The Climefix installation at Hellisheiði. Courtesy Carbfix.
Despite carbon capture seeing a lot of unsupportive if not downright negative press, one company in Iceland is pressing ahead with a seriously viable, large scale technology that turns captured CO2 into rock. By Jeremy Torr.
Hellisheiði, Iceland. September 2021. Using what is the world’s largest working carbon capture plant in the world, a company called Carbfix is pulling carbon emissions from an existing power plant and turning them directly into rock, deep underground. They are currently on target to turn some 12,000 tonnes of airborne CO2 into rock every year, with a small demo plant at Hellisheiði already having sunk some 70,000 tonnes of CO2 below ground since 2014.
“Proud and excited.” - Christoph Gebald, Climeworks CEO. Courtesy Climeworks.
"We are proud, excited - beyond delighted - to have arrived at this stage in our journey to reverse climate change," says Christoph Gebald, co-founder and CEO of Climeworks, the Swiss company that built the carbon extraction plant for Carbfix. “Our plans are super ambitious, but we think (what we are doing) is feasible.”
Once Climeworks’ CO2 extraction system has pulled the gas from the atmosphere, Carbfix’s pioneering technology mixes it with water pumped up from underground (Iceland has plenty) and the resulting, slightly acid, carbonated water is pumped deep into subsurface rocks. The key to the system is that in Iceland – and in many parts of the world – the rocks are basaltic, and also porous.
“The carbonated and slightly acidic water reacts with rocks underground and releases available (positively charged ions) such as calcium, magnesium and iron into the water stream. Over time, these elements combine with the dissolved CO2 and form carbonates that fill up the empty space (the pores) in the rocks,” say the Carbfix research boffins. “These carbonates are stable for thousands of years and can be considered to be permanently stored,” they add.
Even better, this morphing from nasty gas to stable stored rock is fast – during initial tests, the researchers found that 95% of the injected CO2 turns into rock within two years - much faster than previously thought. “The special situation in Iceland is that the carbon dioxide can react very, very fast with the (rocks) underground, and basically be turned into stone,” says Daniel Egger, Climeworks head of marketing.
Other advantages that have become apparent are that the injected carbonated water is denser than the surrounding water in the sub-surface rocks so has the tendency to sink after it has been injected. This is unlike conventional methods of carbon capture and storage, which depend on cap rock to prevent possible leakage of injected gaseous CO2. Not only does the CO2 become rock, it does so below normal water table levels – in previously unoccupied crevices.
The Carbfix teams notes that because young basaltic rocks are highly fractured and porous, the pumped water seeps easily through the interconnects into empty spaces underground. “Basaltic rocks are (also) highly reactive and contain the elements needed for permanently immobilising CO2 through the formation of carbonate minerals,” they explain. “Furthermore, basalt is the most common rock type on the surface of Earth, covering around 5% of the continents and most of the oceanic floor.” Perfect for storing oodles of captured CO2. But how much, exactly?
… and if the power supply is renewable, it costs nothing! Courtesy Climeworks.
“It has been estimated that the active rift zone in Iceland could store over 400 gigatonnes (400 billion tonnes) of CO2,” explain the researchers. “And the theoretical storage capacity of (basaltic) ocean ridges is significantly bigger than the estimated 18,500 gigatonnes of CO2 that has come from all fossil fuel burning on Earth.”
The plant at Hellisheiði offers a bonus in that it produces plenty of carbon-neutral geothermal power to make the new storage system work. But Carbfix claims a plant like this pilot could be constructed in any country with renewable energy, along with the correct or easily accessible rock formations needed to store the mineralised carbon.
Good news for our planet. Now, do we have the will to make it happen?