AGL Loy Yang Upgrades Mine Conveyor

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.

Continuous Conveying

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.

Compact, Contained and Cooled

In a collaborative effort, Rockwell Automation and the AGL Loy Yang engineering team developed a new drive solution, founded on the Allen-Bradley PowerFlex 7000 medium voltage (MV) AC drive. Featuring ‘Direct-to-Drive™' technology – a technology that helps eliminate the need for isolation transformers on applications with either new or existing motors – the Allen-Bradley PowerFlex 7000 MV AC drive provides space-efficient speed and torque control across a range of demanding drive applications.

The mine engineering team came up with an idea to equip each conveyor with a fully self-contained, cooled and removable drive package that could be easily installed or uninstalled on any of the mine's conveyors. This provides AGL Loy Yang with a level of portability that improves production flexibility.

According to Rockwell Automation engineering team leader, John Dunn, the compact nature of the PowerFlex 7000 drive simplified the development of the portable drive packages.

"The transformerless configuration of the PowerFlex 7000 meant we were able to help minimise the footprint of the drive package," he says. “The main electrical feature is the load sharing between different drives on each conveyor. We developed a partitioned stainless steel IP65-rated enclosure, equipped with an air-conditioned cooling system, to house each of the 6.6kV PowerFlex drives.”

The ‘minimal component count' was also a feature of the PowerFlex drive solution, with fewer parts eliminating the number of things that could go wrong.

Seamless Integration

Nine drive packages have been supplied to the Loy Yang Mine site to date. One of the main challenges throughout the upgrade has been integrating Rockwell Automation drive technology with the mine's existing drive technology and control architecture. The first PowerFlex 7000 drive packages interfaced with a PLC5 systems package in the neighbouring switchroom.

ControlLogix® is, in turn, linked to the mine's supervisory control and data acquisition (SCADA) system, via the mine's existing communications network. Each drive package is equipped with an Allen-Bradley electronic operator interface (EOI) located on the front panel of the drive enclosure.

“The drives can be interrogated via these EOIs or through the mine's SCADA system,” says Dunn. “The locally mounted EOIs make it easier for site personnel to access drive diagnostics without opening the dust-proof enclosures and exposing the drives to the elements.”

The Rockwell Automation and AGL Loy Yang engineering team developed a strategy that allowed the new drive packages to seamlessly synchronise with the existing ECC drives.

“Our long standing relationship with Rockwell Automation means integrating new drives at the mine has become a relatively straightforward project to complete. We have a lot of experience using the drives now, making it a fairly easy, run of the mill upgrade that doesn't take too long,” said Collins.

Proven Working Relationship

According to Dunn, “There were key benefits to the level of integration and flexibility achieved at the mine from being involved in this project from its inception and design phase, through to supply and installation.”

However, with upgrades at Loy Yang Mine continuing, there is much work ahead. The AGL Loy Yang team is planning to progressively replace other ECC drives across the mine. “When the first project with Rockwell Automation happened it was very significant for the mine, but our ongoing working relationship means that the drives have become very seamless to integrate,” says Collins.

AGL Loy Yang is currently in the process of constructing a new conveyor using PowerFlex drives inside a new switch room. Additionally, the engineering team is designing a new downhill conveyor based on the Rockwell Automation drive solution that will be used for backfilling the mine.