THE STABILITY OF GAS-FLUIDIZED BEDS: THEORETICAL AND EXPERIMENTAL INVESTIGATION

Oyebanjo Oke, Luca Mazzei*, Paola Lettieri

Department of Chemical Engineering, University College London, Torrington Place, WC1E 7JE, London, UK

T: +44 (0) 20 7679 4328; F: +44 (0)20 7383 2348; E: l.mazzei@ucl.ac.uk

ABSTRACT

The Richardson & Zaki (1954) equation has been used extensively to investigate the expansion profiles of homogeneous gas-fluidized beds. The experimental value of the parameter n appearing in the equation indicates how significantly interparticle forces affect the expansion of these beds, revealing the relative importance of these forces with respect to the fluid dynamic ones. In this work, we modeled the expansion of uniform beds accounting for enduring contacts among particles and wall effects. We solved the model numerically to obtain the bed expansion profiles, back-calculating for each velocity the values of the parameter n. For all the cases considered, we observed that the values of n are higher than those obtained using purely fluid dynamic correlations, such as those advanced by Richardson & Zaki (1954) and Rowe (1987). This effect was even more pronounced in beds of smaller diameter. To validate our model, we carried out fluidization and defluidization experiments, analyzing the results using the Richardson & Zaki equation. We obtained a reasonable agreement between numerical and experimental findings; in particular, the values of n were higher than the corresponding fluid dynamic ones. This suggests that enduring contacts among particles, which are manifestations of interparticle forces, affect the homogeneous expansion of the bed. This effect is further amplified by wall friction.