Enhanced Fluidization of Cohesive Powders

Because of their extremely high specific surface area, fine powders are of great interest for a wide range of applications in the pharmaceutical, chemical and food industries. Nevertheless, decent fluidization of fine powders is yet problematic due to their cohesive nature. At a steady gas flow, the interparticle forces promote the formation of agglomerates among powders, and give rise to persistent gas channels bypassing a significant amount of the inlet gas continuously. Such poor interphase contacts significantly depress overall mixing as well as mass and heat transfer [1]. Over the last decades, many studies adopted additional manipulations on gas or solids, including mechanical vibration, mechanical stirring, and gas pulsation, to alter the fluidization of fine powders [2]. Despite the augmented fluidization observed, the hydrodynamics created and underlying physics remain largely unexplored.

In this contribution, we experimentally compare the fluidization across different industrially relevant assistance, including mechanical vibration and gas pulsation. Fast X-ray imaging, as a non-intrusive measurement technique, provides direct monitoring of local hydrodynamic events and global fluidization development [3]. We also discuss the impact of varying vibration and pulsation conditions on hydrodynamic events such as powder segregation, bubbling and channel formation. The degree of enhancement can be assessed according to the comparison of assisted and conventional fluidization. These results help guide the design, implementation, and scale-up practices of relevant solid processing applications.

[1] J.R. van Ommen, J.M. Valverde, R. Pfeffer, Fluidization of nanopowders: a review, J. Nanopart. Res. 14 (2012) 737.

[2] V. Francia, K. Wu, M.-O. Coppens, Dynamically structured fluidization: Oscillating the gas flow and other opportunities to intensify gas-solid fluidized bed operation, Chem. Eng. Process. 159 (2021) 108143.