Fight against global warming: the challenge of capturing CO2



Scientists are looking, manufacturers are investing and projects are multiplying, driven by the urgency of climate change and the support of public authorities. After spending decades spreading CO2, the main greenhouse gas, by burning coal or oil, man is now trying to capture this enemy n ° 1 to send him back where he came from, underground. And lock him up there.

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Recognized by the IPCC as one of the options to fight against rising temperatures, the principle of capture and geological storage of CO2 (or CCS, “carbon capture and storage”) is not new. Researchers began to take an interest in it in the 1970s; the first experiments date from the end of the twentiethe century; and facilities are already functioning. Without however upsetting the situation for the moment.

Each year, barely 40 million tonnes of CO2 are captured, mainly on industrial sites. “It is not nothing, but it is not enough”, notes Florence Delprat-Jannaud, head of capture programs at the French Institute of New Petroleum-Energies (Ifpen). This represents only a tiny fraction of the 36.4 billion tonnes released in 2021. More than technical, the obstacle is financial and programs have been launched to change this equation.

Limit the energy expenditure of these devices

While the capture stage is the most expensive, this research aims to improve the efficiency of existing systems, already capable of intercepting 90% of their target when leaving the factory. The objective is to limit the energy expenditure necessary to “wash” the fumes and extract the CO.2, while relying on a source of energy that is itself “green”. After 15 years of studies, Ifpen is installing a demonstrator on ArcelorMittal’s blast furnaces in Dunkirk (North).

This system works on the basis of solvents which isolate the CO2. Tested for the first time in real conditions, it could be marketed as early as 2023 and primarily concerns sectors that are very difficult to decarbonize, cement factories and the steel industry. Once captured, the carbon dioxide must then be transported, by boat or pipeline, to be injected in the form of gas, via wells, into natural and deep reservoirs.

Two types of sites have been identified: saline aquifers, where there is water unfit for consumption, and depleted hydrocarbon deposits. In 2024, Europe should thus find an outlet for its carbon dioxide at a depth of 2,600 meters, in the North Sea, within the framework of Northern Lights. Supported by the Norwegian state and oil groups, this project is one of the most ambitious in the world.

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The infrastructure could receive 1.5 million tonnes of CO2, the first year, when it is put into service. Its promoters ensure that the risks of rising to the surface are controlled. “There are natural pockets of CO2 which have not moved for millions of years ”, recalls Eric Oelkers, researcher at the Géosciences Environnement Toulouse (GET) laboratory, for whom the Earth’s subsoil can absorb future emissions for centuries.

“We cannot say that there are no risks, but they are low”

But this geologist is not unaware of the questions of “social acceptability” related to these technologies. “We cannot say that there are no risks, but they are low and relatively well known, adds Sylvain Delerce, doctoral student in the same Toulouse unit of the CNRS. In the debate, it is necessary to put into perspective the risks induced with the risk of leaving the CO2 in the air “. Their laboratory nevertheless participated in the development of an alternative, where the possibility of a leak does not exist: the mineralization of CO.2.

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This transformation is possible by mixing it with water to inject it into volcanic rocks. The technique is used in Iceland by Carbfix, a company resulting from academic research. “It is the natural process of rain, it is just a question of accelerating it” , explains Eric Oelkers, one of the founders of Carbfix. According to him, the two techniques, mineralization or storage in deep reservoirs, are not competing. “There isn’t just one solution that will work”, he insists.

At the same time, researchers are also working on the possibilities of removing CO2 already present in the atmosphere or that diffused by activities such as aviation. For these cases, a process is still in its infancy: direct capture in the air or “Direct air capture” (DAC). Backed by Carbfix and a geothermal plant, the Swiss company Climeworks has just deployed the largest installation of its kind in Iceland, called Orca.

“This solution is a complement that can help us”

Driven by the energy provided by geothermal energy, fans circulate the air and push the CO2 to filters. “The DAC remains extremely difficult to implement, it will be necessary to develop truly disruptive processes, considers Florence Delprat-Janaud. Above all, do not believe that the DAC can distract us from the capture of CO2 in the fumes, where it is easiest. “

The difficulty lies in the low concentration of CO2 of the atmosphere, of the order of 0.04% against 10% when leaving the factory. “Climeworks captures the equivalent of the emissions of 250 Americans in one year, says Roland Séférian, researcher at the National Meteorological Research Center. It’s not the alpha and omega. But this solution is a complement that can help us. “

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During COP26, around twenty countries including France committed to no longer subsidize fossil fuel projects abroad if they are not accompanied by CCS systems. For environmentalists, it is a “sleight of hand” that will benefit the oil industry, which could especially gain a permit to continue to draw oil, gas and coal. .

The debate, again, is not new. “We will need these technologies to eliminate irreducible emissions, comments Roland Séférian. But to say that they are the solution is to distract the decision-makers from the real decisions. This should not become an alibi to not change anything. “

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40 million tonnes of CO2 captured in the world

About twenty large installations are currently operational to capture and store CO2in the world. They prevent the emission of around 40 million tonnes of carbon dioxide.

About forty projects are under development. According to the scenario of the International Energy Agency, this sector should, with other decarbonization levers, capture and store 4 billion tonnes of CO.2 in 2035 to consider carbon neutrality.

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