Planning Considerations for Future Longwalls
M. Venkat Ramana Rao**
There is a definite place for coal in world as well as Indian energy scenario and will
continue to play the dominant role. Presently, Coal provides for around 23% of global
primary energy needs accounting for 38% of world’s electricity generation and it may
increase further with the increase in demand for power. This will clearly indicates that the
demand for coal will reach its peak in the coming years. The expected demand for coal in
India by 2011-12 is about 707 M.T, whereas coal production would be around 550 M.T,
leaving a gap of about 157 M.T. It requires serious thought for reducing the gap by planning
the bulk producing technologies.
In India, maximum share of production is from Opencast mines and underground
mining share is less and losses are more. The scenario is not different in SCCL also. This
situation may not continue for ever as the reserves suitable for opencast mining are
gradually depleting. To meet the future coal demand the only available alternative is bulk
production underground technologies. The present underground mines are operating at
depths of 350m and the future extraction is from deeper horizons. Longwall mining is the
proved technology for extraction of deposits from deeper horizons. So far, The Indian
Longwalls have not presented any signs of success and the production levels are no where
near to the world standards. It is the time that, strategies and plans are to be formulated for
the future Longwalls with high capacity equipment for achieving production levels for
making Longwall economically viable and profitable. This paper attempts to deal with few
design considerations of Longwall equipment for meeting the challenges ahead.
In India, the pace of development of Under Ground mechanization had been tardy
mostly because of improper equipment selection, non-availability of spares & equipment
itself. We have come to a stage wherein no further experimentation is acceptable and the
technologies we are going to adopt in future are suitable for the Indian Geological Conditions
and must produce coal in bulk. Apart from going for modern technologies for deep mining,
we have also to think of liquidating the developed pillars in our country which constitute
around 3 billion tonnes. The variants here could be Continuous Miner and Remote Operated
LHDs wherever feasible and SDL where the gradients are steep. Blasting Gallery is already
successful in SCCL and need to be extended wherever conditions are suitable.
* Additional Manager, Mech. Cell, Corporate Planning
** Under Manager, Corporate Planning
THE SINGARENI COLLIEIRES COMPANY LIMITED, KOTHAGUDEM
All the above mentioned technologies are suitable up to a particular depth i.e.,
450mtrs. At deeper horizons, high capacity Longwalls looks to be the only alternative. In
manual working we essentially have concentration of workers in the face resulting in the
involvement of more persons whenever there are dangerous incidents. Mechanization will
definitely improve the safety standards, as the concentration of workmen becomes much less.
As on date, Indian Coal Mining is recording profits only because of its Opencast
Mines. All most all the Underground Mines in the country are losing. The present
proportion of OC to UG in our country is about 80:20. In future, this may have to go up to
60:40, which means that the UG mines will have to produce not only in bulk but also at an
economical rate. This demands changes in future coal mining technologies in our country in
general and SCCL in particular and for both virgin blocks as well as developed pillars.
Fully mechanized Longwall Mining was started in India in the year 1978 at Moonidih
Colliery and in between 1978 and 1985 a number of longwall units have been installed. In
SCCL, first Longwall face was started in September 1983 at GDK.7 Incline, Ramagundam.
Till now, 69 Panels have been completed successfully and presently 4 units are working with
an average production of 0.3 MT per annum. When we compare with the world standards it
is too low, for example in 2004-05 Australia has produced 73 MT from 24 Longwall Panels
averaging out to 3 MT per annum per panel. This clearly shows the Indian Longwall
performance levels. This paper deals with the reasons for the poor performance and the
designed considerations required for future longwalls to achieve the world production
2.0 ENERGY SCENARIO:
It is an accepted fact that Minerals are essential for the development of modern
industrial society. Economic growth the world over is driven by energy, whether in the form
of finite resources such as coal, oil and gas or in renewable forms such as hydroelectric,
wind, solar and biomass, or its converted form i.e electricity. Coal provides for around 23%
of global primary energy needs accounting for 38% of world’s electricity at present. World
coal consumption is projected to go up to about 6.4 billion tonnes by 2020. Most of this
increase would be primarily in China and India, which are expected to account for about 75%
of the increased consumption.
Among all the minerals available, Coal is playing a dominant role in world’s energy
generation vis-à-vis industrial development with large reserve base. Coal is uniquely placed
in respect of all the elements of energy security.
As the International Energy Agency has commented (1):
“World reserves of coal are enormous and, compared with oil and natural gas,
widely dispersed... The world’s proven reserve base represents about 200 years of
production at current rates... Proven coal reserves have increased by over 50% in the
past 22 years. The correlation of strong growth of proven coal reserves with robust
production growth suggests that additions to proven coal reserves will continue to
occur in those regions with strong, competitive coal industries.”
A brief analysis of the technology wise coal production reveals that most of the world
coal production is coming from opencast mines as the reserves suitable for open pit mining
are more compared to underground and also the opencast technology is less complicated.
Mechanized longwall contribute about 50% of the total hard coal production from
Coal accounts for 63% of our country's energy needs. Commercial energy
consumption in India has grown from a level of about 26% to 68% in the last four & half
decades. The current per capita primary energy consumption in India is about 248 kgoe/year,
which is well below that of developed countries. Driven by the rising population, expanding
economy and the quest for improved quality of life, energy usage in India is expected to rise
to around 450 kgoe/year by 2010 (2). Considering the limited reserve potentiality of
petroleum & natural gas, eco-conservation restriction on Hydel projects and political
perception of nuclear power, coal continues to occupy the centre-stage of India's energy
scenario. Fuel wise break-up of the primary energy consumption is as under (3).
Consumption by Fuel India (%) World (%)
Oil 32 37
Natural Gas 8 24
Coal 54 27
Nuclear Energy 1 6
Hydro-Electric 5 6
Total 100 100
(Source: BP Statistical Review of World Energy 2005)
World Energy Scenario Indian Energy Scenario
Coal based thermal power generation capacity presently stands at 61,476MW and a
capacity addition of around 60,000 MW has been targeted in next 7 years (4). This clearly
presents high demand for coal in near future. Besides energy generation, the other consumer
industries like cements, fertilizers, etc are expanding with increased industrialization creating
increased demand for coal.
Total annual hard coal production in India is about 373.79 million tonnes (m.t)
(2004-05) out of which nearly 80% is from Opencast Mines. Coal India produces about 90%
of total Indian coal production and SCCL’s share is about 10%. The expected demand for
coal by 2011-12 is about 707 M.T, whereas coal production would be around 550 M.T,
leaving a gap of about 157 M.T, which needs to be met by imports/private mining (4).
3.0 COAL RESERVES:
India is the third largest coal producer in the world. With hard coal reserves of around
248 billion tonnes, out of which 93 billion tonnes are proven (3). India holds around 10.2% of
the world’s proved hard coal and lignite reserves and produces around 7% of total world’s
production (3). The depth wise coal reserves of India as on January 2005 are as follows:
(in Billion Tonnes)
DEPTH(m) PROVED INDICATED INFERRED
(In Bt) (%)
0-300 71 66.5 15 152.5 61.5
300-600 6.5 39.5 17 63 25
14 0.5 - 6
600-1200 1.5 10.5 6 18 7.5
0-1200 93 117 38 248 100
(Source: GSI Report, January 2005)
Depth – Wise coal reserves of Andhra Pradesh (Godavari Valley Coal Fields) as on
01.01.2005 in million tonnes is as follows:
PROVED INDICATED INFERRED TOTAL
0-300 5467 2229 102 7798
300-600 2796 2832 553 6181
600-1200 -- 1018 1929 2947
0-1200 8263 6079 2584 16926
Both the tables clearly indicate that the reserves under command area of SCCL are at greater
depth than that of average all India figures. At SCCL most of the existing mines and present
projects are for extraction of deposits with in the depth range of 0-300 metres. To have
sustained production SCCL has formulated projects for extraction of coal reserves locked
within the depth range of 300-600 metres.
4.0 REVIEW OF PRESENT MINING SYSTEMS IN SCCL
Presently SCCL operates 51 underground mines and 11 opencast mines. The technology mix
for the year 2004-05 in SCCL is as follows:
TECHNOLOGY PRODUCTION PERCENTAGE
HS 8.950 30
SDLS 1.395 1
LHD 1.157 2
LW 1.197 4
BG 0.274 3
TOTAL UG 12.973 39
OC 22.329 61
TOTAL 35.302 100
4.1 OPENCAST MINES
The technology adopted in opencast mines varies from shovel dumper to Inpit
Crushing & conveying system, Draglines and surface miners. A few more opencast projects
are under execution.
4.2 BORD & PILLAR TECHNOLOGY
During the last 3years SCCL has introduced SDLs & LHDs in about 14 mines
making them coal filler (loader) free mines. 14 more mines SDL/LHDs are having a mix of
manual mining as well as other technologies like Blasting Gallery and Longwall. In the
balance 23 underground mines, the gradients are prohibitively steeper for introduction of any
mechanization and hence manual mining is being continued in these mines. Scrapers are
introduced in one mine on experimental basis.
4.3 LONGWALL TECHNOLOGY
Though SCCL was one of the few companies to have introduced Longwall
technology early, we only have limited success so far. However in view of the necessity for
faster exploitation of upper seams to enable extraction of high quality lower seams, Longwall
technology was introduced in most of the upper seams which are inferior in quality.
Longwall mining has not really taken off in India, barring a few exceptions of
moderately successful faces (in range of 2500 to 3000 t/day). Even the mines which have
comparatively performed better have not proved economically viable beyond second/third
year of operation due to variety of reasons. In retrospect it appears that the Longwall
technology in India has neither been accepted nor rejected. As on date, SCCL has four
operating Longwall faces (GDK-10A, PVK, GDK-9 and JK-5) collectively producing about
1.197 M.T per annum (2004-05).
4.3.1 REASONS FOR SLOW PROGRESS
Large expansion in open cast mining in the past two decades provided cheaper and
safe method for bulk coal production and as a result long wall had to take back seat.
Clear strategies were not pursued for its sustenance as there was mixed results from
longwall in the early years of its introduction.
Longwalls were introduced mostly in the blocks left over by working bord and pillar
method. Clean and extensive blocks have not been identified. Even the smaller
blocks, which were identified, were of inferior grade coal.
Lack of proper planning in regard to longer length of panels and face lengths.
Inadequate geological information & too many geological surprises resulting in
Selection of inadequate capacity Powered roof supports.
Longwall had to co-exist with the conventional mining in most of the mines, which
caused management problems.
There were deficiencies in the spares management. Most of the spares had to be
imported and the supplies were not reaching in time.
Coal companies were sensitive to the failures of a few long wall faces and were not
prepared to risk huge investments.
Development of Longwall panels could not keep pace with the extraction of Longwall
panels. Reasons for slow progress are delay in dip development & roadway
development which affected the performance. Supporting of gate roadways under the
present system is time consuming and becoming a constraint for faster development
of gate roadways.
Mindset among the persons handling Longwalls regarding achievable capacity per
Indigenization of spares has not been attempted with the required seriousness.
So far, we have been purchasing the Longwall machine with a performance guarantee
of 6 months. The embilical chord between the manufacturer and the coal company
gets almost cut off, resulting in technical snags and non/timely availability of spares.
Inadequate training to technicians and operational persons for maintenance &
operation in the face.
Though Longwall have not achieved any great success, safety, productivity and the
cost of production in Longwall taken alone, are in favour of the same. The accident statistics
reveal that the fatality rate for million tonnes of coal produced by Longwall is comparable to
that of opencast. The technology-wise rate of fatal accidents per million tonne of coal
produced in SCCL from 1991 to 2000 is, 2.21 in hand section 1.1 in Blasting Gallery
Method, 0.39 in Longwall and 0.32 in Opencast Mines (9).
5. PRE-REQUISITES FOR PLANNING LONGWALL:
a) Crushing strength of coal seams:
The coal seam should not have any stone or hard shaley coal bands that cannot be cut
by the Shearer. The hardness of coal is also an important factor. The harder the coal, the
greater would be the load on the Shearer and the efficiency of the Shearer also would be
lower for harder coals. Indian coals have a crushing strength in the range of 300 to
b) Cavability of roof:
For the successful adoption of Longwall method, the roof should be relatively easy to
cave. In some of the Indian coal seams having hard sandstone roof, the roof does not cave
even after extraction of a large area. The roof keeps on hanging until a very large area is
extracted and then starts breaking, transferring heavy pressure on the face supports. The roof
stone does not break into small pieces, but breaks into big boulders. All these conditions can
cause permanent damage to the shield supports at the face and also unsafe roof conditions.
Instances exist where the Longwall system had to be discontinued due to excessive roof loads
damaging the shield supports. Therefore, all possible methods to estimate the caving
behaviour and support requirement is to be ensured and the same shall be utilized in the
correct selection of Supports.
c) Presence of clay bands in the floor of the seam
The presence of clay bands in the floor of the working horizon seam can cause
problems due to slushy floor and failure of the mechanized Longwall system. This is
considered while selecting the spacing of powered roof supports. There should be a balance
between the width of the base and ground pressure exerted.
d) Extent of the property along the strike direction
The Longwall panels are normally laid along the strike on a gentle rising gradient.
The longer the panel length, the lesser would be the time loss in shifting the machinery from
one panel to another. Normally, panel lengths of not less than 1000m are adopted and
preferably panels should be 2000m or longer.
e) Availability of sufficient number of panels
The mechanized Longwall system involves high capital equipment. The consistency
of thickness, presence of dirt bands and inter seams adversely affects the performance of
Shearer. Life of Longwall machinery is considered as 10 years. Hence, the total number of
Longwall panels available and the length of the panels should be such as to sustain the
Longwall working for at least 10years, if not more.
f) Ventilation & Air Conditioning
As the depth of future underground mines crosses 350m, it is very much essential to
think of good ventilation system and provision of spot coolers at different locations for
reducing the heat. For the design of proper ventilation system with air conditioning of deep
underground projects, the technical guidance from various experts of India is to be taken.
g) Mine Drainage
Since at greater depths the water accumulation will be more and huge pumps are
required for pumping the same to the surface. Hence, Planning of drainage system of the
mine and each individual Longwall panel has to consider the depth parameter for selecting
the type of pump and the mode of pumping.
h) Transport of Men and Material
Walking of men to the work place not only consumes the time but also makes the
work persons weak. Since, future Longwalls are planned to achieve world class production
levels, the availability of men and machinery is an important factor in achieving the targets.
Hence, the advanced transport facilities like Free Steered Vehicles (FSV) or Mono Rail
Transport Systems or diesel operated mobile vans, etc are to be permitted and provided for
easy transport of men and material from surface to the work spot.
i) Longwall Mine Design
The Longwall face lengths are presently being planned between 150 m to 200 m. The
lengths of Longwall panels are around 1000m. The marginal panels are planned upto 400 –
500m length. In future, the length of the Longwall panel shall be more 2000 m.
The initial Longwall panels were planned with 4 legged 360T capacity chock shields.
But, with the experience gained over the years, higher capacity chock shields of 450T to
750T are now being envisaged for Longwall projects. A support resistance of 50–60T/Sq.m.
is considered adequate, but the experience in the Company proved the necessity for higher
support resistance in the range of 110 to 120 T/Sq.m under massive sandstone roof.
The single motor (1x375KW) powered Double Ended Ranging Drum Shearers
(DERDS) were used in first two Longwall faces; whereas, for the subsequent as well as
future faces, two motor (2x375KW) powered DERDS are proposed. This facilitates shearers
to operate without excessive strain. The initial Longwall units were planned for an annual
production of about 3.50 to 5.50 lakh tonnes. However, the new units are being projected for
higher annual production in the range of 8.0 to 20.0 lakh tonnes per face, taking into account
the latest technological developments.
Though Longwall faces are being worked abroad at gradients steeper than 1 in 2,
Longwall faces in India, are yet to be attempted in gradients steeper than in 1 in 4. However
with collaboration of experienced mining companies Longwall can be operated in seams as
steep as 1 in 2.5. Only Longwall mining appears to be a possible method of mechanization
for extraction of inclined deposits.
Multi section mechanized Longwall working like Longwall Top Coal Caving (LTCC)
as practiced in China is also not experimented so far in the country but in the future Longwall
projects it may be necessary to plan such technology especially for extraction of thick seams
(e.g III seam of GVCF). This is also possible with foreign participation.
6.0 SPECIFICATIONS FOR FUTURE LONGWALL EQUIPMENT:
The future longwall production capacities are to be near to the world standards, the
equipment with the following specifications may have to be procured for achieving desired
levels of production.
i) All electrical shearer
ii) Web depth : Not less than 0.9 m
iii) Make : The shearer should be limited to the make of Eickhoff / Joy /
DBT with the cutting capacity at least 2000 TPH at a speed of at least 8 meters per
minute while traveling up the hill. The coal compressive strength is 400 Kg/Sq. cm.
iv) Track : Eicho track or better as acceptable to SCCL
v) Under frame : The under frame design should be made
suitable to receive the coal at the rate of at least 3000 TPH and should be capable of
handling reasonable lump size.
vi) Life : Minimum guaranteed tonnage of Coal during
lifetime to be mentioned.
vii) Guidance tools: Proper guidance tools for aligning and horizon control shall
i) Support Capacity : Not less than 1050 T (may be 2 legged version)
ii) Support Density : Not less than 115 T per Sq metre after cut.
: Not less than 135 T per Sq Metre before cut.
iii) Support Width : Not less than 1.75 m.
iv) Operating Range : as per the study and as acceptable to SCCL.
v) Canopy ratio : as minimum as possible & preferably 1:2 & not more than
vi) Rapid yield valve : Gas operated with a flow rate of at least 750 liters per minute
on each leg or any higher version.
Higher flow rate is preferable because of massive sandstone
roof conditions prevailing in SCCL.
vii) Operating Fluid : 5:95 oil in water emulsion
viii) Positive set : The support should be provided with positive set system for
ensuring correct setting load
ix) Base : Rigid Catamaran type with bar, base lift & anti-slew
attachments for creep control.
x) Number of
Cycles : The prototype powered roof support should be tested for
60,000 cycles for life cycle test and Steel structure should be
guaranteed minimum life of 15 years.
xi) Controls : Adjacent /Batch control or higher/better versions or any other
xii) Side Shield : Moveable side shield on one side
xiii) Setting load : 80 % of yield load.
xiv) Monitoring : State of the art powered support monitoring system along
with associated software shall be part of the package.
i) Proper guidance tools for aligning and horizon control shall be fitted.
ii) Minimum 2x630 KW, 3.3KV, 3-phase, 50 cycles, at least 1050 mm wide 34x126
mm twin inboard chain of speed at least 1.26 meters/Sec. and the capacity to convey
at least 2200 TPH, the width shall not be less than 1.0 metre.
i) Proper provisions & equipment for installing pan technicon on BSL.
ii) Length – Minimum 35 to 40 mtrs.
iii) At least 450 KW, 3.3KV, 3-phase, 50 cycles/Sec. 1050 mm wide, 34x126 mm twin
inboard chain of speed 1.4 mtrs/Sec. and the conveying capacity is at least 2300 TPH,
the width shall not be less than 1.0 metre.
6.5 LUMP BREAKER:
i) Crushed Coal to be of 100 mm size.
ii) Not less than 450 KW, 3.3KV, 3-phase, 50 cycles/ Sec.
iii) The capacity of the crusher is 2300 TPH.
6.6 POWER PACK:
i) Proper provisions & equipment to keep power pack & cables, associated auxiliaries
on monorails as part of package.
ii) Not less than 450KW, 3.3KV, 3-phase, 50 cycles/sec.
iii) Around 400 bars, 275 Lpm Reciprocating Pump 2 Nos. for continuous operation and
one number as a stand-bye.
6.7 GATE BELT:
i) Spare gate belt conveyor arranged to duplicate works for erection for gate roadway
drivage & subsequent re-erection for Longwall extraction.
ii) 1400 mm width 3.5 Mtr/Sec., 1000 Mtrs. Length, 2300 TPH, ROM coal carrying
capacity – 4 Nos.
iii) 2x200 KW, 3.3 KV, 3-phase, 50 c/s. each GBC.
iv) Pull cord with lock out facility at an interval of 50 mtrs. and pre-start warning to be
6.8 TRANSPORT AND FACE TRANSFER EQUIPMENT:
Free steered Vehicles (FSV) or any other modern transport vehicle to complete the
face transfer in as short duration as possible are to be planned.
6.9 ELECTRICALS &OTHER EQUIPMENT:
i) All the necessary tools & tackle, modern handling equipment like Hydraulic
/Compressed air operated mono rails, drills, cutters etc in sufficient numbers to run
the project on similar lines with any latest world class Longwall mine are to be
planned along with the package.
ii) Special diagnostic tools for checking functioning of different kinds of hydraulic and
electrical/ electronic valves including vibration and oil condition shall also be
iii) Valve testing, leg testing and hose crimping. Equipment shall also be planned with
7.0 FUTURE PROJECTIONS IN SCCL
The future challenges will be not only to increase in coal production but also to
increase its recovery, productivity, health & safety conditions and environment conditions
besides viability. Considering the above SCCL has formulated its future technology mix as
TECH 2006-07 2011-12 2016-17 2021-22
PROD % PROD % PROD % PROD %
(M.T) (M.T) (M.T) (M.T)
HS 6.005 16 5.225 13 3.780 8 3.620 8
SDLS 3.30 9 2.865 7 1.610 4 1.280 3
LHD 1.655 4 1.110 3 1.12 2 0.680 1
LW 1.205 3 3.900 10 5.600 12 8.500 18
CM 0.400 1 1.800 4 1.770 4 2.000 4
BG 1.210 3 1.150 3 0.920 2 0.920 2
TOTAL UG 14.251 37 16.050 39 14.800 33 17.000 36
OC 21.749 63 24.750 61 30.200 67 30.500 64
TOTAL 37.500 100 40.800 100 45.000 100 47.500 100
7.1 Longwall Mining:
The future projection of coal projects are mostly directed towards extraction of coal
from deep shaft blocks (in the depth range of 300m to 600m) because of likely reduction in
contribution from Opencast and the more or less stagnant production from Underground
mining by Conventional methods.
In case of technological options for deep shaft blocks and for bulk production of coal
from underground mining, particularly at greater depths, the proven technology world over is
Longwall. Longwall faces are being planned with minimum production capability of 2
million tonnes per annum per face. Given our track record, it is really a difficult task even to
envisage such production levels. Hence, SCCL initially wants to implement the Longwall
technology in the following 4 blocks on Risk/gain sharing basis.
a. Adriyala Shaft Project
b. Jallaram Shaft Project
c. Peddampeta Shaft Project
d. Kakatiya Longwall Project (KTK-8&8A)
If required foreign participation in the form of joint venture / partnership / contract
mining may have to be adopted. Bhoopalpalli coalfields of SCCL are steeply inclined where
it is proposed to introduce Longwall technology with foreign participation as there is no
alternative safe method of extraction is possible. If longwall proves to be successful in this
project, probably this will be only commercially operated longwall in Inclined seams as most
of the steep seam longwall faces in other countries are being subsidized.
Considering geo-mining parameters and conditions prevailing in existing mines, it is
required that all the technologies like SDLs ,LHDs ,Scarpers, CM , Blasting gallery methods
and Longwall are required to be continued for extraction of property below 300m. To make
these methods of mechanization successful it is required that Indigenous abilities of
equipment/spares manufacturing and maintenance services are to be upgraded.
For successful implementation of these high capacity longwall projects, it is just not
sufficient to have world class equipment. It requires fully orchestrated efforts connected with
logistics, maintenance, operation and monitoring. It is better have initial high capacity
longwalls to be operated on risk/gain sharing basis. This not only ensures achieving
production levels but also brings in world class mining practices to Indian mining.
It is very important that all the new projects in the virgin blocks are to be planned
with most modern technologies like CM and longwall with production capacities comparable
world averages in such technologies. This alone can bring technological advances to the
nation for making Indian mines comparable with that of mines operating overseas.
It is also required to upgrade research capabilities to the level of internally renowned
mining scientific agencies like CSIRO, NIOSH and RMT. If required MOU /JV are formed
with such organization with active participation of Indian research institutions and coal
companies. This will enhance mining engineering skills in mining matters.
It is required that Concerted efforts are required by the DGMS, policy makers, Coal
companies and manufacturers to translate the ideas into concrete action and reap the benefits
of mechanization in general and longwall mechanization in particular in the years to come.
The authors express their sincere thanks to the Sri R H Khwaja, C&MD, SCCL for
permitting to present this paper. The views expressed are those of the authors and should not
be attributed to Singareni Collieries.
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mechanization in India”.
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before coal industry & strategies ahead (Balrampur Longwall Experience)”.
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“Technological options for future coal mining – A review”.
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10. Information Bulletin published by the Ministry of Coal, India