Published in September 2007 Australian Longwall Magazine
It is busy times at BHP Billiton Mitsubishi Alliance's Broadmeadow punch longwall. During June the mine, together with original equipment manufacturer DBT, completed the manufacture and minibuild of a new armoured face conveyor, beam stage loader, crusher, bootend and monorail system in Newcastle.
The new equipment is part of an $18 million longwall system replacement that will enable the mine to operate with best practice technology and fit-for-purpose equipment.
Located 190km southwest of Mackay in the western limb of Queensland's Bowen Basin, Broadmeadow has been using 'pre-loved' longwall equipment since its inception in 2005. The used equipment was acquired from the former Kenmare mine upon its closure. The Kenmare equipment was designed for that mine's conditions - in particular, a 3m cutting height.
"The application at Broadmeadow has the equipment operating at near to 5m cutting height and the 525kW AFC drives simply cannot cope with the instantaneous slabbing loading events that present from time to time," Broadmeadow engineering manager Steve Moore said.
Moore said the new equipment installed was not for the purpose of increasing the tonnes per hour capacity, but rather to provide equipment with sufficient power and mechanical strength to be able to cope with the challenges of application at Broadmeadow.
With the completion of longwall block 2 at the end of July, Broadmeadow took the opportunity to install the new equipment on longwall block 3, measuring the same width as previous blocks at 200m. The new equipment will feature two AFC drives and a 48mm chain with AFC capacity at around 3000 tonnes per hour.
The new equipment marks a number of Australian firsts. The DBT class 65 CSTs with 1200kW motors are the first of their type to be installed in Australia. Also for the first time, DBT's Powerchain will be installed on the BSL. DBT has specifically developed the Powerchain for higher-capacity face conveyors on longer faces and the BSL application will provide a lower risk testing ground before an AFC application is considered.
The new monorail system will make up an important part of the new look Broadmeadow. It will initially be supplied with two pressure lines, two return lines and two 3.3kV electrical feeder cables.
However, it has the upgrade capacity to increase three lines each if the mine subsequently decides to increase the face length further and/or increase the tonnes per hour capacity.
The monorail features a "rail under rail" materials handling system that will enable the Broadmeadow crew to take the "back breaking" out of manually handling components onto and off the face. Moore said the under-rail is slightly longer than a pillar so access to manoeuvre equipment to/from where it is needed is much easier than the existing system.
The next stage for Broadmeadow will be to widen the face from 200m out to 320m in a circa $40 million project. More equipment - specifically, the DBT roof supports and an extension for the AFC - is currently being manufactured in Germany. This equipment is due to arrive in Australia at the end of November.
The face extension equipment will be installed in early 2008 on longwall block 4. Longwall 4 will be the first of the extended width blocks at 320m. The AFC capacity for longwall 4 will continue in line with the previous block at circa 3000tph.
The AFC has been designed so that if it was ever required to be increased in length beyond 320m or if the instantaneous production capacity was required to be increased, the mine could install a third 1200kW AFC drive with minimal effort and cost.
Moore said a 320m face width was currently figured into the mine's plan until at least block 7. "We are presently working through a concept study to investigate the optimum face width and preliminary results indicate that 370m or 380m is feasible in the application at Broadmeadow at 3000tph," he said.
The mine's decision to go wide was justified against the reduced cost for development - in simple terms, the gate roads are now driven 320m apart instead of 200m, hence reducing development driveage and the cost of associated infrastructure over the life of mine.
While significant benefits can be gained out of a wider face, it is not without its challenges. "We believe one of the major challenges for the wider face will be to steer it, which is why we have embraced automation with great vigour," Moore said.
"We will install some new creep monitoring lasers on the new equipment for longwall 3 and these will provide accurate measurements on the location of the maingate within the gate road in real time to feed back into the automation software."
In terms of engineering controls, Moore said Broadmeadow had paid considerable attention to incorporating "hard barrier" safety controls for all of the routine operations and maintenance activities.
"For example, given the height of the BSL and dust scrubber, access to these items for cleaning sprays and filters can only be achieved by working at heights," he said.
"We have designed and installed a fold-down handrail and platform system that will ensure our people never have to take unnecessary risks in the normal operations and maintenance activities on the equipment.
"We have also installed some purpose-built structures, like laser mounting brackets, to enable the automation equipment to be properly integrated into the design rather than just a bolt-on afterthought."
Other safety initiatives include ensuring the hydraulic system is MDG41 compliant. "We have installed 'Tex-sleeving' and Pirtek 'Pircheck' hose restraints on all high pressure hoses and we have specifically designed hose/cable trays to ensure that all of the high pressure circuits are mechanically shielded from the workplace," Moore said.
"Couple all of this with up-to-date drawings, manuals and a state-of-the-art Link One package and we think we have a pretty safe longwall system. If you get the engineering right in the first place, then safety is far easier to manage on the operating face as far as we are concerned."
