Synergistic reaction investigation of the NiO modified CaSO4 oxygen carrier with lignite for simultaneous CO2 capture and SO2 removal

Natural gypsum ore, being dominated with CaSO4, is quite applicable to be used as an alternative oxygen carrier (OC) in the chemical looping combustion (CLC). However, such overwhelming problems of CaSO4 as its inferior reactivity and potential sulfur release ought to be properly solved. In this research, the NiO modified CaSO4 OC of desired core-shell structure was first prepared using the combined template method. The synergistic effect between the CaSO4 substrate and the doped NiO in the mixed OC during its reaction with a typical lignite was ascertained by comprehensive experimental means combined with thermodynamic simulation. The improved reactivity as obtained for the NiO modified CaSO4 ore was found to mainly ascribe to activation of the reduced Ni on the intractable carbon groups present in the residual char as well as in situ oxidization of the reduced Ni to active NiO again via transfer of the oxygen involved in the unconverted CaSO4. Meanwhile, the gaseous sulfur released from the accompanied side reactions of CaSO4 was directionally fixed. In addition, both strong resistance to sintering and good regeneration of the prepared NiO modified CaSO4 OC were promising to apply in the real CLC system for simultaneous CO2 control and SO2 removal.

Automated summary

In this study, a NiO modified CaSO4 oxygen carrier with a desired core-shell structure was successfully prepared, enhancing its reactivity. Experimental evidence confirmed that the modified gypsum ore activated the reduced nickel in the residual char and oxidized it back to active NiO, while fixing the released sulfur gas from side reactions. The prepared NiO modified CaSO4 oxygen carrier showed promising resistance to sintering and good regeneration for potential application in real chemical looping combustion systems.