Please explain the meaning of carbon capture and storage briefly.
Tobias Pröll: Carbon capture and storage, or CCS for short, means capturing CO₂ that’s generated in industrial processes and in energy production directly at the smokestack for subsequent final storage. Following its capture at the source (for instance in thermal powerplants, in cement factories, or in the chemical industry) CO₂ is typically transported via pipelines or ships to final storage sites where it’s supposed to be permanently stored in deep geological formations such as former oil fields or deep saline sandstone layers.  

The expert

© Silke Bernhardt, silberfoto.at

Tobias Pröll, Professor of Energy Engineering at the University of Natural Resources and Life Sciences (BOKU) in Vienna, deals with energy on a daily basis. Besides avoidance of CO₂ emissions, the development of efficient carbon capturing methods is one of his focus topics. In his view, these are the key questions: How do we finally start implementing large-scale energy transition? And: How do we achieve democratic majorities for that?

In your view, what are sensible uses for CCS? Say, Norway having announced plans for compressing large amounts of carbon dioxide from industrial plants in deep geological formations under the seabed.
CCS comes into play whenever carbon dioxide exists in concentrated form, in other words whenever we classically use coal, oil, and gas as energy sources. More than 90 percent of that serves the purpose of providing energy, including in industrial settings. There, CO₂ is generated in exhaust gas where its concentration exceeds that of the ambient air by a factor of 100 to 500. Technically, it’s like this: the lower the concentration at the source the more energy-intensive the process of removing the CO₂.

How often is the CCS method being used at this juncture?
CCS doesn’t exist yet in this form. There are a variety of demonstration projects; the major ones being in Canada and the United States where CO₂ is separated from exhaust gas but subsequently reused for oil production. It’s injected into oil fields for the purpose of producing more oil. In Europe, we could immediately start capturing and compressing the relatively concentrated CO₂ that’s generated in bioethanol production. It’s being blown into the atmosphere although exactly that would be the low-hanging fruits. That could be a starting point.

CO₂ in empty North Sea gas fields

© Porthos

In Rotterdam, construction of the infrastructure for the Porthos CO₂ transportation and CO₂ storage project was launched this year. Via a compressor station, Porthos transports the captured CO₂ through the port of Rotterdam to an offshore platform at a 20-kilometer (12-mile) distance from the coast. From that platform, the CO₂ is permanently stored in empty gas fields three to four kilometers (1.9 to 2.5 miles) below the North Sea floor. Porthos is planned to be launched in 2026, store some 2.5 million metric tons (2.8 million short tons) per year for 15 years, i.e. some 37 million metric tons (41 million short tons) in total. Thanks to Porthos, the Rotterdam port industry is supposed to emit around 10 percent less CO₂.

Professor Tobias Pröll comments: “Underneath the North Sea floor, there are some porous sandstone formations that used to be filled either with hydrocarbons or are still filled with saltwater. When the cover layers above them are sufficiently diffusion-resistant CO₂ can be stored there with a high probability that it won’t rise again. Experts agree on that. After all, the natural gas was safely deposited there for millions of years as well. If the CO₂ stayed down there even for just several ten thousand years that would effectively counteract global warming. It’s important, though, that CO₂ storage can be only a small part of the total solution. We should prioritize switching as soon as possible from burning fossil energy sources to renewable energies – including all supporting actions. For the rest that’s economically inevitable and for CO₂ from biogenic sources, carbon capture and storage is necessary.

Are there any environmental risks in relation to CCS technology?
Certainly, because there’s no technical measure that entails zero risk. However, the risk of CCS and its probability must be communicated effectively. Dieter Helm, a British economist, said that it’s better being roughly right than being definitely wrong. In the case of the climate crisis, business as usual would definitely be wrong. That entails the biggest risk of us crashing into the wall at full speed. We cannot ignore potential solutions that are supposed to make only a contribution due to potential residual risks. But it’s also clear that just capturing CO₂ will not solve a climate crisis. Capturing CO₂ is just one of the instruments in an orchestra. For the kind of CO₂ streams that we can realistically anticipate also in the climate-neutral future from 2040/2050 on, CCS makes sense. Take waste incineration or cement production for example: Even if I wanted to burn cement with hydrogen, CO₂ could not be avoided because it emanates from the limestone. For that CO₂, we need solutions in the form of CCS.

There are various technologies for capturing CO₂. The direct air capture (DAC) method removes carbon dioxide directly from the ambient air. What’s your take on that technology?
Es ist ein großer Unterschied, ob man stark konzentriertes Kohlendioxid aus einem Industrieprozess oder Kraftwerk abscheidet oder eben aus der Umgebungsluft. DAC ist eine derzeit stark gehypte Technik, bei der man CO₂ direkt aus der Luft Capturing highly concentrated carbon dioxide from an industrial process or powerplant, or from the ambient air, makes a big difference. DAC is currently a heavily hyped technology of capturing CO₂ directly from the air. Technologically, that’s feasible but energy-intensive. DAC requires at least three times as much energy as capturing carbon from smokestacks. In reality, it’s probably even ten times more. DAC only pays off where there’s practically a surplus of renewable energy with no meaningful use for it, such as in Iceland (See info box “CO₂-suction systems in Iceland,” editor’s note). Many countries like Germany for example still have an energy-limiting setting and in a setting like that DAC is currently still in a poor position.  

World’s largest CO₂ suction system

© Climeworks

Mammoth, the world’s largest plant capturing CO₂ from the ambient air, was launched in Iceland this year. Swiss company Climeworks already operates a similar facility in Iceland named Orca that used to be the world’s biggest air filtering plant. Mammoth, however, is ten times larger and therefore able to suck a correspondingly larger amount of carbon dioxide from the air. The plant is designed to filter 36,000 metric tons (40,000 short tons) of CO₂ from the air per year. The collected CO₂ is subsequently dissolved in water and injected into layers of rock where the CO₂ practically becomes petrified, which permanently binds the greenhouse gas.

Professor Tobias Pröll comments: “The process requires massive amounts of energy that, however, is available in Iceland in abundance in the form of geothermal energy. That’s why a project like that only makes sense in places where a surplus of renewable energy exists all year.”

What do you mean by energy-limiting setting?
Energy must always be included in our way of thinking. Whether a process consumes a lot of renewable energy, such as surplus electric power or green hydrogen, is an important consideration. We’re currently living in a fossil reality in which we’re covering about 80 percent of our primary energy demand globally by coal, oil, and natural gas. In that reality, reasoning must be different than in a reality that we may find ourselves in perhaps in 30 years from now when technically available surpluses of renewable energy will in fact be available. Once we’ve achieved that we can reimagine many things that are not feasible today, including DAC. Proposing technologies now that consume additional energy misses the point. After all, we’ve got the climate crisis because we supply ourselves with fossil energy.

If I asked you what captured CO₂ could be used for, what would you say?
Storing and locking it up. There’s definitely no demand for the amounts in which we produce it. There is a market for pure CO₂ but its size is minute. CO₂, for instance, is needed for carbonic acid in the beverage industry. However, the CO₂ emissions of one cement plant could supply all of Europe for that purpose. A second cement plant would already pose a problem, meaning that we’d simply have more CO₂ than we could sensibly use in products in any way.

How do you mean that?
You must always add energy to re-refining CO₂, like for producing synthetic aviation fuels. In that case, CO₂ and hydrogen can be combined chemically to create kerosene in several process steps. However, all the energy is supplied by the hydrogen. In the beginning, we need more energy in the form of hydrogen than we’re subsequently going to have in the kerosene. CO₂ supplies no energy. Carbon dioxide may be an auxiliary substance helping to enhance hauling or using hydrogen as a liquid energy source. But basically, the energy must always be supplied by the green hydrogen that’s on everyone’s lips but that’s practically not available, particularly not at prices that could compete in any way with the current prices of fossil energy sources. Fully packing CO₂ into those kinds of fuels is going to be very difficult, requiring awesome amounts of hydrogen.  

Yet exactly those kinds of ideas exist?
Sure, large international corporations have ambitions in that regard, for instance in Patagonia, of producing hydrogen by means of wind power and producing liquid fuels from that hydrogen that could then be hauled from South America to Europe. All of that depends on the price at which we’ll be able to provide green hydrogen.

But then, how are we going to control our CO₂ emissions?
I believe that we need CO₂ management, meaning that there’ll be CO₂ pipelines, and we’re going to store CO₂ in geological formations as described above. We’re going to have to capture CO₂ from industrial facilities because cement production or waste incineration plants have no alternatives to decarbonizing that process in any other ways. I doubt that we’re going to capture CO₂ on a large scale from the air using DAC.

Are there any countries in Europe that have launched carbon capture projects?
Many countries with North Sea coastlines have programs and are engaged in the CO₂ storage business. In Denmark, there’s the “Greensand” project planning to store up to 13 million metric tons (14 million short tons) of carbon dioxide in the Danish North Sea by 2030. Norway has already offered carbon dioxide storage to Germany as well.

What capacity would carbon capture systems using currently available technology have to have to remove all excess CO₂ from the atmosphere?
I can’t answer that. What I can say is that to compensate for the worldwide emissions you’d have to filter 50 billion metric tons (55 billion short tons) from the air per year. That’s what we’re currently causing. For comparison: In full operation, the Icelandic project with the CO₂ suction system achieves 36,000 metric tons (40,000 short tons) per year.