Coal Preparation » Gravity Separation
The Gekko Systems In-Line Pressure Jig is a mature technology that has been successfully used in the metalliferous industry for over ten years, but has not been systematically tested in the coal industry. It has the potential to efficiently process coal over a very broad range of sizes (30 – 0.25mm) using a low water consumption and simple process that is very successful in the metalliferous industry. It offers the real possibility of a low cost nil consumable way for the Australian coal industry to efficiently process mid-sized coal particles.This would enable existing coal preparation plants to run at considerably higher feed rates simply by installing the In-Line Pressure Jig and increasing screen panel apertures. In addition, higher efficiencies may be achievable by reducing the cut point-particle size effects seen in dense medium cyclone units, particularly for particles smaller than the breakaway size (around 5mm for a 1m DMCs).
A preliminary investigation of the operation of a Gekko Systems In-Line Pressure Jig (IPJ600) was undertaken with raw coal sourced from a Hunter Valley and a Bowen Basin coal mine. The unit was evaluated using the ACIRL Maitland pilot plant facility with volumetric feed rates around 16-17m3/hr and solids concentrations typically around 5%, but ranging up to 22%. The size fraction tested was 6 x 0.5mmWW, with a limited number of tests undertaken with 6 x 0.25mm solids. The top size limitation was due to pilot scale solids handling limitations. The manufacturers claim a larger sized unit could handle up to 30mm.
This unit was able to achieve spiral-like separation efficiencies over a very wide range of D50 cut points:
- D50: 1.43 -1.55, Ep: 0.075 - 0.150 for 6 x 2mm particles.
- D50: 1.48 -1.66, Ep: 0.180 - 0.213 for 2 x 0.5mmWW particles
- D50: 1.80 - 2.00, Ep: 0.282 for 2 x 0.25mm particles.
The results reported were obtained by undertaking a very limited (one at a time) parametric study of feed rate, ragging RD, pulse frequency and stroke length. However, it is unlikely that optimum operating conditions were identified by this preliminary investigation.
It is considered testament to the robustness of the design of the In Line Pressure Jig that such excellent performance was achieved from an obviously un-optimised unit. The unique design feature that led to the good performance was the moving (jigging) of a fully submersed bed of particles on a screen support within a continuum of water. This allowed excellent control of both the dilation (downward screen movement) and the settling stroke (upward screen movement) jigging process, which is unlike a conventional hydraulic jig where settlement is controlled by the settling velocities of the raw feed solids. This is a major improvement to jig design and has the potential to give better efficiencies than conventional jigs.
The areas of optimisation considered to be of primary importance are the pulse rate, pulse amplitude and pulse shape (Nesbitt et al, 2005). These are parameters known to be important to conventional jigs (Wills, 1997), noted to be important in a recent theoretical study of the In-Line Pressure Jig (Nesbitt et al, 2005) and confirmed by the current investigation. It is considered that there is considerable room for improvement for both D50 control and separation sharpness through optimisation of the abovementioned three parameters.
Given the large number of operating variables that need be adjusted, an optimisation approach is highly recommended involving the discrete element modelling/computational fluid dynamics approach recently used so successfully to model dense medium cyclones. This approach has the added benefit of negating any feed coal quality variation and experimentally induced variations on the systematic parametric study. Once the simulations have been completed, larger scale testing would allow the true potential of the In-Line Pressure Jig to be validated.