Application of matrix heat exchangers to thermomechanical exergy recovery from liquid hydrogen

Abstract

This paper reports the outcome of a project aimed at exploring thermomechanical exergy recovery from liquid hydrogen. The basis of this project was the conceptual design, development and testing of a new process for CO 2 removal from air for use in alkaline fuel cells operating with hydrogen stored as a liquid, addressing simultaneously: • thermomechanical exergy recovery from liquid hydrogen, and • its application to CO 2 removal from atmospheric air. This project was an attempt to address these issues by using the cooling available from the vaporisation of liquid hydrogen and/or boil-off vapour, to remove CO 2 from the alkaline fuel cell feed air by refrigeration purification, ie. by freezing the CO 2 out of the air. A schematic description of the process and an energy balance for refrigeration purification for the CO 2 removal are presented, showing that the process relies on high effectiveness heat exchangers and water re-vaporisation. The high effectiveness heat transfer is achieved using perforated plate matrix heat exchangers. Implicit in this work were: • The development of a new sizing procedure for matrix heat exchangers based on an approximate analytical solution for their performance, published recently in this journal. • The development of a new method for construction of perforated plate matrix heat exchangers. • Experimental testing of matrix heat exchanger performance. • The application of matrix heat exchangers to mass transfer, and their use as reversing heat exchangers. Certain questions relating to the recent analysis published in this journal are raised and modifications suggested. Experimental results of heat exchanger effectiveness tests and CO 2 removal tests showed that heat exchangers of the requisite effectiveness were designed and manufactured, and that the proposed process was successful in exergy recovery and CO 2 removal