(201a) Fluidization of Coated Cohesive Powders

Abstract: Fluidized beds are widely used in many powder processes because of their continuous powder handling ability and good gas-solid contacting. According to the Geldart classification, group C powders are too cohesive to fluidize because of the strong inter-particle adhesion forces. However, there are many applications where cohesive powders need to be fluidized for the purpose of mixing, coating, granulation and other powder processing applications. Hence finding novel ways to fluidize cohesive powders has been an active area of research. In previous work by our group, it was found that dry particle coating of a very small amount of nano-sized particles onto group C cohesive particles can significantly improve their flowability. In this work, a series of experiments are performed to investigate the improvement in the fluidizability of group C powders (e.g., cornstarch and aluminum) through dry particle coating of a small amount of nano-sized particles. This investigation examines the effect of various parameters such as, surface area coverage (SAC), guest particle size and host particle size. The results indicate that dry particle coating can improve the fluidizability of cohesive powders dramatically and it appears that such a coating can transform the behavior of group C powders to that of group A powders. It is also found that the SAC, guest particle size and host particle size play an important role on the fluidization behavior of cohesive powders; i.e., there exists a critical SAC that is required to make the coated cornstarch fluidize, and there also exists an optimum guest particle size at which the coated powder exhibits a minimum fluidization velocity. As far as the host particle size is concerned, within the range of group C powders, the experimental results indicate that the larger the host particle size, the better the fluidization behavior.