coal processing in southern africa - fossil · pdf filecoal processing in southern africa ......

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

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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

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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

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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


Liberation Characteristics

• Banded nature of Vitrinite very evident• Generally <6mm for liberation



• 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



• Significant Increase in Yield in small and fine coal sizes



• Roughly Coking Coal yield – 30% DMS, 40% Fine Coal, 30% Slimes Flotation


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)


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


Rotary Breaker – secondary crusher + hard rock removal


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


Secondary & Tertiary D/R Abon Crushers at Mafube


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

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% ROM Feed

% E

xpor

t Coa

l Yie

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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

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

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


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


-0.125 mm to Thickeneris

Product

Discard

TBS

Fine Coal Circuit (Reflux Classifier) for low density product

Desliming Cyclone

Reflux Classifier


-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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