Thin-seam longwall mining can be tough. But try telling that to management and mine workers at the American Eagle operation near Charleston in West Virginia. They'll probably say it's not so bad.
Since starting production in December 2001, the mine has set new benchmarks for producing coal from a thin seam. In the 12 months to December 2002, American Eagle produced 3.295 million clean tons from its 127cm seam – or an impressive 6Mt of raw coal.
The achievement is all the more notable given that it took only 15 months from the time the decision was made to mine to commencement of the longwall. Output per employee averages about 46,000 raw tons per man year for the 120 employees, many of whom had no coal mining experience when mining started.
Operated by contractor Speed Mining, the mine is owned by Arc Light Energy Partner Fund ILP. The principal seam mined, the Eagle seam, has an average height of 167cm, of which 127cm is taken out by the longwall.
Speaking at a recent longwall mining conference in Pittsburgh, Pennsylvania, Speed Mining president Pete Hendrick outlined several reasons for the mine’s success. These included good management and a strong labour team, good equipment and maintenance practices and the use of downtime analysis. “The thing I am most proud of is my workforce,” Hendrick told Longwall USA delegates.
A strong sense of “family” was apparent among the mine’s workforce and the management structure was extremely flat. The mine operates on three nine-hour shifts per day, 5.5 days a week with maintenance activities carried out during two of those shifts per week.
Current longwall panels are 306m wide and about 2622m long. On the longwall an average shift can complete up to 12 passes and about 12.2m of retreat, at shearer speeds of 10.7-12.2m a minute. Despite the fact the shearer drivers did not use automation to control the roof horizon, conditions on the face were excellent, Hendrick said.
Manning on the longwall is typically seven people, including a foreman, a chief electrician, an electrician/mechanic, two shearer operators, headgate operator, miner operator and one “utility” miner. Crews are multi-skilled. Being a union-free operation also means the mine has been able to implement a hot-seat change on the longwall. It takes workers nine hours to get from portal to portal, which results in eight hours at the face.
The longwall system was supplied by DBT America and includes two-leg, 1.75m-wide roof supports with 400mm-diameter legs, yielding at 1270t. The PF-5 pans are 1m wide with a 50mm top deck thickness and a 48mm face chain with four-link flight bar spacing. The supports incorporate an additional feature to assist with providing roof support during longwall change-outs. Each canopy has two holes providing access for bolting through directly into the roof. This means mesh or ropes aren't needed when pulling chocks.
The mine has a spare face conveyor, bulk stage loader, shearer and monorail which allows the next panel to be pre-installed ahead of changeouts. The monorail design allows pipe moves to be carried out in conjunction with setting shearer bits.
Longwall supports are supplied with fluid by four Hauhinco 364-litres-per-minute pumps, powered by 224kW 4160v Reliance motors. An extra one is on standby for on-shift maintenance.
An interesting aspect of the hydraulic supply system is the use of German manufacturer Hamacher’s high-pressure flexible steel pipes instead of hoses. Made from galvanised steel with screw-type couplings, the system was chosen for its longevity, the ability to re-use the pipe, and reduced pressure drop with flow, said Charlie Leonard, mine superintendent. The mine is currently mining its fourth panel with its second set of Hamacher pipes.
The mine uses a Joy 7LS-1-A shearer which has proven very reliable, Leonard said. Shearer availability averaged 96%.
The conveyor system was supplied by Continental Conveyor and incorporates 1.5m trunk belts. Three 895kW, 4160v Moeller electric motors provide power to the AFC. Two of the motors are located on the headgate and one on the tailgate to provide load-sharing functions related to input and output speeds of the chain. The 1190mm stageloader and crusher are powered by 223.8kW 4160v Moeller motors.
Nine transfer points on the plus-6100m belt system are camera monitored 24 hours per day for blockages. Belts are also PLC controlled, allowing production to be monitored and providing the ability to restart belts from the surface.
Entry development averages more than 61m per nine-hour shift and is driven by two Joy 1415 continuous miners and three 10SC shuttlecars. Crews cut coal for two shifts per day and spend the third shift carrying out routine maintenance and performing belt moves. All maintenance activities are co-ordinated by maintenance foreman Harry Fortner, who works very closely with original equipment manufacturer service engineers. He said shearer fluids were changed weekly and fluids in all other gearboxes and drives were sampled monthly. Emulsion filters were changed weekly.
All operators and crews fed information into a whiteboard system, which was co-ordinated and tracked by Fortner. In addition, every shift noted all causes of downtime - a typical shift report for example, listed 30 minutes for structural downtime and five minutes for cable control.
While the mine’s surface facilities are very lean, housekeeping standards underground are very high and a sense of pride is clearly evident among the workforce.
The mine has a 30Mt reserve remaining, potentially taking it through to about 2010. Further work is underway to extend the reserve.
