May 13, 2008

A.S. Issangya, S.B.R. Karri, T.M. Knowlton in “Circulating Fluidized Bed Technology IX” (J. Werther, W. Nowak, K-E Wirth, E-U Hartge eds.) TuTech Innovation GmbH, Hamburg, p. 338


Commercial circulating fluidized bed (CFB) units require efficient operation of the riser and the solids return leg.  The solids return leg can consist of a cyclone dipleg, a standpipe, a baffled (stripper) or an unbaffled bubbling bed.  Jet streaming, also called gas bypassing, can cause severe solids flow and solids/gas contacting problems in the return legs of CFBs.  The objective of this work was to study how horizontal baffles can be used to reduce or eliminate gas bypassing in deep beds.  Tests were conducted in a 0.3-m-diameter unit using 4% fines FCC catalyst particles for bed heights of 0.76 to 3.05 m and gas velocities of up to 1.2 m/s.  Visual observation, differential pressure fluctuations, and radial bubble void fraction profiles were used to determine the effectiveness of horizontal baffles and rods in preventing gas bypassing.  It was found that for a given operating condition, the ability to eliminate gas bypassing depended on baffle spacing and axial location.