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Deep, unused saline-saturated rocks
If CO2 is injected into suitable saline formations at depths below 800m various physical and geochemical trapping mechanisms would prevent it from migrating to the surface.Saline aquifers account for half the known storage capacity - about 1,000bn tonnes of CO2 - though they could ultimately have the capacity to hold as much as 10,000bn tonnes, scientists say
Depleted oil and gas fields
These fields offer significant possibility for storage: in Europe alone there is thought to be the capacity to store 14.5 billion tonnes of CO2 offshore and 13.1 billion tonnes onshore - although environmentalists worry that the multiple bore holes and wells drilled to find and extract oil and gas can increase the leakage risk
Deep unmineable coal seams
A coal bed that is unlikely ever to be mined because it is too deep or too thin may potentially be used to store CO2. Technical feasibility depends on how porous the coal is. If later mined, the stored CO2 would be released
Enhanced coal-bed methane recovery
CO2 can be injected into unmineable coal mines because coal absorbs CO2 if it is sufficiently porous. In the process the coal releases previously absorbed methane, and the methane can then be recovered. The sale of the methane can be used to offset a portion of the cost of the CO2 storage in the early stages of development
Enhanced oil and gas recovery
Declining oil fields can have their economic viability enhanced by the injection of CO2 — which increases oil and gas recovery by between four and 20 percent. The European Commission estimates the enhanced oil recovery storage capacity in the North Sea will range between 200 million and 1.8 billion tonnes of CO2 over the next 25 years, depending on oil and CO2 credit prices and on how much oil is recovered
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SOURCE: BELLONA, CO2 CAPTURE PROJECT, SHELL
Confining layersImpermeable rock layers effectively seal the liquid CO2 and prevent the gas rising to the surface
Groundwater aquiferProtected from potential CO2 leaks by extra layer of steel and cement around injection pipe
After a storage site is full, the prevention of leakage over the long term is critical. The site is capped with a corrosion-resistant cement plug, several meters thick. Long-term monitoring of CO2 leakage will also take place at the surface
Capped oil well
CO2 injection pipeDouble layer steel pipe cemented into 203mm (8in) bore hole
3km
800m
min
imum
A clean waste gas of nitrogen, oxygen and about 10% of the original CO2 flows out into the atmosphere
Waste CO2 gas chilled to 1.7C to speed up the process Chilled CO2 is mixed with ammo-
nium carbonate to produce a clean waste gas and an ammonium barcarbonate slurry
Slurry heated and pumped through a regenerator, where the CO2 is liberated leaving the ammonium carbonate to be reused
The 90% of captured CO2 is pressurised ready for storage. Compression liquefies the gas — and at depth this is intensified, making the CO2 stay liquid
Slurry
Ammonium carbonate
Clean gas
Carbon capture and storage (CCS)
Transporting CO2 from source to storage site can be carried out through pipelines, ships, rail or by road, but low cost and proximity to water make pipelines the most likely option
Pre-combustionIn this process, the fossil fuel is gasified, rather than combusted. This converts the fuel into a mixture of hydrogen and carbon monoxide, also known as synthesis gas, or syngas. Reacting the syngas to steam turns the carbon monoxide into CO2. It can then be separated from the hydrogen gas, creating streams of pure CO2 and pure hydrogen. 90% of CO2 can be removed with this technology, which can only be used in an integrated coal gasification combined cycle power station
OxyfuelHere the fossil fuel is burned, but in 95% pure oxygen instead of air, resulting in a flue gas with high CO2 concentrations, which can be condensed and compressed for transport and storage. Up to 100% of CO2 can be captured in this way, but to date it has only been demonstrated on a laboratory and pilot scale. Much research is needed to develop membranes to efficiently separate oxygen from air
Power stations produce electricity by burning gas or coal, releasing large amounts of CO2 into the atmosphere. Coal-fired power stations are the biggest offenders and also the main source of power for fast-growing China and India. China is completing or opening two 500MW coalfired power plants every week. While cars, aircraft and buildings are also major contributors to global warming, the fact that power stations produce large volumes of CO2 in a single location makes them an ideal collection point. CCS can also be fitted to other industrial processes that produce large quantities of CO2, such as the cement industry
Towns and cities require vast amounts of electricity. Power stations burning fossil fuels are responsible for nearly half of all CO2 emissions. If transport systems in cities are to switch from oil to electric and hydrogen-powered vehicle, the demand for electricity will become much greater
CO2 released into the atmosphere is the main contributor to global warming. In pre-industrial times atmospheric CO2 was about 280 parts per million. It is now 387 ppm and rising fast. The world is on course to hit 450 ppm some time after 2030.
The Intergovernmental Panel on Climate Change is urging a 50%-80% cut in CO2 emissions by 2050. It says carbon capture and storage could make a large contribution
Energy needs CO2 production and capture
Capture options
CO2 in the atmosphere
CO2 storage optionsCO2 transportation Possible cost recovery options
550 ppm
500 ppm
450 ppm — risk of dangerous climate change
400 ppm
350 ppm
300 ppm
1960 70 80 90 2000 10 20 30 40 50 60 70
Rise in atmospheric CO2, parts per million
Best case impact of CCS — saves over 50ppm by 2070
CCS combined with large increases in renewables, nuclear and efficiency
Projected continuing rise in CO2
Diffusion
Circulation
Fossil fuelcombustion and industrial processes
Re-vegetation
Vegetation
Ocean surface
Respiration
Photosynthesis
Decomposition
Deforestation and land use change
Atmosphere
Fossil fuels
Sedimentary rocks
Sediments
Deep ocean
Soils
Carbon fluxes
Carbon stored
SedimentationCO2 geologicalStorage
CO2 geologicalStorage
Oceanstorage
Oil
Goes to domestic supply
Electricity generation
Petrochemical plants
Cement/steel/refineries etc
Gas
Natural gaswith CO2 capture
Mineral carbonation
Industrial uses
Coal
Futurehydrogen use
Biomass
CO2CO2 capturesites
Oil or gasrecovery
Methanerecovery
CO2injection site
Saline-saturated rock
CO2compression site
How pre-combustion capture worksHow post-combustion capture works
CO2
Energy
Exhaust gaswith CO2
Cleanedexhaust gas
Cooling
CoolingHeatexchanger
HeatingFossil fueland air
Scrubbercolumn
Absorbent
Water
Regeneration
Storage
Steam reforming
Power plant
Absorbent
Air
Energy
Absorbant
Fossil fuel
Steam
Water
Hydrogen
Nitrogen
Scrubbercolumn
CO2
RegenerationCO2 plusAbsorbent
CO2 plusHydrogen
Storage
Depth of storageStorage must be at a minimum depth of 800m but could be 3km or more. Pressure at 800m is enough to keep CO2 in a heavy liquid state, reducing the risk of it migrating through fissures to the surface
CO2 and water
WaterCondensation
Powerplant
Air separationunit
EnergyOxygen
Nitrogen
Air
Fossil fuel
Storage
CO2
How capture using oxyfuel combustion works
The carbon cycle
2. Infrared radiation is given off by earth...
3. Most escapes back into spaceallowing the earth to cool
4. But some infrared radiation is trapped by gases in the air (esp CO2), thus reducing the cooling
The greenhouse effectCo2 in its natural state Co2 in its challenging state Co2 in its safe state?Carbon network
Oil field
Oil field
Coal seam
Coal seam
1. Sunlight passes through the atmosphere and warms the earth
5. Increasing levels of CO2 increasesthe amount of heatretained, causing the amosphere and the earth’s surface to heat up
CCS allows 80% to 90% of CO2 to be captured
SOURCE: CO2CRC SOURCE: CO2CRC SOURCE: CO2CRC
Carbon capture can be achieved in three ways. Here is how one post-combustion technology being developed will work
Post-combustionThe tried and tested way of removing pollutants, such as sulfar dioxide, from a power plant is by removing them from the flue gas after the fossil fuel has been burnt to generate electricity. In CCS, the CO2 is separated out, cooled, dried and compressed for transport. 80-90% of the CO2 from a power plant can typically be removed in this way, although a plant fitted with the technology does require between 10% and 40% more energy than a conventional plant. The great advantage is that post-combustion technology can be bolted on to an existing power plant
in association with