Analysis of a Supercritical Hydrogen Liquefaction Cycle

A supercritical hydrogen liquefaction cycle is proposed and analyzed numerically. If hydrogen is to be used as an energy carrier, the efficiency of liquefaction will become increasingly important. By examining some difficulties of commonly used industrial liquefaction cycles, several changes are suggested and a readily scalable, supercritical, helium-cooled hydrogen liquefaction cycle is proposed. An overlap in flow paths of the two coldest stages allowed the heat exchanger losses to be minimized and the use of a single-phase liquid expander eliminates the pressure reduction losses associated with a Joule-Thomson valve. A computational model of the cycle was developed to investigate the effects of altering component efficiencies and various system parameters on the cycle efficiency. Furthermore, a heat exchanger simulation was developed to verify the feasibility and to estimate the approximate size of the heat exchangers in the cycle simulation. For a large, 50-ton-per-day plant with reasonable estimates of achievable component efficiencies, the proposed cycle offers a modest improvement in efficiency over the current state of the art. In comparison to the 30-40% Second Law efficiencies of today’s most advanced industrial plants, efficiencies of 39-44% are predicted for the proposed cycle, depending on the heat exchange area employed.