Analysis of Reactivity of a CuO-Based Oxygen Carrier for Chemical Looping Combustion of Coal

Chemical looping combustion (CLC) of coal was conducted with 12 CuO-based oxygen carriers supported on SiO2, Al2O3, TiO2, and ZrO2 prepared by mechanical mixing. The influence of an inert support and the effect of particle size on the reactivity of CuO-based oxygen carrier particles were studied. Five mixed oxide oxygen carriers composed of different amounts of CuO and Fe2O3 on TiO2 were prepared to study the synergistic effect between two active metallic oxides. It was found that CuO-based oxygen carriers showed high reactivity in redox reactions. The onset temperature of the reduction reaction decreased when TiO2 was added as an inert support. The particles of CuXTi950 showed the highest reactivity to convert the coal. Although the smaller particle size of the oxygen carrier can enhance the coal conversion, it also makes it more difficult in the separation of the oxygen carrier from fly ash and unburned carbon. For mixed oxygen carriers, the synergistic effect between different active oxides was observed. From a reactivity and an energy-balance perspective, particles of CuO-Fe2O3/TiO2 mixed oxide oxygen carriers are suitable for use in CLC of coal. The X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used for the characterization of the fresh and used oxygen carriers. Results support that direct CLC of coal is promising when CuO-based oxygen carriers are used at low temperatures.