Select Committee on Science and Technology First Report


Capture technologies

26. The purpose of CO2 capture is to generate a concentrated stream of pure CO2 for transport and injection into the storage site. CO2 capture technology has been routinely used for many years to separate CO2 from natural gas (known as natural gas 'sweetening') and for industrial processes such as ammonia production. However, none of these applications employ capture technology at the scale that would be required for capturing CO2 from the emissions of a large-scale power plant. Box 2 provides an overview of the three main approaches to the capture of CO2 from emissions: pre-combustion, post-combustion and oxyfuel. A summary of experience to date with capture technology is provided at Annex A.

Box 2: Capture technologies

27. Different capture technologies are likely to be favoured depending on the circumstances, but the costs of the various capture options are expected to be comparable. Jon Gibbins, leader of the UK CCS Consortium (UKCCSC), told us:

There was general agreement that there was no merit in 'picking winners': all three capture options offer potential advantages and should be pursued.

28. The various capture technologies are at varying stages of maturity. Oxyfuel technology is the least developed of the three capture options, although it is generally considered to be a promising option for the future. Gardiner Hill, Manager Group Environmental Technology at BP, explained that the current limitations for oxyfuel capture were "around material choice to manage the high combustion temperatures and the cost of supplying the vast quantities of oxygen required".[35] He predicted that although "there will be some demonstration small-scale of oxy-firing [oxyfuel capture] that will be undertaken by a number of companies in the next five years, […] there is probably a 15-year timeframe [before] we might expect to see [it] perhaps being used on a much larger scale".[36]

29. E.ON UK pointed out that post-combustion capture of CO2 using amine scrubbing "has been used for over 80 years for gas sweetening in the petrochemical industry and there are hundreds of plants in service today".[37] There is also extensive experience of pre-combustion capture for industrial production of hydrogen. Indeed, most of the technology that underpins CCS is tried and tested although it has not yet been combined in a single CCS project at the scale required to make an impact on emissions from power generation. George Marsh, a DTI adviser on carbon abatement technologies, summed it up as follows: "most of the technology that we are talking about is available and deployed. The new thing that needs to be done is to combine it in an integrated process for carbon capture and storage".[38]


30. The hydrogen which is produced by pre-combustion capture can be used for electricity generation, for carbon dilution of natural gas, or as a transportation fuel. BP highlighted the need to "be aware of the economic advantages offered by pre- (as opposed to post-) combustion" capture, commenting that "If the resultant CO2 stream can be securely geologically stored, 'green' power can be manufactured from the hydrogen at a comparable cost to the nuclear or renewable alternatives, or the hydrogen can be added to the natural gas grid as a form of carbon dilution".[39] Air Products further argued that the ability to generate "H2 [hydrogen] from coal as a transport fuel would also break the monopoly position of oil".[40]

31. Fossil fuels can be an important source of chemicals and with the continuing depletion of oil reserves, coal and gas could become significant sources of chemical feedstocks. Out of the three capture options, only pre-combustion capture enables the production of a key chemical, hydrogen, in tandem with electricity generation. Mr Hill from BP noted that this was one of the reasons that he believed China would be interested in pre-combustion technology: "Primarily it will be the pre-combustion technologies that will enable chemicals from coal to really underpin the Chinese economy so they can convert coal to fuels: they will want to convert coal to hydrogen; and they will want to convert coal to electricity without any impact on the environment".[41] Co-production of electricity and chemicals is sometimes referred to as 'polygeneration'. However, the volumes of chemical feedstocks that could be produced through pre-combustion capture are minor compared to power use and it is not yet clear whether polygeneration at a single plant will prove more economical or efficient than producing electricity and chemicals from separate plant.

32. The Royal Academy of Engineering told us that "Pre-combustion carbon capture combined with integrated gasifier combined cycle gas turbine (IGCC) technology is likely to emerge as the eventual natural gas or coal fuelled option that may be sustainable in a carbon constrained world".[42] We agree. Although it is clearly important that pre-combustion, post-combustion and oxyfuel capture technologies be developed, we believe that for new plant pre-combustion capture offers a significant advantage, in a carbon constrained world, as a potential source of hydrogen. As the technology develops, the Government should take into account the potential strategic importance of polygeneration systems based on pre-combustion capture technology and consider the case for putting in place incentives to promote the use of this technology in new build plant.


33. Retrofitting of existing plant with CCS technology could accelerate the contribution that CCS makes to reducing CO2 emissions. However, much of the evidence we received was sceptical about the commercial viability of retrofitting UK coal-fired plant. The UK fleet of coal-fired power stations comprises combustion plant designed more than 30 years ago, which is relatively inefficient in modern terms.[43] Fitting a plant with CCS decreases the thermal efficiency of that plant so retrofitting already inefficient UK coal-fired plant is not likely to make economic sense, given currently available technology. The Royal Academy of Engineering for instance argued that "The efficiency penalty of currently available carbon capture technology is too high to be considered for a simple bolt-on addition to an existing power station" and noted that "the economics of retrofitting a power plant that may be at or beyond its design lifetime or emissions control capability would need close scrutiny".[44]

34. These concerns were echoed by industrial contributors to the inquiry. In oral evidence, Colin Scoins, Director of New Business at E.ON UK, told the Committee: "much of [the UK's] plant is very old, potentially 40 years old. It is probably not an economic decision to retrofit a plant of that age".[45] BP also noted that retrofitting was likely to entail shutting down the plant for a period of about 12 months, which could add prohibitively to the cost. Mitsui Babcock has estimated the cost of these lost 12 months to be around £50M.[46]

35. An alternative would be to undertake a major refurbishment of coal-fired plant by fitting new boilers and turbines to increase the efficiency of the plant substantially - in conjunction with such changes, installation of capture technology might be more attractive. Air Products, for example, argued that the "combination of a boiler/steam turbine upgrade plus the oxyfuel conversion would ensure CO2 capture and delivery to a pipeline system at high pressure with only a very small reduction in overall station efficiency".[47] The DTI also suggested that "for existing coal stations it would be desirable to retrofit advanced boilers with the capture plant".[48] Although the possibility of upgrading some existing plant is an interesting one, its practicability is likely to depend on the specific circumstances of each plant. In our view, no convincing case has yet been made for retrofitting of the UK's ageing fleet of coal-fired power stations with capture technology. Combining retrofitting with boiler and turbine replacement may provide a means of overcoming the loss in efficiency associated with current capture technology, but it remains to be seen whether this will prove economic for the majority of UK coal-fired plant.

36. Due to time constraints, we did not look in any detail in the inquiry at the case for retrofitting gas-fired plant. The Government suggested in its evidence that "For existing gas plant one retrofit option is to retrofit pre-combustion capture and burn hydrogen in the existing gas turbines". It also noted that "Some existing gas turbines may be unsuited for this in which case post combustion capture (flue gas scrubbing) would be the only option".[49] It has also been proposed that retrofitting of gas-fired plant could provide an opportunity to incorporate a coal gasification facility - essentially converting the plant to an IGCC station. We consider this to be an interesting possibility and worthy of further investigation.


37. E.ON UK highlighted the fact that up to 8GW of nuclear and 19GW of coal and oil-fired plant will need to be replaced in the UK by 2015.[50] This is equivalent to nearly a third of the UK's total electricity generating capacity. As discussed later, CCS technology may not be commercialised in time to enable significant amounts of the replacement plant to be built fitted with the technology. Yet new build plant is expected to have a lifespan of at least 30 years and, if CCS is not deployed on a significant scale by 2020, it is hard to see how it will be able to contribute to CO2 emissions reductions in the required timeframe. The UK could then become 'locked in' to unacceptably high CO2 emissions.

38. One possible solution that has been proposed to resolve the mismatch in timescales is the idea of building new plant 'capture ready'. This would mean making a small investment at the time of building to provide the future option of retrofitting capture technology at relatively low cost. At its simplest, capture ready just means giving due consideration to factors such as space and location during the planning stages of building a new plant, in order to facilitate subsequent instalment of CCS technology. The Government told us, for example:

    "Capture ready refers to plant designed to enable CO2 capture equipment to be retrofitted with minimum disruption and in a manner that is optimal for future plant operations. Some key requirements are: availability of land for the capture plant; availability of space for the pipe-work and other systems needed to incorporate capture into the power plant; and the design of boiler and turbine systems to facilitate optimal integration. It has been suggested that location relative to CO2 storage sites might be an additional 'capture ready' criterion".[51]

The Government additionally told us that there was a G8 initiative seeking to arrive at an agreed definition for capture readiness and noted that, once such an agreement had been reached, the licensing and consents process could be used to encourage new plant to be built capture ready. This would be a sensible approach, providing that it could be implemented sufficiently rapidly. We recommend that Government makes capture readiness a requirement for statutory licensing of all new fossil fuel plant. This would compel the developer to demonstrate that consideration has been given in the planning and design of the plant to facilitating subsequent addition of suitable carbon dioxide capture technology, as and when it becomes available and economic.


39. The IPCC report, along with much of the evidence submitted to this inquiry, indicates that the major contribution of CCS to the mitigation of climate change will result from its deployment in the electricity sector. Nevertheless, other applications are also worth investigating. Corus pointed out in written evidence that "the steel industry, worldwide, accounts for approximately 5% of the total anthropogenic CO2 emissions to atmosphere".[52] Corus is thus participating in an EU-funded research project entitled Ultra Low CO2 Steelmaking (ULCOS), the aim of which is to investigate new steel production processes to drastically reduce CO2 and other greenhouse gas emissions.[53] Dr Gibbins from the UKCCSC also emphasised the potential versatility of CCS: "Carbon capture and storage applies immediately to the electricity industry but in the longer term it can be applied to all sectors. You can produce decarbonised energy vectors - that is hydrogen or electricity for use in transport and in the building sector - so it really can apply to a very broad range of our energy usage".[54] Although in the near term CCS is most likely to be employed in the power sector, it has the potential to be applied to a range of industrial processes, as well as in the building and transport sectors. We recommend that the Government support for CCS research includes applications in these sectors.


40. This section focuses on geological storage of CO2 and, more specifically, on the prospects for storage of CO2 in depleted oil and gas fields and deep saline aquifers. Saline aquifers are porous rock formations found deep underground which contain salty water unsuitable for use as potable water. Other approaches to storage, including storage in unmineable coal deposits, are considered in paragraphs 48 to 50. Geological storage of CO2 has been occurring naturally for millions of years and accumulation of CO2 in underground reservoirs for very long timescales is a common geological phenomenon.[55] It is proposed that, by analogy, the CO2 captured from energy production and industrial processes could be injected into suitable geological formations in the earth's crust for extremely long term (tens of thousands of years) storage.

41. The basic principle entails the trapping of CO2 in the pores—spaces between the sand grains—in sedimentary rocks.[56] At the pressures encountered at depths below 800-1000 m, CO2 enters a so-called 'supercritical' state in which it has a density similar to that of a liquid;[57] this enables efficient use of the storage space. There are four mechanisms of CO2 trapping and all may contribute at different times at any one site. Firstly, although the injected CO2 is buoyant in the water in the rock formation, the presence of an impermeable layer of rock above the storage site, known as caprock, provides a seal to prevent the CO2 migrating upwards. Secondly, the CO2 can dissolve in the water which normally fills the pore spaces in the sedimentary rock, helping to trap it in the site. Thirdly, CO2 may move slowly through the rock pores, driven by buoyancy; small bubbles of CO2 are left stranded during this movement and become trapped in disconnected pores. Finally, the CO2 may become trapped through chemical reactions with minerals in the surrounding rock and so, over the long term, may become immobilised in the form of carbonate minerals, similar to those which form natural limestone.

42. There are sufficient candidate geological storage sites for CCS to make a significant contribution to reducing UK CO2 emissions over many tens, or even hundreds, of years. The BGS estimates that the theoretical storage potential of the UK's offshore oil and gas fields is equivalent to at least 4.7 Gigatonnes (Gt) of CO2. This represents approximately 20 years' worth of all present day power generation emissions, although not all of this may be suitable for commercial exploitation.[58] According to the BGS, there is no significant potential for onshore CO2 storage in oil or gas fields in the UK (with the possible exception of the Wytch farm oil field in Dorset). The UK's onshore aquifer storage potential has not yet been fully investigated.

43. There is extensive potential for CO2 to be stored in deep saline aquifers in the North Sea. The BGS memorandum stated:

    "An estimate of 250Gt was calculated in the BGS led Joule 2 (1995) Project for all the aquifers (open and closed) in the UK N. Sea. With UK emissions at over 0.6Gt/year, a third of which comes from power generation it is clear that even if only 10% of this capacity was realized it would serve the UK's needs to beyond the period of fossil fuel dependency".[59]

This would be equivalent to more than 1000 years of storage, based on current UK power generation emissions. The IPCC report estimates global geological storage capacity to be sufficient for CCS to contribute up to 55% of the cumulative mitigation effort needed worldwide until 2100.[60] It should be noted that estimates of the storage potential offered by saline aquifers can vary wildly, reflecting the lack of data in this area.

44. The UK is especially fortunate in that many sources of CO2 generation from onshore power plant and other industries lie within tens or hundreds of kilometres of potential storage sites in rocks beneath the offshore northern and southern North Sea and Irish Sea. This is within easy reach of pipeline transport, as proven by onshore CO2 developments in the US and by offshore oil and gas transport around the UK. The geographic co-location of storage sites and CO2 sources may be less favourable in some other countries, such as Japan, and has yet to be thoroughly investigated in many others. Professor Haszeldine commented on the UK's fortuitous situation in written evidence:

    "From hydrocarbon exploration, we have unrivalled knowledge of our offshore geology. These are some of the world's best-known and most accessible sediment basins, and contain both depleted oil and gas fields and deep aquifers of saline water".[61]

The UK is fortunate in being very well endowed with potential CO2 storage sites, many of which have been thoroughly characterised. This provides the UK with a competitive advantage in terms of access to potential CO2 storage sites, both for its own use and to demonstrate UK geological skills to the rest of the world.

45. In general, more is known about oil and gas fields than saline aquifers leading some people to suggest that the former are better candidates for immediate development as storage sites. The oil and gas fields in the North Sea have been particularly well characterised and both Friends of the Earth and Green Alliance were far more enthusiastic about CCS projects involving storage in oil and gas fields than those involving aquifers. Germana Canzi, Senior Climate Change Adviser for Friends of the Earth, told us: "We feel that the oil industry has a lot of experience with the geology of oil and gas fields and, therefore, we feel more confident that the science about the permanence of the CO2 underground is more certain".[62] The evaluation of offshore saline aquifers for storage purposes is readily achievable, by application of the same techniques as are normally used in offshore oil and gas exploration and production. Oil and gas fields have, in general, been better characterised than saline aquifers so may be more suitable for immediate development. Nevertheless, the best way of furthering understanding of storage of CO2 in aquifers, which provide very substantial storage potential in the longer term, is through large scale demonstration projects.

46. BP commented in its memorandum that the oil and gas industry had "over one hundred years of experience identifying and managing fluids in the deep sub-surface" and noted that the "geological storage of CO2 is very similar to the management of other liquids and gases routinely handled by the industry throughout the world".[63] In addition, BP asserted that "the industry has considerable experience of oil and gas abandonment, and much of this will be used to form the basis for secure [field] abandonment to ensure long term safe, secure storage of CO2 in the rock".[64] Furthermore, the British Geological Survey, which has developed an enviable reputation over its 170 years of operation, has innovated and maintained particular expertise in CCS since the early 1990s. The UK's geological expertise through the hydrocarbon industry and British Geological Survey is recognised to be amongst the best in the world. This expertise should be leveraged to facilitate and promote UK demonstrations of CCS and, ultimately, uptake of CCS internationally.

47. Globally, most experience to date of relevance to CO2 injection has been obtained as a result of enhanced oil recovery (EOR) projects. There are more than 70 EOR projects around the world. Extensive experience in CO2 injection into oil fields, for the purposes of enhanced hydrocarbon production, has been gained over a 30 year period, particularly in North America. The BGS commented on the fact that although there have been many commercial projects involving the injection of CO2 for EOR, "few have been accessible to researchers".[65] At Weyburn and Rangely, there has been large scale CO2 injection for EOR purposes. Apart from EOR projects, there are only two large-scale industrial projects worldwide, at In Salah in Algeria and Sleipner in Norway, where CO2 is being injected underground at a rate of around 1Mt/year. Several more industrial size projects are planned to commence soon; Box 3 contains a summary of current and forthcoming projects involving CO2 storage.

Box 3: CO2 storage: summary of experience


48. Deep ocean storage has been proposed as an alternative to geological storage. In this case, captured CO2 would be directly injected into the deep ocean (below 3000 m) where, being denser than water, it would be expected to form a 'lake', delaying its dissolution into the surrounding water. This storage mechanism is still at the research stage and there is unease about its potential environmental implications. It is not considered to be viable for the North Sea in any case due to the lack of storage sites of appropriate depth. It would also be illegal under current international law.

49. Unmineable coal seams offer another potential CO2 storage opportunity. Enhanced Coal Bed Methane Recovery (ECBM) involves injecting CO2 into coal seams, where it displaces methane and thereby enhances recovery of methane from the coal bed. This can give an economic return to help offset the costs of storage. Professor Peter Hall from the University of Strathclyde and Stephen Jewell from Composite Energy Ltd asserted that "the bituminous coals that constitute most of the resource of the UK have the ability to permanently store CO2".[66] However, the majority of evidence published to date seems to suggest that UK coal is too impermeable to make this a practical option.[67] On the basis of current information, coal seems unlikely to be a major storage option for the UK, at best being of small scale and local significance. We do not, of course, exclude the possibility that future research or developments in technology will alter this situation.

50. Mineral carbonation has also been proposed as an alternative means of storing CO2. Dr Sam Holloway, Senior Geologist at the British Geological Survey, told us: "It is a process that will work but the costs are likely to be extremely high" and asserted that it "would require very considerable advances in order for it to become anywhere near competitive with other methods of sequestering carbon".[68] Dr Riley, also from the BGS, put it in even stronger terms:

    "I think mineral storage is a distraction. The bulk of CO2 storage is going to have to be done by injecting the carbon dioxide underground. The issue of can we create dolomite from seawater will make the problem worse because if you make carbonate from seawater you evolve carbon dioxide back to the atmosphere. It sounds counterintuitive [but] it actually makes the situation worse in the short term".[69]

It has also been argued that it may be possible in future to use 'waste' CO2 as feedstock for other processes. The Royal Society of Chemistry told us that "from a chemical science perspective CO2 can also be seen as potential feedstock for the manufacture of useful chemicals and as such chemical conversion of significantly large amounts of carbon dioxide to inert or commercially useful material is an option that cannot be ignored".[70] The IPCC considered this possibility in its Special Report and concluded that "The potential for industrial uses of CO2 is small" and that "the CO2 is generally retained over short periods".[71] Furthermore, the IPCC cautioned that "Processes using captured CO2 as feedstock instead of fossil hydrocarbons do not always achieve net life-cycle emissions reductions".[72] It is clear that storage in geological formations, providing that it can be done safely and securely, is the most desirable and competitive way of storing CO2 of the currently available options.


51. Captured CO2 obviously needs to be transported to the storage site and there is agreement that this will generally be best done via pipeline. There are already more than 2500 km of pipelines, mainly in the Western United States, transporting 50 Mt CO2 per year from natural sources to EOR sites.[73] The recent IPCC report concluded that there was "no indication that the problems for carbon dioxide pipelines are any more challenging than those set by hydrocarbon pipelines in similar areas, or that they cannot be resolved".[74] The risks associated with transportation by pipeline are discussed in paragraph 90.

52. Captured CO2 is usually compressed prior to transportation in order to decrease the volume occupied by the gas. Providing that the CO2 is dry and free from hydrogen sulphide, the risk of pipeline corrosion is minimal. The IPCC report suggests that it would be "desirable to establish a minimum specification for 'pipeline quality' CO2".[75]

53. In the case of liquefied petroleum gas, liquefaction is used to decrease the volume for transportation by ship. Although similar technology could be applied to liquefaction of CO2, Rodney Allam from Air Products pointed out that transportation of CO2 in pressurised tankers would be expensive and there was a consensus amongst witnesses that development of a global market involving trading of emissions certificates between countries was far more likely, and preferable to, one where countries exported their CO2 for storage in sites in other countries.[76]

34   Q 70 Back

35   Q 124 Back

36   Q 125 Back

37   Ev 25 Back

38   Q 14 Back

39   Ev 85 Back

40   Ev 73 Back

41   Q 168 Back

42   Ev 23 Back

43   POSTnote 253 Back

44   Ev 21 Back

45   Q 122 Back

46   Personal communication. Back

47   Ev 74 Back

48   Ev 183 Back

49   Ev 183 Back

50   Ev 78 Back

51   Ev 182 Back

52   Ev 88 Back

53   As above. Back

54   Q 61 Back

55   IPCC, Special Report on Carbon Dioxide Capture and Storage, Autumn 2005. Back

56   Sedimentary rocks are made up of sediments, laid down millions of years ago, which may be second-hand fragments of other rocks, or remnants of living organisms. Back

57   Supercritical CO2 occupies less than 1% of the space that CO2 gas would fill at normal temperature and pressure. Back

58   Ev 72 Back

59   Ev 72 Back

60   IPCC, Special Report on Carbon Dioxide Capture and Storage, Autumn 2005. Back

61   Ev 133 Back

62   Q 213 Back

63   Ev 138 Back

64   Ev 138 Back

65   Ev 71 Back

66   Ev 85 Back

67   Ev 60, 118, 142 Back

68   Q 79 Back

69   Qq 80-81 Back

70   Ev 145 Back

71   IPCC, Special Report on Carbon Dioxide Capture and Storage, Autumn 2005. Back

72   As above. Back

73   As above. Back

74   As above. Back

75   As above. Back

76   Q 153 Back

previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries index

© Parliamentary copyright 2006
Prepared 9 February 2006