Numerical investigation of different effects of carbon dioxide properties and carbon monoxide oxidation on char particle combustion in actual and fictitious O2/CO2 environments

Abstract

The overall and individual effects of carbon dioxide properties and carbon monoxide oxidation on char combustion were numerically simulated with a continuous-film model in different O2/CO2, O2/N2 and O2/Ar environments, and different CO2 physicochemical properties were artificially changed to distinguish the individual effect on char particle temperature and combustion rate. The results show that the char combustion rate in 21%O2/79%CO2 environment is slightly higher than that in air environment because of two opposite effects of higher char gasification reaction rate with high concentration CO2 and lower char oxidation rate with O2 resulting from lower particle temperature. At the same time, the CO flame front in 21%O2/79%CO2 environment is farther away from char particle surface than that in 21%O2/79%N2 environment because of lower diffusion coefficient of oxygen in CO2 environment although the gas temperature is lower. Furthermore, the net effect of molar heat capacity of CO2 on char combustion rate decreases and the net effect of char gasification reaction with CO2 on char combustion rate distinctly increases with the increase of ambient gas temperature and O2 mole concentration.