SELECTION OF U NDERGROUND COAL MINING TECHNOLOGY FOR DEEP SEATED COAL DEPOSITS, VIZ; CONTINUOUS MINER, LONGWALL, OPERATIONAL & TECHNICAL PARAMETERS CONSIDERED FOR SELECTION OF CONTINUOUS MINER

1. SELECTION OF VIABLE
TECHNOLOGY
FOR
UG COALMINES
U. Siva Sankar
email: uss_7@yahoo.com
Back ground
• The underground production in SCCL
has come to the plateau at 12-13 Mt and
any increase in quantum jump with
present method of working and
technology is looking bleak.
• Added to the above
Depth range is increasing – 350 to 600 m.
Geological disturbances,
Stress regime
Gradient - 1 in 3 to 1in4
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2. Back ground
• Most important is the present cost of
production with SDL and LHD is in the
range of around Rs 2000 per Tonne,
against the company average sales
realization of around Rs 1423/ Tonne.
• The recent wage hike has totally dashed
hopes of viability with SDL and LHD
technology.
COST OF PRODUCTION FOR 2009-10 IN Rs.
• LONGWALL - 1029.65
• BLASTING GALLERY - 1416.53
• CONTINUOUS MINER - 1543.04
• SDL - 1790.03
• LHD - 2068.45
• HS - 3128.40
• RH - 6723.61
• The major contribution of cost of production in
existing Bord & Pillar with HS/LHD/SDL is Wage
component.
– HS -74%
– LHD-60%
– SDL-62%
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3. 3

4. OBJECTIVE
• To design a suitable and viable “Method
and Technology” for the available deposits
keeping in view
– Depth
– Gradient
– Geological disturbances
– Low quality seams in upper horizons
ISSUES
• Depth – Present B&P / Rhombus shaped pillars at more
than 350 m depth would not stand.
• Requirement – long term stability (FoS-2)
• Gradient –1 in 2.5 to 1in 4, there is limitation with
working of technologies like SDL,LHD, and CM etc.
• Requirement - Negotiate /suitable cross gradient or
cutting the floor/ roof stone.
• Geology – faults: Due to presence of faults Longwall
technology is becoming non viable in present coal
blocks.
• Requirement- Viable LW technology (low cost) with
shorter panels of length 500 -600 mtrs
• Low quality seams in upper horizons-(IRR)
• Requirement- ,stowing for lower seams, coal washeries
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5. Technology selection Matrix
Technology Depth (m) Gradient CPT Geological
disturbances
Upto 300-600 Upto1 in Steeper
300 4/5 than 1 in 4
Longwall J J J J J X
SDL / LHD J x J x x J
CM J J J x or J J J
BM J J J x or J J J
x or J indicates both options may work when floor cutting is possible
INFERENCE
• From the above, SDL / LHD deployment is not
viable for deep and steeply inclined deposits.
• The alternative Technologies
– Longwall – The Low cost Longwalls, viable with even
500m to 600m length panels
– continuous miner / miner bolter- The technology
should be able to cut stone roof/floor to overcome cross
gradient problem.
• Alternative method:
– As an alternative to the present Bord&Pillar / Rhombus
type of development, Block development with long
headings and liquidating with Fenders for stability
during development and safety during depillaring.
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6. Recommendations
• Keeping in view of above parameters we can set
out
low cost Longwalls where, 600 to 1000m
panels can be formed
In other cases, where cut out distance
permits and frequent movement with out
damaging the floor is possible a continuous
miner otherwise bolter miner is a suitable
option.
Operational and Technical Parameters
Continuous Miner / Bolter miner
Technical Parameters
• Depth
• Gradient
• Cross Gradient
• Floor Pressure or Ground Pressure
• Cut out Distance
• Number of Entries
• Lead – Pillar Size
• Angle between entries and crosscuts
• Orientation of angled crosscuts
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7. Depth
• At present, the depth of working underground mines in
SCCL is limited to 300m to 400m.
• Most of the Extractable Reserves are lying at a depth
range of 300 to 600m
• Technology for faster extraction of coal seams is to be
deployed to counter the problems of Ground control,
Ventilation with increasing depths in order to ensure
Safety and also to meet future energy requirements.
• If depth exceeds 400 m, Pillar stability is major hindrance
for safety in Bord & Pillar method.
• To over come this, Instead of pillar formation, Block
development with long headings and liquidating the same
with Fenders.
Gradient
The limiting Gradient of Continuous Miner & Shuttle cars is 1 in 6
(91/20) & 1 in 8 (70) Respectively
Gradient of Coal seams vary from 1in 2.7 to 1in 8.
Maximum workable seam gradient is 1 in 4 with apparent dip limited to
1 in 6 due to limiting acute angle of Rhombus pillar
Cross Gradient
While working on apparent dip, if floor is not competent, wheels of
shuttle cars / LHDs move on different individual horizons. This leads to
damage of suspensions and breakdown of equipment.
Joy Mining is offering individual suspension shuttle cars in new versions
on optional basis.
To overcome this, stone floor is to be cut on the rise side of the gallery
to make it level.
Stone cutting will lead to coal degradation during development.
The limiting Cross Gradient of Continuous Miner & Shuttle cars is 1 in
11.5 (50)
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8. Continuous miner development
Cutting into Floor and Roof
Roof cutting for
rectangular roadways
Floor cutting for
rectangular roadways
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9. Gradient & Cross Gradient
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10. 10

11. 11

12. Technical Parameters - Ground Pressure
Ground pressure parameter is considered
1. For with standing partition between two contiguous seams,
2. For with standing of floor coal when working on cross gradient
subjects to frequent movement of machinery.
The compressive strength of the coal can be taken as a least
value of 2.8 MPa (406 Psi) ( I seam of KTK – 5 Incline, NIRM
Report) and maximum of 22.5 MPa.
Tensile strength of the coal can be taken as minimum 0.28 MPa
and 2.25 Mpa as maximum for our coal seams.
Where Parting thickness between working sections is less than
1/5th of the Gallery width, failure is usually in tension.
The ground pressure of Continuous Miner varies from 0.11 MPa
(16 Psi) to 0.22 MPa (32 Psi)
Shuttle car ground pressure varies from 0.834 MPa (121 Psi) to
1.09 MPa (158 Psi)
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13. SPECIFICATIONS OF MINER BOLTER(MB),
CONTINUOUS MINER(CM)
CM or MB MC ACM10/ MB250 MB430* MB 670 MB 750
350 MC 250 MB450
MC255*
Cutting 1.17 – 1.80 - 1.37 – 1.80 – 3.0 – 3.80 –
height 3.1 3.60 2.70 3.0* & 4.5 4.50
(m) 2.10 –
3.70
Cutting 3.50 2.70 4.70 4.72 4.20/6.0 6.60/7.20
Width (m)
Weight 60 39/44* 75 62.30 97 115
(Tonnes)
Ground 0.158 0.11* / - -- 0.17 0.22 0.22
Pressure 0.12
(MPa)
SPECIFICATIONS OF SHUTTLE CARS
Shuttle 1 2 3 4 5 6
car
Capacity 8 11 14 14 16 20
(Tonnes)
Weight 18.1 20.48 22.70 25 27.20 29.50
(Tonnes)
Ground 0.85 0.97 0.94 1.0 0.96 1.09
Pressure
(MPa)
1,2,3 : Low to Medium height Seams, others : Medium to high seams
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14. Technical Parameters -
Cut out Distance or Length of a cut
The maximum unsupported span of the gallery which
can be cut with Cutting machine safely with out any
failure of immediate roof, which may or may not be
supported later
It plays vital role in the selection of Continuous miner
or Bolter miner for particular geo mining condition
Mine CMRI RMR Cut out Distance (m)
GDK 11A 48 12
Incline
(Caving)
VK7 Incline 62 15
(Non- Caving)
Beniawski RMR & Bartons Q – System Approach
VK-7
GDK-11
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15. Basic Geometry of Room & Pillar Workings
Twin Entry Development Layout for
Longwall
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16. Sequence of cutting in Development
2 Left 0m 15-25m
Continuous
Miner 1 Left Main 1 Right 2 Right
“Load-Haul- Twin Boom
Dumper” (LHD) Roofbolter
Shuttle Machine
Cars
Feeder
Breaker Electrical
Equipment
(Load
Center)
Entry Mechanized Room & Pillar Layout
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17. Number of Entries
When the number of entries are less, there are only a few available
working faces results in delays because cyclical mining (including
continuous mining).
When there are many working faces available, an activity can be
shifted to another location without any interruption.
More entries facilitates machines to maneuver easily and quickly
and shuttle cars will have different routes for loaded and empty
cars, thereby reducing travel times.
The more the entries, less is the air resistance. However, with too
many entries, section ventilation may be difficult and prone to
leakages.
One disadvantage of many entries is that it slows down
development and therefore, pillaring. Hence, cash flow may be
small for a long time.
Generally 5 entries Panels are being preferred due to Less
shifting of feeder breaker optimized Lead , Production. (since any
less number of entries causes congestion with bridge conveyors)
Lead
Production & productivity increases with reducing lead
and Vice versa.
Lead mainly depends up on pillar size, so pillar size
should be optimized considering Ground control as well
as techno-economic analysis.
It impacts the haulage cycle times (shuttle or ram car)
since when one car is in an entry, others have to wait
until the entry is cleared.
For larger pillars, such idle waiting times can be long.
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18. Angle between entries and crosscuts
The angle between crosscuts and entries depends on the
machinery.
Bridge conveyors and ram cars, require oblique angles,
while shuttle cars require perpendicular angles.
In case of FCT, spillage is high when the direction of flow
takes a sharp turn
Therefore, oblique angles are to be planned wherever the
conveyor flow direction is expected to change.
Fig. Spillage at Transfer Points
Orientation of angled crosscuts
Angled crosscuts should be aligned with
Major Horizontal stress direction for
ensuring the stability of Trunk road ways
or panel galleries.
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19. Operational Parameters
• Floor Condition
• Watery condition
• Cables handling & Equipment Rerouting
• Damage of Cables & Tyres
• Bolter & Miner Compatibility
• Side spalling
• Floor Heaving
• Fire problem
• Ventilation
• Quality
• Roadway Maintenance
• Extraction of Developed Pillars
Floor condition & watery Condition
The floor coal gets crushed due to frequent
movement of Machinery and lead to formation of
ditches, which in further leads to heightening of
galleries. The Minimum required compressive
strength of floor coal is 15 Mpa for movement of
machinery..
With presence of water used for dust suppression
(≈30 GPM) or seepage water causes slushy
conditions results in skidding of shuttle cars
even on stone floors.
To overcome the above problems
1. Routing cars in different routes & placement of
feeder breaker to facilitate unloading in three
directions
2. Dinting floor on dip side to collect and divert water
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20. Cables Handling & Equipment Rerouting
• In case of electrically operated machinery, cables
handling is cumbersome at the time of operation &
equipment rerouting
• Continuous miner cable to be handled manually & cables
need to be lifted at junctions through which shuttle cars
travel.
Damage of Cables & Tyres
• cumbersome cable handling and slushy floor conditions
leading to damage of cables & tyres of shuttle cars
• Foam filled tyres instead of air filled and also chains
engulf to tyres to prevent the damage of tyres
Bolter & Miner Compatibility
• With Quadra bolter the distance between two side booms
is fixed and it is not possible to use all the booms
simultaneously for bolting, if the spacing between bolts is
to be varied.
• Bottom row of side bolting could not be done with the
dual boom bolter (above 1.5 m from floor)
• Mismatch of Bolter & miner leading to idling of Miner
during development and also during widening of
developed pillars
Ventilation
• For development, 1200 cu.m /min air quantity is required
to facilitate comfortable working conditions.
• Automatic methane monitoring system is incorporated in
CM to cut off power incase of exceeding limits.
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21. QUALITY
• To overcome the gradient problem, Floor stone/coal to
be made level by cutting stone in thin seams.
• For cutting stone floor, Design requirement for cutting
drum is different and only sandvik is offering to cut the
stone up to 35 Mpa compressive strength.
• This will results in to coal contamination, varies from 6%
to 16% depends on seam gradient.
Ground Control Problem
• The success of any extraction method is depends on
Cavability.
• Induced blasting to be adopted where caving is not
regular
• Jumbo drill to be included in the CM/BM package for
Induced Blasting wherever required.
As a final point
• Continuous miner/ Miner Bolter feasibility depends on
the Geo mining parameters.
• Its success depends on suitable mechanized
environment at the mine.
• Facilities like man riding, Good ventilation system,
spares management, availability- utilization and
overall maintenance adds to achieve improved
performance.
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22. ADVANTAGES OF CM/ BM
• The Continuous Miner/BM can extract the coal to full seam
thickness of 4.5m to 5.0m in a single lift.
• Strata control problems can be minimized by avoiding blasting
operations as the depth is increasing 350m and more.
• It gives higher production rates.
• Remote operation leads to safety.
• Risk of spontaneous heating can be reduced due to faster rate of
extraction.
• Moderate Capital cost when compared to Longwall.
Continuous miner Vs Bolter miner
CM BM
Floor degradation Cutting is done by Cutting is done by
tractive force Hydraulic Sumping
Frequent plying to
facilitate bolting
More floor damage Better floor condition
Cut out distance Limits the applicability Eliminates the
and performance problem of cut out
Where cut out distance distance
is more, it gives high
production
Strata Immediate supporting Simultaneous cutting
management is not possible and supporting
possible
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23. SOLUTION
• Quality Geo-tech Information. As depths
are increasing huge investments on
technology, energy activity like supports ,
ventilation etc becomes expensive.
– For a viable design quality geological
information is required.
• Technology suggested:
– Longwall – Low cost Longwalls to work
shorter panels and still viable.
– Bolter miner: Bolter miner instead of
continuous miner in view of cutout distance.
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