Frequently Asked Questions (FAQs) about carbon dioxide (CO₂)

CO₂ is produced by:

• natural processes (e.g. volcanic eruptions, emissions from oceans, human, animal and plant respiration, soil respiration, breakdown of organic matter, forest fires);

• anthropogenic processes (emissions induced by human activities) such as the combustion of fossil fuels, industrial processes (e.g. cement, steel, chemicals) and agriculture.

CO₂ exists in different forms depending on pressure and temperature. The following are relevant to long-distance transmission.

• Gaseous CO₂: At ambient temperature and atmospheric pressure, CO₂ is a colourless, odourless and non-flammable gas. It is mainly present in the atmosphere and used in the food industry and cooling systems. CO₂ is 1.5 times heavier than air.

• Liquid CO₂: By lowering its temperature, CO₂ can be liquefied for transport by ship, train or truck. The temperature conditions for low pressure are -50°C (between 7 and 10 bar) and -30°C (between 15 and 20 bar).

• Dense CO₂: CO₂ that is in a high-density state at a pressure above around 75 bar. Dense CO₂ is commonly used in industrial and technical applications to transport or store larger quantities compared to gaseous CO₂.

The density of liquid and dense CO₂ is contingent on the temperature and pressure and is hundreds of times greater than the density of gaseous CO₂.

To date, in Europe small quantities of CO₂ have been transported exclusively by rail, truck or ship. Nowadays, freight transport dominates the market, mainly for industrial gas and food-grade CO₂.

In contrast, the United States is home to the world's largest CO₂ pipeline network, comprising over 8,000 km of pipelines, mainly in Texas, New Mexico and the Midwest. These pipelines have been transporting CO₂ for decades, predominantly from natural sources (geological CO₂) to enhanced oil recovery (EOR) sites.

Since 1996, Equinor's Sleipner project in the Norwegian part of the North Sea has been storing CO₂ in the Utsira Formation (a deep saltwater aquifer lying approximately 800-1,000 m below the seabed), with a typical injection rate of around 1 million tonnes per year. It was the world’s first commercial carbon capture and storage (CCS) project and the first large-scale demonstration that CO₂ can be stored safely in the long term without leakage. The project has now permanently stored more than 20 million tonnes of CO₂.

The technology has since been developed further and is now being applied on an ever-larger industrial scale:

• Northern Lights (Norway) has been operational since 2025 and offers the transport and permanent storage of CO₂ as a service to various European companies. The first phase has a capacity of 1.5 million tonnes of CO₂ per year, with the expansion to at least 5 million tonnes per year currently under way.

• Brevik CCS (Norway) captures CO₂ at Heidelberg Materials' cement plant. The facility has been operational since 2025 and is designed to handle approximately 400,000 tonnes of CO₂ per year. The CO₂ is transported by ship to Northern Lights for permanent storage beneath the North Sea.

• Greensand (Denmark) has been operational as a large-scale CO₂ storage facility in the EU since September 2026. Initial capacity totals up to 400,000 tonnes per year, with the potential to expand to 4-8 million tonnes per year by 2030.

As such, CO₂ storage is not a new or purely experimental technology: it has been in use for around 30 years and is now evolving into large-scale infrastructure to decarbonise European industry.

Belgium's first CO₂ pipelines are being laid in Antwerp to support industry's decarbonisation projects in the port area. Fluxys c-grid is the local CO₂ transmission system operator responsible for laying and operating the CO₂ network in the Antwerp port area.

Following the granting of the necessary permits in 2023, construction of the first phase of our CO₂ pipeline network began in May 2025 and was completed at the start of the second half of 2026.

The planned CO₂ pipeline between Eynatten and Zeebrugge is a key step in Belgium's development as a CO₂ hub for North-West Europe. This offers a clear advantage for Belgian industry: the more CO₂ is transported via the same network, the lower the transport cost per user. Pooling CO₂ flows from Belgium and neighbouring countries creates economies of scale that make the infrastructure more affordable for all connected businesses. In this way, we are simultaneously boosting the competitiveness of our industry and entrenching economic activity and employment in Belgium.

To realise these economies of scale, Fluxys c-grid is working with the German transmission system operator OGE on the Ruhbens project (Ruhr, Belgium, North Sea). The Ruhbens pipeline is designed to transport dense CO₂. This connection links the Belgian and German CO₂ networks, thereby also giving German industry access to the export hub in Zeebrugge and storage facilities in the North Sea. Pooling larger volumes on a single cross-border network cuts costs for all users.

A pipeline for gaseous CO₂ is operated at a pressure of 35 bar. Existing natural gas pipelines, which have a maximum operating pressure of between 66 and 84 bar, can easily be repurposed to transport CO₂.

If larger quantities need to be transported over long distances, it is better to do so using CO₂ in its dense form. After all, pumping a high-density liquid through a pipe is more efficient than forcing a gaseous product with a much lower density through it. Transporting dense CO₂ requires a higher pressure than is needed to transport gaseous CO₂.

Existing natural gas pipelines cannot be repurposed to transport dense CO₂. Instead, this requires new pipelines with a wall thickness approximately three times that of a natural gas pipe.

The safety of people, infrastructure and the environment is an absolute priority for Fluxys c-grid. As an operator of critical infrastructure in Belgium and Europe, safety is at the heart of all of Fluxys c-grid's activities, from the design and construction of its facilities to their day-to-day operation.

When it comes to the development of gas infrastructure, safety is incorporated right from the outset. The facilities are designed in accordance with recognised industry practices, European standards and the Belgian regulatory framework. This framework sets out the technical requirements relating to design and construction, operation, risk assessment and safety management systems.

In this context, the transmission of CO₂ is no different to that of natural gas, hydrogen or electricity: it is an industrial activity in which safety, from design to operation, is underpinned by our expertise and compliance with safety regulations (as specified in future technical codes included in forthcoming regional legislation) and contractors’ legal obligation to report works.

In Flanders and Wallonia, legislation is currently being drafted to set out the safety requirements for the transmission of CO₂.

With regard to the laying of CO₂ pipelines in the Antwerp port area, Fluxys c-grid Antwerp complies with the provisions of ISO standard 27913:2024 (Carbon dioxide capture, transportation and geological storage — Pipeline transportation systems) as well as the current Technical Codes for pipelines used to transport (gas) molecules.

The future Technical Codes cover four areas:

o Design and construction of pipelines
o Operation of pipelines
o Risk assessments
o Safety management systems (SMSs)

The safety measures intended to prevent or manage incidents are set out in the four Technical Codes.

• During construction:

o Pipes are laid at the minimum prescribed depth (depending on the terrain and risk zone) below ground level to protect them from mechanical damage (e.g. excavation work, agricultural machinery).
o In high-risk areas (roads, railways, watercourses), pipes are often laid deeper or given extra protection (conduit, concrete slabs).
o Coloured plastic warning mesh is erected above pipes.
o Visible markers are installed along the pipeline route (beacons).

• During operation:
o A policy is implemented to provide information and raise awareness among local residents and a wide range of target groups (contractors, engineering firms, etc.) regarding the legal obligation to report works carried out by third parties in the vicinity of transmission infrastructure.
o Preventative monitoring takes place along pipeline routes to detect irregularities such as unreported works. With regard to scheduled works, arrangements are made in advance regarding the safety regulations to be observed (NB: in Belgium, it is a legal requirement to report works carried out near pipes).
o Pipe inspections are conducted using specific technological solutions to check pipes for any irregularities.
o In specific cases, a decision may be made to install a system to record and locate impacts on the pipes.
o A dispatching team ensures the continuous control and monitoring of flows on the network 24 hours a day. A dispatching team is to the transmission of molecules what a control tower is to an airport.
o Should an incident occur on the network, our technicians and specially trained welders at the Intervention Centre are ready 24 hours a day to immediately go to the site to make repairs.

• During risk assessments:
o The methodology and references to standards are prescribed as the basis for risk assessments.

• Safety management system: a safety management system ensures the continuous monitoring and improvement of safety management.

The most obvious solution for storage in the North Sea is the transport of dense CO₂ via pipeline. This solution makes it possible to transport large volumes at a low cost and requires only a facility on the coast to bring the pressure of the CO₂ to the necessary level.

CO₂ can also be transported by ship in liquid form to storage sites in the North Sea. This requires a liquefaction plant and a storage terminal at a port. This solution offers flexibility, particularly during the start-up phase of CO₂ infrastructure.

Lastly, CO₂ can be transported via cross-border pipeline networks to facilities in neighbouring countries. Depending on the infrastructure and destination, CO₂ can be transported in this way in gaseous or dense form.

Belgium intends to export both the CO₂ produced within its territory and that from neighbouring countries. Neighbouring countries have the potential to emit between 60 and 120 million tonnes of CO₂ per year, and the future Belgian pipeline network is ideally situated to import some of these volumes and transport them, together with the CO₂ emissions captured in Belgium, to the export facilities in which Fluxys c-grid is actively involved in partnership with major industrial players.