How to capture and store carbon?

Carbon capture and storage are recognized as one of several tools available to help reduce carbon dioxide levels in the atmosphere. As a possible temporary solution, they can play a valuable role in global efforts to mitigate climate change. But how does it work?

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What is carbon capture and storage?

Carbon capture and storage, also known as CCS, is a process that consists of three main steps: capturing carbon directly from emission sources (or from the atmosphere), transporting it safely, and finally, storing or "burying" it in suitable underground locations.

Historically, emissions linked to fossil fuels have grown exponentially; between 1750 and 2010 alone, about half of all human-produced emissions were generated in the last 40 years of that period. CCS technology focuses precisely on large stationary sources, such as:

• Power plants;
• Oil refineries;
• Cement and steel industries;
• Natural gas processing facilities.

Carbon dioxide capture technologies

There are different methods to prevent carbon from reaching the atmosphere. In thermal power plants, three main techniques stand out:

1. Post-combustion

It is the most common and versatile method, as it can be adapted to existing plants. CO₂ It is "extracted" from the exhaust gases right after the fuel is burned. It's like putting a sophisticated filter in the factory chimney.

2. Pre-combustion

In this process, carbon is removed before combustion. The fossil fuel passes through a gasifier, generating a synthetic gas. CO₂₂ It is separated, leaving behind hydrogen, which can be used as a clean fuel. It is a cheaper option than post-combustion, but difficult to implement in older installations.

3. Oxyfuel Combustion

Here, the fuel is burned in pure oxygen instead of ordinary air. The result is a combustion gas composed almost entirely of water vapor and CO₂.₂As the mixture cools, the water condenses, leaving behind a stream of almost pure carbon. Although highly effective, the process requires a lot of initial energy to separate the oxygen from the air.

Hydrogen transport and production

After being captured, CO₂ It needs to travel to the storage location. The most efficient and economical method is the use of pipelines. In the United States, for example, there are already more than 5.800 km of infrastructure dedicated to this transport. On a smaller scale, ships and tanker trucks can also be used.

Conversion to hydrogen is an alternative for sectors that are difficult to electrify, such as heavy transport and domestic heating. Currently, the cheapest way to obtain it is through methane reforming (using natural gas). However, for this hydrogen to be considered "clean," CO₂₂ The data generated during the reform process must be captured and stored via CCS.

How does carbon dioxide storage work?

The final destination of captured carbon is usually the subsurface. Geosequestration involves converting carbon into a "supercritical" state (with liquid and gaseous properties) and injecting it into porous sedimentary rocks.

The most promising locations include:

• Saline Aquifers: Deep rocks saturated with saltwater that act like giant sponges. They possess immense storage potential beneath oceans like the North Sea.
• Declining Oil Fields (EOR): the CO₂ It is injected to "push" the remaining oil to the surface (Enhanced Oil Recovery). Selling the oil helps fund the project, although burning this additional fuel reduces the overall environmental benefit.
• Unexploitable Coal: Carbon can be injected into deep coal deposits, releasing methane in the process, which can be collected for energy.

In mineral storage, carbon reacts chemically with magnesium and calcium minerals, transforming into solid and stable rock. It is the safest method, as there is no risk of leakage, but it requires a lot of energy to accelerate the chemical reaction, which would take centuries in nature.

What are the costs and risks of CCS?

Implementing CCS is not cheap. Capture and compression increase a power plant's fuel requirements by 25% a 40%which could raise the price of electricity for the end consumer by up to 91 %However, experts argue that the cost of inaction against climate change will be drastically higher.

The main concern is the risk of leaks. The chemical compound is an asphyxiant in high concentrations. Therefore, strict regulations (such as the EU CCS Directive) require:

1. Deep Monitoring: Use of seismic and pressure sensors to observe the behavior of the gas in the reservoir.
2. Shallow Monitoring: Sensors in the ground and in the atmosphere to detect any unwanted migration.

Even in earthquake-prone areas, such as the Nagaoka project in Japan, the technology has proven safe: after a strong tremor in 2004, no leaks were detected, proving the resilience of well-selected reservoirs.

Reducing emissions in industrial processes

CCS can transform sectors that are currently major climate villains:

• Biomass Power Plants: By combining the burning of organic waste with CCS, it is possible to achieve negative emissionsThe plant absorbs carbon as it grows, and when burned, this carbon is buried instead of returning to the air.
• Steel mills and cement factories: These sectors emit the chemical compound not only through the energy they consume, but also through chemical reactions inherent in their processes. Direct capture is often the only way to decarbonize them.
• Natural Gas Processing: Some deposits, such as the Sleipner deposit in Norway, have been extracting the carbon naturally present in the gas and reinjecting it into the subsoil since 1996, thus avoiding carbon taxes and protecting the ecosystem.

Although investment in CCS is high and debate exists about diverting resources from renewable energies, the technology is fundamental for a realistic energy transition. It allows heavy industries to continue operating while global infrastructure adapts, ensuring that carbon remains where it should be: away from our atmosphere.

For businesses and governments, financial incentives — through carbon taxes or credits — will be the driving force that dictates the speed of adoption of this vital solution for the planet.

Take advantage of this opportunity and delve deeper into the topic: Why is decarbonization important?