What Is Carbon Capture and Storage?

Carbon capture and storage (CCS) is a set of technologies and processes for intercepting carbon dioxide emissions at their source, transporting the CO2 to a suitable location, and injecting it into geological formations where it is held indefinitely, preventing the gas from entering the atmosphere. The technique addresses emissions from large point sources such as coal and gas power plants, steel mills, cement kilns, and refineries, where CO2 concentrations in the flue gas are high enough to make capture economical relative to direct air approaches. CCS draws from chemical engineering, geology, fluid mechanics, and materials science, and it appears in virtually every scenario modeled by the Intergovernmental Panel on Climate Change that limits global warming to 1.5 or 2 degrees Celsius.

The three stages of the CCS chain, capture, transport, and storage, each involve distinct engineering challenges and infrastructure requirements. Failure at any stage negates the climate benefit, so monitoring and verification are built into modern CCS project designs from the outset.

Capture Technologies

CO2 capture separates the gas from a mixed flue stream before, during, or after combustion. Post-combustion capture is the most mature approach: flue gas contacts a chemical solvent, most commonly a monoethanolamine solution, which absorbs CO2 selectively, and the solvent is then regenerated in a heated stripping column to release a concentrated CO2 stream. Pre-combustion capture converts a fuel to hydrogen and CO2 before burning, so only hydrogen enters the combustor and the CO2 is separated under pressure. Oxyfuel combustion burns the fuel in nearly pure oxygen rather than air, producing a flue gas of CO2 and water vapor that requires only drying and compression. Research reviewed in an ACS Engineering Au paper on CO2 capture and sequestration covers these pathways along with emerging solid sorbent and membrane-based systems aimed at reducing the energy penalty of the capture step.

Transport and Geological Storage

Captured CO2 is compressed to a supercritical state, typically above 31 degrees Celsius and 73 bar, and transported by pipeline to the injection site. Geological storage targets formations with sufficient porosity and permeability to accept large volumes of CO2 and a caprock of low-permeability rock to prevent upward migration. Deep saline aquifers are estimated to hold more than 1,000 gigatonnes of storage capacity globally, enough to absorb centuries of industrial emissions at current rates, according to IPCC assessments cited by the World Resources Institute. Depleted oil and gas reservoirs are also used, with the advantage that their structural integrity has already been proven over geological timescales. Long-term monitoring using seismic surveys, pressure monitoring, and geochemical sampling confirms that the CO2 plume behaves as modeled and does not leak.

Carbon Utilization

An alternative to permanent storage is carbon capture and utilization (CCU), in which captured CO2 serves as a feedstock for synthetic fuels, chemicals, concrete curing, or enhanced oil recovery. Enhanced oil recovery injects CO2 into depleted reservoirs to improve oil displacement, generating revenue that can offset capture costs, though the subsequent combustion of the recovered oil partially offsets the climate benefit. Synthetic methanol and jet fuel produced from CO2 and green hydrogen represent more permanent utilization pathways, though the energy economics depend heavily on the cost of low-carbon electricity. The British Geological Survey describes both storage and utilization pathways and their respective suitability for different industrial contexts.

Applications

Carbon capture and storage has applications in a range of fields, including:

• Power generation, reducing CO2 from gas and coal-fired plants
• Heavy industry, including steel, cement, and chemical manufacturing
• Hydrogen production, capturing CO2 from natural gas reforming to produce blue hydrogen
• Bioenergy with CCS, removing CO2 from the atmosphere when biomass is grown and its combustion emissions are stored