Carbon capture and storage

Deutsch: CO₂-Abscheidung und -Speicherung / Español: Captura y almacenamiento de carbono / Português: Captura e armazenamento de carbono / Français: Captage et stockage du carbone / Italiano: Cattura e stoccaggio del carbonio

Carbon capture and storage (CCS) refers to a suite of technologies designed to mitigate climate change by capturing carbon dioxide (CO₂) emissions from industrial sources or directly from the atmosphere and storing them in geological formations or other long-term storage solutions. This process is critical for reducing greenhouse gas concentrations in the atmosphere, particularly in sectors where emissions are difficult to eliminate through renewable energy or efficiency measures alone.

General Description

Carbon capture and storage encompasses three primary stages: capture, transport, and storage. The capture phase involves separating CO₂ from other gases produced during industrial processes, such as power generation, cement production, or steel manufacturing. The most common capture methods include post-combustion, pre-combustion, and oxy-fuel combustion. Post-combustion capture, for instance, removes CO₂ from flue gases after fossil fuel combustion, typically using chemical solvents like amines. Pre-combustion capture, on the other hand, converts fossil fuels into a synthesis gas (syngas) before combustion, allowing CO₂ to be separated more efficiently. Oxy-fuel combustion involves burning fuel in pure oxygen, resulting in a flue gas composed primarily of CO₂ and water vapor, which simplifies the separation process.

Once captured, the CO₂ is compressed into a supercritical state to facilitate transport. This is typically achieved via pipelines, which are the most cost-effective and efficient method for large-scale CO₂ transport, though ships may also be used for offshore storage sites. The final stage, storage, involves injecting the CO₂ into deep geological formations, such as depleted oil and gas reservoirs, saline aquifers, or unmineable coal seams. These formations must possess specific characteristics, including sufficient porosity, permeability, and an overlying caprock to ensure long-term containment. Monitoring technologies, such as seismic imaging and pressure sensors, are employed to verify the integrity of the storage site and detect any potential leaks.

In addition to geological storage, alternative methods such as mineral carbonation and ocean storage have been explored, though these remain less developed. Mineral carbonation involves reacting CO₂ with naturally occurring minerals like olivine or serpentine to form stable carbonates, effectively locking the CO₂ in a solid state. Ocean storage, while theoretically capable of sequestering large volumes of CO₂, poses significant environmental risks, including ocean acidification, and is not widely pursued due to regulatory and ecological concerns.

Technical Details

The efficiency of CCS systems is influenced by several technical factors, including the capture technology employed, the purity of the CO₂ stream, and the distance to the storage site. Post-combustion capture, for example, typically achieves CO₂ capture rates of 85–95%, though the energy penalty associated with solvent regeneration can reduce the overall efficiency of power plants by 10–30%. Pre-combustion capture, while more energy-efficient, requires significant modifications to existing industrial processes and is best suited for new-build facilities. Oxy-fuel combustion, though highly effective at producing a concentrated CO₂ stream, demands substantial energy for oxygen production, often via cryogenic air separation.

Transport infrastructure for CO₂ must account for the corrosive nature of the gas, particularly when impurities such as water, hydrogen sulfide (H₂S), or sulfur dioxide (SO₂) are present. Pipelines are typically constructed from carbon steel and coated with corrosion-resistant materials to mitigate degradation. The design pressure of CO₂ pipelines typically ranges from 8 to 15 megapascals (MPa), depending on the distance and elevation changes involved. For offshore transport, ships equipped with cryogenic tanks may be used, though this method is less common due to higher costs and logistical challenges.

Geological storage sites must meet stringent criteria to ensure long-term containment. Depleted oil and gas reservoirs are often preferred due to their proven ability to trap hydrocarbons over geological timescales. Saline aquifers, which are porous rock formations saturated with brine, offer vast storage potential but require extensive characterization to confirm their suitability. The storage capacity of a formation is determined by its porosity, permeability, and the presence of structural or stratigraphic traps. According to the Intergovernmental Panel on Climate Change (IPCC), global geological storage capacity is estimated to range from 2,000 to 20,000 gigatonnes of CO₂, though only a fraction of this capacity is currently accessible due to technical and economic constraints.

Standards and Regulations

CCS projects are subject to a range of international, national, and regional regulations designed to ensure safety, environmental protection, and public acceptance. Key standards include the ISO 27914:2017, which provides guidelines for the geological storage of CO₂, and the EU Directive 2009/31/EC, which establishes a legal framework for the environmentally safe storage of CO₂ within the European Union. In the United States, the Environmental Protection Agency (EPA) regulates CO₂ injection under the Underground Injection Control (UIC) program, specifically under Class VI well permits, which are designed to protect underground sources of drinking water. Additionally, the London Protocol and the OSPAR Convention govern the transboundary movement and offshore storage of CO₂, respectively.

Historical Development

The concept of CCS dates back to the 1970s, when enhanced oil recovery (EOR) techniques first demonstrated the feasibility of injecting CO₂ into geological formations to increase oil production. The first large-scale CCS project, the Sleipner field in Norway, began operations in 1996, capturing and storing approximately 1 million tonnes of CO₂ annually in a saline aquifer beneath the North Sea. Since then, CCS has evolved from a niche technology to a critical component of global climate mitigation strategies. The Global CCS Institute reports that, as of 2025, there are over 40 commercial CCS facilities in operation or under construction worldwide, with a combined capture capacity of approximately 50 million tonnes of CO₂ per year. Notable projects include the Boundary Dam CCS Project in Canada, which captures CO₂ from a coal-fired power plant, and the Gorgon CO₂ Injection Project in Australia, one of the largest CCS initiatives globally.

Application Area

• Power Generation: CCS is primarily applied to fossil fuel-based power plants, particularly those using coal or natural gas. By capturing CO₂ emissions from flue gases, CCS enables the continued use of fossil fuels while significantly reducing their climate impact. Integrated gasification combined cycle (IGCC) plants, which convert coal into syngas, are particularly well-suited for pre-combustion capture due to the high concentration of CO₂ in the syngas stream.
• Industrial Processes: Industries such as cement, steel, and chemical manufacturing are major sources of CO₂ emissions and are often difficult to decarbonize through electrification or renewable energy alone. CCS can capture emissions from these processes, such as the calcination of limestone in cement production or the reduction of iron ore in steelmaking. For example, the Norcem cement plant in Norway has demonstrated the feasibility of capturing CO₂ from cement kilns, achieving capture rates of up to 90%.
• Direct Air Capture (DAC): While not strictly a form of CCS, direct air capture technologies remove CO₂ directly from ambient air, offering a potential solution for addressing historical emissions. DAC systems typically use chemical sorbents or solvents to capture CO₂, which is then concentrated and either stored or utilized. Companies like Climeworks and Carbon Engineering are pioneering DAC technologies, though their scalability and cost-effectiveness remain challenges.
• Enhanced Oil Recovery (EOR): CO₂ captured from industrial sources can be used to enhance oil recovery from depleted reservoirs. This process involves injecting CO₂ into oil fields to reduce the viscosity of the oil and increase its mobility, thereby boosting production. While EOR provides an economic incentive for CCS deployment, it is not a long-term storage solution, as the CO₂ may eventually be released during oil combustion.

Well Known Examples

• Sleipner CO₂ Storage Project (Norway): Operated by Equinor since 1996, the Sleipner project captures CO₂ from natural gas production and stores it in the Utsira saline aquifer beneath the North Sea. The project has successfully stored over 20 million tonnes of CO₂ to date and serves as a benchmark for offshore CCS operations.
• Boundary Dam CCS Project (Canada): Located in Saskatchewan, this project captures CO₂ from a coal-fired power plant and either stores it in a deep saline formation or uses it for EOR. The facility has a capture capacity of 1 million tonnes of CO₂ per year and is one of the first large-scale CCS projects integrated with a power plant.
• Gorgon CO₂ Injection Project (Australia): Developed by Chevron, this project captures CO₂ from natural gas processing and injects it into a deep saline formation beneath Barrow Island. With a design capacity of 4 million tonnes of CO₂ per year, it is one of the largest CCS projects in the world.
• Petra Nova CCS Project (USA): Situated in Texas, this project captures CO₂ from a coal-fired power plant and transports it via pipeline to an oil field for EOR. The facility has a capture capacity of 1.4 million tonnes of CO₂ per year and demonstrates the integration of CCS with EOR.

Risks and Challenges

• Leakage and Containment Risks: The primary risk associated with CCS is the potential for CO₂ to leak from storage sites, which could undermine its climate benefits and pose local environmental hazards. Leakage may occur due to wellbore failure, caprock fractures, or seismic activity. Rigorous site characterization, monitoring, and risk assessment are essential to mitigate these risks. The IPCC estimates that well-selected and managed storage sites are likely to retain over 99% of injected CO₂ for 1,000 years or more.
• High Costs and Economic Viability: CCS is currently an expensive technology, with costs ranging from 40 to 120 euros per tonne of CO₂ captured, depending on the capture method and scale of the project. The high capital and operational expenditures, particularly for capture and transport infrastructure, pose significant barriers to widespread deployment. However, costs are expected to decline as the technology matures and economies of scale are achieved.
• Energy Penalty: The capture process, particularly for post-combustion systems, requires substantial energy input, which reduces the overall efficiency of power plants and industrial facilities. This energy penalty can increase fuel consumption and operational costs, making CCS less attractive without policy incentives or carbon pricing mechanisms.
• Public Acceptance and Regulatory Uncertainty: CCS projects often face opposition from local communities due to concerns about safety, environmental impacts, and the long-term liability of storage sites. Additionally, regulatory frameworks for CCS vary widely between jurisdictions, creating uncertainty for investors and project developers. Clear and consistent policies, along with transparent communication, are critical to addressing these challenges.
• Infrastructure and Scalability: The large-scale deployment of CCS requires extensive infrastructure, including pipelines, storage sites, and monitoring networks. Developing this infrastructure poses logistical and financial challenges, particularly in regions with limited existing CO₂ transport networks. Furthermore, the scalability of CCS is constrained by the availability of suitable storage sites and the pace of technological advancement.

Similar Terms

• Carbon Capture and Utilization (CCU): Unlike CCS, which focuses on the permanent storage of CO₂, CCU involves converting captured CO₂ into useful products, such as fuels, chemicals, or building materials. While CCU can provide economic incentives for CO₂ capture, its climate benefits depend on the longevity of the end product and the avoidance of additional emissions during production.
• Bioenergy with Carbon Capture and Storage (BECCS): BECCS combines biomass energy production with CCS to achieve negative emissions. By capturing CO₂ from biomass combustion or fermentation, BECCS removes CO₂ from the atmosphere, as the biomass originally absorbed CO₂ during growth. BECCS is considered a key technology for achieving net-zero emissions and is included in many climate mitigation scenarios.
• Direct Air Capture (DAC): DAC refers to technologies that capture CO₂ directly from ambient air, rather than from point sources like power plants or industrial facilities. DAC systems can be deployed anywhere, making them highly flexible, but they are currently more energy-intensive and costly than traditional CCS methods.

Summary

Carbon capture and storage is a critical technology for reducing CO₂ emissions from industrial processes and power generation, particularly in sectors where decarbonization is challenging. By capturing, transporting, and storing CO₂ in geological formations, CCS can significantly mitigate climate change while enabling the continued use of fossil fuels during the transition to renewable energy. However, the technology faces substantial challenges, including high costs, energy penalties, and public acceptance issues. Despite these hurdles, CCS is increasingly recognized as a necessary component of global climate strategies, with numerous projects demonstrating its feasibility and potential. As the technology matures and regulatory frameworks evolve, CCS is poised to play a pivotal role in achieving net-zero emissions targets.

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