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States of matter

States of matter

Revealing the invisible

01 May 1998

Industrial Gases
Neil Downie
1997 Blackie Academic and Professional 570pp £110.00/$249.00hb

Physicists, more than most people, are accustomed to dealing with gases. Yet even physicists often treat gases as something to be taken for granted, a sort of Platonic ideal with interesting or useful properties but with little connection to the world outside the laboratory. Whether as natural resources or something to be delivered in cylinders, gases are just there.

But of course gases, at any rate those in cylinders, do not just happen. They are the products of a multi-million-pound global industry that links science, technology and business in a virtuous circle of discovery and development. The story of gases starts at the dawn of science and goes on to touch almost every area of modern life.

Industrial gases are those gases that are commercially important, especially the so-called “merchant gases” that are sold from one company to another and transported in pipelines, tankers, cylinders and insulated flasks. They crop up everywhere, from a steelworks that uses 2000 tonnes of oxygen per day to the semiconductor fabrication plant handling kilogramme quantities of high-purity silane and other exotics.

Truck and aircraft tyres are often filled with nitrogen to reduce the risk of fire. Liquid carbon dioxide dissolves biocides for controlling agricultural pests and bacteria in air-conditioning systems. Ice-cream moulds chilled to -80 °C with liquid nitrogen become “non-stick”. The poor thermal conductivity of krypton is useful in electric lamps and double glazing. Ethylene is used to control the ripening of bananas and other fruit.

Hydrogen, with its low viscosity and high thermal conductivity, is used to cool alternators in power plants. Oxygen improves the economics and environmental performance of many combustion processes. Ultra-pure gases and gas mixtures are essential for semiconductor manufacture, gas chromatographs and particle detectors, while liquid helium cools superconductors and radiation detectors.

Invisible they may mostly be, but gases are all around us. Just as interesting as the applications are the ways in which the gases are manufactured. Even to those of us who know something of cryogenics, compression, expansion and distillation, it is remarkable that we can buy liquid oxygen for around £20 a tonne. Helium is more expensive not only because it has a lower boiling point, but also because of its rarity. Although helium is common in natural gas, only in the US and Poland is the concentration high enough to make extracting the helium worthwhile.

Apart from cryogenic distillation, adsorption technology provides a useful source of smaller quantities of atmospheric gases for applications in which it is important to be able to generate gases near their points of use. Pressure-swing adsorption (PSA) plants are slowly growing in scale, to the point where small steelworks are now using PSA units producing some tens of tonnes of gas per day. Membrane separation systems, currently expensive and limited in scale, promise even greater convenience.

Industrial gases cover such a wide area that they need a big book to do them justice, and that is just what Neil Downie has produced. Industrial Gases is not physically large by textbook standards, but its scope is another matter. It contains four chapters: a brief introduction to gases and the gases industry; two substantial sections on gas technology and industrial applications of gases; and a short chapter on the future of the industry. All four chapters are well balanced, accurate and up-to-date.

After a quick overview of the history of gas manufacture and applications, the introductory chapter summarizes the physics and physical chemistry of gases giving examples of common gases. I found the last part of this chapter the most interesting, since it gives a very competent summary of the structure of the gases industry and its commercial drivers.

The section on gas technology covers manufacture, handling and storage, measurement and analysis, and safety and environmental issues. There is such a lot of ground to cover that the reader may worry about not finding sufficient detail. My own feeling is that, having included the correct amount of background information, the author has got it just right.

However, as someone who specializes in applications for industrial gases, I would have liked more detail in the chapter about how gases are used. But this is nit-picking; the book has to stop somewhere, and this section is well balanced and as detailed as it is possible to be in 200 pages covering such diverse topics as anaesthetics, fertilisers and carbonated drinks. The content is up-to-date and the illustrations are basic but clear, although the index could be better.

Industrial Gases is well written in a refreshingly personal style. Perhaps Downie’s background as a consultant helps here. After all, consultants need to sell themselves, and more than most other scientists and engineers they are likely to suffer if their communication skills are not up to scratch. Combined with the wide-ranging content, the result is as close as a technical textbook gets to bedtime reading.

After I started work in a company making industrial gases, it took me five or six years to gain a reasonable grasp of the industry: its products, technologies, business models and people. With the aid of this book, today’s new recruits can cover much of this ground in five or six days. Industrial Gases will be essential reading for people in the gases industry and an excellent read for anyone who is simply curious about where their laboratory nitrogen comes from.

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