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Auger Mining

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Mining Processes

Auger mining is a surface mining technique used to recover additional coal from a seam located behind a highwall produced either by stripping or open-pit mining. Auger mining is especially employed when contour strip mining has been exhausted and the removal of overburden to access additional coal no longer becomes economically feasible. Auger mining can also be utilized in underground mining when faulty or poor roof conditions are present or other problems preclude the use of other underground mining techniques.[1] A gasoline or diesel engine powered auger drill specially equipped with a cutterhead and flights of varying lengths is used to extract the coal from a seam.[2]

Contents

[edit] History

The recovery of coal using auger drills in surface mining and underground mining has been in practice since before World War II. The first attempts in the U.S. at mining with auger drills occurred in the coalfields of West Virginia in 1945. The auger drills used in auger mining back then were largely adaptations of horizontal rock drills.[3] Today, auger mining is still widely deployed in the Appalachian mountain region of Kentucky and West Virginia.

After the 1940s, the development of auger drill technology increased incrementally, peaking in the 1970s and 1980s. In 1985, a 425 horsepower diesel engine surface auger drill was introduced which could penetrate a coal seam to a depth of 164 feet (50 m), producing 450 tons of coal per day. In 1987, the formation of Brynet Development Corp. led to the launch of an intensive coal auger development program that saw an increase in auger drill power, as well as smaller-diameter cutterheads that could cut across all coal types.[4]

[edit] Process

Auger mining is a low-cost method of recovering coal from horizontal or slightly pitched seams exposed through geological erosion. The practice of auger mining is reserved primarily for extracting coal at depths of up to 1,000 feet (305 m).[5]

Auger drills mounted with cutterheads cut and fracture through both overburden and coal, operating very similar to a drill machine. The cutting action of the auger drill differs from other types of coal cutting machines such as continuous miners in that the machine tends to exploit the lower tensile strength of coal rather than trying to over compensate for its high compressive strength. Therefore, auger drills are able to generate a greater amount of power in cutting coal than a continuous miner. The power of the machine as well as diameter of the cutterhead are the two features that govern an auger drill’s performance. The greater the power of the machine, the greater the depth of coal seam into which it is able to bore down, producing a higher rate of coal.[6]

Augers drills used in auger mining can range from 60 to 200 feet (18 to 61 m) in length to two to seven feet (0.6 to 2.1 m) in diameter.[7] The cutter head on the auger bores a number of openings into the seam, similar to how a wood drill produces wood shavings. The coal is then extracted and transported up to the surface via the spiral action of flights.[8] Additional auger lengths or flights can then be added as the cutter head penetrates and drives deeper down into the bored hole .[9] As the depth of the bored hole is extended, coal production is most likely to decrease. The auger drill will continue to penetrate into a highwall until the maximum torque of an auger is reached, usually at a depth of 492 feet (150 m).[10] Once the coal arrives at the surface, it is lifted up to a dump truck for hauling by a conveyor or front end loader.

More recent developments in auger drill technology have led to the introduction of a new type of auger drilling machine called the thin-seam miner (TSM). As a modification of the surface auger miner, the thin seam miner is actually a type of continuous miner that can cut an entry up to eight feet (2.4 m) wide and up to five feet (1.5 m) high into a coal seam situated under a highwall in surface mines.[11]

Auger mining with drills is a specialized skill and can be accomplished with a team of at least three people.[12] One of the drawbacks is that once the cutter head enters the coal seam, the operator is unable to view the cutting action directly and must rely more on a sense of feel for the machine to determine potential problems.[13]

[edit] Equipment Used

[edit] References

  1. Argonne National Laboratory. Environmental Consequences of, and Control Processes For, Energy Technologies. William Andrew Inc., 1990.
  2. Hartman, Howard L. SME Mining Engineering Handbook: Volume 2. Published by Society for Mining, Metallurgy and Exploration. 1992. pg. 1401 – 1402.
  3. Hartman, Howard L. SME Mining Engineering Handbook: Volume 2. Published by Society for Mining, Metallurgy and Exploration. 1992. pg 1401 – 1402.
  4. Follington, I.L.; Deeter, R.; Share, D.; Moolman, C. A new underground auger mining system. The Journal of The South African Institute of Mining and Metallurgy, January/February, 2001. (accessed: 2008-09-29)
  5. Auger Mining. MiningLife.com, 2008-09-29.
  6. Follington, I.L.; Deeter, R.; Share, D.; Moolman, C. A new underground auger mining system. The Journal of The South African Institute of Mining and Metallurgy, January/February, 2001. (accessed: 2008-09-29)
  7. Coal. Encarta, 2008-09-29.
  8. Hartman, Howard L. SME Mining Engineering Handbook: Volume 2. Published by Society for Mining, Metallurgy and Exploration. 1992. pg. 1401 – 1402
  9. Hartman, Howard L. SME Mining Engineering Handbook: Volume 2. Published by Society for Mining, Metallurgy and Exploration. 1992. pg. 1401 – 1402
  10. About Auger Mining System. Australian Auger Mining, 2008-09-29.
  11. Thin-Seam Miner. Webster's Online Dictionary, 2008-09-29.
  12. About Auger Mining System. Australian Auger Mining, 2008-09-29.
  13. Hartman, Howard L. SME Mining Engineering Handbook: Volume 2. Published by Society for Mining, Metallurgy and Exploration. 1992. pg. 1401 – 1402