Carbon capture: what is it and how does it help combat climate change?

20 May, 2024

Carbon dioxide (CO₂) is a colourless, odourless gas. One of its best-known properties is its ability to absorb heat and release it into the atmosphere. Although nature itself releases CO₂ through the decomposition of organic matter or from sources such as volcanoes and hot springs, these emissions are balanced – also naturally – by mechanisms such as absorption by plants or the oceans.

But activities such as transport, intensive agriculture and industrial processes upset the balance by emitting large amounts of carbon dioxide that remain in the atmosphere and contribute to global warming. These emissions are the cause of rising temperatures, melting poles, rising sea levels, species migrations and extreme weather events.

In this context, the use of clean energy and a change in society’s consumption habits are two necessary steps to reduce carbon dioxide emissions. For sectors where CO₂ abatement is difficult or impossible, carbon capture is a solution to reduce the amount emitted into the Earth’s atmosphere. It consists of capturing carbon dioxide and then storing or reusing it. It is also possible to capture it before it enters the atmosphere, at the source of emission itself, if it is the result of various industrial processes, for example in a factory.

For sectors where CO2 abatement is difficult or impossible, carbon capture is a solution to reduce the amount emitted into the Earth’s atmosphere

Once captured, carbon dioxide can be safely and sustainably stored in deep geological formations or converted into a solid form through a process called mineral carbonation. It can also be reused in various chemical processes, mainly for fuel production.

Carbon capture technology

Carbon capture technologies go by different names depending on their purpose:

CCS

CCS or carbon capture and storage refers to technologies that capture carbon for the purpose of storing it.

CCU

CCU or carbon capture, storage and use are technologies that make the captured carbon usable in different industries.

BECCS

BECCS or bioenergy with carbon capture and storage is a technology that captures and stores carbon, removing it from the atmosphere.

How is CO2 captured?

Currently, the main mechanisms in for capturing carbon in industrial processes that generate large amounts of emissions are as follows:

• Pre-combustion capture. This is a technique used before the combustion of fossil fuels. It consists of separating the carbon through a gasification process to produce carbon monoxide and hydrogen. The carbon monoxide is reacted with water to convert it into CO₂ for storage or other end use. Meanwhile, the resulting hydrogen can be used as an emission-free energy source. Pre-combustion capture is common in the chemical and petrochemical industries.
• Post-combustion capture. This process takes place after combustion. Its purpose is to separate carbon dioxide from flue gases using absorption techniques. This type of capture is common in power plants and industrial factories.
• Oxy-combustion capture. This works by burning the fuel in an atmosphere of pure oxygen, instead of air. The result is a gas that is very rich in carbon dioxide and very dense, making it easy to collect and capture individually. This type of capture, like the previous one, is carried out in power stations and industrial plants.

The most common type of carbon capture today is post-combustion, as it can be used in conventional plants, while both oxy-combustion and pre-combustion require more investment in new infrastructure.

The most widely used carbon capture today is post-combustion, as it can be used in conventional plants

What are the challenges for carbon capture?

In 2023, the Global Carbon Capture and Storage Institute (Global CCS Institute) put the number of CCS facilities at 30. This figure rises to almost 200 if those in the process of construction and development are added. Since 2021, the number of CCS projects has increased by 44%.

These include facilities such as Orca in Reykjavik, the capital of Iceland, which has been operating since 2021 with the aim of capturing 4,000 metric tonnes of CO₂ from the atmosphere each year.

In any case, carbon capture technology can sequester around 33.3 Mtpy CO₂ (megatons of CO₂ per year). This is a significant figure, but still contrasts with the 2,400 Mtpy CO₂ emitted annually. This means 70 times more carbon is emitted each year than can be captured at most. Similarly, the International Energy Agency (IEA) estimates that 8 gigatonnes of CO₂ should be captured each year.

In Spain, the results of the Call For Interest launched by Enagás in the last quarter of 2023 showed the market’s interest in promoting CO₂ transport and storage infrastructures. Of the 206 companies that responded to the consultation, a total of 37 companies are interested in CO₂ capture – they are estimated to be interested in capturing 10.4 Mt/y -, while 53 companies are interested in having infrastructures for transport and storage.