(262b) Characterization of Fluidization Behaviour of Glidant-Added Geldart C Glass Powders

The main objective of this work was the study of the fluidization behaviour of a glass powder in order to allow its application by electrostatic pulverisation. The high density and the small diameter of the original product lead to bed channelling and slugging. To avoid these inconsistency problems, different fluidisation-aide techniques were experimented which were incorporation of easy-to-fluidise large spherical glass particles to the glass powder, the addition of four different types of flow conditioner (or glidants) and the use of mechanical agitation. The quality of fluidisation was determined by monitoring of pressure drop through the bed during fluidisation experiments at decreasing air velocities. Two sizes of spherical glass particles were used as easy-to-fluidize particles. Nevertheless, the fluidization was not obtained by this technique. Using the stirring system, a better but still poor fluidisation was achieved although its quality was improved by adding flow conditioners. An insignificant influence of the stirring speed on fluidization was observed. The addition of easy-to-fluidise particles (glass beads of 300 and 400 µm in diameter) led also to insufficient effects. Four batches containing 1 w/w% of different fluidisation additives (two containing hydrophilic additives and two hydrophobic additives) were tested. Fluidization additives were Aerosils® which are nanosize products based on silica. The fluidisation of products formulated with hydrophilic agents was only achieved using the mechanical agitation. However, glass powder batches containing hydrophobic agents were fluidised without requirement of any mechanical energy. Moreover, differences on fluidisation ability between additives of the same nature were obtained and discussed. In addition, the influence of the proportion of additive has been tested in five batches containing 0.1, 0.2, 0.3, 0.4, 0.5, and 1 w/w% of the hydrophobic agent which led to the most satisfactory improvement in fluidisation behaviour of the glass powder. It was demonstrated that increasing the rate of fluidisation additive beyond a critical value does not lead to further improvement of fluidisation properties.