Numerical and experimental investigation of an “S-shaped” circulating fluidized bed

• An “S-shaped” circulating fluidized bed is proposed.
• The S-shaped design is investigated both numerically and experimentally.
• The flow in the S-shaped design is quite different from that in traditional ones.
• The core–annulus flow structure is suppressed in the S-shaped design.

It has been widely reported that traditional circulating fluidized beds (CFBs) suffer from core–annulus flow structure which is characterized by severe solid back-mixing and non-uniform distribution of solids in both axial and radial directions. In this work, an S-shaped design of risers is proposed and its performance is examined first by numerical and physical experiments. Both experiments show that the flow pattern in the S-shaped risers is significantly different from that in traditional straight risers. Generally speaking, the uniformity of the distribution of solid concentration is improved in the S-shaped risers and the high solid concentration regions are mainly in the center of the riser instead of the regions near the riser wall, with the core–annulus flow structure of a traditional design almost eliminated. The reason for the improvement is that in an S-shaped riser, the high fluid velocity regions move back and forth along the riser wall, which can prevent the boundary layer of solids from being established. This S-shaped design could be useful to improve the solid–fluid contacting in vertical particle–fluid flow systems.

An S-shaped riser has been proposed to tackle the core–annulus flow structure problem suffered in straight risers. The figure shows the spatial distributions of particle axial velocity (I) and residence time (II) during macroscopic steady state: (a), traditional riser; and (b), S-shaped one. The flow structure in the S-shaped riser is quite different from that in the traditional one.Figure optionsDownload as PowerPoint slide