Fine and ultrafine powders (down to nanoparticles) have recently received growing interest in both industrial and academic sectors due to their very distinctive features, mainly coming from their very small primary particle size and very large surface-to-volume ratio. Indeed, due to these characteristics, they can provide better contact efficiency and higher reaction rates per unit volume of reactor than traditional materials in the case of gas/solid and solid/solid reactions. They have been used to produce a large variety of materials, such as catalysts, sorbents, cosmetics, etc. Therefore, the interest in using this type of granular materials in a variety of industrial processes raises many questions about how they can be handled. Therefore, the interest in using this type of granular materials in a variety of industrial processes raises many questions on how they can be handled and processed (e.g. mixing, transporting and modifying the surface properties) in large-scale applications. With reference to this point, among all the available techniques for continuously handling and dispersing granular solids, gas fluidization is one of the most efficient, mainly due to the large gas–solid contact area. The aim of this work is to provide a critical review of experimental/theoretical research and latest progress in the science and technology of gas fluidization of fine/ultrafine particles, thus deeply covering the current international state-of-the-art. In particular, the challenges linked to the extensive use of these powders have been discussed, highlighting and explaining the fundamental aspects needed to comprehend the complexity of the process and provide possible answers/solutions.

Gas–solid fluidization of cohesive powders

Numerical simulation of horizontal jet penetration in a three-dimensional fluidized bed

The quality of gas–solid fluidization of agglomerates of nanoparticles has been greatly enhanced by adding a secondary flow in the form of a high-velocity jet produced by one or more micronozzles pointing vertically downward toward the distributor. The micronozzles produced a jet with sufficient velocity (hundreds of meters per second), turbulence, and shear to break-up large nanoagglomerates, prevent channeling, curtail bubbling, and promote liquid-like fluidization. For example, Aerosil R974, an agglomerate particulate fluidization (APF) type nanopowder, expanded up to 50 times its original bed height, and difficult to fluidize agglomerate bubbling fluidization (ABF) type nanopowders, such as Aeroxide TiO2 P25, were converted to APF type behavior, showing large bed expansions and homogeneous fluidization without bubbles. Microjet-assisted nanofluidization was also found to improve solids motion and prevent powder packing in an internal, is easily scaled-up, and can mix and blend different species of nanoparticles on the nanoscale. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Haibin Li

Papers

Studies on the inclined jet penetration length in a gas—solid fluidized bed

Wave Phenomena to the Three-Dimensional Fluid-Particle Model