Three-dimensional simulation study of co-gasification of coal and biomass feedstock in a pilot-scale fluidized bed gasifier

Co-gasification of biomass and fossil fuel offers an ideal way to improve energy utilization efficiency and enhance gas production selectivity. However, the interaction between fuel and bed material within the co-gasifier, as well as the gas-solid interaction under high temperature and pressure operation, remains limitedly understood. Therefore, a reactive Eulerian-Lagrangian model is constructed to model the steam co-gasification of continuous coal and biomass feedstock within a pilot-scale bubbling fluidized bed. The effects of structural optimization (i.e., the feeding position of fuel) and key operating parameters, including bed temperature, superficial velocity, steam-to-fuel ratio, and fuel blend ratio, on particle and gas properties are investigated. The results reveal that poor mixing and excessive entrainment of fuel feedstocks exist in the gasifier due to inappropriate superficial velocity. The mixing index decreases from 0.364 to 0.322 as the feeding height changes from 80 mm to 200 mm. The gas temperature is uniformly distributed along the radial direction and gradually decreases along the axial direction. Biomass has the largest axial velocity due to small density, followed by coal and bed material. A higher feeding height decreases the axial gas velocity while has limited impact on the heat transfer coefficient of particles. The results can provide insights into understanding complex interactions between fuel, bed material, and gas phase during co-gasification.