An Icelandic Power Plant Is Turning Its Carbon Emissions Into Stone (Really)

A team of engineers and scientists at Iceland's Hellisheidi power plant have developed a method for capturing carbon emissions and converting them into stone for safe storage, according to a study published in the journal Science this week. Documenting work from pilot project Carbfix, the study demonstrates that carbon dioxide and hydrogen sulfide released by the geothermal plant can be mixed with water, injected back into basalt layers deep underground, and converted into rock-hard carbonate in just months--something scientists had initially worried could take hundreds or thousands of years to occur naturally.

The project brought together scientists from Columbia University, the Universities of Copenhagen and Iceland, and Reykjavik Energy, which operates the plant, with the goal of nixing the company's emissions of CO2 and the smelly, poisonous, flammable gas hydrogen sulfide. As the world's largest geothermal facility, the Hellisheidi power plant and one companion plant provide energy for the entire Icelandic capital of Reykjavik (and ample industry beyond) using turbines powered by super-heated water pumped from deep underground. In doing so, the plant produces about 40,000 tons of CO2 a year–just 5 percent the emissions of an equivalent coal-fired plant, but a significant impact that would greatly increase if the country's plan to scale up geothermal energy generation for international export goes ahead. 

Building on previous experiments that had placed only CO2 underground, the team's 2012-2013 pilot project combined 250 tons of CO2, water, and hydrogen sulfide and piped the mixture back underground into volcanic basalt at depths of 400 to 800 meters. Observing its progress through deep wells, the researchers discovered that much of the material had mineralized into stable carbonate within just a few months, and that 95% of it had completed this process within two years. Martin Stute, a hydrologist at Columbia University's Lamont-Doherty Earth Observatory and one of the study's co-authors, explained in a press release, 

This means that we can pump down large amounts of CO2 and store it in a very safe way over a very short period of time ... In the future, we could think of using this for power plants in places where there's a lot of basalt--and there are many such places.

Thanks to its fairly easy access to volcanic basalt and large amounts of water, the Hellisheidi plant can process its CO2 pretty cheaply for around $30 per ton, and has been reinjecting close to 5000 tons of CO2 per year back into the ground since signs of the project's success emerged in 2014. For fossil fuel-powered plants that don't have the natural infrastructure of geothermal ones--and which produce significantly greater CO2 emissions--acquiring the 25 tons of water needed for each ton of CO2 at volume and refining emissions before reinjection drives the price toward a costlier $130 per ton of CO2. According to the team, however, sea water could be used in many operations, while a 2010 study has already identified basaltic seafloors along U.S. coasts that could be suitable re-piping grounds.

Reykjavik Energy's Edda Aradottir, who heads the project, noted that she originally estimated that the process would take much longer than it has, even with the team's improved methods: around 8 to 12 years. "People said there was very little truth to that--they thought it couldn't happen that fast," she said. "Then, it happened much faster. It was a very welcome surprise." 

Check out photos of the Hellisheidi power plant and its carbon processing equipment here.