Metropolitan, located north of Wollongong in NSW, has been in production since 1888 with longwall mining beginning in 1995. The mine has an estimated total of 93 Mt Bulli seam coal, ranging from 2.8m-3.5m in thickness. The current lease contains about 43 Mt of saleable recoverable coal, with possibly 50 longwall blocks to be extracted.
In the short-term mining will target longwall panels 8-14, which contain an estimated 6.8Mt of ROM coal.
The mine's longwall mining has been disrupted because of the existence of the sill, discovered during development of the first block in 1995. This caused blocks to be shortened from around 1560m to 700m. The sill has now reduced to a soft dyke around 0.5m thick and current longwall operations (block 8) have been gradually extended from 1350m in block 6 to 1600m in block 8.
The mine has just extended LW8 by 18m (to 134m) using Shoshone 1.75m shields overhauled by DBT and purchased from the Shoshone mine in USA. The mine's original supports are 1500mm wide, which meant AFC pans had to be altered to accommodate the bigger dimensions. Other changes included modifications to yield valves and ram strokes.
The use of similar configuration supports - DBT, two leg, pontoon with PM4 control - made the compatibility of the original supports with the Shoshone supports a very successful project. The new equipment was performing well and delivering record production rates. The mine is currently producing at the rate of 1.4 Mtpa.
Planning is now underway to further extend the face to 158m, possibly for LW 11 in 2004. This is the maximum length for a single motor drive face and the mine's geotechnical restraints, which include subsidence problems.
The mine's major limiting factor on production is the belt capacity and outdated conveyor system. The AFC is 980mm with twin 108x32 mm chain, with a capacity of 1500 t/h. There are 15 belts in the system, with a theoretical maximum tonnage of 7600 tonne per day at 98% availability.
Continual upgrades to the belt system are planned for the next few years and the mine is currently reviewing the efficiencies of its underground conveying system to look at reducing risk.
On the longwall face, slabbing of the coal has been a major problem since the longwall started, not just for blockages but for the potential of injuring workers on the face. The mine recently introduced the Half Web system of cutting to reduce worker exposure to slabbing. This has given the benefits of a production increase of 15-20%, regulated coal flow on the belts and gave management an alternative option for face control.
Development of roadways is undertaken by cut and flit methods using a Dash 3 narrow head low-profile radio controlled miner and Fletcher Bolter for the main development unit. A 12CM12 Joy continuous miner supported by a shuttle care and Klockner feeder constitutes the second development unit used on a one shift per day basis. Development crews work 17 shifts per week in longwall gateroad development, achieving 180m-240m advance per week.
* Alan Phillips presented a case study on Metropolitan at the AJM Longwall Mining Summit in Yeppoon in March.
