Carbon capture and storage (CCS) technology has yet to make its way into the industry mainstream. Projects around the world tend to be small in scale, and often the methods are too expensive for operators to consider them feasible.
However, new research funded by Reykjavik Energy could challenge this stance. By pumping captured CO2 underground and turning it into stone, the unique project could pave the way for a cheaper and more secure way of dealing with the masses of carbon dioxide produced from burning fossil fuels, and thus help reduce global warming.
Observations and methods
The study was performed in Iceland by a team led by Professor Juerg Matter from the University of Southampton who took their inspiration from nature.
“We know how nature's taking care of CO2 from the atmosphere over a geologic timescale, and that's through weathering,” he says. “Weathering helps to regulate the CO2 concentration in the atmosphere. Silicate minerals get dissolved, and that basically consumes CO2.”
From observations, the team decided they could probably mimic this process and speed it up. They injected CO2 into the basalt rocks which are rich in magnesium calcium silicate minerals, and if that reaction was fast enough it could allow for CO2 to be stored on a larger scale.
Matter began the research at Columbia University in the US, testing in the Columbia River Basalts, followed by extensive deposits in Washington and Oregon. These areas have basalt rocks which are rich in magnesium silicate materials, which are integral to this method of CCS.
The new study was performed in Iceland because Reykjavik Energy offered its geothermal power plant to provide the CO2 emissions.
“If you dissolve CO2 in water, the solution gets really acidic, which then dissolves the calcium magnesium rich silicate minerals out of the rock,” explains Matter. “If you dissolve enough calcium and magnesium out of the rock, the injected CO2 together with this calcium and magnesium basically forms limestone.”
Matter says that from an experimental point of view, it was interesting that the reaction happened quite rapidly. From laboratory experiments, the team knew that the limestone formation reaction would occur, but it was a lot quicker than they expected it to be.
“Within less than 2 years our 220 tonnes of CO2 were basically more or less converted to carbonate minerals,” Matter says. “That was a little bit surprising.”
Advantages and limitations
The main advantage of dissolving CO2 and injecting into basalt is that when it forms limestone, the process is not easy to reverse. As Matter says, “rocks do not leak out of the ground”.
“Convincing the public that we can safely and permanently store CO2 emissions in the form of rocks is quite a strong argument for this technology,” he says. “What we do is drastically reduce any risk of leakage.”
Statoil has been injecting CO2 into sedimentary reservoirs since the 1990s. This is the more conventional method of CCS, which involves injecting captured emissions into depleted oil and gas reservoirs, or in deep salient aquifers. Matter believes that forming rocks is a more permanent option, as there is no chance of the CO2 escaping.
“It would be reversible if you go to the subsurface reservoir and pour acid on the carbonate minerals,” he says. “That would dissolve them, but that's highly unlikely to happen.”
Another advantage of using basalt rocks is that they are found all over the world, on every continent. There are massive basalt formations in the North West of the US, such as in the Columbia River Basalts and at the Deccan Traps in India for example.
“Basically all the ocean crust is basalt, so that's why it's one of the most common rock types on Earth,” Matter adds. “In many oceans the ocean bottom below the sediment is basalt crust, so we have enough basalt to take care of a lot of CO2.”
However, not everywhere is an appropriate site for this method, including the UK, because the amount of basalt isn’t great enough to cope with the vast quantities of dissolved CO2 that would be acquired from fossil fuel plants.
If the subsurface gets “clogged up” with CO2, then no more can be injected, so there is a limit to how much CO2 can be stored at a basalt site. Matter says that this is an area of their experiments that needs further analysis.
“That has to be evaluated, because our pilot test was relatively small,” he says. “We have model calculations but we didn't really stress the reservoir enough in terms of seeing any effect on its storage capacity.”
Every CCS project has challenges in terms of timing, because certain infrastructure is required. Luckily, Matter and his team had an industrial partner so the method could be tested in a fairly realistic setting. However, it was still very time consuming to conduct an environmental impact study beforehand, and it took about a decade from initial discussions in 2006 to final tests and results in 2015.
“On an industrial scale, if you have certain experience, it could be much faster,” explains Matter. “But there were also of different challenges, not only technological and scientific ones;for example we had the economic crisis in Iceland, which delayed things, too. So there are a lot of challenges that you face during such a project.”
A rocky past for CCS
Currently, Reykjavik Energy and the team are working on anew, up-scaled version of the study. The goal is to capture and inject up to 10,000 tonnes of gas per year, which is a massive jump up from the 220 tonnes that were converted to limestone during the research.
However, it won’t necessarily be plain sailing from here on, because CCS projects have a habit of being scrapped. The UK's £1bn carbon capture storage fund was cancelled by the government last November, as was the massive Drax CCS project.
Matter says the upcoming challenges for the team will come in the shape of missing economic support and the right government direction, rather than any technological setbacks.
“If you look at the Intergovernmental Panel on Climate Change fifth assessment report, all the future scenarios for our climate show that we have to reduce our CO2 emissions to avoid significant global warming,” he says. “We certainly have to do a lot of mitigation to reduce the impact of global warming.
"It’s not a technological challenge or barrier that really hinders the development of more of these projects, but I think it is a policy issue and an economic one, because we do not really have the legislation in place.”
CCS projects also cost a lot of money to set up, so there is uncertainty about how they will be funded. The most costly factor is how the CO2 is actually captured in the first place, which can cost between $50 and $150 per tonne of CO2.
Coal plants, depending on their size, can emit hundreds of thousands to a million tonnes of CO2 per year, so one CCS project alone would not be enough to cope with the load.
“To have an impact on CO2 emission reduction, we need a couple thousand of these projects,” Mater says. “So it's a huge, huge challenge.”
Regardless, Matter is confident about the accomplishments of the project and about its future success on a much larger scale.
“In terms of convincing the public - and generally the public is really sceptical on new technology - I think we have quite a good and strong argument or point to show,” he concludes.