Modeling effects of interphase transport coefficients on biomass pyrolysis in fluidized beds

This study numerically characterizes the effects of interphase transport coefficients on the simulation of biomass pyrolysis in fluidized-bed reactors. Numerical modeling of sub-grid structures can affect the evolution of interphase transport coefficients and influence the predictive capability of coarse-grid computational fluid dynamics (CFD) models in simulating fluidized-bed reactors. In this study, a multi-fluid model that solves mass, momentum, energy and species conservations was coupled with chemical reactions to simulate a laboratory-scale biomass fast pyrolysis reactor. Different formulations of drag and heat transfer coefficients were employed. Comparisons between the simulated and experimental results show that the drag coefficient model considering detailed sub-grid structures predicted lower drag forces and performed better than the homogeneity-based drag correlation models. Lower drag forces on solid biomass particles resulted in lower solid biomass outflux, higher gas velocities, and shorter tar residence time, all resulting in higher tar yields. On the other hand, heat transfer correlations had less effect on the temperature distributions and final product yields. These findings indicate that when coarse-grid CFD is used to simulate biomass fast pyrolysis in fluidized-bed reactors, effects of sub-grid structures need to be taken into account in the formulations of drag coefficients. (C) 2014 Elsevier B.V. All rights reserved.