Modeling and simulation of catalytic coal gasification in a pressurized jetting fluidized bed with embedded high-speed air jets

A pressurized jetting fluidized bed catalytic coal gasification process has been developed in China. In order to avoid the hot spot at the bed bottom occurring in the conventional coal gasifier, and to reassign the oxygen distribution in the bed, a pair of embedded high-speed air jets was employed in addition to a bottom central jet. To examine the effects of the embedded air jets on the gas-solid hydrodynamics and the gasification process, a comprehensive model has been constructed by using the two-fluid method incorporated with the kinetic theory of granular flows. The established model was applied in the simulation of a 0.3 t/d process development unit. The bed expansion was validated against the empirical correlation, and the bed pressure drop agreed with the value obtained by the Ergun equation. Some key jetting characteristics, including the jet height, the distributions of particle content, gas and solid velocities were presented. Comprehensive analyses of the simulation results showed that the embedded jets were able to split large bubbles, and improve the gas-solid contacts. A simulation for a conventional gasifier with a single bottom jet was performed, and the results were compared with the proposed embedded jets gasifier. For both schemes, a high temperature zone was predicted along the jet pathway due to a rapid combustion of char particles, the maximum temperature was, however, controlled well below the ash softening temperature for the embedded jets gasifier, mainly due to distributed oxygen supply. The carbon and steam conversions for the conventional gasifier were predicted lower than that of the embedded jets gasifier, indicating the embedded jets have enhanced the reactor performance due to the improvement of gas-solid mixing.