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Coal Processing in Southern AfricaMark Cresswell (Process Engineering Consultant)
DRA MINERAL PROJECTS (PTY) LIMITED
FFF Solid Fossil Fuels in Southern AfricaJohannesburg 11 March 2015
Tweefontein - 2000 t/hr Phola - 2400 t/hr DMO - 2200 t/hr
Some Recent DRA Coal Projects 2008- 2015
SOUTHERN AFRICA COAL PROCESSING
• Coal Washing Plants in Southern Africa• Industry trends in South Africa• Raw Coal characteristics of interest
– Witbank (RSA), Botswana, Madagascar, Mozambique
SOUTHERN AFRICA COAL WASHING PLANTS
Country Number of
Washing Plants Products South Africa RoM 260 Mtpa Raw Coal (2011 DoE stats) Production 224 Mtpa products South Africa ~50 ~98% thermal coalNamibia 0 thermal coal potential Mozambique 3 export coking & thermal coal Madagascar 0 thermal coal potential Botswana 1 Morepule - (domestic thermal) Zimbabwe 2 Hwange (coking, met & thermal coal) Zambia 1 Maamba (thermal coal) Tanzania 1 Kiwri (domestic thermal coal) Production (non SA) 4 Mpta (1.8%) ref. World Coal
SA COAL INDUSTRY – LOCATION OF MINES
SA COAL INDUSTRY - OVERVIEW
• 90% of electrical power (~40 GW) generated from coal• continued use of “middlings” coal (21 – 23 MJ) for
internal power generation while better quality (27.5 MJ coal) for thermal coal export.
• 60 – 70 Mt recent annual thermal coal exports worth ~$6 billion USD / yr to Europe and Far East (2008 – 2012)
• New trend is to also export lower quality coal to Indiaputting pressure on reserves for internal power generation
Exports Mt Year $/t Value of Exports65 2008/13 100 6.5 B$72 2014/15 60 4.3 B$
R/$ 2008/13 8.0 52.0 Billion RR/$ 2014/15 11.8 51.0 Billion R
Minimal effect in Rands
SA COAL INDUSTRY - OVERVIEW
• 35 yrs since last major expansion when the Export trade started, now in major plant renewal and study phase to ensure future power supplies
• Huge future reserves in northern Coal fields (mainly the Waterburg) – logistics challenges - dry areas - remote infrastructure
• Coking & Met coal scarcity, reserves in environmentally sensitive areas eg KZN
SA COAL INDUSTRY• Importance of Washing Plant – how much coal is
washed?• Simplified Analysis of PS Coal Calcs
Standard Eskom (South Africa) power stationNumber of generating units 6 unitsOutput Power/unit 600 MWTotal power station output 3 600 MW total
Calculation of annual energy output
annual operation 8 760 hrs/annumutilization 80 % operating hours at full capacitytotal power output/annum 25 228 800 MWhr/annumconvert to Joules 3.60 MJ/kWhr conversion factor
90 823 680 000 MJ/annum energy requiredEnergy conversion efficiency 37 % (typical Eskom 35 - 39%)Total energy from coal required 245 469 405 405 MJ/annum
Calculation of coal processing capacity required
Average Coal Gross CV 21.5 MJ/kg (range 16 – 23 MJ/kg CV)Gross CV per tonne 21 500 MJ/tAnnual tonnage of coal required 11.4 Million tonnes/annum
3 171 t/MW installedCoal Preparation Plant (CPP) design throughputoperating hours "on coal" 6 500 hrs/annumCPP throughput 1 756 t/hrWashing Plant throughput per MW 0.49 t/hr/MW
SA COAL INDUSTRY – Eskom PS Coal Calcs determining amount of unwashed coal
OthersWestern Cape Koeburg 2 900 1 800 gas / hydro Cahora Bassa 2 000
3 800
Future14 Waterberg Medupi Grootegeluk Exxaro yes 6 800 4 800 15 Witbank Kusile Others + New Largo AAC Inyozi eventually 6 800 4 800
9 600
Future Overall Total 50 958 MW
Eskom Coal Fired Power Stations - simple calculations t/hr/MW
Coal FieldPower Station Main Coal Mine Operator Washing Plant Units MW
Installed MW 0.49
Operating1 Witbank Arnot Arnot + Mafube AAC Inyozi yes 6 350 2 100 2 Witbank Duvha Middelberg + DMO Becsa yes 6 600 3 600 3 Witbank Hendrina Optimum Optimum yes 10 200 2 000 4 Witbank Kendal Khutala Becsa no 6 686 4 116 2 008 t/hr 5 Witbank Komati Koornfontein Becsa yes 1 000 6 Witbank Kriel Kriel AAC Inyozi no 6 500 3 000 1 464 t/hr 7 Witbank Matla Matla Eyesizwe no 6 600 3 600 1 756 t/hr 8 Highveld Camden Ermelo + Golang Golang yes 8 200 1 600 9 Highveld Majuba various coals railed in 15 suppliers 6 665 3 990 10 Highveld Tutuka New Denmark (50%) AAC Inyozi no 6 609 3 654 1 783 t/hr 11 Sasolberg Lethabo New Vaal AAC Inyozi de-stoning only 6 618 3 708 12 Sasolberg Grootvlei Grootvlei no 6 200 1 200 585 t/hr 13 Waterberg Matimba Grootegeluk Exxaro yes 6 665 3 990
total 37 558 7 597 t/hr Required coal t/MW installed 3 171
Annual requirements 119 Approximate unwashed Coal 49 Mtpa direct
SA COAL INDUSTRY – Eskom PS Coal Calcsdetermining amount of unwashed coal
Coal ProcessingMined Coal 260 Mtpa (2011 Eskom stats) ignoring direct coalWashed 65 Mtpa Export (washed) 25% 31% average
Washed 70 Mtpa Eskom (washed) 27% 33% yield 64%sized / de-stoned 49 Mtpa Eskom (direct) 19%by difference 76 Mtpa Discards 29% 36%
100% 100%
Marketable Coal Products 224 Mtpa (ref. Eskom website)% SA coal to Eskom 53% 119 Mtpa to Eskom
210 Mtpa RoM Coal Wash (79% total production)
RAW COAL CHARACTERISITICS
THERMAL COAL QUALITY IN SOUTHERN AFRICAWITBANK
• “Gondowana” Coal with higher mineral matter compared with Northern Hemisphere coals
• Great variability in Yields: 5 – 80% at SG 1.6; 20 – 95% at SG 1.8
-
10
20
30
40
50
60
70
80
90
100
1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
Cu
mu
lativ
e %
Yie
ld
Floats Density
Witbank Seam 2 Data (Western Edge)Cumulative Yield vs Density
Seam 2
Average 2S
ave + 1std
ave - 1std
THERMAL COAL QUALITY IN SOUTHERN AFRICAEASTERN BOTSWANA
• Similar Characteristics and great variability
Mookane D1S5Cumulative Yield
0
10
20
30
40
50
60
70
80
90
100
1.4 1.5 1.6 1.7 1.8 1.9 2 2.1
Floats Density
Cum
ulat
ive
Yiel
d (%
)
THERMAL COAL QUALITY IN SOUTHERN AFRICAMADAGASCAR
• Similar Characteristics and great variability
-
10
20
30
40
50
60
70
80
90
100
1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
Cum
ulat
ive
% Y
ield
Floats Density
Madagascan Coal - Recent + 1940's Boreholes Data Cumulative Yield vs Density
THERMAL COAL QUALITY IN SOUTHERN AFRICAWITBANK vs EASTERN BOTSWANA
FRACTIONAL SULPHUR DISTRIBUTION
• Similar Characteristics - higher sulphur values in SG1.8 Sinks – easy washing scheme
THERMAL COAL QUALITY IN SOUTHERN AFRICAWITBANK vs MADAGASCAR
YIELD vs ASH
• Witbank coal – higher yields for same % Ash
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
YIELD vs ASH
• Moatise coals – target 10 – 12.5% Ash for Coking coals
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
Liberation Characteristics
• Banded nature of Vitrinite very evident• Generally <6mm for liberation
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
Liberation Characteristics
• Significant Increase in Yield in small and fine coal sizes• Roughly Coking Coal yield – 1/3 DMS, 1/3 Fine Coal, 1/3 Slimes Flotation
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
Liberation Characteristics
• Significant Increase in Yield in small and fine coal sizes
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
Liberation Characteristics
• Roughly Coking Coal yield – 30% DMS, 40% Fine Coal, 30% Slimes Flotation
THERMAL COAL QUALITY IN SOUTHERN AFRICAMOATISE COALFIELD – TYPICAL DATA
Liberation CharacteristicsDistribution of Products (typical Witbank)
t/hr %Export Product +0.6mm 411 46%
Middlings +0.6mm 167 19%
Fine Coal middlings 44 5%
Discards 273 31%
Totals 896 100%
Size Class Coking Thermal Discards Total(50 x 1)mm 29% 100% 90% 75%
(1 x 0.25)mm 42% 6% 14%(-0.25)mm 29% 5% 10%
Total 100% 100% 100% 100%
Typical Moatise Product Mass Balance
COAL PROCESSING PLANTS
Solution to Raw Coal Variability is Raw Coal Blending
Large Mine – Raw Coal Stacking and Bucket Wheel Reclaiming -40 000t with emergency parallel lay down area (RSA)
Raw Coal Blending Options
Large Mine – Raw Coal Circular Blending StockpilePortal Reclaimer(NSW)
Raw Coal Blending Options
RSA 65 000t – Raw Coal Circular Blending Stockpile Full & Empty - due to plant running ahead of mine.
Raw Coal Storage Options
2 000t Surge Bin (RSA)
20 000t Conical Earth re-inforced Stockpile
Raw Coal Storage Options
Split to Two Modules
Raw Coal Crushing Circuits
Large Sites required for Open Cast mines to reduce RoM coal from 1.2m to 50mm (Klipspruit)
Raw Coal Crushing Circuits
Tipping Bin, Chain Feeder, Double Roll Primary Crusher
South African Raw Coal Crushing Circuits - 1
Primary Crusher, Rotary Breaker, Screen, Tertiary Crusher
Large Plant Raw Coal Handling & Preparation (significant tramp or parting rock)air dry tonnes basis
D1 + M2 Seam Coal Combined
Loading Bin300 t capacity
Coarse DiscardsApron Feeder + Mineral Sizer-900mm
Open Cast MineRotary Breaker
-350mm 60% mass to oversize (+120mm)
-120mm
CRUSHING PLANT-120mm Feedsize
to raw coal stockpile-50mm crushed product
to Open Cast Mine Pit
100t Capacity Dump
Raw Coal Crushing Circuits
Rotary Breaker – secondary crusher + hard rock removal
Raw Coal Crushing Circuits
Rotary Breaker – Discard of Harder Sandstones and Shales
Raw Coal Crushing Circuits - 2
Primary Crusher, Secondary & Tertiary D/R Crushers
Large Plant Raw Coal Handling & Preparationair dry tonnes basis
D1 + M2 Seam Coal Combined
Loading Bin300 t capacity
Apron Feeder + Mineral Sizer-900mm
Open Cast Mine
-350mm 60% mass to oversize (+120mm)
CRUSHING PLANT-110mm Secondary Product
-50mm crushed product
to raw coal stockpile
100t Capacity Dump
Raw Coal Crushing Circuits
Secondary & Tertiary D/R Abon Crushers at Mafube
Raw Coal Crushing Circuits
Tertiary Crusher maintenance at Goedgevonden
Raw Coal Crushing Circuits for Liberation -Moatise
Scalping Screen before Tertiary Crushing
Raw Coal Crushing Circuits for Liberation -Benga
Careful use of Tertiary Crushing
Raw Coal Feed
6.5 mtpa1 000 tph DRA's design experience
Raw Coal Bin 1 100 tph DRA's design experience6 500 hrs/yr DRA's design experience
Feeder BreakerRotary Breaker
Raw CoalSurge Bin
Scalping Screen
Emergency Stockpile
+100mm-50mm
Optional
Discard Stockpile
+50mm
CPP Average FeedCPP Average FeedCPP Design FeedHours on Coal
Raw Coal Crushing Circuits for Liberation –using Chirodzi tertiary crushing circuit concept
Rotary Breaker as Secondary Sizer plus even more careful use of Tertiary Crushing with extra 10% rejected
General trends in Coal Preparation Plan Design
General Trends in Coal Preparation Plant Separation Units (Southern Africa)1970's - 2015
Coarse Coal Small Coal Slimes-(120 x 12)mm -(25 x 0.5)mm -0.5mm
1970's Bath/Wemco Drum/Jig DM Cyclones / Jig Discard or Flotation
Coarse Coal Small Coal Fine Coal Slimes-(120 x 12)mm -(25 x 0.63)mm -(0.63 x 0.125)mm -0.125mm
1980's Drewboy / Norwalt Bath DM Cyclones Spirals introduced mainly discardedWemco Drum (<750mm dia) Fine Coal DMS x 1 occasional flotation
Coarse + Small Coal Fine Coal Slimes-(90 x 12, 12 x 0.63)mm or -(50 x 0.63)mm -(0.63 x 0.125)mm -0.125mm
1990's (Bath + DM Cyclones) or DM Cyclones Spirals mainly discardedLarcodems plant x 1 occasional flotation
Coarse + Small Coal Fine Coal Slimes-(50 x 0.63)mm -(0.63 x 0.125)mm -0.125mm
2000's DM Cyclones Spirals / 1 x DM cyclones mainly discardedTBS / DM Cyclones occasional flotation
Coarse Coal Small Coal Fine Coal Slimes-(120 x 12)mm -(25 x 0.63)mm -(0.63 x 0.125)mm -0.125mm
2010's Drewboy/Wemco Drum DM Cyclones Spirals / TBS/ mainly discardedLarcodems FSB Dry Sepn (50 x 10)mm Reflux Classifier occasional flotation
DM Cyclone Coal Washing Circuits
• Technology Dominated by the DMS (dense medium separation) method
• Uses magnetite powder and water to create a liquid “medium” of SG 1.35 – 1.90
• Mature technology – first plants built in late1940’s
• DM Cyclone invented and developed by Stami-Carbon (Netherlands)
• Technology licensed worldwide 1950’s – 80’s• Vessels used – DM Cyclones, Wemco Drums,
Peters Baths, Drewboy, Teska Baths
DRA Engineers in Australia checking out experience there
DMS Circuit Design Concepts –SA vs Australia
Difference in yields between Small coal and Coarse coal fractions
32 Klipspruit Bulk Sample Washabilities (50 x 8)mm & (8 x 0.63)mm- Phola CoalExport Yield (Section) vs % ROM Feed
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60 70 80 90 100
% ROM Feed
% E
xpor
t Coa
l Yie
ld (D
MS
Feed
)
Coarse Coal Small Coal Maximum AverageMinimum Coarse Coal ROM Max Small Coal ROM Max MaximumAverage Minimum Linear (Coarse Coal) Linear (Small Coal)
Coarse CoalSmall CoalMin yield
Ave Yield
Max Yield
Coarse Coal Max % ROM
Small Coal Max % ROM
Max Yield
Ave Yield
Min Yield
2 Stage DMC Circuit (Lo-Hi) South Africa –separate coarse & small coal circuits – maximises Export Yield
Low Density Cut
+8 mm
+0.8mm+0.8 mm
High Density Cut
2 - Stage DMC Circuit
-50mm Feedis Product
Discard
Middlings
-0.8 mm Feed
MAFUBE COAL – 940 t/hr
DRA Mafube Plant – first SA use of 1150mm Cyclones
PHOLA COAL 2400 t/hr
DOUGLAS MIDDELBURG OPTIMISATION (DMO) 2200 t/hr
DOUGLAS MIDDELBURG OPTIMISATION (DMO) 2200 t/hr
Simpler 2 Stage DMC Circuit (Lo-Hi) Australia – combining Coarse + Small
Coal with optional Stage 2
Low Density Cut+0.8mm
+0.8 mm
High Density Cut
2 - Stage DMC Circuit
Option
-50mm Feedis Product
Discard
Middlings
-0.8 mm Feed
Glencore’s Goedegevonden & Tweefontein CPP modern Australian type plant in RSA – 2000 t/hr
Glencore’s Tweefontein CPP modern Australian type plant in RSA – 2000 t/hr
Glencore’s Tweefontein CPP modern Australian type plant in RSA – 2000 t/hr
Use of CAD Modelling Techniques in plant design
Plant Section showing “Banana” Screens & 1150mm Cyclones
2 Stage DMC Circuit (Hi-Lo) with intermediate crushing - Mozambique
Interstage Crushing
Low Density Cut+0.8mm
High Density Cut
2 - Stage DMC Circuitwith extra liberation offirst stage product Discard
-50mm FeedisProduct
Middlings
-0.8 mm Feed to Fine Coalis
2 Stage DMC Circuit (Hi-Lo) with intermediate crushing - India
Interstage Crushing
Low Density Cut+13mm
High Density Cut
+0.8mm
2 - Stage DMC Circuitwith extra liberation offirst stage product Discard
-50mm FeedisProduct
Middlings
-0.8 mm Feed to Fine Coalis
Fine Coal Circuit (spirals for >SG 1.7 product)
Fine Coal Washing (0.8 x 0.125)mm
Technology dominated by gravity spirals & teeter bed separator (TBS)
Fine Coal Circuit (spirals + TBS) for low density product
Desliming Cyclone
Spirals
-0.8 mm Feed to Fine Coalis
-0.125 mm to Thickeneris
Product
Discard
TBS
Fine Coal Circuit (Reflux Classifier) for low density product
Desliming Cyclone
Reflux Classifier
-0.8 mm Feed to Fine Coalis
-0.125 mm to Thickeneris
Product
Discard
Fine Coal Washing (0.8 x 0.125)mm – Reflux Classifier with lameller plates
Developed in NSW, Australia – first plant
Fine Coal Washing (0.8 x 0.125)mm – Reflux Classifier with lameller plates
Modern Reflux Classifier with 6mm Lamellar Plate gap
COAL SLIMES (-0.125 x 0)mm - Thickening
Thickening Technology – standard settling technique assisted by use of flocculants
COAL SLIMES (-0.125 x 0)mm – Flotation
Duel Cell –Witbank Coal,
Column & Jameson Cell - Moatise
COAL SLIMES (-0.125 x 0)mm - Filtration
• Raw Water and slimes dams restrictions have lead to introduction of slimes filtration
• Higher inherent moistures in the peripheral Witbank Coal regions so Filter presses being specified in order to make a saleable product.
• Mafube – first major use of TH Filters in RSA• Phola – combination of TH & Lasta Filter presses• Briquetting plants being developed and
constructed
COAL SLIMES FILTRATION
• Filter presses at Phola Coal Plant (120 t/hr capacity)• Lasta & TH Filters used
COAL PRODUCT HANDLING – SA Traditional
Stacking & Bucket Wheel Reclamation, Rail Silo’s
COAL PRODUCT HANDLING
Overhead Stacking - underground conveyor reclamation
CONCLUSIONS
• New era of large throughput coal plant design & construction started around 2005
• Major plants built in• Mozambique (Moatise CF)• South Africa (Witbank & Waterberg Coalfields)
• Future plants in Botswana & Madagascar• Plant efficiency vs. complexity becoming a
factor in DMS circuit design
THANK YOU!
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