The influence of fines size distribution on the behaviour of gas fluidized beds at high temperature

This paper reports some of the results obtained from an extensive experimental campaign aimed at studying the influence on fluidization of changing the size distribution of the fine sub-cuts (particles below 45 μm) of Group A powders with increasing temperature. The fluidization behaviour of an alumina powder was monitored at temperatures ranging from ambient to 400 °C and by adding to the material previously deprived of fines two fine sub-cuts of nominal size 0–25 and 25–45 μm, respectively. In the study presented here the total fines content was kept at 22% by weight for both powders. Results were obtained by performing fluidization tests such as bed collapse test, pressure drop profiles and bed expansion profiles. From the bed collapse test, the influence of fines on the fluidization behaviour of the alumina was analysed and a comparison between the powders was drawn, in terms of dense phase collapse rate, standardised collapse time and bed expansion ratio. The validity of some classical equations used for describing the fluidization behaviour of powders, namely the Richardson–Zaki equation, was tested for the expansion and the collapse experiments.