Chemical Looping Combustion Characteristics of Coal with a Novel CaSO4-Ca2CuO3 Mixed Oxygen Carrier

Resource utilization of the disposed CaSO4 waste as an oxygen carrier (OC) in chemical looping combustion (CLC) is of great meaning as a result of its attractive strengths, such as easy availability, low cost, large oxygen capacity, and avoidance of potential environmental harm. In this research, a novel mixed OC of CaSO4 doped with Ca2CuO3 was first reported and produced using a combined template preparation method. Its reaction behavior with a typical lignite designated as YN was studied, which indicated that doped Ca2CuO3 well enhanced the reactivity of CaSO4 with YN coal. The CO2 yield as formed was greatly accelerated, while SO2 evolved from the CaSO4 side reactions could be effectively controlled, as expected. Furthermore, the potential oxygen transfer mechanism during the CaSO4Ca2CuO3 mixed OC reaction with YN coal was revealed, wherein elemental Cu derived from reduced Ca2CuO3 could regain lattice oxygen inherent in unreacted CaSO4 via its melting interface. In situ reoxidized CuO would decompose and emit O-2 for direct combustion of residual char of YN. Then, migration and redistribution of the sulfur species were completely investigated. Added Ca2CuO3 was found to be reduced to CaO and elemental Cu during its reaction with YN, both of which were able to directionally fix gaseous sulfur evolved from CaSO4 to form CaS and Cu2S, respectively. Thus, the gaseous sulfur retention capacity of this mixed OC was much improved. In addition, the prepared CaSO4Ca2CuO3 mixed OC demonstrated good regeneration capacity and strong sintering resistance as well. Overall, the novel CaSO4Ca2CuO3 mixed OC as reported possessed good reactivity and directional fixation of gaseous sulfur, which benefited from simultaneous carbon capture and in situ desulfurization in CLC, and as such is quite attractive for future application.