Stabilization of atmospheric carbon dioxide (CO₂) levels has become widely accepted as necessary in order to limit the long-term warming of global temperatures by 2 to 3°C and thus avoid devastating environmental consequences. Because the use of fossil fuels is expected to continue to increase in the future, new, innovative strategies need to be placed alongside the already well established ones, such as the use of renewable resources and achievement of better energy efficiency. One such strategy, which has emerged only over the past decade or so, is the idea of capturing the CO₂ from large emitters (such as factories and power plants), transporting it to an appropriate site, and storing it underground for thousands of years. This strategy, or technology, is referred to as carbon capture and storage (CCS).

Many of the practices and technological components of CCS have been in commercial operation for the past several decades, particularly in the oil industry, which has been injecting CO₂ into oil formations to recover additional oil since the 1970s.

Carbon Capture Technologies

There are essentially three types of capture technologies that show the most promise and will be commercially viable in the near future:

• Post-combustion: the CO₂ is separated from the flue gas by a chemical solution after the primary fuel has been combusted;
• Pre-combustion: the primary fuel is transformed to produce hydrogen, and the CO₂ is removed before combustion; and
• Oxy-fuel combustion: the fuel is burned in an oxygen environment, resulting in a CO₂-rich waste gas stream. Once the CO₂ has been captured, it is then compressed, which liquefies it and makes it ready for transport to an appropriate storage site.

CO₂ Transportation

Transportation of CO₂ will occur primarily through pipelines; ships and rail might also come to play a role later, as storage sites are located further from the capture plant. While extensive networks of pipelines that would transport CO₂ already exist, new pipeline infrastructure will be needed once CCS becomes deployed on a large scale.

Carbon Storage

Possible CO₂ storage locations on land include depleted oil and gas reservoirs, un-minable coal seams, and deep saline aquifers; an alternative to land storage is to transport the CO₂ out into the ocean and inject it deep into the ground. The saline aquifers are thought to hold the largest potential capacity for storage. Here, the CO₂ is essentially injected deep underground into the sandstone layers, where it is contained by the natural pressure of the impermeable nonporous cap rock layers above.

An overview of CSS techniques is depicted in Figure 1.

Conclusion

Increasingly, CCS is being seen not as a silver bullet, but as one of the key components in the portfolio of mitigation strategies and measures. It can play a major part in our transition towards a low-carbon economy, and it can become a low-emission option for many emerging and developing economies, whose use of fossil fuels is predicted to increase significantly over the next decades. While demonstration projects are underway, a number of scientific, economic, social, and legal problems remain, preventing CCS from living up to its potential.

About the Author

Marko Maver is a doctoral student in international environmental law at the University of Sheffield in the United Kingdom. Mr. Maver’s research focuses on the legal aspects of carbon sequestration. His Master of Arts dissertation, Carbon Capture and Storage: An Analysis of the Barriers to the Development and Deployment, describes the economic, social, and political barriers to the development and deployment of CCS technologies.

Photograph: Sunflower 2 by Zsuzsanna Kilian, Budapest, Hungary.

Return to the EHS Journal Home Page