Coal Preparation

Improving the Control of Product Coal Moisture Based on Unsaturated Soil Mechanics Principles

Coal Preparation » Dewatering

Published: September 08Project Number: C15061

Get ReportAuthor: David Williams, Stuart Whitton | University of Queensland, Mechanical Advantage

ACARP Project C15061 addressed a Research Priority of improved recovery by reducing product coal moisture.  This was achieved through applying unsaturated soil mechanics principles to better understand the water storage capacity, dewatering and re-wetting of product coal, during processing and on the mine and port stockpiles.  The preliminary application of the approach to samples provided by Anglo Coal demonstrated the potential for it to provide a direct means of assessing the effectiveness of different dewatering methods for different product coal size fractions from different mines, assessing the potential for drying of stockpiled product coal due to gravity drainage, wind and solar action, and assessing re-wetting due to rainfall or watering for dust suppression.  These have implications for the future processing of product coal and for the management of product coal stockpiles to avoid high moisture contents.  The approach has potential to be applied to existing mines based on the testing of the various product coal size fractions, and to new projects based on the testing of borehole samples.

The mining, handling, processing, stockpiling, reclaiming (particularly if this involves dozing) and transportation of product coal results in the production of fines, which have an affinity for moisture.  Improvements in fine coal recovery, and the mining of coal that is prone to breakdown, exacerbate this.  The total moisture content at which product coal is exported has implications for its handleability, shipment and final use.  Excessive moisture makes the coal difficult to unload from ships, there is no financial return from shipping excess water, and excess moisture in the coal requires expending energy to remove it.  Product coal is therefore required to be delivered to the port for export below a specified total moisture content, typically 10 to 11% (based on mass of water/total mass, expressed as a %).  For each 1% by which the product coal exceeds this specified value, a financial penalty is imposed equivalent to the energy value of the extra moisture, up to a rejection moisture, of typically about 15%, at which rejection of the shipment may occur or severe financial penalties are imposed.

Laboratory Soil Water Characteristic Curve (SWCC) testing was carried out on a number of product coal size fractions and composite product coal samples supplied by mines in the Bowen Basin and Hunter Valley.  These samples represented the main coal seams mined, focusing on those that experience or expect to experience problematic product coal total moisture contents.  Field data on total moisture content were also collected from a product coal stockpile at one of the participating mines following 8 days of atmospheric drying, and this product coal was subjected to laboratory wetting up simulations.  The successful conclusion of the project provides a potential means of selecting the most appropriate dewatering technique for a particular product coal size fraction, and best means of managing product coal stockpiles to minimise the likelihood of excessive moisture.  The methodology and experience gained during the course of the project may readily be extended to a greater range of coal measures and specific product coals, and to the design, construction and management of a greater range of product coal stockpiles, both at mines sites and ports.


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