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Carbon dioxide removal

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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], and the OECD [8]

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.[9][10]

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.[11]

Methods

Bio-energy with carbon capture and storage

Main article: Bio-energy with carbon capture and storage

Bio-energy with carbon capture and storage, or BECCS, utilises biomass to extract carbon dioxide from the atmosphere, and carbon capture and storage technologies to concentrate and permanently store it in deep geological formations.

The Imperial College London, the UK Met Office Hadley Centre for Climate Prediction and Research, the Tyndall Centre for Climate Change Research, the Walker Institute for Climate System Research, and the Grantham Institute for Climate Change issued a joint report on carbon dioxide removal technologies as part of the AVOID: Avoiding dangerous climate change research program, stating that "Overall, of the technologies studied in this report, BECCS has the greatest maturity and there are no major practical barriers to its introduction into today’s energy system. The presence of a primary product will support early deployment."[12]

According to the OECD, "Achieving lower concentration targets (450 ppm) depends significantly on the use of BECCS".[8]

Biochar

Main article: Biochar

Enhanced weathering

Main article: Enhanced weathering

Enhanced weathering refers to chemical approach to geoengineering involving land or ocean based techniques. Examples of land based enhanced weathering techniques are in-situ carbonation of silicates. Ultramafic rocks, for example, have the potential to store thousands of years worth of CO2 emissions according to one estimate. Ocean based techniques involve alkalinity enhancement, such as, grinding, dispersing and dissolving olivine, limestone, silicates, or calcium hydroxide to address ocean acidification and CO2 sequestration. Enhanced weathering is considered as one of the least expensive of geoengineering options. One example of a research project on the feasibility of enhanced weathering is the CarbFix project in Iceland.[citation needed]

Artificial trees

A notable example of an atmospheric scrubbing process are the artificial trees.[13][14] This concept, proposed by climate scientist Wallace S. Broecker and science writer Robert Kunzig,[15] 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,[16] 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.[17][18] 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.[19]

Scrubbing towers

In 2008, the Discovery Channel covered[20] the work of David Keith,[21] 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 by 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).[22] 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.[23] 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.[24]

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.[25] 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,[26] 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]

Legal regulation like carbon permits, carbon taxes, or rebates can be implemented to reduce carbon emission. Governing entities can distribute or sell carbon permits to industries for the rights to emit a certain amount of carbon dioxide. If the certificates are tradable, then polluting organizations can buy certificates from their less polluting counterparts. Theoretically this will encourages polluting industries to develop technologies that emit less carbon dioxide because they won’t have to buy extra carbon permits from others. Overtime the demand for carbon dioxide certificates will drop in price because fewer entities need to buy them.

Carbon taxes respond similarly to carbon credit but require regulating as technology changes. Carbon taxes address the external social cost among the emitters by taxing either the supplier or the buyer. Either way, buyers are going to end up facing higher prices. Higher prices will discourage consumers, demand will fall, and suppliers will have to cut back production.

Rebates are popular among producers and consumers alike. If the government has enough money in their coffers, they can create a program which offers rebates to consumers for buying pricy energy efficient, water saving, or environmental friendly product. Consumers can now afford new fancy products while producers reap the profits from selling their high-end products.

See also

References

  1. ^ a b c "Geoengineering the climate: science, governance and uncertainty". The Royal Society. 2009. Retrieved 2011-09-10.
  2. ^ a b "Global Status of BECCS Projects 2010" (PDF). Biorecro and The Global Carbon Capture and Storage institute. 2011. Retrieved 2011-09-10.
  3. ^ Pagnamenta, Robin (2009-12-01). "Carbon must be sucked from air, says IPCC chief Rajendra Pachauri". Times Online. London. 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. Retrieved 10 September 2011.
  5. ^ Hollo, Tim (2009-01-15). "Negative emissions needed for a safe climate". Retrieved 10 September 2011.
  6. ^ "Climate Solver". Retrieved 10 September 2011.
  7. ^ http://ngm.nationalgeographic.com/big-idea/13/carbon-capture
  8. ^ a b "OECD Environmental Outlook to 2050, Climate Change Chapter, pre-release version" (PDF). OECD. 2011. Retrieved 2012-01-16.
  9. ^ 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.
  10. ^ 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.
  11. ^ Lenton, TM (2009). "The radiative forcing potential of different climate geoengineering options". Atmospheric Chemistry and Physics. 9: 2559–608. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ "The Potential for the Deployment of Negative Emissions Technologies in the UK" (PDF). Grantham Institute for Climate Change, Imperial College. 2010. Retrieved 2012-01-16.
  13. ^ "New Device Vacuums Away Carbon Dioxide". LiveScience. 2007-05-01. Retrieved 2009-10-29.
  14. ^ Adam, David (2008-05-31). "Could US scientist's 'CO2 catcher' help to slow warming? | Environment". London: The Guardian. Retrieved 2009-10-29.
  15. ^ Artificial trees designed by Wallace Broecker
  16. ^ The Earth Institute, Columbia University http://www.earth.columbia.edu/sections/view/9
  17. ^ http://www.energynow.com/video/2011/07/29/cleaning-carbon-mess-07312011#
  18. ^ - 'Artificial trees' to cut carbon. Retrieved November 7, 2010.
  19. ^ http://energy.columbia.edu/?id=research_carbon_capture#air
  20. ^ - Discovery Channel, 2008
  21. ^ - David Keith
  22. ^ "End-Use Consumption of Electricity by End Use and Appliance". Eia.doe.gov. Retrieved 2009-10-29.
  23. ^ http://www.scoop.co.nz/stories/SC0410/S00063.htm The Methane Economy
  24. ^ "Can technology clear the air? - environment - 12 January 2009". New Scientist. 2009-01-12. Retrieved 2009-10-29.
  25. ^ "Direct Air Capture of CO2 with Chemicals". The American Physical Society. 2011-06-01. Retrieved 2011-09-10.
  26. ^ "Potential for Biomass and Carbon Capture and Storage" (PDF). IEA Greenhouse Gas R&D Programme. 2011-07-06. Retrieved 2011-09-10.


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