Combustion of wood chips in a CFBC.: Modeling and validation

A mathematical model for the combustion of wood chips in a circulating fluidized bed (CFB) boiler has been developed. The model considers the processes of wood chip drying and devolatilization, population balances of devolatilizing particles, volatiles combustion, population balances of char burning particles, and heat generation in the different regions of the combustion chamber (bottom, splash, and transport regions) and can predict the gas emissions and combustion efficiency as a function of the operating variables. The validation of the model with experimental results obtained in a 12-MWth CFB commercial plant burning wood chips showed some differences between model predictions and experimental results for the oxygen profiles, the average char concentrations, and particle sizes along the riser. To achieve good predictions of biomass combustion in commercial boilers, the model was modified to include the biomass particle fragmentation during the devolatilization and combustion processes and the combustion in the cyclone. Moreover, a way to handle gas mixing problems has been highlighted and included in the model. With these modifications, better agreement between experimental results and model predictions was attained.