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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.
5
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