Lignite is the younger offspring of the coal family. It is a fossil fuel belonging to the Miocene age (25 million years). Popularly known as “Brown Coal”, lignite is tan brown in colour, light to handle and brittle in nature. This fuel is born from vegetable matter having undergone bio-chemical decay to the stage of peat (rotten wood) and then metamorphosed to lignite under the pressure of the soil above through floods, movements of the earth’s crust and dehydration when the pressure of the lignite, particularly the horizontal thrust is further increased, lignite is made more dense, less volumetric and becomes coal as such.

The lignite mined at Neyveli varies in colour from brown to dark brown and has a non-bonded granular structure. Microscopic studies of this sections prepared from bulk samples of lignite indicate that the fuel is composed of a wide variety of plant ingradients, mainly of coniferous nature.

Quality of Lignite:
Lignite contains 65-70% of carbon, 20-25% of oxygen, about 5% of hydrogen and small amounts of nitrogen and sulphur. The average calorific value of lignite is 2400 K.cal/Kg. It cannot be compared favourably with the high calorific value of pure coal. Yet lignite has an advantage of being free burning (non coking), of having low ash and of giving rapid and complete combustion. Since the volatile matter is usually high, lignite burns readily. Air dried lignite is quite suitable for direct burning. For high capacity boilers lignite can be burnt in the pulverized form.

Characteristics of Overburden and lignite

Some of the unique characteristic features of the Neyveli Lignite Mine are:
Occurrent of Ground water Aquifer below lignite bed: Huge reservoir of ground water occurs below the entire lignite bed, exerting an upward pressure of 6 to 8 kg/cm2. Unless this water pressure is reduced before mining, it will burst the lignite seam and flood the Mines. The problem is solved by selective bore wells formation and pumping to depressurise the water pressure to the safe mining condition. The water is being used for the TPS water requirement. The water level is continuously monitored through observation wells for proper ground water management.

Hard overburden strata:
The highly consolidated strata consists mainly of Cuddalore strand stone which is hard and abrasive in nature. The Bucket wheel used for handling large volume of overburdens faced problems due to the hard strata and uses overcome by carrying out suitable modification in the bucket wheel teeth and by instituting a systematic drilling and shatter blasting programme.

MINE – I

Demarcated over an area of 26.69 sq.kms. with a reserve of 365 million tones. Mine-I is situated on the northern part of the field adjacent to the Neyveli Township. This mine has a production capacity of 10.5 million tones of lignite per annum and feeds lignite to the 600 MW capacity of First Thermal Power Station and 420MW Thermal Power Station – I Expansion.

The lignite seam was first exposed in August 1961 and regular mining of lignite commenced in May 1962. German Excavation technology in opencast mining, using Bucket Wheel Excavators, Conveyors and Spreaders is used in this Mine for the first time in India. While overburden thickness varies from 50-95 metres, lignite thickness varies from 10 to 23 metres. The overburden to lignite ratio in this mine is 5.5 to 5 c.metre to one time (about 11 times of overburden is to be removed for mining one tonne of lignite).

In addition NLC deploys conventional mining equipments, viz. dozers, shovels, dumpers, back hoes, pipe layers, Motor Graders, Cranes, etc. as supporting auxiliary equipment.

Conveyor Deployment in Mine-I& 1A as on 01-07-2006

Storm Water Management:
Neyveli mines are located in predominantly monsoonic and cyclonic area where the average rainfall in a year is about 1200 mm and the wind velocity goes up to 160 km per hour Heavy rain flood the open pit bottoms and these difficulties are met by evacuating the flood water through float pump mounted on floating pontoons. Intermediate booster stations pump out the storm water to the surface level.