Enhancement of heat- and mass-transfer processes in a metal-hydride flow-through hydrogen-purification reactor

Abstract

A novel method is proposed to increase the effective thermal conductivity of a metal-hydride (MH) bed by incorporating highly conductive inclusions into it in the form of metal rods made from various materials. The volume fraction of the inclusions, which had a diameter of 0.5 mm and length of 5 mm, ranged from 0.01 to 0.1. The structure of the composite beds was modelled by a specially developed algorithm. The results of the numerical simulation revealed that the effective thermal conductivity of the composite beds increased by 1.44–2.93 times when the volume fraction of the inclusions was 0.1. To estimate the effectiveness of the proposed method, a case study of hydrogen purification from a hydrogen–nitrogen mixture was performed for the cylindrical flow-through MH reactor, with two MH bed types: without inclusions (base case) and with inclusions (volume fraction of 0.1). The alloy fraction saturated by hydrogen and the mass of absorbed hydrogen higher for an equivalent reactor size notwithstanding a 10% reduction in the alloy mass. Moreover, the hydrogen losses were comparable to those of the base case. At hydrogen breakthrough, the fraction of hydride saturated by hydrogen increased from 61.5% to 81%, and the amount of hydrogen absorbed increased by 18.7%. The described method for enhancing the heat- and mass-transfer in MH beds enables the purification of a significantly larger volume of hydrogen with an equivalent number of sorption/desorption cycles.