Speaking at the IIR LONGWALL 2002 conference in NSW last year Bill Stewart, maintenance manager of Enlow Fork, emphasised the importance of eliminating downtime in coal clearance systems.

“We can’t sacrifice maintenance to keep production levels high,” Stewart said. “Elimination of belt downtime was an important factor for our maintenance team and mine management.”

In fact Stewart views belt drives as being as important as ventilation fans – without them you can’t run the mine he says.

Opened in 1990, Enlow Fork, along with the massive Bailey mine, is one of Consol Energy’s top producers. By 1994 Enlow mine had become the highest producing mine in the US with a clean coal production of 7.4M tons.

“This is a record we continued to hold and improve on for seven years until the year 2001 when we produced 10,326,124 tons and Bailey produced 10,327,277 tons,” Stewart said.

In 2001 the mine produced 10,326,124 tons and in 2002 is expected to have mined between 9.5 million and 9.7 million clean tons. This brings the total coal mined over 13 years to 97+ million tons.

Stewart said from the beginning, continuous availability on belts was crucial. Initially each of the two longwalls was serviced by its own 60-inch belt system, dumping onto a 72-inch rope belt at a 16 degree angle for 2,500 feet driven by two 2,500 hp motors. The system serviced two longwalls each with a throughput of 2,500 tons per hour on 9,000 feet by 900 feet panels.

In 1998 the decision was made to increase the panel length and width to 12,000 feet by 1,100 feet and new longwalls were bought with a throughput of 3,500 tons per hour.

To accommodate the increase in output without replacing miles of belt and structure a 5,000 ton underground bunker was installed to allow outbye belts to be kept in place. The bunker serves as a buffer with a continuous output of 3,000- 4,000 tons per hour.

Bunker inby belts are controlled by variable frequency drives, as are longwall and panel development belts, providing the ability to run belts at any speed. Panel development belts can be run at 30 Hz and longwall panel belts at 115% or 70 Hz.

To keep belt availability high and to ultimately increase production the mine is also exploring several new technologies.

A fiber-optic network throughout the mine monitors belt drives in real time at six central locations. Most recently installed in a belt scan system that takes continuous digital images of every mechanical splice in the 72-inch inbye belts to allow repairs to be preplanned. The information is sent via the fiber-optic system to four continuously manned monitors.

“Developed in partnership with Carnegie Mellon University, we hope to be able in the near future to see our belts while they are running at speeds of 800 to 1,000 feet a minute.

“Imagine the gains in not having to repair broken belts – only plan repairs – and also use that time in working sections for preventive maintenance,” Stewart said.

Enlow Fork spends about US$100 per day on preventive maintenance on belts, money well spent according to Stewart. The mine has two foremen and 15 beltmen working per shift.

But as Stewart commented: “Saving one motor, one gearbox, or preventing bearing failure during production time – how much did you save? What is three hours of longwall and miner production worth to you?”