1

NLC’s EXPERIENCE IN MINING LIGNITE - A CASE STUDY

*R.Deivam, **M.Sivakumar

INTRODUCTION:

Neyveli Lignite Mines play a major

role in generating the energy needs of the states

of South India. Lignite mining at Neyveli

commenced about half a century ago by

Neyveli Lignite Corporation Ltd (NLC), a

Government of India Enterprise. Continuous

mining technology using Bucket Wheel

Excavators (BWE), Belt conveyors and Spreaders was adopted. The transfer and

adoption of Bucket Wheel Excavator

technology at Neyveli was a landmark event,

and it has helped the company to reap profits

during its life. The successful deployment of

BWEs was made possible by adopting suitable

modifications in the design of the buckets, teeth

and structural parts to tackle the hard and

abrasive nature of overburden strata. The

lignite mining is also faced with adverse

hydrological conditions caused by confined

aquifer occurring below lignite seam, with an

upward thrust of 5 to 8 Kg/cm2.

The challenges posed by nature on lignite mining were aptly handled in the

Neyveli mines by continuous improvement in

coherence with the technological development

and up-scaling capacity of BWEs and by

continuously optimizing the Ground water

pumping pattern. Initially smaller capacity 350

litre BWEs with 1000 mm fabric belt

conveyors deployed were upgraded to 1400

litre Bridge type BWEs and 2400 mm steel

cord belt conveyors, to augment the lignite production from 3.5 MT/Annum to 24

MT/Annum. The paper traces the history of the

developments introduced in lignite mining at

Neyveli mines during the past five decades.

2. LIGNITE RESOURCES OF INDIA:

Unlike coal, lignite is a low calorific

fossil fuel for producing electricity. About

38.93 billion tones (BT) of lignite reserves of various categories have been identified in India,

(Table. 1) mostly in the states of Tamil Nadu,

Puducherry, Rajasthan, Gujarat, Jammu &

Kashmir and Kerala. Tamil Nadu and

Puducherry possesses 31.74 BT of lignite

(Fig. 1).

Table: 1 Lignite resources of India

State Lignite Reserves in Million Tonnes

Tamil Nadu 31327.02

Rajasthan 4485.43

Gujarat 2662.75

Puducherry 416.61

Kerala 9.65

Jammu & Kashmir 27.55

West Bengal 1.15

Total 38930.16

NEYVELI LIGNITE MINES:

Neyveli Lignite Corporation Limited

(NLC) presently operates four opencast lignite

mines namely Mine-I of 10.5 MT/Annum.,

Mine-II of 10.5 MT/Annum. Mine-IA of 3.00

MT/Annum. and Barsingsar Lignite Project

(BLP) at Rajasthan of 2.1 MT/a. Mine-II is

under expansion from 10.5 MT/Annum. to 15

MT/Annum. (Table-2) The lignite produced is

mainly used for power generation.

* - Dy. General Manager/ Mine Planning/ Mine-I&IA, NLC Ltd.

** - Chief Manager/ Mine Project Planning, NLC Ltd

2

Fig - 1

TABLE-2: SALIENT FEATURES OF NLC MINES

Particulars Unit Mine – I Mine - IA Mine - II BARSINGSAR

(RAJASTHAN)

Mining Area Sq.Km. 27.00 12.00 42.00 9.70

Details Units Mine – I Mine -IA Mine - II BLP

Capacity / Annum Million Tons 10.5 3.0 10.5 + 4.5 2.1

Lignite Reserve Million Tons. 365 120 613 53

OB Thickness Mts. 45 to 110 55 to 110 45 to 103 44 to 118

Lignite Thickness Mts. 8 to 26 6 to 24 8 to 22 15 to 25

Average Stripping

Ratio Tons: m3 1: 5.5 1: 7.0 1: 5.5 1: 4.81

Mining Started on Date 20.05.1957 30.07.2001 14.04.1981 07.08.06

Lignite First

Exposed Date 24.08.1961 24.03.2003 30.09.1984 21.05.2007

Overburden

Excavated * Mill. Cu. Mtr 1405.67 118.98 1000.11 16.50

Lignite Mined * Million Tons. 260.87 14.02 164.10 0.04

Linked Power

Station Name

TPS - I (600MW

& TPS–I

Expn. (2 X 210

MW)

ST-CMS (Pvt.)

(250 MW)

TPS - II (7

X 210 MW + 2 x

250 MW)

TPS

2X125MW

Generation Capacity MW 1020 250 1470 + (500)** (250) **

* As on 1st April 2008 ** Under execution

4485

38930

38930 MT

3

3. METHODOLOGY OF MINING:

The lignite deposit in Neyveli lignite

field forms a part of Cauvery basin. A thick

formation of upper cretaceous, tertiary and sub-

recent sedimentary rocks, both marine and

fresh water are overlaying the Archean

basement. Lignite is mainly of single seam

with 1 in 100 gradient. The overburden in

Neyveli field mainly consists of argillaceous

and ferruginous sandstone.

Continuous mining by Bucket Wheel

Excavator (BWE) – belt conveyor – spreader

combination is deployed for both excavation of

overburden and extraction of lignite in NLC

mines. NLC started with a 350 L. BWE and at

present it uses 1400 L BWEs. A huge reservoir

of artesian aquifer water occurs below the

entire lignite bed, exerting an upward pressure

of 5 to 8 Kg/cm2. Unless this water pressure is

reduced before mining, it will burst the lignite

seam and flood the mines. This problem is

solved by selective formation of bore wells and

pumping to depressurize the water pressure to

safe mining condition. The water is being used

in thermal power station.

4. HISTORY OF TECHNOLOGICAL

DEVELOPMENT:

The Neyveli Lignite Corporation

Limited was formed in November 1956, with a

primary objective of exploiting the lignite

reserves in Neyveli lignite field for generation

of power, as there was burgeoning demand of

power.

The most favourable mining area

containing about 200 MT mineable Lignite was

selected. The Mine was planned with a life span of 57 years, at a production level of 3.5

million tones per annum. The overburden

capping varied between 50 m. to 80 m. and that

of lignite from 10 m. to 25 m., with an average

stripping ratio of 1: 4.

The continuous type of excavators

(BWE) as used in German and Australian

Brown Coal Mining Industries were

recommended for adoption, after various

techno-economic studies. Mining started in

1957 by deploying a set of conventional mining equipments and gradually SME (Specialized

Mining Equipment) were added one by one

from 1958 to 1961. Initially BWE of 350 L.

and 700 L. capacity were introduced with 1000

mm. / 1200 mm. fabric belts and matching

capacity of spreaders.

The development phase of the mine was completed in September 1961. However,

the full production stage of 3.5 MT of lignite

per annum could not be achieved even after six

years (Table-3), due to capacity constraints of

the excavators (BWE’s) working in the hard

strata conditions and other related problems at

Neyveli.

Table: 3

Year 1957-58 1958-59 1959-60 1960-61 1961-62 1962-63 1963-64 1964-65 1965-66 1966-67 1967-68

OB IN MM3

2.40 3.24 3.45 4.07 4.05 3.16 4.68 6.97 9.03 10.52 13.91

LIGNITE IN MT 0 0 0 0 0.00227 0.35 1.20 1.60 2.56 2.46 3.44

Year 1968-69 1969-70 1970-71 1971-72 1972-73 1973-74 1974-75 1975-76 1976-77 1977-78 1978-79

OB IN MM3

16.24 14.84 12.33 15.18 12.78 13.23 12.24 12.25 18.12 16.42 18.04

LIGNITE IN MT 3.98 4.28 3.39 3.72 2.89 3.33 2.94 3.03 4.02 3.58 3.30

Year 1979-80 1980-81 1981-82 1982-83 1983-84 1984-85 1985-86 1986-87 1987-88 1988-89 1989-90

OB IN MM3

23.87 34.25 33.06 33.96 41.49 55.03 60.35 60.90 59.53 62.08 64.36

LIGNITE IN MT 3.25 4.45 5.88 6.40 6.63 7.11 7.29 8.55 10.15 11.41 11.24

Year 1990-91 1991-92 1992-93 1993-94 1994-95 1995-96 1996-97 1997-98 1998-99 1999-00 2000-01

OB IN MM3

64.58 73.07 86.02 83.76 85.37 93.40 94.21 96.50 95.74 100.47 109.05

LIGNITE IN MT 11.76 12.54 13.31 14.15 15.41 17.21 17.35 18.11 18.17 17.55 18.17

Year 2001-02 2002-03 2003-04 2004-05 2005-06 2006-07 2007-08

OB IN MM3

122.25 109.03 116.07 120.44 119.66 128.07 135.83

LIGNITE IN MT 18.37 18.62 20.56 21.57 20.44 21.01 21.59

GROWTH OF OB & LIGNITE PRODUCTION OF NLC FROM 1957 Units in MM3/MT

4

Several improvements and design changes /

modifications had to be carried out in the

bucket wheel excavators which were not able to tackle efficiently the hard, abrasive nature of

Neyveli overburden. The problem of confined

aquifer exerting an upward pressure of 5 to 8

Kg/cm2 at the bottom of lignite had also to be

controlled by adopting a predetermined

pumping pattern which took some years to

develop.

The mine was not able to achieve the

production targets to fulfill the demand of

downstream units and no significant

improvement of production till 1967-68.

During the period of third and fourth

five year plans (1961-65 and 1966-70), it was

also proposed to expand the power station

capacity from 250 MW to 400 MW and then to

600 MW to cope up with increasing demand of

power in the state and to expand the capacity of

mine correspondingly from 3.5 MT/a. to 4.8 MT/a. and then to 6.5 MT/a.

Though expansion of power station

went without any major setback, the

corresponding increase in the capacity of the

mine could not be achieved, even after the

introduction of equipments proposed in the

Project Report. Lignite production continued to

be in the range of 2.4 MT/a. to 3.4 MT/a. as

against the demand of 4.8 MT/a. which would

further increase to 6.5 MT/a. by late 70’s when

the power station reached 600 MW.

The major reasons for the shortfall in SME

production were:

There was no provision for forward

preparation of ground with explosives. On

actual experience it was found that without

forward preparation, it was impossible to keep

BWEs in a healthy stage even when operated at

the rate of production much below the

manufacturer’s specification.

On account of the abrasive nature of hard

Cuddalore sandstone strata, the buckets and

teeth were damaged rapidly causing frequent stoppages and high downtime.

5. EVOLUTION OF BUCKET WHEEL

TEETH:

The physical and geological

investigations showed that the nature of

sandstone in the overburden strata varies from

very coarse-grained hard sandstone to very

fine-grained friable sandstone.

The hematite nodules embedded in the

formation offer a very high resistance to the

teeth of bucket wheel excavator. The cutting

resistance of such strata varies between 150-

200 Kg/cm as against 70 to 100 Kg/cm in West

German overburden strata. The first set of

original teeth supplied by supplier of the

equipment (M/s. LMG) fitted to 350 L. bucket

wheel excavator lasted only 3 ½ hours. This

meant that the excavator had to be stopped for a

major portion of the time for changing the teeth

alone.

Many field tests were carried out by changing the design of the teeth initially spade

shape teeth used in front of bucket had been

changed to ripper type, the angle of fixing them

to the bucket and cutting lips etc. In addition,

tungsten inserts were brazed to the teeth.

Ultimately the life of the teeth could be

improved to more than 250 hours (Fig. 2).

However, the shock loads on account of hard

and abrasive soil conditions, reflected on the

other machinery parts, particularly the bucket

wheel drives, bearings, shafts and ultimately

the loading boom structures. These were

strengthened and modified suitably with the co-

operation of the manufacturers and the material

composition was improved to withstand greater

stresses and strains in the structural parts.

Improvements also made / carried out

progressively in other main parts of the

machines such as turn table, under carriage,

crawlers and pivot points. Details of some

major modification carried out are shown in

Table-4.

Improvements attained out of such

modifications have been substantial and the

experience gained has helped in arriving at the

present set of equipment in which most of the problems have been eliminated.

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Fig.2

LIFE 200 Hours

( Approximatly )LIFE 200 Hours

( Approximatly )

LIFE 250 Hours

( Approximatly )

LIFE 250 Hours

( Approximatly )

LIFE 3 1/2 Hours

( Approximatly )

L IFE 6 1/2 Hours ( Approximatly )

LIFE 2 1/2 Hours

( Approximatly )

LIFE 15 1/2 Hours

( Approximatly )

L IFE 100 Hours

( Approximatly )

L IFE 50 Hours

( Approximatly )

LIFE 100 Hours

( Approximatly )

LIFE 250 Hours

( Approximatly )

L IFE 250 Hou rs

( App roximatly )

L IF E 250 Hou rs

( Ap p ro ximatly )

1.

Fitted in all positions

2.

Hard faced with electrodes

fitted in LH, RH, C1,C2

3.

F itted

in C1,C2

4.

F it ted

in LH, RH

5.

Fitted

in LH, RH

6.

F it ted

in Position C1,C2

7.

Widia Inserts fitted

in Position C1,C2

8. Fitted

in Position LH

( Shorter In Length )

13. 9. F itted

in Position RH

( Longer In Length )

10. Fitted

in Position RH .

4 Inserts

( Longer In Length )

11. F itted in Position LH . 4 Inserts

( Shorter In Length )

12.

With Widia inserts Hard

Faced With Electrods

F itted in Position C1, C2

With Widia inserts Fitted

in RH ( Longer in Length)

Harde Faced With Electrods

14.

With Widia inserts Fitted

in Position LH ( Shorter in

Length ) Harde Faced With

Electrods

E1

RH

C1 C2

LH

E2

E1- Right Corner Tooth

RH- Right Side Tooth

C1- Central Tooth Right

E2- Left Side Tooth

LH - Left Side Tooth

C2 - Central Tooth Left

Forward preparation is also very important for

the performance of BWEs in the hard strata.

Presently more than 45% of the

overburden soil is blasted for loosening of the

Matrix in inside Benches for ease in

Excavation.

TABLE-4 EQUIPMENT MODIFICATIONS INTRODUCED IN BWE AT NEYVELI

Component Problems

Encountered Modification

Bucket teeth Heavy wear due to

abrasion and breaking

Profile modified to suit the cutting condition. Tungsten Carbide hard cutting inserts provided. In addition to

hard facing of wear out areas. Fixing of teeth body to

buckets with high tensile bolts instead of wedges and

ordinary bolts.

Bucket and

cutting bows Heavy wear and tear

Profile modified. Lips are provided with hard facing.

Provided chain backs to avoid build up and spillage.

Bucket wheel

ring chute

Heavy wear and build

up in chute

Thick and wear resistant plates and strips provided.

Ring chute modified with thick wear plates. Hoppers

provided with synthetic material lining to avoid soil

build up and also wear.

Rotary plate Frequent failure of the

Cyclo gears

Cyclo gears modified into planetary gears and also the

fluid coupling was introduced.

Bucket wheel

boom, discharge boom,

Structural failures

Bucket wheel boom head modified with solid plate

construction and all booms made either with plate construction or with built up sections instead of lattice

6

Component Problems

Encountered Modification

Superstructure construction. Super-structure and other booms, built up

construction and plate construction against lattice

construction.

Slewing counter

weight

Frequent failure of

pivot bearing

Bearing with axle modified in the old machines and

slewing counterweight totally eliminated in the new machines.

Number of

conveyor flights

Three conveyors in the

old system. Short belts

required frequent

replacement

Changed to 2 conveyor systems eliminating short

flights.

Slewing center

pivot (700 L.

machines)

Frequent contamination

with soil

Position of the bearing changed and center pivot bearing

strengthened.

Bucket wheel gearbox

Frequent failure in the differential system

Single step down gearbox without speed variation.

Slewing

mechanism

Frequent failure of

Cyclo gears in slewing

system particularly in

350 L. machines

Cyclo gears eliminated and planetary system introduced.

Modification of Bucket to handle Sticky Clay:

In addition to hard abrasive overburden

soil, an entirely different strata was also

encountered in Mine II of NLC, which is

located 5 Km. south of Mine I. A blackish

alluvial clay formation occurs on the top 7 to

17 m. thickness in the southern portion of

second mine. This alluvial clay formation

carried large quantities of “KANKAR” nodules

with very low alumina Al2O3 content and iron

content Fe2O3. When wet, the clay absorbs

water, swell (about 1.6 to 1.7 times) and

become plastic (plasticity index of about 35%),

soft and slushy.

This soil (Alluvial Clayey Overburden) was

choking the bucket and the excavated soil was

not freely discharging from the buckets. The

capacity of the buckets got reduced due to the

clay build up on sides and the back of the

bucket resulting in low excavation rates. At

times the total bucket was fully choked /

packed with clay. About 25 to 30% of the soil

excavated spilled onto the ground necessitating

repeated dozing for clearing and re-handling

the soil.

Fig: 3

Teflon sheet

7

Several modifications were carried out

for the satisfactory handling of the sticky clay

and proper discharge from the buckets.

Various experiment measures tried were:

• Perforating buckets with holes and slots on the sides (which reduce contact area) instead

of plates.

• Providing buckets with linolex rubber

solution.

• Coating buckets with special rubber solution.

• Providing buckets with special ceramic lining

plates

• Lining of buckets with high density

polyethylene (HDPE) Teflon sheets.

The result of lining of Teflon sheets (Anti

friction) was encouraging. Hence, now all

the buckets, chutes leading to the rotary

plates, diverters etc. are all lined with Teflon

sheets(Fig: 3).

Similarly, the solid back of the buckets were cut open and chains were filled to the

back of the buckets. The sticking of the soil

was reduced considerably in the chain backed

bucket due to the whipping action of the chains

and the soil is getting emptied from the bucket

easily, resulting in improved production

performance.

6. 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 2600

K.cal/Kg. It cannot be compared favorably with

the high Calorific value of pure Coal. Yet lignite has an advantage of being free burning

(non coking), having low ash and 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.

Lignite is being mined only through

opencast mining method due to associated geo

mining problems. Continuous mining method

with Bucket Wheel Excavator-Conveyor-

Spreader technology is adopted in all the

Neyveli Lignite Mines.

Problems due to Marcasite:

Occurrence of Marcasite within the lignite

seam is a common phenomenon. Marcasite

which is a Ferrous Sulphide mineral (FeS2)

occurs as thin veins within the lignite seam and

is more predominant in Mine-II. The Marcasite

veins are not uniform and do not follow any

pattern. It is sporadic in nature and hence could

not be segregated while mining. They create clinker formation when fed into Thermal

boilers and affect the performance of the Power

Plant. Hence before dispatch to Thermal

bunkers this Marcasite is separated by hand

picking at Lignite storage bunkers. Due to hard

and abrasive nature, they at times create

problem like damaging the Bucket wheel teeth,

frequent changing of teeth etc during mining

operation.

7. DEPLOYMENT OF CONVEYORS IN

NLC MINES:

Initially from 1959 to 1965 about 8 km

of belt conveyor of 1000mm for lignite

handling (1000 TPH) and 1200mm (2500 TPH)

wide belt conveyors for OB handling were in

operation.

HURDLES FACED SINCE INCEPTION:

In the initial stages the conveyor carrying

capacity was just matching with the carrying

capacity of the loading equipment. While using smaller width conveyor the conveyor were

designed to capacity that matched with

equipments. The Bucket wheel excavator at

times due to loose strata condition used to

deliver spurt loads which will be more than the

excavator capacity. When these load were

transmitted to the belt conveyor, there were

stoppages due to overload, overflowing,

choking of transfer points etc., the above nature

of stoppages lead to snapping of belts, burning

of motors, and also needs manual cleaning of

the loaded belt to the entire stretch. Trouble

shooting and resetting of the electric contactor

relay were time consuming. Due to overload

the high resistance fuse used flown off very

frequently.

Later the conveyor carrying capacity/

handling capacity has been designed at 25 to

30% more than the capacity of the loading equipments. There by the choking of transfer

points and tripping due to overload has been

avoided. More over the running of the conveyor

has become smooth. As the strength of the

conveyor belt is more and designed to carry 30

% more than the loading equipment capacity,

the belt snaps / joint failures are eliminated.

8

The belt joints were snapped/ failed

frequently since this system of power

transmission from motor to belt was normal

gear transmission. As the drive power of the conveyor increased and fluid coupling, slip-ring

transmission etc., were introduced to transmit

the motor power to belt, there is smooth

transmission of power and no belt joint snaps

etc.

The carrying and return idlers were of

fixed type and if any small misalignment of the

conveyor / frames cause the line out of the

conveyor belt and there by damaging of the

costly belt and causing more stoppage for

changing of the belt in premature damage. The

installation of suspended garland type idlers

during 1980s (self aligned idlers) instead of

fixed idlers was one of the major modification /

break through development with belt conveyor

system design. These idlers have an in built

tendency to make the belt run centrally.

Thereby belt edge damaging is totally

eliminated. Moreover the garland idlers station

(or) transfer points. The troughing angles also got standardised and for conveyor of 1500 mm

the troughing angle is 30o and for 1800 mm and

2000 mm conveyors the troughing angle is got

fixed as 40o. Further all the fabric belts have

been removed and only steel cord belts have

been introduced as given in Table-5.

Initially NLC used 1000mm, 1200mm

width fabric belts. Since their tensile strength is

low each of the conveyors has been laid for a

length of 300 to 400 m. Due to short length of

the conveyors the life of the belt was only

10000 hours which warranted frequent

replacement of the belt. In 1970s 1500 mm

overburden conveyor belts were changed to

nylon x nylon with a drive power of 4 x 75 kw

with fluid couplings. However in this case also

conveyor length is restricted to 75 kw motors

by which the conveyor lengths gone up to 500

to 550 m only. In late 1970s, 1800 mm wide

steel cord conveyor belts were introduced with

a drive power of 3 x 400 kw were extended

upto 1.2 km with a carrying capacity of 8000

tph. In 1980s fabric and nylon belts were

removed and steel cord belts were introduced in

a phased manner. Presently steel cord belts of

tensile strength of 4000 kg/cm width of the belt are in operation. The length of the steel cord

belt conveyors are increased to 2.5 to 3.0 km.

The life of the belt also increased to 30000 to

35000 hours.

Details of conveyors - Table No.3

Troughing angle Conveyor

width

‘mm’

Type of belt Strength

of the

belt Carrying

side

Return side

Carrying

capacity

‘tph’

Capacity of

motor used (kw)

1000 Fabric <1000 30 o 0 o 1200 45

1200 NY-NY 1000 30 o 0

o 1400 45

1500 NY-NY 1200 30 o 0

o 1800 75

1500 NY-NY 1200 30 o 10 o 2000 350

1600 Steel cord 1600 30 o 15

o 4700 350

1800 Steel cord 2000 40 o 15 o 8000 400

2000 Steel cord 2250

3150

40 o 15

o 11000 630

2400 Steel cord 4000 45 o 15 o 20000 1250

This 2400mm conveyor troughing angle has been modified as below

2400 Steel cord 4000 40 o 15

o 20000 1250

2400 Steel cord 4000 40 o 15 o 20000 1250

The conveyor procured after 1976 are all

having thyrister control system with induction

motor. The conveyor procured after 1994 are

all having PLC system. The Variable Voltage

Variable frequency drives have been used for

new conveyor in order to have optimum energy

consumption.

SHIFTING OF THE CONVEYORS:

There are shiftable conveyors at the

mine cutting face and dumping yard. At the

mine cutting face / mine advancing side after

completion of each block of 40/80 m face

9

conveyor has to be shifted to tackle the next

fresh block of 40/80 m, since Bucket Wheel

Excavator can cut 40 m block only at a time

and if Mobile Transfer Conveyors is provided

then exploitation of 80 m block is possible. Similarly in the dumping yard, dumping of

each 100 m to 120 m width, the dumping

conveyor has to be shifted 100 m laterally to do

a fresh dumping block.

Since in the initial stages the conveyors

were small in size, the shifting of conveyors

was carried out just by pushing with dozers to

new location. However in due course the

conveyor sizes were increased. The 2000 mm

workshop type drive heads are weighing about

80 to 100 tonnes and were pushed / shifted

using bigger size bulldozers and special

equipment called pipe layers of 90 tonnes

capacity. The 2000 mm conveyors are also

heavy in structure and the steel cord belt

running in this conveyor is also of more in

weight. Hence instead of pushing by dozers, a

unit called pipe layer fitted with shifter head are

used in shifting the conveyors. The 2000mm drive heads of latest type are weighed about

250 tonnes, since all the drive powers / units

with motor, gear box, electrical panel are

mounted on the conveyor itself. They are

weighing 250 tonnes and shifting these drive

station are not possible by just bulldozer and

90 t pipe layers. These heavy drive heads of higher drive powers are moved / shifted using

hydraulic walking pads. These walking pads

are of set (2 nos ) fitted one walking pad at

each side of the drive station. They lift the drive

station using hydraulic power and moved about

half a meter at a time. These walking pads are

having a limitation. They can shift the drive

station with a lifting limit of about 250 tonnes.

Due to these slow process of shifting the idle

time / non production time increases at every

shifting.

More over in due courses the length

and carrying capacity of the conveyor also

increased to tackle the need of high demand in

material handling. Now a days conveyor of 3.0

km with a carrying capacity of 20000 tph, 2400

mm steel cord belt of ST 4000 are in use. These

conveyors having a drive power of 4 X 1250

kw ( 4 motors of 1250KW ) at drive heads with other drive units and electrical kiosks. These

drive units weight is more than 500 tonnes.

These units cannot be moved with walking

pads. Even if it is moved with walking pads,

the slow processing of shifting these conveyors

will increase the down time of costlier

production system. Hence an improved type of

transporting these drive heads called “Transport Crawlers” were introduced. These transport

crawlers can be inserted under these heavy

drive units which can lift the drive units and

move at a faster rate ( 8 m/min ).

IMPLEMENTATION OF VVVF DRIVES

IN CONVEYOR:

NLC has recently procured conveyor

(2000mm & 2400mm) with variable voltage

variable frequency (VVVF) drives motor. This

improvisation is helpful in optimizing power

consumption. The advantages of using VVVF

drives are as follows:

• VVVF drives are fully digital using proven

technology based on pulse encoder

feedback technology for individual motors.

• VVVF drives are able to feed standard

squirrel cage induction motors.

• The power factor of the system is not less

than 0.90, so that there is substantial saving

of energy.

• The drives facilitate smooth starting and

thereby resulting in lesser downtime of the

conveyor / machine.

• The drives have digital control with highly

accurate speed setting and repeatability

ensuring maximum precision for process

control.

• Along with the fault messages, the display

includes energy consumption, motor speed

and elapsed running time etc. for easy

monitoring, which replaces the analog

metering and reduces cumbersome wiring.

• Provision to connect to PLC through

suitable bus. Built-in monitoring unit to

view the online status, faults, parameter

values.

• Provision to up-load / download of drive

parameters to a laptop PC and vice-versa.

• Special testing instruments, laptop

computer with suitable software, are

available for recording and load analyzing

of VVVF drives.

• The application of mechanical brake is

possible at any desirable speed as specified

by the machine builder, through PLC

software programme.

10

GROUND WATER CONTROL (GWC): (Fig :4)

(Fig :4)

As already mentioned the aquifer water

with upward pressure below lignite has to be

controlled / tackled for safe mining operation.

The ground water operations started in 1961,

for depressurization of aquifer. As the mine

advanced, the pattern of pumping was also revised from time to time for the maximum

draw down with optimum pumpage. In 1961-64

– these pumpings were from ground level

(surface pumping grid pattern). The pump

wells were operated around the mine at surface

level. There were more than 60 wells with a

pumping capacity of 55,000 to 60,000 GPM.

This pattern was changed to bench

pumping grid pattern and spoil bank pumping

pattern from 1964 to 1968 by which the

pumping was carried out at various bench

levels which were closer to lignite extraction.

By this, the pumping was reduced to about

50,000 GPM. The lignite bench pumping grids

were introduced in 1971, pumping on the

lignite bench on both side, the pumping from

this grid pattern was further reduced the

pumping quantum to 36,000 GPM.

Bund wells (From 1986 To 1995):

Bund was formed with overburden

materials on the mine floor after the excavation

of lignite. By this, the quantum of pumping has

been reduced to about 30,000 GPM. However

there was problem in drilling and establishing the wells in the dumped soil.

Present pattern of pump wells (From 1995

onwards): Fig: 5

To cope up with fast advancement of

mine cut and increased lignite production, a

decision was taken to establish pump wells in

the advancing side of the mine cut on the top /

middle bench level (Lower Overburden bench) and stage by stage brought down to lignite floor

level and operating the wells in the de-coaled

area after completion of lignite mining. It was

decided to operate two rows of pumping (160

to 200 m. between rows) on the de-coaled area.

By this pumping was drastically reduced to

20,000 to 25,000 GPM in Mine-I. The similar technology was adopted in all the mines.

Currently about 60,000 GPM of Ground Water

alone is pumped out in all the three mines put

together to excavate 24 MT / Annum. Where as

the same quantity of water was pumped for

mining 3.5 MT/Annum in early days.

Ground water wells

1960’s: Surface & periphery

60 Wells :Discharge 60000GPM

1970’S :Surface and top Bench

of the mines (Non-Mining

Activity Region)

40,000 to 50,000 GPM

1980’S(Late) : Spoil bank & on

the flanks (North & South).

30,000 to 35,000 GPM

1. WELLS ON THE GROUND LEVEL

2. SURFACE WELLS BENCH WELLS AND

FLANK WELLS ON THE (NORTH &

SOUTH)

3. INSIDE SPOIL BANK WELLS AND ON

THE FLANKS (NORTH & SOUTH)

(1960’s)

(1970’s)

(Late 1980’s)

11

8. PRESENT PLANS:

By various improvements /

modification, and technological developments

made in mining technology, NLC’s confidence

level has increased and opened new mine cuts.

Presently, NLC is operating 3 mines at Neyveli

and one

Bucket Wheel Excavators at NLC:

mine at Rajasthan totally producing 26.1

MT/Annum of lignite. GMDC at Gujarat also

adopted this technology of mining and

produced 7.0 MT of lignite during 2006-07.

EQUIPMENT

CAPACI

TY

(Litres)

Total

Bucket Wheel Excavator

(Bridge type)

1400 6

Bucket Wheel

Excavator

(Normal type)

1400 8

BWE with deep cut 700 6

facility

BWE without deep cut

facility 700 9

Bucket Wheel

Excavator 500 2

Bucket Wheel

Excavator 350 2

Bucket Chain

Excavator 500 1

Grand Total = 34 34

MOBILE TRANSFER CONVEYOR:

Spreaders at NLC: MOBILE TRANSFER

CONVEYOR CAPACITY Total

11,000 TPH MTC 11

6,400 TPH MTC 7

4,700 TPH MTC 3

4,050 TPH MTC 2

Total 23

Spreading Equipments capacity Total

20,000 TPH Spreader 4

11,000 TPH Spreader 5

8,000 TPH Spreader 1

6,000 TPH Spreader 4

4700 TPH Spreader 1

Total 15

A3

A2

A1

Fif.5

ADVANCING

SIDE

WELL”A1”- DRILLED AT MIDDLE BENCH ON THE ADVANCING SIDE AND BEING

CONVERTED TO (BY CUTTING THE CASING PIPES AS A2 BOTTOM BENCH WELL(A3)

LIGNITE BENCH WELLS IN STAGES AS THE MINE PROGRESS. PRESENT PUMPING IS IN THE

RATE OF 20,000 TO 25,000 GPM.

Fig.5

12

Length of Conveyors at NLC Mines in KM as on 1st April 2008:

Width 2400 mm 2000 mm 1800 mm 1600 mm 1500 mm

Type of Belt Steel cord Steel cord Steel cord Steel cord Steel cord Fabric

Total = 148.17 Kilometer 42.62 71.64 5.39 15.85 6.17 6.5

There are plans to open new mine at

Jayamkondan in TamilNadu, Bithnok and

Hadla in Rajasthan & Valia in Gujarat and

additional projects at Neyveli to achieve the

goal of reaching 55 MT/annum of lignite in

2011-12 and 88 MT/Annum. in 2016-17 and to

touch 150 MT/annum. during 2031-32.

Table .7 Projected Production schedule upto

end of XV plan (2031-32)

New Initiatives

Presently, the following are the improved

technology implemented at NLC.

• Wireless Based Centralized Monitoring

Operation and Control System in Mine-IA

Top Bench:

Wireless based automation control in Mine-

IA consisting of one 700 L. BWE, one 4420

cubic meter/hour of MTC, five 1600 mm.

Conveyor of total length 5000 meters

(approximately) and one 4420 cubic

meter/hour spreader including networking of existing programmable logical control

stations for centralized monitoring, operation

and control. This would be very helpful for

operation as well as maintenance without

much wastage of productive time.

• PLC Based Automation System for Lignite

Bunker – Mine-I: PLC based automation

control for Mine-I lignite bunker conveyors

and machines including retrofitting of relay

logic with PLC in conveyors and Bunkering

machines, networking, centralized control,

operation, monitoring two way industrial

paging system and CCTV system was

implemented during

2006 in Mine-I. This has enabled in evolving

an automated system in operating lignite

bunker for smooth dispatch of lignite to various

downstream units.

The SMEs procured for Mine-IA and Mine-I

Expansion are of with PLC and other advance controls. Hence, the working hours of these

equipments are touching more than 6000 hours

per year. The equipments ordered for Mine-II

expansion are all incorporated with latest art of

technology like VVVF, PLC etc.

• Mining equipment maintenance management

system (MEMMS) (SAP based):

This system is to reduce the Breakdown, plan

preventive maintenance, reduces the stoppage

duration and also to reduce the inventory. Equipment details, maintenance task details,

manpower, spare parts are computerized. For

the work either planned or Breakdown, Work

order will be generated with all the required

information and tools to complete the work.

Based on the feedback from the maintenance

division equipment history, failure analysis,

job cost will be carried out.

End of XI PLAN XII PLAN XIII PLAN XIV PLAN XV PLAN

Year 2011-12 2016-17 2021-22 2026-27 2031-32

State

Tamil Nadu 24.516 38.096 55.096 64.000 75.000

Gujarat 23.730 37.830 39.904 44.000 48.000

Rajasthan 7.680 12.008 13.000 22.000 27.000

Total 55.926 87.934 108.00 130.00 150.00

% Annual growth

for plan period 12.51 11.5 4.51 4.01 3.10

13

• Drilling Development:

In Neyveli drilling is carried out for catering

to blast hole drilling, ground water control

wells and exploratory wells. Ground water

control wells are drilled in various diameters,

namely 4”, 12”, 24”, 36” and 42”. The

technique used to drill the large dia. hole >

24” is reverse circulatory method, were as

smaller diameter are drilled by straight circulated method. The pipes used are usually

MS pipes for large dia. and GI pipes for small

dia

• Seepage Control Technique in Lignite Mines:

In the year 2003, Mine-II faced acute seepage

problem in overburden benches (surface and

top) hampering the movement of machinery

and equipments. Several pumping / yield

tests were conducted in the large, small and

medium size bore wells with various capacity pumps and after studying the potentiality of

the combined aquifer (semi confined and

water table) zones the strategy of dewatering

were finalized. Dewatering of the combined

aquifer zones through various capacity of

pumps say 50, 100, 200 & 500 GPM has

been found effective method and has been successfully implemented to start within the

surface bench and subsequently shifted to the

ground level about 150 to 200 m. away from

the mine edge. The above dewatering is being

done as a pre-mine dewatering strategy,

wherein about 40 wells (4000 GPM) are

pumping intermittently (different capacities)

as and when the water levels fluctuate and

saturate the aquifer zone.

9. ENVIRONMENTAL CHALLENGES

AND ITS MANAGEMENT:

NLC handles the challenges posed by different environmental factors sagaciously.

The details relating to the challenges posed by

individual environmental factors viz. air, water,

land, humans etc and the environmental

management measures adopted by NLC to

handle these challenges are described in the

following pages.

Air pollution Control Measures:

NLC has been able to maintain these

good air quality standards by adopting proper

control measures for preventing air pollution,

which are enumerated below.

a) Deploying machineries with Electrical

power: Most of the machineries used in

mines are electrically operated and hence

the emission of noxious gases, which is

usual with diesel-operated machines, has been substantially reduced.

b) Dilution of gaseous emissions: The

Neyveli lignite mines are spread over a

large area and have a normal width to

depth ratio, which develops adequate

natural ventilation and dilution of

gaseous emissions through wind

sweeping and vertical mixing of air.

c) Green belt development: NLC had raised

171 lakh trees in the region over a period

of time. Dense foliage has been created in

the township, which has yielded multiple

benefits to the community. Besides being

a barrier against dust penetration into the

township, the dense foliage has reduced

the mean temperature by about 2 degree

Celsius, attenuated the noise generated

from the adjoining mines and thermal

poser plants and reduced the levels of

sulphur dioxide in air. It is found that a tree-belt of 10 metres has the capability

to bring down the noise level by 10

decibels and a cluster of trees in an acre

of land has the potential to absorb six

tones of sulphur dioxide.

d) Sharp teeth for Bucket Wheel Excavator

(BWE): Adequate precautions are taken in using sharp tooth for bucket wheel

excavators to reduce dust production.

e) Chutes at transfer points: Necessary

chutes are provided in all the conveyor

transfer points. Wipers/ cleaning devices

are provided underneath the conveyor

belt.

f) Water spraying at BWE excavation face:

High-pressure jet of water is sprayed at

active face where lignite is extracted by

BWE, which prevents generation of dust

at source.

g) Water spraying on haul roads by mobile

and fixed sprinklers: The lignite transport

road and access roads of overburden

benches are regularly sprayed with water

with the help of mobile and static water

sprinklers.

h) Dust extractors and wet drilling: All blast

hole drills have been equipped with dust extractors. Wet drilling is practiced for

drilling Ground Water Control (GWC)

wells.

14

i) Black topping of service roads: The

arterial service road connecting all

benches is black topped. The lignite

transportation roads have been Laterite

topped. Besides the truck operators engaged in lignite transportation have

been cautioned not to overload the

truck, which may cause spillage,

generating dust due to crushing by

running trucks.

j) Dust masks: The BWE operators and

persons working in the vicinity of the

BWE have been issued with dust

masks.

k) Electro Static Precipitators (ESP): High

efficiency ESP (100%) is installed in

the Flue gas exhaust of Thermal power

plants. Tall chimneys upto a height of

220 metres are constructed for wide

dispersion of flue gases.

WATER ENVIRONMENT:

Lignite mining and its associated

activities not only uses a lot of water but also

affects the hydrological regime of the area and

often affects the water quality. Large and deep

opencast mine usually have great impact on the

hydrological regime of the region. Moreover

the surface runoff water through nallahs and canals get polluted due to the waste generated

in mining and power generation operations.

Water Conservation and Pollution control

measures:

The measures taken by NLC for water

conservation and pollution control measures are

enumerated below.

a) Optimisation of ground water

pumping: Over the years NLC has

evolved the GWC pumping in mines

by taking concerted efforts towards

optimizing the pumping operations.

Pumping is done close to the location

of lignite extraction and a localized

draw down effect is obtained which

is just required to extract lignite

safely. A number of pumps are

operated simultaneously to obtain a

synergistic net draw down and a

calculated risk is taken by planning

the pumping operations for keeping a

positive pressure head of 5 to 7 meters above the Lignite bottom.

b) Rainwater harvesting & Artificial

recharging: Rainwater harvesting

system has been introduced in the

mines, power plants and township.

Artificial recharging of ground water

in the catch-ment areas has been

taken up by constructing check dams,

percolation wells and recharge wells

in Nadiyapattu and Maligampattu

villages near Neyveli and has proved

very successful. The geological plan

of Neyveli region showing the

recharge area and the location of the

villages is shown in Figure-II. The

photos of check dams and the

consequent effects in post-monsoon

period is shown in Figures-III & IV

c) Storm water treatment: 8000 GPM of

storm water pumped from Mine-I has

been diverted to treatment plant at

surface. The treated water is sent to

township for domestic use with

consequent reduction in groundwater

drawl from township bore wells.

d) Utilization of storm water for TPS:

NLC is taking steps for diverting

15,000 GPM of storm water from

Mine-II to Thermal Power Station-II

(TPS-II) and Thermal Power Station-

II Expansion after treatment in

treatment plant.

e) Sewage treatment plant: A modern

sewage treatment plant has been

established for treating sewage water

from township and the treated water

is let out for irrigation purpose. The

plant is operating effectively as per

the standards set by Tamil Nadu

Pollution Control Board (TNPCB).

15

Figure-II: Geological plan

showing villages where artificial

recharging is experimented

Figure-III: Check dam in

Nadiyapattu village (Before

Monsoon)

Figure-IV: Water storage in

upstream side (After Monsoon)

79° 15' 20' 25' 30' 35' 79 40’0

11 25’0

30'

35'

40'

45'

11°50'11°50'

45'

40'

35'

30'

25'

SETHIATHOPPU

VADALUR

BAY OF BENGAL

ERI

PERUMAL ERI

MINE I

MINE II

LIGNIT

E BOUNDARY

GADILAM RIVER

TO KUMBAKONAM

MANIMUKTA NADHI

TO CHENNAI PONNAIYAR RIVER

VELLAR RIVER

79° 50'45'40'35'30'25'20'79° 15'

11° 20'

NEYVELI

TOWNSHIP

SRIMUSHNAM

VEERANAM

TO CHENNAIBAHUR

PERUMAL ERI

TANK

WALAJA

VELLAR RIVER

PORTONOVA

MINE I EXPAN.

1A MINE

MINED OUT

MINED OUT

MINE II

MINE II EXPAN.

MINE III

South of Vellar Block

PANRUTI

KADAMPULIYUR

VRIDHACHALAM

ERI

BLOCK- B

BAY OF BENGAL

Kiramangalam Block

CUDDALORE

NEYVELI LIGNITE FIELD - GEOLOGICAL MAP

Sca le:

Pla te No.:

NEYVELI LIGNITE CORPORATION LTD., NEYVELI

1 : 1.75 Kms. A4 Signa ture :

N

S

EW

BLOCK

RECHARGE AREA

MINING LEASE BOUNDARY

191.28 mt 120. 0 mt

173.72 mt

98.41 mt

438.20 mt

375.0 mt

329.0 mt

75.87 mt

329.0 mt

GEOLOGICAL EXPLORATION DIVISION

LIGNITE BOUNDARY

LEGEND

ARCHAEANCRETACEOUSTERTIARYALLUVIUM

2

1(Maligampattu Village)

(Nadiyapattu Village)

79° 15' 20' 25' 30' 35' 79 40’0

11 25’0

30'

35'

40'

45'

11°50'11°50'

45'

40'

35'

30'

25'

SETHIATHOPPU

VADALUR

BAY OF BENGAL

ERI

PERUMAL ERI

MINE I

MINE II

LIGNIT

E BOUNDARY

GADILAM RIVER

TO KUMBAKONAM

MANIMUKTA NADHI

TO CHENNAI PONNAIYAR RIVER

VELLAR RIVER

79° 50'45'40'35'30'25'20'79° 15'

11° 20'

NEYVELI

TOWNSHIP

SRIMUSHNAM

VEERANAM

TO CHENNAIBAHUR

PERUMAL ERI

TANK

WALAJA

VELLAR RIVER

PORTONOVA

MINE I EXPAN.

1A MINE

MINED OUT

MINED OUT

MINE II

MINE II EXPAN.

MINE III

South of Vellar Block

PANRUTI

KADAMPULIYUR

VRIDHACHALAM

ERI

BLOCK- B

BAY OF BENGAL

Kiramangalam Block

CUDDALORE

NEYVELI LIGNITE FIELD - GEOLOGICAL MAP

Sca le:

Pla te No.:

NEYVELI LIGNITE CORPORATION LTD., NEYVELI

1 : 1.75 Kms. A4 Signa ture :

N

S

EW

BLOCK

RECHARGE AREA

MINING LEASE BOUNDARY

191.28 mt 120. 0 mt

173.72 mt

98.41 mt

438.20 mt

375.0 mt

329.0 mt

75.87 mt

329.0 mt

GEOLOGICAL EXPLORATION DIVISION

LIGNITE BOUNDARY

LEGEND

ARCHAEANCRETACEOUSTERTIARYALLUVIUM

2

1(Maligampattu Village)

(Nadiyapattu Village)

16

f) Dry ash disposal: NLC’s Two Thermal

Power Stations ( TPS-I & I Expn.) are

provided with dry fly ash collection system

and the 80% of the fly ash generated in

these plants are utilized by cement and

other industries. Installation of modern dry

ash collection system in TPS-II is under

progress and will be completed during

2008. Efforts are taken to utilize 100% of

the generated fly ash.

Land degradation Control Measures:

NLC takes necessary measures for minimizing these damages on land by properly

maintaining external dumps, adhering to a

systematically planned reclamation programme,

stabilisation of slopes, adopting innovative

methods and growing soil specific trees for

reclamation of the land. These measures are

discussed below.

To counter changes in temperature and

other atmospheric conditions extensive

afforestation within the mine lease area has been

done. So far around 171 Lakhs trees have been

planted since the inception of project. The details

of Afforestation done in Neyveli region is given

in Table-VI

a) Integrated Farming System: NLC has embarked on a project for transforming

the mine dump spoils into productive

agricultural lands through an eco-friendly

“Integrated Farming System” in

collaboration with Tamilnadu

Agricultural University (TNAU) at an

estimated cost of Rs.450 Lakhs. The

system envisages integration of various

enterprises viz. agricultural crops,

horticultural crops, forestry, animal husbandry, fishery, mushroom, biogas

etc., which have greater potentialities.

These enterprises not only supplement

the income but also help sustain the

productivity of the dump spoils and

thereby restore the ecosystem. The

project is being implemented with the following objectives.

� Standardization of crop husbandry and

allied enterprises for generating profitable

agricultural production system.

� Evaluation of seed hardening and seed pelleting technologies for various tree and

crop species for the successful

establishments in mine spoil.

� Monitoring soil physical and bio-chemical

properties in rehabilitated mine spoil

ecosystem.

� Physiological manipulation to improve the

growth and productivity of crops through

chemicals and growth regulators.

� Conducting green house and pot culture experiments and planting forest and fruit

trees.

� Exploitation of microbial systems for

improving the mine spoil to sustain crop

production.

� Assessing the carrying capacity of pasture, growth rate, production performance and

economic traits of animals.

� Monitoring the restoration potential of

biodiversity in the restored mine spoil.

b) Top soil Reclamation: The topsoil

contains all nutrients and micro-organisms

to raise agricultural crops. But the topsoil

gets mixed into a heterogeneous soil, since

the BWE can cut the soil to a minimum

height of 4 metres. In areas where topsoil is

found to be highly fertile it is identified and

stored separately for later topping in dumps

or refilled areas.

c) Bio-reclamation using Bio-fertilizer: A

pilot plant facility was setup to produce

various strains of baterial bio-fertilizer

using lignite as carrier and applied to mine

spoil in order to improve the microbial

activity and fertility of the soil. Field

experiments were carried out with various

microbes viz. nitrogen fixing and

phosphate solublizing microbes in crops

viz. green manure, maize and ragi.

Application of bio-fertilizer increased the

soil fertility, crop productivity by 15 – 40%

on using a dosage of 8kg/ha each of 4

baterial strains viz. Rhizobium,

Azospirilum, Azotobacter and

phosphobacteria. The total microbial activity achieved was to the tune of 0.6 –

1.1 million/ gm of soil.

d) Utilisation of Fly ash in Reclamation: Lignite fly ash is highly alkaline in nature,

texturally suitable for improving certain

important physical parameters of both mine

spoil and the lateritic soils of Neyveli and

rich in available plant nutrients viz., Ca,

Mg, K, P, S, Cu, Zn, Mn, Fe, B, Mo etc.

Field experiments were conducted with

different doses of fly ash in Neyveli

17

lateritic soil and back filled mine spoil over

a period of 4 years. Crops like paddy,

groundnut and maize were tested and found

that 20T/ha of fly ash increased the yield of

paddy by 20-40%. Application of fly ash @

200T/ha in lateritic soil increased the yield

of groundnut and maize by 30-60%.

e) Reclamation using Lignite based Humic

acid: Humic acid is the dark humus found

in soil and made up of organic matter

derived from plant breakdown by microbial

action. NLC has successfully developed a

process for extracting humic acid in the

form of Potassium humate from lignite.

Humic acid helps to retain the nutrients and

soil moisture, supports microbial activity,

and nitrogen fixation, and increases the

yield from 20-30% in mine spoil.

f) Formation of water fowl refuge, ponds

and picnic spots: An artificial lake of 10 acres has been developed in the backfilled

area and mines seepage water is pumped

into the lake. Fishes have been introduced

and the lake has been developed and

maintained such that it acts as a refuge for

migratory birds and hundreds of species visit it during different seasons. Figure-V

shows the water fowl refuge created in

Mine-I afforestation area. A picnic spot

was also created with boating facilities,

along with a mini zoo with rabbit, peacock,

dove, spotted deer, duck etc.

g) Satellite imagery studies: Satellite

imagery studies are conducted using

Remote Sensing data once in every two

years, to studying the changes in land use

pattern and levels of improvement in the

environment of the mining area.

h) Ash Pond Reclamation: Abandoned ash pond in thermal power stations causes air

pollution in windy season. To arrest the

menace, a trial was taken up in

collaboration with TNAU and Lime,

Farmyard manure, Red earth, Press mud, Bio-fertilizer were applied in the excavated

pits in recommended dosage. Plant species

like Neem, Casurina, Cashew, Teak, White

babul and Tamarind were planted and the

plants were found to have better growth

which helped to arrest soil erosion and dust

generation completely.

9. ALTERNATIVE TECHNOLOGY FOR

FUTURE:

To gain fully, utilized vast potential of

lignite deposits, which are uneconomical for

conventional mining, the following non-

conventional alternative technology is considered

by NLC in future.

� Underground Coal Gasification (UCG)

� Coal Bed Methane (CBM)

Coal Bed Methane:

o CBM is a natural gas produced by bio-

thermogenic degradation of buried plant

material during the process of coal formation.

o Methane is associated with all coals including

lignite.

o Coal and lignite beds are both source and

reservoirs.

o There is a vast lignite resource at Mannargudi

block of Tamil Nadu. There is totally 23.2

BT of lignite at Mannargudi in an area of 750

Km2 to a depth of 150m to 600m with a

lignite thickness up to 100m. This deposit is

of greater potential for development as CBM

Field.

o At the instance of NLC, the Mannargudi

lignite deposit has been proposed for

undertaking CBM exploration under the promotional exploration program.

Underground Coal Gasification (UCG):

NLC in its effort to diversity its resource base

for power generation intends to develop and use

the technology of UCG in lignite resources.

A technical delegation from NLC and

Ministry of Coal, Government of India (GOI)

visited UCG site at Chinchilla, Australia and it is

of the view that UCG can provide commercial

quantities of industrial gas which can be used for

power generation and supply at competitive rate.

In view of the successful demonstration of

UCG development recently in Chinchilla,

Australia there is a possibility in India also for

tapping the energy from uneconomical lignite

block by advantageously utilizing UGC for

possible power generation.

Due to the in-situ specific nature of the UCG

project, a pilot scale UCG testing evaluation and economic assessment of development and

utilization are essential for implementation of full

scale UCG project in Indian condition.

A project titled “Underground Coal

Gasification (UCG) and its utilization for power

generation studies in lignite deposits in

Rajasthan” has been undertaken by NLC under coal S&T grant of Ministry of Coal, Department

of Science and Technology (DST).

18

Concluding Remarks:

NLC is successful in adopting the continuous

mining technology and also contributing in the

development of continuous mining technology by

constant modification and development of the

technology to suit hard abrasive strata condition.

The lignite production was only 2.5

MT/Annum in mid of 60’s and there was a

quantum jump in production of lignite after 80’s

and reached the level of 31 MT/Annum presently.

There is a scope for further development in

lignite production due to enormous demand of

power. Already plans are on anvil to start various

lignite mines and linked power projects to

achieve the goal of production of 150 MT/Annum

of lignite in 2031-32.

Abbreviation:

NLC – Neyveli Lignite Corporation Limited. S&T - Science and Technology

BWE – Bucket Wheel Excavator. Mm3/ MM3 – Millions cubic meter

MT/A – Million Tons Per annum. MT- Million Tons

GOI – Government Of India BT – Billion Tons

TPS – Thermal Power Station SME- Specialized mining Equipment

350L – 350 Litre etc. GPM – Gallons per minute