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Predictive Control of Screen Process Efficiency

The durability of critical wear components, the ability to predict their remaining life, and their improved operating efficiency was identified by the Australian coal industry to be a long-term strategic objective. Polymer screen panels used in high-capacity multisloped screens (banana screens) are a critical wear component that can affect both availability of the plant and plant performance. As a screen panel wears more oversize material is presented to downstream processing unit operations such as spirals and flotation plants, this oversize material has detrimental affects on the operating efficiency of these unit operations and can result in considerable yield losses. In addition, the maintenance of the screen panels is often done on a reactive basis or carried out at times when it is not needed resulting in unnecessary stoppages to the plant. If the plant operators can predict when the screen apertures/misplaced material reaches a point where yield loss is excessive and screen maintenance is required then reactive screen maintenance can be eliminated. This article describes the plant work undertaken during the course of the project, the results of the plant work, and the next steps towards developing a model describing the wear and the effect this wear has on downstream processing. Two plants were chosen for the test work; the first a plant with desliming banana screens cutting at nominally 1.8 mm with the oversize (30 mm × 1.8 mm) reporting to a primary 1 m DMC and the undersize to classifying cyclones and spirals. The second plant was desliming the 50 mm top-size feed again using banana screens at a cut-point of nominally 0.4 mm; the 50 mm × 0.4 mm was cleaned using a primary 1 m dense medium cyclone and the desliming screen undersize nominally 0.4 mm × 0 mm was treated using column flotation. Both these circuits incorporated secondary processing of the primary DMC rejects using secondary DMCs to produce a thermal coal. Screen apertures were measured over a period of 10 to 12 weeks using an optical-image analysis technique and samples taken of the screen products either just prior to the aperture measurement or immediately after.