Carbon capture and storage: why is it such a key pillar of Net Zero plans?
Putting carbon dioxide deep into the ground is one of many tools that will help us on our path to Net Zero. But how did it come to be such a big part of emission reduction plans, and is it safe?
At COP26 last year, two words were on everyone’s lips — Net Zero. In order to achieve this ambitious but necessary target, we need to reduce emissions of carbon dioxide (CO₂). But that is easier said than done.
The natural world plays a major part in capturing and storing CO₂. But due to the amount humans have put into the atmosphere since the industrial revolution, we need to give nature a hand.
Every day industry and power generation releases CO₂ into the atmosphere. Some of the biggest emitters — like coal-fired power stations — are rightly being phased out as we increase our reliance on renewable energy (though there’s still some way to go). But heavy industries like steel and concrete production are a much thornier problem, and very difficult to fully decarbonise.
Carbon dioxide capture and storage (CCS) technologies are one of the most promising ways we can buy ourselves the time needed to make major changes to our infrastructure and adapt to living in a carbon-constrained world.
It’s estimated CCS could capture up to 90% of CO₂ released during the burning of fossil fuels in electricity generation, and some think they could even be used to help us go beyond Net Zero into negative emissions. But CCS technologies are sometimes seen as a little unpalatable compared to things like renewable energy and tree planting. What’s made them such a central part of Net Zero plans?
How does the technology work?
Carbon dioxide capture and storage is the collection of CO₂ produced by industrial plants, power stations and other sources, which is then stored deep underground. CO₂ is captured at the source and compressed into a liquid state. The liquid can then be transported, via pipelines or ships, before being injected into porous rock deep underground.
Suitable storage sites contain rocks with tiny pores, such as sandstone, which can be filled with dissolved CO₂. These need to be topped with layers of impermeable rock such as clay or shale to stop CO₂ from escaping back into the atmosphere. It will then stay stored underground for a geologically long time — hundreds of thousands to millions of years. Oil and gas have been trapped underground for hundreds of millions of years by impermeable rocks such as those that are now being used to trap carbon dioxide.
The sites that are suitable for storage in the UK are mainly offshore — depleted oil and gas reservoirs, coalbeds or deep saline aquifers, where the geology is appropriate. We know these sites have been stable for a very long time, as the geology has previously stored fossil fuels for up to hundreds of millions of years.
Do we have to store the captured CO₂ underground?
Although there is plenty of space to safely store the captured carbon dioxide underground, there are ways it could put it to use.
One option is to sell it to other industries that can use the CO₂ to manufacture plastics, boost their greenhouse crop yields or even put the fizz in your soda. For example, Climeworks is using the CO₂ they capture to put the bubbles into drinks bottled by Coca Cola HBC Switzerland.
Another option is using the CO₂ to feed algae which can then be harvested and turned into biofuel.
The world’s first carbon capture and storage project
The first commercial CO₂ storage project began operation in 1996 at the Sleipner gas field in the Norwegian sector of the North Sea. It was opened as a direct response to environmental legislation.
Since then, around 1 million tonnes of CO₂ from natural gas have been captured and stored every year. The total amount now stored there is equivalent to the annual emissions from ten million cars.
The site was the first demonstrate that CO₂ could be stored long-term in deep underground rock, and is considered a benchmark for the industry and legislation.
Is carbon capture and storage safe?
Concerns about the safety of CCS technology, specifically the storage part, have been raised by the public. Comparisons have been made with other technologies that concern geological structures, such as hydraulic fracturing (“fracking”), as well as concerns about what would happen if the CO₂ leaked out.
But there is good evidence for its safety. CCS has been used successfully and safely at the Sleipner carbon storage site for over twenty-five years. Since its inception, it has been closely monitored, including by scientists from the British Geological Survey.
Using advanced 3D imaging studies, BGS characterised the store before injection and tracked the location of CO₂ after injection in the subsurface. Their work helped show that all of the captured CO₂ is securely confined within the storage reservoir.
This key evidence demonstrated the safety of CO₂ storage, changing the way it was seen by scientists and policymakers. But what about the public?
In a new public dialogue last year, commissioned by the UK Government and UK Research and Innovation’s Sciencewise programme, there was support for CCS, on conditions that included ensuring the technology was safe, guaranteed contribution towards Net Zero and clear benefits to local communities.
Will it stall progress?
Some have raised concerns that CCS makes it too easy to continue the status quo, and will encourage industries to drag their feet on ditching fossil fuels. But projections show that even if we work as fast as possible to implement the UK’s Net Zero plans, we can’t achieve them without CCS.
This is partly due to complex industries like steel and cement mentioned above. They require intense heat generation that is difficult to do without burning fuel. For both steel and cement, CO₂ is a siginificant by-product of the chemical process, so it’s practically impossible to get it to Net Zero. And one of the main ingredients used to turn iron into steel is coal. At present, cement and steel are responsible for around 15% of global CO₂ emissions.
Experts are working hard to find ways to make these industries sustainable, from electric arc steel furnaces to finding alternatives to limestone-based cement. But a lot of new technology will need to be developed and entire plants will have to be replaced, all without harming our ability to keep up with our need for infrastructure and homes.
This enormous undertaking has a timescale of decades, and in the meantime, old factories and power stations are here to stay. Carbon dioxide capture and storage is the only feasible way to minimise the harm they’re doing to our climate. Far from being a replacement for renewable technologies and nature-based solutions, carbon capture and storage is a vital part of implementing these approaches and giving them time to work.
What next for Carbon Capture and Storage?
Projects are now underway to find the most suitable areas for storage of captured CO₂. There are more than 500 potential storage sites in the offshore UK.
Thanks to the UK’s offshore geology, it has one of the biggest storage potentials in Europe. The British Geological Survey (BGS) hosts CO₂ Stored, a state of the art database that uses geological data to show potential UK storage sites that could store over 70 billion tonnes of CO₂ deep under the UK seabed.
CO₂Stored was developed by The British Geological Survey and The Crown Estate through funding from the Energy Technologies Institute, and the database is now hosted and developed by BGS.
In Scotland, several companies and research organisations, including Pale Blue Dot Energy Ltd, National Grid Plc and the University of Strathclyde, are developing offshore pipeline, subsea and well infrastructure to transport and inject CO₂ offshore for long-term secure storage.
One example of a storage site is the saline aquifer ‘Endurance’, which is in the southern North Sea, around 145km offshore from Teeside. Endurance has the capacity to store 450 million tonnes of CO₂.
Projects in the northeast of England aim to capture two million tonnes of CO₂ annually by 2026, enabling a reduction of Teesside’s emissions by one third through a partnership with industrial stakeholders.
CCS is an evolving area of research that is expected to play a significant role in helping the UK meet its climate and environmental targets. Increased use of this technology is crucial to enabling the enormous changes that will have to take place in coming decades. CCS is considered an essential tool to prevent atmospheric concentrations of CO₂ from reaching a tipping point.
Want to know more?
If you’re a UK taxpayer, your contributions helped fund this work, via UK Research and Innovation — the funding body that allocates government funds for research — and the British Geological Survey, the Engineering and Physical Sciences Research Council and the Natural Environment Research Council.
You can listen to broadcast journalist Kim McAllister and the British Geological Survey’s Professor Mike Stephenson on the Emission Impossible podcast where they discuss ‘How can we get CO₂ safely back into the ground?’ Or read the Sciencewise article ‘New public dialogue finds public giving conditional support to the roll-out of carbon capture usage and storage.’
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