Investigation on a three-stage hydrogen thermal compressor based on metal hydrides

In this paper we report our recent investigation about a there-stage hydrogen thermal compressor based on metal hydrides (HTC) in order to reach an overall compression ratio 28:1. The research was focused to: (i) elaborate hydride alloys with good storage capacity and higher thermodynamic characteristics acquired by tailoring of their properties; (ii) develop new technical solutions based on advanced materials, and fast mass and heat transfer for a hydrogen storage-compression reactor; (iii) built up a prototype of the HTC. Cyclic performance of the hydrogen compressor is studied following up the operating parameters: supply pressure, storage volumes, cold and hot fluid temperatures, cycle duration. The experiments show that the HTC can attain a high overall compression ratio 28:1, it will raise the hydrogen pressure from 2 bars to 56 bars, using three hydride compression stages working between 20 and 80°C. Cycling the compressor at a short absorption-desorption cycle, about 2 minutes, a satisfactory hydrogen flow rate was obtain 10 l/cycle, which ensures a hydrogen flow rate about 300l/hour using a small quantity of hydride alloy, about 360 g. To improve the efficiency and economics of compression process, HTC prototype based on metal hydrides must operate in conjunction with advanced hydrogen production technologies from renewable resources.