Carbon capture and storage (CCS) technology may be less effective at mitigating power plant emissions than previously thought, a new US study has found.
In a paper published this week and funded in part by the US Department of Energy, researchers at the Massachusetts Institute of Technology (MIT) Department of Earth, Atmospheric and Planetary Sciences concluded that, after carbon dioxide (CO2) is injected into the ground in the sequestration stage of CCS, less of the gas is converted to rock than has been thought – and in fact only “a small fraction” of the CO2 becomes rock.
Researcher Yossi Cohen, the study’s co-author, said: “The expectation was that most of the carbon dioxide would become solid mineral. Our work suggests that significantly less” will be converted.
In the CCS process, CO2 is injected around 2100 metres below the earth’s surface and stored in brine aquifers where a chemical reaction turns it into rock. In modelling this process, the researchers found that only the CO2 that first touched the brine turned solid, producing a “clogging” effect.
“This can basically close the channel,” said Cohen, “and no more material can move farther into the brine, because as soon as it touches the brine, it will become solid.” The CO2 that is unable to penetrate this solid rock will remain gaseous, or it can come into contact with precipitation and dissolve into a liquid state.
“If it turns into rock, [the CO2 is] stable and will remain there permanently,” said Cohen. “However, if it stays in its gaseous or liquid phase, it remains mobile and it can possibly return back to the atmosphere.”
The researchers cautioned that further study is needed in order to establish a success rate for CCS given that each situation is different, and that multiple aspects of the rock will influence how much CO2 can be mineralized.
While the US Environmental Protection Agency has estimated that CCS could eventually mitigate up to 90 per cent of power plant and industrial emissions, its progress has been slow and beset by setbacks and lack of funding. This month four of Europe’s leading utilities announced a decision to opt out of a decade-long CCS project, citing prohibitive costs.