CFD analysis of biomass steam gasification in fluidized bed gasifier: A parametric study by the assessment of drying stage

In this study, CFD analysis was performed based on a comprehensive pyrolysis chemical reaction model to simulate the gasification process of biomass in a fluidized bed gasifier using almond shells as the biomass feedstock. A novel multi-phase CFD model consisting of 33 chemical reactions that cover all of the drying stages, detailed primary and secondary pyrolysis stages, as well as gasification stage, was adopted for the first time. Gasification temperature and steam-to-biomass ratio were selected as the main parameters and their effects on produced gas composition, lower heating value, char yield, tar content, and tar components were evaluated. The obtained results of the base case agreed to a reasonable extent with the results of the previous experimental works. According to the results, an increase in gasification temperature enhanced the mole fractions of H2 and CO. Therefore, it was recommended to use higher temperatures and steam-to-biomass ratio for production purposes of H2 and CO. The lower heating value decreased by a factor of 14.7% and 1.86% for increased values of gasification temperature and steam-to-biomass ratio, respectively. It was also observed that CH4 mole fraction has a strong effect on the lower heating value of the produced gas. Furthermore, char yield was found to have a declined trend with increasing gasification temperature; however, the reverse was valid with increasing steam-to-biomass ratio.