27 Apr 2010, 6:31 PM
Geologists have refuted a report which in January had cast doubt on a technology to bury greenhouse gases underground, and on which some policymakers have pinned hopes to fight climate change. British geologists and engineers rejected the doubts on Monday, pointing to pilot projects in an email to Reuters, following a report about January's article in the Guardian newspaper on Monday.
Carbon capture and storage (CCS) involves trapping and storing underground carbon dioxide produced by power plants which burn fossil fuels. Some academics say that the world's efforts to limit dangerous climate change depends on CCS, which can in theory almost eliminate carbon emissions from burning coal and so give the world time to develop cheap fossil fuel alternatives.
The trouble is that the full chain of CCS processes from trapping and piping to burying underground carbon dioxide (CO2) produced by power plants is untested at a commercial scale.
Pressure levels in underground aquifers could reach levels where projects either could not pump any more CO2 in, or force the greenhouse gas to leak into the atmosphere, rendering the process worthless, argued a paper published earlier this year. "The physics is so straightforward," said Christine Ehlig-Economides, co-author of the paper published in the Journal of Petroleum Science and Engineering.
"When you try to inject something into an existing formation which is already at pressure, it (pressure) has to go up," she told Reuters on Monday. "The models that people are using more often than not do not accommodate this."
The paper had argued that an aquifer may need to be the size of a U.S. state to store CO2 from a single power plant. She acknowledged criticism of that "general" assertion and said the authors had applied the model to particular acquirers and showed that these could in fact store CO2 for 25-30 years from clusters of power plants.
"If that's sufficient for everyone, fine. If you're really sincerely talking about accommodating large numbers of power plants, already spending impossible amounts of money and energy to capture, get this CO2 in the ground we need to be spending very close attention to what it entails," she said.
British geologists rejected the doubts, pointing to tests such as Norway's Sleipner project.
"The most profound error is that the subsurface is not made of sealed boxes," said Edinburgh University's Stuart Haszeldine and Martin Blunt from London's Imperial College. It is well known ... that below ground contains many hundreds of meters of porous rock suitable for CO2 storage."
Norway has buried millions of tonnes of CO2 for more than a decade below the seabed of the North Sea between Britain and Germany. "It's not anywhere hear the volumes you're talking about for real operations, for even a small power plant," countered Ehlig-Economides, referring to Sleipner.
A wider concern about CCS is cost. It is expected to add about $1 billion to the capital cost of a power plant and cut efficiency by a quarter. European Union Energy Commissioner Guenther Oettinger said on Monday he doubted that the technology would take off in Germany, because of the difficulty forcing states to take and store CO2 from each other.