Carbon dioxide capture, transport and storage technologies
Posted May 23, 2008on:
Carbon dioxide capture and storage (CCS) in geological formations is a potentially important climate change mitigation measure in the coming decades, as geological formations can store large amounts of CO2 (as well as other gases or liquids) for thousands of years. However, CCS has not been widely used to date. The largest CO2 storage project to date (at the Sleipner field in the North Sea) has been injecting approximately 1 million tonnes of CO2 per year since 1996 into a saline formation.
CO2 emissions are produced from a wide variety of combustion-related and industrial processes sources.CO2 emissions from large point sources, such as power plants, refineries or cement plants, could be captured, transported and stored in several different ways.The technologies used within each step of the carbon dioxide capture and storage chain are at different stages of development. Some are mature/widely applied; some are economically feasible in some conditions, while other technologies are at the demonstration phase. Geological CCS projects (developed as CDM projects, or not) could involve different combinations of capture, transportation and storage technologies. In turn, this could lead to a wide range of potential CDM project types.
CO2 capture already occurs in some energy and industrial activities. For example, CO2 separation routinely occurs in industries where CO2 is required as an input to a manufacturing process (e.g. production of urea). CO2 must be stripped from natural gas during exploitation of fields with significant CO2 content. CO2 is also extracted in refineries, ammonia plants and hydrogen plants.
“Pre-combustion” separation of CO2 can occur during the partial combustion of fossil fuels, used for example in the production of hydrogen or hydrogen-rich fuels. Electricity generation from Integrated Gasification Combined Cycle (IGCC) plants also requires pre-combustion separation of CO2.
“Postcombustion” CO2 capture from flue gases is also possible, e.g. via absorption or flue gas treatment (IPCC 2005). This can be used to capture CO2 from electricity generation plants (and indeed is the only option for CO2 capture from existing power plants), although it is energy-intensive and so entails an energy penalty. Oxyfuel combustion refers to a technology under development whereby fuel is combusted in oxygen and re-circulated flue gas, rather than air (which is mainly made up of nitrogen). The exhaust gases from oxyfuel combustion contains thus mainly CO2 and H2O (water vapour), rather than nitrogen. As the vapour can be easily condensed, the waste gas is largely CO2.
Transport of CO2 can be done by pipeline or ship. Commercial-scale transport of CO2 via pipeline and ship/tankers already occurs (IPCC 2005). Pipeline transport is normally of compressed (gaseous) CO2, whereas transport on ships is often of liquefied CO2, as this takes less volume. Liquefaction of gases is routinely used, e.g. for the transport of liquefied petroleum gas (LPG) or liquefied natural gas (LNG).
There are also different ways in which CO2 can be stored. These include various underground geological formations such as oil and gas fields (in use or abandoned), saline formations or coal seams (mineable or unmineable). Experience with storing CO2 in these types of formations varies. For example, the largest CO2 storage project to date (at the Sleipner field in the North Sea) has been injecting approximately 1 million tons of CO2 per year since 1996 into a saline formation. Other demonstrations, pilot or commercial projects, exist to inject CO2 into depleted gas fields and coal mines.
CO2 is being re-injected into various oil fields to increase the rate and amount of oil produced. Such enhanced oil recovery (EOR) can also use other fluids for the same purpose, notably water and steam.
Globally, CO2-based EOR projects inject around 40 million tonnes of CO2 per year – of which 30 million come from natural underground sources of CO2 and about 10 million tonnes is captured from industrial plants. The use of CO2 for EOR can provide a valuable near-term opportunity for gaining storage experience, but this needs to be done at the right time in the life of a particular field. Enhanced gas recovery and enhanced coal bed methane recovery are in development phase.