About the value and efficiency of Renewable Energy
S F Bush with D MacDonald
If you would like to see a copy of the text as it was before publication, please click on the link: UKEnergy8
Published by the Institution of Chemical Engineers, vol 83, No A6, pp 646-654
S F Bush
This paper reports both practical and theoretical results from some 82 projects conducted with 70 small and medium-sized enterprises (SMEs) over the last 8 years. The companies are found in the plastics, chemicals, food, metal fabrication and electrical components sectors of manufacturing industry. The objective of the projects has been to develop new science-based products and/or processes, or improvements to these – occasionally all of these things.
The initial choice of a project and its subsequent management have been subject to a specific techno-economic assessment procedure evolved by the Centre for Manufacture’s partnership with NEPPCO Ltd – a company specialising in research and development for the process industries. As described in the paper, this procedure now deploys a techno-economic model (TEM) which links quantitatively the inputs and outputs of: research and design, investment and production, sales and marketing, over any given time period. The TEM allows market share and return on investment trajectories to be generated for an innovative change under various assumptions about the competition and the company management’s own characteristics. The paper demonstrates the importance of what may be termed the stoichiometric principle of innovation, i.e. optimum financial performance requires the resources devoted to product design, process efficiency, investment in plant and in selling, to be kept in strict proportion to each other.
S F Bush with J M Methven
The rate of crosslinking of a BF3-amine-epoxy-glass fibre composite manufactured by Microwave Assisted Pultrusion (MAP) is increased over that for the average (bulk) temperature of the mixture by a factor of at least 3. This is accounted for by postulating a non-equilibrated temperature in the system of at least 80K that originates from the significantly higher dielectric loss of the amine complex compared with that of the epoxy resin. It is proposed that a general class of systems in which specific reaction pathways can be selected using microwave energy is that where there is an uneasy compromise between a high temperature to achieve an industrially useful overall rate and a low temperature to avoid decomposition through parasitic side reactions.
S F Bush, with O K Ademosu
Process Pathways Analysis generalizes the familiar concept of reaction pathway to allow changes in physical state to be described in broadly the same way as chemical changes. While applicable to all chemical processes, the approach is particularly relevant to polymerization, where the product is required in specific physical as well as chemical forms, and where the phases in which reactions may be carried out – solution, suspension, melt, liquid, gas – greatly affect the viability of candidate processes. Five processes for making Styrene-Maleic Anhydride copolymers have been explored using the PPA approach. Experimental and predicted results are compared for key chemical and physical properties.
S F Bush
The paper identifies Design as the engineering function which will be most profoundly changed by current and projected developments in hardware and software. In hardware the three current classes of computer – the mainframe, multi-user mini and single user micro – are shown as likely to reduce essentially to two – the mainframe and the workstation. For software, the application of Artificial Intelligence (AI) in the form of an Expert System or Designer’s Assistant is seen as the most important new development affecting Engineering.
To understand the potential impact of computing on Design, a design inheritance factor is defined and the concept of parallel as opposed to serial design introduced. The ways in which the projected computing developments will enhance the one and facilitate the other are described.
S F Bush
The relatively low growth rates, around 3% per annum or less, projected for the next ten years, contrasted with those obtaining when most of the current chemical processes were designed, prompts a re-examination of the economies of scale for a number of reasons. In the last few years, under the spur of sharply increased energy prices, much effort has naturally been devoted to increased energy utilization efficiency. A number of such endeavours have, by occasioning a re-examination of existing designs, enabled savings in capital as well as energy to be made. None-the-less, when design inefficiencies have been stripped out, energy is the resource we use to achieve intensification or volumetric compactness. The relationship between energy efficiency and intensity rules in an approximate way in all industries, including Man’s oldest industry, agriculture, as has been pointed out by Green (1), (Table 1):
| Technology | Food produced (annual needs) | Space used (hectares) | Chemical energy out/ Chemical energy in |
|---|---|---|---|
| Bushmen | 1 | 1300 | 1 |
| British farmworker | 50 | 10 | 0.4 |
While the detailed figures depend on precise definition, the trend is clear. Equally clear for optimal design is the need to determine the fundamental limiting relationship between energy efficiency (including availability) and intensity, for the generality of chemical processes. Le Goff (2) has recently addressed this problem in connection with the design of heterogeneous reactors.
There is additional reason to examine the design fundamentals of polymerization reactors in particular and that is because the products (i.e. polymers) are now demanded in ever-increasing variety. The period 1950-1970 of rapid scale increases has been followed to-date by a period of adaptation of the processes and modification of the basic polymers (polyethylene, PVC, polystyrene, etc) designed and introduced in the former period under basically different assumptions. Additionally a number of second-generation polymers (e.g. polycarbonates, poly(phenylene oxide)) have become fully commercial during the current period. As will be indicated, there are thus both significant similarities and differences with the general class of chemical processes and both general and particular principles to apply.
(1) M B Green (1976), Lecture to the Society of Chemical Industry.
(2) P Le Goff (1980), Chemical Engineering Science, 35, 2029-2063.
(3) K G Denbigh (1957), “Principles of Chemical Equilibrium”, pp 71-72.
(4) H Brauer (1982), Institute of Chemical Engineers Symposium, 78, T5/11-19.
(5) P J Tail (1980), Macromolecular Chemistry, 1, SPR, Roy. Soc. Chem. 3-21.
(6) K H Laidler (1965), “Chemical Kinetics”, p 70 ff.
(7) G I Taylor (1954), Proc. Roy. Soc. A220, 446-467.
(8) S F Bush (1969), “The Design and Operation of Jet-stirred Reactors for Chemical Kinetic Studies”, Trans. I. Chem. E. 47, 59-72.
(9) R S Brodky (1966), in Uhl and Grey “Mixing”, p 52.
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
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.
S F Bush
The application of the jet principle to four chemical engineering design objectives is described. The four applications are to:
The applications thus cover a range of viscosities and phases on both the laboratory and full scales. The experimental and theoretical results on which the designs are based are given. Some general conclusions about the utility of the jet principle in mixing and heat transfer are derived.
S F Bush
A basis for the design of jet-stirred reactors is proposed. A number of reactors for continuous-flow chemical kinetic studies have been constructed on this basis and the fluid flow in the reactor has been examined by means of a hydraulic model. Experiments on dispersion have also been carried out. An analysis of the dispersion achieved by the design leads to simple formulae for the mixing time and the fluid recirculation.
The fluid recirculation in the reactor is found to be close to design predictions. Results of experiments using these reactors for the study of exothermic reactions are presented. In general, the spread of temperature within the reactor (a practical measure of effective mixing with exothermic reactions) has been found to be small and comparable with that obtained with high-speed paddle-stirred reactors.
See also the section on Measurement of Reaction Kinetics.
