PSU miner Coal India (CIL) is looking afresh at underground (UG) mining, with an aim to resume existing UG operations in the long term, and in the short term using the punch entry method to get underneath depleted opencast (OC) mines and extract more reserves. Using this method for the first time, CIL is virtually converting some OC mines to UG mines.
The company also plans to deploy 10 highwall machines in four OC mines this fiscal, with capex between ` 800-1,000 crore. The machines will extract the coal that an opencast mine leaves as non-extractable after reaching its ultimate pit level. A CIL executive told FE such coal can’t be extracted manually.
The projected production potential has been estimated at 5 million tonne a year. A longwall mining project entailing capex of `200 crore is already under way in South Eastern Coalfields (SECL). Three more such projects will start in Eastern Coalfields ( ECL) this year.
The executive said contractors engaged for the projects will share the capex on a 50:50 basis, and CIL will have to bear half the cost. Longwall mining could further lead to making punch entry into coal-depleted opencast mines.
“Punch entry will actually make holes in an opencast mine and could create a horizontal pathway to access underground coal in the opencast mine. Punch entry could be done through a mix of technologies, and CIL plans to identify and implement five such mines in a phased manner till FY24,” he said. The entire punch entry process would be mechanised and there would be no miner going underground, ensuring operational safety.
Capex for the punch entry system will be estimated as and when the project progresses and based on the technology used. But it is likely to be on a sharing basis, the executive said.
The company had closed down all underground mines one by one for techno-commercial unviability. But it is exploring ramping up UG production fourfold to 100 million tonne (MT) by FY30 from 25.6 MT in FY22.
“UG output is environmentally clean, minimally invasive on land degradation and is society friendly. Around 70% of the country’s coal reserves are conducive for UG mining,” the CIL executive said, adding the aim was to make UG production sizeably supplementary to the OC output. At the current rate, mineable coal reserves at existing OC mines will slowly start decreasing.
Since nationalisation of mines in 1975, UG output has contracted 57.7% till FY22, while OC production has expanded 8.5 times. UG mines were loss-incurring and had longer gestation periods with lack of skilled labour, unavailability of indigenous equipment, and high departmental production cost.
But UG production could now become techno-commercially viable with the availability of mass production technologies indigenously and well-trained skilled labour. Outsourcing to contractors would scale down cost of production, and the gestation period is considerably lower. CIL thus plans to steadily scale up the use of locked-up UG coal assets, he said.
Paste-fill technology, another environment friendly frontier which involves high-speed stowing, will be compatible with mass production technologies. Instead of conventional sand stowing, it uses fly ash to fill the void created by extracting coal from UG mines. Such a system is in advanced stages of implementation at ECL.
Among mass production technologies, CIL will introduce 50 continuous miners by FY25 with peak production potential of 25 MT a year. Currently, 21 such machines are deployed at ECL, Central Coalfields and SECL, producing 9 MT a year.
Two powered support longwall (PSLW) machines operating at ECL and Bharat Coking Coal (BCCL) produced 1.58 MT in FY22, 40% higher than 1.13 MT produced in FY21. Two more PSLWs with a total capacity of 4.5 MT a year are soon to be deployed at BCCL.