Coal Mining and Transportation
In the centuries since early humans learned that the black rocks they picked up on the ground would burn, we have had to look for coal below that was hidden below the earth's surface. One of the areas it was easiest to find was where it appeared as one of many layers of materials along the side of a hill.
Then we found we could follow the coal layer (seam) deeper and deeper into the ground. Some mining sites today in the United States may be close to 500 feet underground.
Mining is classified by the method needed to reach the coal seam. When the coal is found close to the Earth's crust and taking away the overlying layers of material is not too expensive, surface mining is used to remove the top layers of materials and expose the coal.
If coal is found in layers far from the surface, underground mining is the preferred technique. Vertical or slanted holes ("shafts") are cut down to the mining area underground for ventilation for the workers and for transporting the miners, equipment, and coal. Common types of underground mining are the drift, shaft, and slope mining methods.
In the mine, coal is loaded in small coal cars or on conveyor belts which carry it outside the mine to where the larger chunks of coal are loaded into trucks that take it to be crushed (smaller pieces of coal are easier to ship, clean, burn, etc.).
The crushed coal can then be sent by truck, ship, railroad, or barge. You may be surprised to know that coal can also be shipped by pipeline. Crushed coal can be mixed with oil or water (the mixture is called a slurry) and sent by pipeline to an industrial user.
|
