Carbon sequestration

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Carbon sequestration refers to the long-term storage of carbon dioxide (CO2) in the biosphere, underground, or in the ocean to reduce the buildup of CO2, the principal greenhouse gas in the atmosphere. This can be accomplished by maintaining or enhancing natural processes; various entities are also working on developing novel techniques to dispose of carbon dioxide.

Some of the techniques are:

  • Sequestering carbon in underground geologic repositories
  • Enhancing carbon sequestration of the terrestrial biosphere through CO2 removal from the atmosphere by vegetation and storage in biomass and soils.
  • Carbon sequestration in the oceans[1]


How it Works

First, carbon must be captured from the polluting source(s) such as power plants before it gets into the atmosphere. Then it must be transported to the area of sequestration, where it is stored either underground, in the ocean, or in some other form of man-made carbon sink.

  • Geological sequestration -- The geological storage of CO2 in order to reduce greenhouse gases was first proposed in the 1970s but did not gain support until more research was done on it in the 1990s. To store CO2 geologically, it must first be compressed. Then it can be stored in sedimentary basins, oil fields, depleted gas fields, and deep coal seams.[2]
  • Storage in biomass and soils -- The IPCC Third Assessment Report estimates that about 100 billion metric tons of carbon over the next 50 years could be sequestered through forest preservation, tree planting and improved agricultural management. This would offset 10-20% of the world's projected fossil fuel emissions.
  • Storage in the ocean -- CO2 can also be stored offshore in the continental shelf or deep marine sedimentary basins; however, many marine sediments are too thin for geological storage.[3]

Projects

The U.S. Department of Energy's Fossil Energy program is a portfolio of technologies that attempt to capture and permanently store greenhouse gases.[4] According to DOE, to be successful, carbon sequestration techniques and practices must:

--Be effective and cost-competitive,
--Provide stable, long term storage, and
--Be environmentally benign.

The cost of sequestration using current technology is estimated to be from $100 to $300 per ton of carbon emissions avoided. The goal of the DOE's program is to reduce the cost of carbon sequestration to $10 or less per net ton of carbon emissions avoided by 2015.[5]

Specific carbon sequestration initiatives include:

  • The Midwest Geological Sequestration Consortium (MGSC), one of seven regional partnerships created by the U.S. Department of Energy, has begun injecting carbon dioxide (CO2) in a field project in Wabash County, Ill. It is the first of the Regional Carbon Sequestration Partnerships to inject carbon dioxide into a coal seam in the United States. The pilot project is testing the viability of turning unmined coal deposits into a source of useable energy by extracting natural gas, specifically coalbed methane, trapped in the coal.[6]
  • The Weyburn-Midale CO2 project is burying carbon dioxide from a coal gasification plant in North Dakota in a depleted oil field in Saskatchewan.
  • The Salah gasfield project in Algeria, run by BP, strips CO2 from local natural gas and injects it back into the ground.
  • Statoil, a large Norwegian oil and gas company, has a similar project at two places in the North Sea.[7]

Risks & Possible Drawbacks

Some scientists have brought up questions about the feasibility of sequestration projects. For example:

  • Capturing CO2 emitted from coal-fired plants may be unrealistic because the stream of CO2 they emit is relatively thin. Further, goal gasification projects that mix water and oxygen with coal to create usable hydrogen and carbon monoxide (which can be converted to liquid CO2) are expensive to run, as they consume a quarter of the energy they produce just to keep operating. And they may take decades to make a significant contribution to power production.[8]
  • CO2 injected into a geological formation must be closely monitored because if the gas should escape it could be deadly.
  • Conservation and sequestration result in higher stocks of carbon but can lead to higher carbon emissions in the future if ecosystems are severely disturbed by natural or man-made changes.[9]
  • If implemented inappropriately, "biological mitigation" projects may pose risks such as loss of biodiversity, community disruption and ground-water pollution. And they may reduce or increase emissions from other (non-CO2) greenhouse gases.[10]

Other Resources

www.economist.com/special reports


References

  1. Carbon Sequestration. U.S. Dept of Energy Office of Science.
  2. Underground Geological Storage. Intergovernmental Panel on Climate Change.
  3. Underground Geological Storage. Intergovernmental Panel on Climate Change.
  4. Carbon Sequestration. U.S. Dept. of Energy.
  5. Carbon Sequestration R&D Overview. U.S. Dept. of Energy.
  6. "DOE launches carbon sequestration project". Wyoming Business Report.
  7. The Future of Energy: Dig Deep. The Economist.
  8. Why Carbon Sequestration Won't Save Us (Article with excerpt from Tim Flannery's book, The Weather Makers). Treehugger.com.
  9. IPCC Third Assessment Report: Options to Limit or Reduce Greenhouse Gas Emissions and Enhance Sinks. UNEP/GRID-Arendal.
  10. IPCC Third Assessment Report: Options to Limit or Reduce Greenhouse Gas Emissions and Enhance Sinks. UNEP/GRID-Arendal.