Experimental validation and CFD modeling study of biomass fast pyrolysis in fluidized-bed reactors

In this work, an Euler-Euler multiphase computational fluid dynamics (CFD) model, which couples a biomass particle pyrolysis model with a multi-fluid hydrodynamics model for gas-particle flow, is used to describe a biomass pyrolysis process, and model predictions are compared to experimental data produced in a lab-scale fluidized-bed reactor. A parametric study of operating conditions was also performed. The kinetic model is based on superimposed hemicellulose, cellulose, and lignin reactions. General biomass feedstock can be represented through the initial mass composition with respect to the three components. The gas-particle flow is modeled with a multi-fluid description (gas, sand, biomass) derived from the kinetic theory of granular flows. The predicted product yields at the reactor outlet are presented and compared with the experimental measurements for both pure cellulose and red oak pyrolysis, and encouraging quantitative agreement is achieved. The model is then applied to investigate the effect of various operating conditions on the pyrolysis product yields in the reactor. Results indicate that biomass particle size and superficial gas velocity influence tar yield and residence time considerably with a fixed bed height. For the range of operating temperature studied, the model captures the trend of biomass decomposition versus temperature and shows an optimal temperature of about 500 degrees C for bio-oil production as reported in the literature. Different biomass feedstocks are also simulated and model shortcomings are discussed. (C) 2012 Elsevier Ltd. All rights reserved.