Carbon Capture Technology

Point-Source Carbon Capture

Post-combustion capture, the most mature approach, removes CO2 from the flue gas of power plants or industrial facilities after combustion. The dominant technology uses chemical absorption, where flue gas is passed through a solution of amine-based solvents (typically monoethanolamine or advanced proprietary formulations) that selectively bind CO2 molecules. The CO2-rich solvent is then heated in a regeneration column to release concentrated CO2 (at 95 to 99% purity) for compression and transport, and the regenerated solvent is recycled. This regeneration step requires significant thermal energy, reducing the net power output of a coal plant by 25 to 40% and a gas plant by 15 to 25%, a major economic penalty called the parasitic energy load.

Pre-combustion capture converts fossil fuel into a mixture of hydrogen and CO2 (called syngas) before combustion, then separates the CO2 from the hydrogen. The hydrogen is burned cleanly while the concentrated CO2 stream is captured. This approach is used in integrated gasification combined cycle (IGCC) power plants and hydrogen production facilities. Oxy-fuel combustion burns fuel in pure oxygen rather than air, producing a flue gas that is primarily CO2 and water vapor, simplifying the capture step to condensing out the water. The Air Separation Unit required to produce pure oxygen adds significant cost and energy consumption.

As of 2025, approximately 40 commercial-scale CCS facilities operate worldwide, capturing roughly 45 million tonnes of CO2 per year, less than 0.1% of global annual emissions of approximately 37 billion tonnes. The largest operating project is the Gorgon facility in Western Australia, which captures CO2 from natural gas processing and injects it into a deep saline formation beneath Barrow Island. Norway's Sleipner and Snohvit projects have safely stored CO2 beneath the North Sea since 1996 and 2008 respectively, providing valuable long-term data on geological storage behavior. The track record shows that point-source capture from concentrated CO2 streams (natural gas processing, ethanol production, hydrogen manufacturing) is technically proven, while capture from dilute post-combustion flue gas remains expensive and has seen several high-profile project cancellations due to cost overruns.

Direct Air Capture

Direct air capture (DAC) removes CO2 directly from ambient air, which contains roughly 420 parts per million CO2, a concentration approximately 300 times more dilute than coal plant flue gas. This extreme dilution makes DAC thermodynamically and economically more challenging than point-source capture, but offers the unique advantage of being deployable anywhere regardless of proximity to emission sources, and the ability to achieve net negative emissions by removing historical CO2 from the atmosphere. Two primary approaches have reached commercial demonstration: solid sorbent systems and liquid solvent systems.

Climeworks, the Swiss company operating the world's largest DAC facility (Orca, commissioned in 2021 in Iceland at 4,000 tonnes CO2/year, and its successor Mammoth at 36,000 tonnes/year), uses solid amine-functionalized sorbent filters that bind CO2 at ambient temperature. When saturated, the filters are heated to approximately 100 degrees Celsius using geothermal energy to release concentrated CO2, which is then dissolved in water and injected into basaltic rock formations where it mineralizes into carbonate minerals within two years, permanently converting gaseous CO2 into stone. Carbon Engineering, acquired by Occidental Petroleum, uses a liquid potassium hydroxide solution that absorbs CO2 in large air contactor units, followed by a high-temperature calcination step (900 degrees Celsius) to regenerate the solvent and produce a concentrated CO2 stream.

Current DAC costs range from $400 to $1,000 per tonne of CO2 captured, far above the $50 to $100 per tonne considered necessary for large-scale deployment. Cost reduction pathways include larger facility scale, improved sorbent materials with higher capacity and faster kinetics, waste heat utilization, and learning-by-doing as the industry scales. The U.S. Department of Energy's DAC Hubs program has awarded $3.5 billion for four regional DAC hubs targeting 1 million tonnes per year each, aiming to demonstrate cost reduction toward $100 per tonne. The 45Q federal tax credit provides $180 per tonne for CO2 captured from air and permanently stored, creating a significant financial incentive for DAC development.

CO2 Transport and Geological Storage

Captured CO2 is compressed to a supercritical fluid state (above 73.8 atmospheres and 31.1 degrees Celsius) for efficient transport via pipeline or ship. The United States already operates approximately 8,000 kilometers of CO2 pipelines, primarily serving enhanced oil recovery (EOR) operations in Texas and the Permian Basin. Proposed CCS projects would require substantial pipeline expansion, raising concerns about pipeline safety (CO2 is an asphyxiant at high concentrations), land use for rights-of-way, and environmental justice impacts on communities along pipeline routes. Ship transport of liquefied CO2 is being developed as an alternative for offshore storage sites and cross-border transport, with Northern Lights (a Norwegian joint venture) planning the first commercial CO2 shipping operation.

Geological storage injects CO2 into deep rock formations at depths typically exceeding 800 meters, where pressure and temperature keep it in a dense supercritical state. Suitable formations include depleted oil and gas reservoirs (which have proven containment integrity over geological time), deep saline aquifers (porous rock formations saturated with brine, which offer the largest global storage capacity estimated at 6,000 to 25,000 gigatonnes of CO2), and basalt formations (where CO2 reacts with minerals to form solid carbonates). Multiple trapping mechanisms secure the CO2 underground: structural trapping beneath impermeable caprock, residual trapping in pore spaces, solubility trapping as CO2 dissolves in formation fluids, and mineral trapping as CO2 reacts with rock minerals over centuries to millennia.

Monitoring, verification, and accounting (MVA) technologies track the behavior of stored CO2 to verify containment integrity and detect any potential leakage. Techniques include seismic surveys (monitoring the extent and migration of the CO2 plume through the reservoir), pressure monitoring in injection and observation wells, geochemical sampling of formation fluids and overlying groundwater, surface flux measurements using eddy covariance or accumulation chambers, and satellite-based surface deformation monitoring using InSAR. The Sleipner project's 25-year monitoring dataset demonstrates that geological CO2 storage can be safe and permanent when sites are properly selected and managed.

The Role of CCS in Climate Strategy

The Intergovernmental Panel on Climate Change includes CCS in most modeled pathways to limiting warming to 1.5 or 2 degrees Celsius, particularly for decarbonizing industrial processes where no alternative exists. Cement manufacturing, which releases CO2 both from fuel combustion and from the chemical decomposition of limestone (calcination), cannot be fully decarbonized without either CCS or a complete replacement of Portland cement chemistry. Steel production via blast furnaces, chemical manufacturing, and certain refining processes similarly produce process emissions that electrification alone cannot eliminate.

Critics raise several concerns about relying on CCS in climate strategy. The technology's track record of cost overruns and underperformance (several high-profile projects have captured less CO2 than planned or been cancelled entirely) undermines confidence in projections. The majority of captured CO2 to date has been used for enhanced oil recovery, which produces additional fossil fuels and partially offsets the emissions benefit. The moral hazard argument suggests that CCS promises allow fossil fuel companies and governments to delay the transition to renewables by offering a technological fix that may never materialize at the necessary scale.

The most defensible role for CCS in climate strategy focuses on applications where alternatives are limited: industrial process emissions from cement, steel, and chemicals, waste-to-energy facilities, and potentially combined with bioenergy (BECCS) or direct air capture to achieve net negative emissions needed later this century to draw down accumulated atmospheric CO2. Using CCS to extend the life of coal and gas power plants is harder to justify economically, since new renewable generation with storage is increasingly cheaper than operating existing fossil plants with added capture equipment.