South African Coal Quality for

Independent Power Producers

Johan de Korte

CSIR

South African Coal Quality for

Independent Power Producers

& Lesley Jeffrey

SRK Consulting

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

CBIPPP

• 2500 MW

• 600 MW maximum capacity per station

• May have multiple smaller units

• Pulverised coal/fuel (PF)

• Fluidised Bed (FB)

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

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)

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?

Grootvlei PF plant

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)

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

Leipa, Germany circulating

FB plant

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

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

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

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

Possible discard sources

Discard dumps Slurry ponds

Fine coal stockpiles

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

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

Somewhere in Europe …..

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

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

Discard facility status 2001

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

More recently …

• KZN technical discard study in 2015

• Coal Discard Steering Committee (DMR,

EDTEA, DWS)

• Priority list of dumps suitable for

exploitation

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

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

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

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