A Study on Transient Behavior of Off-gas Impurity Concentration from Metal Hydride

Biomass-derived hydrogen (Bio-H-2), which is one of the renewable energy sources is attractive due to a low environmental burden. Regarding the potential applications of Bio-H-2, which can be a fuel of polymer electrolyte membrane fuel cells (PEMFCs) is a promising candidate, although removal of contaminants is absolutely necessary. In addition, the storage tank has an important role. Compared to the conventional batteries (e.g. Li-ion batteries), the battery of PEMFCs with a hydrogen storage container has to have the performance benefit of its operating time to some extent. Therefore, we proposed the use of the metal hydride to purify and store of Bio-H-2 in the previous research. According to the characteristic which is hydrogen can be selectively adsorbed into the metal hydride, it was found that methane in Bio-H-2 was removed by the metal hydride and that the absorbed hydrogen ratio of 96.9% is achieved. In order to increase the absorbed hydrogen ratio, the operating controls of absorption of Bio-H-2 including the concentration arrangement of off-gas components would be necessary. Because off-gas is used for the supplemental heat energy for the reactor, an optimal control is significant. Thus, the operating conditions of the metal hydride (e.g. a pressure, a hydrogen concentration, a temperature and the off-gas flow rate) should be analyzed. We investigated that the off-gas components during the adsorption process were analyzed considering the various temperatures and the off-gas flow rate of the feed gas. According to our experimental results, the amount of off-gas was increased, the methane concentration of off-gas was decreased in the absorption process. The existence of methane in initial volume from the storage tank was detected. However, the concentration rapidly decreased and became close to 0%.