Carbon Capture Storage: Issues and Debates

What is Carbon Capture and Storage (CCS)?

Carbon Capture and Storage, also known as CCS, is a relatively new method for burning coal in power stations, without releasing carbon dioxide into the atmosphere. The carbon dioxide is effectively captured by various methods detailed below, and is then stored underground in oil and gas fields, saline aquifers, or non-mineable coal seams. There are different ways of carrying out CCS, and there are also issues and debates around the efficiency, safety and costs of CCS. As a result CCS is still in the pilot phase and is yet to be rolled out across all coal power stations in the UK. However, in April 2009 the Government introduced a policy requiring any new fossil fuel power station to be built “carbon capture ready”, so that CCS can be retrofitted at a later date [1].

The technical bit

There are three types of CCS.

Oxyfuel combustion - This involves burning coal in pure oxygen, to produce heat, which produces steam, which turns a turbine to produce energy. Removing air from oxygen requires a lot of energy and so can reduce the efficiency of the power plant. Ash, sulphur and nitrogen are removed when the coal is burned, and carbon dioxide is left. Pressurising carbon dioxide to 70 atmospheres will transform it into a liquid with a similar density as crude oil, making it easier and more efficient to transport it to a long-term storage site [2].
Pre-combustion CCS - An example of pre-combustion is Integrated Gasification Combined Cycle (IGCC). This is (in a nutshell) where coal is sent into a gasifier to react with oxygen and steam. The resulting gas is then pushed through different chemical processes to remove ash, sulphur and finally carbon dioxide. These processes leave a hydrogen gas which is used to power turbines to produce electricity. The excess heat from the chemical reactions is also used to produce steam which again produces more electricity. This greatly improves the efficiency of the power station.
Post-combustion CCS – The UK prefers this method of CCS, primarily because it can be retrofitted to existing power stations, and new stations do not have to be built. It is a very similar system to pre-combustion CCS, removing ash and sulphur, and making use of heat to produce steam. However, once the carbon dioxide is captured, it is pressurised as in oxyfuel combustion, and transported to storage.

What are the main issues and debates surrounding CCS?

CCS is not carbon free. Coal is carbon-heavy in its mining and transport [3]. Coal and the resultant liquefied carbon dioxide may have to travel hundreds of miles to and from the power station. Coal mining tends to release methane, carbon dioxide, and carbon monoxide, both directly from the coal seams as they are exposed, and subsequently from discarded shales and mudstones [4].
Coal is a finite resource, so CCS can never be a sustainable energy supply (even though it is relatively clean). It can only be a temporary solution to cutting carbon emissions.
CCS has the potential to reduce carbon dioxide emissions from power stations by around 90% [1].
Current estimates show that we could store up to 40 years of global carbon dioxide emissions in the world’s known oil and gas fields [5]. Whilst offering a quick fix, their storage is finite, so again CCS is not a sustainable, long term solution to cutting carbon emissions of coal power stations. The life span of new power plants is around 50 years [6]. Therefore, the new power plants being built today, if all were used for carbon capture, would outlive the carbon storage of oil and gas fields.
However, saline aquifers are 100 times bigger than oil and gas fields, which could mean that there is potential to lock away carbon dioxide for at least several centuries [5].
One problem is that while some nations are well-endowed with oil fields or saline aquifers, such as the UK, others have few [5]. This probably indicates why the UK is quite keen to develop CCS technology, as it has the storage facilities readily available.
Experts estimate the average cost of retro-fitting Britain’s aged power stations at about £1bn each [7].

There is the worry that focusing on CCS technology takes interest and finance away from other cleaner ways of generating energy, such as renewable energy technologies like solar power and wind power which will eventually be one of very few ways to power our world once fossil fuels eventually run out.

References

[1] Environment Agency (2010) http://www.environment-agency.gov.uk/static/documents/Research/(13)_CCS_mitigation_Final_May10.pdf

[2] BBC News http://news.bbc.co.uk/1/hi/sci/tech/7586569.stm

[3] BBC News http://news.bbc.co.uk/1/hi/uk_politics/8015676.stm

[4] Mackay, D. (2009) Sustainable Energy without the Hot Air. UIT Cambridge.

[5] BBC News http://news.bbc.co.uk/1/hi/sci/tech/7584162.stm

[6] Greenpeace http://www.greenpeace.org.uk/blog/climate/the-new-coal-rush

[7] The Guardian http://www.guardian.co.uk/environment/2008/sep/05/carboncapturestorage.carbonemissions1