(423c) Numerical Investigation of Solid Residence Time Distribution in a Circulating Fluidized Bed Riser for Catalytic Upgrading of Biomass Pyrolysis Vapors

Fast biomass pyrolysis is receiving more attention recently as it offers a promising technology to utilize renewable biomass resources for liquid transportation fuels. A circulating fluidized bed of catalyst material is commonly employed to upgrade the biomass pyrolysis vapor providing large throughput, excellent heat and mass transfer characteristics, and its controllable solid residence time distribution. The resident time distribution of solid catalyst is important to determine the product quality during the vapor phase upgrading process. Accurate prediction of catalyst residence time distribution is valuable for the design and scale up of reacting circulating fluidized bed systems. A multiscale Eulerian-Eulerian approach for modeling gas-solid flow in a circulating fluidized bed riser is used to model flow behavior and thus determine solids residence times. Several mesoscale drag models (e.g. filtered models) are employed and examined to consider their effect on particle clustering.  Tracer particles are created from a labeled solid phase species and the solid residence time distribution is predicted by solving the solid phase transport equations for the labeled solids species. Subsequently, numerical predictions of pressure drop, solid volume fraction distribution, solid mass flux and solid resistance time distribution under different flow conditions are validated against of corresponding experimental data available in the literature. It is found that the flow hydrodynamics and solid mixing are well predicted.