Based on the Eulerian?Lagrangian method, a 3D computational fluid dynamics (CFD) model of a two-stage dry coal powder entrained flow gasifier was established and the coal gasification process in the entrained flow bed was simulated and analyzed using the homogeneous and heterogeneous multistep chemical reaction kinetics to define the coal gasification reaction, the k?? model was used to describe the gas phase turbulent flow, and stochastic tracking method (STM) was used to indicate motion track of char particles. At the oxygen/coal mass ratio of 0.9, 1.0 and 1.1, respectively, different reaction mechanisms were simulated to determine the optimal reaction mechanism according to the published experimental conditions. Further, the effect of coal/oxygen ratios in the upper and lower stages on the coal gasification characteristics were studied at the oxygen/coal ratio of 1.0. The results showed that the reaction mechanism adopted a complete combustion reaction of coke and volatiles and neglected the participation of CO in the gas phase combustion reaction (Case E), the simulation results was in good agreement with the experimental data with an error of less than 2%. In the case of total oxygen/coal ratio of 1.0, the reaction mechanism of Case E was selected to examine the effect of coal/oxidant between the various stages on the overall performance of the gasifier. When the primary feed (A?A) coal and oxidant reached and exceed 50wt% of the total feed, the overall performances of the gasifier such as syngas composition, carbon conversion and active ingredients were optimized. The carbon conversion rate reached 99.6% when 70wt% coal and 60wt% oxygen were injected at the first nozzle (A?A level), and the maximum synthesis gas yield was 78.24mol% when the first nozzle injected 50wt% coal and 50wt% oxygen.
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