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Carbon Dioxide Sequestration
Carbon dioxide sequestration is a process by which carbon dioxide is removed from the atmosphere and stored indefinitely. There are several methods available, some new and relatively unproven, some as (theoretically) simple as planting trees. An exstensive CO2 sequestration website is under construction by the IEA: http://www.co2sequestration.info/
The first step in sequestration is carbon dioxide capture.
Numerous schemes are possible, some comercially available at present, but
all with a significant cost. An advantage of a Solid Oxide Fuel Cell
power generation is that the exhaust gas contains carbon dioxide and water
but little else, significantly reducing carbon dioxide capture costs.
Further developments of fuel cell systems (perhaps PEM) will allow separation
of Carbon Dioxide as part of the power generation process.
(reference and further info to follow)
A brief description of sequestration methods is given below:
Geological Sequestration
Carbon Dioxide can be pumped into underground coal oil and gas fields and
into saline aquifers. There is significant evidence to suggest that
these techniques can reliably retain sequestered carbon dioxide as many high
purity naturally formed carbon dioxide accumulations have been found.
It is hoped that studying these natural systems will give insight into how
longterm sequestration can be acheived.
A by-product of coal and oil sequestration is enhanced methane production.
This methane can be recovered and the value of the methane used to offset
sequestration costs. The amount of methane is approximately half (by
mol) that of carbon dioxide sequestered. The Dutch government has a
significant feasbility and R&D program underway. Initial indicators
are that economic feasibility is not unrealistic provided that carbon dioxide
reduction bonuses are implemented. Similar pilot projects are underway
in Austrailia and the US.
Ocean Sequestration
The ocean is a primary component of the natural carbon cycle, acting as a
resevoir to balance atmospheric carbon dioxide levels. It is thought
that by deep ocean release of carbon dioxide the amount of carbon dioxide
held can be sigificantly increased. Studies are underway to determine
retention times.
Another method of increasing ocean sequestration is by increasing phytoplankton
growth and hence natural draw down (as plankton dies it sinks taking with
it the carbon captured through photosynthesis). Several trials have
been caried out with positive results. Future work will address concerns
about ecosystem imbalance. This mechanism may infact work against us,
as increased sea temperatures result in lower CO2 solubility - which mans
that global temperature increase caused by green house emmissions could trigger
further 'natual' CO2 emissions compounding the problem...
Mineral and Biological Sequestration
One method of overcoming the gradual leakage of carbon dioxide back into the
atmosphere is to chemically combine it with naturally occuring minerals such
as magnesium silicate. This process happens naturally over long timescales
but research suggests that significantly faster conversion rates are possible.
Biological conversion into carbonates, methane or renewable fuels have also
been investigated.
Terrestrial Sequestration
Afforestation and changes in farming practices can increase carbon sequestration
in terrestrial ecosystems. Work has been done to evaluate the scale
and economic feasability with which such schemes could be implemented.
If you know about Carbon Dioxide Sequestration and want to contribute, please contact me .
Reference:
Greenhouse Issues - July 2001. - http://www.ieagreen.org.uk
A free bimonthly newsletter published by the International Energy Agency on
worldwide developments in the field of greenhouse gas abatement and mitigation.