(634f) Modeling Effects of Drag Force On Biomass Particles in a Fast Pyrolysis Reactor

Qingang Xiong and Song-Charng Kong

Department of Mechanical Engineering, Iowa State University, Ames 50011-2161, IA, USA

Email addresses: xiong@iastate.edu (Q. Xiong), kong@iastate.edu(S. Kong)

Abstract Various drag models are implemented in this study to investigate their effects on biomass particle in a fast pyrolysis reactor. Thermochemical conversion of biomass to produce fuels via fast pyrolysis has become increasingly important. In this study, an open-source CFD code, OpenFOAM, is used to model the evolution of biomass particles in a fast pyrolysis reactor. In the simulation, both gas and biomass particles are treated as interpenetrating continua and the kinetic theory of the granular flow is employed to close the solid stress. Biomass particles are fed from the side and the product gas exits from top. In order to focus on the issue of drag relations, a simplified lumped reaction model is used to represent the pyrolysis process. Drag relations derived from homogeneous fluidization and closures from heterogeneous analysis (e.g., EMMS/Matrix model) are compared in terms of product yields and distributions. It is found that homogeneity-based drag relations, due to their lack of considering sub-grid structures in each computational cell, give relative poor predictions while for those heterogeneity-based models, the simulation appears to be better. Detailed results about the effects of model formulation will be presented. Such results indicate that for gas-solid flows, regardless of chemical reactions, sub-grid structures need to be considered in inter-phase drag force within the framework of  the two-fluid model.