Q&A on CCS

UPDATED FEBRUARY 2023

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. The first three licences was granted in January 2023.

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

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?

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.

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. Carbon storage is possible offshore, near shore and on land.

Analyses from the Geological Survey of Denmark and Greenland (GEUS) from 2021 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. On the other hand, it would be more expensive to store CO₂ offshore than onshore.

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