Is CO2 capture the key to achieving carbon neutrality?

(This article was originally published in the French version of the French National Academy of Sciences Journal No. 16) Science Notebook）

In early February 2024, the European Commission published a report setting out broad guidelines for European industrial carbon management, with one of the core messages being that if we are to limit global warming to 1.5°C, we will have to rely on the capture and storage of carbon dioxide (CO₂). According to the Commission, carbon capture and storage (CCS) will be key to removing around 280 million tonnes of CO₂ from the atmosphere each year by 2040, rising to around 450 million tonnes by 2050. This shows how heavily Brussels is relying on this approach. The problem, however, is that, as an article published a few days later in the journal Science put it, nature The EU’s reliance on this technology is not without danger, points out. And for good reason: the rollout of CCS has encountered many obstacles.

A 2023 report by the Global Carbon Project, an organization that aims to quantify global greenhouse gas emissions and their causes, estimates that carbon dioxide emissions from human activities (industry, transport, heating, etc.) are around 40 billion tons per year.₂ It is the main greenhouse gas causing global warming. According to the Intergovernmental Panel on Climate Change (IPCC), a temperature rise of more than 2°C will lead to a significant rise in sea levels and more frequent extreme weather events such as floods, storms and droughts.

Capturing residual emissions

To achieve carbon neutrality by 2050, the IPCC focuses on two major solutions: first, reducing emissions by cutting energy consumption, improving energy efficiency, and gradually replacing most fossil resources (oil, natural gas, etc.) with zero-carbon energy (solar, wind, nuclear and tidal energy); second, removing carbon dioxide from industrial flue gases or even directly from the air.

The latter option is difficult to achieve, however—the largest facilities currently operating capture only 4,000 tons of CO2 per year, a drop in the ocean compared to annual global emissions. The same cannot be said for removing carbon directly from flue gases, however, especially those produced by the chemical reactions required to produce a variety of materials. For example, while one-third of a cement plant’s CO2 emissions come from the combustion of fossil fuels in its kilns, the remaining two-thirds are produced by the thermal decomposition of limestone, cement’s main raw material.

These residual emissions can be captured by many natural carbon sinks, such as oceans, forests or peatlands, which sequester CO2 in the form of organic matter through the biochemical process of photosynthesis. However, these ecosystems can only capture a little more than half of today’s CO2 emissions, which is already a large number. But as climate change accelerates, the efficiency of carbon sinks may become less, especially if the surface area of ​​carbon sinks shrinks due to the loss of natural and semi-natural land due to fire, drought and urban and other artificial development (called “land grabbing”). Hence the need for artificial capture of CO2.

“Although natural carbon sinks could reduce 80% of remaining emissions by 2050, most experts agree that CCS will be essential for the remaining 20%. says Jacques Pironon, research professor at the GeoRessources Laboratory in Nancy (northeast France), who is involved in the CCS study.

Burying chimney gases underground

Specifically, CCS aims to capture carbon dioxide contained in flue gases directly from chimneys and store it underground. “CCS has three main stages: capture, transport and storage of CO2₂All of these are based on specific technologies,” Florence Delprat-Jannaud, president of Club CO₂, explains that the group is dedicated to promoting discussions and initiatives among industry and research players interested in CCS. To date, there are three main approaches to CO₂ treatment:₂ capture. “The most mature is post-combustion technology, which aims to extract CO2 from the flue gases produced by combustion. The oil and gas industry has been using it for a century.” In this method, CO2 is absorbed by an amine-based solvent, a compound that binds to the gas, says Florent Guillou, design process engineer at IFP Énergies Nouvelles.

The second method is pre-combustion capture, i.e. “It involves removing carbon dioxide before the fuel is burned. The specific method is to convert the combustibles into a synthesis gas composed of carbon monoxide and other gases, and then inject steam to convert part of the energy into carbon dioxide and produce hydrogen at the same time.” Finally, the third method, CO2 capture through oxycombustion, is a technology that uses pure oxygen instead of air to burn fuel in industrial processes that require combustion. “The resulting flue gas consists almost exclusively of carbon dioxide and water vapor, which can be easily separated,” Gillou explained.

Recovering oil and gas fields

To transport the captured CO2, “The gas is liquefied to reduce its volume and then transported to a storage location by pipeline, ship, train or truck,” Delprat-Jannaud added. Next comes the storage phase, “It can be carried out in a variety of underground structures at depths exceeding 800 meters, such as deep saline formations (porous, permeable rock formations filled with saltwater that is unfit for drinking), depleted oil and gas fields, and igneous rocks such as basalt and peridotite”.

For Pironon, “Former oil or gas fields are the easiest option to implement, as CO2 can be injected through existing wells. In addition, the oil industry has been using enhanced oil recovery for decades, where CO2 is introduced into oil reservoirs at the end of their life to reduce the viscosity of hydrocarbons, making it easier to recover them.” However “There are more saline layers and the storage capacity is the largest”Del Prat-Gianno stressed that, according to the IPCC, these geological formations could contain 10,000 billion tonnes of CO2 globally, enough to store all our CO2 emissions for centuries to come.

As for igneous rocks, “They provide long-term storage capabilities by mineralizing CO2 into carbonates, in other words, they solidify and stabilize very quickly in rock in just a few years, compared to the hundreds of thousands of years required in deep saline formations.”points out Pascale Bénézeth, research professor at the Toulouse Geosciences Environment Laboratory, who is working on the scheme.

Deploy CCS at scale

In fact, CCS is not a new technology.”Since the 1990s, Europe has supported a large number of pilot research projects.” Pironon said that in the early 2010s he helped evaluate the world’s first integrated industrial chain for carbon dioxide capture, transport and storage, which was tested on the Old Continent at a pilot plant developed at Total Energy’s industrial site in Lac, southwestern France. “Today, there are 41 full-chain CCS projects worldwide. Even better, Europe’s first commercial transport and storage scheme is about to come online: Norway’s Northern Lights project plans to store 1.5 million tonnes of CO2 per year under the North Sea from 2024, increasing to 5 million tonnes from 2026,” Delprat-Jannaud was ecstatic.

However, she also issued a warning: “The world captures only about 45 million tonnes of carbon dioxide each year, and in a decade’s time, to achieve carbon neutrality, you’ll need to capture 50 to 100 times that amount.” Therefore, large-scale deployment of CCS is needed. For example, “In the case of France, which plans to store 15 to 20 million tonnes of CO2 per year by 2050, the number of storage sites required will of course depend on the capacity of the facilities, but for the amount stored at the Northern Lights project, we would need about ten such facilities. We would also have to link them with the transport infrastructure.“Unfortunately, however, the deployment of CCS is being hampered by a number of obstacles.

In a study published in 2021, a team led by Xavier Arnauld de Sartre, research professor at the TREE Energy and Environmental Transitions Laboratory Researchers from the University of Pau (southwest France) identified several types of barriers by studying the specific cases of about ten European storage projects, based on news articles and social science studies.

Social, technical and political barriers

An interesting finding is that the deployment of CCS is hampered by its low acceptance among the population. “However, this factor played only a small role in delaying its deployment.” The researchers noted.Public opposition is partly due to potential dangers of the technology, such as the possibility of triggering earthquakes if CO2 is injected too quickly, or the risk of gas leaks. However, according to IPCC data, “Geological storage is reliable, with an overall leakage rate of less than 0.001% per year.” Another difficulty facing CCS, according to Arnold de Sutter’s team, is its immaturity. “The TRL (Technology Readiness Level) measures the maturity of a technology, including its integration into a full system and industrialization, and geological storage ranks between 6-7 out of 9.” The researchers added.

As far as capture is concerned, “There is still a need to improve the efficiency of existing technologies and reduce their costs, especially in terms of energy consumption,” Pironon believes that. In fact, at present, “The cost of each ton of CO2 captured, transported and stored using CCS is between €80 and €150, while on the European market each ton of CO2 emitted (and paid by industrial operators if it exceeds the authorisation limit) is worth around €90,” Delprat-Jannaud noted that, in terms of storage, accurate identification of potential reservoirs will be crucial. Specifically for igneous rock options, “The challenge is to identify initial pilot sites in France. For example, Réunion Island and New Caledonia are potential evaluation targets”, Isabel Martínez, a researcher at the IPGP Geophysical Institute, explains.

Finally, the study by Arnauld de Sartre and colleagues highlights several other major barriers to CCS deployment:There is a lack of consensus among the various actors on the technologies to be adopted and the development strategies; there is a lack of economic models that clearly define who will pay for storage; and finally, there is weak political commitment to CCS”On this last point, the team concluded in another study currently being published:Due to France’s deindustrialization and the strong development of carbon-free energy provided by nuclear power, the country has invested little in decarbonization.”However, as Delprat-Jannaud points out,The only option to combat climate change is to deploy CCS at scale. Fast! ” ♦