Q & A on CCS

Technical Articles

The abbreviation “CCS” refers to the capture and subsurface storage of CO2, and the technology contributes to reducing carbon emissions into the atmosphere. The 2020 Danish climate agreement for energy and industry, etc. includes a commitment to including CCS technology as a key aspect of Denmark’s work to achieve its climate-political goals.

We have collected a series of questions and answers concerning the technology behind CCS and the potential in Denmark.

In June 2021, a political agreement was entered comprising a range of initiatives, including the launch of the process to grant licences for CO2 storage in subsea areas of the Danish section of the North Sea. This would allow storage in depleted oil and gas fields to commence as early as in 2025.

What is CCS?

CCS is short for “Carbon Capture and Storage”. Through the application of CCS technology, CO2 is collected and stored in underground deposits. If the CO2 collected is used directly rather than stored, the process is known as CCU (Carbon Capture and Utilisation).

How does CCS work?

CCS technology comprises three main phases:

Capture: Carbon dioxide (CO2) can, for example, be collected or “captured” from large point sources such as power plants and industrial production facilities. For instance, it may stem from power plants using fossil fuels, waste or biomass, or from large, energy-intensive industries and biogas plants.

Transport: Pipelines, trucks and ships can all be used to transport large volumes of CO2. In gas form, CO2 can be transported through pipelines in the same way as any other gas. If it is to be carried by trucks or ships, the CO2 first needs to be cooled down and compressed. Cooling CO2 transforms it into a liquid, which takes up significantly less space than its gaseous form.

Storage: CO2 must be stored in suitable, tightly sealed geological structures that are often located several kilometres below the surface. Facilities for storing CO2 can be established both onshore and offshore.

The illustration shows the process:

1. CO2 is captured from CO2 sources such as industry or energy production
2. The gas is compressed and transported to a suitable reservoir
3. CO2 is injected into the reservoir


CCS technology process

Illustration: GEUS


How do you capture carbon dioxide?

The method for extracting CO2 from flue gas and then collecting it is based on a number of well-known technologies. Some of them are already effective and in widespread use, while others still require additional development to become fully efficient and competitive.

The most common and mature technology for capturing CO2 is, where the carbon dioxide is “washed” out of the flue gas following combustion of fuel (Post combusting). This technology makes it possible to capture 90 percent or more of the CO2 emitted.

It is also possible to capture CO2 through pre-gassing before the combustion of fuel (Pre combusting), or by replacing the air supply in the combustion process (Oxyfuel combusting). However, both these methods require substantial alteration of existing set-ups or the construction of completely new power plants.

Last but not least, it is possible to capture CO2 directly from atmospheric air (Direct Air Capture – DAC). This involves passing the air through a chemical solution or through a filter that binds the CO2. This technology is energy-intensive and expensive, but contains appreciable potential for achieving what are known as “negative emissions”.

How can CCS contribute to combating climate change?

A number of initiatives are being run in parallel in Denmark with the objective of limiting the emission of CO2 to the atmosphere. The emphasis in recent decades has largely been on energy efficiency measures and transitioning to renewable sources of energy.

CCS technology has the potential to make a significant contribution to achieving Danish goals for reducing greenhouse gas emissions. In fact, application of CCS can actually remove CO2 from the atmosphere. This means that the CO2 captured and stored can be deducted from the overall carbon accounts.

How widespread is CCS?

According to The Global CCS Institute, there were about 65 CCS facilities either in operation or under construction around the world in 2020. The technology has, in principle, been in use since 1930s, when it was used to purify the air in submarines.

There are no full-scale CCS projects operating in Denmark as yet, but a number of demonstration projects have been launched, working with the different main phases in CCS. In 2020, funds were made available via the EUDP research programme for a number of projects focusing on both the capture of CO2 and its long-term storage. It will also be possible to apply for funding via EUDP in 2021 and 2022.

Injection of CO2 can also be used for EOR (Enhanced Oil Recovery). The method has not been used in Denmark, and the purpose of injecting and storing CO2 is not to enhance the oil and gas production.

What is the potential for CCS in Denmark?

The future potential for the capture of CO2 is difficult to predict, as it depends heavily on factors such as the development of the industrial and energy sector.

CO2 must be stored in suitable and clearly limited geological structures located between 800 and 3,000 metres subsurface. In addition, there must be a sealing layer on top to ensure that the CO2 remains in the underground facility. It is possible to establish storage facilities for CO2 beneath both land and sea.

Analyses from the Geological Survey of Denmark and Greenland (GEUS) indicate that it there is suitable geological structures to store between 12 and 22 billion tonnes of CO2 in the Danish subsoil. This is equivalent to 400–700 times the volume of CO2 emitted by Denmark annually.

The oil and gas fields in the Danish section of the North Sea feature structures that may be well-suited to use as storage facilities when the fields have been depleted. Another advantage of these subsea geological structures is that they are well-documented. Moreover, some of the existing infrastructure i.e. platforms and pipelines could potentially be used or retrofitted in connection with the transport and storage of CO2. This means that it could be possible to commence storage in depleted oil and gas fields in the North Sea earlier than in coastal or onshore storage facilities. On the other hand, it would be more expensive to store CO2 offshore than onshore.

How is the use of CCS being promoted?

The 2020 Danish climate agreement for energy and industry, etc. highlights the importance of the capture and storage of CO2 in the country’s work to achieve its climate-political goals. The agreement paves the way for projects to capture, transport and store CO2 in Denmark.

However, it will be necessary to set up a pool of funds in order to promote the capture, storage and utilisation of CO2 in Denmark. The plan is to phase in the pool as from 2024, and it is estimated that it will be worth DKK 815 million annually once it is fully in place.

The Climate Agreement also stipulated the preparation of a strategy for CCS in Denmark, so as to assure the development of new technologies – including those associated with CCS. The Danish Government plans to prepare a roadmap for CCS over the course of 2021. This roadmap marks the first step in a consolidated strategy for the capture and storage of CO2 and comprises three main tracks:

• The first is to introduce a new system of permits to allow environmentally responsible and secure storage in Danish subsoil.
• The second is to make it possible to import and export CO2.
• The third is to mature additional potential for the storage of CO2 in Denmark in the longer term.

A political agreement about CO2 storage was concluded in June 2021, making it possible to import, export and transport CO2 across national borders, and to store CO2 in Denmark.

The agreement comprises a range of initiatives, including the launch of the process to grant licences for CO2 storage in subsea areas of the Danish section of the North Sea, thus allowing storage in depleted oil and gas fields to commence as early as in 2025.

The CCS technology is economically challenged, and regulation and funding are necessary to promote the use of the technology in Denmark.


Sources: The Danish Energy Agency, GEUS, Equinor, IEA.org, The Danish Ministry of Climate, Energy and Utilities’ CCS proposal, June 2021