RHEOLOGICAL AND FLUIDIZATION BEHAVIOR OF POWDERS OF DIFFERENT PARTICLE-SIZE DISTRIBUTION

While the importance of fines in determining the rheological and fluidization behaviour of powders has been recognized by many research workers, there has been little previous work aimed at understanding and characterizing the influence of fines content. In this project two particulate materials, spent FCC and glass, were examined. For each material, the behaviour of three size distributions of essentially identical surface-volume mean diameter (53 and 73-mu-m) but different fines contents and size spectra was studied. In addition, two narrow-sized fractions with smaller and larger average size were investigated for comparison. Characterization to study the role of fines included shear, cohesion, fluidization and collapse tests. These tests were performed under carefully controlled conditions to minimize possible disturbances from surface effects due to moisture and attrition, and from changes in size distribution by elutriation and comminution. The flow and fluidization properties of powders were found to be influenced by the particle size distribution. Collapse test results are affected by the bed height chosen. The expansion capability of bubble-free fluidized beds correlate reasonably with the interparticle adhesion force found from shear tests. The common assumption that minimum bubbling occurs by separation of particle contacts following complete balancing of interparticle adhesion forces by the overall force of hydrodynamic drag is questionable.