Experimental assessment of copper oxide for liquid chemical looping for thermal energy storage

Abstract

The potential of copper oxide for both thermal energy storage and oxygen production in a liquid chemical looping thermal energy storage system has been assessed with thermogravimetric analysis. Liquid chemical looping thermal energy storage is a recently proposed system with potential to enable both the storage of thermal energy (through sensible heating, phase change and thermochemical reactions) and oxygen production. The process of isothermal reduction and oxidation of molten copper oxide was verified experimentally by heating the material isobarically, reducing or oxidising it isothermally, and then cooling it again isobarically. The isothermal reduction and oxidation reactions were achieved by varying the partial pressure of oxygen through the change in the concentrations of nitrogen and oxygen. This confirmed that copper oxide can be reduced in the liquid state by changing the partial pressure of oxygen in the system. Nevertheless, the extent of reduction in the assessed range of oxygen partial pressure in the liquid phase is approximately 2%, while this value in solid phase is approximately 10%, which implies that the thermochemical storage is mainly occurred in the solid phase. The reduction and oxidation cycles were repeated for 10 cycles. Superimposed on the cyclical weight change was an additional weight loss that was attribute to a side reaction between the copper oxide and alumina crucible.