(404a) Air Capture: Does It Make Sense?

The UK Government has ratified the Climate Change Act which sets legally binding CO2 emission reductions of 80% by 2050. At this level, one has to start to consider capturing CO2 directly from air. This was proposed by Lackner (2003) as a feasible option that would require relatively small units. More recent studies (Baciocchi et al. 2006; Keith et al. 2006) have looked at detailed designs and process options, but in the analysis the main focus is on the energy requirement. Keith et al. (2006) argue that it would be possible to use fossil fuels and still be within the requirement of an overall carbon negative technology, while Nikulshina et al. (2006, 2009) opt for a solar concentrator to drive the high temperature regeneration process.

As the discussion on the use of air capture develops (Sarewitz and Nelson, 2008), one really needs to have a simple analysis that points out the pros and cons of the technology. A back of the envelope thermodynamic analysis is presented to show the effect of recovery on the energy requirement as well as the size of the units in comparison to more traditional carbon capture from coal fired power stations. The results indicate that recoveries greater than 50% are required and on the basis of the same volume of CO2 captured the scale of the units will be at least two orders of magnitude larger. Some conclusions on the potential for developing air capture will be presented.

References

Baciocchi R., Storti G. and Mazzotti M. (2006) Chem. Eng. Proc. 45: 1047-1058.

Keith D.W., Ha-Duong M. and Stolaroff J.K. (2006) Climatic Change 74: 17-45.

Lackner K.S. (2003) Science 300: 1677-1678.

Nikulshina V., Hirsch D., Mazzotti M. and Steinfeld A. (2006) Energy 31: 1715-1725.

Nikulshina V., Gebald C. and Steinfeld A. (2006) Chem. Eng. J. 146: 244-248.

Sarewitz D. and Nelson R. (2008) Nature 456: 871-872.