Published in March 2006 Australian Longwall Magazine

Theories on how to tame the seam abound but no mine has yet succeeded in consistently teasing big volumes of coal out of the vast thick seam resource.

Now, following years of grappling with a raft of strata, Anglo Coal’s Moranbah North mine may just have paid its dues as output settles back to respectable tonnages.

Longwall mining started in February 1999, a year in which the mine produced just over 4 million tonnes. By 2004 output had declined to a meagre 2Mt after mining ground to an eight-month halt following a tailgate fall. The ventilation path was lost and the mine eventually resorted to driving a new tailgate to recover the remaining face gear. Close to 500m of retreat was lost.

Some in the industry questioned the mine’s longevity as workforce morale dipped and turnover grew.

Since then however a gradual renaissance has been occurring at the operation as stability returns, along with coal flow. Mining manager Gareth Jones, an outspoken and focused individual, has been at the operation for just over a year and is overseeing the operation’s recovery, though there remain many challenges.

In 2005 the mine produced 4.7Mt of coal and is expected to produce around 5Mt in 2006. The current life-of-mine plan extends to 2026 at annual rates of between 5Mt and 6Mt.

In January, the mine pulled off something of a feat under Jones’ guidance with the extension of the current face width from 165m to 260m. Amazingly, this was done mid-panel.

A pre-driven roadway was driven ahead of the advancing longwall, into which 54 roof supports were installed and pressurised to the roof.

“Then what you have to do is come along with the longwall like a lunar module and dock the two ends of the face,” Jones said.

In the lead-up to the docking a few cyclical loading events and a cavity threatened the outcome but in the end the three day process went smoothly with the two face-ends docking within 30mm accuracy, far better than the 300mm allowed in the plan. A one chock space between the two face-ends was later filled with a spare chock enabling mining to resume at the 260m width.

Jones attributes the success of the plan to good management, a bit of luck and the ability of the workforce that drove the longwall into position; though he says he wouldn’t like to do it again in a hurry.

The face extension was undertaken as an alliance contract with contracting company SBD Services. Jones is a fan of alliance contracts because their structure allows mine management to retain control over a job.

Several contracting companies are in fact currently working at the mine doing a range of jobs including conducting primary driveage, installing secondary support and installing ventilation structure.

Contractor Walter Mining is carrying out two contract jobs at the mine. One is the driveage of mains development using an ABM20 supplied by the mine, while the second is first workings bord and pillar mining in the northern part of the lease where the resource is too shallow for longwall techniques. In 2005 bord and pillar production, introduced to supplement longwall output, was just short of 500,000t.

The mine recently ordered a new Joy 12CM12-D miner configured as a place change machine to supplement development gear. It includes a 38-inch wide conveyor, Joy’s new OPTIDRIVE AC traction, and JNAII control/radio.

Other contractors include Mackay-based Mastermyne doing specialist drilling and blasting work and Coalroc doing outbye services.

Mining of the current panel LW6 concludes in about July/August with the face length to be extended out to 300m in the next panel LW7. Thereafter mining will remove four 1900m long panels to the north of the current mains, which run to the northern boundary of the mine’s lease.

A significant aspect in Jones’ management philosophy is rigorous maintenance regimes that are strictly adhered to. He will not for instance delay a maintenance day if the face comes under a cavity – a typical occurrence at the mine (see geotechnical article).

“Lots of operators don’t want to stop when they have a cavity. You can get into the vicious cycle where if you’re not producing enough coal people want to keep going and cancel the maintenance,” he said.

“I don’t believe Australia does enough predictive maintenance and we also tend to use equipment for far too long.”

The mine is currently focusing on a strategy to simplify the existing conveyor belt and structure, said engineering superintendent Jason Cleary. Work is currently upgrading and simplifying the electrics on the conveyor and at the next longwall move the drift conveyor belting is due to be changed.

With section belts 1800mm wide sheer manhandling of the gear is a daily challenge for beltmen.

Two new Joy BSLs are being ordered as well as two new pump stations and by the end of 2007 a new shearer is on the cards. Sometime this year the mine plans to order a new set of roof supports but the exact timing on this is as yet unclear. With the current global demand for equipment delivery ex-OEM is currently 18 months to two years from date of order.

With two sets of chocks the mine will be able to pre-install each panel and have a walk-on, walk-off mining capacity.

The mine bought an additional 25 new Joy shields last year, which are currently installed...click here to read on.