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

Abstract

This paper reports some experimental observations on the effect of temperature on the fluidization of three fresh FCC catalysts and an equilibrium (E-cat) FCC tested at ambient pressure and at temperatures up to 650°C. The bed collapse test was used as a quantitative test to characterise the fluidization behaviour. It provides a sensitive and discriminating means of 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 this paper. Fluidization of the three fresh FCC catalysts improved with increasing temperature, the deaeration rate of these catalysts decreased as temperature increased. On the other hand, the deaeration rate of the E-cat FCC increased with increasing temperature, as the catalyst became less aeratable due to the dominant role of the interparticle forces (IPF) over the hydrodynamic forces (HDFs). The characteristics of the surface of this catalyst changed as a function of temperature. Where changes in fluidization at high temperature were observed, the factors responsible were investigated. To this end thermo-mechanical analyses were carried out, and the results obtained are discussed. Comparisons of experimental dense phase collapse rates with theoretical predictions are also reported. Deaeration rates obtained for the fresh FCC catalysts are predicted fairly well from a modified form of the Richardson–Zaki equation and from Abrahamsen and Geldart's correlation. The experimental collapse rates obtained for the E-cat FCC could not be matched 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 material to behave in a similar manner to a Group C material. The experimental values obtained for the minimum fluidization velocity are reported and compared with prediction. Results obtained from the bed collapse test are also presented. The dense phase collapse rate is compared with prediction obtained using the modified form of the Richardson–Zaki equation. The results emphase that a purely hydrodynamic equation can predict the fluidization behaviour where the IPFs do not show a dominant role over the HDFs.