Carbon capture, storage, and utilization

The level of CO₂ in the atmosphere is at its highest since the 19th century due to the combustion of fossil fuels.

Carbon capture and carbon storage are technologies that are regarded as useful in reducing carbon emissions and thus global warming.

At DTU, we conduct research into carbon capture, carbon storage, and how to utilize non-stored CO₂ to create new chemicals and green fuels.

What is carbon capture utilization and storage?

The abbreviation for Carbon Capture Storage is CCS.

Recently, however, a ‘u’ has begun to be added, so that the abbreviation is CCUS, which stands for Carbon Capture Utilization and Storage, because it is expected that, in future, CO₂ will become a valuable resource that will not only be captured and stored, but must also be utilized as part of the climate action.

Today, carbon can be captured from the smoke from industries and from CHP plants, or it can be separated from biogas plants instead of just emitting the CO₂ into the air.

Take biogas for example. It consists primarily of the greenhouse gases methane and CO₂. Biogas can be burned off immediately to generate heat, but it is also possible to upgrade it by separating the two gases. Methane can, for example, be utilized in natural gas supply, while CO₂ must be captured instead of simply being emitted into the surroundings.

One way of capturing CO₂ is to conduct it through long pipes down to a liquid, which, among other substances, consists of various additives that help absorb the CO₂ in the liquid. When the CO₂ has been absorbed in the liquid, it can be separated and stored underground. This is done by pumping the CO₂ into the many small cavities of the underground, while the above clay layer acts as a lid.

Calculations from GEUS have shown that the underground in Denmark can probably contain up to 22 billion tonnes (GT) of CO₂. This is equal to between 500 and 1000 years of the total Danish emissions at the current level. Therefore, work is being done to commence carbon storage in Denmark.

Instead of storing the CO₂ from the biogas absorbed in the fluid, it can also be recovered in a purer form without sulphur and other biogas residues, which turns it into a resource (that is a product) which can be resold and utilized for other purposes such as for production of chemicals and, in the long term, also green fuels (Power to X).

At DTU, the researchers are therefore studying how CO₂ can be both captured most efficiently, stored, but also utilized as a future resource.

Why is carbon to be captured and stored?

CO2 can be captured by treating flue gas with a liquid. This takes place in a kind of filter called a scrubber. Here the gas is washed with the liquid, the liquid being poured over a structure with a large surface as the gas passes by. The CO2 dissolves in the liquid and thus the gas is purified.

There has been increasing interest in carbon capture since the UN’s Climate Change Panel announced in 2018 that carbon capture is unavoidable if we are to limit global warming.

The level of CO₂ in the atmosphere is at its highest since the 19th century due to the combustion of fossil fuels. There is general agreement that atmospheric CO₂ is the main cause of global warming.

The vast majority of countries have acceded to the Paris Agreement, which means the temperature increase must be kept to below 1.5 degrees C. For this to be realistic, current emissions of CO₂ and other greenhouse gases must be stopped.

The Danish Government has therefore undertaken to meet a climate goal of reducing carbon emissions by 70 per cent by 2030, and emissions must be zero by 2050.

Research and further development of carbon capture utilization and storage are essential in achieving these goals.

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How far has Denmark come with carbon capture?

Towards 2030, Denmark will primarily be reducing emissions by capturing and storing CO₂ underground. The reason is that carbon capture and storage is an existing technology that is now to be tested and scaled up. DTU contributes to this development.

For example, DTU has developed a mobile plant that can capture CO₂ from biogas plants and power plants and acquire important operational experience. One of the challenges is to reduce energy consumption so that carbon capture does not become expensive. Therefore, one of DTU’s research areas is how to compose the chemical liquids used to capture CO₂ and how to use heat pumps, etc. to minimize energy consumption. Research is also being conducted into how carbon capture can be linked in an integrated energy system.

RELATED ARTICLE: Carbon capture - climate gain and good business.

How far has Denmark come with carbon storage?

On the carbon storage side, there is experience from abroad. The Geological Survey of Denmark and Greenland (GEUS) is therefore cooperating with DTU to establish the technical potential for carbon storage in the Danish underground.

Calculations from GEUS have shown that the underground can probably contain up to 22 billion tonnes (GT) of CO₂. This is equal to between 500 and 1000 years of the total Danish emissions at the current level.

How far has Denmark come with carbon utilization?

The technologies for using and utilizing CO₂ to produce, for example, green fuels are not yet so developed that they can contribute with significant reductions. Therefore, carbon utilization is a research area for DTU.

An example of carbon utilization is that electrolysis can be used to convert power from wind turbines and solar cells into green hydrogen, after which gases and liquid fuels can be produced by adding carbon from CO₂ to the hydrogen (Power-to-X).

Research will help ensure that Denmark is ready for carbon utilization as a resource towards meeting the climate goal of being carbon neutral by 2050.

What are the future prospects for CCUS?

Towards 2030, researchers are working with industry and authorities to develop and test already known carbon capture and storage technologies, so that they can scaled up and contribute with the necessary reduction as soon as possible.

At the same time, research is being conducted into how the technologies can become as sustainable and effective as possible. For example, some of the latest advanced capture technologies have disadvantages in terms of high temperature and pressure, as well as use of solvents and other chemicals. In the long term, more environmentally-friendly solutions involving enzyme technology and microbial biotechnology must be developed in this field.

In the longer term, CCUS systems in Denmark must be an integral part of a green energy system, as carbon capture is quite energy intensive. The carbon capture of the future will run on green power as part of the electrification of society.

By 2050, the research is expected to have come so far that CO₂ will become a raw material for production of sustainable fuels. Therefore, infrastructure and secure transport of captured CO₂ must be planned, but also in integration with hydrogen storage and Power-to-X production facilities.

In the even longer term, there will also be a need to develop technologies for direct air carbon capture, as the current technologies are all targeted at carbon sources, such as energy-producing plants, industry, etc.

In a future fossil-free society, we are likely to see a carbon shortage because it is utilized for fuels and other purposes. At that time, captured ‘green’ CO₂ will be the only way to reduce atmospheric levels of CO₂ and the only source of CO₂ as a raw material.