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Science & Hi Tech: Squeaky clean fossil fuels

Posted on 02.05.2005 - 09:28 EDT in SCIENCE & TECH NEWS by ginamc

New SientistCAN we continue to burn fossil fuels and still hope to halt global warming? It seems unlikely - and with the cost of generating wind and solar electricity falling, perhaps unnecessary. Despite this, big money and big politics are lining up behind the development of "zero-emission" power plants that burn coal or gas but release no carbon dioxide.

The latest advocates are former fans of renewable energy at the European Union, who say the strategy will be "essential" if the EU is to meet targets for limiting the emissions of the greenhouse gas CO2. This month, at a conference in Brussels, Europe's new commissioner for energy, Andris Piebalgs, said the EU could cut CO2 emissions while continuing to burn its native coal and lignite. And still stay economically competitive.

One way to do this, Piebalgs said, is to embrace clean coal technologies - a move that would chime with the Bush administration's push for clean-coal technology in the US. The other is to store CO2 by capturing it before it leaves power plants and burying it underground. These are now the EU's two top priorities in energy research, something that will anger environmentalists who want the world to abandon fossil fuels as quickly as possible.

One technique to stop power stations producing CO2 is to pass emissions though chemical scrubbers which contain amines that react with and trap CO2. Similar technology is already used to remove CO2 from natural gas, to boost the proportion of hydrogen it contains. "It's just a matter of scaling up," says Julio Friedmann, a former ExxonMobil geologist now at the University of Maryland. In future, the carbon could even be removed from fuel before it is burnt.

To bury the CO2 securely underground, the gas has to be compressed, then injected under pressure down a pipeline into redundant coal seams, old oil or gas wells, or porous rocks filled with salt water.

On a rig in the North Sea, the Norwegian company Statoil already strips a million tonnes of CO2 each year from natural gas at the Sleipner gas field and buries it in a saline aquifer without ever bringing it to land. At the Salah gas field in Algeria, energy giant BP last year began reburying a similar amount of CO2 in sandstone 2 kilometres down. Old oil and gas fields stored hydrocarbons safely for millions of years, raising hopes that the same can be done for CO2 from power stations.

Oil companies like the idea, because injecting CO2 into oil wells can flush out any remaining oil. As the oil dissolves the CO2, its viscosity falls and its volume increases, forcing it out under pressure. This technology too has been shown to work: more than a million tonnes of CO2 a year is being injected into the Weyburn oilfield in Saskatchewan, Canada, to flush out the remaining oil.

In a similar way, the coal industry expects to be able to inject CO2 into coal seams, and recover methane gas into the bargain for use as fuel. An EU trial is under way in Poland.

Most major industrial regions have convenient CO2 burial grounds, Harry Audus of the International Energy Agency told the Brussels meeting. In the US, virtually all the top 500 CO2 emitters are within 150 kilometres of suitable geological formations. And Europe has a large potential burial ground in former oil and gas wells beneath the North Sea.

Old oil and gas fields stored hydrocarbons safely for millions of years. The same could be done for CO2 from power stations

Global estimates of the geological space available for the economic burial of CO2 are sketchy. But Audus estimates that around 11,000 billion tonnes of CO2 could be disposed of underground (see Graph), several times the likely emissions of CO2 from burning fossil fuels in the coming century. This could at least give the world extra time to give up its reliance on fossil fuels.

At an estimated current price of $40 to $60 per tonne of CO2, carbon storage and burial is still not cheap, though its proponents say it could soon compete with renewable energy. The Intergovernmental Panel on Climate Change will present a detailed report on carbon capture and storage to signatories of the Kyoto protocol in November. After that, says Audus, "it should become an accepted mitigation option".

Source: New Scientist

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