After working for several years on the Carbfix pilot program, researchers at Iceland's largest geothermal power plant may have eliminated a major obstacle thwarting the battle against global warming.
They demonstrated in a new study that when the plant's CO2 emissions were pumped and sequestered into basalt rock formations, gas molecules began carbonizing into minerals within months — practically overnight from a geological point of view (read the press release).
Study coauthor Martin Stute, a hydrologist at Columbia University’s Lamont-Doherty Earth Observatory, explained the project's ramifications, saying, “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.”
This should eliminate the fear that has undermined CCS adoption from the beginning: that pure liquid or gaseous CO2 pumped deep into reservoirs could seep through fissures and cracks back to the surface and into the air.
With CCS almost dead in the water, in 2014 the Intergovernmental Panel on Climate Change issued a dire warning as the climate clock loudly ticked. The IPPC cautioned that without widely adopting and deploying CCS, the world may not be able to safely limit the global warming produced by old and new coal plants.
Until this breakthrough in Iceland, the primary culprit retarding progress was the chemically nonreactive geology at the sites selected for sequestration: sandstone, or deep, salty aquifers.
In that type of reservoir, when compressed, pure carbon dioxide is injected as a supercritical fluid, monitoring engineers are left hoping that massive layers of overhead rock (known as caprock) will seal in the loosey-goosey CO2 forever. But miscalculations can cause fractures and leaks, with normal injection rupturing a literally and conceptually fragile reservoir.
This isn't a theoretical problem. It's already happened in Algeria, when the In Salah CCS project was shut down in 2011 because sequestered CO2 fractured the caprock that should have locked it below ground forever.
Earthquakes are also a possibility. Chevron's CCS storage reservoir at its Gorgon LNG facility is about thirty miles from an active fault lying off the coast of Australia. Ultimately, after private insurers refused, the government had to step in and indemnify the project — forever — which may be the world's worst bait-and-switch insurance policy, if the movie Mad Max is an accurate preview of Australia's post-carbon politics.
Nervous scientists have also warned that Norway’s Sleipner CCS project, which stores pure carbon under the North Sea, risks leaks from fractures in the seabed rock.
To weaken the environmental case even more, coal plant CCS causes additional pollution, since most captured CO2 is piped directly to oil fields for enhanced oil recovery (EOR), causing heavy oil to flow up the well. Of course, this new oil is burned. In a good-news-bad-news scenario, one analysis claims that up to 185 percent more oil per well can be extracted using CO2 injection.
Parasitic heat loss
Still not convinced?
It takes a lot of energy to capture CO2 from the waste stream of a coal plant, where it is "captured chemically,” Bill Moomaw, author of a 2005 IPCC report on CCS, explained to Wired. Power plants equip flues with filters filled with amines that strip out and bind to the CO2 molecules.
Afterwards, the amines are released by heating the solution until the CO2 turns back into a gas, which is cooled down again — drastically, to about 30 to 40 degrees Fahrenheit — so that it becomes a pumpable liquid.
The energy loss is so great, according to Moomaw (who rounds-up to make a point) that you have to add a coal power plant for every three coal power plants using carbon capture and storage. Again, this isn't theoretical. At Saskpower's Boundary Dam CCS project in Canada, a 150-MW turbine was replaced with new one rated at 161.1 MW to account for parasitic load.
The secret sauce: dissolving CO2
Now that it's obvious why there are so few CCS projects, why has one popped up in Iceland? Because the country's sitting on top of a volcano, literally riding the magma (see Lamont-Doherty Earth Observatory video).
The 300 MW Hellisheidi geothermal power plant provides energy for Iceland's capital, Reykjavik, by tapping heat along with gas pockets 1.2 miles below the surface. The process releases steam, which makes up 99.5 percent of the emissions. The rest is mostly carbon dioxide and small amounts of hydrogen sulfide. So in spite of geothermal's green image, the process isn't completely clean.
Every year the plant produces 40,000 tons of CO2, which is just 5 percent of a coal-fired plant's emissions but still significant to the Icelandic government that pushed for the study.
Since Iceland's volcanic rock is almost entirely basalt, mixing and dissolving the gases with the water pumped from below caused the injected carbon to quickly form a whitish, chalky mineral as soon as it came into contact with the rock.
Researchers followed earlier lab experiments showing that, unlike the sedimentary rocks used in other projects, basalt contains plenty of calcium, iron, and magnesium to precipitate out injected carbon. The experiments also showed that large amounts of water should be added to suppress reservoir drift and up-migration while accelerating the chemical reaction, a key innovation trumping pure carbon dioxide.
At first no one knew how fast this might happen. Previous studies estimated that in most rocks, it would take hundreds or even thousands of years. In the basalt below Hellisheidi, 95 percent of the injected carbon was solidified within less than two years.
Edda Aradottir, who heads the project for Reykjavik Energy, initially thought solidification might take 8 to 12 years, which was already much faster than previous studies indicated. “People said they thought it couldn’t happen that fast,” she said. “Then, it happened much faster.”
In 2012, the project started with a proof-of-concept using pure, commercial-grade CO2. That worked, so the team started pumping power plant emissions of CO2, hydrogen sulfide, and other gases 500 meters deep into the basalt.
Cores drilled from the injected area showed the rock was heavily laced with whitish carbonate veins, apparently produced by the process.
To follow up, in 2014 Reykjavik Energy started injecting carbon dioxide at the rate of 5,000 tons per year. Monitoring indicates that mineralization hasn't slowed down, said Aradottir. The company plans to double the injection rate.
There is one possible glitch — or literal burp — marring Carbfix's rosy outcome: a separate study out this May identified subterranean microbes that release methane after feeding on carbonate minerals, which could cause reservoir digestive failure, so to speak.
Researchers found them in a completely different site, hot-tubbing and brunching in a California spring. Nevertheless, microbiologists from the Paris Institute of Earth Physics have already started studying the Carbfix microbes to see how they interact with carbon.
The great promise
Assuming for now that the self-indulgent California microbes are a nonstory, Sigurdur Gislason, a study coauthor, reaffirmed that the project's greatest promise would be with fossil-fuel-powered plants, smelters, and other heavy industries that produce far more emissions.
Although the main stumbling block is the amount of water required, he also said that seawater could be used, which would allow big cities, often located near oceans, to readily adopt the technology.
In a twofer, a 2010 Lamont study had already outlined basaltic seafloors off US coasts that could be used to take up emissions. Basically all the world’s seafloors are made of the porous, blackish rock, as are about 10 percent of continental rocks.
Researchers even found one ocean ridge covering tens of thousands of square kilometers that could store the total amount of CO2 already emitted into the atmosphere.
The storage potential of all the ocean's ridges is around 10 times larger than the CO2 emissions from burning all of Earth’s fossil fuel. There finally may be a light at the end of the climate-warming tunnel, although the outcome, according to Carbfix scientists, is a now matter of political will.
Is this already too little too late?
Images: Iceland geothermal plant, ThinkGeoEnergy; various, Kevin Krajick/Lamont-Doherty Earth Observatory