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Columnists
Sustainability
and Sustainable Development
Larry
Olson, PhD Professor ASU
Polytechnic
Larry
Olson, PhD., Professor, Arizona State University Environmental
Technology Management Program. Dr. Olson holds a Ph.D. in Chemistry from
the University of Pennsylvania, and is an environmental chemist with
interests in remediation technologies and international environmental
management. He can be reached at 480-727-1499 or by email at Larry.Olson@asu.edu.
Carbon
Sequestration
December
/ January 2009/10
In
a previous column we looked at various means of capturing carbon dioxide
from flue gases in power plants. Pilot plants are now being constructed
around the world including a partnership in Charleston, West Virginia
between Dow and the French power plant construction company Alstrom in
which Dow’s amine system will be used to capture 1800 tons per year of
CO2.
Alstrom is also working with a Polish utility to try to capture 100,000
tons per year. Worldwide there are some 5000 large power plants with
annual CO2
emissions of 10 billion metric tons and some 1000 cement manufacturers
emitting 900 million metric tons per year that are potential candidates
for carbon capture.
But to mitigate anthropogenic
carbon dioxide emissions, we must not only capture CO2
but find a way to store it permanently so that it does not enter the
atmosphere. One option under active consideration is to pump CO2
deep underground into salt formations or spent oil and gas wells where
there is an impermeable cap over the formation to keep the gas from
migrating back to the surface. It is estimated that in the U.S. alone
there is the potential to sequester hundreds of billions of tons of carbon
dioxide in this way, and around the world at least 20 Gigatons capacity.
Capture of carbon dioxide from
a point source is followed by compression to a supercritical fluid, with
the density of a liquid but flow properties like a gas, and then transport
through a pipeline to an appropriate geological site. There are about 3900
miles of CO2
pipeline now in existence in the U.S., compared to almost 1 million miles
of natural gas pipelines. Obviously, a major expansion of this pipeline
system will be necessary, including the politically thorny issue of siting
interstate pipelines. But the risks associated with carbon dioxide
pipelines have been shown to be less than that of natural gas lines.
CO2
has been injected underground to enhance oil recovery for more than 35
years, so we have some experience with this technology. But the scale
which is being proposed and the time frame of storage open up a whole new
set of questions. Possible problems include contamination of drinking
water sources, leakage of injected or displaced fluids, and disturbance of
ecosystems. Regulatory oversight of this technology will need to be
developed.
Risk assessments for the carbon
sequestration process are critical, but each site is unique, even within
the same geologic formation. There should be plans for mitigation and
remediation in case of unexpected situations. Problems in long term
storage could include cap rock failure, seismic events and transmission
through faults and fractures. Proper characterization of deep geologic
formations is critical for long term storage, but for much of this we
depend upon penetrating wells. These very wells also represent a pathway
for CO2
to escape back into the atmosphere and so will have to be plugged before
injection begins.
Finally, the ability to
quantitatively account for Greenhouse Gas reductions will be critical in
order to comply with international protocols. This process, called MMV for
Measurement, Monitoring, and Verification, isn’t necessarily
straightforward and proper procedures will need to be developed and tested
in order to prove that carbon has been permanently removed from the
atmosphere.
For more information about carbon capture and
storage see http://pdf.wri.org/ccs_guidelines.pdf.
2008/1234
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