carbon capture and storage, how does it work?

The development of renewable energies and energy efficiency are two essential pillars of efforts to mitigate climate change.

But, given the magnitude of the reduction in emissions to be achieved, the experts from the International Energy Agency (IEA) and the IPCC consider that the use of technologies for capturing, storing and recovering CO is essential to achieve the objective of carbon neutrality.

The DMX process for capturing CO, the fruit of a decade of research in the laboratories of IFP Énergies nouvelles, is now being demonstrated on the site of Arcelor Mittal in Dunkirk, a steel giant that emits more than 11 million tonnes of CO each year.

The captured CO could be transported and then stored in the North Sea, for example on the site of the Norwegian NNorthern Lights, which also signed its first commercial agreement last August for the transport and storage of CO, this time captured at an ammonia and fertilizer plant in the Netherlands.

The objective of capturing, storing or recovering carbon dioxide (better known by the acronyms CCS or CCU for carbon capture and storage Where carbon capture and use) is to help decarbonize industry: it is a set of technologies that capture and store and/or use CO rather than letting it escape into the atmosphere. Indeed, heavy industry is the source of almost 20% of global CO emissions today. In France, the National Low Carbon Strategy (SNBC) sets an 80% reduction in industrial emissions by 2050 compared to 2015.

In the IEA’s “sustainable development” scenario, these capture technologies would contribute 15% to the cumulative reduction of CO₂ emissions in 2070.

To read also:
Carbon neutrality: what to remember from the new IEA report?

How ? By separating CO from industrial fumes, to store it in deep underground geological formations and thus isolate it from the atmosphere, or to use it as a resource in the production of biofuels or fertilizers, for example.

About thirty large-scale installations are currently in operation around the world to decarbonize electricity production (coal power plant, gas power plant) and industry (steel, cement, chemicals) and 35 to 40 million tonnes are thus captured and stored annually, compared to the 34 billion tonnes of CO that were emitted in 2020. It is estimated that 50, or even 100, times more would have to be captured and stored by 2035 to meet carbon neutrality objectives – which calls for the deployment of the CCUS on a large scale, in Europe and in the world. Given the current maturity of technologies, this is possible by 2030.

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First step in the chain: capture

Capture technologies have been operational for decades, particularly for certain applications such as thermal power plants, but they are still expensive. New, less energy-intensive and more efficient processes are thus being tested in the first demonstrators such as the one in Dunkirk. Today, it is also a question of integrating these processes into a dedicated sector.

There are three main families of processes. The first, “post-combustion” capture, consists of extracting CO from industrial fumes from the combustion of fossil resources (wood, natural gas, oil and coal) using a solvent that has an affinity for the molecules of CO. Positioned downstream of industrial processes, this technology can be implemented on pre-existing installations and applied to the treatment of fumes from various industries. If the capture rate exceeds 90% of the CO₂ emitted, it is nevertheless accompanied by a high “energy penalty” required during the separation of the CO from the solvent, which leads to a high implementation cost, i.e. between 10 and 100 euros per ton of CO avoided (and therefore not emitted).

The second family, called “oxy-combustion” capture, consists of carrying out combustion in the presence of (almost) pure oxygen, rather than in air. The combustion gas thus produced consists almost exclusively of water vapor and CO. It is then much simpler to extract the CO than when it is diluted in nitrogen from the air. This technology thus presents a lower energy penalty but requires a retrofit of the combustion chamber. It is therefore envisaged for certain applications, such as cement plants, and for new biomass and fossil fuel conversion units.

Finally, the third family, known as “precombustion” capture, consists in extracting the CO upstream of combustion by transforming the initial fuel into a “syngas”: this involves gasifying the fuel to obtain a mixture of CO + H0, then to carry out a chemical transformation to obtain a CO + H mixture and finally to extract CO by solvent. The implementation of this process needs to be integrated upstream, at the time of the construction of the industrial unit.

This process makes it possible to capture CO at the level of industrial installations, but also to remove CO₂ present in the atmosphere, as at the Orca site in Iceland (which should capture around 4,000 tonnes per year).

How to transport CO₂ and store it?

Further down the chain, CO is transported in the same way as natural gas, by pipeline, train or boat, depending on the quantity of CO to be transported and the distance. Transport and storage infrastructures therefore do not pose any particular technical problem, but they must be secured and maintained, as required by all industrial equipment.

Then, the captured CO is stored in old hydrocarbon deposits or porous rocks (deep saline aquifers). The CO is injected in dense form at a depth of at least 800 meters. It is then trapped by chemical and geological mechanisms: dissolution in the brine (salt water) present in the rocks, immobilization in the pores of the rocks, then, eventually, mineralization.

Underground storage capacities in Europe are roughly estimated at 300 billion tonnes, or the equivalent of 100 years of global emissions in 2019, but these capacities and the integrity of the sites still need to be confirmed so that operational storage projects CO, like that of NnorthLights, can see the light of day.

The storage sites are subject to rigorous selection in order to guarantee the sustainability and security of the storage over the long term (migration of CO outside the storage site). The storage operations are accompanied by a monitoring protocol which integrates, among other things, geophysical monitoring of the behavior of CO in the subsoil, gas measurements and deep sampling in the subsoil and on the surface, monitoring of microseismic events, etc.

What economic models for the deployment of these technologies?

The benefit of the deployment of these sectors is essentially linked to the reduction of CO emissions, to which the carbon markets for example (emission quota systems) give an economic value: the capture, transport and storage or recovery are not technologies independent of each other, but links in the same value chain.

This is why the deployment of the sector must be coordinated over time and on a voluntary territory by means of investments in shared operational projects on the scale of France and Europe. The deployment of “CO hubs” – networks collecting the CO emitted by different industries and pooling transport and storage infrastructures – is anticipated. This is the case, for example, of Hauts-de-France and Normandy, which are working on the development of a hub for the capture and transport of CO and the Nor projectthether Lights which works for its part in a commercial CO transport and storage project.

Developed within the framework of European research projects such as Strategy CCUS on the basis of technical factors (volumes of CO involved, geographical areas concerned, possible uses of CO near the places of capture, possible storage places) and environmental (via the life cycle analysis methodologies), the scenarios also take into account economic and social factors, such as job creation and the concerns of local communities, which must be associated with construction as soon as possible. of a project.

The challenge today is to create the conditions to allow the deployment of the CCUS sector on a large scale from 2030. If the technologies are there, financial support mechanisms and a regulatory framework are necessary to accelerate the implementation of the sector. In the current state of estimates, the price of the carbon quota emitted is still lower than the expenses that manufacturers would have to incur to invest in these facilities, ie between 50 and 180 euros per ton of CO2 avoided.

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