Bush and P Dyer, The experimental and computational determination of complex chemical kinetics mechanisms, Proceedings of the Royal Society, A. 351 33-53 (1976).

Paper to the Mixing and Polymer Processing Conference of the European Federation of Chemical Engineering, Delft, Holland

S F Bush with E Jongen.

Introduction

A major problem in the manufacture of a number of important polymers such as polyethylene, polyester and nylon, is the occurrence of non uniformities which show up as streaks and blobs in film and cause breaks in filament. The major source of this problem lies in the fact that during manufacture a tiny fraction of the material is exposed to reaction conditions very significantly different from those applying to the bulk of the material, by virtue of the exceptional residence times developed at vessel walls. Such non uniformities are particularly likely to occur at cooling surfaces since the unavoidable tendency to stick there is enhanced by the increase in viscosity through the thermal boundary layer.

The present paper outlines a description of the reaction and flow of polyethylene and ethylene through tubes from which there is a substantial extraction of heat. The driving force is provided by pressure drop.

In the high pressure stirred autoclave process, the reaction in the tube is incidental to its main function of cooling the polymer and reducing pressure (by about 400 atmospheres) at the outlet from the autoclave. In the tubular process, the overall pressure drop through a tube is greater (around 2000 atmospheres), since the tube is itself the main reactor. The chemical kinetics and fluid mechanics equations have been set up to cover both cases, but the applications referred to in this paper arise from the autoclave process.

See also the section on Applications to Existing Products and Processes.

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.  

Summary

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.

Introduction

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.

Paper to the Institute of Mechanical Engineers Conference, Control in Process Engineering, 16th-17th May 1972.

S F Bush, ICI Europa.

Summary

Generally, the application of automatic control theory to chemical processes has not so far led to the same dramatic improvements as in electrical and mechanical systems. The paper seeks to determine the reason for this and traces the essential developments which seem to bear on this fact. It is found that in its approach to the control of chemical processes, control theory has been implicitly limited to working outside what may be termed the currency of a process. If this view is accepted, two new possibilities arise for the development of control theory and for its fruitful application: firstly, in the physico-chemical design of a process and secondly, in the design of computer control.