[USCC] More info on Carbon Sequestering

[Jim McNelly]

New Method Could Reduce Carbon Dioxide Levels Safely

By Catherine Lazaroff

WASHINGTON, DC, August 31, 1999 (ENS) - Scientists at the U.S. Department
of Energy’s Office of Fossil Energy have developed a way to bind carbon
dioxide (CO2), a greenhouse gas, with common minerals. The method could
someday be used to reduce the amount of CO2 that human activities add to
the atmosphere. 

The burning of fossil fuels like oil, gasoline and coal sends huge amounts
of CO2 into Earth’s atmosphere. Rising CO2 levels have been blamed for
worldwide environmental changes, including global warming. Though global
emissions of carbon from fossil fuels fell last year, humans still added
6.32 billion tons of new CO2 to the air in 1998. 

Some researchers have been working on ways to remove some of the excess
atmospheric CO2, and prevent the dumping of more CO2 into the air. These
methods, called carbon sequestration or carbon fixation, range in scope
from planting more carbon thirsty crops and forests to pumping large
amounts of liquid CO2 deep into the ocean. 

The method announced last week by the Department of Energy’s (DOE) Los
Alamos National Laboratory would bind carbon to common minerals including
serpentinite and peridotites. The resulting combination, called a mineral
carbonate, could be used to prevent CO2 from fossil fuels from reaching the
atmosphere. 


As forests are turned into farmland, the amount of CO2 absorbed by
vegetation is reduced (Photo courtesy U.S. Department of Agriculture)
"Our approach to sequestering CO2 is based largely on two simple
observations," says Los Alamos team leader Klaus Lackner. "First, carbon
dioxide is not the energetic ground state of carbon, namely one can extract
additional energy from carbon by reacting the carbon dioxide generated in
combustion with magnesium or calcium bearing minerals to form stable
mineral carbonates. Second, although large volumes will be needed, the
required minerals are extremely abundant and can be readily mined." 
To combat rising CO2 levels, the DOE announced in July it has formed two
study centers to study carbon sequestration in soils, plant life and the
oceans. One center, led by the DOE's Oak Ridge, Pacific Northwest and
Argonne national laboratories, will focus on land based sequestration. The
other center, led by the DOE's Lawrence Berkeley and Lawrence Livermore
labs, will study ocean carbon sequestration. The DOE has allocated $9
million to these centers. 

Plants take in CO2 and put out oxygen, making them an excellent natural
resource for mopping up excess CO2. Studies show that some forests,
including tropical rainforest and Douglas fir stands in the U.S. Pacific
northwest, can sequester large amounts of carbon. But other studies
conclude that humans have put so much extra CO2 into the air that simply
planting more trees will not be enough to significantly reduce atmospheric
CO2. 

A study by scientists at the Woods Hole Research Center in Massachusetts,
published in the July 23 issue of the Journal "Science," found that
deforestation and fossil fuel burning in the U.S. added about 27 billion
tons of carbon to the air between 1700 and 1945. Since then, replanted
forests and cropland have removed only about two billion tons of carbon. In
the 1980s, greener land management practices offset only 10 percent to 30
percent of U.S. fossil fuel emissions. 


Oceans absorb more than 50 percent of the CO2 produced by humans, and some
scientists think they could be used to store even more (Photo courtesy
Ocean-Atmosphere Carbon Exchange Study)
Artificial carbon fixing comes with a raft of problems. For example, an
experiment is now underway at the Natural Energy Laboratory of Hawaii
examining whether oceans could serve as storage bins for excess CO2. Oceans
already absorb between 50 percent and 80 percent of the carbon produced by
humans. The lab’s plan is to pump liquid CO2 deep into the ocean, where
scientists believe it would remain in liquid form due to the high pressures
of extreme depths. 
But some environmentalists have criticized the plan, saying warming oceans
would allow the CO2 to turn back into a gas and escape into the air.
Another concern is that the CO2 would make the oceans more acidic, at least
in a localized area, and harm marine life. 

"I don't know any environmental group who is in favor of ocean dumping,"
says Gary Cook of Greenpeace USA. 


Natural sources also add CO2 to the atmosphere. At Lake Nyos in Cameroon, a
1986 underwater eruption sent a deadly cloud of CO2 flooding through a
nearby village (Photo courtesy John P. "Jack" Lockwood, consulting
volcanologist)
Another major concern with large scale CO2 sequestering is that CO2 in its
natural state is a gas. Given a chance, it will escape from storage and
revert to a gaseous state. For many proposed methods of CO2 storage, a
physical barrier to prevent the escape of CO2 would have to be maintained
indefinitely. 
Since CO2 is heavier than air, a sudden release into the atmosphere would
cause the gas to flow near the ground, where it would form a blanket that
would smother all life in its path. The danger of storing gaseous CO2 has
been demonstrated by natural disasters caused by sudden releases of carbon
dioxide. 

In 1986, an underwater eruption at Lake Nyos in Cameroon released enormous
amounts of CO2. The dense gas swept downslope, smothering 1,746 people and
several thousand cattle. Most of the victims were found within two miles of
the lake, but deaths were reported at distances up to six miles from the
lake. 


This cow was smothered by CO2 flowing from Lake Nyos in Cameroon (Photo
courtesy John P. "Jack" Lockwood, consulting volcanologist)
The new method introduced by the DOE avoids these risks by capturing the
CO2 in a solid form. The process could be carried out on a massive scale,
sufficient to bind - in theory - all CO2 produced by humans. The DOE says
there is a large enough supply of the necessary minerals to collect all the
CO2 from the remaining world’s supply of coal. 
The process would also be economical, the DOE says. 

"We have shown that a reasonable goal for this approach is a disposal cost
on the order of 0.8 to two cents per kilowatt hour," says Lackner. 

The engineering concepts and process design that allow scientists to bind
CO2 as a mineral carbonate are described in a paper from the Los Alamos
National Laboratory, the Chichibu Onoda Cement Co., the University of
Tokyo, and the Harvard School of Public Health in Vol. 11, No. 2 of the
international journal "World Resource Review." 

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