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This work aims to clarify the potential effects of the H2O gasification reaction on the characteristics of chars under oxy-fuel combustion conditions with wet recycle. Chars of a Chinese sub-bituminous coal were prepared in a fluidized-bed/fixed-bed reactor at 1350 K under CO2/N2, H2O/N2, and CO2/H2O atmospheres. Structures of the chars undergoing some extent of gasification were characterized with a micro-Raman spectrometer, Fourier transform infrared spectrometer, and the N2 adsorption technique. Char combustion reactivity was also obtained in a thermogravimetric analyzer to reveal the effects of structure changes on the char combustion reactivity in oxy-fuel combustion. The results indicate the H2O gasification reaction can really take place and accelerate the char consumption in CO2/H2O, but the effect extent is lower than that in H2O/N2. The H2O gasification reaction would affect the chemical structures of the char with increasing H2O concentration in CO2/H2O, and different phenomena are observed for the change of char characteristics at high H2O concentration and low H2O concentration. The N2 adsorption data indicate more pores > 10 nm and less pores < 3 nm would form during the H2O gasification reaction compared to the pores forming during the CO2 gasification reaction. The H2O gasification reaction can also influence the pore structures of the chars in CO2/H2O, and the pores transform to relatively large pores with increasing H2O concentration, corresponding to a decrease of the Brunauer–Emmett–Teller surface area (S BET) for the char. The changes of char structures induced by H2O gasification reaction have obvious influences on the char combustion reactivity in oxy-fuel combustion, and a higher concentration of H2O in the atmosphere would result in a char with lower reactivity.

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