Optimum output temperature setting and an improved bed structure of metal hydride hydrogen storage reactor for thermal energy storage

Abstract

As the well-known solid hydrogen storage materials, metal hydrides (MHs) have been developed systematically for decades. During recent years, due to the development of thermal energy storage (TES) market, they have also received much attention gradually as the excellent TES materials because of the high energy density, low cost, and good reversibility. In this study, the stabilized discharging performance of an MH reactor for TES was investigated by numerical simulation. A mathematical model combining multi-physics and proportional-integral controller was established. Based on finite-time thermodynamics, gravimetric exergy-output rate (GEOR) considering the control requirement, finite-material, and finite-time constraints was defined. For a given reactor, the output temperature setting could be optimized based on GEOR. Besides, the effects of the reactor parameters on the optimum output temperature setting were systematically studied. The heat transfer analysis indicated the occurrence of the axial non-uniform reaction in the bed due to the inherent increase in the temperature of heat transfer fluid, resulting in the decrease of both GEOR and material availability. Accordingly, a new tapered bed structure (L/Do = 600/50 mm) was proposed to effectively improve the discharging efficiency from 76 to 90% and GEOR from 65 to 120 W kg−1, which provides a helpful guidance for the advanced designing and construction of MH reactor for the practical TES applications.