Jennie C. Stephens is an Assistant Professor of Environmental Science and Policy at Clark University. Her research focuses on technologies and policies associated with confronting global climate change.
- Carbon capture has a sparkling future, new findings show
- Carbon capture success in Wisconsin
- The key to safe subsurface storage of CO2
- Storage Of carbon dioxide A vexing question
- Major potential CO2 storage in the North Sea
- Pennsylvania wants to allow power companies to capture carbon dioxide emissions and put them into the ground.
- Carbon Capture and Sequestration (CCS) from the World Resources Institute
- Blogs on Carbon Sequestration
- EPAs Frequently Asked Questions about Carbon Sequestration
- US Department of Energy’s Key Research and Development Programs for Carbon Sequestration
- Carbon Sequestration in Terrestrial Ecosystems
- Carbon Capture Journal
Introduction
The term “carbon capture and storage (or sequestration)” (CCS), refers to a set of technologies designed to reduce carbon dioxide (CO2) emissions from large-point sources such as 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. This article covers only CCS and not other types of carbon sequestration activities whereby CO2 is removed from the atmosphere and stored in vegetation, soils, or oceans. Forests and
agricultural lands store carbon, and the world’s oceans exchange huge amounts of CO2 from the atmosphere through natural processes.
An integrated CCS system would include three main steps:
1. capturing and separating CO2;
2. compressing and transporting the captured CO2 to the sequestration site; and
3. sequestering CO2 in geological reservoirs or in the oceans
Electricity-generating plants are among the most likely initial candidates for capture, separation, and storage, or reuse of CO2 because they are predominantly large, single point sources for emissions and contribute the largest proportion of CO2 emissions compared to other types of fossil fuel use in many countries, including the United States (See Table 1.) Large industrial facilities, such as cement-manufacturing, ethanol, or hydrogen production plants, that produce large quantities of CO2 as part of the industrial process are also good candidates for CO2 capture and storage.
a. CO2 emissions in millions of metric tons for 2006; excludes emissions from U.S. territories.
b. Total does not sum to 100% because of rounding.
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.