Carbon dioxide removal

See also: Bio-energy with carbon capture and storage, Biochar, Carbon dioxide scrubber, Carbon capture and storage, Geoengineering, and Greenhouse gas remediation

Carbon dioxide removal (CDR) methods refers to a number of technologies which reduce the levels of carbon dioxide in the atmosphere.^[1] Among such technologies are bio-energy with carbon capture and storage, biochar, direct air capture, ocean fertilization and enhanced weathering.^[1]

CDR is a different approach to removing CO₂ from the stack emissions of large fossil fuel point sources, such as power stations, as this reduces emission to the atmosphere but cannot reduce the amount of carbon dioxide already in the atmosphere. It is by some regarded as a branch of geoengineering,^[1] while other commentators regard CDR as a form of carbon capture and storage.^[2]

CDR methods are supported by a range of individuals and organisations such as IPCC chief Rajendra Pachauri,^[3] the UNFCCC executive secretary Christiana Figueres,^[4] the World Watch Institute,^[5] the World Wide Fund for Nature WWF^[6] and the Lenfest Center for Sustainable Energy at the Earth Institute, Columbia University.^[7]

As CDR removes carbon dioxide from the atmosphere, it creates negative emissions, which is a cost effective way of dealing with small and dispersed point sources such as domestic heating systems, airplanes and vehicle exhausts.^[8][9]

The mitigation effectiveness of air capture is limited by societal investment, land use, and availability of geologic reservoirs. These reservoirs are estimated to be sufficient to sequester all anthropogenically generated CO₂.^[10]

Proposed methods

Bio-energy with Carbon Capture and Storage

Main article: Bio-energy with carbon capture and storage

Biochar

Main article: Biochar

Enhanced Weathering

Main article: Enhanced weathering

This is being attempted at the CarbFix project.^{[citation needed]}

Artificial trees

A notable example of an atmospheric scrubbing process are the artificial trees.^[11][12] This concept, proposed by climate scientist Wallace S. Broecker and science writer Robert Kunzig,^[13] imagines huge numbers of artificial trees around the world to remove ambient CO₂. The technology is now being pioneered by Klaus Lackner, a researcher at the Earth Institute, Columbia University,^[14] whose artificial tree technology can suck up to 1,000 times more CO₂ from the air than real trees can,^{[citation needed]} at a rate of about one ton of carbon per day if the artificial tree is approximately the size of an actual tree.^[15][16] The CO₂ would be captured in a filter and then removed from the filter and stored.

The chemistry used is a variant of that described below, as it is based on sodium hydroxide. However, in a more recent design proposed by Klaus Lackner, the process can be carried out at only 40 °C by using a polymer-based ion exchange resin, which takes advantage of changes in humidity to prompt the release of captured CO₂, instead of using a kiln. This reduces the energy required to operate the process.^[17]

Scrubbing towers

In 2008, the Discovery Channel covered^[18] the work of David Keith,^[19] of University of Calgary, who built a tower, 4 feet wide and 20 feet tall, with a fan at the bottom that sucks air in, which comes out again at the top. In the process, about half the CO₂ is removed from the air.

This device uses the chemical process described in detail below. The system demonstrated on the discovery channel was a 1/90,000th scale test system of the capture section, the reagents are regenerated in a separate facility. The main costs of a the full plant will be the cost to build it, and the energy input to regenerate the chemicals and produce a pure stream of CO₂.

To put this into perspective, people in the U.S. emit about 20 tonnes of CO₂ per person annually.^{[citation needed]} In other words, each person in the U.S. would require a tower like the one featured on the discovery channel to remove this amount of CO₂ from the air, requiring an annual 2 Megawatt-hours of electricity to operate it. By comparison, a refrigerator consumes about 1.2 Megawatt-hours annually (2001 figures).^[20] But by combining many small systems such as this into one large system the construction costs and energy use can be reduced.

It has been proposed that the Solar updraft tower to generate electricity from thermal air currents also be used at the same time for amine gravity scrubbing of CO2.^[21] Some heat would be required to regenerate the amine.

Example CO₂ scrubbing chemistry

Main article: Carbon dioxide scrubber

Quicklime process

Quicklime will absorb CO₂ from atmospheric air mixed with steam at 400 °C (forming calcium carbonate) and release it at 1,000 °C. This process, proposed by Steinfeld, can be performed using renewable energy from thermal concentrated solar power.^[22]

Economic factors

A crucial issue for CDR methods is their cost, which differs substantially among the different technologies, some which are not developed enough to perform cost assessments of. The American Physical Society estimates the costs for direct air capture to $600/tonne with optimistic assumptions.^[23] The IEA Greenhouse Gas R&D Programme and Ecofys provides an estimate where 3.5 billion tonnes could be removed annually from the atmosphere with BECCS (Bio-Energy with Carbon Capture and Storage) at carbon prices as low as €50,^[24] whereas a report from Biorecro and the Global Carbon Capture and Storage Institute estimates costs "below €100" per tonne for large scale BECCS deployment.^[2]

See also

• Biorecro
• Carbon negative
• Climate change mitigation scenarios
• Geoengineering
• Lithium peroxide
• List of emerging technologies
• Low-carbon economy
• Negative emission
• Virgin Earth Challenge
• Carbon dioxide for chemical transformations

References

1. ^ ^{a b c} "Geoengineering the climate: science, governance and uncertainty". The Royal Society. 2009. http://royalsociety.org/Geoengineering-the-climate/. Retrieved 2011-09-10. 
2. ^ ^{a b} "Global Status of BECCS Projects 2010". Biorecro and The Global Carbon Capture and Storage institute. 2011. http://cdn.globalccsinstitute.com/sites/default/files/GCCSI_Biorecro_Global_Status_of_BECCS_110302_report.pdf. Retrieved 2011-09-10. 
3. ^ Pagnamenta, Robin (2009-12-01). "Carbon must be sucked from air, says IPCC chief Rajendra Pachauri". Times Online. London. http://www.timesonline.co.uk/tol/news/environment/article6938298.ece. Retrieved 13 December 2009. 
4. ^ Harvey, Fiona (2011-06-05). "Global warming crisis may mean world has to suck greenhouse gases from air". Guardian Online. http://www.guardian.co.uk/environment/2011/jun/05/global-warming-suck-greenhouse-gases?intcmp=122. Retrieved 10 September 2011. 
5. ^ Hollo, Tim (2009-01-15). "Negative emissions needed for a safe climate". http://blogs.crikey.com.au/rooted/2009/01/15/negative-emissions-needed-for-a-safe-climate-world-watch-institute/. Retrieved 10 September 2011. 
6. ^ "Climate Solver". http://www.climatesolver.org/show.php?id=1316853. Retrieved 10 September 2011. 
7. ^ http://ngm.nationalgeographic.com/big-idea/13/carbon-capture
8. ^ Vergragt,P., Markusson, N., and Karlsson, H.: (2011)“Carbon capture and storage, bio-energy with carbon capture and storage, and the escape from the fossil-fuel lock-in”, Global Environmental Change, Volume 21, Issue 2, pages 282-292.
9. ^ Azar, C., Lindgren, K., Larson, E.D. and Möllersten, K.: (2006)“Carbon capture and storage from fossil fuels and biomass – Costs and potential role in stabilising the atmosphere”, Climatic Change, 74, 47-79.
10. ^ Lenton, TM; NE Vaughan (2009). "The radiative forcing potential of different climate geoengineering options". Atmospheric Chemistry and Physics 9: 2559–608. http://www.atmos-chem-phys-discuss.net/9/2559/2009/acpd-9-2559-2009.html. 
11. ^ "New Device Vacuums Away Carbon Dioxide". LiveScience. 2007-05-01. http://www.livescience.com/technology/070501_carbon_capture.html. Retrieved 2009-10-29. 
12. ^ Adam, David (2008-05-31). "Could US scientist's 'CO2 catcher' help to slow warming? | Environment". London: The Guardian. http://www.guardian.co.uk/environment/2008/may/31/carbonemissions.climatechange. Retrieved 2009-10-29. 
13. ^ Artificial trees designed by Wallace Broecker
14. ^ The Earth Institute, Columbia University http://www.earth.columbia.edu/sections/view/9
15. ^ http://www.energynow.com/video/2011/07/29/cleaning-carbon-mess-07312011#
16. ^ - 'Artificial trees' to cut carbon. Retrieved November 7, 2010.
17. ^ http://energy.columbia.edu/?id=research_carbon_capture#air
18. ^ - Discovery Channel, 2008
19. ^ - David Keith
20. ^ "End-Use Consumption of Electricity by End Use and Appliance". Eia.doe.gov. http://www.eia.doe.gov/emeu/recs/recs2001/enduse2001/enduse2001.html. Retrieved 2009-10-29. 
21. ^ http://www.scoop.co.nz/stories/SC0410/S00063.htm The Methane Economy
22. ^ "Can technology clear the air? - environment - 12 January 2009". New Scientist. 2009-01-12. http://www.newscientist.com/article/mg20126901.200-can-technology-clear-the-air.html?full=true. Retrieved 2009-10-29. 
23. ^ "Direct Air Capture of CO2 with Chemicals". The American Physical Society. 2011-06-01. http://www.aps.org/policy/reports/popa-reports/loader.cfm?csModule=security/getfile&PageID=244407. Retrieved 2011-09-10. 
24. ^ "Potential for Biomass and Carbon Capture and Storage". IEA Greenhouse Gas R&D Programme. 2011-07-06. http://www.eenews.net/assets/2011/08/04/document_cw_01.pdf. Retrieved 2011-09-10.