Highwall Mining - A Technological Solution for Safe Extraction of Blocked Coal

摘要

The total geological reserve of coal in India as on 1.04.13 is approx. 299 billion tonne up to a depth of 1200 meters. This includes seam of thickness 0.9 and above. We all know that all the reserves are not mineable. At the same time; all the mineable reserves are not extractable. Ratio of normal reserve to extractable reserve is only 4.7:1 That way our extractable reserves will be much lower unless we go for some advanced technology for increased recovery of coal. At present, coal seams having thickness 0.9-to1.5 m are not being extracted due to absence of any appropriate mining technology. In fact, even in case of opencast mining, thin seams are not being mined for operational inconvenience and precious coal are being treated as waste and dumped with the overburden. Thus we are not only loosing valuable coal but also creating an environment for dump fire and consequently polluting the environment. In the 40's, USA faced similar situation for mining thin seams. Appalachian coal field of West Virginia in United States is a hilly terrain and contains good quality coking coal having thickness as low as 0.4 m. At that time, no technology for mining thin seams was available. With the improvement of technologies as well as equipment in mining, an extension to the field of Appalachian in the form of Opencast mining took place. But when mining operation went into very high stripping ratio, the method was loosing priorities. Auger mining had been applied and it had penetration depth of 100-150 meters but recovery was very low. Ordinarily, the highwalls represent the end of the surface mining job. Inevitable at some point, mining reaches a limit where the cost becomes prohibitive to remove any more overburden. What signals the end for one technology looks like the opportunity for another.