(248b) Fluidization of Nano-Sized Particles – Design and Operation Issues

This paper presents some experience gained from the design and operation of a fluidized bed for nano-sized particles. The fluidization column was constructed from transparent glass, with an internal diameter of 50 mm and wall thickness of 6 mm. The particles used were Aerosil R974 (Degussa) hydrophobic silica, with particle size and density for the primary particles of 12 nm and 2200 kg/m3, respectively. The fluidizing gas was high-purity nitrogen. The aim of our study was to obtain an improved understanding of fluidization characteristics of nano-sized particles.

It has proved to be very challenging to build a problem-free fluidized bed for nano-sized particles. Major problems encountered in our study include particle intrusion in the gas distributor plate, particles sticking to bed walls and to the distributor plate (especially after storing particles in the bed for more than 48 hours), and frequent blockage of in-line filters, for exhaust gas, just outside the bed.

Our experimental results have confirmed that nano-sized particles may be fluidized in the form of particle aggregates, and that considerable bed expansion may be achieved when the superficial gas velocity is increased beyond the minimum fluidization velocity for the aggregates. In this paper, we also present experimental observation of distinct differences in fluidization characteristics between fresh and used particles and between shallow and deep beds.

Acknowledgment: The authors wish to thank Professor Alan Weimer of the University of Colorado, Boulder, for his help in the design of the experimental facility used in this study.