Geoscience Reference
In-Depth Information
I use the example of coal because that is the most plentiful fossil
fuel and a leading candidate for a large-scale CCS deployment. Engi-
neers think that CCS with natural gas will be less expensive at today's
natural gas prices in the United States, but the basic principles outlined
for coal are similar for natural gas. We can simplify by assuming coal is
pure carbon. Then the basic process is:
Carbon
+
oxygen
→
energy as heat
+
CO
2
So combustion produces a desired output (heat that can be used for
electricity generation) plus an undesirable externality, CO
2
.
The trick is to capture the CO
2
molecules before they enter the atmo-
sphere. CO
2
separation is currently in operation today in oil and natural
gas fi elds. However, existing techniques operate at a small scale and are
not appropriate for deployment in large coal-fi red electrical generation.
One promising technology is integrated gasifi cation combined cycle
with CO
2
capture. This process would start with pulverized coal; gasify
it to produce hydrogen and carbon monoxide; further react the carbon
monoxide to produce highly concentrated CO
2
and hydrogen; separate
out the CO
2
with a solvent; then compress the CO
2
; and fi nally ship the
CO
2
and store it. All this sounds complicated, and it is, but it is not much
more complicated than the technologies that are currently used in gen-
erating electricity from coal.
The major issues with CCS are cost and storage. The cost of electric-
ity rises when CCS is added because energy is necessary to separate the
CO
2
from the emission stream. According to the MIT study, the cost of
electricity generation rises by 3 to 4 cents per kWh with CO
2
capture.
This adds about 60 percent to the generation cost for current technolo-
gies, but the MIT team projected that it would add only 30 percent to
the cost of generation for advanced technologies.
10
While the CO
2
capture is the expensive part of the process, trans-
portation and storage are likely to be the more controversial parts. One
problem is simply the scale of the materials that would be stored. The
most likely storage sites are porous underground rock formations such
as depleted oil and natural gas fi elds. Another issue is the risk of leak-
age. This would not only reduce the value of the project (because the
