Carbon dioxide stored at the bottom of the sea? It just might work...
The new paper on carbon capture and storage demonstrates that the hydrates become an impermeable ‘cap’ that keeps the carbon dioxide below it from migrating back up to the sea floor
New York — A Cold War-era joke has an American economist asking a Soviet peer how the communist economy is progressing. "In a word: good" the Russian responds. "In two words: not good."
So it goes this century with the rapidly changing energy industry. Advances are taking place in clean energy, transport and efficiency that may have rightfully been considered miraculous a decade ago.
But here’s the catch: as fast as everything is proceeding, it’s still not fast enough. The International Energy Agency (IEA) reported last year that a critical technology — capturing carbon dioxide emissions from generators and either burying or otherwise disposing of them — isn’t expanding fast enough. The IEA reported that current carbon capture and storage (CCS) facilities are capable of handling just 7.5% of the emissions the world will need eliminated every year by 2025. This is necessary if nations are to meet the goal of keeping any increase in global warming below 2°C.
In China, researchers have been looking for ways to accelerate CCS. They decided to look out to sea.
On land, CCS isn’t just promising in principle — it’s been shown to work. There will be more than 20 large-scale capture facilities available by the end of the year, according to the Global CCS Institute. However, there’s still concern about making sure the carbon dioxide, once buried, stays buried. The same can be said for the idea China has about burying carbon dioxide at sea. For companies and countries to exploit the vastness of the ocean floor, they also need some kind of confidence that it’ll stay there.
By studying the long-term interactions of major physical forces in "unconsolidated marine sediment", such as loose silt, clay and other permeable stuff below the sea floor, researchers Yihua Teng and Dongxiao Zhang report that extreme conditions at the bottom of the ocean essentially hold carbon dioxide in place, "which makes this option a safe storage".
Under great pressure and low temperature, carbon dioxide and water trapped in the sediment below the sea floor crystallise into a stable ice called hydrate. (Through a similar process, energy-rich methane freezes with water beneath the ocean and terrestrial permafrost, a potential source of energy being scrutinised by China, Japan, the US and others.)
The new paper on CCS demonstrates, through simulation, that the hydrates become an impermeable "cap" that keeps the carbon dioxide below it from migrating back up to the sea floor. Peking University’s CCS research receives support from the multinational metals, mining, and petroleum company BHP, according to the paper.
The research appears this week in the journal Science Advances. The study should provide some confidence, the scientists write, that ocean carbon dioxide storage remains a viable tool in the push to reduce emissions of the most dangerous heat-trapping gas, even as commercialisation of the process remains way off. In the meantime, there are other questions to answer, including how carbon dioxide may behave differently under different kinds of geological conditions.
The big assumption, as with most underground carbon dioxide storage scenarios, is that there’s no telling what the Earth’s living geology will do over the centuries and millennia. Fractures in the sub-sea sediment, either pre-existing or created by tectonics or carbon dioxide injection itself, could open a pathway for carbon dioxide to escape — though significant uncertainty remains. "In our assumption," the scientists write, "the unconsolidated marine sediment is intact."