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BACKGROUNDER
Indian mineral industry has contributed significantly to make the nation self-sufficient in coal. To meet the demands of thermal, cement and other users, the production trends in coal and lignite sectors have shown a remarkable increasing trend over last few years. While extracting the deep-seated coal deposit and also to increase the present production capacity, the coal mines have been compelled to modernize the mining technology, particularly in the fields of blasting and production.
Coal producers have already tried to open up big surface coalmines in various coalfields. This has further necessitated the importance of adopting better mining technology in the above mines by applying scientific and economic approaches while selecting the mining equipment and introducing the state-of-the-art technology. In this process it is important to adopt the blasting technology suitable for the mine as it affects the subsequent operations involved in the mining and processing.
In India, cartridge explosives dominated the surface coal mines until the bulk explosives in the form of slurry and emulsion entered into the explosives market. Since the volume of overburden removal is increasing day by day, the majority of coal sectors have already been switeched over to blasting with bulk explosives. As far as the type of explosive is concerned, the coalmines are currently using the slurry or emulsion based explosives with the gradual exit of NG based explosives from the market.
Regarding the accessories, most of the coal mines have been changing over to the shock tubes system as more quantity of explosives are consumed in every blast and also to ensure the safety while conducting the blasts in the proximity of human dwellings to the blast site. In association with Indian school of mines, the "Air-Decking" by means of providing the conventional plugs (drill cuttings) was tried at the last row of holes in the dragline benches lying parallel to the ultimate pit-geometry and the blast results have come up with better pit-slope control and less ground vibration.
In India, the development of giant surface mining ventures like Bina and Jayant with setting up of higher coal production targets (upto 10 million tonnes per annum) calls for systems to remove large volume of overburden in shortest possible time. This has resulted in major changes in overburden/ interburden excavation technology in surface coal mines from shovel mining to dragline mining.
Draglines have gained popularity in India for overburden stripping because of their flexibility and high production rate. Since the giant projects are coming up more in the coal sector in recent times, the shovel mining faces big challenges in fulfilling the production demand. Hence, the Indian surface coal mining has been switching over from shovel mining to dragline mining for removal of overburden/interburden in most of large sized coalmines to accommodate high rate of overburden removal and subsequently, high production rate with low cost of production.
The dragline mining was initially introduced in India in early 60's, and the first waling dragline was commissioned at Kurashia in 1961. Presently, there are about 42 draglines deployed to remove overburden ranging in bucket capacities from 4 cu. m to about 29-30 cu. m. Coal India Limited (CIL) has now standardized the draglines in two sizes, which are 10/70 and 24/96 for their mines. The economic life of a dragline has been assumed by CIL to be 27 years.
Northern Coalfields Limited (NCL) is the only subsidiary company of CIL, where the entire coal production is mined by opencast mining method. Another unique feature of the company is that about 40 per cent of the large volume of excavation is done with the help of larger walking draglines. Draglines are used in all the mines of NCL except in Jhingurda, Kakri and Gorbi.
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