Modeling of single-particle char combustion under O2/H2O conditions: Effects of temperature and steam concentration

Abstract

In this study, the single-particle char-O2/H2O combustion kinetic model was modified based on the one-dimensional unsteady mass and heat transfer equation coupled with the Maxwell–Stefan multicomponent diffusion coefficient. Numerical simulations of char-O2/H2O combustion at different reaction temperatures and H2O concentrations were performed. The simulation results show that the average temperature of a char particle decreases with increasing H2O concentration, and the particle temperature is higher in the inner layer than in the outer layer. Without H2O, O2 consumption in the boundary layer accounts for 50% of the total O2 consumption at different temperatures. Higher temperatures and H2O concentrations promote competition for O2 by homogeneous reactions in the boundary layer. Char-O2/H2O combustion is simultaneously controlled by O2 external diffusion and internal diffusion. Control by O2 internal diffusion is hardly affected by the H2O concentration. The contribution of the gasification reaction to carbon consumption increases with increasing temperature and H2O concentration. Increasing the H2O concentration three-fold from 5% increases the contribution of the gasification reaction to carbon consumption 1.96-fold at 1373 K, but only 1.25-fold at 1673 K.