The fly ash recirculation technique offers irreplaceable advantages in the sustainable utilization of biomass energy and plays a vital role in enhancing the combustion efficiency of biomass boilers. In this study, a biomass boiler equipped with a hydraulic vibrating grate was selected as the research subject. A systematic numerical simulation was conducted to optimize the structure of the fly ash recirculation ports and the direction of the secondary air. Three types of recirculation port structures, three secondary air directions, and three particle size distributions were evaluated to investigate their effects on the flow characteristics of fly ash particles within the furnace. The results indicate that the configuration with dual recirculation ports and downward-oriented secondary air yields the best performance in promoting the secondary combustion of fly ash, increasing the particle residence time by 32.6% compared to the baseline case. This study provides a theoretical basis and design reference for optimizing biomass boiler structures to enhance secondary combustion of fly ash.
 

biomass boiler, discrete phase model, fly ash particles, numerical simulation, secondary air