Novel concepts for metal hydride storage tanks – Numerical modeling, simulation and evaluation

Kurzfassung

The efficient, space-saving and safe storage of hydrogen is a major challenge that needs to be overcome for enabling renewable energy systems. Metal hydrides are a possible solution. But the key challenge is the identification and development of the most promising metal hydride material as well as the ideal tank design for an efficient hydrogen absorption / desorption in terms of energy demand / storage losses and loading / unloading time. Against this background this paper aims to identify suitable combinations of medium and low-temperature metal hydride materials in combination with three different tank design concepts. The goal is to determine which material fits best for each combination and could thus be a suitable solution for a future implementation in stationary and mobile applications of metal hydride storage tanks. To achieve this goal a finite element method (FEM) modeling and simulation of materials and construction designs in COMSOL Multiphysics is realized. The results are analyzed in terms of hydrogen absorption rate, temperature profile over time, and the necessary energy demand for the overall storage process. The results show that for the low-temperature metal hydride investigated here, the tank design is of subordinate importance, allowing for more application-specific design. For medium-temperature metal hydrides, the investigated construction concepts show heterogeneous results. For fast hydrogen absorption and minimal external heating time, the suggested rectangular tank design might be a promising option, requiring only 28% / 29% of the heating energy of the cylindrical concepts. If the goal is to achieve the most complete hydrogen absorption, the base design concept investigated here, consisting of a cylindrical tank with metal hydride material rolled up in a spiral, is the most favorable solution; achieving a hydrogen loading of about 3.6 wt–% for the medium-temperature metal hydride. The low-temperature metal hydride achieves a total hydrogen absorption of around 1.4 wt-% in the optimum concept. For concepts with higher operating temperatures, preheating the storage tank before feeding in the hydrogen could improve the absorption process (only examined here).