(688b) CFD-PBM Simulation of Catalytic Coal Hydrogasification in a Pressurized Fluidized Bed

Catalytic coal hydrogasification (CCHG) is a promising technology for the coal-to-SNG process. In this presentation, we report a numerical attempt of CCHG in a bench-scale pressurized fluidized bed batch reactor (36 mm i.d., 3 MPa, 1123 K) with Geldart A particles. The coal particles have a density of 1200 kg/m³ and an average diameter of 131 um.

A fine-grid (four times the particle diameter) cold simulation is first conducted by TFM-KTGF with the Gidaspow drag model. The predicted bed expansion height agrees with the empirical correlation. And bubble characteristics are obtained from the transient data by using a post-processing code. In order to reduce the computational cost, a coarse-grid CFD-PBM model is developed in which the bubbling fluidized bed is divided into a discrete bubble phase and a dense emulsion including a pseudo solids continua modeled by KTGF. A modified bubble coalescence and breakup model was implemented in PBM to describe the bubble size variation. A pseudo bubble-emulsion drag model is used for simulating the momentum exchanges between gas bubbles and the solids belong to the emulsion phase, and the Gidaspow drag model is for the emulsion gas and emulsion solids. The mass transfer between the bubble and the emulsion gas is derived the Davidson-Harrison correlation. The cold simulation results (bubble size, bubble size distribution) agree with the fine-grid TFM-KTGF results. Then catalytic coal hydrogasification kinetics is coupled into the CFD-PBM simulation. In the hot model, the particle density is assumed as a function of the carbon conversion, and the particle size is kept constant according to the experimental measurement. It is found that bed heights and bubble sizes increase with the decrease of the particle density. The methane yield and the carbon conversion are also predicted and compared with the experimental results.