A study of the effect of H2O on char oxidation during O2/H2O combustion using reactive dynamic simulation

Abstract

In present work, the effect of H2O on the oxidation of char during O2/H2O combustion is investigated by reactive molecular dynamics simulation (ReaxFF MD). The simulation results show that H2O promotes the overall carbon conversion of char, which is consistent with the experimental results. By analyzing the distribution of H2 yield, the contributions of the char-H2O gasification reaction to the overall carbon conversion at different temperatures are quantitatively determined. The activation energy of char-H2O gasification reaction obtained from ReaxFF MD simulations is 199 kJ/mol. The contributions of the oxidation reactions to the overall carbon conversion in O2/H2O combustion are also obtained. The results show that the carbon oxidation is enhanced by the reactivity of H2O. The effect mechanism of H2O on char oxidation is revealed by analyzing the distributions of OH radicals·H2O significantly increases the concentration of OH radicals through the reaction of H2O with O radicals. Then, the contribution of H2O to the oxidation rate of char at different char conversions in O2/H2O combustion is quantitatively determined based on the assumption that char oxidation and char gasification reactions occur at separate active carbon sites. Finally, the effect of H2O concentration on the contribution of H2O to the oxidation rate of char is investigated. The results show that the oxidation rate contributed by H2O is enhanced with increasing H2O concentration.