Carbon capture and storage

The term "carbon capture and storage" (CCS), also known as "carbon capture and sequestration", refers to a set of technologies designed to reduce carbon dioxide (CO₂) emissions from large-point sources including coal-fired power plants to mitigate climate change. CCS technology involves capturing CO₂ and then storing the carbon in a reservoir other than the atmosphere, instead of allowing it to be released into the atmosphere where its accumulation contributes to climate change.

Several different categories of strategies for storing carbon are possible and have been proposed; these include storing carbon in terrestrial ecosystems, the oceans, and underground in geologic formations. Terrestrial carbon storage refers primarily to biological carbon sequestration in the biosphere relying on the photosynthetic process of capturing and converting atmospheric carbon dioxide into organic carbon. Ocean storage generally refers to the injection of captured CO₂ directly into the oceans but also includes other mechanisms of enhancing oceanic uptake of carbon. Geologic carbon storage refers to the injection of captured CO₂ into underground, naturally occurring geologic reservoirs that will trap the gas to prevent it from re-entering the atmosphere. Another proposed approach often referred to as mineral carbonation involves chemical reactions that transform the carbon in gas-phase CO₂ into solid-phase carbonate minerals. Among these different carbon storage approaches, geologic storage has emerged as the method with the greatest potential for large-scale CO₂ emissions reductions in the near term.

A complete CCS system involving geologic carbon storage includes four basic steps with different technologies required for each step: (1) capture the CO₂ from a power plant or other concentrated stream; (2) transport the CO₂ gas from the capture location to an appropriate storage location; (3) inject the CO₂ gas into an underground reservoir; and (4) monitor the injected CO₂ to verify its storage. Technologies that are commercially-used in other sectors are currently available for each of these components. CO₂ capture technology is already widely used in ammonia production and several other industrial manufacturing processes as well as oil refining and gas processing. CO₂ gas has been transported through pipelines and injected underground for decades, most notably in West Texas where it is used to enhance oil recovery (EOR) of declining-production wells. Some 3-4 million tons of CO₂ per year is currently successfully stored underground at several locations, including Sleipner in the North Sea, Weyburn in Saskatchewan, Canada, and In Salah in Algeria. Technologies to monitor the carbon dioxide and verify its storage are also available. The integration and the scaling-up of the existing technologies to capture, transport, and store CO₂ emitted from a full-scale power plant, however, has not yet been demonstrated, although this is the goal of the US Department of Energy’s FutureGen project.

The concept of engineering systems to deliberately capture and store CO₂ has evolved in the past twenty years from a relatively obscure idea to an increasingly recognized set of potential climate change mitigation options. While the technical feasibility of CCS involving underground storage in geologic formations has been demonstrated in other applications and several demonstration projects, this technology is unlikely to be used widely until regulations on carbon emissions are instituted so that reducing carbon dioxide emissions into the atmosphere provides an economic benefit that will offset the cost of implementing the technology. Although studies on the risks associated with injecting CO₂ underground have found minimal concerns, widespread of adoption of CCS technology could also be limited by public acceptance due to the novelty of the concept as well as by uncertainties resulting from the lack of demonstrated full-scale integration of the technology.

Further Reading

• Anderson, S., and R. Newell, 2004, Prospects for Carbon Capture and Storage Technologies: Annual Review of the Environment and Resources, v. 29, p. 109-42.
• IPCC Special Report on Carbon Dioxide Capture and Storage. Intergovernmental Panel on Climate Change, Working Group III. December 2005
• FutureGen Program (U.S. Department of Energy)
• Socolow, R. H., 2005, Can We Bury Global Warming: Scientific American, v. July, p. 49-55.
• Stephens, J. C., and B. v. d. Zwaan, 2005, The Case for Carbon Capture and Storage: Issues in Science and Technology, p. 69-76.