(315e) An Investigation of the Effect of Process Conditions on the Fluidization Behaviour of Gas Fluidized Beds Linked with Rheological Studies

Authors: 
Lettieri, P. - Presenter, University College London
Bruni, G. - Presenter, Department of Chemical Engineering, University College London
Elson, T. - Presenter, University College London
Yates, J. - Presenter, University College London
Newton, D. - Presenter, BP Chemicals


The industrial employment of fluidized bed technology involves processes that are strongly dependent on the operating conditions, such as temperature and particle size distribution of the material. In particular, the presence of fines represents a major issue for fluidized bed industrial applications, which typically employ between 10-50% by weight of fine material in order to maximize reactor performance. However, the relative importance of the various fine sub-cuts on the fluidization behaviour has not been fully understood as yet.

This paper reports on a study of the effect of realistic process conditions on the fluidization behaviour of powders. A Geldart Group A alumina was fluidized at temperatures ranging from ambient to 400ºC and by changing the size distribution of the fines below 45µm. The effect of temperature was to improve fluidization for both powders; significant differences in the fluidization behaviour were detected at each temperature when changing the fines size distribution.

Furthermore, a mechanically stirred Fluidized Bed Rheometer (msFBR) has been developed to characterize the flow properties of powders at process conditions. Experiments were carried out at ambient temperature on the Geldart Group A alumina samples differing in fines size distribution, at rates of aeration ranging from the fixed bed to the incipiently fluidized bed. The effect of changing the impeller depth on the torque measurements was also analysed. The Herschel-Bulkley's model was fitted to the experimental data and it highlighted yield stress behaviour at gas velocities below umf and power law behaviour at gas velocities above umf. A set of experiments was also carried out on powders belonging to the Geldart Group B and C, in order to test the capability of the msFBR technique to discriminate between different fluidization behaviours.

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