Hydrogen storage for fuel cell systems with stationary applications— I. Transient measurement technique for packed bed evaluation

Data are presented on a metal hydride storage unit used as a hydrogen source for a 500 W fuel cell power supply system powering the electrical components of a gas furnace. The investigated packed bed had special design features for the internal heat transfer optimization: the hydride material was packed into Al foam, and an inner coaxial U-shaped tube enabled removal of heat by a heat transfer agent. This design enables recuperating heat from the gas furnace, by circulating the hot exhaust through the U-shaped tube, to compensate for the heat absorbed during hydrogen desorption. A transient measurement technique is used to evaluate the heat transfer properties of the storage unit. The method is based on a combination of transient temperature measurements, which provides data on heat exchange properties of the storage unit, as well as an estimate of the hydriding enthalpy ΔH for hydrogen desorption. In the absence of heating, the discharge is controlled by the rate of heat transfer between the container walls and the ambient atmosphere. The method provides a simple procedure for evaluating the value of the maximum flow of hydrogen which can be released, so that the entire amount of hydrogen stored in the packed bed can be discharged. When a heating agent is circulated through the U-shaped tube in the storage unit, the maximum discharge rate can be increased by an order of magnitude and the heat exchange with the ambient atmosphere becomes un-important.