PNB 400 Final Report

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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


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Ventilation .......................................................................................................................................... 24

Production Rates............................................................................................................................ 24

Unit Costs .......................................................................................................................................... 24

Personnel ........................................................................................................................................... 25

6. Msobo Coal .................................................................................................................................. 26

Location and background ........................................................................................................... 26

Mining method and activities .................................................................................................... 28


Ventilation .......................................................................................................................................... 30

Unit Costs and Personnel .......................................................................................................... 30

7. Sasol ............................................................................................................................................... 32

Mine Background ........................................................................................................................... 32

Brandspruit Colliery ...................................................................................................................... 32

Mining Method ................................................................................................................................. 33



Ventilation .......................................................................................................................................... 35

Middelbult Colliery- Ithemba Lethu Shaft ................................................................................ 37

Background ....................................................................................................................................... 37

Mining Method ................................................................................................................................. 37


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

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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

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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

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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.

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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.

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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.

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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

36

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.

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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

Documents

PNB 400 Final Report