December 6, 2021


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Filter carbon dioxide from the air

The world’s largest system to filter and store carbon dioxide from the air has been commissioned in Iceland (Imago Photo)

In a small town near Zurich, Climeworks operates a pilot plant that captures and stores 900 tons of carbon dioxide from the air each year. In other words, a system by which past CO2 sins can be fixed, so to speak. However, the resource requirements are significant. Among other things, 250 liters of water is needed to filter a ton of carbon dioxide from the air, explains Professor Felix Kreutzig of the Mercator Institute for Climate Change Research in Berlin, who conducted a life-cycle analysis of direct air capture systems. Efficiency can be greatly increased through renewable energies. The electricity demand for such systems could still be used more rationally, but in the future, in the second half of this century, such systems could become important.

Very large amounts of carbon dioxide can be filtered from the air

Ralph Krauter: How do air filter systems that have considered the consumption of their resources work?

Felix Kreutze: These are systems that filter carbon dioxide from the air by binding this carbon dioxide to absorbent chemicals. These absorbents are then released again under the action of heat and transported away in a concentrated stream, so to speak, so that they can be stored somewhere. Systems differ in which sorbent is taken and the temperature needed to dissolve the sorbent chemicals back in, there are high temperature regimes and those that pass are only 100 to 120 degrees.

Krauter: How much carbon dioxide can in principle be filtered from the air with such devices?

Kreutzig: The good thing about this technology is that it’s unlimited in principle, which means that we can really, very large amounts of carbon dioxide from the air. The problem, of course, is that it costs and also requires a certain amount of material. But there are no fundamental limits to what can be filtered.

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250 liters of water for one ton of carbon dioxide

Krauter: First of all, you have precisely identified the necessary resources, for example, to filter tons of carbon dioxide from the air. What do you need for that?

Kreutzig: You need different resources, metal, water, there is also a certain amount of air pollution. To name a few, about 250 liters of water is needed for one ton of carbon dioxide. It is also important that the process requires energy, which also produces some carbon dioxide, which is why a ton of filtered air comes in only from 700 to 900 kg, depending on how it is actually done underground.

Krauter: In other words, the technology isn’t incredibly effective yet?

Kreutzig: It’s not that efficient, but there is an option to do it more efficiently. We have considered that, and the central option of course is to put the power source primarily on renewable energies with solar and wind plus the required heat, for example with heat pumps, so that you can significantly increase efficiency. This is of course one of the desired goals here.

Electricity requirements can now be used more rationally

Krauter: Let’s talk about not very low power requirements, which you can also define more precisely for the first time. A total of 1,000 kWh per ton of CO2 caught from the air is included in your analysis. Is this more or less compared to other climate protection measures?

Kreutzig: This is too much. So that’s the big problem with this technique, otherwise it looks great. It has a very high demand for electricity, and here I would also say that this technology should not use this electricity now, it is more logical to use heat pumps in buildings, for example, to supply electricity to the transport area, so we will need the additional electricity that we produce now. But: if we actually implement these measures in 2040 with normal standards, in quotation marks, climate protection measures, we can also use electricity, for example, photovoltaics and wind to use air capture systems.

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Possibility in the second half of the century

Krauter: So if we look to a somewhat distant future, where a lot of green electricity is available from solar or wind power, this technology could become important. What potential do you see for capturing live air in the medium and long term?

Kreutzig: I see a relatively large potential, partly because it is compared to other, often discussed, bioenergy and bioenergy with carbon capture and storage, ie linking carbon dioxide to wood block burning, for example, compared to this technology, direct air capture very little Land is intensive, uses far fewer land resources and is more technologically scalable, and there are better learning curves here. That’s why I see direct air capture, if at all, as a possibility to stabilize the climate in the second half of the century. So you should go in that direction.

Avoid carbon dioxide now

Krauter: The technology is currently being tested on a larger pilot scale, including in Switzerland. What needs to happen now so that we can actually tap into this potential, which I just identified, in ten or twenty years, when we hope to have a lot of green electricity available?

Kreutzig: We have to think in two directions here. I have previously argued that climate protection should now focus above all else on conventional measures to avoid carbon dioxide emissions. However, at the same time, we must think about what needs to happen next after 2040, 2050, that is, we now really need research initiatives and the opportunity to experiment with what also works on a large scale. This means that we must continue to invest in research into capturing live air in an affordable and efficient manner.

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Think about research investments

Krauter: Does what you have found now have anything to do with the current climate conference in Glasgow? And if so, what is the substance that you will cut down to the negotiators there?

Kreutzig: The point is that, on the other hand, the climate goals to 2040 and 2050 are ambitiously contemplated – this would actually work independently of direct air capture – but at the same time outside of these targets, research investments are also being considered, Which will then follow, likely offset carbon dioxide emissions in 2050 and this also enables rich countries, which also have accumulated a lot of carbon dioxide debt, to make their contribution thereafter.

The statements of our interlocutors reflect their own views. Deutschlandfunk does not take statements made by its interlocutors in interviews and discussions as its own.