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Rosemary Falcon 2012
COAL RESOURCES OF SOUTH AFRICA AND THEIR UNIQUE QUALITIES
CHALLENGES AND OPPORTUNITIES IN USING HIGH ASH, LOW GRADE COALS IN MODERN POWER GENERATING PLANTS IN SOUTHERN AFRICA
1
Rosemary M S Falcon
IPP March 2016
IPP 2016
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. The challenges in South African coals
4. Experiences of low grade coal combustion in South Africa and Botswana
5. Solutions - Approaches towards cleaner coal usage
FOSSIL FUEL DISTRIBUTION IN AFRICA
3
COAL GAS OIL
IPP 2016
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. The challenges in South African coals
4. Experiences of low grade coal combustion in South Africa and Botswana
5. Solutions - Approaches towards cleaner coal usage
S. HEMISPHERE – GONDWANA COAL
- formed in cold to cool temperate
conditions in Permian times (280-300
Million years ago)
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EUROPEAN-USA COAL - formed in
Equatorial conditions in
Carboniferous times (300-350
Million years ago)
HOT STEAMY EQUATORIAL SWAMPS IN THE
NORTHERN HEMISPHERE DURING COAL FORMING
TIMES (Carboniferous) IPP 2016 6
ECCA - RECONSTRUCTION OF NO 1 AND EARLY NO 2
SEAM CONDITIONS -
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Major floral
vegetation
changes
Reflecting
major
climatic
events during
Karoo times
NB: Note
coal Seam
occurrences
during floral
changes
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KAROO BASINS IN SOUTH-CENTRAL AFRICA (AFTER CATUNEANU ET AL., 2005).
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Cross section through the coal-bearing basins and the
Kaapvaal Craton in South Africa during Permian and Triassic
times
1 - Permian
2 - Triassic
Kaapvaal craton
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Cape Fold Mountains
Zimbabwe
Cape Fold Mountains Zimbabwe
Karoo inland sea
Karoo inland sea
COALFIELDS OF SOUTH AFRICA
11
COALFIELDS OF SOUTH AFRICA
N
INDIAN OCEAN
ZIMBABWE
BOTSWANA
LESOTHO
SWAZILAND
MO
ZA
MB
IQU
E
Nongoma
Vryheid
Ladysmith
Standerton
Volksrus t
UtrechtNewc astle
2
7
1312
14
16
17
Ermelo
8
Molteno
Potgietersrus
Springs
Pretoria WitbankBelfast
Vereeniging
Bloemfontein
Thabazimbi
Richards Bay
Durban
5
10
NORTHERNCAPE
EASTERN CAPE
FREE STATE
NORTH WEST PROVINCE
LIMPOPO PROVINCE
MPUMALANGA
KWA ZULU NATAL
GAUTENG
1
3
4
6
11
9
Welkom
18
19Indwe
COALFIELD
1) Tuli (Limpopo) 2)
3) Mopane (Western
4) Tshipise (Central
5) Venda-Pafuri (Eastern 6) Springbok Flats 7)
8) 9) Free State
10) 11) South Rand
12)
13)
14) 15)
16) 17)
18) Somkele19) Molteno -Indwe
Waterberg
Soutpansberg)
Soutpansberg)
Soutpansberg)
Witbank
Kangwane
Vereeniging - Sasolburg
Highveld
Ermelo
Klip RiverUtrecht
VryheidNongoma
15
Coal reserves 1982 - 55 BT est (Petrick) 2000s - 30 BT est (Prevost) CENTRAL BASIN - 80% - Bitum C Witbank, Highveld, Ermelo Thermal, petrochemical, export, industry KWA-ZULU NATAL - 1% - Bitum C-Anth A Coking, anthracite, lean Bit A, LIMPOPO – 15% - Bitum D-Bitum A Soft coking, pci, thermal, export FREE STATE – 4,% - Bitum D Thermal
IPP 2016 Source ; X Prevost
KAROO SEA DURING ECCA COAL-FORMING TIMES
N
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DISTRIBUTION OF THE COAL SEAMS IN THE MAIN KARRO BASIN
FREE STATE
MPUMALANGA
KZN
HIGHVELD
14
MAJOR SEAMS ACROSS THE KAROO BASIN, SOUTH AFRICA KWAZULU-NATAL , ERMELO, WITBANK TO FREE STATE
Different sequences of seams in each area
Number ID Number ID Letter ID Named ID
IPP 2016
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So Major changes took place over the coal-forming period in Southern Africa i.e.
•Geological sedimentological changes
•Climatic changes •Vegetational changes
ALL OF WHICH AFFEC THE DISTRIBURION OF COAL
SEAMS AND THEIR QUALITIES
DISTRIBUTION AND QUALITRY OF COAL IN SOUTH AND SOUTHERN AFRICA
Summary – Coal Quality Distribution
Coals in South Africa vary in quality in the following ways:
– Between Coal basins (age, sedimentary environment, vegetation)
– Between coalfields (rank, type and grade)
– Between seams (climate, vegetation, sedimentary environment)
– Laterally and vertically within one seam (in-seam variations)
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Run-of-Mine Production
333.6Mt
“Washing”
Screening
Discards 74.8 Mt
209.4 Mt
124.2 Mt
Stocks
Synfuels 42.9 Mt
Electricity 128.2 Mt
Local Use 25.9 Mt
Exports
78.7 Mt
69.8 Mt 11.9 Mt 35.0 Mt
5.0Mt 31.0 Mt 93.2 Mt
11.9 Mt
29 17 IPP 2016
Source ; X Prevost
South African Local Sales 2015
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Coal provides: • 93% Electricity • >30% liquid fuels • 95% C Reductants
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. The challenges in South African coals
4. Experiences of low grade coal in combustion in Southern Africa
5. Solutions - Approaches towards cleaner coal usage
Coal A Coal B
Gross Calorific Value MJ/kg ad : 28,70 28,93 Proximate Analyses %ad :
Inherent Moisture 3,7 2,4 Volatile Matter %ad 30,5 28,9 Ash Content %ad 11,1 12,2 Fixed carbon 54,7 56,5
Combustion efficiency 83,0 66,0 C in ash% 4,4 15,5
1. SPECIFICATIONS OF TWO COALS
NB: THE SAME PROXIMATE ANALYSES BUT DIFFERENT COMBUSTION PROPERTIES
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DO NOT ASSIST IN PREDICTIONG THE FOLLOWING:
Bulk volatiles and fixed carbon versus Macerals and their proportions in coal
Vitrinite - Highly porous char – fast burn-out
Inertodetrinite - Mixed char – moderate burn-out
Inert Inertinite - Dense char – long burn-out
FORMS OF CHAR FROM MACERALS AND THEIR RELATIVE BURN OUT TIMES
Coal A Coal B
Gross Calorific Value MJ/kg ad : 28,70 28,93 Proximate Analyses %ad :
Inherent Moisture 3,7 2,4 Volatile Matter %ad 30,5 28,9 Ash Content %ad 11,1 12,2 Fixed carbon 54,7 56,5
Combustion efficiency 83,0 66,0 C in ash% 4,4 15,5
Organic Composition % :
Maceral comp (vitrinite%) 62,0 30,0 Rank (RoV random%) 0,73 0,75
1. SPECIFICATIONS OF TWO COALS
NB: THE SAME PROXIMATE ANALYSES BUT DIFFERENT COMBUSTION PROPERTIES
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0
5
10
15
20
25
30
35
40
45
50
% Proportion
0-10 10 to 15 15-20 20-25 25-30 30-35%
% Ash in in-situ coal
Proportion of SA Coal in Ash Ranges (ex Petrick
& Horsfall, 1977)
Proportion of SA CoalReserves in ash ranges (%)ex Petrick Horsfall
(after Petrick ; Horsfall, 1977)
2. QUALITY OF COAL - ASH CONTENT
SOUTH/SOUTHERN AFRICA’S COAL REMAINING RESERVES CONTAIN A HIGH ASH CONTENT.
Very little left
26 IPP 2016
and 35-65% now being mined
LOW ASH COAL – HIGH VOLATILES - all volatiles combustible
HIGH ASH COAL (CLAYS) – HIGH VOLATILES - most incombustible
Clays
CLEAN COAL
Vitrinite - no visible
minerals
DIRTY COAL
Vitrinite + abundant
layered clays (black) 27
EFFECT OF HIGH ASH COALS: LIMITED LIBERATION OF MINERALS DUE TO NATURE OF THEIR DISTRIBUTION IN COAL
Scale: 200 microns from side to side
In each photograph
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CLASSIFICATION AND CATEGORISATION OF COALS
DEGREES OF INCREASING DIFFICULTY IN IGNITION AND COMBUSTION
LEADING TO HIGHER COMBUSTION TEMPERATURES
USA and European Carboniferous coals
Witbank-Highveld coals
KWZ Natal coals
Reactive –Vitrinite)
Inert (Inertinite)
x x x x x x
x x x x x x
28 IPP 2016
4. COMBINED ASSESSMENT – RANK AND TYPE OF COAL
VARIATIONS IN TYPE AND RANK OF COALS FROM DIFFERENT
REGIONS
>15% variation in coal quality and consistency causes problems
in combustion: ignition, flame control, burnout and boiler
efficiency
TYPE
RANK
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. The challenges in South African coals
4. Experiences of low grade coal in combustion in Southern Africa
5. Solutions - Approaches towards cleaner coal usage
LARGE SCALE POWER GENERATING PULVERISED FUEL BOILER
LETHABO POWER STATION (4 600 MW) • Extreme difficulty in ignition • Mark7 burner design • 8m added to height of boiler • 1m extra between rows of burners • Tube mills selected to ensure extra fine pf sizes • Burner mouths melted • Pop-corn fly ash blocked air heaters • Unusually high % of fly ash
MATIMBA POWER STATION (4 500 MW) • Ignition and combustion difficulties when boilers were designed for coal from one zone without taking into account different coal qualities (organic maceral %) qualities in another zone. i.e. non-design coals
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FLUIDISED BED BOILERS
• Corrosion of the sparge pipes below the rims • Agglomeration of particles in the moving bed • Ash deposits dropping down to the base • Difficulties in ash removal • Difficult temperature control • Ash agglomeration (BFBC)
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32
A: Excellent combustion –1549oC
B: Irregular combustion –1789oC
C: Poor ignition on grate –1721oC
D: Massive ignition, throughout chamber –1793oC
EFFECT OF VARYING ORGANIC MATTER ON COMBUSTION
TEMPERATURES AND FLAME CHARACTERISTICS 4 South African coals with varying organic matter
• CVs - 25,5 to 26,9 MJ/kg •Ash - 15 to 17% ad
Source: R Taole , M Andrews 2013
IRREGULAR EFFICIENCY
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SUMMARY
South Africa faces a future with
– High ash coals (difficult to upgrade or beneficiate)
– High inert Inertinite coals (difficult to ignite, long burning)
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EFFECT OF USING POORER GRADES OF COAL (HIGH ASH AND INERT ORGANIC MATTER) ON CO2 EMISSIONS
Rise in CO2 in Eskom over 10 years
Eskom 2012
Eskom grid emission factor
0 1 000 2 000 3 000 4 000 5 000 6 000 7 000
China
USA
Russia
India
Japan
Germany
Canada
UK
Iran
Korea
Italy
Mexico
Australia
Saudi Arabia
Indonesia
France
Brazil
South Africa
Spain
Ukraine
Million tons CO2
SOUTH AFRICA PLANS TO
INTRODUCE CARBON TAX IN
2016/17 – DESPITE THE VERY
HIGH RELATIVE COSTS OF THE
ABATEMENT
SA is responsible for 1.1% of total global CO2 emissions,
but South Africa has committed to reducing its emissions
by 35% and 45 % within the next 15 years.
CO2 EMISSIONS FROM SOUTH AFRICA IN ABSOLUTE TERMS IS VERY SMALL
Source IEA - Top 20 CO2 Country emitters, 2008
35 IPP 2016
CHALLENGE: CARBON TAX AND CARBON CAPTURE AND STORAGE
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SOUTH AFRICA PLANS TO INTRODUCE CARBON TAX IN 2016/17 – DESPITE THE VERY HIGH RELATIVE COSTS OF THE ABATEMENT.
SOUTH/CENTRAL SOUTHERN AFRICA HAS LITTLE OR
NO SUITABLE GEOLOGY TO UNDERTAKE CO2 STORAGE (in South Africa, less that 1,5% on land; in excess of 1 000 kms to the nearest gas fields.
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. The challenges in South African coals
4. Experiences of low grade coal combustion in South Africa and Botswana
5. Solutions - Approaches towards cleaner coal usage
MINERAL MATTER ORGANIC MATTER
Inorganic matter behaviour MINERALS MACERALS Organic Matter Behaviour
Viscosity Devolatilisation
Agglomeration Ignition
Ash Formation Char formation
Peak Temperature
Burnout
Affects the Boiler : Affects the Boiler : Ash deposition Flame stability Slagging, Clinkering, Fouling Heat output Erosion Heat transfer zones Precipitability Rate of coal consumption Ash Handling Carbon-in-ash Particulate emissions Gaseous emissions
ASH CHAR
COST EFFICIENCY
Process Efficiency Plant availability
Plant capacity
MATCH COAL QUALITY TO PROCESS PLANT
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REDUCE EMISSIONS THROUGH INCREASED EFFICIENCY OF POWER PLANT – GLOBAL AND SA SCENARIO
39 Source IEA CCC
Efficiency gains using
today’s technology can cut
CO2 emissions by 33%
CCS technology can produce 50% loss but efficiency loss
of 7-12% points
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PROPOSED MEDIUM TO LONGER TERM SOLUTIONS FOR CLEANER COAL-FIRED ENERGY PRODUCTION IN
SOUTHERN AFRICA:
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• INCREASED EFFICIENCY IN POWER PRODUCTION • PC – Super- and Advanced supercritical power generation
• CFBC -- for high ash usage, in-bed SOx reduction, low water
consumption, flexible fuels
• CO-FIRING WITH BIOMASS – 1:1 coal:biomass reduced CO2 by 50%
• UNDERGROUND GASIFICATION
• CO-GENERATION - use of waste heat
• HYBRIDISATION - coal and solar
• CARBON CAPTURE AND STORAGE OR USE - unlikely?
CONCLUSION
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COAL HAS A SIGNFICANT ROLE TO PLAY IN THE PRODUCTION OF ENERGY IN DEVELOPING COUNTRIES, NOT LEAST OF WHICH IS IN SOUTHERN AFRICA.
THIS CAN BE ACHIEVED PROVIDED THAT THE LOW GRADE COAL QUALITIES ARE UNDERSTOOD AND MOST SUITABLE TECHNOLOGY IS DESIGNED TO USE THEM
THANK YOU!
ACKNOWLEDGEMENTS
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• The author wishes to acknowledge the contributions made by associated colleagues in the research reviewed above: – Dr Pasi Vainikka – VTT, Finland – Dr Samson Bada – University of the Witwatersrand (Wits), Johannesburg – Mr Rets Taole – PhD candidate, Wits Johannesburg – Mr Mike Andrews – MS Consulting, Johannesburg – Mr David Brooks – Babcock Engineering, South Africa
• This research was undertaken under the auspices of the SARChI Chair of Clean Coal Technology funded by the National Foundation for Research (NRF) of South Africa.
Coal and Carbon Technology Research Group, University of the Witwatersrand,
Johannesburg, South Africa [email protected]
