Hydrogen recovery from big-scale porous metal hydride (MH) reactor: impact of pressure and MH-thermophysical properties

Abstract

An advanced ANSYS FLUENT-based model was developed for hydrogen recovery from a multi-tubular fixed-bed metal hydride (MH) reactor of large-scale design. The model was firstly validated by comparing its results to specific experimental data. Mass and heat transfer processes inside the fixed bed were investigated for various pressures and thermochemical characteristics of the MH (thermal conductivity, porosity and reaction parameters). The findings were reported as average, local and spatial changes in the metal’s bed temperature and hydrogen content. During the initial stage of the endothermic desorption (t<100 s), the bed temperature dropped dramatically in all cases . During this time, there was a massive emission of hydrogen. The bed temperature was then raised due to the reactor’s external convective heating, while the hydrogen release continued until the MH was completely dehydrided. The dehydrogenation rate of the MH was enhanced when the discharge pressure was raised. Furthermore, some other characteristics of the MH, i.e., porosity, thermal conductivity, desorption rate constant and activation energy, significantly impacted the resulting mass and heat fluxes inside the bed material.