Metal hydride reactor for dual use: Hydrogen storage and cold production

Abstract

In case a metal hydride system is used for gaseous hydrogen storage application, the overall efficiency of the storage system can be significantly improved when the corresponding cooling or heating effect is additionally integrated into the application. In this study, it is analyzed how the efficiency of the gaseous hydrogen storage as well as the temperature level of the cold production can be adjusted using a simple, modular, air-cooled metal hydride reactor. For the study, a Hydralloy C5-graphite composite has been selected as reference material, and as geometry a simple tubular shape has been considered. In the first part of the manuscript, an analytical approach is presented analyzing the three different regimes in which a metal hydride reactor can be operated: to store hydrogen (Regime I), produce cold (Regime III), or to couple both options as “dual use” (Regime II), depending on the mass flow rates of hydrogen and air. In the second part of the manuscript, results of a detailed numerical study are presented and evaluated with respect to the outlet air temperature and the hydrogen utilization factor of the hydride reactor. It is shown that in Regime I, a high utilization factor and in Regime III, low outlet air temperature levels can be reached. Furthermore, in the “dual use” regime, the reactor can produce a cooling effect at different temperature levels and still show a high hydrogen utilization factor. In the last part of the manuscript, the effects of a modular reactor system as well as the operation of the reactor in pressure control mode are discussed to extend the basic description of the problem.