Solids motion in fluidised beds of fine particles

Abstract

Although there has been ongoing research on fluidised beds for the past 70 years, the interaction between particles and rising bubbles and the general solids motion in bubbling fluidised beds are still not fully understood. The work presented in this thesis uses the method known as Positron Emission Particle Tracking (PEPT) to track the motion of a single radioactively labelled particle inside a fluidised bed. Recent developments in PEPT include new ways of labelling micron sized tracer particles that can be as small as 60 μm and the new mobile camera system also known as the Modular PEPT camera that can follow particle trajectories in equipment of various sizes and geometries. So far, PEPT has only been used to investigate fluidised beds of Geldart group B and D particles due to the previous limitation in the size of tracer particles. The results outlined in the thesis include group A particles (aluminium oxide) fluidised at atmospheric pressure in an 8 cm internal diameter bed and at elevated pressure in a 15 cm internal diameter bed and group B particles (sand) fluidised at atmospheric pressure in a 15 cm internal diameter column. The three areas that have been investigated are the use of particle trajectories to measure the properties of rising bubbles and the dispersion and general solids motion together with solids circulation as a measure of particle mixing. The protocols required to process the PEPT data used in the thesis were originally set by Stein (1999) but modified and improved versions are proposed and used. The PEPT results are in general agreement with existing models and results published by other researchers. A set of Matlab programs to analyse the results of PEPT experiments and which can be readily used by other users is presented