Monolithic Ceramic Redox Materials for Thermochemical Heat Storage Applications in CSP Plants

The present work relates to the investigation of cobalt and manganese oxide based compositions as candidate materials for the storage of surplus energy, available in the form of heat, generated from high temperature concentrated solar power plants (e.g. solar tower, solar dish) via a two-step thermochemical cyclic redox process under air flow. Emphasis is given on the utilization of small structured monolithic bodies (flow-through pellets) made entirely from the two aforementioned oxides. As compared to the respective powders, and in addition to the natural advantage of substantially lower pressure drop that monolithic structures can offer, this study demonstrated that structured bodies can also improve redox kinetics to a measurable extent. Cobalt oxide was found to be superior to manganese oxide both from an estimated energy density and from a redox reactions kinetics point-of-view. Among the redox conditions studied, the optimum reduction-oxidation operating window for the former oxide was determined to be in the range of 1000-800 °C, while for the latter material no clear conclusion was drawn with reduction reaching its maximum extent at 1000 °C and oxidation occurring in the range of 500-650 °C. In both cases, no significant degradation of redox performance was observed upon cyclic operation (up to 10 cycles), however manganese oxide showed notably slower oxidation kinetics.