Dynamical and thermal property of rising bubbles in the bubbling fluidized biomass gasifier with wide particle size distribution

Abstract

In-depth understanding of the dynamical and thermal property of bubbles is required to elucidate the phenomena occurring in a bubbling fluidized gasifier. In this work, numerical simulation is conducted for the biomass gasification in a three-dimensional bubbling fluidized bed through the multiphase particle-in-cell method. After validating the numerical results with experimental data, the impact of particle size distribution of sand material on the dynamical property (i.e., the rising velocity, spatial distribution, volume) combined with the thermal property (i.e., gas species, temperature, pressure, density, thermal conductivity) of the rising bubbles in the system are explored. The results demonstrate that large bubbles have a high mass fraction of combustible gases. Along the bed height, the bubble temperature, specific heat and thermal conductivity continuously increase while the density and pressure decrease. Compared with the boundary, the bubble interior has a higher temperature, smaller density, and more combustible gases. Enlarging the particle size distribution width increases the bubble volume, aspect ratio, mass fraction of combustible gas in the lower part of the bed, temperature and the thermal conductivity of bubbles, but decreases the rising velocity, density and pressure of the rising bubbles. The results obtained provide a new perspective regarding the effect of particle size distribution on the bubble property especially the first report regarding the thermal property of the rising bubbles in the bubbling fluidized gasifier, which will be beneficial for the in-depth understanding for the fundamental aspects and also the practical operation for this kind of apparatus.