Book Review: Prof. Ralph G. Scurlock’s Stratification, Rollover and Handling of LNG, LPG and Other Cryogenic Liquid Mixtures

by M.E. Garrett MBE,

This monograph provides comprehensive guides to the often counterintuitive behavior of cryogenic mixtures and to how good practice can minimize the risk of catastrophic events. The theoretical basis for the phenomena described is followed by a full discussion on the practical implications and results, often with real life examples.

The first chapter outlines the purpose of the book and has a useful table of reference data and a clear list of the definitions used in this field of engineering. Scurlock’s mention here of the La Spezia incident in 1971 emphasizes the importance of understanding and predicting the behavior of cryogenic liquid mixtures and thereafter safely handling these potentially dangerous materials. Subsequently the author describes how heat flows into stored cryogens and the ways it permeates into the system; the convective patterns in quiescent liquid stored in an insulated tank are illustrated.

Scurlock then uses direct experiments to detail various insulation techniques and carefully examine convective heat flows. Chapter three finishes with a very useful section on unexpected heat sources that have sometimes puzzled even experienced engineers.

The surface evaporation of boiling cryogenic liquids is much more complex than was once thought, and Scurlock uses his fourth chapter to discuss this thoroughly, summarizing much meticulous research. The mechanisms are clearly explained and some experiments described that illustrate the theory and introduce the important, often unexpected, phenomenon of rollover.

Rollover occurs when stratified cryogenic liquids spontaneously and violently mix, releasing a large quantity of boiloff gas at a very rapid rate and over a long period. It is particularly relevant to LPG and LNG storage because of composition variation and because the flammability of the vented gas can be a major hazard. The theory, experimental verification and results are examined carefully and provide a good understanding of the buildup to the hazard.

Rollover results in a sudden uncontrolled pressure rise, and in large storage tanks the roaring vents and apparent lack of response produces a very fearsome situation. This is compounded by both the asphyxiation and fire hazard of the escaping gas as well as the risk of cold burns from pipes and valves that often freeze and become difficult to operate under these circumstances. The escaping inflammable gas hazard can spread for a considerable distance downwind, with the possibility of a conflagration if exposed to a source of ignition. The situation, however, can be mitigated and in chapter 6.14 Scurlock gives clear advice on controlling the developing situation and minimizing risk. Scurlock also discusses vacuum insulated storage tanks operating in a zero loss mode. It is interesting that these do not show any risk from roll¬over behavior because of the changed dynamics of heat flow into the liquid. Engineering constraints, transportation and cost limit the size of these tanks, although NASA has one of 900,000 gallons for liquid oxygen storage.

Cryogenic liquids also have to be transferred and are often close to their boiling point. If the liquid does boil, a mixture of gas and liquid is formed that has adverse effects on mechanical pumping, causing cavitation and loss of prime. Scurlock describes methods to cope with this, as well as handling inevitable two-phase flow during cooldown of pipes and tanks.

In chapter nine, he gives a review of safe handling and storage that—although succinct—is very useful indeed and covers many practical points often overlooked.

In summary, this book is an impressive collection of years of theoretical and hands-on experience presented in a straightforward and logical manner. It is a clear, authoritative instructive on the hazards and handling of cryogenic liquids, supported where necessary with theory, data and example. It is an excellent example of its kind and essential reading for those involved with these unusual materials.

Open BookeBook – $39.99 suggested retail price, ISBN 978-3-319-20696-7
Soft Cover – $54.99 suggested retail price, ISBN 978-3-319-20695-0