Overview
The mine is located 105 km southeast of Gillette, Wyoming, U.S.A. and it
is considered to be the world's largest surface-strip operation.
The North Antelope Rochelle Mine began operation in 1983 and produces
the lowest sulfur coal in the United States - 0.2% sulfur at a heat value
ranging from 8,600 to 8,800 Btu per pound. The operation employs three
draglines along with five overburden truck-and-shovel fleets. The coal is
hauled by truck to one of three hoppers at the complex, where it is crushed
and ultimately conveyed to 15,000-ton silos for loadout on unit trains.
In 2011, North Antelope Rochelle mine of Wyoming, USA shipped record
volumes as the largest and most productive coal mine in the world.
The operation employs 1,080 people and annually provides the local
economy with $63 million in wages and benefits.
Location
Wyoming, at the big flat river' in Delaware language, is the tenth
largest state in the U.S. It is sparsely populated.
The mine is located some 65 mile southeast of the 20,000 people city of
Gilette, which is the county seat of the Campbell County. Because it is
situated in the middle of the coal, coalbed methane and oil richPowderRiver
Basinthe city proudly calls itself the 'Energy Capital of the Nation'. It
boasts a newspaper, one local television station and an airport.
Geology
The Powder River Basin is sandwiched in between the Black Hills and the
Big Horns Mountains and is a result of their uplifting, an event that ended
45 million years ago. At that time the region indulged in a rainy
subtropical climate that favored the development of large palm trees on the
land and crocodiles in very large swamps and lakes that riddled the flat
basin floor.
Over the next 25 million years rivers and heavy tropical rains
transported and deposited huge amounts of dead vegetation in the swamps,
thus creating thick layers of extremely pure peat. In time the peat got
buried under subsequent sediments and by being subjected to high pressure
and temperature was transformed into one of the world's lowest ash content
coals - the Fort Union and Wasatch Formations. During the last million
years the sedimentary layers lying on top of the coal seams were eroded
away thus bringing the coal close to the surface.
The North Antelope Rochelle mine exploits the Wyodak-Anderson coal seam,
which ranges from 60 to 80 feet (9.1 m to 24.4 m) thick and lies from 50 to
350 feet (15.24 m to 107 m) below the surface in the reserve area.
The sub-bituminous coal averages approximately 8,800 Btu/lb, 4.44
percent ash, and 0.20 percent sulfur, making North Antelope Rochelle coal
the cleanest in the United States.
Remaining coal reserves dedicated to the mine cover nearly 22,000 acres
(8,900 ha) with about 1.2 billion tons of recoverable coal.
Mining & Operation
The North Antelope Rochelle surface strip mine is the world's largest
and the most productive mine in North America.
The North Antelope Mine began operation in 1983; the adjacent Rochelle
Mine began production in 1985. In 1999 the two mines were combined, thus
becoming the largest coal mining operation in theUnited States.
The mine is a conventional truck and shovel mining operation employing
three 60 cubic yard draglines along with five overburden truck-and-shovel
fleets (80-yard shovels, two 240-ton and three 190-ton trucks) for
overburden removal.
The overburden thickness is 150 feet resulting in a stripping ratio of
2.5:1.
Cast blasting is the method of choice and it is used to remove
overburden from above the coal seam and move it into a previously mined
pit. Some 25 to 50 percent of overburden could be moved without involving
any mining equipment.
The mine operates on two 12-hour shifts per day, 365 days per
year.
Processing
Coal is sourced from four pits and is trucked to one of the three
hoppers, where it is crushed according to specifications (2 inch) and
conveyed to one of the five over the track 15,000 t silos for loadout on
unit trains.
The silos, plus a 55,000-ton slot storage facility, are able to load
more than 150 cars per unit train at 6,600 tons per hour rate. A totally
computerized batch weigh bin system is also in place.
Two concentric loop tracks connect with the Burlington Northern Santa Fe
and Union Pacific railroads joint trackage.
New blending and loading facilities were also completed in the first
half of 2008. These improvements were designed to lower the cost structure
by reducing reliance on truck fleets, while also increasing capacity.
The mine produces low-sulfur, sub-bituminous coal suitable for power
generation without any preparation other than crushing.
Coal from the mine is delivered to 36 customers that own 60 power plants
throughout U. S.
