The influence of interparticle forces on the fluidization behaviour of some industrial materials at high temperature

This paper reports some experimental observations on the effect of temperat ure on the fluidization of three fresh FCC catalysts and an equilibrium (E- cat) FCC tested at ambient pressure and at temperatures up to 650 degrees C . The bed collapse test was used as a quantitative test to characterise the fluidization behaviour. It provides a sensitive and discriminating means o f assessing the changes in the materials' aeratability between ambient and high temperature fluidization. The dense phase collapse rates were obtained from the collapse profiles and the experimental values are reported in thi s paper. Fluidization of the three fresh FCC catalysts improved with increa sing temperature, the deaeration rate of these catalysts decreased as tempe rature increased. On the other hand, the deaeration rate of the E-cat FCC i ncreased with increasing temperature, as the catalyst became less aeratable due to the dominant role of the interparticle forces (IPF) over the hydrod ynamic forces (HDFs). The characteristics of the surface of this catalyst c hanged as a function of temperature. Where changes in fluidization at high temperature were observed, the factors responsible were investigated. To th is end thermo-mechanical analyses were carried out, and the results obtaine d are discussed. Comparisons of experimental dense phase collapse rates wit h theoretical predictions are also reported. Deaeration rates obtained for the fresh FCC catalysts are predicted fairly well from a modified form of t he Richardson-Zaki equation and from Abrahamsen and Geldart's correlation. The experimental collapse rates obtained for the E-cat FCC could not be mat ched with theory. The physical properties of a highly porous Group A powder were changed deliberately in order to highlight under which conditions the fluidization behaviour is dominated by the IPFs. These results demonstrate how temperature can increase the effect of IPFs, causing a Group A materia l to behave in a similar manner to a Group C material. The experimental val ues obtained for the minimum fluidization velocity are reported and compare d with prediction. Results obtained from the bed collapse test are also pre sented. The dense phase collapse rate is compared with prediction obtained using the modified form of the Richardson-Zaki equation. The results emphas e that a purely hydrodynamic equation can predict the fluidization behaviou r where the IPFs do not show a dominant role over the HDFs. (C) 2000 Elsevi er Science S.A. All rights reserved.