Separation of gases

Separation of Gases W.H. Isalski, Monographs on Cryogenics (In collaboration with the British Cryogenics Council), Clarendon Press, Oxford, UK, 1989, ISBN 019 8548117, £35.00 This book is one of the monographs sponsored by the British Cryogenics Council and therefore is concerned primarily with cryogenic processes for separating gases. It perhaps could have been more aptly titled 'Cryogenic Gas Separation Processes'. It is the successor to the 'standard' work of Martin Ruhemann first published in 1940. Since that time there have been many new developments and the author faced a daunting task. It is difficult in the space of a monograph to cover in detail all aspects of the present wide ranging applications of cryogenics to gas separation and purification but the author has managed to succinctly describe the essential features of all the main processes. This is probably the book's main value, in providing a most useful reference to where such processes can be effectively applied. It covers, for example, air separation and the recovery of rare gases, refinery off-gas processes including recovery of hydrogen, LPG and ethane/ethylene, recovery of industrial gases from petrochemical and fertilizer processes, including hydrogen liquefaction and natural gas processing and liquefaction. There is a relatively brief chapter on non-cryogenic processes such as adsorption, including pressure swing separation, absorption and the use of membranes but mainly from the viewpoint of purification for a subsequent cryogenic process. Although there is a short qualitative comparison of these with cryogenic processes. In the introductory chapter there are one or two points with which one might quibble. There is no mention of one of the first industrial processes for the separation of air, the Brin process for producing oxygen, which was the start of the air separation industry and also the deliberate use of exergy analysis as a tool to identify areas of process inefficiencies occurred in the 1950s, not in the 1970s and 80s as claimed by the author. After the introduction there is a useful chapter on the sources and uses of the various industrial gases, including their basic physical properties, which gives a useful backcloth against which the subsequently described separation processes can be viewed. In the reviewers view what should follow at this stage in the book is a chapter on the fundamental principles involved in cryogenic separation processes, i.e. the reversible work of separation, the thermodynamics of methods of producing the refrigeration needed, implications of irreversibilities in heat exchangers and the distillation step, etc. Various aspects are dealt with for specific processes

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in subsequent chapters but an early chapter on the principles involved would have been'of value, as for example in the book 'Cryogenic Engineering' edited by Hands. In the introduction to the chapter on air separation by a cryogenic process the work of Linde in first liquefying air on a significant scale is mentioned, but the work of Tripler in the USA and Hampson in the UK was also significant and should have been mentioned. Another small point is that in the section on hydrogen liquefaction (pp. 178-184) no mention is made of the 7 (US) tons/day unit built by Airco in 1967. This was of interest in that it was built essentially for industrial supply. At the end of the chapters dealing with the various separation processes mentioned earlier there is a very useful chapter dealing with the hardware used in the separations described in the book, including compressors, expanders, pumps, heat exchangers, distillation equipment including trays and packings, and storage equipment. Finally there is a chapter, rather too brief, on design methods. This is mainly concerned with equations of state and thermodynamic properties (which are undoubtedly of great importance). An example is also given of computer aided design and simulation. A little more on the factors involved in heat exchanger design, fluid flow and distillation calculations as applied to cryogenic plant would perhaps have given this chapter more value, although a number of such aspects are dealt with in describing the various processes. The book is however a monograph and clearly there is a limit to the amount of data it can include. It is a very useful review of the application of cryogenic processes to gas separation and in the space available it could not deal in detail with all aspects of the subject. As such it is a book which should be on the shelf of all engineers involved in this area. It is the first real book on the subject, at least in the English language, by someone personally involved in the area since Martin Ruhemann's classic work in 1940 and in view of the enormous developments in scale and applications (if not in principles) since then it is inevitably, as a monograph, more descriptive.

J.B. Gardner Consultant BOC Group, Windlesham, Surrey, UK