Print8.3.4: Highwall Mining
Highwall mining is very similar to auger mining in its concept, where the entry into the coal seam in made at the highwall of the ultimate pit limit. The difference lies in the use of a more sophisticated machine, known as a highwall miner. The highwall miner shares some common elements with a continuous mining machine. It has bit-laced cutting drum, and the coal is fed back through a materials handling system to the bench by the highwall, where it is loaded out. That’s where the similarity stops.
The highwall miner is equipped with sophisticated monitoring and a remote control system. It is important to maintain accurate control of the cutting head so that it remains in the coal seam, rather than drifting up or down into the adjacent rock layers, and so that a constant rib thickness is maintained between holes. Unlike the continuous miner, where a shuttle car is waiting at the tail to load out the coal, the highwall miner needs to move the coal from the cutting head to outside the highwall. Essentially, there is a flexible conveyor train following the cutting head. There is a significant amount of support equipment required outside of the hole, adjacent to the highwall, to provide power and handle the cables and hoses. The computerized supervisory control system and operator station are located within the highwall miner’s structure that is located adjacent to the highwall. This picture with the artist’s cutaway shows a highwall mining machine.
What do you gain with the added complexity and cost of a highwall miner over an auger? The highwall miner can advance 1200’ under the highwall compared to a typical 300’ for an auger. Recovery rates improve from roughly 30% for an auger to near 50% for a highwall miner. The highwall miner can adapt more easily to varying seam thickness or other changes under the highwall. Its production rate can be much higher than an auger, and, in general, the unit cost of coal mined with the highwall miner will be less than with an auger. The risk of worker injuries is less with a highwall miner, primarily because the likelihood of a cave-in is less than with an auger; and attempting to remove an auger from a caved hole is fraught with dangers. On the negative side, the highwall miner does not reduce the concern over acid mine drainage.
Here is a photo of the highwall showing the holes created by the highwall miner.
