MgH2 intermediate scale tank tests under various experimental conditions

Magnesium hydrogenation being an exothermic reaction, the loading time of a tank is limited by heat extraction. The compaction of ball-milled MgH₂ associated with Expanded Natural Graphite was used to improve the thermal conductivity of the resulting compacts. Taking advantage of these compacts, an intermediate scale tank (1.8 kg MgH₂) cooled down by forced air circulation was designed. The absorption is initiated at 90 °C. Since the intrinsic kinetic is not the limiting factor, the hydrogen pressure does not affect the loading process. The loading time is strongly dependent on the cooling efficiency. However, beyond a given air flow rate it doesn’t decrease any more, the heat transfer being limited by the thermal conductivity of the compacted disks. During desorption, the maximum hydrogen flow (25 Nl/mn) is directly proportional to the thermal power of the heating system. The tank absorbs 1170 Nl, has a specific-energy of 270 W h/kg and a system volumetric-density of 42 gr/l.