Abstract
Today, hydrogen powered trains like the Alstom Coradia iLint store the hydrogen in 350 bar composite vessels, distributed on the roof of the driving units. While these stores provide an acceptable weight and volume for this application, it is by far too high to supply e.g. shunting locomotives and others with much more severe restrictions on weight and volume of the hydrogen store. Another drawback are the high hydrogen loading pressures, requiring rather high capital expenditures for the composite vessels themselves as well as for necessary hydrogen compressors, as well as high operational expenditure, e.g. for energy supply and maintenance of the compressors.
An alternative solution can be hydrogen storage in metal hydrides at loading pressures < 50 bar, allowing for direct loading from high pressure electrolysers. There exist metal hydrides which provide storage densities of 100 kg H2/m3 and more in the materials, to be compared with only up to 25 kg H2/m3 in 350 bar stores. Furthermore, these metal hydrides show temperatures of operation below 100°C, which can be efficiently thermally integrated with low temperature PEM fuel cells. However, they are usually very heavy (storage capacities below 20 kg H2/ton of material against >40 kg H2/ton in high pressure stores) and thus are regarded not to be suitable for locomotive applications.
Materials that show storage capacities higher than 70 kg H2/ton and thus more than high pressure stores do exist, but at present require temperatures of operation above 300°C. A solution to the problem of supplying sufficient heat to the storage could be to store the heat from the hydrogen loading reaction of the metal hydride itself in a suitably designed heat storage, which vice versa than provides the necessary heat for the hydrogen release reaction for supplying the fuel cell.
This talk describes the basic principles of design and operation of such a so called adiabatic tank system. A small scale prototype will be realised in a project funded by the German Karl-Vossloh Stiftung and tested related to mobile applications, in particular railways.
