Hydrodynamic characteristics of pyrolyzing biomass particles in a multi-chamber fluidized bed

Variation of particle diameter during biomass pyrolysis is an important consideration for hydrodynamic characteristic of reactor. A hydrodynamic model considering particle shrinkage for multi-chamber fluidized bed is developed, via computational fluid dynamics coupled with discrete element method (CFD-DEM). By comparison with experimental data measured by PIV, it is found that the model can give a better representation of gas-solid fluidization in multi-chamber fluidized bed. Particle swarm-scale analysis is conducted focusing on the spatial and temporal properties of gas-solid hydrodynamics. Results show that pyrolysis of poplar sawdust with average diameter of 0.75 mm can be achieved in 30 s at 550 °C. Drying and dehydration, rapid pyrolysis, slow carbonization take 1.5 s, 17.5 s and 11 s respectively. Drying and dehydration occur mainly in the first chamber, and the third chamber is the main region for slow carbonization. Superficial gas velocity has quite limited effect on semicoke distribution.