Capturing CO2

Engineers in the US believe they have come up with a novel solution that mitigates the risks often associated with geologic carbon-dioxide sequestration.

The standard approach to carbon capture and storage involves extracting CO2 from a fossil-fuel burning power plant, compressing and transporting the captured carbon dioxide and injecting it into a deep underground formation.

The biggest risk associated with geologic carbon-dioxide sequestration is that the CO2, which is less dense than water, will escape from the storage formation through buoyancy.

But engineering professor Steven Bryant, who directs the Geological CO2 Storage Research Project at The University of Texas at Austin, believes he and his team have come up with a novel solution.

Instead of injecting the compressed CO2 directly into a deep underground formation, Bryant’s alternative plan is to drill wells in the deep salt-water filled formation, pump out the salt water, dissolve the carbon dioxide into the salt water in a mixing tank at the surface and then inject the CO2-laden water back into the same formation.

The CO2-laden water is much denser than the compressed CO2 and slightly denser than the original brine.

Thus, it will have no tendency to rise toward the earth’s surface, in contrast to compressed CO2, which is buoyant under typical storage conditions.

‘This process has several advantages, but the most important is that it eliminates the risk of sequestered carbon dioxide escaping from the storage formation,’ Bryant said.

Although the process does cost more than the standard approach, it is not prohibitively more expensive.

‘In essence, the incremental cost can be regarded as the price of risk reduction.

‘This is an important consideration because all stakeholders will want the greatest assurance of secure storage for the lowest cost,’ added Bryant.