This is one of many projects mine personnel have been involved with against a backdrop of coping with frictional ignition problems. Between May 2002 and July 2003 the mine experienced four frictional ignitions on the longwall face. What the mine has done to tackle this issue is a fascinating story of dogged determination and rule-breaking thinking (the subject of an article in the June 2004 edition of Australia’s Longwalls.)

Along with an extensive range of controls and systems the mine has adopted a revolutionary approach to shearer drums and their configuration. Reverse RAC drums have been adopted with modified ventilation flow paths.

Sorting out the FI problem has been a major and ongoing challenge for the mine but has been conducted in parallel with other projects such as improving coal clearance infrastructure.

“Once we had overcome the FI problem we needed to take the longwall to its rated capacity and make sure we would not be hampered by infrastructure restrictions,” said operations manager Simon Burnett.

To achieve this, planned maintenance was increased from 12 hours per fortnight to 12 a week on the trunk conveyors. Contractors removed all clips from the system and replaced them with vulcanized splices. Suspect idlers are also being systematically weeded out.

“What it meant was that planned maintenance increased from 6 hours a week to 12 hours, but unplanned maintenance dropped significantly,” Burnett said.

“In July/August last year we were averaging 79% availability on trunk conveyors. This improved to an average 90% and is up at 95% for the last two months. The philosophy was simple. When we were free of FI constraints, and we could run the shearer at 14.5m/s the belts weren’t going to stop us,” Burnett said.

Burnett said the last 5% improvement is attributable to the installation of a Northern Conveyor Alliance dewatering station in February 2004. This was necessary because of the high volumes of water – up to 1,000 litres/minute– generated by the RAC drums.

It was observed that at 23 minute intervals, when the shearer was in the maingate and water volumes built up, a sloth of water and fines would hit the conveyor system and trip transfer points.

The dewatering stations allows longwall coal to travel through a transfer point with a tripper drive. The coal flows over an inclined screen which removes the water and fines. Coal that travels on to the prep plant is dry and has better piling characteristics and less fines.

At the moment mine personnel are cautiously optimistic about the future. “We have put a large number of controls in place to manage frictional ignitions but are fully aware that this work is far from completed and as such we need to continue the research and development work that commenced with previous mine owners MIM, and has continued under new owners Xstrata Coal,” Burnett said.