Axial and lateral solids distribution modeling in the upper region of circulating fluidized beds

A method for approximating the axial and lateral distribution of solids in the upper region of a circulating fluidized bed (CFB) has been developed. The model assumes a core–annulus structure, but has the advantage that little empirical or experimental data are required as input. A Lagrangian model was constructed to determine the radial particle dispersion and deposition in the dilute upper region of the CFB. Particles are tracked through a turbulent flow field using a particle/eddy interaction time to describe the effect of the interaction between the particles and fluid, and using a collisional timescale to describe the effect of particle collisions. Emphasis in model development was placed on capturing enough of the underlying physics to eliminate uncertainties and geometry specific approximations associated with empirical correlations, while retaining enough simplicity to allow for quick calculation of the internal solids structures and trends within a CFB. Calculated dispersion coefficients, core/annulus voidages, velocities, and diameters are compared to experimental data in CFBs, FCC reactors, and dilute pneumatic transport multiphase flows. Results show good agreement between predicted and measured values in the dilute regions of CFBs. Agreement between the model and measured axial solids distributions in the lower dense (acceleration) region of CFBs is also surprisingly good. However, the model is not intended to be used in this region since the core–annulus structure no longer exists here.