Capturing CO2

To limit global warming, we need to emit less carbon dioxide (CO₂) in future and also remove large amounts of CO₂ from the atmosphere. This is the only way to prevent temperatures from rising by more than two degrees Celsius. Researchers involved in the DACStorE project are working on a technology to help achieve this aim.

In May 2024, a Swiss company’s plant called “Mammoth” was put into operation in Iceland. It is designed to pull 36,000 tonnes of carbon from the atmosphere annually, which is then permanently stored underground. It is the largest of around 20 direct air capture and storage (DACS) plants worldwide to date.

As a greenhouse gas, CO₂ is a major cause of climate change. Removing it from the atmosphere and storing it underground at first seems to be a simple solution to climate change. “But this is an unrealistic assessment,” says Jülich scientist Dr. Freia Harzendorf from the Institute of Climate and Energy Systems (ICE-2): “DACS technology is not a solution that allows us to continue as before without needing to undergo an energy transition and change our way of life.” She cites three reasons for this: Firstly, DACS systems require a lot of energy. If they use energy from fossil sources instead of renewables, then this does not help to protect the climate – quite the opposite in fact. Secondly, the systems are very expensive, as is their operation. It is usually cheaper and more sensible to avoid CO₂ emissions into the atmosphere in the first place. Thirdly, it is uncertain whether there is sufficient suitable storage space for enormous quantities of CO₂.

Despite these limitations, DACS systems are an important component in the fight against climate change. According to the Intergovernmental Panel on Climate Change (IPCC), without the removal of CO₂ from the atmosphere, it will not be possible to limit the human-induced global temperature increase to below 2 degrees Celsius above pre-industrial levels in the medium term. In the Paris Agreement, most countries made a commitment to limiting global warming to 1.5 degrees Celsius. Germany wants to help ensure this goal is reached through its Federal Climate Change Act, which outlines an aim to achieve greenhouse gas neutrality by 2045. Germany would then no longer contribute to an increase in the concentration of greenhouse gases in the atmosphere. This goal can be achieved in two ways: either no more greenhouse gases are emitted at all, or emissions that are difficult to avoid are offset by measures that remove greenhouse gases from the atmosphere, i.e. through what are referred to as “negative emissions”.

CO₂ emissions that have been particularly difficult to avoid so far are those in some areas of agriculture as well as in the ceramics, chemicals, and glass industries. “Our analyses have shown that DACS processes offer a way of offsetting such CO₂ emissions from as early as 2035,” says Harzendorf. Jülich system research studies have shown that in Germany, around 57 million tonnes of CO₂ will have to be removed from the atmosphere and stored in order to achieve greenhouse gas neutrality by 2045. According to the Jülich calculations, the capture costs for each tonne of CO₂ using the DACS process, which is used, for example, by the Mammoth plant in Iceland, will average € 290 per tonne of gas in Germany. “Nevertheless, DACS processes are a promising option,” Harzendorf believes.

However, to extract the calculated amount from the atmosphere by 2045, this would require more than 1,500 plants with the same capacity as the Mammoth plant. In the DACStorE project, Forschungszentrum Jülich, five other Helmholtz centres, and TU Berlin are therefore working on a rapid, ecologically and economically sustainable ramp-up of DACS technology. Freia Harzendorf is the scientific director of the project. The aim of the DACStorE project is to further develop the technology and explore various approaches to reducing energy consumption and costs. In addition, the scientists are also analysing social acceptance levels and drafting recommendations for legal regulations and political measures.

At Jülich, the researchers are currently identifying the best DACS locations worldwide and designing systems that are optimized for the respective conditions. Harzendorf’s team takes into account the most efficient and reliable supply of renewable energy, the availability of storage sites, and the transport routes to them. “Regional differences in temperature and humidity also play a role,” says Harzendorf. Initial analyses already show that the energy requirements of DACS plants in different German regions differ by up to 15 % due to the respective weather conditions alone.

Text: Frank Frick / Pictures: © 2024 Climeworks AG; www.fotostudio-juenger.de

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