Carbon Dioxide Capture at Coal Power Stations
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CAPTURE OF CO2AT
COAL POWER STATIONS
THIRUSHKA T. GOVENDER
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REDUCING
CO2EMISSIONS
OPERATE POWERPLANTS AT THEBEST EFFICIENCY
INVEST INCLEAN COAL
TECHNOLOGIES THAT
IMPROVE THELEVEL OFEFFICIENCY INCOAL-FIREDPOWERPLANTS SUCH
CARBONCAPTURE ANDSTORAGE(CCS)
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Process based on capturing CO2 and storing insuch a way that it does not enter theatmosphere
3 different carbon-capture strategies are beinginvestigated today :o Post-combustion captureo Pre-combustion Captureo
Oxy-fuel combustion
CARBON CAPTURE ANDSTORAGE
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POST COMBUSTIONCAPTURE
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PRECOMBUSTION CAPTURE
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Combustion of Coal takes place inpure Oxygen
Therefore the flue gas is mainlycomprised of CO2 and watervapour (which may be cooled and
condensed to remove the water )so there is no separation problem
Such plants require oxygen
OXY FUEL COMBUSTION
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Separation & recoverymethods
Features
Absorptionmethod
Chemicalabsorption
Chemical reaction using a CO2
absorbentLarge amount of energy required
Physicalabsorption
Absorbent used to physicallyremove CO2CO2 released by depressurization
Membraneseparation
Polymermembrane
Differences between gas speedsof transmission through
membrane
Liquidmembrane
Membrane holding a carriersubstance that selectivelytransmits CO2
Inorganic Transmission through a porous
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Conventional to use scrubbers to removeCO2 from exhaust gas which energyintensive & expensive
Challenge lies in developing a method thatcan be inexpensively and easily retrofittedinto existing power plants.
Following new technology is beingresearched: Zeolite Crystals Nanotechnology Membranes Bio CCS Algal Synthesis
New Methods of CO2Capture
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Omar Yaghi,a chemist at UCLA combinedorganic molecules and metal atoms to formhighly porous crystals
Structure resembles industrial
materials called zeolites
1 litre of UCLA crystals stores up to 80l ofCO2
They're made of metal atoms bridged by one
CRYSTALS TO CAPTURECO2
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New type of membrane internationallypatented by researchers at the NorwegianUniversity of Science & Technology in
Trondheim
Membrane made of plastic material ,
structured by means of nanotechnology
Catches CO2 while other waste gasesallowed to pass freely
Membranes based on nano-structuredmaterials are eco-friendl and will reduce the
NanotechnologyMembrane
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CO2 and other gases in exhaust gas streamis injected into membranes containing wastewater and select strains of algae
The algae ,together with sunlight/UV-lightconvert that CO2 and use it to reproduce toform an oil rich biomass that doubles inmass every 24hrs
AdvantagesTechnology is entirely retrofittable to existing
plants ,regardless of the composition of the
exhaust gas stream
Bio CCS Algal Synthesis
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If Carbon Capture is to be implemented- suitablemeans of storing the resultant gas must be found
The sequestered CO2 must remain isolatedindefinitely if the capture and storage strategy isto be effective
Therefore all sequestration sites must be
monitored closely for decades or longer
CARBON STORAGE
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FOUR STAGES OF CCS
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Depth > 800m
Impermeable Cap Rock
Porous Rock (not Cavern)
Long term mineralisation
STORAGECHARACTERISTICS
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Technology for CCS not currently practised inSA
South Africa emits over 400 million tonnes ofCO2 annually of which ~60% arecapturable and therefore potentiallyavailable for CCS
South African CCS center (SACCSC)established in 2009 directed by TonySurridge
CCS IN SOUTH AFRICA
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CCS TIME SCALE IN SA
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CO2 EMISSIONS IN SOUTHAFRICA
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ATLAS ON GEOGRAPHICALSTORAGE OF CO2 IN SA
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Potential Storage (excluding Karoo) 150 Gt 98% offshore
Need 4 Gt to Store 40 Mt/yearFurther investigation :
Karoo under further investigation Zululand basin (UK Govt end Mar2011) Onshore Outinequa Basin (europe Aid start Feb
2011)
ATLAS SUMMARY
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Major problem is gas leakages
Cost of sequestration process is quite high at
the moment
Excessive use of this method slows down
search for cleaner sources of energy
DISADVANTAGES OF CCS
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QUESTIONS ????
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