digital divide network - article database

If we traced back to 50 years ago, we will find two major types from which coal was produced -underground or surface. And then as the technology advancing, methods of recovering coal from the earth have undergone great changes.

Fifty years ago when most coal mining was done manually, underground mines accounted for 96 percent of the coal produced each year. Today, almost 60 percent is produced from surface mines. Most underground mines in the United States are located east of the Mississippi River, although there are some in the West, particularly in Utah and Colorado.
Most coals are extracted by room-and-pillar method using mining machines such as crusher, grinding mill etc. the coal mining machine breaks coals into pieces and then convey them to the ground in shuttle cars and conveyor belt. In this process, we do not need blasting and it will be repeated until the coal seam is mined.
Another method, called longwall mining, accounts for about 20 percent of production. This method involves pulling a cutting machine across a 400 to 600 foot long face (longwall) of the coal seam. This machine has a revolving cylinder with tungsten bits that shear off the coal. The coal falls into a conveyor system which carries it out of the mine. The roof is supported by large steel supports, attached to the longwall machine. As the machine moves forward, the roof supports are advanced. The roof behind the supports is allowed to fall. Nearly 80 percent of the coal can be removed using this method. The remaining 11 percent of underground production is produced by conventional mining which uses explosives to break up the coal for removal.
About 50 percent surface coal in the US is located in the West states and most of them are in the west of Virginia. Surface mining is used when coals are close to the earth surface which making underground mining impractical.
If some company wants a surface mine, it must gather information about climate, vegetation, mining machine, such as magnetic separator, etc. then, it applies to the federal government for a mining coal permit.
Most surface mines follow the same basic steps to produce coal. First, bulldozers clear and level the mining area. The topsoil is removed and stored for later use in the reclamation process. Many small holes are drilled through the overburden (dirt and rock above the coal seam) to the coal seam. Each is loaded with explosives which are discharged, shattering the rock in the overburden. Giant power shovels or draglines clear away the overburden until the coal is exposed. Smaller shovels then scoop up the coal and load it onto trucks, which carry the coal to the preparation plant.

Sand washing equipment : http://www.crusher-export.com/sand_washer.htm
hammer crusher : http://www.hxjq-crushers.com/26.htmIf we traced back to 50 years ago, we will find two major types from which coal was produced -underground or surface. And then as the technology advancing, methods of recovering coal from the earth have undergone great changes.

Fifty years ago when most coal mining was done manually, underground mines accounted for 96 percent of the coal produced each year. Today, almost 60 percent is produced from surface mines. Most underground mines in the United States are located east of the Mississippi River, although there are some in the West, particularly in Utah and Colorado.
Most coals are extracted by room-and-pillar method using mining machines such as crusher, grinding mill etc. the coal mining machine breaks coals into pieces and then convey them to the ground in shuttle cars and conveyor belt. In this process, we do not need blasting and it will be repeated until the coal seam is mined.
Another method, called longwall mining, accounts for about 20 percent of production. This method involves pulling a cutting machine across a 400 to 600 foot long face (longwall) of the coal seam. This machine has a revolving cylinder with tungsten bits that shear off the coal. The coal falls into a conveyor system which carries it out of the mine. The roof is supported by large steel supports, attached to the longwall machine. As the machine moves forward, the roof supports are advanced. The roof behind the supports is allowed to fall. Nearly 80 percent of the coal can be removed using this method. The remaining 11 percent of underground production is produced by conventional mining which uses explosives to break up the coal for removal.
About 50 percent surface coal in the US is located in the West states and most of them are in the west of Virginia. Surface mining is used when coals are close to the earth surface which making underground mining impractical.
If some company wants a surface mine, it must gather information about climate, vegetation, mining machine, such as magnetic separator, etc. then, it applies to the federal government for a mining coal permit.
Most surface mines follow the same basic steps to produce coal. First, bulldozers clear and level the mining area. The topsoil is removed and stored for later use in the reclamation process. Many small holes are drilled through the overburden (dirt and rock above the coal seam) to the coal seam. Each is loaded with explosives which are discharged, shattering the rock in the overburden. Giant power shovels or draglines clear away the overburden until the coal is exposed. Smaller shovels then scoop up the coal and load it onto trucks, which carry the coal to the preparation plant.

Sand washing equipment : http://www.crusher-export.com/sand_washer.htm
hammer crusher : http://www.hxjq-crushers.com/26.htm