India is one of the world’s biggest producers of coal, with 80% of output currently coming from open pit mines.
Underground mining accounts for around 20% of national output, and is mostly carried out by conventional bord and pillar mining methods. Underground productivity is, however, poor and averages 0.75 tonnes per man-year.
One of the companies with big growth plans is listed entity Tata Steel, a leading producer of steel. Group steel output is currently around 5 million tonnes per annum, and by 2010 is predicted to reach 15Mtpa. To meet this demand, the company needs a steady and growing supply of coking coal.
The company owns six mines, operating in the coal-rich Jharia coal field in Jharkhand, the only coking coal source in India, about 60km north-west of Calcutta.
Small-scale mining in the area has been undertaken for the last 150 years, largely from 6-7 major seams, though the area has 19 major seams. As a result, the area is a patchwork of small operations governed by historical boundaries that make it difficult to introduce large-scale high-productive technology such as longwall mining methods.
The area is infamous for another reason: subsurface mine fires, some of which have been burning for many years and which have consumed many tonnes of coal and made many million more inaccessible.
Bord and pillar mining is carried out at five of Tata Steel’s mines, which contain thick seam reserves up to 9m in height. Multi-level mining methods recover coal at 3m seam heights and in-seam recovery averages 60-65%.
These operations, which include a 5Mtpa annum opencut mine, produce around 7Mtpa of coking coal.
Tata Steel has a long-term strategy to increase coking coal output from current levels of around 7Mt to 20Mt by 2010.
“We have a plan to acquire newer areas over the next year or so to overcome the restraining influences that govern these older mines. Then we plan to introduce new mechanised mines, probably longwall mines,” said R S Singh, general manager (Jharia) for Tata Steel.
Singh said the inappropriate application of longwall mining technology in India in the past had resulted in production being lower than planned.
Parts of India’s coal fields are overlain by massive sandstone bodies, and according to Singh, this was not adequately taken into account in the design of the roof supports.
On the issue of mine safety at Tata Steel’s mines, Singh said roof and pillar falls were one of the biggest risks underground. Roof and rib bolting is commonly used and Tata Steel is focussing on improving its understanding of rock mechanics and caving at the level of mine design.
Another major risk is the underground temperature. Some mines are in workings at 600m depth and temperatures in India’s hot summer can become very high for workers. Refrigeration is too costly, given the dispersed layout of typical bord and pillar operations. Efforts to increase quantities of fresh air are underway to ensure a comfortable working environment.