Thermal conversion processes of solid biomass
BEST has developed a flexible 3D CFD model for the simulation of solid biomass combustion in grate furnaces. The model considers the biomass fuel bed as an ensemble of representative particles, where each of these particles undergoes thermal degradation processes. The conversion of these particles is modelled by a thermally thick particle model, which is able to describe the most essential characteristics of the thermal degradation of the biomass particles, such as the intra-particle temperature gradient, the reaction rates of drying, devolatilisation and char oxidation. Moreover, BEST has extended the model for torrefaction and gasification in fixed beds.
Further model development is ongoing e.g. on the movement of the particles in the packed bed, the release of nitrogen species and ash forming elements.
Gas phase temperature [°C] in a vertical cross-section of the furnace (left) and particle temperature [°C] (right) of a 180 kW grate furnace (woodchips with water content of 21%; wet based moisture content) [Mehrabian 2015]