(86d) Kinetics and CFD Model Validation for Combustion of Coal Char Using Cu-Based Chemical Looping with Oxygen Uncoupling (CLOU) Carriers

Authors: 
Burgess, W. A., National Energy Technology Laboratory
Means, N. C., National Energy Technology Laboratory
Howard, B. H., National Energy Technology Laboratory
Smith, M. W., National Energy Technology Laboratory
Shekhawat, D., National Energy Technology Laboratory
The chemical-looping combustion with oxygen uncoupling (CLOU) process uses gaseous or solid hydrocarbon fuels and is a promising carbon capture and storage (CCS) technology. In CLOU, the uncoupling of gaseous O2 from the oxygen carrier CuO is thermodynamically favored at temperatures above ~ 1000° C and pressures less than ~ 0.1 bar O2. The CLOU carrier chosen for this study was the CuO/Cu2O oxygen carrier system, while the choice of fuel was coal char obtained from the pyrolysis of Powder River Basin (PRB) coal. The overall reduction rates of the CuO oxygen carriers were investigated using a drop-tube fluidized bed reactor in the temperature range of 850°C – 1100°C. The intrinsic activation energy and Arrhenius prefactor for the CLOU reaction were determined from these experiments, along with the apparent activation energy and Arrhenius prefactor for the overall CuO reduction. In addition, a computational fluid dynamics (CFD) model was developed and validated for prediction of the overall CuO reduction kinetics based on the amount of PRB coal char charged to the reactor and the known kinetics of the individual CLOU, combustion, gasification, and CuO reduction reactions occurring within the system. The PRB coal char added to the reactor consumes the O2 uncoupled from the CuO, driving the thermodynamic equilibrium of the CLOU reaction in the direction of Cu2O product formation such that this reaction is now favored at temperatures as low as 900° C.