A novel developed weighted exponential sum model for char cloud conversion behavior under air- and oxy-combustion: Experiments and kinetics modeling analysis

Abstract

Comprehension of the fossil fuel chemical reaction conversion behavior benefits to insight micro physico-chemistry mechanism of burning chemical kinetics especially for conventional air-fired combustion and oxyfuel combustion. Detailed combustion reaction experiments and a novel developed kinetics model were proposed to investigate coal char conversion behavior under enriched-oxygen and high carbon dioxide dilution environment compared with air environment in present work. Primary characteristic parameters, i.e., combustion conversion rate, conversion ratio, burnout time, etc., mainly affected by limited chemical interactions between char oxidation reaction and gasification reaction, were studied under typical environments, i.e., O2/CO2, O2/Ar, CO2/Ar, O2/N2, using detailed experiments and a novel developed kinetics model, i.e., the weighted exponential sum model (WESM). Present kinetics predictions were also compared with previous typical kinetics models, i.e., the homogeneous reaction model (HRM), the shrinking core model (SCM), the modified volumetric reaction model (MVRM). Results showed that present kinetics model gave relatively more coherent predictions of the char conversion rate, conversion ratio, the maximum conversion rate and burnout time compared with those predicted by HRM, SCM and MVRM models, respectively. Meanwhile, the contribution ratio from endothermal gasification chemical reaction, i.e., C+CO2→2CO, on char maximum conversion rate was 41.1% and 45.2% in 1473 K and 1663 K, respectively. Correspondingly, the maximum and average interaction contribution ratios (χinteramax,χinteraave) decreased as 9.0% and 1.7%. The maximum rate ratio for oxyfuel combustion increased from 52.7% to 61.7%, and the average rate ratio slightly increased from 52.5% to 54.2% in these combustion reactions.