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CARBON CAPTURE AND STORAGE.
Introduction.
It is now widely acknowledged that the emission of CO2 from the combustion of fossil
fuels is the major contributor to climate change. One particular option under
consideration as a measure for stabilizing greenhouse gas concentrations is Carbon
Capture and Storage (CCS). This technology would have the potential to reduce
current green house gas emissions while still allowing fossil fuel use. Carbon capture
and storage is a three step process, whereby the CO2 arising from the combustion of
fossil fuel is captured, transported and finally stored in underground geological
formations. It may thus be viewed as a bridging technology to a future when energy
production will be based on renewable sources. Furthermore, it would have the
potential to sustain an existing quality of life by maintaining secure power generation
and simultaneously avoiding dramatic climate change.
The Process of Carbon Capture and Storage.
The main sources of CO2 emissions can be divided into power production, industry,
transport and other sectors which include, commercial, public services, agriculture
and residential. In order for CCS to be effective it needs to be applied to large,
stationary point sources, such as fossil fuelled power plants or large industrial single
point emission processes. The implementation of CCS to smaller industrial CO2
sources is at present expensive and impractical.
The first stage of the process involves the capture of CO2. There are different types of
CO2 capture systems, these include: post combustion, pre-combustion and oxyfuel
combustion. Various factors influence the selection of the capture system - these
include the concentration of CO2 in the gas stream, the pressure of the gas stream and
the fuel type, for instance, whether it is solid or gas. The technology for post
combustion is well understood and used in power plants. Pre-combustion capture is
applied in fertilizer manufacturing. This process is more elaborate and costly, but, the
higher concentrations of CO2 in the gas stream and the higher pressure make the
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separation process easier to achieve. Oxyfuel combustion uses high purity oxygen,
which results in high CO2 concentrations in the gas stream and results in easier
separation of CO2. However, this technology is in the demonstration phase and
requires further development before it can be used at full scale.
The preferred method for transporting large amounts of CO2 over distances of around
1,000 km is by pipeline. For larger distances, transportation by ship is preferable. It is
also possible to have the CO2 transported by road or rail but these options are less
attractive. In most gas pipelines the flow is driven at the upstream end by use of
compressors and in some instances there is a need for intermediate compressor
stations. In cases where the CO2 contains moisture, its removal from the stream would
be necessary to prevent pipeline corrosion and to avoid the cost of building dedicated
pipelines specifically constructed of corrosion resistant material.
The issue of storage has highlighted three types of geological formation that are under
consideration, these include: oil and gas reservoirs, deep saline formations and
unminable coal beds. Storage sites can be in the form of onshore or offshore
sedimentary basins. The storage process would be achieved by injecting CO2 in dense
form into a rock formation below the earth’s surface. Suitability of storage would be
determined in terms of rock formations that are capable of holding liquids. For
instance, consideration would be given to sites where fluids such as natural gas, oil or
brines have previously been retained. It would also be necessary to determine if the
overlying cap rock would provide an effective seal and a geological characterization
would be required to determine this. Coal beds may also be used for storage in
situations where the coal is unlikely to be mined and is of suitable permeability,
however this option requires further consideration.
The process of injection is likely to involve the same technologies that have been used
in the oil and gas exploration and production industry. These would include well
drilling and injection technology, computer simulation of the storage reservoir and
methods of monitoring from existing applications. In relation to storage, consideration
must also be given to the geographical relationship that exists between the source of
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the CO2 and the potential storage site. Ideally the shorter the distance the better in
terms of minimising transport costs. Initial research has shown that globally a small
proportion of large point sources are located close to potential ocean storage.
However, current available literature regarding the matching of sources to storage
sites is limited.
Fig. 1 Illustrates the CCS Process (Source: Frosts Meditations, Carbon Capture and Storage).
The Issues surrounding Carbon Capture and Storage.
There are various issues surrounding the case for using carbon capture and storage as
a method of combating climate change. These include factors such as cost, incentives
for use, environmental impacts, safety and legal concerns along with the issue of
public perception.
In terms of cost, factors for consideration include the type of power station or industry
involved, the cost of other technologies, economies of scale and transport distances. It
is expected that initial costs of deployment will be high but these costs will decrease
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substantially as the technology is proven on a commercial scale. The European Union
(EU) Emissions Trading Scheme (ETS) will provide the main incentive for using
CCS. According to the EU legal framework, CO2 that is captured and safely stored
will be considered as not emitted under the ETS.
The primary environmental concern associated with CO2 is global warming, however,
it is possible that CO2 could be released during transport or injection or over time
from geological storage. Seepage out of geological storage into environments not
adapted to CO2 could have detrimental effects and a greater understanding of the
potential impacts on marine and land environments is required. Other points of
concern include monitoring and long term responsibility for a site, particularly when a
project is complete.
From a safety and legal perspective, the EU has recently adopted draft proposals for a
CCS Directive. This should provide a legislative framework for a full source to sink
CO2 chain which should address issues such as site selection, authorisation,
monitoring plans, stewardship, liability and third party access. In 2007, the London
and OSPAR accords were amended to facilitate under sea geological storage of CO2.
In terms of public perception CCS may not be well known by those outside of the
energy sector. Therefore early success or failure will have an influence on attitudes, as
will levels of concern regarding climate change. It is possible that CCS will appear
more attractive by comparison to nuclear energy. In order for CCS to be positively
accepted then a programme of early and thorough public communication regarding
the risks and the alternatives will be required.
Carbon Capture and Storage from an Irish Perspective.
From an Irish perspective, the geological viability of injection and storage in a
suitable location on or offshore has been identified as the critical factor for the
advancement of CCS on this island. A recent study has estimated that the island of
Ireland has about 93,000 Mt of potential carbon dioxide storage capacity. The main
storage sites proposed include the Kinsale Head in the North Celtic Sea, the
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Portpatrick Basin in the North Channel and the Clare Basin on the west coast. The
depleting gas field at Kinsale could theoretically provide a carbon sink for
Moneypoint and Cork for 50 years. The key risk identified for this site is containment,
however, it is possible that this could be remedied through the appropriate use of
cement barriers. The Portpatrick and Clare basins are not well explored and there is a
scarcity of data, hence the potential storage cannot be comprehensively assessed.
Other storage sites of interest include the extensive Peel Basin and the East Irish Sea
Basin.
Fig. 2 Key Sedimentary Basins examined for this All-Island Ireland Study. (Source: Assessment of the
Potential for Geological Storage of CO2 fro the Island of Ireland.)
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The major point source emissions for the island come from the power, alumina and
cement industries. The study indicates that the power sector would be the primary
target for evaluation namely at three sites; Moneypoint, Kilroot and Cork. Some other
industrial sectors are considered too small for CCS while the technology of carbon
capture from cement plants is in its early phase internationally. In relation to
transporting the CO2 from the point source, the study suggests that the most efficient
method would be via pipeline to the storage site. The captured gas would be
compressed at point source and transmitted supercritically in dense liquid phase
through the pipeline. It would then be injected into the selected storage site.
This report recommends the need for further geological studies to address current
gaps in knowledge regarding prospective storage sites on the island of Ireland. A
further recommendation is that Ireland takes an early lead and opts to undertake one
of the EU pre-2015 CCS demonstration projects. It also encourages price support to
be given to CCS in order to incentivise operators, this would be similar to what is
offered to other low carbon power generators. The study also recommends that
emerging international guidelines regarding the environmental monitoring of CCS be
applied to Irish carbon storage projects.
Conclusion.
Carbon capture and storage is a technology with the potential to reduce greenhouse
gas emissions while still allowing the use of fossil fuels. Perhaps the best overall
strategy for reducing CO2 emissions would be the use of a combination of measures.
These would include; the use of increased energy efficiency, a change from the use of
fossil fuels to renewable energies and the implementation of the use of carbon
capture and storage on a wide scale.
Further Information.
• Assessment of the Potential for Geological Storage of CO2 for the Island of
Ireland, Sustainable Energy Ireland, Environmental Protection Agency,
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Geological Survey of Ireland and Geological Survey of Northern Ireland,
September 2008.
•
Carbon Dioxide Capture and Storage in Ireland Costs, Benefits and Future
Potential, Sustainable Energy Ireland, August 2006.
•
Intergovernmental Panel on Climate Change, Special Report on Carbon Dioxide
Capture and Storage, Cambridge University Press, 2005.
•
CO2 Sink (http://www.co2sink.org/)
•
Carbon Capture and Storage (CCS) Parliamentary Office of Science and
Technology, Postnote, March 2005, Number 238.
•
Emerging Energy Technologies in Ireland: A Focus on Carbon Capture and
Hydrogen, Sustainable Energy Ireland, November 2005.
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