Gas–solid flow patterns in a novel multi-regime riser

A novel circulating fluidized bed riser which features an enlarged bottom and a draft tube has been introduced and investigated in terms of its applicability for FCC. Multi-flow regimes were observed in this novel riser, which had a dense bottom and a dilute upper region. The flow pattern in the bottom part almost had no effect on the flow behavior in the upper part. The dense bed height could be adjusted easily. A funnelform draft tube enabled the solids to follow two flow patterns: an upward flow to the riser top and a downward flow from the annulus to the riser bottom. A solids distribution ratio was proposed to qualify this distribution relationship. Furthermore, the flow structure in the bottom region was depicted, and an obvious core-annulus countercurrent structure was observed.

► Multi-flow regimes were observed in this novel riser.
► The draft tube was able to distribute the solids into two different flow patterns.
► A solids distribution ratio concept was proposed to qualify the distribution relationship.
► The flow structure in the bottom region was depicted.