The new textbook ‘Low Loss Storage and Handling of Cryogenic Fluids: The Application of Cryogenic Fluid Dynamics’ by Ralph Scurlock, F.I.Mech.E., C.Eng., M.A., D.Phil, is a particularly timely publication for all users of low temperature hydrocarbon liquids, including LNG, LPG and liquid ethylene.
The book provides the necessary information and advice to achieve the maximum obtainable economy in the storage and handling of hydrocarbon liquids with boiling points below ambient. The cost of this hardback will be recovered by savings in the cost of liquid used, within a few days of reading it and applying its suggestions.
In the book, the author has distilled the findings of his research over 50 years into vapour column properties, convective heat transfer and the behaviour of cryogenic liquids in storage. These findings are thought to be unique and have never been published within a single cover before.
The contents develop a logical understanding of the extraordinary evaporative behaviour of all low temperature liquids, and how heat in-leaks from the environment reach the liquid to cause surface evaporation only, or more colloquially, ‘boil-off’. The book then goes on to discuss all the insulation techniques available for reducing the heat in-leaks.
Very importantly, it discusses how the ‘cold’ in the boil-off vapour can be employed to absorb some, or all, of the heat in-leaks before they reach the liquid. In this way, the boil-off can be significantly reduced, by simple, low-cost techniques.
A major part of the book then discusses in detail the evaporation of multi-component low temperature mixtures, including:
1. Those mixtures in which the components are totally soluble in each other, like liquid air, liquefied natural gases LNG, and liquid petroleum gases LPG.
2. Dilute solutions in which one component, such as carbon dioxide, water and acetylene, has limited solubility in the major liquid component, such as nitrogen, methane, higher hydrocarbon, and mixtures such as LNG and LPG.
This major part of the book is, perhaps, an eye-opener to many readers because the boil-off from mixtures can have features not met so frequently with pure, single components liquids. Rollover, vapour explosion and other boil-off transients are considered at length as a consequence of stratification. Avoidance of stratification is therefore the prerequisite for safe storage and handling of mixtures.
•Firstly, there is a significant difference in composition of hydrocarbon mixture vapours above the liquid mixtures in a storage tank, to the text-book (T- x) diagrams. This is because (T- x) diagrams relate to free-boiling liquids in, for example, distillation columns: not to surface evaporation in an insulated storage tank. In addition, hydrocarbon liquids exhibit the wet-wall phenomenon of the Marangoni effect, arising from surface tension driven film-flow up the tank walls. Both effects lead to the enhanced composition of the vapour with the low boiling point component.
•Secondly, stratification in cryogenic liquid mixtures is determined by both temperature and composition differences between layers. The stability and breakdown of convective stability is then determined by the complex process of double diffusive convection which is described qualitatively in the book.
•Thirdly, the mechanisms of rollover are described and discussed from experience with producing over 100 rollovers in the laboratory. There are 2 modes or types of rollover, 2 spontaneous convective mixing mechanisms and a dramatic release of thermal overfill energy with the accompanying rise in boil-off, when the lower layer mixes upward into the upper layer.
•Fourthly, all rollovers are preceded by stratification which can arise from a number of causes, including custody mismanagement and auto-stratification processes.
•Fifthly, prevention and avoidance of rollover are discussed, together with the necessary instrumentation to detect stratification, and the appropriate installed auxiliaries to remove stratification.
•Finally, a section on stratification via sub-cooled liquid is discussed, whereby a hazardous situation is immediately created for sea-going tankers.
Dilute solution mixtures are discussed because they can present problems when the solubility limit is exceeded by changes in temperature and pressure as well as composition, and precipitation of solids takes place. Some of these solids, such as acetylene, are chemically unstable and present a hazard.
A practical chapter on achieving successful liquid transfer, by the avoidance of 2-phase flow, is a ‘must’ for all handling operations.
After a chapter discussing the thermal designs of 12 low loss systems, with scales from a 10mm diameter sample cell up to a 100 metre diameter storage tank, the final chapter on safety includes some unique comments based on experience with handling cryogenic liquids over 50 years.
This book is therefore an important handbook to be read and used by, all users of boiling hydrocarbon liquids and their liquid mixtures, as well as air component liquids, below ambient temperatures, particularly in the huge liquefied hydrocarbon energy industry today, using LNG and LPG in single tank quantities up to 400,000 m3.
The author, Ralph Scurlock, is Emeritus Professor of Cryogenic Engineering, and formerly Director of the Institute of Cryogenics, University of Southampton, UK.
He has run training courses and research projects on LNG and LPG Technology for many years at Southampton University and The School of Navigation, now Warsash Maritime Centre, Warsash, Southampton.
In 1999, Ralph Scurlock was selected by the US Cryogenic Engineering Committee for the Samuel C. Collins Award for his contribution to cryogenic technology. He was the first person from outside the US to be awarded this biennial prestigious prize since its inception some 40 years ago.
He is the author of some 300 papers and reviews, and several books including ‘Low Temperature Behaviour of Solids’ (1965), ‘History and Origins of Cryogenics’ (1994), and ‘Low Loss Dewars and Tanks’ (2004).
His new book is published by Kryos Publications, 22 Brookvale Road, Southampton, SO17 1QP, United Kingdom, Tel/Fax 0044 (0)23 8055 4665. Price: £55.00 sterling or approx. $116.00 US dollars or €93.00 Euros, plus postage and packing.
For further information, see the Kryos Publications website at: www.kryos.co.uk