Matching of kinetics of CaCO3 decomposition and CuO reduction with CH4 in Ca-Cu chemical looping

Ca-Cu chemical looping (CaL-CLC) based on calcium looping is a novel and promising process for CO2 capture. The concept utilizes the heat released from the exothermic reduction of CuO to support the endothermic regeneration of CaO-based sorbents. Therefore, it is important for the two major reactions to have matching kinetics. This work assesses kinetics of the two reactions in a calciner under the conditions of interest for CaL-CLC. The reaction rates of the decomposition of CaCO3 and reduction of CuO-based material with CH4 were measured in a TGA by varying the temperature and gas atmosphere, and two gas-solid reaction models were utilized for the determination of the kinetic parameters. On the basis of these results, a dynamic model was developed to investigate the simultaneous reduction of CuO and decomposition of CaCO3 in an adiabatic fixed-bed reactor operating at 1 atm. The simulation results showed that the reduction of CuO completed extremely fast under all test conditions, and it could lead to hot spots in the calciner. It was found that addition of steam into the reducing gas could enhance the reaction rate of CaCO3 decomposition and help it match the fast rate of CuO reduction, then reduce the formation of hot spots. Also, steam could be used to control the movement of reaction front. Although CO2 could be used to control the reaction front as well, the higher CO2 partial pressure in CH4 was found to slow down the decomposition of CaCO3 leading to incomplete reaction.