Metal hydride storage for hydrogen vehicle

A range of these alloys have been evaluated and the most promising have been tested with respect to hydrogen storage capacity, heat of sorption, plateau pressure and activation process. The results from these measurements together with the results later in the project resulted in the selection of the alloy E77 (MmNi5-xSnx) from GfE. The similar alloy E60 finally selected did have a slightly higher plateau pressure and a capacity of 25 deg. C of 1.32 weight-%. Two test tanks were constructed capable of containing kg of E60. The test tanks were used for investigating important scale-up parameters such as heat conduction and materiel expansion during hydrogen sorption. Results from the first test tank gave a storge capacity of E60 of 1,40 weight-% but also that the material expansion must be dealt with in the design of the storage. The metal hydride in the second test tank was placed in small aluminium boxes around a water-cooled tube. The tests showed this heat exchanger construction to work satisfactory. The filling and emptying of the storage could be done in 20 and 30 minutes respectively. Especially the flow rates are important in a car application and 92-% capacity obtained within 30 minutes is satisfactory. It was not possible to make any firm conclusion with respect to effect of the material expansion/contraction after only 10+15 cycles, but there was no visible damage to the boxes. The influence of impurities in the hydrogen did not seems to be critical, however some extension of fuelling times were observed when technical hydrogen (99,9% pure) was used. The hydrogen capacity was not influenced. A 15 Nm3 hydrogen storage was designed based on the initial storage specification, the tested metal hydride material and the well functioning test tank. The storage is divided into 3 modules. The safety of the construction was examined by DGC and their recommendations have been followed. A module was constructed. The storage module was activated and tested with respect to capacity and flow rates. The storage capacity was 390 g H2 (4.8 Nm3) and in accordance with the earlier results. The hydrogen storage density is 60% higher than in similar compression storage with hydrogen at 200 bar. The discharge time was 3,5 hour in contrast to the expected 1 hour. This must be caused by heat transmission contact problems at one or several spots in the storage. A specification for the hydrogen storage module was made: Working pressure, max: 50 bars. Working pressure, min: 1 bar. Flow rates: 10-50 l/min. Discharge time: 3.5 hours. Storage capacity: 390 g Hydrogen. Weight of metal hydride: 29 kg. Weight of module: 69 kg. Volume of storage: 17,5 l. It was decided based on the obtained results not to construct the complete storage since the hydrogen could be discharge with high enough flow rates but also because the total weight of a 20 Nm3 storage would be 300 kg. The storage can be made when the heat transmission problems have been solved and when the weight of the storage has been reduced. The hydrogen storage should also be made as one unit and not divided into modules from a safety point of view