Three-dimensional MP-PIC simulation of the steam gasification of biomass in a spouted bed gasifier

Abstract

By coupling the heat transfer and chemical reactions, biomass-steam gasification in a lab-scale spouted gasifier is numerically simulated via the multiphase particle-in-cell approach. The proposed model is firstly validated with the experimental results. Then, the spatial distributions of biomass particles, spout-annulus boundary, the gas species, the gas-solid flux, together with the influences of operating parameters are discussed. The results demonstrate that: (i) similar to the well-known Brazil nut effect, density-induced segregation of biomass and sand species results in the accumulation of large-diameter biomass species near the bed surface. High temperature does not change the general distribution of the spout-annulus boundary; (ii) the gaseous products mainly concentrate in the fountain; enlarging the bed height and biomass diameter reduces but increases the mole fraction of CO and H2, respectively. The steam-biomass ratio has a promoting effect on the production of H2, while higher gasification temperature reduces the H2 yield; (iii) enlarging the bed height and steam-biomass ratio decreases and increases the vertical flux of both the gas and solid phase in the dense region, respectively. The increase of bed height and steam-biomass ratio reduces and enlarges the gas voidage, respectively. The results obtained in this work provide meaningful insights regarding the presence of Brazil nut effect induced by the density difference and the complicated multiphase flow in the spouting apparatus, which will be beneficial to the design and optimization of this kind of gasifier.