Published in September 2006 Australian Longwall Magazine
The relatively new Broadmeadow mine, with just 12 months of longwall operating time under its belt, is already looking forward to its next stage of growth.
A major investment in a new $40 million high-capacity longwall system will enable the mine to widen the longwall face from 200 to 320 metres and enhance Broadmeadow and BHP Billiton Mitsubishi Alliance’s competitiveness in the international coking coal market.
The Broadmeadow punch longwall proposal was conceived as early as the 1990s when options were investigated to start an underground on the Goonyella open cut lease. During mine feasibility stage, a trial adit was driven from the southern end of Goonyella’s ramp 4 pit for a distance of 3.2 kilometres due east.
This trial mine reached a depth of 280 metres – giving BMA a clear insight into the expected mining conditions. A number of alternatives were considered for the mine layout including both conventional (north-south) and punch (east-west) options. According to senior geotechnical engineer Robert Coutts a (east-west) punch layout was selected as the preferred option because of the prevalence of (north-south) oriented thrust faults.
The faults are well-known at Broadmeadow thanks to a comprehensive 3D seismic program conducted prior to mining by Velseis. The seismic program located 100% of the faults greater than two metres in displacement.
In July 2003, the project was approved and subsequently Steve Rowland was appointed as the general manager. In June 2004, development had begun with the first longwall shear taken on the August 24, 2005.
The new mine is located 190 kilometers south west of Mackay in the western limb of Queensland’s Bowen Basin. Drawing on a large coal reserve, this year Broadmeadow will produce 3.9 million tonnes of high quality coking coal.
Last financial year, Broadmeadow produced 2.3Mt, 2Mt of which was supplied from the longwall. Rowland said a major milestone was 1,005,000 tonnes of mine site production was achieved in the fourth quarter, 941,000 tonnes of which was delivered from the longwall.
The longwall system currently consists of 116 DBT 2-leg roof supports with PM4 control system; DBT Electra 3000 shearer with total installed power of 1440Kw including 2 x 600Kw cutter motors and 100Kw haulage motors; and Joy AFC with TTT drives. The face utilises a uni-di cut and takes 50 minutes to traverse the face up and back.
The longwall was started using a mixture of new and old equipment from the redundant Kenmare mine at Blackwater. One of the challenges has been interfacing the Kenmare equipment (designed for a 3.8 metre seam) to the Goonyella middle seam (8 metres thick of which the mine extracts the basal 4.7m). The old equipment included items such as the AFC, BSL and the coal clearance system.
“Adapting equipment that was fit for purpose for another seam has been one of the biggest challenges - making it compatible with the technology that is out today,” Rowland said.
Broadmeadow were conscience during the design of the mine to minimise the impact of gas. This has meant that the design of the first panel was driven below a gas content level where drainage would be required. The next two panels have been limited by a 4-5m thrust fault. The long term mine plan will have panels reaching depths of up to 450 metres where gas drainage will be required in the future.
Due to the 4 metres of coal that is left behind in the goaf, it has been extremely important to have a robust monitoring system, Rowland said. The gas levels are monitored by real time, tube bundle system and an intensive bag sampling regime from both the tail gate and from various goaf seals.
In terms of ventilation, punch longwall mining requires a ventilation fan with a very wide range of duty points. Pressures at the start of the panel can be in the order of 3kPa, at take off the pressure can be as low as 300Pa. This range requires a custom built fan and drive combination.
The premium coal mined from Broadmeadow is conveyed 1.5 kilometres on belts to Goonyella Riverside mine and blended with the opencut coal to deliver the Goonyella product. The coal clearance system consists of maingate conveyors feeding into an inpit conveyor that transfer to a ramp conveyor - this lifts the coal from the pit floor to the surface stockpile.
Broadmeadow’s conveyor belts are rated at about 3,500t an hour. With the old Kenmare AFC – designed for a 3m seam - the mine can’t match the capacity of the belts, however with a new AFC and BSL the mine will add 2400Kw and have the capacity to match the belts. “If we had a more robust conveyor - we’d be cutting more,” Rowland said.
He said equipment availability on the longwall started out at about 23% but has averaged up towards 50% over the last couple of months; “a reasonable rate considering we went from producing about 200,000t a month to producing 400,000t a month”
At time of writing, Broadmeadow was not running at full capacity in the lead up to its first longwall move.
“I’ve got a young, inexperienced crew, who mostly will be coming into their first longwall move. We have been doing the risk assessments associated with the longwall move; with the state of the industry and the availability of contractors to assist with the longwall move - we’re going to probably end up moving the longwall ourselves.”
“I think there is latent capacity but until we get the fit for purpose gear we’re going to sit back and serve our customer - Goonyella Riverside,” Rowland said.
After the Broadmeadow team showed what they could do with old equipment in the first half of 2006, BMA approved in mid-July, a $40 million investment to widen the face to 320 metres.
The $40 million face expansion is expected to be delivered in March 2008. The expansion will require Broadmeadow to purchase an additional 120 metres of shields, a new AFC, BSL and upgrade the mine electrics.
“The shields are just a duplicate of what we’ve got but with some modifications. The AFC and BSL is being upgraded to probably one of the most powerful in the world right now.”
The AFC will be rated at 2400Kw on the 200m face and when the face is widened to 320m, it will add a further 1200Kw of power to...click here to read on.
