PROBLEMS OF BULK STORAGE AND SHIPPING OF LIQUID HYDROGEN IN VOLUMES OF 10,000 TO 100,000 CUBIC METERS AT ONE BAR PRESSURE

摘要

This paper discusses concern about the safety and serious risk assessment of the large scale bulkrnstorage, shipping and handling of liquid hydrogen.rnWhile hydrogen is very attractive as a green fuel and energy store, some of its physical properties providernincreasing problems if the proposed usage increases beyond a limit of, say, 1000 m~3 of liquid hydrogen,rnunder pressures rising to 10 to 15 bar to achieve zero boil-off, in a vacuum insulated container. Cryogenicrntechnology is currently not able to store larger volumes in vacuum insulated tanks under pressure with zerornboil-off, or even at one bar pressure with continuous boil-off. At first sight, the successful shipping andrnstorage of bulk LNG over the past 45 years suggests a satisfactory way forward. In fact, the properties ofrnbulk liquid hydrogen compare unfavourably with those of LNG, and the LNG technology cannot be adaptedrnwith the same degree of safety and economy.rnThe problems start with the large volume of boil-off hydrogen gas produced and its extreme flammabilityrnabove a composition in air of only 4% hydrogen. Safe disposal of this boil-off presents a major problem,rnwhich is enhanced by the fact that the density of LH_2 is 6 times less than that of LNG, and the latent heat ofrnevaporation per unit volume is 7 times less: hence the volume of boil-off hydrogen gas is seven times greaterrnfor the same heat influx.rnFor ship and shore tanks with gas-purged foam insulation, the only safe purge-gas is helium which has arnthermal conductivity k-value 5 times greater than nitrogen or methane purge used for LNG tank insulation.rnThe net boil-off rate of LH_2 using the conventional one metre thickness of foam insulation can therefore bernexpected to be 35 times larger than the working figure of 0.2% per day for stored volumes of LNG.rnThese and other handling problems, together with the associated hazards of disposing of the gas safely, eitherrninto the atmosphere, or flaring it off or re-condensing it, appear to make proposals for bulk liquid hydrogenrnusage not viable for both safety and economic reasons. This paper will review this lack of viability.