Flow in stirred media mills

Flow in stirred media mills

PhD with Integrated Studies (2017-2021) sponsored by EPSRC and Imerys 

Stirred media mills are commonly used for the fine grinding of minerals such as calcium carbonate. However, fine grinding has a very low energy efficiency due to energy dissipation as heat, noise or vibrations. Hence, there is potential for a lot of improvements to be made.

 In stirred tanks, the power draw can be predicted by relating the Reynolds number to the Newton number. However, the Reynolds number includes a viscosity term, which is difficult to determine for high solid content slurries which also contain around 50 vol% grinding media. Additionally, this slurry-grinding media combination is non-Newtonian and the shear rate in the mill is difficult to measure or predict and varies throughout the mill. This research considers different ways of determining a viscosity to use in calculating the Reynolds number. It also looks at which additional material properties may need to be taken into account for Reynolds-Newton curves to reliably predict the power draw in stirred media mills. This includes using vane rheometry, tribology and particle size measurements.