Combined heat and power production based on renewable aluminium-water reaction

Abstract

Reduction and oxidation of aluminium offers an affordable solution for long term energy storage. Aluminium can be produced by reduction of alumina in smelter plants based on an electrowinning process that uses renewable electricity. It can be stored loss-free for as long as desired, and used as a “renewable energy carrier” from which heat and power can be produced by oxidation. A combined heat and power production unit based on aluminium as a “renewable fuel” is presented in this paper. It includes an aluminium-water reaction that produces hydrogen, aluminium hydroxide and heat, as well as a fuel cell that produces electricity from the hydrogen. It was designed for a throughput of 50 g Al per hour and a hydrogen production rate of 5.5 g/h, corresponding to an energy turnover of 400 W. Experiments were carried out over several hours and the production of heat and hydrogen was recorded and quantified. The results demonstrate the general feasibility as well as a high conversion efficiency of more than 90%. Analysis and further treatment of the resulting solid reaction products confirmed that the obtained aluminium-hydroxide may be converted into alumina and thus eventually re-introduced into a process for the production of aluminium again.