Exergy analysis of self-ignition combustion synthesis for producing rare-earth-based hydrogen storage alloy

A new production system for rare-earth-based hydrogen storage alloys is proposed. We applied self-ignition combustion synthesis (SICS) utilizing hydrogenation heat of metallic calcium. The required primary energy and total exergy loss (EXL) for the production of 1 kg of LaNi5 alloy with the proposed and conventional systems were evaluated. The results revealed that the production of raw materials accounted for more than 90% of the total EXL in both systems. Specifically, the use of calcium had decisive effects on the total EXL of the system for producing LaNi5 alloy. The proposed system reduced the total EXL by 14.6 MJ/kg-LaNi5 as compared with the conventional system. The SICS was remarkably exergy-saving because the heating temperature was decreased by utilizing the hydrogenation heat of calcium and the product absorbed hydrogen without an activation treatment.