Influence of size-induced segregation on the biomass gasification in bubbling fluidized bed with continuous lognormal particle size distribution

摘要

Via the multiphase particle-in-cell approach, the biomass gasification in a three-dimensional bubbling fluidized bed with sand material of wide particle size distribution (PSD) is numerically simulated. The gas and solid motion are solved by treating the gas as the continuum medium in the Eulerian framework and numerical parcel in the Lagrangian framework, respectively. After validating the numerical results with experimental data, the radial and axial segregation induced by the wide PSD and chemical reactions, combined with the particle-scale information of both particle type (e.g., temperature, heat transfer coefficient, constituent mass fraction, and solid residence time) are discussed. The results demonstrate that obvious radial and axial segregation impact the spatial distribution of temperature and heat transfer of both particle types. The skewed distribution of the residence time of biomass particles is obtained. Biomass particles exiting the bed behave with large carbon content. PSD width exerts an evident influence on the spatial distribution of heat transfer coefficient, mass, and constituent content of biomass particles. Enlarging the PSD width enhances the gasification performance of biomass particles with the reduced mass and increased residence time for biomass particles in the bed, and the reduced char residual in the biomass particles lost. The results obtained in this work provide new insights regarding the presence of the radial and axial segregation induced by the wide size distribution and chemical reactions, which can be beneficial for the scale-up and the in-depth understanding of the fundamental mechanisms for the gasification process in this kind of reactor.