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 sourc e for a 500 W fuel cell power supply system powering the electrical compone nts of a gas furnace. The investigated packed bed had special design featur es for the internal heat transfer optimization: the hydride material was pa cked into Al foam, and an inner coaxial U-shaped tube enabled removal of he at 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 me asurement technique is used to evaluate the heat transfer properties of the storage unit. The method is based on a combination of transient temperatur e measurements, which provides data on heat exchange properties of the stor age unit, as well as an estimate of the hydriding enthalpy Delta H for hydr ogen desorption. In the absence of heating, the discharge is controlled by the rate of heat transfer between the container walls and the ambient atmos phere. The method provides a simple procedure for evaluating the value of t he maximum flow of hydrogen which can be released, so that the entire amoun t of hydrogen stored in the packed bed can be discharged. When a heating ag ent is circulated through the U-shaped tube in the storage unit, the maximu m discharge rate can be increased by an order of magnitude and the heat exc hange with the ambient atmosphere becomes un-important. (C) 2000 Internatio nal Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.