Background
What is CCS?
Carbon dioxide capture and storage (CCS) — also known as "geosequestration" — is a process whereby CO2 is captured from large point sources, compressed, transported and injected into deep (below 800m) geological formations for permanent storage.
The specific steps involved in CCS include:
- Capture of the CO2 from large single point sources, such as electricity plants that rely on thermal fuel, petroleum, gas and various other energy and industrial processes. The CO2 can be captured in various ways. The three main options are:
i) post combustion capture (after the fuel has been burned, as in a typical thermal electricity plant);
ii) pre-combustion capture, in which the fuel source is oxidised to produce syngas which can then be used in a variety of processes; and
iii) oxyfuel combustion, in which thermal fuel is burned in pure oxygen (rather than air), resulting in an emission stream of virtually pure CO2 and water vapour.
- Transportation of CO2 from source to storage site. Through pipelines or by ship.
- Injection through drilled wells into carefully selected geological formations. Stringent criteria will need to be set for assessing whether a geological formation is suitable for long-term storage of CO2. A selection of issues for assessment will include whether the site is onshore or offshore; what "capping" layers exist above the injection formation; the porosity and depth of the formation; seismicity of the area; whether the area has been subjected to intensive exploration and drilling.
- Ongoing, long-term storage of CO2 in the geological formations into which it has been injected. Examples of geological formations that could be considered for assessment for storage potential include:
o Depleted Oil and Gas Reservoirs
o Un-mineable coal seams; and
o Deep Saline Aquifers
Why do CCS?
CCS is considered to be a crucial technological addition to the protfolio of climate change mitigation options. The IEA estimates that CCS could contribute up to 28% of global CO2 emissions reductions by 2050.
Current Applications:
CCS is a system that could be added to most large point sources of carbon emissions, most often characterised by existing thermal plants, to reduce their current CO2 emissions. New plants could be designed from inception to deploy CCS.
Other Considerations:
The individual technologies involved in the CCS process are not new, but, as yet, they have not been demonstrated together as a complete chain at a commercial scale. In particular, it is not possible at this early stage in CCS deployment to "prove" that CO2 will behave as predicted in the sites in which it is stored. Moreover, CCS technology is very expensive.
As CCS projects are technically complex and will likely cover large areas (either directly or indirectly) it is important that health and safety considerations and environmental consideration are addressed.
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