Modern American Coal Mining Methods And Applications Pdf

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Choosing a mining method

The various methods of mining a coal seam can be classified under two headings, surface mining and underground mining. Surface and underground coal mining are broad activities that incorporate numerous variations in equipment and methods, and the choice of which method to use in extracting a coal seam depends on many technological, economic, and social factors.

The technological factors include, at a minimum, the number of seams, the thickness and steepness of each seam, the nature and thickness of the strata overlying the seams, the quality of the coal seams, the surface topography , the surface features, and the transportation networks available. Economic factors include energy demand and its growth, the supply and cost of alternative sources of energy, coal quality and the cost of coal preparation, the selling price of coal, advancements in technology that affect costs of production, and environmental legislation.

Social factors include prior history of mining in the area, ownership patterns, availability of labour, and local or regional government support.

It is a general rule that technological factors dictate a clear choice between surface and underground mining, whereas economic and social factors determine whether a coal reserve will be mined at all. Some coal reserves, however, are surface-mined first and then deep-mined when the coal seam extends to such great depths that it becomes uneconomical to continue with surface mining. The point where it becomes economically necessary to switch from one method to the other can be calculated with the aid of stripping ratios , which represent the amount of waste material that must be removed to extract a given amount of coal.

Stripping ratios can also consider the selling price of coal, and a certain minimum profit can be added to the total cost of producing and marketing the coal for a more thorough cost-benefit analysis.

Analysis of world coal production indicates that contributions from surface and underground production are approximately equal. Anthracite seams less than 10 percent of world coal production are generally mined by underground methods, whereas lignite seams 25 percent are most often surface-mined.

Bituminous seams approximately 65 percent are mined in roughly equal proportions by both methods. Surface coal mining generally involves the following sequence of unit operations: 1 clearing the land of trees and vegetation, 2 removing and storing the top layers of the unconsolidated soil topsoil , 3 drilling the hard strata over the coal seam, 4 fragmenting or blasting the hard strata with explosives, 5 removing the blasted material, exposing the coal seam, and cleaning the top of the coal seam, 6 fragmenting the coal seam, as required, by drilling and blasting, 7 loading the loose coal onto haulage conveyances , 8 transporting the coal from the mine to the plant, and 9 reclaiming lands affected by the mining activity.

Surface techniques can be broadly classified into 1 contour strip mining , 2 area strip mining, 3 open-pit mining , and 4 auger mining. Contour mining is commonly practiced where a coal seam outcrops in rolling or hilly terrain. Basically, the method consists of removing the overburden above the coal seam and then, starting at the outcrop and proceeding along the hillside, creating a bench around the hill.

In the past, the blasted overburden spoil was simply shoved down the hill; currently, soil is either carried down the mountain to fill a chosen valley in horizontal layers or is replaced on the working bench itself in places where coal has been removed.

If the break-even stripping ratio remains favourable, further cuts into the hillside will be made. Otherwise, if there are sufficient reserves under the knob of the hill, the coal may be recovered by underground mining or by augering. This trench is extended to the limits of the property in the strike direction. After coal removal, a second cut is made parallel to the first one, and the overburden material from this cut is placed in the void of the first cut. The process is repeated in successive parallel cuts until the stripping ratio indicates that continued surface mining is uneconomical.

In open-pit mining of the coal seam, several benches are established in both the overburden strata and the coal seam. The open-pit method is generally practiced where thick coal seams are overlain by thick or thin overburden; it is also used for mining steeply pitching coal seams.

In the beginning stages of mining, considerable volumes of overburden materials must be accumulated in large dump areas outside the mine. Auger mining is usually associated with contour strip mining. Coal recovery rates approach 60 percent with this method. The cutting heads of some augers are as high as 2.

As each stem works its way into the coal seam, additional auger stems are added, so that hole depths of more than 60 to metres are not uncommon. Problems of subsidence , water pollution , and potential fires are associated with augering. Highwall mining is an adaptation of auger mining. Instead of an auger hole, an entry into the coal seam is made by a continuous miner, remotely operated from a cabin at the surface. The cut coal is transported by conveyors behind the miner to the outside.

The entry can be advanced to metres into the coal seam, after which the miner is retreated to the surface and repositioned to drive an entry adjacent to the previous one. Advantages over augering include higher productivity, greater safety, and lower cost. A variety of equipment is used in a surface mining operation. In land clearing, topsoil removal, and preparation of the mining area for subsequent unit operations, bulldozers and scrapers have extensive applications.

These pieces of equipment have grown bigger and better over the years. Currently, scrapers for rock have bucket capacities of 33 cubic metres 1, cubic feet; about 47 tons of material , and scrapers for coal have capacities of 43 cubic metres 37 tons. Bulldozers have blade capacities up to 30 cubic metres. Where strata are hard, drilling and blasting are necessary. Blastholes are generally drilled from the surface, are vertical, and vary in diameter from 25 to centimetres.

In some mines, horizontal holes are drilled into the overburden with the drill sitting on the coal surface. The holes are charged with explosives that are based on a mix of ammonium nitrate and fuel oil ANFO in dry mix, slurry, or emulsion form.

It is common to have a bulk-explosive truck drive into the area where holes have been drilled to fill holes with custom-designed explosive mixtures. Overburden removal is the most important operation in the system. When the haul distances are small for example, to 1, metres and the overburden material soft, a fleet of scrapers can load, haul, and dump the overburden.

Where distances are very small for example, 30 to 40 metres , mobile front-end loaders, or wheel loaders, may be used to load, haul, and dump. At greater haul distances, a fleet of trucks may be necessary, the trucks being loaded by front-end loaders. Three types of shovel are currently used in mines: the stripping shovel, the loading or quarry-mine shovel, and the hydraulic shovel.

The hydraulic mining shovel has been widely used for coal and rock loading since the s. The hydraulic system of power transmission greatly simplifies the power train, eliminates a number of mechanical components that are present in the loading shovel, and provides good crowding and breakout forces. Hydraulic and loading shovels are available with capacities up to and over 30 cubic metres.

The capacity of the loading shovel is carefully matched with the haul unit into which the load will be dumped. In open-pit coal mines, the haul units for overburden material are usually large, off-highway, end-dumping trucks; their capacities range from 35 to tons.

The stripping shovel has a large bucket, usually sits in the pit on the top of the coal seam, digs into the overburden material, and deposits it in the adjacent mined-out area. Draglines are by far the most commonly used overburden-removal equipment in surface coal mining. A dragline sits on the top of the overburden, digs the overburden material directly in front of it, and disperses the material over greater distances than a shovel.

Compared with shovels, draglines provide greater flexibility, work on higher benches, and move more material per hour. The largest dragline in operation has a bucket capacity of cubic metres. The bucket-wheel excavator BWE is a continuous excavation machine capable of removing up to 12, cubic metres per hour. The most favourable soil and strata conditions for BWE operation are soft, unconsolidated overburden materials without large boulders.

In these mines, the wheel excavators deposit the overburden and coal materials onto high-speed, high-capacity belt conveyors for transport to the mined-out areas of the pit and the coal stockpile, respectively. In the United States , wheel excavators have been used in combination with shovels or draglines, with a wheel handling soft topsoil and clay layers and a shovel or dragline removing hard strata.

Coal is usually loaded by front-end loaders, loading shovels, or wheel excavators into off-highway, bottom-dump trucks for transport to the stockpile. In small operations, it can be loaded into on-highway trucks for direct shipment to customers. In some open-pit operations with BWEs, rail haulage is practiced in the benches themselves, coal and overburden being loaded directly into railcars by the wheel excavator.

Nevertheless, in BWE operations belt haulage is preferable, as it facilitates continuous mining. Equipment used in reclaiming mined lands includes bulldozers, scrapers, graders, seeders, and other equipment used extensively in agriculture.

Reclamation operations, which include backfilling the last cut after coal removal, regrading the final surface, and revegetating and restoring the land for future use, are integrated with the mining operation in a timely manner in order to reduce erosion and sediment discharge, slope instability, and water-quality problems.

A primary goal of reclamation is to restore or enhance the land-use capability of disturbed land. Various reclamation programs aim at restoring the ground for farming and livestock raising, reforestation, recreation, and housing and industrial sites. Even spoil banks that can be revegetated present only minor problems and have great potential for development. There are, however, marginal and problem spoils such as those containing acids or toxic wastes that require special attention and additional planning.

Coal mining Article Media Additional Info. Article Contents. Load Previous Page. Choosing a mining method The various methods of mining a coal seam can be classified under two headings, surface mining and underground mining. Surface mining Surface coal mining generally involves the following sequence of unit operations: 1 clearing the land of trees and vegetation, 2 removing and storing the top layers of the unconsolidated soil topsoil , 3 drilling the hard strata over the coal seam, 4 fragmenting or blasting the hard strata with explosives, 5 removing the blasted material, exposing the coal seam, and cleaning the top of the coal seam, 6 fragmenting the coal seam, as required, by drilling and blasting, 7 loading the loose coal onto haulage conveyances , 8 transporting the coal from the mine to the plant, and 9 reclaiming lands affected by the mining activity.

Mining methods Surface techniques can be broadly classified into 1 contour strip mining , 2 area strip mining, 3 open-pit mining , and 4 auger mining. Contour strip mining Contour mining is commonly practiced where a coal seam outcrops in rolling or hilly terrain. Open-pit mining In open-pit mining of the coal seam, several benches are established in both the overburden strata and the coal seam.

Auger mining Auger mining is usually associated with contour strip mining. Equipment Dozers and scrapers A variety of equipment is used in a surface mining operation. Drilling and blasting Where strata are hard, drilling and blasting are necessary. Shovels and trucks Overburden removal is the most important operation in the system.

Draglines Draglines are by far the most commonly used overburden-removal equipment in surface coal mining. Wheel excavators The bucket-wheel excavator BWE is a continuous excavation machine capable of removing up to 12, cubic metres per hour.

Coal removal Coal is usually loaded by front-end loaders, loading shovels, or wheel excavators into off-highway, bottom-dump trucks for transport to the stockpile. Reclamation equipment Equipment used in reclaiming mined lands includes bulldozers, scrapers, graders, seeders, and other equipment used extensively in agriculture.

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Digging deeper: Mining methods explained

Room and pillar variant of breast stoping , is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out while "pillars" of untouched material are left to support the roof overburden. Calculating the size, shape, and position of pillars is a complicated procedure, and is an area of active research. Room and pillar mining can be advantageous because it reduces the risk of surface subsidence compared to other underground mining techniques. However, because significant portions of ore may have to be left behind, recovery and profits can be low. The room and pillar system is used in mining coal , gypsum , [4] iron , [5] and uranium [6] ores, particularly when found as manto or blanket deposits, stone and aggregates , talc , soda ash and potash.

It's been 30 years since the classic Mining Technology: Theory and Practice was published, and much has changed in the coal mining industry during that time. The energy provided by coal mining is still essential to human welfare, but the mine operating environment is dramatically different. Surface mine production has doubled and scientific knowledge about mining has advanced, while new information technologies have attracted public attention to mining disturbances, and global competition requires more efficient operations. There are almost billion short tons of coal reserves in the United States, but reclaiming this supply has become more challenging because of deeper deposits, the impacts of environmental regulations, and the ventilation demands from increased mechanization in the coal mines. Modern American Coal Mining: Methods and Application covers a full range of coal mining and coal industry topics, with chapters written by leading coal mining industry professionals and academicians.

Digging deeper: Mining methods explained

The various methods of mining a coal seam can be classified under two headings, surface mining and underground mining. Surface and underground coal mining are broad activities that incorporate numerous variations in equipment and methods, and the choice of which method to use in extracting a coal seam depends on many technological, economic, and social factors. The technological factors include, at a minimum, the number of seams, the thickness and steepness of each seam, the nature and thickness of the strata overlying the seams, the quality of the coal seams, the surface topography , the surface features, and the transportation networks available. Economic factors include energy demand and its growth, the supply and cost of alternative sources of energy, coal quality and the cost of coal preparation, the selling price of coal, advancements in technology that affect costs of production, and environmental legislation.

Mining explained.

Coal mining

Gold Mining Methods Some modern commercial placer operations are quite large and utilize heavy equipment and river diversions. Gold mining in Alaska. By , surface mining was conducted with steam shovels designed for coal mining.

Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. An underground mine consists of the portals entrance and exits to the mines , mains, submains, panels, and working faces. The panels are the working sections of the production operation. Depending on the mining method, a working section can have one or more working faces.

Room and pillar mining

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