It is not often that a long life mine can claim to have jettisoned its existing mining methods for something totally new, but the Yallourn coal mine in Victoria has done just that.
Like all Latrobe Valley lignite mines, Yallourn has long used technology developed in Germany for its own vast brown coal reserves: fleets of bucket-wheel dredges operating on a series of benches with an elaborate conveyor system that constantly needs moving to convey the brown coal to the adjacent power station.
Following privatisation in 1996, the new owners realised that the aging fleet of dredgers were becoming increasingly expensive to maintain and to operate, and were no longer able to ensure the coal supply reliability needed.
The power station has a minimal surge bin so needs high levels of supply availability.
The owner, now called TRUenergy, realised that in order to remain a competitive supplier in the national electricity market it needed to make significant changes.
Therefore, the company decided to invest $500m in a long-term upgrade of the power station and mine. The mine upgrade includes development of Maryvale Field to secure supply of coal until 2032. Production from the existing East Field runs out in 2007, although an extension will now push this out to 2011.
However, in order to access the Maryvale Field and extend the East Field mine the project had to divert the Morwell River (see full story on page 16).
The operation also had to introduce a mining method that can provide 100% coal supply reliability to the Yallourn W power station.
But before that, the mine acted on the problem of the dredgers. In conjunction with its alliance partner, the Roche Thiess Linfox (RTL) joint venture, it investigated options that could produce substantial cost savings.
The final solution was to opt for an innovative mining method using large GPS-guided dozers to push at least 2400tph of coal into feeder breakers that load coal onto conveyors.
Under the Yallourn Mine Alliance, RTL commenced its five-year contact for the operation of the mine in September 2002 following successful trials of the new mining system earlier in the year. Its contract is for the 17.5Mtpa of coal production at an average of 2400tph.
The new mining system uses Caterpillar D11R Carry Dozers fitted with GPS equipment and a special brown coal blade. Using a 3.6m high, 90m3 blade means the driver needs the GPS to know the exact whereabouts of the dozer as it pushes coal into hoppers feeding the more than 38km of conveyer belts that feed the power station.
Instead of benches, the dozer operates on a continuous 4:1 slope ripping and pushing the coal in flitches on to a specially designed feeder breaker capable of handling up to 3000tph.
This skid-mounted unit, which is moved along the face, sizes the coal that is then passed via a link transfer conveyor on excavator tracks to a hopper. The hopper in turn feeds the face conveyor leading to the power station surge bin.
The RTL alliance currently has three flat-bed feeder breakers, Caterpillar D11 Carry Dozers, two smaller Caterpillar D8 cleanup dozers, as well as various mine support plant.
The upgraded conveyor systems include two face conveyors, and extra cross over points.
Overburden removal is by a single dredger and truck-shovel at an annual rate of around 5Mbcm.
Benefits of the new technology include reduced mine operating and maintenance costs as well as the flexibility to use new equipment without the need for a major investment.
From a production standpoint, coal supply reliability is improved because the units can process 3000tph at peak output compared with the 2400tph that is demanded by the power station.
The dozer-feeder breaker can also operate in all weather.
In addition to accurate positioning, the GPS system gives enhanced reporting of mine productivity and overall mine planning with the GPS precisely calculating volume of coal excavated by hour, shift and so on.
Other flow-on benefits include a significant reduction in power consumption by the mining operations, and continued opportunities for further enhancement of the system and overall operations.
TRUenergy estimates the new method will save $85m over the next 10 years through increases in productivity.
A further benefit of the system is safety. The LTIFR has plunged from 9 to 3.9 since the introduction of the new technology and the TIFR is down from 218 to 58.9.