Energy resources: Coal
Energy resources: Coal

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Energy resources: Coal

2.2 Winning coal in former times

Coal was probably first used as a fuel by early Chinese civilizations, and there is evidence for coal working in the UK since Roman times. However, early approaches to mining were limited by the available technology, and left much of the coal behind.

At first, coal was dug from seams exposed at the surface in shallow excavations into valley sides that followed the coal seam. The amount of coal that could be extracted from these trenches and from adits (short horizontal tunnels) was small, even when wooden props were used to stop the overhanging roof from collapsing. The first true underground mines, which signified some knowledge of hidden coal seams, were bell pits. Miners would dig a vertical shaft down to a coal seam less than 10 m below the surface. Once the underground seam was reached, the coal was worked outwards in all directions from the bottom of the shaft. When the bell pit became unsafe, the shaft was simply abandoned and a new one started nearby (usually 20-30 m distant).

Digging vertical shafts through overlying strata over 10 m thick is somewhat unproductive, and so pillar-and-stall working was later adopted. As Figure 8 shows, a rectangular grid of tunnels was driven horizontally into the coal from the base of a vertical shaft. Later, the wide pillars of coal within the grid were systematically removed from the furthest limits of the mine back towards the shaft, allowing the roof to collapse (Figure 8b).

Figure 8
Figure 8 (a) and (b) Pillar and-stall workings involved driving a right-angle grid throughout the whole area to be worked, leaving support pillars. In (b) the roof has subsided after removal of the pillars. (c) Longwall workings that removed all the coal as working advanced became common in the 19th century.

For coal seams at depths greater than 300 m, the support pillars were often crushed by the weight of overlying rock and so longwall mining was widely used after 1850. This technique involved a 'wall', usually about 30 m long, being cut into the coal seam in one continuous process, advancing away from the shaft (Figure 8c). Any stone available (for example, sandstone within the seam) was built into support walls 2-5 m wide running at right angles to the working face. These walls and wooden props were used to support the roof after the coal was cut and to prevent crushing of the coal at the working face.

Poor ventilation and drainage limited the size of these early mines. As soon as shafts were sunk beneath the water table, mines began to flood and had to be abandoned if they flooded faster than they could be drained. Flooding ceased to be a major problem following the introduction of steam pumps as early as 1712 in UK mines.

As mines extended further underground, ventilation became a significant problem. Fires were lit at the foot of an 'upcast' shaft — one of a pair of shafts close together. The upward movement of hot gases drew a corresponding draught of fresh air into the mine through the nearby 'downcast' shaft. This method continued to be used until the advent of mechanical air pumps in the 1830s.

Coal extraction became more efficient in the mid-19th century with the invention of rotary cutters powered by compressed air. However, even in the mid-20th century miners still relied on picks, shovels and crowbars to win coal from seams inaccessible to machines. By the early 20th century, electric conveyor belts were used to transport the coal away from the coalface. Even though coal could be cut and loaded onto conveyor belts in one continuous automated operation, the manual loading of coal was commonplace until the 1950s and 1960s.

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