Published: 13 May 2024
Contributors: Amanda McGrath, Alexandra Jonker
Carbon capture and storage (CCS) is the process of capturing and sequestering carbon dioxide (CO2) emissions before they enter the Earth’s atmosphere. The goal of CCS is to mitigate climate change by preventing large amounts of greenhouse gas emissions from contributing to global warming and environmental disruption.
The CCS process involves collecting the CO2 that results from industrial operations, power plants and other sources and then transporting it to a storage site, typically underground, where it is stored permanently. CCS is sometimes referred to as carbon capture, utilization and storage (CCUS), in reference to the fact that captured carbon can sometimes be used as a product to facilitate other industrial processes.
Reducing the amount of greenhouse gases in the atmosphere is essential to slowing climate change. Transitioning to renewable energy sources is a vital part of reaching this goal. But fossil fuels will remain part of the global energy mix for some time, due to their prevalence and the challenges of switching to more sustainable options. CCS allows for the cleaner use of these fossil fuels by reducing the amount of CO2 they release.
The main concentrations of CO2 emissions come from large-point sources, such as large-scale industrial facilities, natural gas processing, refineries and power plants, which are ideal candidates for CCS projects. In 2022, 46 million metric tons (also called tonnes) of carbon dioxide globally were captured and stored; by 2030, such projects are predicted to capture and store 254 million metric tons of carbon dioxide per year globally.1 As more countries and companies seek to reach net-zero emissions and invest in clean energy strategies, interest in CCS projects and carbon capture technology grows.
CCS is a three-step process that involves capturing, transporting and storing carbon dioxide (CO2).
There are three main types of CO2 capture: post-combustion, pre-combustion and oxyfuel combustion. Each method has its advantages and challenges. The choice depends on factors such as the type of power plant or industrial facility, the specific characteristics of the fossil fuel being used and overall economic considerations.
- Post-combustion: The most common type of CO2 capture is post-combustion, which captures CO2 after fossil fuels are burned and converted into electricity or heat. The resulting flue gas is separated into a concentrated stream of CO2 using a solvent, then compressed and transported for storage. This method is often used when updating existing power plants.
- Pre-combustion: Pre-combustion involves removing CO2 before the fossil fuel is burned. The fossil fuel is partially oxidized before combustion, producing a mixture of hydrogen and carbon monoxide. Water is then added to convert the carbon monoxide into CO2, which can be captured and stored. This method is more efficient than post-combustion capture but requires a more complex and costly setup.
- Oxyfuel combustion: This method involves burning fossil fuels in pure oxygen instead of air to produce a flue gas that is mainly CO2 and water. After the water vapor is condensed, nearly pure CO2 is left, which can be compressed and transported. This kind of CCS technology is still in the early stages of development and is not yet in use on a large scale.
Once CO2 is captured, it is transported to a storage site. This is typically done using pipelines, through the same technology that is used to transport natural gas and oil over long distances. Ships or trucks can also be used for shorter distances or if the terrain is difficult.
Carbon storage, also known as carbon sequestration, involves the long-term and permanent means to store CO2 to prevent its release into the atmosphere. There are several types of carbon storage:
- Geological storage: This involves injecting CO2 deep underground into geological formations. These can include depleted oil fields or gas reservoirs, inaccessible coal seams or saline aquifers. Deep geological formations are the most common method for carbon storage so far.
- Ocean storage: This method involves injecting CO2 directly into the ocean at great depths. There, it dissolves or forms stable compounds. However, this method raises environmental concerns due to its potential impact on marine ecosystems, and it is not currently considered a viable option.
- Mineral carbonation: In this process, CO2 reacts with certain types of porous rock formations to form stable minerals. These reactions happen naturally over thousands of years but can be sped up with industrial processes. While this provides a permanent solution for CO2 storage, it is currently expensive and energy-intensive.
- Biological sequestration: This involves the capture and storage of CO2 through natural means—for example, plants absorb CO2 as they grow, storing the carbon in their tissues and the soil. Bio-based strategies include reforestation and carbon farming techniques that maximize storage and minimize emissions.
Captured and stored CO2 can either be left permanently or used in other industrial processes. The most common way of using stored carbon is for enhanced oil recovery (EOR). With this technique, the captured CO2 is injected into an oil field to increase the amount of crude oil that can be extracted.
Typical oil extraction methods can leave a large amount of oil behind; EOR projects make extraction more efficient. And because the CO2 is left behind, this technique also offers the benefit of a long-term storage option.
While there are benefits, EOR also makes it easier to continue using fossil fuels for power generation. For this reason, it is seen as part of a broader strategy to transition to renewable energy sources and aid emissions reduction, rather than a complete solution.
The methods of carbon capture previously described are typically used for large-point sources such as power plants or industrial facilities and capture newly created carbon emissions before they are released. But there are other approaches to carbon capture that can help address carbon emissions that are already in the atmosphere. This is known as carbon dioxide removal (CDR). There are two common methods of CDR:
- Bioenergy carbon capture and storage (BECCS) is a strategy that uses bioenergy as a power source instead of fossil fuels. Biomass absorbs CO2 from the atmosphere during its growth; when it is burned for energy as biofuels, the CO2 emissions are captured and stored. This makes BECCS a potential “negative emissions” technology, as it could result in a net removal of CO2 from the atmosphere.
- Direct air capture and carbon storage (DACCS) focuses on capturing CO2 directly from the air, rather than from a point source such as a power plant. Direct air capture (DAC) strategies can also result in negative emissions, as they work to remove CO2 already present in the atmosphere.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC) and the International Energy Agency (IEA) have both reported that CCS is a key part of their strategies for reaching global net-zero emissions goals by 2050. Different countries and regions are approaching CCS in their own ways. Here are a few examples:
The United States has about 10 large-scale CCS facilities in operation, including the Petra Nova project in Texas. As the world's largest post-combustion carbon capture project, it captures over 1 million metric tons of CO2 per year from a coal-fired power plant and uses it for EOR in a nearby oil field. The government provides financial incentives for CCS through the 45Q tax credit, which offers a tax credit for each metric ton of CO2 captured or stored.
Canada is home to several significant CCS projects, including the Weyburn-Midale field, which has been operational since 2000 and stores about 2 million metric tons of CO2 per year. The Canadian government supports CCS through funding for research and development, as well as regulatory measures that encourage its use in oil sands operations.
Norway is a pioneer in CCS. The Sleipner Field in the North Sea has been capturing and storing CO2 since 1996, making it one of the longest-running CCS projects. The CO2 is separated from natural gas extracted from the field and then injected into underground saline formations. The country’s government provides funding for these projects, viewing CCS as a key tool for achieving its climate goals.
As the world's largest emitter of CO2, China sees CCS as an essential part of its strategy to reduce emissions. It has several pilot CCS projects and is investing heavily in research and development. However, large-scale deployment of CCS in China is still limited.
The European Union (EU) supports CCS through its Emissions Trading System, which can make CCS financially attractive by putting a price on carbon emissions. However, progress on CCS has been slow in Europe, with only a few operational projects.
Despite its potential, CCS faces several challenges. The cost of capturing, transporting and storing CO2 can be high, and carbon capture technology is still in various stages of development. While costs are expected to decrease as CCS technology matures, they remain a significant barrier to widespread deployment. CCS also requires a considerable amount of energy, which can increase the overall emissions of a power station or industrial facility if not managed properly. This is known as the "energy penalty" of CCS.
Expansion of CCS is also limited by geography, as not all regions have suitable sites for the storage of CO2 and the feasibility of establishing new ones is limited. There are also concerns about the long-term stability of permanent storage sites and the potential for leakage. While the risk is considered low, any leakage could undermine the effectiveness of CCS in emissions reduction and climate change mitigation. But as energy technologies evolve and projects become more cost-effective, CCS is expected to be an important method for managing carbon emissions from major producers.
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Footnotes
1 Carbon capture. Use, transport and storage (Link resides outside ibm.com), U.S. Department of Energy (DOE), June 2023