The Oaky North mine located in Queensland’s Bowen-Basin currently deliver around 5 million tonnes per annum of high quality export coking coal for their joint venture operators Xstrata. This modern longwall operation has undergone several expansion stages since its opening in the late 1990s under MIM ownership, with a further equipment expansion expected over the next 18 months as extraction travels further into the rich seam.
The current longwall extraction is over six and a half kilometres from the ramp stock pile, and coal is transferred along a series of four belt conveyors that are designed around
Dodge CST (Controlled Start Transmission) technology.
The Dodge CST, available from Baldor Australia , is a patented 2-in-1 drive that combines a planetary gear reducer and hydroviscous clutch specifically engineered to deliver and synchronise 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 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.
Oaky North are currently operating 15 CST units, with 4 additional units available for pre-installation into the next longwall conveyor. Planning is in progress for the purchase of additional CST units for the installation of two new trunk conveyors for upcoming mine development.
According to Tim Strong, Senior Mechanical Engineer, Oaky North, he have worked with these CSTs and have not faced any serious reliability issues or lost production from these units. All units are reported through their SCADA system, and maintenance generally comprises oil sampling and analysis on a regular monthly basis and oil and filter changes as and when required. Oaky North have duplex filter banks on each unit, allowing the maintenance crew to switch over on-site, which then enables simple replacement of off-line filters.
According to George Willet, Outbye Services Coordinator, Oaky North, the CSTs are simple to look after. The trick is to look after the oil, which is critical to good longevity.
There are currently 14 CST models, ranging in torque capacity from 280,000 in-lb to 2.5 million in-lb, which are suitable for motors up to 3MW. The efficient incorporation of helical and planetary reduction gears and the hydro-viscous clutch (which is on the output side) results in a compact footprint, provides high torque density and allows direct coupling of motor, CST and conveyor drum. Motors are started under no-load, reducing electrical delivery problems and mechanical stress on all components.
A PLC controller (which can synchronise up to four drives) provides an appropriate S-curve start-up ramp through managed hydraulic pressure to the clutch pack. Mine-wide connectivity is delivered through DH+ datahighway, Ethernet or other popular proprietary links. To complete the unit, a pump and air-cooled heat exchanger recirculates, cools and filters the oil from the CST. The CST clutch technology has proven easier to balance than alternatives and is very forgiving on shock loads and surges, which are a major concern for conveyor failure.
Tim Strong outlined the CST arrangements preferred at Oaky North. Their conveyor system comprises a maingate conveyor (LC01), two trunk conveyors (TC01 and TC02) and the ramp conveyor (RC01). The maingate is long at up to 4000 metres and a 90 metre climb. Oaky North have 4 x 280KR CSTs (each 320kW) at the head and 2 x 280KR CSTs at each of two tripper locations. These units keep overall height down, which is more suitable for their underground locations. The trunk conveyors (TC01 and TC02) are 2600m and 1450m respectively with a total climb of 63m. These are each fitted with 2 x 1120K/1MW CST units mounted at the head. These conveyors are rated at up to 6500tph.
The ramp conveyor RC01 is 1376m long with a climb of 115m. It has 3 x 1120K/1MW drives, arranged in tripper configuration about mid station. The CSTs cater for both fully laden and empty conveyor start-ups, smoothly ramping up to around 4.4m/sec operational speed and delivering and synchronising nearly 10MW of power throughout the conveyor network.