Simplified sub-models for coal combustion are widely used in CFD simulation of pulverized coal fired boiler. A large-scale boiler was simulated to investigate the effects of some advanced sub-models. Through calculating several cases using different sub-models, it is known that the predicted ignitability of burners is closely related with the generation of H_2. In the case without taking into account H_2, the burners show poor ignitability. Using a multi-step mechanism for gas combustion, including char gasification and detailed compositions of volatile largely improve the ignitability of burners. The good ignitability also leads to more heat absorption in boiler and less CO in furnace. CO can be also increased because of the char gasification and detailed compositions of volatiles. Therefore, it is necessary to using multi-step mechanisms for gas combustion, char gasification, and detailed compositions of volatiles to obtain more accurate simulation results.
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