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Glossary · Energy industry & energy transition

Carbon capture

CO2 capture Glossary Energy power system CCS Climate protection Industry

Carbon capture refers to technical processes that separate carbon dioxide from a gas stream. This gas stream can be the flue gas of a power plant, a process gas from the cement, lime, steel or chemical industry, raw biogas during upgrading to biomethane, flue gas from a waste incineration plant, or ambient air. Capture alone does not solve a climate problem. It is the first step in a chain. Afterwards, the captured CO2 must be compressed, transported and either used or permanently stored. Only this chain as a whole determines the climate impact.

Key figures: tonnes, capture rate, energy demand

Carbon capture is measured mainly in tonnes of CO2 per year, by the capture rate and by the energy demand per tonne captured. The capture rate indicates what share of the CO2 in the treated gas stream is separated. A plant with a 90 percent capture rate therefore does not remove 90 percent of all climate-relevant emissions of a site. It removes 90 percent of the CO2 from the gas stream that is actually routed through the capture plant. Not covered are emissions from fuel supply, from auxiliary energy, from plant construction, from leakages and from partial streams that bypass the plant. To put it plainly: a filter on the main chimney has no effect on the secondary chimney.

Methods

There are several technical approaches. In post-combustion capture, CO2 is separated from the flue gas after combustion, often using amine-based scrubbing solutions. These solutions bind the CO2 and release it again when heated. The regeneration heat required for this is a major part of the energy demand. In pre-combustion capture, the fuel is first converted into a synthesis gas consisting of hydrogen and CO2. The CO2 is then separated before the energy use. Oxyfuel processes burn the fuel with nearly pure oxygen. This produces a flue gas that consists essentially of CO2 and water vapour. However, the oxygen has to be obtained from the air with high energy expenditure. In addition, there are membranes, adsorption processes, cryogenic separation and direct capture from the air (Direct Air Capture, DAC). Which method is suitable depends on CO2 concentration, pressure, temperature, impurities, mode of operation and the desired purity. As a general rule: the more dilute the CO2 in the gas stream, the higher the effort per tonne.

Distinction from CCS, CCU and negative emissions

Carbon capture must be distinguished from CCS, CCU and negative emissions. CCS (Carbon Capture and Storage) comprises capture, transport and permanent geological storage. CCU (Carbon Capture and Utilisation) refers to the use of CO2 as a raw material, for example for chemical products, synthetic fuels or building materials. This use relieves the climate only if the CO2 remains bound in the long term or reliably replaces fossil CO2 and the entire process chain causes lower emissions overall. A synthetic fuel releases the CO2 again after a short time when it is burned. Negative emissions arise only when CO2 is removed from the atmosphere and permanently stored. Examples are bioenergy with carbon capture and storage (BECCS) or Direct Air Capture with geological storage (DACCS). Capture at a fossil power plant lowers its emissions compared with operation without capture. However, it does not remove CO2 from the atmosphere.

Significance for the power system

First, carbon capture can reduce the emissions of dispatchable fossil power plants, provided such plants continue to be used to cover the residual load. A gas-fired power plant with capture has different costs, efficiencies and operating requirements than one without. Capture requires heat, electricity or both, for example for regenerating the solvent and for CO2 compression. As a result, the net efficiency falls, and with the same fuel input the plant feeds less electricity into the grid than a comparable plant without capture. In the electricity balance, therefore, what counts is the net amount that remains after the plant's own consumption, not the gross generation.

Second, carbon capture concerns energy-intensive industrial processes. In cement clinker and lime, CO2 arises not only from fuel use but also from the chemical decomposition of limestone in the material. Some basic chemical processes also cause such process emissions. These cannot be completely avoided by renewable electricity. If CO2 is captured there, new electricity and heat demands arise, as well as new location dependencies. In addition come requirements for CO2 pipelines, compressors, intermediate storage and storage sites. The question thus shifts from the individual factory to the infrastructure connecting many sites.

Third, carbon capture itself can become a significant electricity consumer. Direct Air Capture works with very low concentrations: air contains only around 420 to 430 ppm CO2, i.e. about 0.04 percent. According to MIT, about 1.8 million cubic metres of air must be passed through the plant for one tonne of CO2. Including compression, most of the proposed processes require, converted, at least about 1.2 megawatt hours of electricity per tonne. For ongoing projects, the IEA cites estimated costs of 500 to 1,900 US dollars per tonne. If such plants are operated on a large scale, their electricity and heat demand and their mode of operation must be taken into account in the planning of generation and grids. A flexibly operated plant can fit better with times of high renewable feed-in. A plant with continuous heat or process demand, by contrast, behaves more like a steady industrial load.

Common misunderstandings

Captured CO2 is not the same as avoided emissions. The entire process chain lies in between. For the climate impact, what counts is how much CO2 would have been emitted without the measure and how much is actually captured. Likewise relevant are the additional emissions from energy use, the safety of transport and storage, and the length of time the CO2 remains bound. With fossil fuels, a high capture rate at the stack can be partly devalued, for example by methane emissions in the gas supply chain or by the additional fuel demand. In biogenic processes, the balance additionally depends on the origin of the biomass and the quality of storage.

Nor is carbon capture a blanket alternative to expanding renewable energy, to direct electrification or to greater efficiency. Where electricity and heat applications can be efficiently replaced with renewable electricity, heat pumps or electric processes, capture is often more expensive and more energy-intensive than switching directly. The case is different for unavoidable process emissions and for residual emissions that remain after technically and economically reasonable reduction measures. There, capture can take on a task that pure electrification cannot perform.

Economic assessment and infrastructure

The economic assessment depends heavily on the system boundary. Costs per tonne of captured CO2 often refer only to the plant at the site. A robust assessment also includes compression, transport, storage access, monitoring, liability, energy supply, outage risks and permits. If the nearest suitable storage site is hundreds of kilometres away, a company cannot judge capture solely by the costs of the absorber and solvent. CO2 networks can create economies of scale but raise coordination questions: Who builds the pipelines? Who guarantees storage access? Who bears the risk of low utilisation? According to which rules are transport charges set?

Legal framework in the EU and Germany (as of November 2026)

In the EU emissions trading system, Article 12(3a) of Directive 2003/87/EC provides the following: no allowances need to be surrendered for emissions that are considered, after verification, to have been captured and transported to a storage site permitted under the CCS Directive 2009/31/EC. Under paragraph 3b, this also applies to CO2 that is permanently chemically bound in a product. This binding must be so stable that the CO2 does not enter the atmosphere either during normal use or during disposal. CO2 converted, for example, into fuels therefore does not automatically fall under the exemption. According to the Directive, capture and utilisation projects must achieve a net reduction of emissions.

In Germany, the amendment of the Kohlendioxid-Speicherungsgesetz (Carbon Dioxide Storage Act) entered into force on 28 November 2025. Since then, the law has been called the Kohlendioxid-Speicherung-und-Transport-Gesetz (KSpTG, Carbon Dioxide Storage and Transport Act). It permits commercial storage for the first time, which was previously limited to research and demonstration projects, and also regulates the transport of CO2 by pipeline. Storage is in principle permitted offshore in the exclusive economic zone and on the continental shelf. Marine protected areas are excluded. Onshore, storage remains impermissible nationwide, except for research. However, the federal states (Länder) can permit it in their territory by way of an opt-in. CO2 from coal-fired power generation is effectively excluded from access to CO2 pipelines and storage sites. Gas-fired power plants, by contrast, are not excluded. This was controversial in the Bundestag hearing.

Beyond this, carbon capture touches further areas of law. In energy law, the issues are electricity procurement, grid charges and the classification of flexible loads. Industrial policy becomes relevant when carbon contracts for difference (Klimaschutzverträge), funding programmes or public infrastructure decisions determine which sectors gain access to CO2 transport and storage. Technical feasibility alone therefore does not yet make a plant marketable.

Security of supply and operating behaviour

A power plant with carbon capture can provide dispatchable capacity if fuel, the capture plant and a storage route are available. However, capture can change the plant's dynamics. Solvent circuits, heat integration and CO2 compression do not respond arbitrarily quickly to load changes. During start-up and shutdown, the effective capture rate can temporarily fall. If such a plant is started frequently, efficiency, maintenance needs and costs change. For capacity mechanisms, reserve concepts or the assessment of flexibility, stating the installed capacity is therefore not sufficient. Ramping behaviour, start-up times and the availability of CO2 offtake also count.

Conclusion

Carbon capture makes residual emissions technically addressable, but not automatically harmless. It requires energy, infrastructure, rules and long-term responsibility. The term does not describe a finished climate protection measure but a separation process within a longer chain. Which role capture can sensibly play in the power system and in industry can only be judged if several factors are considered together: the origin of the CO2, the capture rate, the additional energy demand, transport, use or storage, and institutional oversight.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 17:36

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