Report: APP CMHS Project 1

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3.3.7. Thick Seam Mining

A coal seam of 4.5 m or greater is classified as a thick seam in China. There are two main mining methods applied to thick seams in China – Multi-slice longwall (MSL) and longwall top coal caving (LTCC). The inherent operational problems and high costs associated with the multi slicing longwall method (MSL), and the legislative requirement from the central government of a 97 % (minimum) recovery rate of mineable coal seams prompted the development of longwall top coal caving (LTCC) technology in 1982. The technology continued development and outperformed MSL in 1995. The LTCC technology is now widely used in Chinese coal mines. It has been successfully applied at Austar Coal Mine in Australia since 2005.

In LTCC, the lower part of the seam is extracted by a conventional shearer cutting operation and the remaining top coal in the seam is allowed to cave into the goaf at the rear of the support from where it is recovered on a rear Armoured Face Conveyor (AFC) – see Figure 43. As the roof caves, the broken roof coal is collected through gates in the top-middle or top-rear of a specially developed shield canopy. Two conveyors in the front and tail can cater for cutting and caving in parallel, thus forming two separate coal removal operations within one working face (Figure 44 and Figure 45).

Figure 43 LTCC configuration

Figure 44 Rear AFC and back of the roof supports

Figure 45 End discharge of AFC to BSL

Figure 46 Typical LTCC support

One of the key components in LTCC face equipment is the supports that allow caving at the rear and recovery of the coal through the sliding caving door. A typical LTCC support is shown in Figure 46.

The LTCC system has a wide application in a variety of ground conditions; it is a simple and systematic process, potentially high productivity and has many operational and economic advantages over MSL and high reach single pass longwall faces. Some of the key benefits for thick seam mining with LTCC technology include:

  • Significantly less development metres / longwall tonne mined

  • Less longwall changeovers / longwall tonne mined

  • Less face equipment cycles / longwall tonne mined

  • Increased resource recovery

  • More easily managed horizon control compared to high reach longwalls

  • Improved capital utilisation.

    Critical safety factors enhanced by the LTCC method are reduction:

  • In face height and potential exposure to fall of ground

  • Roof support instability

  • Face gas and dust generation due to slow ventilation velocity

  • In the amount of coal left in the goaf that can exacerbate spon com.

Some of the mine sites with successful thick seam mining technologies include:

  • Yankuang Coal Mining Group

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