LAUSR

Abstract Reliable kinetics of char gasification are of great importance for accurate prediction of the reductive atmosphere in air-staged combustion of pulverized coal, which is critical in controlling nitrogen and sulfur species for the optimized design and operation of boilers and burners. In this study, a new method of obtaining char gasification kinetics from realistic air-staged combustion experiments is proposed. Firstly, a real combustion atmosphere, including the temperature and concentration fields of air-staged combustion in an actual boiler, is simulated in an electric-heated down-firing furnace by controlling the stoichiometric ratio of air to coal. In-situ char gasification is observed by obtaining gas and solid reaction data from staged combustions with stoichiometric ratios in the range of 0.6–0.9 at temperatures of 1200–1400 °C. Secondly, a detailed char combustion/gasification model with emphasis on coupling between the discrete phase and gas phase is developed and verified. The single film model based on nth order Arrhenius-type equations is used in the char combustion/gasification model, with consideration of particle boundary layer diffusion. The effect of reduced reactivity of the char at high degrees of conversion is included in the kinetic model. Thirdly, the in-situ char gasification kinetics are determined via a CFD-aided rigorous mathematical optimization process. A direct search algorithm is used to accelerate the optimization process. Finally, the determined kinetics are verified at wide ranges of temperatures, residence times, and stoichiometric ratios. Compared with char gasification kinetics from ex-situ char gasification experiment using the same coal, it is demonstrated that the kinetics of in-situ char gasification are very different from kinetics derived from ex-situ char gasification experiment. Therefore, reliable kinetics of in-situ gasification are necessary when predicting the fuel conversion and gas phase species in modern air-staged pulverized coal combustion boilers.