Chemical-looping combustion (CLC) is a promising combustion technique with efficient CO2-capture at low cost due to inherent gas separation. In a CLC process, a metal oxide is circulated between two reactors, wherein they undergo changes from an oxidized form in the air reactor to a reduced one in the fuel reactor. In the case of chemical-looping with oxygen uncoupling (CLOU), the oxygen carrier releases oxygen in the gas phase in the fuel reactor as shown in the figure. This enables a high rate of conversion of char from solid fuels, as it eliminates the need for the gasification step needed in normal CLC with solid fuels.
Only certain pure metal oxides of Co, Cu and Mn have an equilibrium partial pressure of oxygen suitable for CLOU. Due to its favorable thermodynamics (facile redox properties) and agile kinetics (high reactivity), CuO is a promising CLOU material, in addition to being an excellent oxygen carrier in the combustion of gaseous fuels.
In this work, the performance of CuO-based oxygen carriers supported on ZrO2 stabilized by calcium oxide, magnesia and ceria will be presented to assess their suitability as oxygen carriers for solid fuel combustion. The samples were prepared by freeze-granulation and the reactivity was examined in a laboratory fluidized bed reactor under cyclic oxidizing and reducing conditions, simulating the CLOU process. Owing to the fast release of oxygen by CLOU particles, the reaction rates were investigated using coke as the fuel of choice. The influence of reaction temperature and oxygen concentration on the rate of reaction was also studied.