In India lignite is excavated on a large scale at Neyveli Lignite Project by mechanised opencast mining employing bucket wheel excavators and other heavy duty matching equipment. India is among the four countries after West and East Germany and Australia to engage in lignite mining on a large scale and Neyvcli mines are the largest lignite mines in Asia 'forked by Neyveli Lignite Corporation
The Neyveli Lignite Project is located at Neyveli in South Arcot District of Tamil Nadu. Situated in far South, having no coal mines, the project fulfils to a great extent, the requirements of solid mineral, fuel in that region and has, therefore, a special significance. Lignite based two pit-head thermal power stations, one of 600 MW and the other of 1470 MW capacity contribute nearly 40% of electricity con sumption of Tamilnadu.
Lignite is a low calorific fossil fuel with a gross calorific value of 2600 to 3000 kcl/kg (as received samples) with the following proximate analysis:
Moisture 45-60%; ash 3-6% (in some cases even less than 3%; V.M. 22-26%; F.C. 20-26% (in a few cases even less than 18%; grindability index 108 to 127.
The average bulk density (in-situ) is 1.15 gm/cc or 1.15 te/m3. Total sulphur content is less than 1%
The Neyvcli Lignite Complex consists of the following units, all based on lignite (in 1995)
(1) Opencast mining project, No. 1 Mine, to extract 6.5 million tonnes/year of lignite proposed to be expanded lo 8.5 MTe/yr in the second expansion scheme. Ultimate planned capacity 10 Mte/yr.
(2) No. 2 Mine Project. It has an instated capacity for producing 10.5 million tonnes/yr lignite. This mine caters to the requirements of thermal power station If which has been expanded from initial installed capacity of 3 x 210 MW to 8 x 210 MW.
(3) Two thermal power stations, one of 600 MW and the other of 1470 MW capacity, as stated above.
(4) Fertiliser plant lo manufacture urea; capacity 1,30,000 te/yr.
(5) Briquetting and L.T. carbonisation plant producing car bonised briquettes called LECO for domestic use. Capacity 2,62,000 te/yr. Certain carbo-chemicals are produced as byproducts.
(6) Clay washing plant, capacity 6000 te/yr of washed clay.
Reserves of lignite at and around Neyveli spread over 400 km2 are estimated to be around 3300 million te. Out of these, mineable reserves within the parameters of not less than 8 m lignite thickness and not more than 110 m overburden thickness work out to be 1500 million te.
No. 1 mine is spread over an area of about 15 km2 with deposits of 230 million te of lignite. Average thickness of lignite seam is about 15 m at a depth of 70 m and the lignite bed dips at 1 in 100. The overburden thickness increases from 50 to 100 m at the rate of 1 in 100 towards south-south west direction of the mine field. The lignite thickness ranges from 11 to 25 m. No 1 mine is planned to produce ultimately 10 M te of lignite per year.
The ratio of overburden to lignite is nearly 5:1 and quite favourable for extraction by bucket wheel excavators which remove, without blasting, the overburden as it consists mostly of soft rocks. Lignite being soft needs no blasting and it also is excavated by bucket wheel excavators.
The project is situated near the sea and control of artesian water under high pressure below lignite is a serious problem. The artesian water exerts an upward thrust of nearly 6-8 kgf/cm2 on the base of lignite and there is risk or water bursting through the lignite seam on removal of overburden. Nearly 1,35,000 lit/min of water is pumped out with the help of nearly 50 bore hole pumps, most of them located around the area being worked out, to maintain pressure of water below the lignite at a safe level. Water table is kept below the lignite floor by such peripheral bore hole pumping and 15-20 te of water has to be pumped out for each te of lignite mined.
The second mine is planned for an initial capacity of 4.7 million te/yr of lignite (1st phase) and the final capacity in 2nd phase will be 10.5 million te/yr, This second mine will extract lignite from 26 km- area south of the first mine and the deposits of extractable lignite are 390 million te.
Excavation and Transportation: Presently (10.5 Mte/year stage) the overburden is removed in 4 benches (Surface, Top, Middle & Bottom). The Top two benches (Surface and Top) arc equipped with two 1400 litres bucket wheel excavators (BWE), a system of 2400 mm width conveyors and a spreader of 20,000 TPH capacities each. The third bench (Middle Bench) comprises one 1400 litres BWE, a system of 2000 mm width conveyors and a spreader of 11,000 TPH capacity. The fourth bench (Bottom Bench) is equipped with two 700 litres BWEs, a system of 2000 mm width conveyors and a spreader of 11,000 TPH capacity. The lignite bench has three 700 litre BWEs and a system of 2000 mm width conveyors. The excavated lignite is transported to a storage bunker on the surface of the mine. From there, lignite is reclaimed to the Thermal Power Station II by two Reclaimers of 2000 TPH capacity each and a system of 1800 mm width belt conveyors.
Fig 5.23 Plan of second mine cut at Neyveli Lignite Corporation Lid.
Dewatering Arrangements:
The principle of controlling the ground water is depressurisation by dewatering with large scale continuous pumping from a series of pump wells situated at hydro logically calcu lated distances around the mine. The pumpage of ground water is presently at the rate of about 150 Cu.m/minute from about 35 to 40 pump wells in the Second Mine. By the large scale pumping operation all that is achieved is keeping the pressure under control locally below lignite.
Storm Water Control:
Neyveli, being close to the eastern coastal area and being in the cyclonic belt, has a normal annual rainfall of 1200 mm to 2000 mm. The rain water during the monsoon months (October to December) poses many problems in the operation of the mine. This storm water is coursed to the deepest point of the mine by a pattern of toe and cross drains, where pumps mounted on pontoons are deployed in these sumps and the pontoon pumps are shifting accoring to the configuration of the lignite floor. Storm water from the sumps can be pumped directly to the surface with high head pumps mounted on pontoons.
Drilling and Blasting:
The overburden in the Northern half of the mine consists of hard Cuddalorc Sandstone which needs blasting before excavation. Presently about 30% of the total overburden is to be blasted in the Surface and Top benches.
Communication:
Due to enormous size and multifarious activities special communication facilities are provided through wireless be tween various machines, conveyors, drive head/tail end stations and service yards to the Control Room for smooth co-ordination of all activities in the mines. Separate frequencies/channels have been provided so that there exists no interference in communicationsamongst various machines and yards. Paging system is also planned to be introduced for quicker contacts.
Exploration work is going on for the third mine of proposed 10 million te/yr capacity. The third mine, area 25 km3, will be located to south of the second mine.
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