A metal hydride compressor for a small scale H2 refuelling station

Abstract

The use of hydrogen as energy vector implies the development of the necessary infrastructures for hydrogen handling. A two-stage metal hydride compressor was developed and integrated in a small-scale hydrogen refuelling station at prototype level. In this work, the compression on site of green hydrogen using metal hydrides is exhaustively presented taking into account all the necessary aspects to bridge the gap between the laboratory and the real application. In particular, all aspects for the setting up of a metal hydride compressor, i.e. selection and characterization of selected metal hydrides, sizing of the plant components, design and the tests aimed to optimize the working performances are presented and deeply discussed, including energy consumption and efficiency necessary to build up a commercial system. The compressor employs two commercial alloys, i.e. a La0.9Ce0.1Ni5 from Labtech in the first stage and the Hydralloy-C5 from GfE in the second one. Working between room temperature for absorption and 150 °C for desorption, the hydrogen produced by the electrolyser at 28 bar is compressed up to 250 bar, resulting in a compression ratio of about 9. The metal hydride compressor has a final power consumption of 614 W, of which 85 W are linked to the hydrogen sorption reactions, while other contributions come from the pumps involved in the plant and the dissipations. The compressor presents an isentropic efficiency of about 11% for less than 1 kg of powder in each stage and an average H2 flowrate of 104 Nl/min is observed. The performances of the plant were optimized and maintained for a working time of about 245 h.