Cleaning of fine coals by dense-medium hydrocyclone

The efficiency of separation for fine coal in a 150 mm dia. dense-medium hydrocyclone has been determined. The partition curves have been measured for particles in the size ranges −500 μm +425 μm, −300 μm +250 μm, −150 μm +125 μm and −90 μm +75 μm. The cut point for separation increases with a decrease in particle size and the efficiency of separation decreases as particle size decreases. The cut point of separation varies with medium specific gravity but the efficiency of separation does not. Neither the cut point of separation nor the efficiency of separation is greatly influenced by the cyclone feed rate, provided that overloading does not occur.

The results lead to an accurate predictive model for the calculation of the partition curve as a function of coal particle size and medium specific gravity. The model allows the prediction of the performance of a dense-medium hydrocyclone for the washing of fine coal having arbitrary washability characteristics and particle size distribution. The model is used to demonstrate that a two-stage dense-medium hydrocyclone configuration can significantly improve the cleaning performance for a coal that has good ash-liberation characteristics. However, multi-stage dense-medium hydrocyclones do not offer any real performance advantages for coal that has poor ash-liberation characteristics.