Coal direct chemical-looping combustion (CLC) and coal gasification CLC processes are the two basic approaches for the application of the CLC technology with coal. Two different combined cycles with the overall thermal input of 1,000MW (LHV) were proposed and simulated, respectively, with NiO/NiAl2O4 as an oxygen carrier using the ASPEN software. The oxygen carrier circulation ratio in two CLC processes was calculated, and the influence of the CLC process parameters on the system performance such as air reactor temperature and the turbine inlet supplementary firing temperature was investigated. Results found were that the circulation ratio of the oxygen carrier in the coal gasification CLC process is smaller than that in the coal direct CLC process. In the coal direct CLC combined system, the system efficiency is 49.59% with the CO2 capture efficiency of almost 100%, assuming the air reactor temperature at 1,200 °C and the fuel reactor temperature at 900 °C. As a comparison, the system efficiency of coal gasification CLC combined system is 40.53% with the CO2 capture efficiency of 85.2% when the turbine inlet temperature is at 1,350 °C. Increasing the supplementary firing rate or decreasing the air reactor temperature can increase the system efficiency, but these will reduce the CO2 capture efficiency.
