Numerical study on heterogeneous reaction characteristics of a single coal char particle under air- and oxy-fuel combustion: Effects of particle motion

Research and development of low-carbon combustion technology are necessary to satisfy the requirements of carbon neutrality. Oxy-fuel combustion technology is deemed a promising low-carbon technology it requires further investigation due to N2 replacement by CO2. This study aims to investigate the effects of particle motion modes (i.e., translation and rotation) and their speeds on char reaction characteristics under air- and oxy-fuel combustion. The translational and rotational speeds are described by the particle Reynolds numbers Rep and particle swirl Reynolds numbers Rep,w, respectively. The results indicated that the flame peak temperatures were reduced by 5.1% and 20.4%, and the particle temperatures were decreased by 13.1% and 9.2% under air- and oxy-fuel combustion, respectively, with an increase in the Rep values. However, the peak temperatures of the flame and particle were minimally affected by different Rep,w values. Char consumption rates and the reduced effects on the rates due to N2 replacement by CO2 were enhanced when the Rep values increased. The rates remained nearly unchanged, and the reduced effects remained constant at ∼20% with an increase in the Rep,w values. The proportions of each heterogeneous reaction were nearly unaffected by the increase in the Rep and Rep,w values, the proportion of gasification reaction increased with N2 replacement by CO2, and the surface Damköhler numbers (Das) of oxidation and gasification reactions were predicted. The Das,oxi and Das,gas values decreased significantly with an increase in the Rep and Rep,w values from 0 to 150. The Das values affected by rotational motion speeds (Rep,w) were more significant than those affected by translational motion speeds (Rep).