Coarse-grained CFD-DEM simulation and enhancement mechanism analysis of spouted fluidized bed biomass gasification reactor: effect of pulsed gas flow

Spouted fluidized beds are widely used in biomass gasification process because of their high heat transfer efficiency, excellent mixing performance, and broad feedstock adaptability. However, the dead zone formed at the bottom of the reactor can significantly inhibit syngas yield. To mitigate these adverse effects, this study introduced pulsed gas flow to optimize the biomass gasification process through periodic disturbances, thereby improving the syngas yield. Firstly, this study employed CFD-DEM simulation method and innovatively incorporated a coarse-grained model to address the high computational resource demands of the traditional DEM, achieving a 176 % improvement in computational speed while ensuring its accuracy. Based on the proposed model, the frequency and amplitude parameters of pulsed gas flow on particle flux, heat transfer, and syngas molar fraction characteristics in the spouted fluidized bed biomass gasification reactor were analyzed and thus the optimal frequency and amplitude of pulsed gas flow were determined as 4 Hz and 0.8 m/s, respectively. Furthermore, this study investigated the effects of optimal pulsed gas flow on the gasification process at different biomass particle flow rates, sizes, and densities. Compared with continuous gas flow, pulsed gas flow increased syngas mass fraction by up to 15.6 % at different biomass densities. In contrast, the effects of the biomass particle flow rate and size on the syngas mass fraction were less significant. Finally, via the comparative analyses of the hydrodynamic characteristics, heat transfer, and reaction rates in the spouted fluidized bed reactor, an enhancement mechanism of pulsed gas flow on the biomass gasification process was proposed. This study offers a theoretical foundation for understanding the enhancement mechanism of pulsed gas flow on the biomass gasification process in spouted fluidized beds.