(566r) Computational Fluid Dynamics Modeling of Heat Transfer in Three Phases of Biomass Particles, Bed Materials and Gas during Fluidized Bed Gasification

Agyemang, S., North Carolina Agricultural and Technical State University
Wang, L., North Carolina Agricultural and Technical State University
Shahbazi, A., North Carolina Agricultural and Technical State University

Gasification has been identified as an energy-efficient, environmentally-friendly and economically-feasible technology to partially oxidize biomass into a gaseous mixture of syngas consisting of H2, CO, CH4 and CO2.  High-quality syngas can be further used to catalytically synthesize liquid fuels and produce hydrogen. Fluidized biomass gasification involves complicated heat transfer among the three phases of biomass particles, bed materials and fluidized gas. During fluidized bed gasification, a bed material such as sand is used as a heat carrier to directly supply heat to biomass particles. The biomass fluidized bed gasification process involves both particle-particle heat transfer and gas-particle heat transfer. There is limited research on heat transfer through particle-particle interaction during fluidized bed gasification. However, it is critical to understand how the biomass particle-bed particle interaction on the temperature profile of biomass particles in order to predict the yield and quality of syngas during fluidized bed gasification. In this research, a computational fluid dynamics (CFD) model is developed to analyze the behavior of three-phase, reactive gas-particle-particle flow with heat transfer via both gas-particle and particle-particle interaction during fluidized bed gasification of biomass. A commercial Fluent CFD software package is used as a basic platform for the computational model. A mathematical sub-model is developed to calculate the dynamic particle-particle heat transfer coefficient. A user defined function (UDF) is then developed to incorporate the sub-model into the Fluent CFD simulation platform. Experimental data are used to validate the CFD model with and without consideration of the particle-particle heat transfer. The model is used to predict the effects of biomass particle size, temperature, biomass/bed material ratio, biomass loading rate on the yield and composition of syngas using the CFD model.