New approaches to improve the uniformity of the radial solids concentration distribution in CFB risers

The so-called core-annulus structure, that is, lower solids concentration in the center region and higher solids concentration in the near wall region along the circulating fluidized beds (CFB) riser, usually has a negative effect on the performance of CFB risers since it may greatly decrease the reactor efficiency and controllability. In order to improve the performance of industrial CFB risers, two potential approaches are proposed in this study: (1) the use of the center-sparse side-dense air jets arrangement for the gas distributor and the side-covered arrangement for the solids distributor and (2) the use of the air jet from the riser circumference. The results show that the patterns of the inlet gas distributor and solids distributor have significant effect on the flow structure in both the entrance region and the fully-developed region in the riser. The gas distributor with center-sparse side-dense air jet arrangement improves the uniformity of the radial solids distribution, while the center-dense side-sparse air jet arrangement steepens the non-uniformity of the solids radial profile. The core-annulus structure can also be greatly flattened by applying a side-covered solids distributor, while it can be heavily steepened by employing the center-covered solids distributor. The results also show that by employing the circumferential air jet approach under appropriate jet velocities, the maximum solids concentration in the near wall region can be greatly reduced, the entrance region can be shortened, and the uniformity of the flow structure can be greatly improved.