(248a) Fluidization and study of the nanometric powders behavior: Numerical approach to estimate the agglomerates sizes

This work focuses on the fluidization of Three types of TiO2 powders: Anatase (99% of TiO2), Rutile 1 (95% of TiO2 and 5% of Al) and Rutile 2 (96.5% of TiO2 and 3.5% of Al, Si) the average diameters of the powders are 253 nm, 360 nm and 362 nm respectively. These powders belong to the group C of the Geldart Classification and are characterised as cohesive powders with a nonfree flow and a difficult fluidization. The fluidization of the powders was carried out in a glass column of 103 mm inner diameter and 1500 mm height. The experiments and analysis performed included measurement of the physical properties of the powders as the particle size analysis, density, specific area and shape factor of particles, and the flow properties of the powders as the Hausner index, the angle of repose, the angle of slide, consolidation and shearing (via shear cell testing). The results obtained with the nanometric powders TiO2 show a more complex behaviour than the micronic powders, with a low strength values (Hausner index, angle of repose and angle of slide) the TiO2 powders have a free-flow or intermediate-flow and a non-free-flow for a higher strength intensities (consolidation and shearing). This behavior is related to the structure of the nanometric particles in packed bed, the evolution of this structure made up of individualized and spherical agglomerates shape is not perturbed by stress of low intensities. Indeed, the latter seems to modify the structure of powder (group C of Geldart classification) to acquire a typical behaviour of group A, B or D in the Geldart classification. With high stress values the individualized agglomerates are disintegrated and the powder is reduced to a more compact structure. The fluidization of TiO2 powders seems to evolve more in a homogeneous way than the micronic powders. This behaviour is related to the initial structure made up of stable agglomerates. Thus this fluidization is made by agglomerates with a gas velocity of 4000 to 100 0000 times the gas velocity for fluidizing the primary particles. A numerical approach based on a force balance in agglomerating fluidised beds was developed in order to estimate the agglomerates sizes.