New possibilities unveiled in ocean storage of excess power plant emissions
Lab researchers have presented evidence that a new method for capturing
carbon dioxide from power plants and placing it in the ocean has less
impact on marine life than atmospheric carbon dioxide release or other
global warming mitigation methods, such as direct injection and ocean
fertilization.
LLNL earth scientists Greg Rau, Ken Caldeira and Kevin Knauss showcased
the research, called carbonate dissolution, Wednesday at the 2001 fall
meeting of the American Geophysical Union in San Francisco.
The proposal would hydrate the carbon dioxide in power plant flue gas
with water to produce a carbonic acid solution. This solution would be
mixed with limestone — which neutralizes the carbon dioxide by converting
it to bicarbonate — and then would be released in the ocean. This
process occurs naturally (carbonate weathering), but at a much slower
pace.
"You are altering the chemistry of the carbon dioxide that causes
a less drastic change to ocean pH (acidity) and is less biologically harmful
than other methods such as direct injection ocean carbon sequestration
and ocean fertilization," said Rau, an LLNL guest scientist who also
works as a senior researcher with the Institute for Marine Sciences at
UC Santa Cruz.
Whether carbon dioxide is released in the atmosphere or the ocean, eventually
about 80 percent of the carbon dioxide will end up in the ocean in a form
that will make the ocean more acidic. While the carbon dioxide is in the
atmosphere, it could produce adverse climate change. When it enters the
ocean, the acidification could be harmful to marine life.
"If the carbon dioxide were reacted with crushed limestone and seawater,
and the resulting solution released to the ocean, the limestone would
buffer the pH (acidity) of the ocean and prevent it from becoming more
acidic," Caldeira said. "Furthermore, the dissolved limestone
would tend to keep the carbon dioxide in the ocean and out of the atmosphere.
This process would occur naturally anyway, but on about a 6,000-year time
scale."
LLNL scientists are now engaged in both experimental and modeling work
to study the feasibility of the proposed method of ocean carbon sequestration.
Caldeira said initial results appear promising.
Researchers believe that the carbonate dissolution process would expand
the capacity of the ocean to store carbon dioxide while minimizing the
amount of carbon going back into the atmosphere, unlike some of the other
forms of carbon dioxide sequestration.
Direct injection of carbon dioxide into the deep ocean will likely negatively
impact marine organisms and their ecosystems, due to the increased acidity.
Recent research shows that the acid-base imbalance can cause exoskeletal
components to decay, retard growth and reproduction, reduce activity and
cause loss of consciousness and even death to deep ocean marine life because
of a disruption of oxygen-transport mechanisms (Science, Vol. 294, p.
319-320).
In addition, Caldeira showed in previous studies that unless carbon dioxide
is converted to some other form before injection, it will degas back to
the atmosphere when diffusion or ocean circulation returns it to the ocean
surface.
In ocean fertilization, the biology of phytoplankton (which grows close
to the ocean surface) is changed so that it increases the conversion of
carbon dioxide to biomass. The conversion is likely to transport acidity
from the surface ocean to the deep ocean.
Rau said private companies operating power plants would need incentives
to start a carbonate dissolution program.
"They need motivation to sequester carbon dioxide, and they need
methods that are effective and are economically and environmentally practical,"
he said.
"Carbonate dissolution allows a power plant to continue burning fossil
fuel but eliminate at least some of the carbon dioxide that is emitted,
and in a way that is probably less expensive and more environmentally
friendly than other carbon dioxide sequestration methods."
LLNL researchers presented their findings Wednesday at the AGU meeting
during a press conference titled "Global Warming Mitigation."