Capturing a market for CO2

Extracting the “NOx, SOx and rocks” from fossil-fired power plant flue gases is commonplace, but what about the CO2? The list of measures available for cutting CO2 emissions from the power industry normally includes such strategies as switching fuels (eg from oil and coal to gas), investing in CHP, renewables, biomass, or even nuclear power. There is also the important option of building more efficient coal-fired power stations (such as Boxberg – with a net efficiency of over 42 per cent on lignite). But, of course, increasing efficiency can only decrease CO2 emissions, never eradicate them.

What has tended to get less attention is the concept of capturing the CO2 generated at fossil-fired power plants and disposing of it. This notion, however, now seems to be attracting growing interest, particularly among those contemplating zero-emissions power plants for the long term future.

Last year saw the launch of the EU funded GESTCO project, which is making a major assessment of the potential capacity for geological storage of CO2 in Europe, while this year we had the start-up of the European CO2 network “CO2NET”, which aims, among other things to push sequestration up the energy policy agenda. As well as seven oil companies, members of CO2NET include Vattenfall and several other power generation companies. Denmark-based electricity generator Elsam is also considering joining and is looking at the possibility of taking CO2 from its coastal power plant sites and injecting into North Sea oil fields.

CO2 separation and sequestration is technically feasible and the technology needed to apply it to power plants could be demonstrated and be made commercially available in perhaps a decade or so. Capture options include precombustion processes (fuel reforming to produce CO2 and H2, with CO2 recovery prior to combustion), use of pure oxygen to combust fuel instead of air so that the exhaust is untainted with nitrogen, and post combustion CO2 extraction technologies (eg amine absorption).

Once you have got the CO2 you need to dispose of it on a grand scale. Among the options are: storage in deep salt water aquifers; use for enhanced coal bed methane extraction; enhanced oil recovery; storage in depleted natural gas fields; and storage in mined salt structures. Some of the processes required for disposal are already well established and used in the oil industry, where there has been a recent spate of projects involving re-injection of CO2. In the USA about 30 million t of CO2 is being sequestered annually in enhanced oil recovery projects. At Weyburn in Canada, an enhanced oil recovery project is importing CO2 from the Dakota gasification plant in the USA through a 320 km pipeline. At the Sleipner gas field in the Norwegian North Sea, where excessive CO2 must be extracted from the gas before it is saleable, some 1 million t/y of CO2 has been injected into a deep saline aquifer since about 1996. The North Sea has the potential to store 800 billion t of CO2 (about 800 years’ output from European power plants).

The problem is making the economic case. Recent estimates suggest that if present technologies were applied to the power sector they would add 50-60 per cent to the unit costs of electricity production. According to Lars Strömberg of Vattenfall, who presented a paper on power plant CO2 sequestration strategies at the recent VGB Kraftwerke 2001 conference (Brussels, 10-12 October), this is still “cheaper than producing electricity from biomass”. Indeed, he believes that “CO2 emissions from coal and other fuels can probably be eliminated by CO2 separation and underground deposition at lower cost than most of the renewable alternatives.” And if this can be achieved “coal can be considered a sustainable solution, since resources are so large and widespread.” According to figures presented at the VGB conference by Lars Stromberg the cost of avoiding 1 ton of CO2 emissions is about $50 for the sequestration option (which could fall to around $35 with “known but non-optimised technology”). This compares with over $100/ton CO2 for solar, $80/ton CO2 for wind, $70/ton CO2 for hydro, and around $65/ton CO2 for biofuels. The cheapest option is conversion from coal to gas, which costs about $12/ton of CO2 avoided.

The economic attractions of sequestration are also greatly improved where the CO2 can be used for something useful and profitable, eg enhanced oil recovery and coalbed methane extraction. This is the thinking behind a Shell/Siemens-Westinghouse fuel cell generation project inaugurated last year which aims to use CO2 from the cell for enhanced oil recovery.

Compared with solar power or offshore wind farms, the idea of burning fossil fuels and then capturing the CO2 and disposing of it seems nevertheless somehow technologically inelegant. It should also be borne in mind that these comparisons are all very well but no-one has applied the CO2 capture and sequestration option to an actual power plant – yet (although the Canadians plan to have capture technology retrofitted to a power plant by 2007).

However, proponents of sequestration point out that it has the potential to enable coal, which is plentiful and still predominates in power generation, to remain a key part of the energy supply picture, while at the same time allowing CO2 emissions to be cut.

This appeals to the Bush administration, which, while it may have declined to sign up to Kyoto, has cited sequestration as a key part of its strategy for addressing climate change. “Carbon sequestration is an important option to study because it offers a way to address the global warming issue without having to make radical overhauls of our existing energy systems,” said US Energy Secretary, Spencer Abraham.

The US DoE is funding a number of research projects in the area and has the goal of “developing sequestration approaches that cost $10 or less per ton of carbon”, which corresponds to about 0.2 c/kWh.

Sequestration is aiming at a moving target, as the costs of alternative CO2 reduction options, eg the renewables, are progressively falling. But if the costs of sequestration technology can be brought down to anywhere near the US DoE target it would certainly merit some very serious consideration.