Exploitation of thermochemical cycles based on solid oxide redox systems for thermochemical storage of solar heat. Part 2: Redox oxide-coated porous ceramic structures as integrated thermochemical reactors/heat exchangers

Abstract

The enthalpy effects of reversible chemical reactions can be exploited for the so-called thermochemical storage of solar energy. Based on the characteristics of the oxide redox pair Co3O4/CoO as a thermochemical heat storage medium and the advantages of porous ceramic structures like honeycombs and foams in heat exchange applications, the idea of employing such structures coated with a redox material like Co3O4 as a hybrid sensible-thermochemical solar energy storage system in air-operated concentrated solar power plants has been set forth and tested. Small-scale, redox-inert, oxide and Silicon Carbide foams and honeycombs were coated with Co3O4 and tested for cyclic reduction–oxidation operation in Thermo-Gravimetric Analysis studies within the temperature range 800–1000 �C. Such supports demonstrated repeatable, quantitative, cyclic reduction–oxidation behavior, employing for the redox reactions the entire amount of the oxide material coated, even at very high loading percentages reaching 200 wt% for all oxide supports and one variety of Silicon Carbide support tested. The longevity of such systems was tested successfully up to 100 consecutive cycles, at the end of which the coated supports maintained their structural integrity, together with the same, quantitative reduction–oxidation performance of the Co3O4 loaded.