Dynamics and control of continuous distillation units

Dynamics and control of continuous distillation units

Automatica, Vol. 13, pp. 449 450. Pergamon Press, 1977. Printed in Great Britain Book Review Dynamics and Control of Continuous Distillation Units O...

149KB Sizes 8 Downloads 122 Views

Automatica, Vol. 13, pp. 449 450.

Pergamon Press, 1977. Printed in Great Britain

Book Review Dynamics and Control of Continuous Distillation Units O . RADEMAKER, J. E. RIJNSDORP and A. MAARLEVELD

Elsevier, Amsterdam (1975) 726 pages APPROPRIATE control schemes for complex pro-

control aspects including practically all possible

cesses can be designed adequately only on the basis of a thorough analysis of the dynamic behaviour of the units involved. For the distillation process in particular no textbook linking these two subjects has been published so far, although many differing control schemes are in operation all over the world. It is this gap that the authors aim to fill with their book, in which they also present a wealth of experimental data to back up the theory. Furthermore, the presented methodology is claimed to be useful in studying other types of countercurrent processes and their control requirements. A monumental book like this deserves an extensive review. Comments should be expected, both as regards the contents and the ease with which one is able to enter the book from various angles. At first glance the following points struck me:

schemes and compares them with published work. After a clear and short introduction, chapter 2 discusses tray dynamics, heat and mass balances for binary and multicomponent systems. Also the passive analogue network approach to visualize and compute dynamics is introduced. These electrical circuits are built up to resistances and capacities and are claimed to be superior to signal-flow computation methods. Dynamic responses can be calculated--or at least the formulae can be set u p - for various interconnected variables, like concentrations, heat capacity, mass flow, etc. This is discussed in detail in chapters 3 and 6, which also include polar diagrams and Bode plots. Even the electrical network representing a complete distillation unit with values for all capacities and resistances is listed. Experimental data are given both in chapters 5 and 6, but again in such detail that it is doubtful whether many readers really will find this useful. A further problem is the authors' use of an overwhelming number of variables and that the relation to the physical meaning of several mathematical substitutions is not easy to follow right through. The reader, as a consequence, is often forced to thumb back and look for the definitions and context of the symbols used. Chapter 7 concludes the discussion on dynamics by giving a very good review of all essentials. The bibliography on dynamics is exhaustive, and broken down according to aspects discussed in the book. The second part starts with an interesting discussion on the degrees of freedom and the six main manipulable variables (correcting conditions). Chapter 9 gives all basic control scheme for mass balance, temperature, pressure, quality control, etc. and combinations thereof. Furthermore, criteria for selecting the appropriate scheme are given and compared with literature. The number of possible control schemes is further extended in chapters 10 and 11 for special cases. All in all 47 schemes are discussed. However interesting, again it is very difficult later to trace back the meaning starting from some arbitrary scheme. If quick consultation for a specific control problem is wanted, one is practically forced to start at the beginning of

Respect for the perseverance of the authors to finish this job; congratulations ! The treatment of the subject matter is very thorough and rigorous, and characterized by encyclopedic-like completeness of possible control applications: Being conceived at an industrial research laboratory as an aid in practice, it seems a pity that the main subjects published now have been studied before 1968 : Very extensive literature (before 1971) is not just listed, but also briefly discussed. This is very commendable, although comparing too many different applications between some 25 to 30 authors embarasses the reader, and current interest may be doubtful: It is unfortunate that reporting on more recent developments--computer control, optimizing control, digital algorithms--has, perhaps unwillingly, been sacrificed in favour of wanting to be (too) complete about earlier experiences. More detailed reading is clearly wanted. The book consists essentially of two parts. Chapters 1 to 7 very rigorously discuss the dynamics of the distillation unit, and chapters 8 to 14 treat the Received 25 October, 1976. 449


Book Review

chapter 9. Chapter 12, like 3 and 6, gives a dynamic analysis of the control systems, including polar diagrams, electrical networks etc. C o n t r a r y to this, perhaps redundant, chapter a more practical discussion on quasi-static analysis of control schemes is presented in chapter 13. Without embarking on rigorous dynamics (only slow changes are considered), the authors deal with the sensitivity of changes in steady-state conditions, and provide important quantitative information on multivariable control performance. Finally, chapter 14 gives an extensive list of papers on control of distillation units, published before 1968 and supplemented to 1971 in Appendix IV.

it is advisable, I think, first to read chapters 1.8, 9 and 13, and then pass on to 2, 7 etc. Courses, like the recently organized posldoctor¢ll~, course based on this book will prove useful to p r o m o t e the methods described. Moreover, it will be a challenge to find an o p t i m u m compromise between completeness of theory and experimental data, on the one hand, and the need for briefness and selectivity of the audience (potential users) on the other hand. Perhaps, as an additional result, an abbreviated and updated version will come into being.

In conclusion, after having spent some time on this book, I got more and more fascinated. Perhaps the appreciation of the contents is dynamic as well, and shows an inverse response: at first one is overwhelmed and feels embarassed, then a more powerful positive feeling breaks t h r o u g h and clearly becomes predominant. In practice, m a n y y o u n g process-engineers have little experience with distillation units and learn the hard way. This b o o k can certainly be of help, also for experienced distillers. Anyway, ifcontrolis the motive to pick up this book,

Biographical note


Gerard Duyt]es, born 1935,graduated in Technical Physics at the University of Technology, Delft, Holland in 1958.After two years of research with the Dutch Navy he worked until 1965 with the Royal Dutch/Shell Group in the Exploration and Production Department, where he was specifically concerned with oilreservoir engineering. Having gradually come more into contact with the control of processes in general, he joined, in 1965, the Central Research Organisation of DSM/Holland; since 1973 he is heading the department of Mathematics and Process Control. A significant part of the department works on model building, control and optimization of chemical processes, with or without the aid of process computers. Duyt]es has published some papers on this subject.