Building negative emission solutions with "belt and braces"

For Stockholm Exergi, the answer begins with something unexpectedly ordinary: most of the chain already relies on proven industrial technology.

– This is not science fiction. It is established chemistry and proven logistics. What we are doing is connecting several tried-and-tested components in a new way to create what are known as negative emissions, says Fabian Levihn, Head of Research and Development at Stockholm Exergi and Docent at KTH.

To transport the carbon dioxide efficiently, it is cooled and compressed into liquid form – the same principle used in many industrial processes and in the handling of other gases.

– It is a large system to build, but the principle itself is simple: you cool and compress it step by step until it becomes liquid.

An intermediate storage facility is also being built in Värtahamnen, since vessels are not always in port. Safety has guided everything here, from location to sizing.

– We are truly working with belt and braces. The storage tanks should not be too large – instead there should be several smaller ones. They are positioned so that a vessel cannot reach them even if something goes wrong. Connections are dimensioned to be shut down quickly, and the facility is designed so that any potential leak is directed away from areas where it could pose a risk to the public.

Once the gas has become liquid, storage partner Northern Lights takes over the responsibility. The transport to Norway takes place in robust systems in the form of modern gas vessels of the same type already used globally.

– Gas is already transported all over the world. In this context, carbon dioxide is fairly “well-behaved” compared with many other substances that are shipped.

If something were to occur during transport, the risk profile is different from what many might imagine.

– Liquid carbon dioxide is heavier than air. In the event of a leak, it settles as a white, low-lying cloud along the ground or water surface and then disperses. High concentrations can be asphyxiating, which is why the vessel design is aimed at minimising the likelihood and managing the consequences if the unthinkable were to happen.

Once in Norway, the carbon dioxide is piped out to sea and pumped into geological formations for permanent storage, covered by around 300 metres of water and approximately 2,600 metres of rock. Fabian describes the formation as “a stone sponge” with pores in the rock filled with saltwater. Under high pressure, the carbon dioxide is locked into the formation and stabilises further over time.

– Norway has been storing carbon dioxide since 1995. It is not a new thing. The experience is extensive, and it is possible to monitor how the carbon dioxide behaves in the bedrock using geological measurements and surveillance.

A large part of the safety work takes place in the permitting process: risk analyses, computer simulations, and consultations with relevant authorities.

– Ahead of the environmental permit, we analysed the most extreme conceivable scenarios and then developed measures to reduce the risk. We have held several consultations and dialogues with authorities and are working to address questions and explain what we are doing.

For Fabian, the goal is not just to build one facility, but to pave the way for more.

– If we get this right, safety will not be an obstacle but an opportunity. And that is how more projects can follow.