Effect of Char Loading on Reduction Kinetics of Cu-Based Oxygen Carriers in a Drop-Tube Fluidized-Bed Reactor at Temperatures from 850 to 1100 °C: Experiment and CFD Modeling

Chemical-looping combustion with oxygen uncoupling (CLOU) is a process using gaseous or solid hydrocarbon fuels and is a promising carbon capture and storage (CCS) technology. In CLOU, combustion of the fuel is achieved through the release of gaseous O-2 from an oxygen carrier material such as CuO and is favored at high temperatures and low O-2 partial pressures. The primary objectives of this study were to (1) compare values for the apparent rate constant k(ov)(T) for the overall rate of reduction of a CuO carrier, either alone or in the presence of coal char obtained from the pyrolysis of Powder River Basin (PRB) coal, and (2) develop and validate a computational fluid dynamics (CFD) model for the CuO/PRB coal char system based on known kinetics of the individual CuO and Cu2O reduction, combustion, and gasification reactions. Two oxygen carriers consisting of 20 wt % CuO/Al2O3 and 9 wt % CuO/Al2O3 were prepared by physical mixing and by incipient wetness impregnation (IWI), respectively. Kinetic analyses were conducted in the temperature range of 850-1100 degrees C. The CFD model typically reproduced experimental values of k(ov)(T) to within +/- 10%. The increase in k(ov)(T) caused by addition of only 0.075 g of PRB char per gram of CuO was modest at 1100 degrees C, but was more than 3-fold at 850 degrees C. Combustion and gasification of the coal char not only produced CO, opening another pathway for CuO reduction in addition to the CLOU reaction, but also resulted in the over-reduction of Cu2O to the undesired metallic Cu. Production of Cu metal increased with respect to char loading.