Exploitation of thermochemical cycles based on solid oxide redox systems for thermochemical storage of solar heat. Part 5: Testing of porous ceramic honeycomb and foam cascades based on cobalt and manganese oxides for hybrid sensible/thermochemical heat storage

Abstract

Cascaded ThermoChemical Storage (CTCS) of solar energy is a concept targeted to increase the volumetric energy storage density and address the thermocline temperature distribution inside regenerative sensible-only storage systems. CTCS involves the use of cascades consisting of different thermochemical systems, distributed in a rational pattern inside the storage module tailored to their thermochemical characteristics and to the local heat transfer medium temperature. In the case of air-operated Solar Thermal Power Plants such cascades can consist of porous structures incorporating different redox pair oxide materials that can come in direct contact with the air stream used as heat transfer fluid and operate as compact, hybrid sensible-thermochemical storage modules in series. Having previously identified the Co3O4/CoO and Mn2O3/Mn3O4 redox pairs as the most promising single-oxide systems for solar energy thermochemical storage, lab-scale (£ 25 mm), Co3O4- and Mn2O3-coated, porous cordierite honeycombs and foams were prepared and tested with respect to their thermochemical characteristics in one- and two-oxides cascaded configurations employing redox oxide quantities in the range 15–150 g. For such Co3O4-loaded cascades thermochemical storage was clearly demonstrated as heat uptake/release at constant temperature under proper testing conditions. Besides, the additive effect of thermochemical on sensible storage within the same storage volume was visualized. The operating conditions of cascades including both Co3O4 and Mn2O3 were dictated by the redox behaviour of the Mn2O3/Mn3O4 pair. Under proper conditions, such two-oxides-cascades could undergo cyclic reduction-oxidation and operate in complementary temperature ranges during oxidation; however the thermal effects of only the CoO oxidation reaction could be materialized into temperature rise of the air stream exiting the cascade.