Beyond the Stereotype
There is more to the stereotype of coal mining than just a dangerous job full of blackened workers digging within the darkened depths of the earth. Many different considerations and parts need to be understood and taken into account when mining coal. It is important to understand how coal is mined in order to see beyond the classic trope and further comprehend coal mining and coal mines in Limburg.
Over the centuries, many methods of mining have been used to dig up coal. Today, various techniques are used. The method chosen depends on factors such as the location of the coal within the ground, the size of a coal seam, and geological factors (Coal mining, n.d.). You can find a basic overview on how the process of mining coal works in the adjacent video!
Surface vs. Underground mining
In present day, there are two ways to mine coal: surface mining and underground mining. Surface mining typically utilizes large machinery to dig up coal. In general, surface mining removes a higher proportion of coal deposits than underground mining. A major drawback of surface mining is its destruction of natural habitat, landscape, and large areas of land. (ADMIN, 2014)
Underground mining is what most people picture when they think of coal mining. This way of mining uses sophisticated equipment to dredge up coal deep underground (ADMIN, 2014). Below you may find some videos showcasing some of the powerful equipment used.
While underground mining is more expensive than surface mining, it is overall more productive, profitable, and safer than surface mining (ADMIN, 2014). Despite this, there are greater risks, particularly to the miners, such as mine collapses and explosions, along with environmental impacts such as abandoned shafts and flooding (ADMIN, 2014). Because of this, ventilation, lighting, and water control are critical considerations in underground mining (Underground Mining, n.d.).
Among both surface and underground mining, various techniques can be employed to mine coal. Different equipment can be used depending on the method chosen.
Coal Production from Surface Mining
(Coal mining, n.d.)
Underground Extraction Methods Usage
(Coal mining, n.d.)
Methods of Extraction
Strip mining is a type of surface mining that exposes coal by removing earth above each coal seam. The long strips of earth removed is referred to as “overburden.” These strips are deposited either outside the planned mining area, known as out-of-pit dumping, or in empty areas left from mining the coal and removing other overburden. This second method is known as in-pit dumping. It is often necessary to fragment the overburden with explosives before carting it away. Once the overburden is removed, the coal seam is exposed and can be mined. However, equipment to be used depends on geological conditions since some overburden may be looser than at other locations. (Coal mining, n.d.; U.S. Department of the Interior, Office of Surface Mining Reclamation and Enforcement, 1987)
The surface mining method called contour mining consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside. This method is most commonly used in areas with rolling to steep terrain. It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate this issue, other techniques are now used, namely refilling mined-out areas and leaving a barrier of natural material. The limitations of contour mining are both economic and technical. When the operation reaches a certain quota, it is no longer profitable to continue. Additionally, depending on the equipment used, it may not be technically feasible to exceed a certain height of highwall. At this point, mining coal via the augering method is more economical. (Coal mining, n.d.)
Mountaintop coal mining is a surface mining practice involving removal of mountaintops to expose coal seams, and disposing of associated mining overburden in adjacent “valley fills.” Valley fills occur in steep terrain where there are limited disposal alternatives.
Mountaintop removal combines area and contour strip mining methods. In areas with rolling or steep terrain with a coal seam occurring near the top of a ridge or hill, the entire top is removed in a series of parallel cuts. Overburden is deposited in nearby valleys and hollows. This method usually leaves the ridge and hilltops as flattened plateaus. The process is highly controversial for the drastic changes in topography, the practice of creating head-of-hollow-fills, or filling in valleys with mining debris, and for covering streams and disrupting ecosystems. (Coal mining, n.d.; U.S. Department of the Interior, Office of Surface Mining Reclamation and Enforcement, 1987)
Longwall mining accounts for about 50 percent of underground coal 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 onto an armored chain conveyor or 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 percent coal recovery rate when surrounding geology allows their use. Once the coal is removed, usually 75 percent of the section, the roof is allowed to collapse in a safe manner. (Coal mining, n.d.; Coal Mining. World of Coal, 2009)
Image Credit: Eickhoff, 2009, Retrieved from http://www.eickhoff-bochum.de/de/
Continuous mining is an underground method that utilizes a Continuous Miner Machine with a large rotating steel drum equipped with tungsten carbide picks that scrape coal from the seam. Operating in a “room and pillar” (also known as “board and pillar”) system—where the mine is divided into a series of 20-to-30-foot (5–10 m) “rooms” or work areas cut into the coal bed—it can mine as much as 14 tons of coal a minute, more than a non-mechanized mine of the 1920s would produce in an entire day. Continuous miners account for about 45 percent 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. (Coal mining, n.d.)
Room and pillar mining consists of coal deposits that are mined by cutting a network of rooms into the coal seam underground. Pillars of coal are left behind in order to keep up the roof. The pillars can make up to forty percent of the total coal in the seam, however where there was space to leave head and floor coal there is evidence from recent open cast excavations that 18th-century operators used a variety of room and pillar techniques to remove 92 percent of the in situ coal. However, this can be extracted at a later stage, known as “retreat mining.” (Coal mining, n.d.; Coal Mining. World of Coal, 2009)
Shortwall mining, a method currently accounting for less than 1 percent of deep underground coal production, involves the use of a continuous mining machine with movable roof supports, similar to longwall. The continuous miner shears coal panels 150 to 200 feet (45 to 60 meters) wide and more than a half-mile (1 km) long, having regard to factors such as geological strata. (Coal mining, n.d.)
How Coal Was Mined in Limburg
The primary method used in Limburg was blast mining. Blast mining is an underground method to mine coal. This method uses explosives to first break up the coal seam so that it can be carted away via conveyor belts or wagons to the central loading areas (Darling, 2011).
Although it was a popular method in Limburg and is generally considered an older method of coal mining, it is still used today in some parts of the world (Underground mining (soft rock), n.d.). Nowadays, blast mining accounts for less than 5% of the total underground coal production (Coal mining, n.d.). In Limburg, however, it was used to make up most of the coal production. For more on the type of equipment used in blast mining, check out the “At Work” sub-page under Daily Life in our Collection section.
Map of coal mines in Limburg by end of 1974
A popular and important aspect of coal mines is their shaft. While not all mines use one, shaft mines were the type of mines often found in Limburg. With their completely vertical shafts that plunge straight into the earth, shaft mines are arguably the quintessential image of coal mining.
Shaft mining is used when the rock, ore, or mineral is located too deep underground for surface mining to be viable, as was such the case for Limburg (Underground Mining, n.d.).
Since Limburg mines were also built on wetlands, large pumps had to be put underground to pump up all the water in the mines (Mijnbouw in Limburg, 2018). Because shaft mines were considerably deep, this made the mines a hot and muddy place to work in. Nevertheless, the Limburg mines were considered some of the safest in the world when still operating (Mijnbouw in Limburg, 2018).
Despite the eventual downfall of coal mining in the region, the headframe and shaft from some Limburg mines can still be seen today, such as in the case of the Dutch Mining Museum in Heerlen. Coal mining comes with its fair share of dangers and profits. By knowing how it works, the lives of miners, the coal industry, and mines in Limburg can be better understood.