Second law analysis of hydrogen liquefiers operating on the modified Collins cycle

Hydrogen liquefaction systems have been the subject of intense investigatio ns for many years. Some established gas liquefaction systems, such as the p recooled Linde-Hampson systems, are not used for hydrogen liquefaction in p art because of their relatively low efficiencies. Recently, more promising systems employing the modified Collins cycle have been introduced. This pap er reports on second law analyses of a hydrogen liquefier operating on the modified Collins cycle. Two different modifications employing the cycle in question were attempted: (1) a helium-refrigerated hydrogen liquefaction sy stem and (2) a hydrogen-refrigerated hydrogen liquefaction system. Analyses were carried out in order to identify potential areas of development and e fficiency improvement. A computer code capable of computing system and comp onent efficiencies; exergy losses; and optimum number and operating conditi ons of compressors, expanders, aftercoolers, intercoolers. and Joule-Thomso n valves was developed. Evaluation of the thermodynamic and transport prope rties of hydrogen at different temperature levels was achieved by employing a hydrogen property code developed by researchers at the National Bureau o f Standards (currently NIST). A parametric analysis was carried out and opt imal decision rules pertaining to system component selection and design wer e reached. Economic analyses were also reported for both systems and indica ted that the helium-refrigerated hydrogen liquefier is more economically fe asible than the hydrogen-refrigerated hydrogen liquefier. Copyright (C) 200 1 John Wiley & Sons, Ltd.