Hydrogen storage systems based on hydride-graphite composites: Computer simulation and experimental validation

The design of hydride-based hydrogen storage systems is non-trivial because numerous physical, chemical and engineering principles have to be considered. In particular, gas and heat transport properties of the hydride bed are crucial for a high-dynamic tank operation. Since most hydrides show low intrinsic heat conductivities, auxiliary materials or structures inside the reaction zone are beneficial. For that purpose, hydride-graphite composites with strong anisotropic thermal conductivities have been developed recently. Here, a comprehensive numerical model to simulate the dynamics of hydrogen storage tanks based on pelletized hydride-graphite composites is presented. Among other common characteristics it includes anisotropic thermal conduction properties, convective heat transport as well as local shrinkage and swelling effects in the hydride bed. For experimental validation, a room temperature AB 2-type hydrogen storage alloy was used in form of alloy-graphite pellet s whose specific materials parameters were experimentally obtained and implemented into the computer simulation. In view of the thermodynamic properties of the AB2-type alloy, a novel mathematical formalism was developed to describe realistic pressure-composition isotherms. The comparison of experimental and simulation results reveals a good agreement. Thus, the validated model allows predictive studies on tank design and operation scenarios.