Simulation of co-gasification of coal and wood in a dual fluidized bed system

Abstract

A comprehensive three-dimensional (3D) model based on multiphase particle-in-cell (MP-PIC) approach is developed to simulate the co-gasification process of coal and wood in a dual fluidized bed (DFB) system. The pyrolysis of coal and wood, formation and conversion of tar and gaseous pollutants, as well as gasification and combustion reactions are integrated with dense gas-solid flow and heat transfer. The pilot DFB system comprises a bubbling bed gasifier and a fast fluidized bed combustor connected by loop seals. The model correctly predicts profiles of pressure and temperature, the yield and components of the product gas. The gas composition distributions, allocations of particle mass, and solid residence time inside the reactors are explored. The effects of various fuel blend ratios and particle sizes on gasification performances are also investigated. The results show that increasing coal ratio accelerates the steam gasification due to higher char content, which results in the increment of H2 and CO concentrations. The tar content in the product gas continues to decline, while the emissions of NH3 and H2S increase. The size variation of feedstock is not enough to dramatically affect product gas components. The tar content and product gas yield appear a slight upward trend with the smaller size. The variations of NH3 and H2S concentrations are consistent with those of bed temperature.