Biomass combustion in a 140kW fixed bed boiler: A joint experimental and modeling study

Computational Fluid Dynamics (CFD) modeling and experimental campaigns have been performed to investigate the performance of a 140 kW biomass fixed-bed boiler. The most widely used modeling approaches in literature, such as those representing the biomass bed as a single or a series of interconnected perfectly stirred reactors, were shown to be unsuited and affected by large uncertainties on the model definition. Indeed, point measurements just above the fuel bed, performed in this work, have shown that, despite the small bed dimension, temperatures are strongly not uniform. In the present work, a simple and efficient method to overcome these limitations is suggested by representing the biomass bed as a porous medium with sources and sinks of chemical species and energy. In this manner the impact of the primary air injection on the resulting field is taken into account. The predictions provide a satisfactory agreement with the available measurements, even though improvements have to be made especially for better describing the kinetics.