The fluidization of light solids by gases under pressure and heavy solids by water: A study of the transition between aggregative and particulate fluidization

Abstract

As the result of an experimental study of the fluidization of light solids by gases under various pressures and the fluidization of heavy solids by water, a general family of curves has been produced relating a generalized fluid velocity to a bed porosity function for a series of values of a parameter P involving the fluid and solid properties only. This correlation satisfies both liquid- and gas-fluidised beds and indicates that there is no fundamental difference in mechanism between a liquid-fluidized bed and a gas-fluidized bed. It also enables direct comparison to be made between flow through a fluidized bed and flow through a fixed bed of similar porosity. By treating an aggregatively-fluidized bed as a two-phase system and making reasonable assumptions about the rise of bubbles the general bed expansion correlation is used to produce general correlations of mean bubble velocities, frequencies, concentrations and volumes in terms of the mean bed porosity and the parameter P. These correlations predict that a gas system normally has a comparatively small number of large bubbles and appears to fluidize aggregatively. A liquid system may have a large number of small bubbles and appear to fluidize particulately although certain liquid-solid systems will fluidize aggregatively. The values of the bubble characteristics for both liquid and gas systems are in approximate agreement with those observed. These correlations can also be used to predict the fraction of fluid passing through the bed in bubble form and hence gives assistance to the estimation of the efficiency of the fluidized bed as a chemical reactor. The effect of gas pressure on this efficiency is also discussed.