Clean Coal? New Technology Buries Greenhouse Emissions
for National Geographic News
|May 2, 2006|
As energy prices continue to climb, researchers are stepping up
their efforts to turn black, dirty coal into a green, clean fuel of
Burning coal releases greenhouse gases that have been linked to global warming. But researchers are finding ways to convert coal into a zero-emissions source of electricity.
"When you try to burn coal or convert it to something else, you've got to deal with pretty difficult mineral matter," said Gordon Couch, a technologist with the International Energy Agency's Clean Coal Centre in London.
"You've got sulfur, pyrite, quartz, silica, and all kinds of stuff in with the coal."
Researchers have made progress in limiting some of these emissions in recent years, Couch says.
"For example, about 98 percent of sulfur can now be removed from emissions," he said.
But coal combustion also produces large amounts of carbon dioxide, or CO2, the major greenhouse gas. That's why the long-term goal of clean-coal research is zero-CO2 emissions.
A key to achieving this, Couch and other researchers say, is to capture the carbon dioxide and send it underground instead of releasing it into the atmosphere.
Many technologies now being developed are trying to perfect this so-called carbon-capture technique.
"To reduce [emissions] to zero, you've got to capture the carbon and stick it in the ground," Couch said.
In March the world's largest prototype carbon-capture coal plant opened in Esbjerg, Denmark.
The goal of the pilot plant is to develop technology that will allow the European Union (EU) to reach its target of capturing and storing 10 percent of its total carbon dioxide emissions and 30 percent of the CO2 produced by conventional power stations.
Researchers at the plant aim to develop new types of solvents that can be used to trap CO2 and convert it into solid form as carbon.
"The gas is washed with a liquid solvent. Then you have to compress it and put it down a hole," said Harry Audus, manager of the International Energy Agency's greenhouse-gas research program, based in Cheltenham, England.
"The idea is to improve the capture rate of CO2," he added.
He says new solvents and carbon-capture techniques developed at the plant will also be cheaper and more energy efficient than those currently available.
The project aims to cut the cost of carbon capture by half, from the current 50 to 60 euros (U.S. $62 to $74) to 20 to 30 euros ($25 to $37) per metric ton of CO2.
The Esbjerg project is only the latest venture aimed at addressing the European Union's pledge to cut carbon emissions under the 1992 international agreement known as the Kyoto Protocol.
Still, fossil fuels are expected to provide 85 percent of the EU's energy in the foreseeable future, according to European Science and Research Commissioner Janez Potocnik.
The new Denmark plant will help develop ways to "reduce emissions in the medium term as we move to large-scale use of renewable, carbon-free energy sources," Potocnik says.
In the U.S., President George W. Bush recently pledged two billion dollars for developing new technologies for clean coal.
Among the initiatives is the one-billion-dollar FutureGen project, a partnership between government and the private sector with the goal of building the world's first emissions-free fossil fuel plant. The site of the plant is to be announced soon, with construction set to start in three years.
The ten-year project aims to integrate all existing clean-coal technologies, laying the groundwork for developing power plants that emit no airborne pollutants.
These technologies include coal gasification, in which steam and oxygen are used to turn coal into a synthetic gas that primarily consists of hydrogen. The gas is then combusted to generate electricity.
This gas burns hotter and cleaner than coal, so it is seen as a more efficient fuel. It also gives off greater concentrations of CO2 than combusted coal, which makes the emitted gas easier to trap.
The captured CO2 will be stored deep underground in saline reservoirs and unmineable coal seams. The CO2 can also be pumped into oil and gas formations to help push the fuel to the surface.
"In doing this you can actually recover more oil and gas, as you can use the CO2 to force them out of the ground," Audus said.
Supporters of the project say it should help enable countries carry on using coal as an energy source without polluting the atmosphere.
"FutureGen could allow the world to use advanced coal technology to fuel our planet in an environmentally conscientious way," said U.S. Secretary of Energy Samuel W. Bodman in a statement last month.
Couch says the goal of zero-emissions coal power is "a realistic prospect."
"But we're looking some years into the future," he said.
"FutureGen, for example, is not going to produce its results for quite some time."
In the meantime the world's appetite for coal-fired electricity is expected to grow.
The International Energy Agency anticipates a 43 percent increase in the use of coal as a primary energy source by 2020.
The demand comes in large part from the fact that coal is cheaper and more abundant than oil or natural gas, which estimates suggest are set to run out in 40 years and 60 years, respectively.
(See National Geographic magazine's "Future Power.")
"There's far more coal than oil," Audus said.
"Even the most pessimistic person would probably be fairly happy to concede there's at least 200 or 300 years of coal in the ground."
"In which case," he added, "clean coal technologies will be extremely useful."
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