Carbon capture and storage (CCS) is a process that involves capturing waste carbon dioxide (CO2) from large point sources, such as fossil fuel power plants, transporting it to a storage site, and depositing it where it will not enter the atmosphere, normally underground in geological formations. Large-scale CCS could play a pivotal role in reducing CO2 emissions from industrial activities such as electricity generation and manufacturing.

How Does Carbon Capture Work?

There are currently three main methods for capturing CO2 from large point sources:

Post-combustion capture involves separating CO2 from flue gases after fuels such as natural gas or coal have been combusted in power plants or industrial processes. The CO2 is then compressed and prepared for transport and storage. This method can be retrofitted to existing power plants.

Pre-combustion capture removes CO2 before fuel combustion in power generation. The CO2 is extracted after gasification or partial oxidation of fuels such as coal, biomass, or natural gas. The remaining gases, primarily hydrogen, are then used to generate power via gas turbines or fuel cells.

Oxy-fuel combustion involves burning fuels in pure oxygen rather than air, which produces a flue gas that consists mainly of CO2 and water vapor. The water is separated and the captured CO2 is again ready for transport and storage.

In all three methods, the captured Carbon Capture and Storage can be highly pressurized into a supercritical fluid for ease of transportation via pipeline to long-term storage locations.

Where Can Carbon Dioxide Be Stored?

There are several potential geological storage options for the long-term containment of captured CO2:

Depleted oil and gas reservoirs: These underground formations have already held hydrocarbon deposits and have sealing caprock above them to prevent escape of fluids. Injecting CO2 can help extract residual oil and also sequester the greenhouse gas permanently underground. Monitoring is ongoing at various active CO2 injection sites.

Deep saline formations: Porous rock layers saturated with highly saline water found miles below the Earth’s surface offer the largest storage potential. CO2 would mix with the formation waters and become denser than the surrounding rocks, making it stable for thousands of years. The CO2 Safety case in pore waters is under study in live projects worldwide.

Unmineable coal seams: CO2 can be adsorbed onto the internal surface area of coal, replacing methane in place. This form of enhanced coal bed methane recovery also provides long-term storage. Pilot CO2-ECOB projects have delivered promising subsurface behaviour results.

Basalt formations: CO2 reacts with ultrabasic volcanic basalt rocks to form solid carbonate minerals over timeframes of decades to centuries, securely trapping emissions as part of the natural rock composition. Piloting of this mineralization process is now advancing.

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