Back on track

IT’S been more than eight months since New South Wales mining group Centennial Coal took over the Tahmoor longwall mine. Now the mine is back in the black.
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Staff Reporter

Published in September 2005 Australian Longwall Magazine(updated Dec 2005)


In the lead-up to the buy-out of the company’s owner Austral, uncertainty over the mine’s future and ongoing technical problems conspired to result in frequent stoppages, poor productivity and an unmotivated workforce.


With the bulk of these issues now behind it, Tahmoor has turned the corner under the control of Centennial, which now owns approximately 86% of Austral.


Since Centennial took control of the operation in April, it has put in place an array of changes to lift productivity and get the mine back into profit.


Addressing various engineering issues with the longwall equipment, changing the management and shift structure, re-designing the ventilation plan, and increasing development are all well underway.


In 2005-06 the mine will produce 2.1 million tonnes of coking coal. While this was down on the ambitious targets set by the previous owners, the new one was more realistic, said Centennial’s general manager (Southern Operations) Gavin Taylor, particularly given that this fiscal year will see three longwall moves.


Production will ramp up steadily to 2.7Mt next year and will reach maximum expected output of 3.5Mt the year after.


Taylor said a lot had been achieved in the months since Centennial took over, with the mine making a profit in the first two full months of operations. Tahmoor produced 531,000t ROM during the June quarter .


The major technical challenge facing new management was the mine’s ventilation system, which was inadequate, causing many gas-related stoppages. The relatively lower roadways, at a cutting height of 2.6m the seam section on average is 2.2m making Tahmoor a thin-seam operation) and smaller cross-sectional areas contribute to generally high resistances overall.


The bottom line: not enough air getting to working faces to dilute gas adequately. Technical services manager Peter Robbins said the mine had developed a three stage approach to deal with the problem. Short term steps are well in hand to minimise leakage by upgrading stoppings and seals, and reducing stowage to lower resistance. Medium-term, a new high pressure low volume fan will be installed in January, 2006 with the longer term plan being new fans once the new return airways have been driven. The short term remedial work has already seen an increase in face quantities of some 271%.


Existing fans operate at pressures of around 2.6 kilopascals, delivering around 38 cubic metres of air onto the longwall face. This needs to at least double and the new fans will, at 5 kPa and 500 cums more than adequately meet that requirement.


Tahmoor’s gas is largely carbon monoxide, making the mine susceptible to outbursts on development. Gas does not liberate readily from the coal in some areas and is described as tight. This is mainly related to the presence of calcite in the coal cleats, as well as geological features that exist in the immediate mining lease area, causing horizontal stress-related deformation of the coal itself. Between normal-to-drain coal and difficult-to-drain coal, permeability differed by three to one, said the mine’s geotechnical engineer Dieter Bruggemann. At present, Bruggermann is completing a PhD at Wollongong University related to seam gas liberation. The aim of his research is to develop a predictive tool for gas liberation based on a set of indices.


Tahmoor has an extensive in-house gas drainage program. This year alone the mine’s drilling crew will drill 132km of in-seam gas drainage holes. A further 28km will be drilled into seams under the future blocks as gas permeates up into the working face from underlying seams.


Drilling is carried out ahead of development mining with the aim of reducing in-seam gas from around 13 cubic metres per tonne to around 3.5cu.m/t.


Tahmoor was one of the first operations to acquire Advanced Mining Technologies’ (AMT’) new Drill Guidance System (DGS) for coal seam degasification, the latest upgrade of Directional Drill Monitor (DDM MECCA).


Turning to the management structure Taylor said what was in place before was not conducive to efficiency. A flatter structure had been introduced which encouraged greater information flow and higher levels of accountability, he said.


The roster was changed from a four shift per day, seven-hour roster to a three shift per day, eight-hour system, with the ability to hot seat change with a voluntary one hour “tweenie”. These changes are already delivering dividends.


Access into the mine is via a ramp on a dolly car. It takes roughly seven minutes to reach pit bottom 400m below the surface.


The mine’s lost time injury frequency rate is just below the state’s average figures, but Taylor is determined to get these even lower.


“We need to refocus our efforts and continue driving injury frequency rates down,” he said.


A number of safety initiatives are underway under the direction of the mine’s occupational health and safety committee, which Taylor says is excellent.


“I can’t speak highly enough of those guys and the local check inspector Greg Saunders. With their enthusiasm, we will turn safety around.”


Change management group risk-e has also been commissioned to lead a safety culture change process.


The approach, dubbed Leading with Safety, aims firstly to continuously reduce injuries, but also, through safety, involve the workforce in performance improvement throughout the business.


Risk-e methods have been used at a number of underground coal mines, including Centennial’s Clarence Colliery and the BHP Billiton operations in the Illawarra. Typically, the number of people injured at these sites has halved during the first two years of implementation.


Like every other Australian mine, manpower shortages at Tahmoor are an ongoing issue. At Tahmoor three miners are currently studying for undermanager qualifications, but Taylor remains particularly concerned about the shortage of second-class ticket holders in the industry in general.


The current longwall block, 23A, is a mere 800m long. This is because of the presence of a very hard igneous intrusion that has a dyke associated with it, which exists between LW23A and 23B. The longwall will stop short of the igneous intrusion and the equipment relocated to panel 23B on the other side.


Mining near the Victoria Park zone has here to read on.

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