South African Coal Quality for Independent Power Producers · 2016-04-05 · South African Coal...
Transcript of South African Coal Quality for Independent Power Producers · 2016-04-05 · South African Coal...
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South African Coal Quality for
Independent Power Producers
Johan de Korte
CSIR
South African Coal Quality for
Independent Power Producers
& Lesley Jeffrey
SRK Consulting
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Overview • Coal Baseload Independent Power Producers
Programme (CBIPPP)
• Generation technologies for coal IPPs
• Pulverised fuel
• Fluidised bed
• Coal qualities
• Coal sources
• Location & logistics
• Dumps & slurry ponds
• By-products
• Important points
• Conclusion
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CBIPPP
• 2500 MW
• 600 MW maximum capacity per station
• May have multiple smaller units
• Pulverised coal/fuel (PF)
• Fluidised Bed (FB)
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Generation technologies for
IPPs
• Pulverised fuel/coal
• most common technology (Eskom)
• smaller range of coal qualities
• Fluidised bed
• lower grade coal
• co-fire with other “waste” fuels
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Pulverised fuel 1 • Fuel preparation - coal pulverised <75 μm
• Operate close to atmospheric pressure
• 1300 – 17000C
• 50 – 1300 MW units, mostly 300 – 700 MW
• Two types:
• subcritical (drum-type water tube boiler)
• super/ultra-critical (once-through Benson
boiler)
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Pulverised fuel 2
• Lower ash, higher CV coal
• Fuel impurities have greater impact on
combustion efficiencies
• External de-sulphurisation
• need to retrofit most RSA plants – cost &
engineering implications for older stations
• Economic in RSA at 600MW?
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Grootvlei PF plant
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Fluidised bed 1 • Operate at lower temperatures than PF
• No fuel preparation required – fuel sits on a bed
with long residence time in combustion chamber
• Use lower quality coal (higher ash, lower CV,
higher TS)
• But - need higher volumes with lower qualities to
generate same heat value
• Opportunity for declining quality of mined raw coal
• Particle size depends on plant type & fuel grade
• Two types:
• bubbling (older technology)
• circulating (newer technology, higher efficiency)
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Fluidised bed 2 • Up to 600 MW, mostly 20 – 350 MW
• Smaller subcritical units have similar efficiencies to larger super/ultra-critical units
• In-furnace de-sulphurisation
• local air quality restrictions on sulphur emissions
• limestone (CaCO3) or lime (CaO) with high calcium + magnesium content as sorbent
• typically require CaCO3 content > 80%
• opportunity for limestone mines
• main limestone deposits in Western Cape, Northern Cape and North-West
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Leipa, Germany circulating
FB plant
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Province District / City / Town
Western Cape Vredendal, Piketberg-Saldanha-Riebeeck
West, Bredasdorp-Heidelberg- Robertson
Northern Cape Danielskuil-Lime Acres-Christiana-Taung,
Richtersveld
North West Lichtenburg-Zeerust-Mafikeng
KwaZulu-Natal Marble Delta
Mpumalanga Marble Hall, Groblersdal
Eastern Cape Port Elizabeth-East London
Free State Kroonstad, Welkom, Warden
Limpopo Mokopane, Thabazimbi
Gauteng Pretoria-Lyttleton-Meyerton-Mooiplaas,
Vereeniging
DME Report R49/2005. Dolomite and Limestone in South Africa: Supply and demand 2005
Location of limestone
deposits
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Coal quality comparison
Quality PF (Eskom) FB
CV 20 – 21 MJ/kg ~10 MJ/kg
Volatile Matter > 20% > ~10%
Ash < 30% < ~60%
Total Moisture < 11% Preferably low –
affects heat balance
AFT > 13000C Not critical
Nitrogen < 1% Low
Sulphur 0.7 – 2.0% < ~2.5%
Size ~50 mm with
maximum 30% <3 mm
< 20 mm
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FB fuels
• FB can burn almost any fuel - provided PS designed for that particular fuel
• Lower quality coals
• Reduced need to beneficiate RoM coal
• Reprocess discard dumps
• need to destone/beneficiate
• Co-fire with biomass, municipal waste
• Environmental advantage - reduce existing discard dumps & municipal waste dumps
• Higher sulphur coals than PF, lower S emissions
• Coal resources need to be properly characterised
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Coal sources for FB
• Coal volumes
• 100 MW: 360 – 400 ktpa (8 Mt for 20 years)
• 500 MW: 1.8 – 2 Mtpa (~40 Mt for 20 years)
• Previously unsuitable coal resources
• lower quality deposits
• smaller deposits
• discard coal ( ~60 Mtpa in RSA; accumulated total ~1 Bt)
• mostly bituminous, little anthracitic
• size 100 mm - 100 μm
• fine/ultrafine material in slurry ponds (±5% of RSA RoM; no current market)
• Biomass
• Municipal waste
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Possible discard sources
Discard dumps Slurry ponds
Fine coal stockpiles
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Dumps & slurry ponds 1
• Need to be drilled and sampled across the entire body, not just at the surface or along the edges
• Auger drill in grid pattern to base
• Wet slurry ponds unstable – specialized drilling required
• Quality segregation in slurry ponds due to differential settling of particles
• Dump shelf life – too weathered to use
• Impact of weathering on coal qualities
• lower volatiles (VM almost gone in ~15 years)
• higher inherent moisture
• friable – lots of fines
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Dumps & slurry ponds 2
• Dump qualities more variable due to production of different primary products over time
• Dumps that have already been reprocessed for Eskom may still be suitable for FB
• Model & estimate resources & qualities
• Dump reclamation affected by disposal methods – e.g. compacted newer discard over old burning discard; slurry within compacted discard “dam”; slurry over un-compacted discard, slurry in prepared opencast voids
• Reworking existing dumps may be uneconomic due to low yields
• Can potentially employ dry processing technologies to reduce capex and opex
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Somewhere in Europe …..
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Discard qualities in 1990
In the words of Prof Philip Lloyd,
“It isn’t called discard coal for nothing”
Source: Lloyd, PJ; 2000; The potential of coal wastes in South Africa”, Journ. SAIMM, p.69 - 72
40%
30%
20%
10%
0%
<15
Per cent volatiles
Per cent discard in given category
15-24.9 25+
<40% ash
40-49.9
50+% ash
30%
25%
20%
15%
10%
5%
0%
<15
Percent fixed carbon
Per cent discard in given category
15-29.9 30+
<40% ash
40-49.9
50+% ash
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2001 discard/duff inventory
• This data > 15 years old!!
• Most discards in small dumps (<5 Mt)
• Dumps covered > 4 000 ha
• Most from defunct collieries
• Most slurry from active collieries
• Most active dumps ~15 years old
• Most defunct dumps ~ 50 years old
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Discard facility status 2001
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Approximate discard
qualities 2001
Quality Dumps Slurry
CV Mostly 10 – 15, less
15 - 50 20 - 25
Volatile Matter 16 - 20 17 - 27
Ash 40 - 50 20 - 30
Fixed Carbon 20 - 40 40 - 55
Sulphur 1 – 3 0 - 2
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More recently …
• KZN technical discard study in 2015
• Coal Discard Steering Committee (DMR,
EDTEA, DWS)
• Priority list of dumps suitable for
exploitation
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Location & logistics • Near suitable collieries/discard dumps/slurry
ponds
• Transporting of fine material problematic
• pelletising and briquetting not economically viable in most cases
• conveyor: mix fines & ultra-fines with coarser material to act as a carrier
• slurry pipeline: dewater at PS
• Screen bowls, filter presses
• BALF (Boundary Air Layer Flow – technology under development) – use a pneumatic cyclone to separate H2O to cyclone overflow, dried coal to underflow
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By-products
• Discard – very low grade carbonaceous
material; requires disposal i.e. discard dumps
• Fly ash – cement manufacture
• Bottom ash – brick making
• Dump rehabilitation and removal of slurry
ponds
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Important points
• Sufficient secure coal resources for +20 years may not be available at a single source
• may need to come from multiple sources
• PS close to existing fuel sources
• Transportation issues for fine coal
• Potential challenges with ownership, accessibility, liabilities, permitting
• New dumps subject to new regulations
• Ash and final discards will require disposal
• Gypsum (by-product of sulphur capture) – market or dispose?
• Need many technical skills
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Conclusion
• FB an attractive technology for CBIPPP
• Using lower quality coals can:
• Utilise remnant deposits
• Reduce large discard dumps/slurry ponds
• Requires significant investigative work upfront
• Downstream consequences
• By-products & waste dumps
• Not a Get-Rich-Quick scheme