Select Committee on Science and Technology Written Evidence

Annex 1


Carbon capture

  The separation and capture of carbon dioxide is neither difficult nor new. Chemical sorbents such mono- and di-ethanolamine (MEA and DEA) will selectively remove carbon dioxide from gas streams. The carbon dioxide is released on regeneration of the sorbent simply by heating. At least four leading systems are commercially available.

Carbon dioxide can be extracted before or after the fuel is combusted. The options are sometimes represented as: post-combustion by retrofitting existing plant; pre-combustion by gasification; and the use of oxy-fuel combustion with capture. It is possible to capture carbon dioxide from the flue gases of existing power plants. However, it is very inefficient and costly because of the vast volume of gas that has to be scrubbed. The flue gases are at atmospheric pressure and at a low carbon dioxide concentration—between 3-10%. The efficiency penalty would be about 10 percentage points from the 35-38% current efficiency level of a coal power generation plant due to the power consumed in the scrubbing process. While such systems will achieve the goal of emissions reduction, other ways of approaching the problem need to be examined if the cost of CCS is to be reduced.

Carbon dioxide can be captured much more efficiently in two ways,

    Increasing the concentration of carbon dioxide in the stream being scrubbed

    Increasing the pressure of the gases being treated to minimise the volume being handled

  Air contains about 80% nitrogen so the bulk of the flow through a boiler is inert thus substantially diluting the carbon dioxide content. Hence, if carbon dioxide is to be captured in bulk, the separation of the nitrogen from the air is an important option to be assessed.

However, the status of the technologies is such that a watershed is approaching. If power alone is to be generated at minimum cost, steam systems may have a cost advantage. If carbon dioxide capture is required as a major step towards establishing an equilibrium level in the atmosphere, then gasification appears to offer the least cost route to capture in conjunction with power generation.

Carbon dioxide can be transported to a suitable storage site via pipeline or ship. The former is a mature market, with approximately 3,000km of land-based carbon dioxide pipelines in existence, the majority in North America. The use of existing oil and gas pipeline infrastructure to transport carbon dioxide is also a possibility; however wet carbon dioxide (plus other substances such as sulphur dioxide) is corrosive, which may render these pipelines unusable. Gas dehydration is therefore employed to ensure minimal corrosion of the pipeline. Carbon dioxide pipelines are currently designed to transport carbon dioxide at approximately 100bar, with upstream compressors providing the necessary compression (although some pipelines require intermediate compressor stations). These compressors and their associated pumps must be purpose designed to avoid damage due to the poor lubricating characteristics of dry carbon dioxide. Shipping of carbon dioxide to storage sites is at an early stage of development. The carbon dioxide is transported in liquid form (this time at -50C). However the sheer magnitude of shipping required might prove a considerable challenge.


Utilisation of carbon dioxide is one means by which it can be prevented from reaching the atmosphere. At present, the most common application for carbon dioxide is in Enhanced Oil Recovery (EOR), this process having been implemented in West Texas since the 1970s. EOR is the application that has the greatest potential, with leading oilfield services companies such as Halliburton and Schlumberger expressing interest. It is also a means of carbon storage—hence the current interest of oil majors such as BP.


In relation to carbon storage clearly the period of storage needs to be on a very long timescale compared with human timescales; the cost of storage, including transportation, needs to be minimised; environmental impact needs to be minimal; and the storage method should not contravene any national or international laws and regulations. The three basic mechanisms are geological storage, ocean storage and ecological sinks. The first two of these can be linked directly with power plants, however the third is a storage mechanism which is not tied to any particular carbon dioxide source.

Figure 1 below indicates the approximate global capacity of the various storage options. It shows that the ocean has the highest storage capacity. Deep saline formations, depleted oil and gas reservoirs and coal seams all offer reasonable storage potential, but ecological sinks and utilisation have minimal capacity. The figure also demonstrates the vast global storage potential for carbon dioxide (1,000s of GtC).

  Sources: Carbon Capture and Storage from Fossil Fuel Use, Howard Herzog and Dan Golomb, Massachusetts Institute of Technology Laboratory for the Energy and the Environment, July 2005. Solutions for the 21st Century Zero Emissions Technologies for Fossil Fuels, May 2002, International Energy Agency Working Party on Fossil Fuels, McKee B., Technology Status Report

UK storage capacity is generally in proportion to global storage capacity, although depleted oil fields offer a comparatively greater opportunity for the UK.


The first, and to date only, commercial-scale project dedicated to geological carbon dioxide storage is in operation at the Sleipner West gas field, operated by Statoil, located in the North Sea about 250 km off the coast of Norway. The natural gas produced at the field has a carbon dioxide content of about 9%. In order to meet commercial specifications, the carbon dioxide content must be reduced to 2.5%. At Sleipner, the CO2 is compressed and injected via a single well into the Utsira Formation, a 250 m thick aquifer located at a depth of 800 m below the seabed. About one million metric tons of carbon dioxide have been stored annually at Sleipner since October 1996, equivalent to about 3% of Norway's total annual CO2 emissions. A total of 20 Mt of CO2 is expected to be stored over the lifetime of the project. One motivation for doing this was the Norwegian offshore carbon tax, which was then about $50 (USD) per tonne of CO2 (the tax was lowered to $38 per tonne on January 1, 2000). The incremental investment cost for storage was about $80 million. Solely on the basis of carbon tax savings, the investment was paid back in about 1.5 years.

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Prepared 9 February 2006