A refined global reaction mechanism for modeling coal combustion under moderate or intense low-oxygen dilution condition

This study first assessed the performance of four global mechanisms, including the Westbrook and Dryer (WD) and Jones and Lindstedt (JL) mechanisms, and two preliminary refined versions of them (WD1/JL1), for predicting coal combustion under moderate or intense low-oxygen dilution (MILD) in a lab-scale furnace. The WD/WD1 mechanisms could predict coal MILD combustion well, while the other two performed unsatisfactorily as they greatly overestimated the CO levels. A refined global mechanism (RJLM) was then proposed by modifying some sub-reactions of the JL1 mechanism. The applicability of the proposed RJLM was subsequently tested by modeling coal MILD combustion in both lab- and pilot-scale furnaces. Generally, the RJLM can accurately predict the distributions of temperature and major species in either the lab- or pilot-scale furnace than the JL1 mechanism. The results also indicated that low-oxygen coal MILD combustion occurs under a slow-chemistry regime with Da ≈ 1 and Ka > 1. This demonstrates that coal MILD combustion is jointly controlled by the non-ignorable time scales of flow mixing and the chemical reaction. Moreover, as the JL/JL1 mechanisms overestimated the CO levels of coal MILD combustion, they overestimated the predominant role of slow chemistry in coal MILD combustion. In contrast, the RJLM can accurately predict the microscopic characteristics of coal MILD combustion.