Geology Reference
In-Depth Information
Coal-Mining Machines
Surface Coal Mining
T
he ever-expanding surface mining industry and dramatic increases in productivity have been the direct result of
increase in size and efficiency of the equipment used. Surface mining operations employ equipment similar to that
used in the construction industry. This includes bulldozers, drilling machines, front-end loaders, hydraulic back-
hoes, giant draglines, power shovels, bucket wheel excavators, scrapers, and off-road haulage trucks.
Bulldozers are self-propelled track-mounted machines equipped with a large steel blade attached to their front. Bulldozers
are used to push, level, and grade soil and rock over short distances during the mining and reclamation phase of an
operation.
Borehole drilling machines are used to drill numerous boreholes through the overburden to load with explosives
which loosen the overlying rock to facilitate excavation. Drilling machines are diesel or electrically powered.
Front-end loaders are rubber tired tractors equippedwith a large bucket that is used to load soil, rock, and coal into trucks
to be transported to a spoil disposal area or to a coal preparation plant for further processing. Hydraulic backhoes are
equipped with a bucket at the end of a large boom and are used for a multitude of tasks in a surface mining pit.
Draglines are machines that have a very large bucket hanging by a cable from a long boom attached to the front of the
machine, as shown in the introductory figure of this section. The bucket is cast a considerable distance from the dragline
by swinging and dropping the bucket in one motion. The bucket is filled with overburden by retracting the cable which
pulls the bucket back towards the dragline. The filled bucket is then lifted and rotated to the disposal area and dumped by
lifting the rear of the bucket, again by retracting cables. Draglines can be giant mining machines such as the
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weighing in at over 13 000 tons with a bucket capacity of 220 cubic yards or 325 tons (American Electric
Power, 2008). These machines efficiently excavate and cast overburden in one cyclical motion from a location on the
top of the overburden. The large draglines are called walking draglines because they are moved by being lifted on large
pads and moved forward by rotating large cams. Smaller draglines can move on crawler tracks.
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The development of steam power shovels was the primary technology that created the large-scale surface mining
industry. The steam power shovel loaded the overburden into the off road haulage trucks to be transported to a spoil
disposal site. The steam power shovel has been replaced with large electric or diesel powered shovels.
Bucket-wheel excavators are large excavating machines equipped with a long boom on which is mounted a rotating
wheel encircled with buckets along its outer edge. The boom is directed into the material to be excavated and the
buckets rotate into the overburden scooping up the material which is then dumped onto a conveyor system for
transport to a disposal site. Bucket-wheel excavators are best suited to removing unconsolidated overburden that
does not contain large rocks or require blasting.
Scrapers are self-propelled rubber tired vehicles that can be used to remove and transport unconsolidated overburden. They
are self-loading by pushing forward and lowering a metal plate to scrape and lift dry-unconsolidated overburden into a
hopper located in the center of the vehicle. After hauling, the overburden is unloaded by opening the bottom of the hopper
while moving forward and using gravity to place a thin layer of overburden at the disposal site or an area being restored.
Off-road haulage trucks are used to transport the overburden to the designated disposal sites. The capacity and size
of the off-road haulage trucks increased concurrently with the development of high-capacity power shovels.
Today
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s modern off-road haulage trucks are truly gigantic, some capable of carrying loads of 300 tons or more.
Underground Coal Mining
Unlike machines used in surface mining, machines used to mine coal in the underground are specifically designed
for that single purpose. Such machines include continuous miners equipped with tungsten carbide cutting teeth that
rip the coal from the working face to form the rooms in room-and-pillar mining. Coal shearing machines and
hydraulically operated roof support systems are used in the longwall setting. In addition, ventilation equipment,
rock dusters, roof bolters, shuttle cars, personnel vehicles, scoops, underground rail, coal conveying, and water
pumping systems are employed in underground mining.