What is carbon capture?

Carbon dioxide (CO₂) emissions generated by human activities have led to an accumulation of greenhouse gases in the atmosphere that is causing an increase in the Earth’s temperature and thus climate change.

Carbon capture and storage (CCS) methods are being widely studied in the scientific field. Several scientific reports, such as the IEA report on Net Zero and the latest IPCC report (2023) have mentioned the need to implement CCS methods to reinforce current mitigation measures against climate change.

In this article we will tell you what carbon capture and storage is, and what are the advantages of this new technology. We will also review the current projects and industries that have already implemented this technology.

What is carbon capture and storage (CCS)?

Carbon capture and storage, also known as CCS (carbon capture and storage), is a process that consists of capturing CO₂ emitted by power plants and other industries.

Carbon capture and storage methods seek to capture carbon dioxide (CO₂) that is generated as a result of industrial processes (fossil fuel burning, steel production, natural gas, etc.) in such a way that these emissions are not released into the atmosphere.

In this way, the accumulation of these emissions in the atmosphere is prevented and thus its contribution to climate change is avoided.

This capture is followed by the transport and storage in deep underground reservoirs. CO₂ can be captured, stored and transported in different ways, depending on the processes involved.

How does carbon capture and storage work?

Carbon capture and storage is a three-stage process:

1. CO₂ capture
2. CO₂ transport
3. CO₂ storage

1.   CO₂ capture

In the first stage, CO₂ is captured from the emission source. These sources are found in different industrial processes that release CO₂ as a product of some chemical reaction along the process.

Once captured, the CO₂ is compressed and transported through pipelines or tanker trucks to the storage site.

2.   CO₂ transport

In the second stage, the CO₂ is transported from the emission source to the storage site.

CO₂ can be transported in two different ways:

• Through pipelines (piping). The CO₂ is transported to the reservoirs where it will be stored. This method is the most effective for short to medium distances.
• In high pressure vessels inside ships or trains. This method is used for long distances or particular purposes.

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3.   CO₂ storage

In the third stage, CO₂ is stored in geological reservoirs deep underground that have no value to humans.

Geological reservoirs include salt formations, deep aquifers and depleted oil and gas fields. CO₂ is injected into the reservoir and sealed to prevent leakage.

This is important because we must not untap these formations for any reason, otherwise there is a risk that all that CO₂ will be released back into the atmosphere.

It can also be injected into formations rich in certain minerals which, over time, react chemically with the CO₂ to give carbonates. This solves the leakage problem of the previous method, as the CO₂ is converted to another compound through a chemical reaction.

Finally, CO₂ can be used as a reagent in some processes. For example: carbonation of carbonated beverages, urea production, or methanol production.

Examples of Successful Carbon Capture and Storage Projects

Carbon capture and storage methods are already operational worldwide.

According to the Global Carbon Capture and Storage Institute, as of 2023, there are a total of 30 plants operating with this system and a total of 196 plants under construction and development. Since 2021, the number of CCS projects has grown by 44%.

The image below shows the global distribution of CCS plants according to the latest report (2022) of the Global CCS Institute:

Which industries are currently using carbon capture and storage methods?

Industries currently using these methods operationally are (number of operational plants in each industry is shown in parentheses):

• Natural gas, power and fossil fuels (16).
• Fertilizers (4)
• Ethanol (4)
• Hydrogen (2)
• Other (4)

Other industries that are exploring CCS implementation due to the high CO₂ emissions generated in their processes are:

• Iron and Steel
• Cement
• Waste incineration

The following is a list of the main industries that currently have CO₂ capture and storage (CCS) plants in their facilities.

Natural gas processing (12 operating plants)

Natural gas is a compound consisting mainly of methane, extracted from fossil reserves. This fuel generally contains CO₂ that must be removed before it can be marketed for domestic use (as cooking gas, for example).

The CO₂ that is removed ends up being released into the atmosphere, so CO₂ capture plants in these processes seek to prevent this from happening.

For these plants it is estimated that, if they are close to the fields where the CO₂ will be injected, the cost of compressing, transporting and storing it is 15 to 20 dollars per ton of CO₂.

The progress in the studies on CO₂ processing at the exit of natural gas plants is very important due to the importance that this fuel has acquired in recent years as a “transition” fuel.

Iron and steel production (1 operating plant)

The iron and steel production industry is responsible for approximately 7% of global CO2 emissions.

In iron and steel production plants, CO₂ is produced as a result of the chemical reaction of reducing iron ore to pig iron. Pig iron is the raw material used to make steel, and its production process involves burning coal in a blast furnace at high temperatures.

For this reason, among the technologies researched and implemented to reduce these emissions are CO₂ capture methods such as CCS.

Hydrogen production (2 operating plants)

The use of hydrogen to obtain energy is one of the topics of the moment. When manufactured with renewable energies, the use of hydrogen does not generate greenhouse gas emissions.

One of the potential uses of hydrogen is car batteries, which would replace the use of fossil fuels for this purpose.

98% of the hydrogen produced today is manufactured from coal (gasification) and natural gas (methane reforming).

Both processes generate a large amount of CO₂ emissions. These processes are compatible with CO₂ capture processes (CCS). There are currently 2 operational CO₂ capture hydrogen production plants in the world. Between them they have a production capacity of 600,000 tons of hydrogen per year.

Direct air capture (DAC)

Unlike CCS  methods, these methods seek to capture CO₂ from the atmosphere once it has already been released.

The operation of these methods is based on the fact that, through a fan, air flows into a structure containing chemicals capable of retaining CO₂. This retained CO₂ can then be stored or used for other purposes.

Once the CO₂ is retained from the air stream, the “CO₂-free” air is returned to the atmosphere. In general, it is not possible to completely clean the air but it is returned with lower CO₂ concentrations than the initial air input.

An important advantage of these methods is that they avoid CO₂ transport costs. These infrastructures are placed in strategic locations so that the CO₂ obtained can be used for another process or stored in locations close to the capture facility.

The following image presents a comparison between the carbon capture methods mentioned in this article (CCS and CCS):

Carbon capture and storage challenges and limitations

Carbon capture and storage currently faces significant challenges and limitations. Some of them are:

• They are expensive technologies, which in the case of CCS ends up raising the cost of the manufactured product, affecting the consumers of the product.
• A large amount of energy is required to capture and transport CO₂. If this energy is not obtained from renewable sources, more CO₂ could be released in the process than is captured.
• There are concerns about safety and the possibility of CO₂ leakage in the case where it is stored in geological formations underground.
• In the DAC method, unlike in fixed source methods (CCS), CO₂ is very diluted in atmospheric air (approximately 0.041% of the atmosphere, which is equivalent to 410 ppm or mg/l). This means that a large amount of energy and resources are required to extract CO₂ from the air circulating in the atmosphere.

Conclusions

Carbon capture and storage is an important technology that can help reduce global CO₂ emissions and combat climate change. This assertion is based on recently issued authoritative reports, such as those of the IEA and the IPCC.

Although it faces challenges and limitations, there are currently around 30 operational projects worldwide and more than 100 in the construction and development stage.

It is important to emphasize that, in the long term, further progress must be made in the transition to renewable energy sources and cleaner technologies. But carbon capture and storage can be a solution in the short and medium term.