Gas fluidization of natural graphite flakes

Abstract

Demand for high purity graphite is expected to greatly increase in the coming decades. Mined graphite is purified to the final purity specification via thermal and/or chemical fluid-solid processes. As fluidized bed electro-thermal purification is a promising technology, the physical characterization and cold-flow fluidization of Canadian natural flake graphite was undertaken to better understand the gas-solid dynamics. Three commercial graphite particle batches were characterized. Mean Sauter diameters of the three particle populations measured by microscopy were 89, 63 and 51 μm. The modified sieve analysis and permeametry yielded similar mean diameters. Particle sphericities were determined to be 0.34, 0.36 and 0.40 respectively. Channelling near the surface occurred near minimum fluidization (vmf) but eventually disappeared with increasing gas velocity. This led to a partial fluidization state before achieving complete fluidization with the delay, which was observed to be up to around 3vmf, being greater for the smaller particles. Minimum fluidization velocity was determined to be 0.063, 0.028 and 0.011 m/s respectively. Complete fluidization was observed at velocities of approximately 0.070, 0.046 and 0.035 m/s respectively. Finally, wall effects due to the presence of a central electrode did not significantly impact overall fluidization characteristics.