A circulating fluidized bed (CFB) biomass gasification model is developed in the present study. The model consists of sub-models for devolatilization, tar cracking and a chemical reaction network of main gasification reactions and nitrogen chemistry. Unlike the most of the previous biomass gasification models, devolatilization of biomass particles is modeled with a limited rate, which is selected from the literature based on woody biomass fuels. To predict the tar content of the gasification gaseous products, kinetics for tar evolution and cracking is adopted from literature and included in the model. All model parameters are chosen for a typical woody biomass — pinewood chips. The partition of fuel nitrogen between volatiles and char is also specifically chosen for pinewood based on the available experimental data from literature. Volatile nitrogen is assumed to consist of NH3, HCN and N2 with the distribution between three species as input parameters to the model. A total of forty global chemical reactions are included in the model, of which twenty-eight reactions belong to fuel-nitrogen reaction network. Individual reaction rates are selected from the literature, wherever possible, based on studies of woody biomass fuels. Modeling of the hydrodynamics of the riser is simplified by using solids concentration profile along the riser as an input to the model. Both gaseous phase and solids phase are assumed to be in plug flow. Modeling results are compared with the experimental results published in the literature. Predicted effects of bed temperature and equivalence ratio on main gaseous composition, tar content and NH3, HCN emissions generally agree with the literature data.

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