Underground mining

Underground mining

Coal wash plant in Clay County, Kentucky.Most coal seams are too deep underground for opencast mining and require underground mining, which method currently accounts for about 60% of world coal production. In deep mining, the room and pillar or bord and pillar method progresses along the seam, while pillars and timber are left standing to support the mine roof. Once room and pillar mines have been developed to a stopping point (limited by geology, ventilation, or economics), a supplementary version of room and pillar mining, termed second mining or retreat mining, is commonly started. This is when miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible. A work area that is involved in pillar extraction is called a pillar section. Modern pillar sections use remote-controlled equipment, including large hydraulic mobile roof-supports, which can prevent cave-ins until the miners and their equipment have left a work area. The mobile roof supports are similar to a large dining-room table, but with hydraulic jacks for legs. After the large pillars of coal have been mined away, the mobile roof support's legs shorten and it is withdrawn to a safe area. The mine roof typically collapses once the mobile roof supports leave an area.

There are five principal underground mining methods:

• Longwall mining accounts for about 50% of underground production. The longwall shearer has a face of 1,000 feet (300 m) or more. It is a sophisticated machine with a rotating drum that moves mechanically back and forth across a wide coal seam. The loosened coal falls on to a pan line that takes the coal to the conveyor belt for removal from the work area. Longwall systems have their own hydraulic roof supports which advance with the machine as mining progresses. As the longwall mining equipment moves forward, overlying rock that is no longer supported by coal is allowed to fall behind the operation in a controlled manner. The supports make possible high levels of production and safety. Sensors detect how much coal remains in the seam while robotic controls enhance efficiency. Longwall systems allow a 60-to-100% coal recovery rate when surrounding geology allows their use.
• Continuous mining utilizes a machine with a large rotating steel drum equipped with tungsten carbide teeth that scrape coal from the seam. Operating in a “room and pillar” (also known as “bord and pillar”) system—where the mine is divided into a series of 20-to-30 foot “rooms” or work areas cut into the coalbed—it can mine as much as five tons of coal a minute, more than a non-mechanised miner of the 1920s would produce in an entire day. Continuous miners account for about 45% of underground coal production. Conveyors transport the removed coal from the seam. Remote-controlled continuous miners are used to work in a variety of difficult seams and conditions, and robotic versions controlled by computers are becoming increasingly common.
• Blast mining is an older practice that uses explosives such as dynamite to break up the coal seam, after which the coal is gathered and loaded on to shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with “cutting” the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5% of total underground production in the U.S. today.
• Starwall mining, a method currently accounting for less than 1% of deep coal production, involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, having regard to factors such as geological strata.
• Retreat mining is a method in which the ceiling of the mine is held up by wooden beams. The beams are removed, allowing the ceiling to collapse so miners can reach the coal. This is one of the most dangerous forms of mining owing to imperfect predictability of when the ceiling will collapse and possibly crush or trap workers in the mine.

Modern surface mining

Modern surface mining

Trucks loaded with coal at the Cerrejón coal mine in Colombia.When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast or open pit) mining methods. Typically, for coal, strip mining is used. Strip mining exposes the coal by the advancement of an open pit or strip. The earth above the coal seam(s) is known as overburden. A strip of overburden next to the previously mined strip is usually drilled. The drill holes are filled with explosives and blasted. The overburden is then removed using large earthmoving equipment such as draglines, shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the underlying coal seam will be exposed as a strip known as a 'block'. This 'block' of coal may be drilled and blasted (if hard) or otherwise loaded on to trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it.

Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Opencast coal mines can cover many square kilometers.

Most open cast mines in the United States extract bituminous coal. In South Wales open casting for steam coal and anthracite is practiced. In Australia and South Africa open cast mining is used for both thermal and metallurgical coals. Surface mining accounts for around 80% of production in Australia, while in the USA it is used for about 67% of production. Globally, about 40% of coal production involves surface mining.

Mountaintop removal is a form of surface mining that takes place at the topmost portion of a mountain, and is a technique that is commonly applied in Appalachia in the United States. Utilized for the past 30 years, mountaintop mining involves removing the highest part of the mountain for the maximum recovery of coal. The process is highly controversial for the drastic changes in topography, the practice of hollow fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.

Coal Mine

Coal mining

Coal mining is the extraction or removal of coal from the earth by mining. When coal is used for fuel in power generation it is referred to as steaming or thermal coal. Coal that is used to create coke for steel manufacturing is referred to as coking or metallurgical coal. In the United States, UK, and South Africa, a coal mine and its accompanying structures are collectively known as a colliery. In Australia, 'colliery' usually only refers to an underground coal mine.

History

The oldest continuously worked deep-mine in the UK and possibly the world is Tower Colliery at the northern end of the South Wales valleys in the heart of the South Wales coalfield. This colliery was started in 1805 and at the end of the 20th century it was bought out by its miners rather than being allowed to be closed. Tower Colliery was finally closed on the 25th January 2008.
The World Championships in coal-carrying take place every Easter Monday, at Ossett, West Yorkshire, UK. The race starts from the site of the old Savile & Shaw Cross colliery.
The first commercial coal mines in the United States were started in 1748 in Midlothian, Virginia, near Richmond, Virginia.
In the 1880s, Coal-cutting machines became available (prior to that, coal was mined underground by hand using a pick and shovel.)
By 1912, surface mining was underway with steam shovels specifically designed for coal mining.

Methods of extraction

The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and also the geology and environmental factors of the area being mined. Coal mining processes are generally differentiated by whether they operate on the surface or underground. Many coals extracted from both surface and underground mines require washing in a coal preparation plant.

Modern surface mining

Trucks loaded with coal at the Cerrejón coal mine in Colombia.When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast or open pit) mining methods. Typically, for coal, strip mining is used. Strip mining exposes the coal by the advancement of an open pit or strip. The earth above the coal seam(s) is known as overburden. A strip of overburden next to the previously mined strip is usually drilled. The drill holes are filled with explosives and blasted. The overburden is then removed using large earthmoving equipment such as draglines, shovel and trucks, excavator and trucks, or bucket-wheels and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the underlying coal seam will be exposed as a strip known as a 'block'. This 'block' of coal may be drilled and blasted (if hard) or otherwise loaded on to trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it.
Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Opencast coal mines can cover many square kilometers.
Most open cast mines in the United States extract bituminous coal. In South Wales open casting for steam coal and anthracite is practiced. In Australia and South Africa open cast mining is used for both thermal and metallurgical coals. Surface mining accounts for around 80% of production in Australia, while in the USA it is used for about 67% of production. Globally, about 40% of coal production involves surface mining.
Mountaintop removal is a form of surface mining that takes place at the topmost portion of a mountain, and is a technique that is commonly applied in Appalachia in the United States. Utilized for the past 30 years, mountaintop mining involves removing the highest part of the mountain for the maximum recovery of coal. The process is highly controversial for the drastic changes in topography, the practice of hollow fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.

Wildlife photography

Wildlife photography

Wildlife photography is the act of taking photographs of wildlife. Wildlife photography is regarded as being one of the more challenging forms of photography.

Requirements are:

• a technically sound photographer, such as being able to expose correctly.


• advanced photographic equipment. While wildlife photographs can be taken using basic equipment it is made easier with advanced equipment. For example, 600mm lenses in conjunction with the latest autofocus camera bodies are generally required for bird photography. As an alternative, less expensive superzoom bridge cameras (with equivalent focal lengths exceeding 500mm, 800mm+ with a teleconverter) can produce excellent results, despite being far less expensive and more portable than a SLR body with a supertelephoto lens. Due to their small sensors these cameras are limited to ISO 100 to achieve optimum image quality which can be a hindrance with fast moving animals or in less than ideal lighting situations (dawn or dusk).


• Good field craft skills. Wildlife is usually difficult to approach thus a knowledge of the animal's behaviour is needed in order to be able to predict actions. An ability to stalk animals is often also required. Hides may be required when photographing more timid subjects as these conceal the photographer.