Distribution and particle-scale thermochemical property of biomass in the gasifier of a dual fluidized bed

Abstract

Steam-gasification of biomass feedstock via dual fluidized bed has been proven to be an efficient and promising approach for the thermochemical conversion of biogenic fuels into the high-quality nitrogen-free syngas. However, very little is known about the actual behavior of the biomass fuels in the bed. In this work, the reactive gas-solid flow in a full-loop pilot-scale (1MWth) dual fluidized bed biomass gasifier is numerically simulated with the multiphase particle-in-cell approach. The aim of this study is to explore the species segregation and particle-scale thermochemical property of biomass material. The results show that the species segregation induced by the size and density differences gives rise to a preferential distribution of biomass material close to the bed surface. The undesired segregation phenomenon inhibits the sufficient mixing of biomass and heat carrier, and results in the particular distribution of thermochemical property of biomass material, which therefore requires further optimization of geometrical design. Lagrangian tracking of solid phase provides insight in the particle-scale thermochemical properties (i.e., temperature, heat transfer coefficient, carbon content) of biomass material. The observation of lognormal distribution and large value in the splash zone of biomass heat transfer coefficient enhances the understanding of the heat transfer behavior of biomass material. Biomass locating near the bed surface has the largest temperature. The promoting effect of wider size distribution of heat carrier on biomass dispersion provides a guidance for the process operation. The results of this study provide a fundamental understanding of the high-fidelity microscopic biomass property in the gasifier of dual fluidized bed, which will be beneficial for the optimization of the process designs.