Shape Effect of the Riser Cross Section on the Full-Loop Hydrodynamics of a Three-Dimensional Circulating Fluidized Bed.

In this work, numerical simulation is carried out in a three-dimensional full-loop pilot-scale circulating fluidized bed to explore the shape effect of the riser cross section on the typical flow characteristics of the bed via the multiphase particle-in-cell (MP-PIC) method. The gas and solid phases are modeled with the large eddy simulation and Newton's law of motion in the Eulerian and Lagrangian frameworks, respectively. The proposed model has been well validated with experimental data, followed by evaluating the typical core-annulus structure and the nonuniformity of the solid phase distributed along the radial and axial directions of the riser. Then, the particle-scale information of the solid phase distributed in different parts of the system is explored. The results demonstrate that (i) the square riser gives rise to a higher solid inventory in the standpipe owing to the stronger circulation intensity; (ii) the thickness of the solid back-mixing layer reduces along the riser height; the solid back-mixing tends to concentrate in the four corners, while it is not obvious near the sidewalls of the square riser; and (iii) nonuniform distribution of the particle-scale information of the solid phase (e.g., mass, flux, drag force, and slip velocity) can be observed. The square riser gives rise to comparatively more uniform axial mass distribution, a larger rising solid flux, larger horizontal transportation velocity between the core and annulus regions, and a larger horizontal dispersion coefficient in the riser, as compared with the corresponding ones in the circular riser.