Novel Aids to the Fluidization of Ultrafine (Group C) Particles

Many products such as catalysts, pigments, fertilizers, cements, ceramics, and pharmaceuticals are currently manufactured in particulate forms. In the chemical industry, for example, more than half of the products and at least three-quarters of the raw materials are in granular form. According to Prof. Geldart, particles can be classified into four groups and very fine particles (20-30 mm or smaller in size) are classified as cohesive particles (Geldart group C powders). Group C particles are difficulty to handle due to the presence of very strong interparticle forces. When subject to fluidization, those fine and cohesive particles tend to channel and agglomerate significantly, resulting in poor fluidization or even complete de-fluidization. On the other hand, ultrafine particles are very useful in many cases such as in chemical, advanced material, food and pharmaceutical industries, given their smaller size and large surface area.

To effectively utilize the benefits of group C particles, the most important issue is to properly fluidize those fine and cohesive particles. We have carried out systematic studies to investigate the fundamentals of interparticle forces and to develop novel techniques to overcome inter-particle forces so as to achieve the smooth fluidization of ultrafine Geldart Group C powders. A variety of fluidization aids including mechanical vibration, acoustic agitation and surface modification by dry particle coating with novel flow conditioners have been carefully studied. Among other things, effective technologies have been developed to incorporate nanosized flow conditioners to significantly enhance the flowability of very fine Group C particles (US Patent 6,833,185, plus more patents pending). By employing this novel dry-particle surface-coating technique and a variety of patented flow conditioners, fine powders can be made to fluidize smoothly and behave like Group A powders with large bed expansion. This novel surface-coating technology has been found very useful in many cases and has formed a platform technology which support several of our key technologies developed such as the ultrafine powder coating technology and the tablet coating technology.

This technology with comprehensive patent protection can also benefit many industries. For example, finer powders generally results in better quality of the final products in the ceramic industry; finer catalyst particles lead to higher catalyst activity in chemical reactions; and finer particles enhance the mechanical properties of powder metallurgy products. More than a dozen of articles and patens have been published so far by our group in this field.