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Rosemary Falcon 2012
OVERVIEW OF COAL RESOURCES OF SOUTHERN AFRICAAND 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-OIB JULY 2015
IEA.CCC 2015
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. Experiences of low grade coal combustion in South Africa and Botswana
4. Solutions - Approaches towards cleaner coal usage
FOSSIL FUEL DISTRIBUTION IN AFRICA
3
COAL GAS OIL
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. Experiences of low grade coal combustion in South Africa and Botswana
4. Solutions - Approaches towards cleaner coal usage
KAROO BASINS IN SOUTH-CENTRAL AFRICA (AFTER CATUNEANU ET AL., 2005).
IEA.CCC 2015 5
CRUSTAL STRUCTURE OF SOUTHERN AFRICA
Granitic stable Cratons(islands of granite)
With
Inter-cratonic mobile belts (subsided areas where deposition takes place and coalfields form)
Simplified Structural Framework of Southern Africa (with cover rocks removed) showing the ancient cratons and surrounding metamorphic
provinces
Cross-sections through the Coal-bearing Basins and the Kaapvaal Craton in South Africa during Permian
8
ZIMBABWE CRATON
Coal forming environments occurring in Paralic and Limnic environments
PERMIAN
KAROO SEA
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
EUROPEAN-USA COAL - formed in Equatorial conditions in Carboniferous times (300-350 Million years ago)
CLIMATE CHANGES OVER THE PERIOD THAT THE COALFIELS WERE FORMING
HOT STEAMY EQUATORIAL SWAMPS IN THE NORTHERN HEMISPHERE DURING COAL FORMING
TIMES (Carboniferous)
S. HEMISPHERE – GONDWANA COAL- formed in cold to cool temperate conditions in Permian times (280-300 Million years ago)
ECCA - RECONSTRUCTION OF NO 1 AND EARLY NO 2 SEAM CONDITIONS -
Major floral vegetation changes Reflecting major climatic events during Karoo times
NB: Note coal Seam occurrences during floral changes
IEA.CCC 2015 15
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
COALFIELDS OF SOUTH AFRICA
16
N
INDIAN OCEAN
ZIMBABWE
BOTSWANA
LESOTHO
SWAZILAND
MO
ZAM
BIQ
UE
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 PRO VINCE
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 State10) 11) South Rand12) 13) 14) 15) 16) 17) 18) Somkele19) Molteno -Indwe
Waterberg
Soutpansberg)
Soutpansberg)
Soutpansberg)
WitbankKangwane
Vereeniging - Sasolburg
HighveldErmeloKlip RiverUtrechtVryheidNongoma
15
Coal reserves1982 - 55 BT est (Petrick)2000s - 30 BT est (Prevost)
CENTRAL BASIN - 80% - Bitum CWitbank, Highveld, ErmeloThermal, petrochemical, export, industry
KWA-ZULU NATAL - 1% - Bitum C-Anth ACoking, anthracite, lean Bit A,
LIMPOPO – 15% - Bitum D-Bitum ASoft coking, pci, thermal, export
FREE STATE – 4,% - Bitum DThermal
KAROO SEA DURING ECCA COAL-FORMING TIMES
N
DISTRIBUTION OF THE COAL SEAMS IN THE MAIN KAROO BASIN
The major coal seams in the Witbank and Highveld Coalfields and their typical sedimentary
environments of formation Seams
5
43
21
20
MAJOR SEAMS ACROSS THE KAROO BASIN, SOUTH AFRICAKWAZULU-NATAL , ERMELO, WITBANK TO FREE STATE
Different sequences of seams in each area
Number ID Number ID Letter ID Named ID
Chrono -stratigraphic Correlation of Coal seams between Witbank and the Waterberg
“Bar-Code” Coals above
Normal “Witbank0li
ke seams below
WATERBERG COAL
SEQUENCE
WITBANK COAL
SEQUENCE
WATERBURG SEQUENCE
COAL SEAMS WITH VITRITE PROFILE (V)
NB: low vitrinite proportions in lower seams and high
proportions in upper zones
Vitrites
SEAMS VITRITE PROFILE
Clay-rich carbonaceous shales
UTILISATION OF THE DIFFERENT COAL “BANDS” OR “ZONES”
Source: Kumba/Exxaro
South Africa’s Coal Chain 2014
Run-of-MineProduction
333.6Mt
“Washing”
Screening
Discards74.8 Mt
209.4 Mt
124.2 Mt
Stocks
Synfuels42.9 Mt
Electricity128.2 Mt
Local Use 25.9 Mt
Exports78.7 Mt
11.9 Mt
24
93.2 Mt5.0Mt 31.0 Mt
35.0 Mt11.9 Mt69.8 Mt
Prevost 2015
SOUTH AFRICA’S COAL RESOURCES
IEA.CCC 2015 25
• The new estimate of approximately 60 billion tonnes run-of-mine (ROM) compares with the previous estimate of 55.3-billion tonnes in 1987 (SACRM).
• ROM refers to raw coal potentially available for delivery to coal preparation facilities or for stockpiling after it has been mined.
• The increase in reserves is despite the fact that 7.5-billion tonnes of coal have been mined during the 24-year period between the two estimates.
• The increase is attributed to increased reserve and resource estimates for the Waterberg, Tuli and Soutpansberg coalfields following more extensive exploration work.
MID ZAMBEZI COAL FIELDS - WEST ZIMBABWE
Dark orange – Jurassic-Cretaceous sedimentsGreen - Batoka BasaltsPale Orange - Upper KarooGrey – Lower Karoo (coal)RED – Basement
Hwange
Lubimbi
Lusulu
Busi
Sengwe
Yellow – Kalahari sand
Barber 2015
TOTAL RESOURCES
WESTERN COALFIELDSMilibisi, Matabolo, Gwembe
EASTERN COALFIELDBubye (only)
10,1 BT + Sengwe field 0,4 Bt
TOTAL 10,5 BT
IEA.CCC 2015 27
MID ZAMBEZI COAL RESOURCES
Barber 2015
COAL QUALITIES WESTERN COALFIELDS
MILIBISI (Hwange)
MATABOLO(Lubimbi)
GWEMBE
Vols %ad 15-32 21-54 21
Ash %ad 15-29 16-34 22
CV MJ/kg 23-29 22-25 23
Swell 0 - 8 0-2,5 0
Rank RoM% 0,5 - 0,79 0,4 – 0,8 0,5 – 0,6
Mozambique
IEA.CCC 2015 28
TOTAL RESOURCES
9,5 BT in 2009
BENGA HARD COKING COAL
Vols %ad 21.8 Weightedaveragesacross targeted seams
Ash %ad 10.5
Vitrinite% 81
Rank Rom%
1,4
Swell 8,5
BENGA EXPORT THERMAL coal
Vols %ad 20
Ash %ad 22 Target ash, may vary
I.H20 %ad 0,8
CV MJ/kg 26,7
MOZAMBIQUE COALFIELDS
Vasconcelos 2009
MUCANHA-VÚZI AREASeveral borehole programs: thickness of the Karoo sequence in the Chicôa-Mecúcoè area, especially in Mucanha-Vúzi sub-basin varies a lot
Cross sections: half-graben structureevident,
Seams dipping southwards.
Dip of the strata increase to the south.
Deepening of the basin to the west, as a consequence of the complicated faulting affecting this basin.
S N
W
SW
E
NE
KAROO IN TETE
Vasconcelos 2009
MOZAMBIQUE COALFIELDS
NE-SW orientation
Two main faults divide the basin into 3 blocks:
Profiles 1 and 2: perfect graben structure
Profile 3: half-graben structure
Central and Northern blocks: Ecca Formation is very deep
Rio Moola Fault
Rio Txiune Fault
METANGULA BASIN (Niassa)
Vasconcelos 2009
MOZAMBIQUE COALFIELDS
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)
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. Experiences of low grade coal in combustion in Southern Africa
4. Solutions - Approaches towards cleaner coal usage
Coal A Coal BGross Calorific Value MJ/kg ad : 28,70 28,93
Proximate Analyses %ad :Inherent Moisture 3,7 2,4Volatile Matter %ad 30,5 28,9Ash Content %ad 11,1 12,2Fixed carbon 54,7 56,5
Combustion efficiency 83,0 66,0C in ash% 4,4 15,5
1. SPECIFICATIONS OF TWO COALS
NB: THE SAME PROXIMATE ANALYSES BUT DIFFERENT COMBUSTION PROPERTIES
Coal A Coal BGross Calorific Value MJ/kg ad : 28,70 28,93
Proximate Analyses %ad :Inherent Moisture 3,7 2,4Volatile Matter %ad 30,5 28,9Ash Content %ad 11,1 12,2Fixed carbon 54,7 56,5
Combustion efficiency 83,0 66,0C 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
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 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
35IEA.CCC 2015
and 35-65%
QUALITY OF COAL - ASH CONTENT Should definition change for future high ash reserves?
Boundaries based upon the International Classification of Seam Coal : UN-ECE 1993
COAL:Definition to increase to 65% or 70% ash?
ROCK?
36IEA.CCC 2015
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)
37
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
IEA.CCC 2015
CLASSIFICATION AND CATEGORISATION OF COALS
USING RANK AND REACTIVE/INERT ORGANIC
MATERIALS
DEGREES OF INCREASING DIFFICULTY IN IGNITION AND COMBUSTION
ALEADING TO HIGHER COMBUSTION TEMPERATURES
X - USA and European Carboniferous coals
Witbank-Highveld coals
KWZ Natal coals
Reactive –Vitrinite)
Inert (Inertinite)
Variations in Organic Composition of
Coals from different Regions x x
xx x
x
x xxx x
x
38IEA.CCC 2015
3. QUALITY OF COAL - ORGANIC MATTER
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
40
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
IRREGULAREFFICIENCY
IEA.CCC 2015
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
water
steam
coal
dust collectors
stack
FLUIDISEDBED COMBUSTION
FLUIDISEDBED
COMBUSTION
combustion air
limestone
8500C
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)
INDUSTRIAL WATERTUBE BOILERS AND SPREADER STOKERS
SA Coal Fired Spreader stokers are experiencing:-
• Poor ignition of coal fines when air-born• Delayed combustion • High level freeboard fire-ball• Extreme slagging and fouling • High percentage of fines carryover• High back- end temperatures• High grate temperatures and damages • Fusing and erosion of refractory linings
43IEA.CCC 2015
EFFECT OF USING INCREASING PROPORTIONS OF 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
ChinaUSA
RussiaIndia
JapanGermany
CanadaUK
IranKorea
ItalyMexico
AustraliaSaudi Arabia
IndonesiaFrance
BrazilSouth Africa
SpainUkraine
Million tons CO2
SOUTH AFRICA PLANS TO INTRODUCE CARBON TAX IN
2016 – 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, 200845IEA.CCC 2015
CHALLENGE: CARBON TAX AND CARBON CAPTURE AND STORAGE
IEA.CCC 2015 46
Ø SOUTH AFRICA PLANS TO INTRODUCE CARBON TAX IN 2016 –DESPITE THE VERY HIGH RELATIVE COSTS OF THE ABATEMENT.
Ø 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.
Ø THIS WILL ERADICATE MANY MAJOR INDUSTRIES AND POTENTIAL INDSUTRIAL DEVELOPMENTS IN THE COUNTRY
CONTENTS
1. Introduction
2. Coal resources in Southern Africa
3. Experiences of low grade coal combustion in South Africa and Botswana
4. Solutions - Approaches towards cleaner coal usage
EMISSIONS REDUCTION PROGRAMME THROUGH INCREASED EFFICIENCY OF POWER PLANT – SOUTH AFRICAN SCENARIO
48Source 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
IEA.CCC 2015
MINERAL MATTER ORGANIC MATTER
Inorganic matter behaviour MINERALS MACERALS Organic Matter BehaviourViscosity DevolatilisationAgglomeration IgnitionAsh Formation Char formation
Peak TemperatureBurnout
Affects the Boiler : Affects the Boiler :Ash deposition Flame stabilitySlagging, Clinkering, Fouling Heat outputErosion Heat transfer zonesPrecipitability Rate of coal consumptionAsh Handling Carbon-in-ashParticulate emissions Gaseous emissions
ASH CHAR
COST EFFICIENCYProcess EfficiencyPlant availability
Plant capacity
UNDERSTAND THE ROLE OF COAL QUALITY ON PERFORMANCE
MINIMISE THE ADVERSE EFFECTS OF LOW GRADE COAL QUALITIES IDENTIFY ISSUES THEN IDENTIFY KEY IMPACT FACTORS
AND METHOD PURPOSE TOPICS TO RESEARCHMaximise combustion efficiency in current subcritical boilers by matching coal qualities to boiler specifications and operating efficiently
•To minimise fuel consumption•To reduce CO2 emissions
R&D required in Southern Africa• Coal Characterisation• Coal Beneficiation to upgrade• Combustion optimisation/ adapt’n
Maximise higher efficiency in future plant using supercritical, ultra supercritical and FBC technology
• To reduce SOx•To reduce CO2 emissions•To reduce NOx• To use sized low grade coal
R&D required for low grade•FBC, CFBC + FGD• PF Supercritical/ultra-sc +FGD+CCS• IGCC +CCS
Minimise SOx and Hg by increased beneficiation and by using flue gas desulphurisation (FGD)
•To minimise pollution SOx capture technology is mature •FGD• Minimise S/Hg, forms pre/post use
Minimise NOx using Low NOx burners and selective catalytic reduction (SCR)
To minimise pollution NOx burner technology is mature• Understand source of NOx in SA• Reduce impact of C inefficiency
Reduce particulate matter and Trace Elements using bag filters or electrostatic precipitator (ESP)
To minimise pollution PM>2,5 capture is mature; PM<2,5 not• R&D in mineral-ash conversion • Slagging, fouling, fly ash formation• <PM2,5 formation and capture • Trace element distribution
Minimise CO2 using (i) capture and storage technologies (CCS) and (ii) developing areas of utilisation (CCU)
To reduce CO2 • CCS R&D required in SA- underway• Co-firing with biomass: supply?• CCU through algal technology• UCG - reduces mining, produces syngas, for power/CTL, storage CO2 50M
INIM
ISE
CO2
MIN
IMIS
E N
ON
-CO
2 PO
LLU
TAN
TS
INCR
EASE
EFF
ICIE
NCY
IEA.CCC 2015
PROPOSED MEDIUM TO LONGER TERM SOLUTIONS FOR CLEANER COAL-FIRED ENERGY PRODUCTION IN
SOUTHERN AFRICA:
IEA.CCC 2015 51
• CARBON CAPTURE AND STORAGE OR USE (?)
• INCREASED EFFICIENCY IN POWER PRODUCTION - CFBC
• CO-FIRING WITH BIOMASS
• UNDERGROUND GASIFICATION
• CO-GENERATION (use of waste heat)
• HYBRIDISATION (coal and solar)
• RENEWABLE ENERGY SOURCES – SOLAR AND WIND
CONCLUSION
IEA.CCC 2015 52
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
IEA.CCC 2015 53
• 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, School of Chemical and Metallurgical Engineering
University of the Witwatersrand, Johannesburg, South Africa
