Catalytic gasification is a promising technique applied in various clean coal technologies including the coal to hydrogen energy; the coal based synthetic natural gas (SNG), and the chemical looping coal conversions. Currently, a pressurized jetting fluidized bed is developed for large-scale SNG processes in China. Traditionally, gasification agents (mainly oxygen and steam) are introduced through a central jet and a conic distributor from the bottom of the gasifier, and the control of the solids temperature in the grid zone is a critical issue for the reactor design and scale-up. As a solution, a pair of high-speed air jets is embedded in the bed for the control of the gas solid reactions, and for suppressing the peak temperature of the bed. A quantitative description of the effect of the air jet on the bubble dynamics and the mass and heat transfer process is of great importance.
In this presentation, we report a comprehensive two-fluid model which combines the kinetic theory of the granular flow (TFM-KTGF) and the catalytic coal gasification. The model has been validated against a bench-scale air-char jetting fluidized bed coal gasifier, and applied in a PDU catalytic gasifier with two embedded air jets. Several important gas-solid hydrodynamic properties, such as the bed expansion, the bubble size and the jet penetration height were obtained via a careful post-processing of the simulation data, and compared with literature correlations. Specifically, the bubble size was obtained from an image post-process of the contours of the gas volume fraction by using MATLAB, and the jet penetration height was predicted by measuring the axial momentum dissipation of jets. The heterogeneous reactions of pyrolysis, char-O2 and char-H2O were taken into account along with the homogeneous reactions of methanation and water gas shift. The distributions of gas species concentrations (CO, CO, CH4, H2, H2O) were predicted.
The simulation results showed that the two embedded jets developed separately, and interacted with the surrounding bubbles. Of particular note, the rising bubbles were split by the jet-induced shear layer, and a high temperature zone with a maximum over 1400 K was observed along the jet pathway due to the rapid combustion of char particles. The conversion efficiencies of carbon and steam were computed based on the outlet gas species concentrations, and agreed with the experimental results. Overall, the embedded high-speed air jets revealed a potential of improving the gasifiers’ performance via an enhancement of the mass and heat transfer of gas and solids.
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