Premier coal mine: the future burns brightly
The long-term future of Wesfarmers Premier Coal’s open cut coal mine at Collie south east of Perth in Western Australia is now assured.
In August the mine won a major 25-year coal contract to supply Western Power with all its coal from July 2006, except for that under existing contracts with Griffin Coal. This means Premier Coal will supply all the fuel for coal-fired generation in WA in the near future.
Collie, 200km south of Perth by road, has a history of coal mining that spans over 100 years with more than 180Mt coal won from 24 underground and 13 open cut operations in that time. The last underground mine closed in 1994 leaving only the Premier coal mine and the nearby Griffin mine in production. Premier is the larger of the two mines producing around 3.4Mtpa while Collie is the only producing coalfield in WA.
The owner-operated Premier mine is set midway between the Collie and Muja power stations with a currently defined total coal resource of 360Mt and coal reserves sufficient to carry the mine beyond 2040 at today’s production rates.
The Premier mine produces low sulphur (0.3-0.8%), low ash (4-9%) sub bituminous steaming coal that primarily feeds the Collie, Muja and Kwinana power stations with a much smaller amount of “nut” product travelling by road to Iluka Resources’ mineral sands operation at Capel.
The black coal bearing sequence in the Collie Coal Basin has more than 50 seams, in a 700m stratigraphic section, that range in thickness from 0.5m to 12m. The Basin, with its 2400Mt resource, covers an area of 224km2 and is 27km-long by 13km wide.
Mining
Wesfarmers Premier Coal general manager Patrick Warrand tells Australian Mining that mining is a fairly straightforward process for an open cut operation.
To begin with, only 30-40% of the topsoil and overburden removal requires blasting. In operational Pits 1 and 4, very weak overburden is removed primarily by electric shovels and hauled by 240t trucks to dumps outside the pits. Later, this overburden, which is dumped so as to manage any acid generation potential, is used as backfill as the mine progresses.
As the seams are pretty flat, the overburden and coal is mined in strips.
Thicker coal seams require some blasting; indeed, Warrand says the operation blasts a higher percentage of the coal than the overburden.
Mining follows the coal seams where the slope is shallow, while benching is used in steeper dipping areas. Interburden horizons and steep zones are usually mined using hydraulic excavators.
The exposed coal seams are carefully cleaned with Caterpillar D11R dozers and Caterpillar 24H graders before mining with Hitachi 2500 or Komatsu PC1600 hydraulic excavators in backhoe configuration.
Pit 1 is mining four seams of the Premier Coal Measures and will reach a maximum depth of 75m. Plans for a “deeps” option is under consideration, which may extend the depth to over 200m.
Pit 4 extracts eight seams from the Muja Coal Measures that occurs in a relatively steep synclinal structure where overburden and thicker interburden are benched. Pit 4 has a life of around eight to nine years and will eventually meet up with the Muja mine, operated by Griffin Coal, and will reach a maximum depth of some 200m.
The truck and shovel fleet consists of three P&H 2800 shovels, hydraulic excavators, fifteen 240t trucks, including Caterpillar 793Cs supplied with trays especially designed for Premier, and various ancillary mobile equipment.
Among the latest technology in use at the modern operation is a Modular Mining system that tracks all in-pit mining equipment via GPS and that shows in real-time where each load is travelling, when it is loaded, when it leaves and when it dumps.
Vulcan 3D geological and mine planning software is used to update the evolving mine plan. Conceptual plans span 30 years with detailed plans covering periods of five to 15 years.
A supporting Computer Aided Earthmoving System uses on-board computers, GPS software as well as data radios and receivers to transmit planning designs wirelessly to operators so they can see where they are relative to the design area, what the surface is and where the final design surface is located.
Processing
Because Collie coal is clean, the operation is in the very enviable position of not requiring a wash plant. Instead, the coal is simply crushed and screened in a modern, highly automated processing plant to ensure it is suitable for the customer.
Two people operate the plant, run by a Citect control system using Allen Bradley PLCs: one in the control room and other person loading trucks and trains, and collecting samples.
Coal from the mine is delivered to the 1200tph plant via a 500t-capacity bin and then conveyed on an apron feeder through a primary crusher where it is sized to less than 200mm. After screening and crushing to less than 50mm, the coal is conveyed to a transfer station where it is automatically sampled every two hours.
The sized coal is spread on to a 60,000t-capacity longitudinal stockpile in thin layers by a Malco stacker-reclaimer system.
This rail-mounted system stacks the coal in a chevron pattern, which results in a highly consistent coal quality when reclaimed.
An on-line ash analyser continuously monitors coal quality as the product is stockpiled.
Finally, the coal is delivered to the Collie and Muja power stations by overland conveyor systems maintained by power station maintenance staff. Other deliveries are made by rail or truck after loading at the train load-out system.
One train a day carrying around 1500t of coal makes the trip to the Kwinana power station on the coast just south of Perth.
Unlike most other mining operations around Australia, Premier does not face any labour or skills shortages; in fact, its fully unionised workforce is very stable at around 280 employees who have an average length of service of over 20 years. On top of this, Premier trains 16 apprentices at any one time.
While the operation has plenty of experienced labour, most who live in or around nearby Collie, it is not immune from industrial problems as highlighted earlier this year when maintenance personnel pulled a 9.5-week strike over a new enterprise agreement and rosters changes.
Meanwhile, while production over the past 10 years has increased five-fold, safety in that period has improved dramatically with LTIFR plummeting from a high of 38 in 1996 to zero in 2003.
This figure has crept above five this year, but Warrand says this is partly due to a number of sprains and muscular-skeletal problems, some of which are historical and relate to the average age of the workforce, which now stands at 49-years-old.
Another area of excellence for which the mine is increasingly being recognised is its rehabilitation work. The mine site office sports a host of trophies including a Golden Gecko for its outstanding environmental work (see box).
The mine’s environmental work goes beyond simply reclaiming the land to transforming rehabilitated areas into community assets like the impressive Lake Kepwari, formerly the Western-5B open cut mine.
Future favourable
Warrand says the recent 25-year Western Power contract was won not just on the quality, consistency and price of the product, but also on the operation’s reserves, new facilities and environmental record.
He says the contract allows Premier to upgrade some of its mobile equipment, which will include buying a Liebherr 994B excavator.
The contract win also relieves some of the competitive pressure from gas, which has increased significantly in recent years.
Warrand says coal’s percentage of power generation will continue to decline from its current share of around 42% because the next base load power station, due to come on stream in 2008, will run on gas. Both Wesfarmers and Griffin Coal put in bids, but lost out to gas.
In addition, one of the old generation units at the Muja power station will retire in April 2007, which will further shift the balance towards gas, and reduce the total amount of coal produced at Collie.
But Premier is not sitting on its hands. In another move to sure up its future, the operation is looking to produce commercial quantities of char through a process that will reduce the high 26% moisture content of Collie coal.
Warrand says little or no Collie coal has shipped overseas because it tends to spontaneously combust, which can make shipping problematic.
Warrand says the char process is one way to stabilise the coal and reduce the dust in order to make it attractive for export.
“The char also has a higher carbon content so it helps with some mineral processing kilns,” Warrand says.
Pending the successful study of market opportunities for char, a small R&D pilot plant will start up by the end of next year.
2-Dec-2005