Effects of Stefan flow and CO oxidation on char particle combustion in O2/CO2 atmosphere

Abstract

Stefan flow occurring at the surface of char and CO oxidation in the boundary layer are often neglected in the conventional pulverized-coal air combustion. In this work, effects of Stefan flow and CO oxidation in the oxy-fuel burning are investigated numerically and experimentally. A mathematical model is firstly developed for the combustion of a carbon particle. Comparisons with the experiment data exhibit better agreement for the present model than that neglecting the effects of Stefan flow and CO oxidation. Predictions also show that neglect of the Stefan flow and CO oxidation results in overestimating the particle temperature, shortening the burnout time, and especially, being unable to predict the particle extinguishment and the final burnout rate correctly. Notable effects of Stefan flow and CO oxidation on the burnout time generally appear under conditions of lower O2 concentration, lower reactivity, lower gas temperature and larger particle size where the combustion is prone to be controlled by reaction kinetics and gas diffusion simultaneously (Regime II). On the contrary, the effects of Stefan flow and CO oxidation are relatively insignificant on the burnout time in the diffusion-controlled combustion (Regime III). However, whether the Stefan flow and CO oxidation could be neglected in such cases still depends on the actual combustion conditions and simulation results.