Large-scale hydrogen liquefier utilising mixed-refrigerant pre-cooling

For an energy supply chain based on liquefied hydrogen, low parasitic energy consumption throughout the chain, from conversion to end-use, is a prerequisite for competitiveness with other energy carriers. The viability of the chain from the viewpoint of efficiency and cost is to a large extent dependent on the efficiency of the liquefier, which is the dominant power-consuming process in the chain. Hence, an innovative large-scale, high-efficiency hydrogen liquefier based on mixed-refrigerant (MR) pre-cooling has been developed. The liquefier employs MR pre-cooling down to a hydrogen temperature of 75 K while below this temperature, a reversed helium/neon Brayton cycle provides the requisite cooling. Two MR-based liquefier models have been derived. In the first, Joule-Thomson throttling valves are employed for MR expansion, while these have been replaced with liquid expanders in the second. With 21 bar hydrogen feed pressure and an ambient temperature of 300 K, the resulting figures for specific liquefaction power are 6.48 and 6.15 kWh/kg(LH2), respectively. Based on current models, a reduction in the range of 45-48% from that of state-of-the art may be obtainable. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.