Fluidization of fine particles and its applications

Based on the force balance of the particle bed under vibration, a new correlation for predicting of the minimum fluidization velocity ( umf) for fine particles has been derived by taking both the interparticle forces and the effects of vibration into consideration. A general correlation for the minimum fluidization voidage (&egr; mf) showing the relationship between &egr;mf and particle size as well as vibration intensity is also obtained from the experimental data. The newly derived correlation for the prediction of umf combined with the one for &egr;mf proves to be superior to the existing correlations for particles of Geldart groups A, B and D, although the application of the present correlations remains unsatisfactory for group C particles.;Fundamental studies of the influence of gas type and temperature on the fluidization behaviour of groups C and A particles have been carried out. For all the particles tested, the fluidization quality in different gases generally shows the following priority sequence: Ar > Air > N2> He > H2. It is also found that a higher bed temperature usually leads to a larger bed voidage, a higher bed pressure drop as well as a lower umf. Possible mechanisms governing the operations of gas type and temperature in influencing the fluidization behaviour of fine particles have been discussed with respect to the changes in both gas properties and interparticle forces. It is suggested that the influence of gas type and temperature on fine particle fluidization is mainly through varying the gas properties (especially the gas viscosity). The increased gas viscosity may account for the improved fluidization quality of fine particles, as shown by either using a gas of higher viscosity or elevating the bed temperature. (Abstract shortened by UMI.).;A novel "online sampling" technique that can prevent the disruption of agglomerates when sampling the agglomerates from a fluidized bed has been developed and has been applied to the investigation of the agglomeration behaviour of cohesive particles during fluidization with and without mechanical vibration. A new model for the prediction of agglomerate size has also been established on the basis of an energy balance. Effects of gas velocity and mechanical vibration on agglomeration for two group C powders in fluidization are examined experimentally and theoretically.