Effects of riser geometry on gas-solid flow characteristics in circulating fluidized beds

The performance of a circulating fluidized bed strongly depends on its parameter settings, including that of riser geometry. In this study, a laboratory-scale circulating fluidized bed with three different riser geometries (circular, square, and rectangular) that had the same cross-sectional area and height was operated under two static bed heights (20, and 35 cm). Electrical capacitance tomography was combined with differential pressure transducers and an optical-fiber probe to measure the solids' volume fraction, differential pressure fluctuations, and radial particle concentration variations. Computational particle fluid dynamics simulations were also performed. The results showed that single bubbles appeared in the bottom region of the circular and square risers and double bubbles in the bottom region of the rectangular riser. The autocorrelation of capacitance signals was periodic for the circular and square risers and nonperiodic for the rectangular riser. The radial particle concentration profiles showed a single-core annulus structure in the circular and square risers, but a double-core annulus structure along the long side and single-core annulus structure along the short side in the rectangular riser. Shannon entropy analysis showed that fluidization was less disordered and most predictable for the rectangular riser. (C) 2019 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.