Converting from bord and pillar operations to longwall has required a change in the working philosophy at Xstrata Coal's United mine in New South Wales. People management breakthroughs and automation technology have been keys to the mine's success.
Located 15km west of Singleton, the mine converted to longwall mining from bord and pillar operations in 2002. Now on its second longwall panel, the mine is churning out coal with development well ahead of budget.
The shift to longwall mining necessitated rigid reinforcement of the importance of standards and housekeeping, the straightness of roadways, floor horizon, roof bolting standards, roof monitoring and equipment maintenance. Extensive training was undertaken to help mine personnel appreciate the importance of understanding the equipment and systems involved. This is paying dividends in the form of current results.
"It was more important when we were a bord and pillar mine to cut coal than to drive the roadways straight," said operations manager, Jim Middleton.
Longwall mining takes place in the 3m-thick Woodlands Hill seam, directly underneath the active Wambo opencut mine. Blasting on the surface occasionally impacts the underground operation and workers are required to vacate production areas until blasting is completed, depending on where it occurs. From the underground point of view, surface gas wells drawing goaf gas have to be located with the opencut mining operations in mind. Despite the challenges, the relationship between the two mines was one of mutual co-operation, Middleton said.
United has just begun mining its second longwall after successfully completing the first panel change-out in about four weeks (from last coal to first coal cut). The longwall move was completed on schedule, within budget and, most importantly, without significant injury.
"To ensure success, we implemented a significant number of risk assessment processes involving supervisors, operators and staff," Middleton said.
Phil McNamara, mine manager and longwall superintendent, has been with the longwall project from specification stage, and has been the driving force behind the high standards of automation, workforce skills and systematic approach. The longwall consists of four-leg Joy supports, salvaged from the closed Teralba operation. Manufactured in the mid-1980s, the chocks underwent a full overhaul prior to commissioning and were fitted with the RS20 control system. The Joy 4LS5 shearer is equipped with Joy's JNA electrics and horizon control system.
Coal is cut at a height of 2.8-3.2m using bi-di, conventional operation. Cutting coal using an automation system has been a major contributor to keeping control of the horizon, and since the start of LW1 horizon control and face automation had been used on every shear, Middleton said.
The shearer operator, who remains on the maingate side of the chock advance, drives the leading drum in manual from tailgate to maingate, which stores the roof horizon in the shearer's internal memory. The trailing drum is then referenced to the lead drum on this tailgate to maingate shear to cut the full seam. The shearer returns to the tailgate on complete “memory cut”, allowing the operator to remain on the fresh-air side of the advancing supports.
Middleton said major benefits were that the operator was kept out of the dust, horizon control was excellent and face equipment damage was minimised. In addition, preparation plant yield was 3% over budget due to less stone dilution in the coal.
The Joy AFC has two 522kW two-speed drives and regularly hauls more than 2200 tonnes per hour. The longwall belt is only 1200mm wide, and has a lift of 120m over the 3.1km length. Two megawatts of installed power are transmitted via a tripper and host using VVVF drives at 4.5m per second. The longwall belt is normally well loaded and the belt is extensively protected from damage via tracking protection and rip/tear at the boot-end, tripper, drivehead and jib.
Bob Dixon, maintenance superintendent, has overseen a change in focus at United to a systematic, consistent engineering system, and an overhaul of the electrics, air, water, conveyors and mobile equipment infrastructure upgrade procedures.
"Engineering availabilities have been more than satisfactory as a result of the approach of his (Dixon's) engineering group," Middleton said.
The mine is currently on a five-day week with three 8.5-hour shifts a day. Development units have been performing particularly well, averaging 240m per week, with one Joy 12CM12 continuous miner. The mine has progressively increased its pillar length from 60m to 90m, and then to 102m.
The importance of development is reflected in the bonus system, half of which is paid on development performance. To date, development float has stayed at about three months.
United's gas make is about 3000 litres per second out of the mine, managed by a combination of goaf drainage and ventilation. Total longwall ventilation is 90 cubic metres per second and total mine ventilation is 230cu.m/s. The mine is investigating gas utilisation methods that might include co-generation using gas and waste coal.
United's average weekly output is roughly 70,000-80,000t, including about 1000m per month of development from a single panel. "For an old set of gear to regularly get that kind of tonnage is pretty reasonable on a five-day week, and it's a real credit to the blokes at the face and the people that manage the operation," Middleton said. Published in Australia's Longwalls, September edition.
