Coal Preparation » Gravity Separation
The project objective was to quantify the changes in DMC operational conditions with respect to medium stability and particle crowding .
The project had two main components:
· A pilot scale DMC (150mm) was employed to investigate medium stability and particle crowding in well controlled experiments; and
· Analysis of mediums from selected plants to link under/over flow densities to medium qualities was undertaken.
Detailed audits were conducted at four coal preparation plants in NSW and Queensland. Additional information was also available from a previous ACARP Project C15053. The results indicated that:
· There were significant differences in the size distributions and the composition of the mediums between these plants; and
· The amount of non-magnetics in the medium is not constant, and this could have implications on the performance of the DMC circuit.
· It appears that a good quantitative understanding of the medium in a DMC circuit is required for optimal plant performance, particularly when operating at relatively low feed medium densities.
· The ability to add additional non‐ magnetic material to the correct medium in a plant should be considered, particularly for plants operating at low feed medium densities. The redirection of a small amount of the thickener underflow would be one source of this material.
· It has been shown that the CSIRO 150 mm dense medium cyclone test can be used as a direct comparison to compare different clay/coal and magnetite concentrations and how they will affect the efficiency of the plant scale cyclone with confidence.
· The conclusions raise the issue of having some understanding of the amount of non‐magnetic material in the DMC circuit medium for good DMC circuit control. The potential variation of the amount of non magnetic material in a circuit and the factors affecting it should be investigated.
· Smart sensors which provide information on the overflow and underflow medium densities, and monitoring the amount of non‐magnetic material in the correct medium could significantly improved control and optimisation of a DMC circuit. This should be considered further.
It can be concluded that even while the small coal is in the medium, and would add to the apparent density of the medium, it does not contribute to the effective medium density. This should be taken into account when reconciling the density of separation with the feed medium density.