Catalyst filled heat exchanger for hydrogen liquefaction

Abstract

Cryogenic hydrogen liquefaction plants have a uniquely designed plate fin heat exchanger (PFHE) in which the fin channels are filled with an ortho-para hydrogen conversion catalyst (O-P catalyst). This PFHE can save liquefaction energy by reducing the heat of liquefaction. Despite the unique heat exchanger design, there are few studies on the thermohydraulic performance of the PFHE for the hydrogen liquefaction process. In this study, the thermohydraulic performance of a PHFE filled with an O-P catalyst is investigated in two steps. In the first step, pressure drop experiments are performed using a cylinder filled with commercial O-P catalyst. The pressure drop is approximately five times lower than that of the Ergun's equation. Therefore, we propose a new correlation for the porous channel filled with the O-P catalyst and apply it in the numerical research, which is the second step. According to the results, the difference in Nu/f1/3 between the new empirical correlation and the Ergun's equation is up to 1.6 times, and the exergy efficiency of the CPFHE is underestimated by Ergun's equation. Furthermore, we report the impact of the design parameters on the heat transfer and pressure drop on a PFHE filled with catalyst. This CPFHE is a counter-flow heat exchanger and includes a porous hot laminar stream and two cold laminar streams through the plain-fin channel. The design parameters are selected based on the fin height and fin spacing. Among the various fin channel designs, the most effective one involves a fin height of 4 mm and a fin spacing of 0.7 mm. Interestingly, at the same Re number, the variation in Nu/f1/3 is almost twice the variation in the fin spacing. Based on these results, we discuss the impact of the design parameters on the PFHE performance, using the performance evaluation plot. Therefore, this study is expected to provide insights and guidance for designing PFHEs in hydrogen liquefaction plants.