Carbon dioxide air capture

Definition: The trapping or elimination of carbon dioxide emitted from industrial or commercial sources before it can enter the atmosphere

Carbon dioxide capture and sequestration or storage is anticipated to play a bridging role between carbon dependence and a sustainable low-carbon energy future by serving as the critical enabling technology that will lead to a significant reduction in CO₂ release into the air while allowing industrial processes such as the burning of coal for power generation to continue to meet global energy needs.

The term “carbon dioxide air capture” is used to describe a set of technologies aimed at preventing the carbon dioxide (CO₂) emitted from industrial or commercial sources from entering the atmosphere. The processes involved are also commonly referred to as carbon dioxide capture and sequestration or carbon capture and storage (CCS). The geoengineering technique of scrubbing (absorbing) CO₂ from ambient air is also sometimes referred to as CSS, as are biological techniques that employ organisms (such as plankton) and organic matter to capture CO₂ from the air.

In CCS, the process of capturing CO₂ from a large emissions source is often coupled with the subsequent compression of the gas, storage of the gas (for example, by injecting it into deep underground geological formations or into deep ocean masses called saline aquifers, or by converting it into the form of mineral carbonate), and recycling of the gas to enhance industrial processes, such as that seen in CO₂-assisted enhanced oil recovery (EOR), in which CO₂ gas is injected into an oil-bearing stratum under high pressure to cause oil to be displaced upward.

The CCS process begins with the capture of CO₂ generated by a power station or other industrial facility, such as a cement factory, steelworks, or oil refinery. The CO₂ can be captured before, during, or after the source’s combustion (burning) of fossil fuels. Precombustion capture involves the separation of fossil fuels into hydrogen and CO₂ before they are burned. For example, in the instance of coal, the process involves the conversion of coal into a synthetic gas (syngas) made up of carbon monoxide and hydrogen. The syngas is reacted further with steam to produce a CO₂-hydrogen mix. Further processing produces a mix with a high concentration of CO₂, which is separated out. The remaining hydrogen is then utilized as a CO₂-free energy source that produces only heat and water vapor when combusted. Precombustion capture technology has been widely implemented in the fertilizer industry as well as in natural gas forming.

In oxy-fuel combustion, burning of the fossil fuel in oxygen instead of air results in an exhaust gas that is CO₂-free. This technology is commonly used in the glass furnace industry. In postcombustion capture, the CO₂ is separated from flue (exhaust) gases after the combustion of fossil fuels. The CO₂ content is usually much lower than in the gas that is separated during oxy-fuel combustion or precombustion capture, with the volume of CO₂ in the range of 3 percent to 15 percent by volume.

Challenges to Implementation

One challenge facing CCS is the demonstration of its efficacy and safety on an industrial scale at competitive cost. While CCS is known to be safe and is well understood in terms of the fundamental science and technical requirements, no evidence has been gathered regarding the process’s long-term impacts on the environment (for example, the safety of storing CO₂ in geological formations) or possible danger to humans (for instance, if CO₂ leaks from storage).

CCS applied to a modern power plant could reduce CO₂ emissions by up to 90 percent compared to an equivalent plant with no CCS devices, but the implementation of CO₂ capture is significantly more expensive than the use of traditional systems of emissions control. For example, capturing and compressing CO₂ increases the fuel requirement of a coal-fired plant by as much as 25-40 percent. It is estimated that the cost of energy produced by a new power plant with CCS is from 21 percent to 91 percent higher than that produced by a non-CCS power plant.

Aside from the cost and technical challenges of CCS, a regulatory framework needs to be established to support CCS and to clarify at regional, national, and international levels the long-term rights, liabilities, and technical requirements associated with the use of CCS technologies. Moreover, before investors, scientists, politicians, and industries can be persuaded that CCS is a worthwhile investment, agreements need to be reached on a price on carbon emissions and on whether a carbon tax, cap-and-trade regime, or other carbon-trading/taxation framework will be implemented.

Bibliography

Hanjalić, K., R. van de Krol, and A. Lekić, eds. Sustainable Energy Technologies: Options and Prospects. London: Springer, 2008.

Kutz, Myer. Environmentally Conscious Fossil Energy Production. Hoboken, N.J.: John Wiley & Sons, 2009.

Rackley, Steve. Carbon Capture and Storage. Boston: Butterworth-Heinemann, 2009.

Rojey, Alexandre. Energy and Climate: How to Achieve a Successful Energy Transition. Chichester, England: John Wiley & Sons, 2009.

Shiosani, Fereidoon P. Generating Electricity in a Carbon-Constrained World. Burlington, Mass.: Academic Press, 2009.