1
Table of Contents List of Figures .......................................................................................................................................... 3
List of Tables ........................................................................................................................................... 4
1. Introduction ..................................................................................................................................... 5
2. Khutala Coal ................................................................................................................................... 5
Mine background and General Information .......................................................................... 5
Mining Method .................................................................................................................................... 6
Mining Activities ................................................................................................................................. 6
Coal cutting ..................................................................................................................................... 6
Roof Support .................................................................................................................................. 7
Tramming ......................................................................................................................................... 7
Pillar design and Support .............................................................................................................. 8
Equipment Selection ....................................................................................................................... 8
Production rates ............................................................................................................................. 10
Personnel ........................................................................................................................................... 11
3. Shanduka Coal ........................................................................................................................... 12
Mine Background and general information ........................................................................ 12
Mining Method and Mining Activities .................................................................................... 14
Equipment Selection .................................................................................................................... 14
Production rates and Unit costs .............................................................................................. 15
Personnel ........................................................................................................................................... 15
4. Penumbra Coal Mining ........................................................................................................... 16
Background ....................................................................................................................................... 16
Mining Method ................................................................................................................................. 17
Equipment and Personnel ......................................................................................................... 17
Pillar Design and Support .......................................................................................................... 18
Ventilation .......................................................................................................................................... 18
Production Rates and Unit Costs ........................................................................................... 18
Challenges ........................................................................................................................................ 19
5. New Denmark Colliery ............................................................................................................ 20
Mine Background ........................................................................................................................... 20
Mining Method & Activities ........................................................................................................ 20
Pillar Design and Support .......................................................................................................... 22
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Equipment Selection .................................................................................................................... 23
Ventilation .......................................................................................................................................... 24
Production Rates............................................................................................................................ 24
Unit Costs .......................................................................................................................................... 24
Personnel ........................................................................................................................................... 25
6. Msobo Coal .................................................................................................................................. 26
Location and background ........................................................................................................... 26
Mining method and activities .................................................................................................... 28
Equipment Selection .................................................................................................................... 29
Ventilation .......................................................................................................................................... 30
Unit Costs and Personnel .......................................................................................................... 30
7. Sasol ............................................................................................................................................... 32
Mine Background ........................................................................................................................... 32
Brandspruit Colliery ...................................................................................................................... 32
Mining Method ................................................................................................................................. 33
Pillar Design and Support .......................................................................................................... 35
Equipment Selection .................................................................................................................... 35
Ventilation .......................................................................................................................................... 35
Middelbult Colliery- Ithemba Lethu Shaft ................................................................................ 37
Background ....................................................................................................................................... 37
Mining Method ................................................................................................................................. 37
Pillar Design and Support .......................................................................................................... 38
Equipment Selection and Personnel .................................................................................... 39
Ventilation .......................................................................................................................................... 39
Production Rates and Unit Costs ........................................................................................... 39
Challenges ........................................................................................................................................ 39
8. References ................................................................................................................................... 40
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List of Figures
Figure 1 Location of Khutala Colliery (BHP Billiton, 2014) ................................................... 5 Figure 2: Typical cutting sequence (BHP Billiton, 2014) ........................................................ 7 Figure 3: Joy Continuous Miner (12HM31B) (BHP Billiton, 2014) ..................................... 8 Figure 4: Joy Shuttle Car (10SC32-56C) (BHP Billiton, 2014) ........................................ 9 Figure 5: FFE Feeder breaker. (BHP Billiton, 2014) .............................................................. 10 Figure 6 Location of Graspan Complex (Infomine, 2014) ............................................... 12 Figure 7: The location of Continental Coal Operations .................................................... 16 Figure 8: Twin decline shafts at Penumbra Coal. (Conti Coal Presentation, 2014)
..................................................................................................................................................................... 17 Figure 9: Map of wetland at Penumbra Coal. (Continental Coal Presentation,
2014) ......................................................................................................................................................... 19 Figure 10 Longwall section layout. ............................................................................................. 21 Figure 11: Basic Chock support illustration .............................................................................. 23 Figure 12: Map Showing Msobo Coal Mine ........................................................................... 26 Figure 13: The stratigraphy of Msobo Coal Reserves ............................................... 27 Figure 14> Location of the shafts at Brandspruit ................................................................ 32 Figure 15: The cutting sequence using the Nevid Method ............................................. 33 Figure 16: The Nevid Method pillar extraction. .................................................................... 34 Figure 17: Basic air flow through a Nevid section. ............................................................. 36 Figure 18 Location of Middelbult Colliery ................................................................................ 37 Figure 19: The 4-seam layers. ..................................................................................................... 38
4
List of Tables
Table 1: Equipment used at Shanduka Coal ......................................................................... 15 Table 2: The total number of people employed at Shanduka Coal. .................................. 15 Table 3: The pillar design and support specifications at Penumbra Coal. .............. 18 Table 4. Table showing equipment and details .................................................................... 23 Table 5: Underground equipment used at the mine .......................................................... 29 Table 6: Personnel specifications ............................................................................................... 30 Table 7: The type of equipment and the total number ...................................................... 35 Table 8 Pillar design and support specifics ............................................................................ 38
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1. Introduction
Between the period of the 28th of January and the 7th of February 2014, a total of
six coal mines were visited. These mines are located in differing environments
and therefore utilise specialised mining methods for that particular area.
Moreover, there are varying challenges faced by each mines. Each of the six
mines visited is described in terms of the mining methods, pillar design and
support, equipment, personnel and other relevant factors.
2. Khutala Coal
Mine background and General Information
Khutala colliery is located in Ogies as shown in figure 1 and is part of the
Witbank coalfields. This coalfield is part of the Vryheid formation under the Karoo
Super group.
Figure 1 Location of Khutala Colliery (BHP Billiton, 2014)
BHP Billiton owns the colliery. The mine has an open cast operation as well as
an underground operation. The open cast operation mines the 2, 4 and 5 seams
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while the underground operation only mines the 2 and 4 seams. Plans are in
place to turn the underground operation into an open cast operation to be able to
mine the high-grade coal in the 5 seam. The seams have the following features:
No.2 Seam ranges from 0.5 to 20 meters in thickness but at the mine it
is about 7.1m with a calorific value of 20.05MJ/kg. It is 108.61m from
surface.
No.4 Seam ranges from 0.5 to 6.5 meters in thickness but at the mine it
is 6.2m (average) with a calorific value of 18.29MJ/kg. The distance from
surface is 83.42m
No. 5 Seam ranges from 0 to 2 meters in thickness but at the mine, the
seam is 1.63m thick and has a calorific value of 28MJ/kg. It is 60.56m
from surface.
The mine supplies coal to the Kendal Power station and the tender was approved
in September in 1986. The contract expires on 31 December 2033. The 4320
MW base load power station was made in such a way to accommodate the
quality of the coal in the reserve. It is the biggest power station in Africa. It is a
dry-cooled operation since water is a constraint in the area and thus there is a
need to recirculate the water. The coal has calorific value of MF 19.6Mj/kg (4680
Kcal). The power station supplies 9-12% of South African electrical power
demand. It has a maximum burn rate capacity of 17million tons per annum.
Mining Method Mechanized bord and pillar is the mining method that is being used to mine the 4
and the 2 seam. Conventional bord and pillar is used in areas where dykes are
encountered. Mining is done from the right to the left for ventilation purposes.
The mining height is about 4.5m while the mining width (bord) is 6.8m.
Mining Activities
Coal cutting A continuous miner (CM) is used to cut the coal, which it loads onto the shuttle
cars that then take it to the feeder breaker. The CM sumps in 0.5m from the roof
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into the face at a distance of 0.85m. It then shears down to fill one 20t shuttle car.
The CM cuts 12m before support is installed. The development per shift is
usually 50m. The cutting sequence as shown in figure 2, is in such a way that
there is always through ventilation and the tramming on the CM is less as well as
the cable handling. The effective cutting time on the CM is normally 160 minutes
per shift, which simplifies to 12t per min. The CM also has 93% availability and
40% utilization.
Figure 2: Typical cutting sequence (BHP Billiton, 2014)
Roof Support The roof support installed in a normal bord and pillar development end are 1.8m
long roof bolts that are spaced 1.5m apart. It normally takes 20-25 minutes to
install support with a Fletcher roofbolter for a 12m development end.
Tramming The mine also has an incline shaft for the conveyor belts that transport the coal
from the feeder-breaker to surface. The incline shaft is about 7m wide and it
accommodates 2 belts. The configuration is such that there are surge bins that
accommodate the ore from both seams and ensure that the conveyor belt is
loaded properly. The conveyor belt speeds vary from 2m/s to 3m/s.
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Pillar design and Support The pillars are designed in such a way that the total extraction of the mine is only
40%. The safety factor with regard to the main development is 2 while for the
secondary development it is 1.6. The mine also uses full cover mesh for back
bye areas as well as Oslo straps for where sidewall nets are joined.
Equipment Selection In the production sections the mine uses a number of different mining machines
that are fit for different purposes. At the face, the mine uses continuous miners of
which there are twelve 12HM 31 Remote Control JNA 2 Continuous Miners as
shown in figure 3 and two 12HM21 Onboard Joy Continuous Miners.
Figure 3: Joy Continuous Miner (12HM31B) (BHP Billiton, 2014)
The number of continuous miners matches the number of sections, which makes
it a continuous miner per section. The mine is working on phasing out the
onboard continuous miners as a means of reducing the number of people
exposed to the working face and thus reduce fatality caused by on board
continuous miners. The aim is to have sections that are operated by remotely
controlled continuous miners.
Onboard continuous miners have an overall length of 12 m and a height of 5.5m.
The maximum cutting width is normally 3.65m while the cutter head is 1.118m.
The cutting speed is around 50 rpm. The continuous miners loading rate can go
up to 20t/min. The spacing and lacing is around 0.0762. The machine itself
weighs 103t.
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The mine uses a total of nine roof bolters to install support. These consist of
Fletcher twin boom roofbolters and five Rham twin boom Roofbolters. The
Fletcher twin roof bolters have the capacity to do 200 roofbolts per shift and they
utilise dry drilling as a means of drilling. The Rham twin roof bolters have the
capacity of doing 20 bolts per hour with sidewall bolting capacity. These Rham
roof bolters can only operate at heights ranging from 2.5m to 5.5m with the hole
dimensions being from 23mm to 42mm. They have an overall length and width of
6.2m and 3.2m respectively. They have an average weight of about 28tons.
The mine has forty-two 10SC 22 20t C and D type Shuttle Cars and thus three
per section. The shuttle cars carry the coal from the continuous miner to feeder
breaker. The Joy 10 SC 32 56C shuttle cars, shown in figure 4 have an overall
length and width of 9.24m and 2.72m respectively. These machines weigh 27t
and have a loading capacity of 20t. The tramming speed ranges from 2.50m/s
when empty to 2.2m/s when loaded.
Figure 4: Joy Shuttle Car (10SC32-56C) (BHP Billiton, 2014)
The other machines which form part of the underground fleet include bird
machines, stone duster (Bateleur), Sandvik LHD (LS191) and a feeder breaker.
The Stone dusters are used to spray stone dust frequently as a means of
preventing coal dust explosions. Stone dust is usually a primary inerting agent
such as calcium carbonate. The mine has fourteen FFE Feeder breakers, 1 per
10
section. The FFE Feeder breaker as shown in figure 5 has a capacity of 850t/hr
and feeds the conveyor.
Figure 5: FFE Feeder breaker. (BHP Billiton, 2014)
Production rates The total production is around 11Mt with the underground operation producing
9Mt while the Open cast operation produces the remaining 2Mt (Portion 16). The
production from the underground sections comes mainly from the 2 Seam (4Mt)
and the 4 seam (5Mt). Currently the mine has 14 sections in operation that run
on a 3 shift system (Monday Morning Saturday Morning) in a 24-hour cycle that is as follows:
Day shift: 06:20 16:00 (Bank to Bank)
Afternoon shift: 14:20 00:10
Night shift: 22h20 08:10
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Personnel The mine has a total of 2801 employees of which 1697 are owned by the
company while the remaining 1104, are contractors. The personnel required per
section per shift are:
2 Artisan
1 Miner
1 Supervisor
2 Continuous Miner Operators
1 LHD driver
6 Multi-skilled operators.
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3. Shanduka Coal
Mine Background and general information Shanduka Coal produces thermal coal as well as anthracite coal to a lesser
extent. It is operated in partnership with Glencore International and owns the
Middelburg complex, Umcebo complex and the Springlake colliery. The
Middelburg complex consists of the Graspan complex (as shown in figure) and
the Middelburg Townlands sections as shown in figure 6. The Umcebo complex
on the other hand contains the following sections: Middelkraal, Kleinfontein,
Klippan and Wonderfontein. The Springlake colliery is suited in KwaZulu Natal,
and it is where anthracite coal is mined.
Figure 6 Location of Graspan Complex (Infomine, 2014)
Both the Middelburg complex operations are open cast. The Run of mine
Production of the Middleburg complex is 7.3Mtpa while the overburden is 22.1
Mbcm per annum. The total number of operating pits is 7 of which 3 are on the
Graspan section and the remaining four are on the Townlands sections. The 3
pits at Graspan are: Block A, Northwest pit and South pit while for the Townlands
sections they are: Block D, Block B, Steelcoal East and Steelcoal west. The pits
each have different seams and challenges, which are as follows:
Block A - Mining is being done in the 2 seam and the 1 seam, which is all
export coal.
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Northwest pit - Mining is being done in the 1 seam, 2 seam, portions of the
3 seam and recently the 4 seam. The challenge is that the coal obtained
is normally Eskom coal and export coal, therefore the mining should be
such that it provides the quantity required for both export and commercial
supply ( Eskom). The Eskom coal is only just crushed while the export one
goes through the whole beneficiation process.
South pit Similar geology as the north pit but the mining is much easier
because the Eskom and export coal are in separate layers unlike in the
north pit.
Block D consist of the 2 seam, 3 seam and a bit of the 4 seam. A
contractor known as JCI is doing the mining. The quality of the coal here is
quite good.
Block B consist of the 1 seam, 2 seam, 3 seam and the 4 seam but the
quality of the coal is not that good and thus it sold to Eskom coal. Andru
mining is the contractor responsible for mining the pit.
Steelcoal East consist of the 1 seam, 2 seam and the 3 seam. Here
there is both Eskom and export coal. Andru mining is also responsible for
mining this pit.
Steelcoal West consist of the 1 seam and the 2 seam. Sandton was
responsible for mining this this pit but now Shanduka itself is going to take
over.
The plant capacity at Graspan is sub-divided into the Export main plant (180
000t), secondary wash plant (90 000t) and Eskom crushing plant (150 000t). The
discard from the main export plant becomes the feed material for the secondary
wash plant, which gives out a different quality product. The plant capacity at
Townlands per month is sub-divided into the Export plant (110 000t), inland plant
2 (75 000t), Steelcoal plant (120 000t) and Eskom crushing plant (60 000t). The
Eskom plant works on a 20 CV and it involves crushing and screening the coal.
The Export plant works on a 26.2 CV and the inland plant as well as the
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Steelcoal plant both work on a 23.5 CV. The mine doesnt discard their tailings
and fines but rather blend them with other the Eskom low CV coal.
Mining Method and Mining Activities Both the Graspan sections and Townlands sections are open cast operations.
The Townlands section is a truck a shovel operation that is contractor operated
with an overburden of 11.3 BCM. The Graspan operation is also a truck and
shovel operation but in this case it is operated by Shanduka themselves; with an
overburden of 10.8 BCM. The tramming distance at Graspan is usually 2.5km to
the processing plant. The blocks of the pits are 600m with strips of 50 m at a
width of 40m. The stripping ratio is normally 4:6.
To deal with the water problem at the pit, the mine uses 160kpa pressure diesel
pumps at every bench. The ramps are inclined at 30. The mine uses ANFO and
electronic detonators in their blasts with an effective burden of 5.5m. The blast
radius is around 600m. The blast design includes a pre-split that has a spacing of
2m between the holes. The burden to spacing ratio on the bench is 5mx5m. The
expected swell factor after the blast is normally 30cm. The timing between the
holes is about 10ms while the timing between the rows is 15ms in a blast design
timing sequence.
The mine uses the roll over method of disposing its waste and this involves
throwing the waste over parts that are planned for rehabilitation to form a base.
The soil removal personnel are always two strips ahead of the bench being
prepared for a blast. The mine uses a double loading method for the truck and
shovel operation. It normally takes 5 minutes to and from the processing plant
after the truck has been fully loaded.
Equipment Selection One of the parameters that provide minimum cost for the targeted production in a
mine is surely the suitability of the machines/equipment selected. Moreover,
equipment selection directly affects the pit design and production planning. At
Shanduka Coal equipment selection was made according to many factors related
to the ore and mining conditions of this region. It was explained that the main
15
purpose of equipment selection is to choose the optimum and cost effective
equipment. The following table shows the equipment used at Shanduka coal.
Table 1: Equipment used at Shanduka Coal
Type of Equipment
Total Number of Equipment
Excavators 47
Dozers 41
Trucks 198
Front End Loader 56
Production rates and Unit costs The life of mine of the reserve is 27Mtons and sellable production is 3.2MTpa,
Townlands reserve is left with 7years of mining and the life of mine of Graspan
reserve is also 7years. Townlands produces 3.33MT per annum. Graspan
produces 4MTpa and export at R368/ton and sell to Eskom at R147/ton.
(Mabogoane, M. 2014)
Personnel Shanduka opencast runs on a three shifts per day system. The day shift runs
from 6am to 4 pm, the afternoon shift runs from 4:30pm to 10pm and the night
shift runs from 10:30pm to 2am. They is a 30minutes break during each shift.
The following table shows the total number of people employed on this mine:
Table 2: The total number of people employed at Shanduka Coal.
Contractors 1800
Own labour 833
Total labour 2633
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4. Penumbra Coal Mining
Background Penumbra Coal is one of twelve coal operations currently under Continental Coal
Limited in Ermelo as shown in figure 7 below.
Figure 7: The location of Continental Coal Operations
The New Order Mining Right was awarded in May 2010. Development then
started in September 2011 and the first coal production was in November 2012.
The total capital costs as in January 2012 amounted to R319 million. Penumbra
has a forecasted 10 year life of mine with measured gross in-situ coal resources
amounting to 13Mt.
The mine is located 2km from the wash plant and rail siding. The plant is
relatively small with a capacity of 300t/hour. The coal yield is between 48-51%.
Total fines amount to 7% and these are blended with the export product. About
6000 Kcal of coal is exported at R700/t.
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Mining Method Access to the mine is by twin decline shaft of 360m length as shown in figure 8
below.
Figure 8: Twin decline shafts at Penumbra Coal. (Conti Coal Presentation, 2014)
The decline dips at 5 and increases to 8 as the length increases due to the
dolerite sill encountered underground. Mining is done at depths of between 50-
115m. The C-lower seam with an average seam height of 1.8m is mined.
The mine uses the Bord and Pillar mining, with 2 fully mechanized Continuous
Miner production sections and 1 Drill and Blast section. The mine is located in an
area with geological features such as dykes, faults and most frequently
sandstone rolls. The Drill and Blast operation is therefore used when these
features are encountered due to its flexibility.
Equipment and Personnel Each CM section consists of
2 x Continuous Miners
4 x 10t Shuttle Cars
1 Single-Boom Roof bolter
A total of 12 people work 2 shifts/day, 5days a week for each CM section. The
Drill and Blast section is operated by a contractor and has 28 people per section
on a full production shift.
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Pillar Design and Support The Continuous Miner section visited was at a 58.7m depth below surface. The
pillar design and support specifications are shown in Table x below.
Table 3: The pillar design and support specifications at Penumbra Coal.
Bord width 6.5m
Pillar centres 14m
Pillar width 7.5m x 7.5m
Width to Height Ratio 4
Number of roads 7
Roof Bolt length 1.5m
Support dimensions 1.5m x 2m
Safety Factor >1.6
The pillar center dimensions are subject to change due to the constantly
changing geological conditions.
Ventilation The mine uses 11KW force fans and ventilation brattices for the underground
workings. Two fans with capacity of between 60-80m3 are used. Velocity is
maintained at 1.2m/s.
Production Rates and Unit Costs The target production per mechanized panel is 1600t/shift at an advance of 50m.
The entire mine achieves a production rate of 50 000t/month ROM. However,
sandstone rolls cause a drastic drop in the production rate when encountered as
they have to be mined out. Mining of the sandstone rolls in order to return to the
seam comes at a cost of R100/ton. For one month in 2013, the mine lost R4
million due to this.
The Drill and Blast section achieves lower production rates and costs more than
the CM sections. The CM sections cost 70 % of Drill and Blast. The operating
costs for the mining operation are R220/ton. The plant operating costs are on the
other hand are R40/ton.
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Challenges The location of Penumbra near wetland is a serious challenge faced by the mine.
Figure 9 below shows the surface view of the mine.
Figure 9: Map of wetland at Penumbra Coal. (Continental Coal Presentation, 2014)
Water flows into the mine resulting in the weathering of the roof and side walls of
the shaft. On the 26th of December 2013, the mine experienced a roof collapse
in the decline shaft as a result of subsidence. When water reaches the shaft
bottom, it results in poor floor conditions that cause the Continuous Miner to get
stuck. To counter the effects of water, the mine practices water interception
cementitious material on the roof and side walls. The water that intercepted is
directed down the shaft to a reservoir and then pumped out of the mine. The
other major challenge faced by the mine is the intersection of unforeseen dykes,
dolerite lenses and stone rolls. These reduce production rates and increase
operating costs.
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5. New Denmark Colliery
Mine Background New Denmark Colliery (NDC) is wholly owned by Anglo American Thermal Coal
and is the deepest Anglo coal mines in South Africa, approximately 210m. It is
located 30 km from Standerton and 165 km from Johannesburg. It was
commissioned in 1982 and mines Bituminous coal. NDC uses three production
shafts namely Central, Okhozini and West Main shaft. The mine supplies
Eskoms Thutuka Power Station with approximately 4.5 million tonnes of coal
each year.
NDC mines the No.4 seam which has an average thickness of 1.95m and varies
from 1.5m to 2.5m. The roof in the mine consists of Sandstone and the floor of
Siltstone. It has 1 Longwall (LW) section and 7 Continuous Miners (CM) sections.
Mining Method & Activities The only Longwall mining section in South Africa is done at NDC in the Okhozini
shaft. Longwall mining requires a constant seam thickness with a stable elevation
that doesnt change over large areas. The reserve should be relatively large
because of the extensive amount of time it takes to relocate the LW equipment.
This mining method causes caving of overlying strata which can lead to a
considerable amount of surface damage and groundwater disturbances. The
subsidence at NDC is 0.5m and it takes 5 years for it to reach surface.
Precautions must be taken to minimalise these disturbances like buying out the
surface area to ensure no damage is done to the publics property.
The development for a LW mining section is done with CMs in a Chain road
style. This means that there is a three road development at each side of the LW
section. The face of the LW section is 230m-243m wide and has a thickness of
2.1m. The development done allows for an air intake and return which will
ventilate the LW section. It also provides the space needed for the placement of
the conveyor belt which will transport the coal out of the mine.
21
Figure 10 shows the layout of a LW section. The advancing direction of the face
can be in reverse or in advance. Okhozini is advancing in reverse, thus they
developed onto the end of the coal seam and now they are progressing back to
the shaft with the LW. This gives the mine better knowledge about the geological
features the might encounter.
The double drum shearer produces 6200t/shift and extracts 93% of the coal. This
is a huge improvement on the CMs 800t/shift and 40% extraction. The minimum
width that the shearer can cut is 1.85m and its cutting depth is o.93cm with a 1m
drum.
The Armoured face conveyor (AFC) is a conveyor belt that is used to transport
the coal from the LW face onto the transport conveyor belt via the stage loader at
the side of the face. It is also used as an anchor for moving the support chocks. It
is durable and flexible and has a self-cleaning action.
The activities of a LW section start off with the Shearer that shears in a parallel
direction to the face. The AFC discharges the coal from the face onto the
transport conveyor belt. The hydraulic chocks moves forward whilst the shearer
move down the face. Goafing commences once the hydraulic chocks are moved
Figure 10 Longwall section layout.
22
into their new positions. The coal is transported out of the mine and further
conveyed to Thutuka Power Station. Transport to and from the LW and CM
sections can take 30-60 minutes.
Pillar Design and Support The Multi-road sections are used for CM production and development areas. It
consists of 8-10 roads. The center to center distances of these pillars are
25m19m and the road width is 7.2m. It provides enough space for 2 returns,
belt road, tractor road and 3 intakes.
The Chain-road section is solely for LW development purposes. It consists of 3
roads that provide sufficient space to place a return, tractor road and conveyor
belt. The center to center distance is 30m19m.
The sandstone roof is very competent at 80Mpa and the floor is 30Mpa. The
support in the CM sections is done with a double boom Joy roofbolter. The
roofbolts are 1.1m long and 22mm in diameter. The roofbolts are spaced
1.8m1.8m apart. The holes are drilled and filled with a spin-to-stol resin that
mixes and hardens when the roofbolt is inserted into the hole. 1.5m Roofbolts is
sometimes used in the spilts when needed.
Bigger pillars are left in between the CM and LW sections these pillars are
30m25m and are called crush pillars. They are used as support together with
the Chocks to prevent premature goafing. Once the LW advances the pressure
of the overlying strata will be placed onto these pillars and they will eventually
collapse/goaf.
The LW uses 129 hydraulically powered chocks for support, ideally for 2.35m.
These chocks are imported from the UK and they are ideal for thinner seams and
softer floor conditions. They move forward one by one as the shearer passes.
Controlled goafing commences once the chock are moves forward. It takes
approximately 3 months to disassemble and relocate the LW section and this is a
major drawback in LW mining.
23
Figure 11 shows a cross section of the chocks support system. It supports the
roof while the shearer advances and stops the goafed material to enter the
cutting face.
Equipment Selection Table 4. Table showing equipment and details
Equipment Detail
Joy AAA CM 3,6m Drum, 1 cycle=11 tonnes(60-90sec), 200m Cable
Roofbolter Double boom
Battery Hauler 16 tonne capacity
Feeder Breaker 75m from CM
Battery Bay 1 battery bay per section,3 batteries per car, 80m from face
Sandvik LHD 7 tonne capacity
11Kw Transformer 1 per section
Equipment Detail
LW Shearer 695 tonnes per cut
Armored Face Conveyor Coal transport
Hydraulic Chocks 129 chocks
Transport conveyor Coal transport
Headpiece Support
Tailpiece Support
Stage Loader disposes coalfrom AFC to transport conveyor
Figure 11: Basic Chock support illustration
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Ventilation Air is supplied through the intake via 400kW surface fans that sucks the air
through the workings. These fans are located on the return airways ventilation
shaft. Brattices are installed to direct the fresh air along the intake onto the face.
The volume of air on the face is 53-60 m3/sec. The speed of the air in the intake
is 2.5m/sec. Once it enters the face 0.5m/sec of air will filter through the area that
has goafed, located behind the support Chalks. The face speed will thus be
2m/sec. Sensors placed 75m into the tailgate measure the ventilation speed and
detect gasses. Airview is the brand of sensors used. The quality of the air is also
measured before it enters the face.
The ventilation in the CM sections require 30m3/sec at a speed of 1m/s. Force
fans are used to supply air onto a face when the CM cut exceeds 12m in length.
Production Rates The LW optimally produces 6200t/shift and a CM section produces 800t/shift.
The combined monthly production rate target of the 7CM sections with the LW
section is 318 000 tonnes/month, but the actual production is 160 000
tonnes/month. This is significantly lower that the target. It may be because of the
40% availability of the LW and the 2-3 hours of CM productivity per shift.
Unit Costs The operating costs which include mining activities costs R35/tonne and the
Engineering activities costs R65/tonne. Transport cost is R60/tonne. The total
cost of producing one tonne of coal is R300 and this includes the operating and
engineering costs. The final cost is R360/tonne which includes the total cost of
production with the transport cost.
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Personnel Personnel per shift in a CM section for production/development:
1Miner
1Electrician
1Fitter
2Operators
2Supporters
1Diesel Driver
1Control Stick
Maintenance crews consist of 6-11 people, usually 7 artisans and one foreman.
The expertise and the number of personnel for the maintenance shift depends on
what maintenance is required to be done for that specific shift.
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6. Msobo Coal
Location and background Msobo Coal mine is a new mine that started in 2011 with a business plan to
acquire established coal mines near Ermelo in South Africa. Msobo successfully
negotiated the purchase of the Highveld coal reserves which were previously
owned by Xstrata before 2011. This makes the Msobo coal mine project a brown
field project with a life of mine of 30years. Msobo coal mine is located in Breyten,
Mpumalanga (figure 12).
Figure 12: Map Showing Msobo Coal Mine
The Msobo coal reserve is under the Ermelo coal fields and they mine the Below
Seam (BL) which is seam A,B,C and D as shown (in figure 13) below. The
geology of the Msobo reserve falls under the stratigraphy of the Karoo Super
group, Ecca group in the Karoo Basin. The Ecca group is a group of sedimentary
geological formations found in the Southern Africa.
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It consists of mainly shale and sandstone as shown (in figure 13) below, laid
down in the sandy shorelines of swamplands during the Permian Period. (Davies,
P & Brant, J. 2010)
Figure 13: The stratigraphy of Msobo Coal Reserves
Xstrata also granted prospecting rights to Msobo coal in Chrissiesmeer,
Mpumalanga. Chrissiesmeer is a large wetland area. It is home to various frog
species, insects, birds, small game and their predators. This includes various
endangered species such as cranes and allegedly some newly discovered
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endemic species of fish and frogs. In 2010, even before Msobo coal came into
scene, the landowners of the wetlands area started taking collective steps to
declare the Chrissiesmeer wetlands a protected environment under the
Mpumalanga Biodiversity Stewardship Programme. Now Msobo coal is faced
with a tough decision to choose between coal and wetlands. It remains unclear
whether Msobo coal will support the plans for the protected area. If they
successfully oppose it, the past four years of hard work to declare the area
protected will become redundant and the whole wetlands area will become
vulnerable to exploitation in search of finite coal reserves. (Fuls,F. 2.013)
Mining method and activities The most economical method of coal extraction from coal seams depends on the
depth and quality of the seams, geology and environmental factors. Coal mining
processes are differentiated by whether they operate on surface or underground.
At Msobo coal they mine both on surface and underground and 60% of the coal
is from surface and 40% is from underground. During our visit at the mine we
visited their underground operation where they are mining 20m-120m below
surface. Mineable coal reserves at Msobo coal are mainly mined through two
mining methods. In underground operations board and pillar (12m by 18m
centres) method is used. Continuous Miners (CM) are used to cut the coal and
the CM loads the coal on a shuttle car which takes about 45seconds to fill this
shuttle with average capacity of 20tons. The shuttle car takes the coal to the
Buffalo feeder breaker. Each feeder breaker has a total power capacity of 50kW.
The coal is then transported to surface stockpiles by 1200mm conveyors.
(Marshall, T.2014)
After every 12m advance the Fletcher twin boom roof bolter comes in to support.
Lengths of the bolts used are 1.5m, 1.8m and 2.1m depending on the roof
conditions. This type of support is called the suspension support system. Four
roof bolts are installed in a row, 1.5m apart and 1.5m in advance. Drilling and
blasting is undertaken where conditions do not allow the use of a CM. These
conditions include geological discontinuities like faults and dykes but this is
29
sporadic at this reserve. They load and haul all waste material out of the pit to
expose coal and stockpile for final void rehabilitation. The General Manager
(Tammy Marshal) explained that they only load and haul topsoil material and
mainly weathered waste material determined through geological limit of
weathering which is in turn dumped back in the void as part of their continuous
rehabilitation program. Semi carbonaceous materials are dozed over in the void.
(Marshall, T.2014)
Equipment Selection The mine is equipped with electrical, mechanical and other equipment that
contribute to achieving conditions for safe operations and healthy environment.
To make sure the mine complies with the DMR requirements, the maintenance
team and the competent Artisans available to maintain the machines and
equipment at regular intervals. Foremen, GES and the engineer do the follow up
inspections on weekly and monthly basis to ensure compliance. The table below
shows the equipment used per section to get the coal to surface. (Marshall,
T.2014)
Table 1: Showing equipment used underground
Table 5: Underground equipment used at the mine
Main equipment:
Continuous Miner
Roof Bolter
Shuttle car (by 3)
Feeder breaker
Conveyor belt
Additional equipment:
Sandvik ED7 LHD
JA Engineering Scoops
Aim Tractors
Toyota and Nissan LDVs
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Material is transported from surface to work areas by flameproof tractors and
telecom trailer systems. Men are transported to and from workplaces using
flameproof tractors and man carrying trailers or man carrying non flameproof
LDVs. (Marshall, T.2014)
Ventilation All underground workings make use of a ventilation method. This is done by
means of air crossings and ventilation stoppings so as to ensure that all
production sections have an independent fresh air intake, and thereby, creating
independent ventilation districts. At Msobo coal they is a ventilation fan on the up
cast shaft which sucks up 150m3/s of air. Sufficient air quantity is supplied to
each production section to maintain an average air velocity in the last through
road (LTR) of 1.0m/s and not less than 0.60m/s at any point in the LTR. When
cutting takes place with a CM the velocity on the intake side of the CM will not be
less than 1.0m/s. (Davies, P & Brant, J. 2010)
Unit Costs and Personnel At Msobo coal the unit cost for underground operations is R200/ton and most of
the coal is exported and the remaining coal is sent to Eskom. The table below
shows the underground personnel per CM section and drill and blast section. At
this coal mine the average workforce has 18years work experience. The mine
works on a two shift cycle per day. Day shift starts at 5:30am to 3:30pm and the
Night shift starts at 2pm to 2am. (Marshall, T.2014).
Table 6: Personnel specifications
Production Sections
No. of workers
Dyke Development crew No. of workers
Shift Overseer 1 Miner 1
Miner 1 Jack Hammer operator 3
CM Operator 2 Roof Bolter Operator/HDV Driver Whombat
3
Roof Bolter Operator
4 Labourer General 1
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Shuttle car operator
3 Roof Bolter Assistant 1
LHD Operator Scoop
1 Total 9
Multi Skilled Tractor Driver
1
Labourer Belts FB Att
1
Labourer General Pinch bar att
1
Total 15
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7. Sasol
Mine Background Sasol has five mining operations in Secunda which all mine the nr.4 seam, these
are Brandspruit, Middelbult, Twistdraai, Bosjesspruit and Syferfontein. Two
different mines were visited while at Sasol, Brandspruit Colliery and Middelbult
(iThemba Lethu Shaft).
Brandspruit Colliery Brandspruit is the oldest of these 5 collieries and commenced in June of 1977. It
mines at a depth of 135m with a coal seam that is 3.7m in height on average.
The mine uses 9 Continuous Miner (CM) sections to produce 7.2Mt of coal per
annum. Brandspruit employs 1100 employees with approximately 450
contractors.
Figure 14 shows the Shafts and basic geography of Brandspruit. Originally the
main shaft was the only one but the travelling distances increased and thus shaft
2 and 3E was sunk. Main Shaft includes a man, ventilation and decline shaft.
Figure 14> Location of the shafts at Brandspruit
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The decline is for transporting the coal out of the mine. 2 and 3E shafts only have
one shaft which is divided into a man and ventilation shaft. The coal from 2 and
3E shafts are transported via conveyors to the main shaft where it connects with
the decline for removing the coal. The decline conveyor transports coal all the
way to Sasol Synfuels Secunda plant. 2 Shaft has a 5 year LOM left. Future
operations include the Impumulelo Shaft which will be in operation from 2015
Mining Method Stooping is done with the Nevid Pillar extraction method. This method is done
from the limit of the Bord and Pillar excavation in a reverse direction, thus back to
the shaft. It causes the stress on the pillars to be redistributed onto smaller pillars
which will lead to disturbances in the surrounding walls and pillars and will
eventually lead to the goafing of the roof. This method allows for the goafing to
be done in a safe and controlled manner. Areas with unfavourable geological
features and dams are not stooped.
The pillar sizes differ between sections and thus the stooping pillar sizes differs
too. Stopper pillars are left to prevent unexpected failures. They are spaced in
every 3 rows and act as yield pillars. Figure 15 shows the cutting sequence of the
Nevid method. The sizes used in the figure may vary. The CM cuts at a 45
degree angle. This allows the CM operator to be a safe distance away and under
supported roof.
Figure 15: The cutting sequence using the Nevid Method
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Figure 16 shows a Nevid pillar extraction section. The sequence of the CM cuts
is indicated with the numbers. The Lone pillar in the goaf area is the Stopper
pillar. Policemen, which are wood poles or sticks, are placed in the haulage
areas in and around the stooping section. They are used as a warning that
goafing has started. They tend to bend and crack once there is roof movement.
Figure 16: The Nevid Method pillar extraction.
60% of the pillars are extracted. The CM doesnt exceed 15m per cut when doing
stooping. This allows for a double lift to be taken and also makes the cable
handling easier. The three triangles left ensure that the goaf is kept away from
the center rib and that the goaf happens at least two rows away from where the
CM is cutting. The goaf is also less violent.
It is crucial to plan the stooping beforehand and prepare the section by marking
off the 45 degree angles with red paint to show the CM operator where his next
cu should be. The cuts must be inspected by supervisors to improve their
awareness and knowledge of the section.
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Pillar Design and Support The Nevid Method allows for the strongest possible remaining pillar to be next to
the CM. Mininmum pillar sizes from center to center is 28m28m. The sandstone
roof varies from a laminated to a competent roof which has to be supported
accordingly.
Equipment Selection Table 7: The type of equipment and the total number
Ventilation Figure 17 shows the basic ventilation of a Nevid Stooping section. The air from
the intake is directed to where the CM is cutting and then straight to the return
airway. The return airway is also known as the bleeder road. Methane is common
in coal mines and special care is taken to measure and control the leaking
methane.
Production Equipment Amount
Continuous Miner 9
Shuttle Cars 30
Aro Roof Bolter 1
Fletcher Roof Bolter 13
Other Roof Bolters 6
Feeder & Crushers 11
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Figure 17: Basic air flow through a Nevid section.
The CM operator is placed in the intake to avoid dust and gasses. Auxiliary fans
is not necessary when doing the Nevid method but they are needed in the normal
CM sections where cuts can easily exceed 24m.
37
Middelbult Colliery- Ithemba Lethu Shaft
Background Middelbult Colliery is located in Secunda in the Mpumalanga Province. It is
owned by Sasol as part of the Sasol Complex in Secunda. The figure below
shows its location.
Figure 18 Location of Middelbult Colliery
The iThemba Lethu The project is an extension of Middelbult Colliery and thus it
is a brownfields project. Ithemba Lethu Shaft is located on the Zandfontein farm
in Secunda. The shaft is a split person-and-materials and ventilation shaft. The
shaft uses a 40MW substation built by Eskom. Approximately R140 million
capital was required for this project. Coal is transported along the underground
conveyor system and does not come to surface at the iThemba Lethu shaft.
Mining Method Bord and Pillar mining is used to mine the 4 m seam using a Continuous Miner. A
Drill and Blast section is used to mine through geological features like dykes.
Middelbult Colliery
38
The 4-lower seam is mined at iThemba Lethu. The 4-upper seam is 0.5-1m thick
and it is not mined due lots of methane releases. Figure 19 below shows both the
4-seams and the sandstone roof.
Figure 19: The 4-seam layers.
Pillar Design and Support The mine uses a bord width of 7.2m with 25m pillar centres as shown in table 8
below.
Table 8 Pillar design and support specifics
Bord width 7.2 m
Pillar centers 25m
Barrier Pillar 28.8m
Width to Height Ratio 4
Number of roads 7
Roof Bolt length 1.8m
Support dimensions 2m x 2m
Roofbolts are used to support the sandstone roof and these are normally 1.8m.
On rare occasions, 1.5m roofbolts are used per Rock Mechanics discretion. The
39
bolts are placed 2m x 2m apart. Supporting is done after every 15m advance by
the continuous miner. Moreover, the support system used is such that the
continuous miner stops if more than 2 faces are unsupported faces.
Equipment Selection and Personnel The equipment used per mechanized section is as follows:
3 x Shuttle Cars (20 tonne)
1 x Fletcher Roof bolter
1 x Continuous Miner
Equipment is installed with a close-proximity system which brings to a halt a
machine when it is near people. This ensures a safe working environment in the
section. A total of 13 people work in one section.
Ventilation Two 750 kW fans are used for ventilation. In the section, every road is installed
with a Dura-fan. Each Dura-fan produces up to 8m3/s air capacity.
Production Rates and Unit Costs A section has a target of 50 m advance per shift. However, this target is barely
reached due to machine breakdown, bad ground floor conditions and
inexperience of the employees. An advance as low as 15m per shift can be
reached when the continuous miner breaks down. The amount of coal extracted
amounts to an average of 1350 tonnes/shift.
In-section costs amount to between R60 and R70 per tonne of coal. For the
whole Middelbult Colliery, the total costs average R170 per tonne.
Challenges The challenges faced at iThemba Lethu include faults, dykes and methane
releases. The accumulation of water underground is also a major problem as it
slows down machinery and thus reducing production.
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8. References
1. BHP billiton. (2014). Khutala Colliery (2 seam underground visit).
2. Davies, P. & Brant, J.2010. Coal vs. Biodiversity Xstrata.Leerdersboek
3. Fuls, F. 2013. Choosing between coal and wetlands in Chrissiesmeer.
Mpumalanga:Lapa.
4. Infomine. (2014, February 23). Retrieved February 23, 2014, from
www.infomine.com/index/properties/Graspan.html
5. Mabogoane, M. (2014). University of Pretoria ( Presentation).
6. Marshall, T.2014. University of Pretoria presentation.
7. New Denmark Colliery visit
8. Penumbra Coal Mine Visit 2014
9. PMY 320 Handbook, Chapter 6: Underground Coal Mining
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