Particle motion in fluidised beds.
Gas fluidised beds are important components in many process industries, e.g. coal
combustors and granulators, but not much is known about the movement of the solids.
Positron Emission Particle Tracking (PEPT) enables the movement of a single,
radioactive tracer particle to be followed rapidly and faithfully. Experiments were
carried out in columns sized between 70 and 240mm diameter, operating in the
bubbling regime at ambient process conditions using particles of group B and D
(Geldart Classification). Particle motion was tracked and the data applied to models
for particle movement at the gas distributor as well as close to other surfaces and to
models for particle circulation in beds of cohesive particles. In the light of these data,
models for particle and bubble interaction, particle circulation, segregation, attrition,
erosion, heat transfer and fluidised bed scale-up rules were reassessed. Particle motion
is directly caused by bubble motion, and their velocities were found to be equal for
particles travelling in a bubble. PEPT enables particle circulation to be measured,
giving a more accurate correlation for future predictions. Particle motion follows the
scale-up rules based on similarities of the bubble motion in the bed. A new group of
parameters was identified controlling the amount ofattrition in fluidised beds and a
new model to predict attrition is proposed.