Coal Preparation » Fine Coal
The objective of this project is to develop an enhanced coal processing spiral, which incorporates learnings from recent improvements in spiral design that have been implemented in other mineral processing operations.
Baseline testing was conducted on coke and thermal coal feed types, on the following spiral models: LC3 8 turn (multiproduct box fitted); LD7 RC and CT1.
Baseline testing identified the best performing MT coal spiral model to conduct comparisons with the CT1, as the configurations were updated based on each round of testing. The LC3 8-turn spiral model was identified as most suitable one for the comparison basis.
As part of the testing program, five configurations were trialled with the industry supplied coal feed material, leading to a final configuration. This final configuration was then tested as part of a rougher/cleaner circuit to determine whether it could outperform the LC3 8-turn spiral:
- Configuration 1: set up to simulate the current coal spiral models (LC3 8 turn and LD7RC).
- Configuration 2: set up the same as Configuration 1 with an additional module attached to test the benefit of an additional splitter whilst not exceeding the LC3 8-turn frame height.
- Configuration 3: set up as a 12-turn spiral without exceeding the maximum height of an existing LC3 8-turn spiral frame. The objective being to remove as much reject material as possible through the fixed diameter splitters and to allow the remaining material to separate more efficiently along the remainder of the spiral trough surface.
- Configuration 4: set up based on the Configuration 3 test results having removed too much material to reject. Re-pulpers were fitted as a trial in this configuration.
- Configuration 5: set up based on the Configuration 4 results having not removed enough material to rejects. A re-pulper was fitted to each module.
A small bleed-out run at 4.0 tph and 35% solids (w/w), was performed using 'CT1 configuration 5' to generate enough material for sighter tests to be conducted on the LC3 8-turn spiral model as a cleaner stage. This was to determine whether the CT1 could be utilised to remove high ash rejects at a high feed rate. This would enable retrofitting of the units into existing plants. The expectation was that final product qualities could be improved by treating the initial CT1 product over another CT1 or an LC3 8-turn spiral model.
Within the project report a table shows the best individual tests results from each of the site samples tested, including rougher/cleaner circuit configurations. Despite testing these various circuit arrangements, involving the CT1 and LC3, with both low ash and high ash feeds, the current CT1 profile used in 'Configuration 5' was unable to outperform the LC3 8-turn across a single stage of operation.
This project did show that the CT1 spiral was able to operate under a wide range of feed conditions, up to 5.0 tph, despite treating coarser particles compared to the typical feeds originally intended for this spiral type.
Overall, all the project did not meet the stated objectives, despite an expansive test work program and the number of circuit configurations trialled.
The CT1 spiral was originally designed as a mineral sand spiral and would require a profile update closer to the LC3 profile to obtain better outcomes. This represents a fundamental shift in the design of the CT1 and would require a significant redesign before it could be tested again in a similar program.