Investigation of Submodels in Computational Fluid Dynamics Simulations of a Large-Scale Pulverized-Coal-Fired Furnace: Significant Role of H-2

摘要

Certain simplified submodels of coal combustion, whose precision can be inadequate for certain situations, are widely used in computational fluid dynamics (CFD) simulations of a pulverized-coal-fired furnace. A large-scale furnace was simulated to explore the effects of certain advanced submodels. Comparing the simulation results in four cases to different submodels shows that the ignitability of burners is closely linked to the amount of H-2 generated. In the baseline case, which disregards H2, we obtained very poor ignitability for all burners. Using a four-step mechanism instead of a two-step mechanism for volatile combustion and considering the char gasification (C-H2O) and detailed composition of volatiles are all clearly likely to improve ignitability. Meanwhile, superior ignitability also increases the heat absorbed by walls, reduces gas temperatures at the furnace exit, and reduces CO in the furnace. CO can also be increased by accounting for char gasification (C-CO2) and the detailed composition of volatiles. These results indicate the need to consider advanced submodels with accounting for multi-step mechanisms of volatile combustion, char gasification, and detailed volatile compositions to obtain relatively precise simulation results for heat transfer and distribution of gas species.