coal mining

  • 格式:doc
  • 大小:29.50 KB
  • 文档页数:2

History of coal mining
Coal was only used as a means of household heating, however, after industrial revolution it providing the main source of primary energy for industry and transportation. By the late 20th century,due to its low cost and abundance, coal also provided 22 percent of the world's energy, and was used to generate approximately 40 percent of electricity worldwide.
underground mining
Underground mining requires digging a shaft to where the coal seam(煤层)is found. The traditional room and pillar method requires leaving pillars of coal in place to help support the mine roof where miners work. Now longwall mining method (长壁开采)uses hydraulic roof supports, having increased the amount of coal able to be extracted
The problem of mining
1)、Dust & Noise Pollution
◆Dust at mining operations can be caused by trucks being driven on unsealed
roads, coal crushing operations, drilling operations and wind blowing over areas disturbed by mining.
◆Main sources of noise pollution are blasting, movement of heavy earth moving
machines, drilling and coal handling plants.
2)、Mining subsidence(煤矿坍陷)
Mine subsidence can be a problem with underground coal mining, whereby the ground level lowers as a result of coal having been mined beneath. The major factors affecting the extent of subsidence are seam thickness and its depth beneath the surface. Roof collapse will often start within 24 hours of coal extraction, but the full effects are transmitted rather slowly upwards, eventually resulting in subsidence at the surface. But it may be over 10 years before the surface is completely stable again. 3)、Water pollution
Most underground and some surface mines lie well below the water table(地下水位). Both therefore have the potential to pollute any groundwater that flows through them. Waste water from coal preparation plant and mine water are other sources of water pollution
Conclusion:
There are many environmental reasons why coal is a rather undesirable source of energy. Burning it introduces large amounts of gases into the atmosphere that harm the environment in a variety of ways, as well as other, solid waste products. Coal
extraction leads to spoil heaps and mines that scar the landscape, land subsidence that affects roads and buildings, and in some cases water pollution.
The downside is that continued burning of coal could lead to dire consequences for the environment in the coming centuries, unless ‘cleaner’ ways can be found to harness energy from it. Coal is twice as important globally as any other fuel in generating electricity, and could remain so for the next 200 years。