Published in the May 2007 American Longwall Magazine
Mining commenced at the Twentymile mine near Steamboat Springs, Colorado – about three hours northeast of Denver – in 1983 using continuous miner development sections. Longwalling began six years later, in December 1989.
After initially taking coal from the longwall at the mine’s West Mine District, work efforts switched to the East Mine District in 1996, and then to its current North District operations. Over that time, according to officials, the total linear roadway with bleeders, main development and crosscuts has equated to a staggering 275 miles, a figure that has grown even more since it was initially computed in 2002, and is held firm with more than 17,000 pillars.
Workers are carried to active sections using a commonplace western US find, diesel trucks, in a trip clocking in at about 20 minutes. Overburden ranges between 1200 and 1650 feet, making both travel and ground control issues minimized.
Once at the longwall face, even the most height-inclined individual would find it comfortable to work, as the company cuts the 9.5ft Wadge seam of the Yampa coal field. The longwall retreats an average 2500ft monthly and transports some 35,000 tons daily from its panels measuring an average 10,000ft long and 1000ft wide. Seven individuals work the longwall face on any given shift.
Coal is swept from the face using a DBT EL3000 shearer with a 78in drum diameter and 1m web onto a brand-new 1000ft face conveyor with 42mm chain. Officials for the company said the system employs DBT series 45 CST gearboxes and has three new motors running 1250hp each.
Room for movement was a consideration with the new AFC, according to mine manager Mike Ludlow. The new equipment is intended to provide upgraded drive frames with solid sprockets, which will allow 48mm chain use as well as potentially increased horsepower.
A longwall move was just completed at Twentymile in early February. Moves at the mine typically take 16 days, and the face is bolted with 6ft resin bolts.
The move into the 26th panel in the 20 right section was not just any move, however – it stepped Twentymile into its prime with new equipment that is intended to encompass greater power, higher capacities, and overall more efficient operation for the mine.
A new AFC system was the heart of that move, as were new shields – this time designed for an impressive 65,000 cycle life. With an increased width of 2.05m, crews and planners found that 24 fewer shields were needed than at the most recent face (150 versus 174 including gate shields).
Shield speed was also upped hydraulically and electronically, aimed at allowing a more rapid advance and more efficient operation of the face as a whole.
Also new were the stageloader and crusher: the 1732mm stageloader is intended to provide a higher installed horsepower, nearly double the weight and significantly increased capacity. It is also notably longer and wider than the previous unit.
The crusher, a DBT 2000mm, almost doubled its installed horsepower with the new machine and the mine transitioned from a direct drive to a belt drive system. Ludlow noted that an existing face conveyor motor will be incorporated for the purpose of powering the crusher.
Other new items it incorporated with the new panel were emulsion pumps and a new electrical system. Twentymile did choose to re-use a few items from the component set, including the dust scrubbers, monorail and tailpiece for the face.
Twentymile mine has three active sections that are mines using Joy 12CM12 miners. Gate road entries are on 55 and 135ft centers with crosscuts and 250 and 125ft centers. Six-foot resin bolts are installed using a Fletcher dual boom bolter in a pattern of four to six per row with roof meshing.
Coal, extracted from the sections at a rate of about 175ft per shift, is carried away on 10SC 32 shuttlecars, and Stamler feeder breakers help prepare the output for their conveyor trip.
The conveying system encompasses 12 miles of Continental Conveyor beltline from active sections to surface. The main line conveyor system is made up of 72in belts that transport coal at a rate of 7500tph to an underground 350t bunker.
From there, the coal then is conveyed to the surface at 5500tph on a 60in conveyor line. “The total system has over 36,000hp to accomplish this task,” Ludlow said.
With Twentymile being a 24/7 operation, one may think maintenance at the 400-worker complex would be a challenge. According to Ludlow, both preventive and predictive maintenance is practiced.
Miners at the Colorado mine champion working 40-hour weeks made up of 10-hour shifts to bring output to its many customers, which is primarily delivered via a very busy rail and truck system beginning just behind the portal office. Management estimates that greater than 90% of the coal being shipped out is raw output.
“Twentymile is on the Union Pacific Railroad line and daily loads two to three unit trains, each 100 to 115 cars long, carrying 11,000t of coal each trip to customers in nearby Colorado communities and points as far away as Mississippi,” parent company Peabody said.
Most miners have pride in their work and in their mine, and workers at Twentymile certainly maintain that attitude. As the mine’s front gate welcoming sign reads, “A world-class mine…Exceptional people”, and that is carried throughout the operation, from production to safety to a teamwork mentality.
“Twentymile’s success can be attributed to the dedication and innovation of our employees,” said Ludlow of the mine team. “I am constantly amazed at the creativity of our employees.
“No mater how challenging a task is, our employees find ways of making it easier, faster and safer.”
In fact, Twentymile is ramping up to 12 million tons of annual production by next year to serve growing customer demand, and the mine is well on its way toward that goal. In March 2007 alone, more than 1.04Mt was mined towards that target.
Additionally, with more than 80Mt remaining on its reserve base and a constant eye toward growth, this mine has and will keep its hold on the western Colorado landscape for a long time to come.
