Experimental investigation on hydrogen transfer in coupled metal hydride reactors for multistage hydrogen purification application

Abstract

Three stage metal hydride hydrogen separation system was tested, wherein each stage was configured with 1.2 kg of LaNi4.7Al0.3, LaNi5 and La0.9Ce0.1Ni5, placed in descending order of their equilibrium bed pressure respectively as R1 (La0.9Ce0.1Ni5) > R2 (LaNi5) > R3 (LaNi4.7Al0.3). Hydrogen absorption capacity obtained for R1, R2 and R3 were 15.91 g, 15.93 g and 16.02 g respectively for 3rd activation cycle, performed at 30 bar and 25 °C. For coupled reactor operation, optimum hydrogen transfer was for desorbing reactor at 90 °C and absorbing reactor at 20 °C, which was 12.31 g for R1 to R2 in 350 s, 13.33 g for R2 to R3 in 300 s and 13.38 g for R1 to R2 in 280 s, constituting to 1.03, 1.11 and 1.12 wt% of hydrogen storage respectively. Further, the system was tested for hydrogen purification, wherein inlet sample with 80% impurity (18% Ar, 20% CO2, 20% N2, 20% CH4 and 2% CO) and 20% H2 was used for purification study. According to Thermal Conductivity Detector (TCD) results, the system delivered 91.54%, 99.996% and 99.9999% pure hydrogen respectively for stage 1, stage 2 and stage 3 purification. The system works within low temperature range of 20–90 °C.