Research and development for a metal hydride tank with double coil type heat exchanger below 1.0 MPa (G) operation

•A metal hydride tank with 50 kg of MmNi5 alloy is investigated with pressures below 1.0 MPa.•The normal capacity achieves 94% of the maximum value with constant hydrogen flow rate.•The reaction heat recovery rate is above 72% with constant hydrogen flow rate.•The normal capacity achieves the maximum with intermittent hydrogen flow rate.•A vacuum thermal insulator is developed and applied to the metal hydride tank.

A metal hydride tank has been developed with the aim of recovering the reaction heat of a metal hydride for the Totalized Hydrogen Energy Utilization System application. The metal hydride tank, which had the same geometrical configuration as one previously evaluated at SRNL, was fabricate with a different composition of the metal hydride alloy for operation below 1.0 MPa (Gauge). The hydrogen mass flow data from hydrogen production by renewable energy (solar power) and the fuel cell operation, which were obtained at SRNL, were used for the testing at AIST. The relatively large heat leak from the tank support of the metal hydride tank at SRNL was confirmed, and thus the tank support was replaced in this work. Furthermore, a vacuum thermal insulator was developed and applied to the metal hydride tank. This resulted in overall tank size reduction without reducing the thermal insulation performance.