COMBUSTION MODELING OF CFB BOILER FURNACE BASED ON AN EULER-EULER APPROACH

摘要

For the better design of large scale CFB boilers, reliable multi-dimensional modeling which can be used to predict the heterogeneous distributions of gas and solid concentration as well as temperature in the furnace is necessary and demanded. A model describing the complex combustion process in a CFB boiler furnace has been developed. The model consists of several essential sub-parts: the hydrodynamics of the bed, combustion of fuel, and overall mass balance of the furnace. In the computational fluid dynamics (CFD) study on hydrodynamics in a CFB boiler, the Euler-Euler approach is used, in which both gas and solid phases are considered as interpenetrating continua with the interaction through drag and energy dissipation caused by particle fluctuation. The constitutive equations for solid phase are derived from the kinetic theory of granular flow (KTGF). Some simplifications of the complicated theoretical equations with empirical correlations are adopted, to save computing time and skip the currently unknown phenomena. Drag coefficient between gas phase and solid phase is modified by the energy-minimization multi-scale (EMMS) principle. A simplified description of reaction process is also adopted. The present model was applied to predict the hydrodynamic and combustion behaviors in a commercial 135 MW_e CFB boiler. Some primary results are obtained and discussed in comparison with the measured data. Prediction results agree with the experimental data in general, confirming the correctness of the model. More reliable experiments are needed for the model improvement in the future.