Coal Preparation » Gravity Separation
Screen failures are a major issue in the coal preparation industry, and a failure can result in considerable lost product time and damage screen structures such as supports and feed and discharge boxes. The g-force at which these screens operate is typically in the range from 4g to 5g and normally recommended or setup by the screen manufacturer. The reduction of that g-force by just 1g would result in a significant reduction (20%) in the forces acting on the screen and screen support structures.
Pilot plant studies in earlier ACARP projects showed that the g-force on the pilot screen could be reduced with no detrimental effect on the screen efficiency and where the g-force was reduced on a 3.2m by 6m multi-sloped drain and rinse in a Bowen Basin Plant with no effect on the efficiency of the screen and no further failure of screen components on that screen over the first year.
The objective of this project was to reduce the g-force on the previous drain and rinse screen and to reduce the g-force by approximately 1g and to monitor the desliming screen with CSIRO failure analysis instrumentation.
Reducing the screens by approximately 1g was successful and showed no reduction in efficiency of either screen. There was a bed depth increase of 28mm for the desliming screen and 31mm for the product drain and rinse screen as calculated for increased residence times of 4.4 seconds for the desliming screen and 2.98mm for the product drain and rinse screen. The increase in bed depth did not appear to have a detrimental effect on the operation of the screens.
The failure monitoring was carried out over a period of three months during this time no unusual events or failures occurred. While it was the intention of the research team to monitor over a longer period circumstances prevented this occurring. This plant can produce either one or two products and as such the screen loadings can be lower in a single product and higher in dual product mode. Alarm limits would need to be set for both these modes with either an automated change over based on screen readings or a manual change over.