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 The Grasstree mine, which is located within the rich German Creek formation in Queensland’s Bowen-Basin, is currently delivering around 4 million tonnes per annum of high quality export coking coal for its joint venture owners Anglo Coal Australia Pty Ltd and Mitsui Pty Ltd.
Grasstree, two other underground mines and an open-cut operation nearby are all managed by Capcoal Management Pty Ltd, an Anglo Coal subsidiary. Mining leases controlled by Capcoal cover some 27,345 hectares, and estimated resources exceed one billion tonnes.
The Grasstree mine is a modern longwall operation which commenced development in 2002 and began delivering coal in 2006. Longwall coal clearance is carried to the surface via a series of belt conveyors, elevating the coal more than 250m over a 6 kilometer track. Two main trunk conveyors which can deliver up to 6000tph are designed around Dodge CST (Controlled Start Transmission) technology, and are engineered to easily cater for the 4500tph longwall capacity plus development unit output.
The Dodge CST is a patented 2-in-1 drive that combines a planetary gear reducer and hydro-viscous clutch specifically engineered to deliver and synchronize power and to control acceleration of high-inertia loads such as long-haul conveyors. There are more than 2000 CST units in operation around the world with about 180 of these in Australia. CSTs have a proven track record on conveyors up to 10kM in length in coal, gold, iron ore and copper mines, cement and power generation as well as port facilities. Clutch-only versions are also highly effective for braking in decline application.
The first of the Grasstree trunk conveyors GCV006, delivers the coal over 1600m with a climb of 60m. This conveyor uses an 1800mm belt normally operating at 4.28m/sec for a capacity of 6,000tph. The conveyor is driven by three 630K CST drives mounted at the head, two driving the main pulley and one driving the secondary pulley. This conveyor also incorporates a tripper drive utilising another CST 630K, and there are provisions for an additional 2 tripper units as the belt is lengthened.
During mine development, a 1000 tonne underground bin was constructed in an excavated cavity between trunk conveyor GCV006 and GCV005. This smooths the flow of coal through the conveyor system, and provides additional production flexibility and prevents the need for total shut-down during short delays in production or clearance.
A vibrating feeder delivers a controlled flow of coal from the bin onto trunk conveyor GCV005 which has a length of 2500m and a climb of 80m. Using a 1600mm steel cored belt operating at 4.3m/sec, this conveyor is conservatively rated at 4,500tph. Conveyor GCV005 is driven by four 550kW/3.3kV, 4 pole Reliance motors which are direct coupled to 630K CST drives. These are in-turn direct coupled on each side of the primary pulley and secondary pulley in a horizontally opposed arrangement. For easy transport in and out of the mine shafts, Grasstree has arranged the motors, CST drives and hydraulic circulating pumps neatly on skid platforms. Cooling units are on separate skids and placed to suit the available space and air flow requirements.
“This was a ‘package’ contract”, explained Rod McClure, Baldor-Dodge-Reliance National Sales Engineer – Mining. “Not only did we supply the CST drives, but we also supplied all of the 3.3kV Reliance primary drive motors, the heat exchanger units and circulating pumps. We also manufacture conveyor pulleys and are one of the worlds largest suppliers of mounted bearings and power transmission components. We have also now developed dedicated control software, and our experienced CST engineering team can provide a high degree of design and pre-installation analysis as well as on-site and return to base maintenance support ”.
Bill Laing, Baldor Field Service Engineer – Mining, has had many years of experience with CST drives and provides front-line support to the mines. Bill said, “CST technology has proven to be very reliable and robust. They are very maintenance friendly. Generall
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