Coal to Kilowatts
With an annual output of approximately 30 million tonnes of brown coal and four million cubic metres of overburden (soil that overlays the coal seams), AGL Loy Yang Mine is the largest coal-producing mine in the southern hemisphere. The mining process and the transportation of the coal from the bottom of the mine to the power stations is largely automated and features a range of sophisticated mining and materials handling technologies.
Huge electric-powered bucket-wheel dredgers, 50 metres high and 190 metres long, patrol the open-cut mine ‘benches', each excavating up to 4,000 tonnes of coal per hour on average. The bucket wheel of each dredger feeds on-board dredger conveyors, which in turn deposit the coal onto main transfer conveyor systems on each level of the mine.
Each transfer conveyor system comprises multiple separate conveyors, each with a belt-width of two metres and a travel speed of 5.2 metres/second (19 km/h). With a combined length in excess of 25kms, the mine's conveying system transfers the freshly mined coal from the mine floor to the surface. The transfer conveyor systems transfer the coal to a raw coal bunker, which has an 80,000-tonne capacity.
The coal is then transported directly from the bunker (also by conveyor) to two separate power stations located at the ‘mouth' of the mine. These are AGL Loy Yang's 2,210MW power station and GDF Suez's Loy Yang B 1,000MW power station.
Providing a steady flow of coal feedstock to the coal bunker is essential to keeping the power generation process online and producing cost-effective electricity. As the coal bunker only has enough capacity to fuel 20 hours of power generation, the conveying system is under pressure to perform.
The legacy transfer conveyor drive systems at Loy Yang Mine were based on water-cooled eddy-current coupling (ECC) technology. When first installed many years ago, the ECCs were the ideal drive solution for providing high torque over a wide speed range – perfect for hauling enormous quantities of coal from the bottom of the mine to the surface.
However, it had become clear to the AGL Loy Yang Mine engineering team that the legacy drive systems were struggling to move the coal as efficiently as they believed was now possible. Furthermore, the existing Eddy Current Coupling drive systems were becoming increasingly difficult to maintain and the control systems unreliable.
“The ECCs are an older method of conveyor control and as the mine continued to grow we needed additional power so it was clear that we needed to move towards a more modern system,” said Robert Collins, electrical superintendent at AGL Loy Yang Mine.
“The need to keep up with increased power demand provided AGL Loy Yang with the opportunity to implement a drive solution incorporating the latest technology that would work effectively in the mine's rugged environment,” said Collins.
With the large number of conveyors on-site, AGL Loy Yang focused on implementing the drive technology in a gradual manner to enable integration with the existing drive systems and control architecture.