Numerical Investigation of Flow/Chemistry Interactions During Biomass Gasification In a Fluidized Bed Reactor

A current limitation to the efficiency of biomass gasification for the production of biofuels is the high level of tars usually found in the product gas, causing fouling of downstream equipment. Tar formation is a relatively slow process involving bi-molecular reaction pathways, and is therefore likely to be affected by local flow conditions. In this context, developing primary tar mitigation strategies requires a better understanding of the coupled chemical and physical processes occurring inside the reactor. In this work, two- and three-dimensional simulations of biomass gasification in a lab-scale fluidized bed reactor are conducted using a Lagrangian approach to handle the solid phase. The biomass gasification chemistry is described using a semi-detailed kinetic model assembled from literature data and recent experimental measurements performed at the National Renewable Energy Laboratory. Statistical analysis of the particles and velocity fields is conducted to investigate the effect of biomass volatilization on the dynamics of the bed. A posteriori analysis of products distribution, gas mixing and residence time inside the reactor is used to explore tar formation pathways during gasification, and how those are impacted by the dynamics of the bed, especially the bubbling process.