Use of Coal as Fuel for Chemical-Looping Combustion with Ni-Based Oxygen Carrier

Chemical-looping combustion is an indirect combustion technology with inherent separation of the greenhouse gas CO 2 . The feasibility of using NiO as an oxygen carrier during chemical-looping combustion of coal has been investigated experimentally at 800−960 °C in the present work. The experiments were carried out in a fluidized bed, where the steam acted as the gasification−fluidization medium. Coal gasification and the reaction of oxygen carrier with the water gas take place simultaneously in the reactor. The oxygen carrier particles exhibit high reactivity above 900 °C, and the dry basis concentration of CO 2 in the exit gas of the reactor is nearly 95%. The flue gas composition as a function of the reactor temperature and cyclic reduction number is discussed. At 800−960 °C, the dry basis concentration of CO 2 in the flue gas presents a monotonously increasing trend, whereas the dry basis concentration of CO, H 2, and CH 4 decreases monotonously. The concentrations of CO 2, CO, H 2, and CH 4 in the flue gas as a function of cyclic reduction number present a para-curve characteristic at 900 °C. With the increase of cyclic reduction number, the dry basis concentration of CO 2 decreases remarkably, while the dry basis concentrations of CO, H 2, and CH 4 increase rapidly. Moreover, the peak value of H 2 concentration is less than that of CO. The performance of the NiO-based oxygen carriers was also evaluated using an X-ray diffractometer and a scanning electron microscope to characterize the solid residues of oxygen carrier. The results indicate that NiO is one of the suitable oxygen carriers for chemical-looping combustion of coal.