Numerical study of biomass gasification in a 0.3 MWth full-loop circulating fluidized bed gasifier

Biomass gasification process in a three-dimensional pilot-scale circulating fluidized bed (CFB) gasifier is numerically simulated via the multiphase particle-in-cell approach. The physical and thermochemical properties of gas and solid phases (i.e., temperature, density, and viscosity, pressure, and species) in the gasifier under high temperature are comprehensively explored. The results show that the size- and density-induced segregation causes the accumulation of biomass particles in the standpipe. Elutriation of biomass particles leads to the presence of low-temperature endothermic zones and high-temperature exothermic regions in the riser. The large contents of combustible gas species exist in the left part of the riser. Continuous decrease of O-2 is due to gas species oxidation, while the reduction of N-2 results from the release of gas species. The dense region has a large content of N-2 but a small content of combustible gas species. Large turbulent gas viscosity appears in the riser. Enlarging the gas velocity decreases the solid concentration but increases the gas temperature. Gasification temperature has an insignificant influence on the solid concentration and the contents of combustible gas species. Based on the relationship between the solid transportation and gas-solid thermochemical properties, the current work provides a guideline for the optimization of CFB gasifiers, for example, the loop seal is advised to be optimized to enhance the gasification performance of this kind of apparatus.