A Fluidized Bed Biomass Combustion Model with Discretized Population Balance. 1. Sensitivity Analysis

A model of a 1 MW th atmospheric bubbling fluidized combustor burning waste wood fuel (feeding) is presented. The model incorporates both the solid and gas phases. The bed is assumed to consist of two phases, of which the emulsion phase takes both gas and solids into account, while the bubble phase consists only of gas. A wide size distribution of biomass feed, representative of the actual boiler feed, has been assumed. The model calculates the gas composition, velocities, and other important hydrodynamic parameters in both the emulsion and bubble phase. A particle size distribution model is included to calculate elutriation losses of fine char particles. This approach is novel in the sense that a population balance for fine particle class is derived, using the well-known mass balance principles, and a coupled discretized population balance equation, valid for the whole particle size range, is presented. The model takes into account devolatilization, fragmentation, and attrition of the solid phase along with gaseous profiles. It includes nine components for which differential equations have been derived and solved to calculate species concentration at any point along the bed height. In total, 20 particle size classes have been considered, 10 of which are considered as feed and the rest as fine classes. The model aims to assess the effect of different parameters on boiler performance and gaseous emissions. A sensitivity analysis of the gaseous emission profiles with respect to different variables and parameters defining different submodels has been carried out. A homogeneous NO x model has been included with individual kinetic parameters for relevant species. It has been found that gas hydrodynamics play a significant role, and the system can be optimized using these parameters.