A New Strategy to Help Capture Greenhouse Gas

Scientists trying to combat the so-called greenhouse effect are looking for new ways of capturing and storing carbon dioxide emissions from smokestacks.
Each day, 5,000 tons of compressed carbon dioxide flow from a natural gas plant in central North Dakota beneath the prairie, through 200 miles of pipes, to an oil field in Saskatchewan.

There, the carbon dioxide is pumped nearly a mile below ground into depleted oil reservoirs, where it is expected to remain for thousands if not millions of years, away from the earth's atmosphere and climate.

Most efforts to cut emissions of carbon dioxide one of the main "greenhouse gases" contributing to the world's rising temperatures take one of two approaches. One is developing alternative energy sources, like nuclear and solar power, that do not produce greenhouse gases. The other is trimming energy use through conservation and more efficient appliances and cars.

Now scientists and policy makers are exploring a third strategy: snaring carbon dioxide from smokestacks before it reaches the air and storing it in the ground or ocean.

On Monday, President Bush (news - web sites) said, "We all believe technology offers great promise to significantly reduce emissions, especially carbon capture, storage and sequestration technologies."

That could eventually help the administration reconcile the divergent goals of its energy and climate policies, enabling the construction of power plants that burn fossil fuels while still cutting harmful emissions.

"If you want to stabilize CO2 emissions over a long period of time, we think carbon sequestration is essential," said Robert S. Kripowicz, acting assistant secretary of energy for fossil energy.

But not all the technologies are ready, and financing of research in the United States remains modest, about $40 million a year. As acknowledged by Mr. Bush, current carbon dioxide scrubbers are too expensive. The Department of Energy (news - web sites) has set $2.75 as a reasonable cost for storing a ton of carbon dioxide. Current technologies cost 15 to 20 times as much.

The science of what happens to the sequestered carbon dioxide is also incomplete.

A small quantity of carbon dioxide is harmless it provides the fizz in soda but a cloud of it can be deadly, as in 1986 when carbon dioxide-rich waters from a lake in Cameroon in West Africa suddenly welled to the surface and suffocated 1,700 people. Most scientists contend a sudden, catastrophic release of carbon dioxide from a storage site is unlikely, but environmentalists worry that the carbon dioxide could harm nearby ecosystems, particularly if it is injected into the oceans.

The $15 million project in the Weyburn oil fields in southern Saskatchewan has attracted little attention, in part because it is unremarkable in many aspects. Oil drillers have for years injected carbon dioxide into wells, not to avert global warming, but to increase the flow of oil.

"You can think of it as a detergent," said Roland Moberg, general manager of the Petroleum Technology Research Center in Regina, Canada, which oversees the project. "It washes out additional oil."

What is new about Weyburn and an earlier effort by a Norwegian oil company in the North Sea is that scientists are watching whether the carbon dioxide stays down. A similar project is scheduled to begin in New Mexico this year. Researchers are also creating computer models to predict how the carbon dioxide will shift in the coming years.

The Weyburn fields will eventually hold about 20 million tons of carbon dioxide from the Dakota Gasification Company plant in Beulah, N.D. Until the project started last September, the 12,000 tons a day of carbon dioxide produced by the plant was all released into the air. The carbon dioxide is produced as a waste product from the transformation of coal into natural gas.

Though the disposal of carbon dioxide is straightforward, the technology for pulling it out of emissions is not. A study by Alstom Power Inc. found that installing carbon dioxide scrubbers on a power plant in Ohio would cost several hundred million dollars, sap one-third of the plant's power output and double to triple the cost of electricity.

"Technically, we can do it," said Dr. Nsakala Y. Nsakala, a principal consulting engineer at Alstom in Windsor, Conn. But, he said, "To get something that is commercially viable from a cost point is probably a decade away."

Many environmentalists take a cautious view of carbon sequestration intrigued by the potential, but worried that policy makers might conclude that a simple technological fix exists for global warming.

"As long as it doesn't displace support for efficiency and renewable energy programs," said David Hawkins of the Natural Resources Defense Council. "The first line of defense should be minimizing the creation of CO2 in the first place."

A larger controversy is where to put the carbon dioxide. Depleted oil and natural gas reserves appear to raise the least concern the geologic formations that capped the oil and gas underground for millions of years presumably can hold the carbon dioxide as well but they probably offer enough space to put away the carbon dioxide from a few decades of fossil fuel burning worldwide.

Deep saline aquifers and unminable coal deposits might hold a few centuries worth of carbon dioxide, but are less well understood.

The potential capacity of the deep oceans perhaps a trillion tons of carbon dioxide or more dwarfs those on land. But as ocean waters well up, much of the carbon dioxide would rise back to the surface and into the air, perhaps within a few centuries. Environmentalists also say deep-sea creatures could suffer. The dissolving carbon dioxide makes the water more acidic.

Burning of fossil fuels currently releases about 25 billion tons of carbon dioxide a year, of which about a third, or 25 million tons a day, is absorbed by the oceans.

"We already have an ocean CO2 disposal program," said Dr. Peter G. Brewer, a senior scientist at the Monterey Bay Aquarium Research Institute in Monterey, Calif. "We just pretend we don't."

For several years, scientists led by Dr. Brewer have been conducting what would be called tabletop experiments, except that they are done at the bottom of Monterey Bay.

In 1998, the scientists, using the robotic arms of the institute's small research submarine, squirted about five pounds of liquid carbon dioxide into a glass beaker more than two miles down. To their surprise, the clear blob quickly swelled as chemical reactions drew in surrounding sea water. Viscous tendrils burbled out of the beaker, then bounced and rolled along the sandy floor.

The carbon dioxide does not appear to bother the fish, Dr. Brewer said.

A larger experiment to inject about 60 tons of liquid carbon dioxide from a ship to a depth of 2,600 feet off Hawaii has run into opposition from environmentalists and has been delayed.

The 60 tons of carbon dioxide, which would be piped from a ship several miles offshore, is minuscule in relation to what the oceans absorb from the atmosphere, the researchers said. "You're not going to have any visible mortality," said Howard J. Herzog, a research engineer at the Massachusetts Institute of Technology (news - web sites) who is involved in the project. "We may affect the bacteria."

Isaac D. Harp, president of the Coalition Against CO2 Dumping, agreed that the experiment itself would not cause much harm, but said that it would provide impetus for larger experiments and then full- scale implementation. "The oceans serve so many beneficial purposes," he said. "Why go screw it up?"

Mr. Herzog said the experiment was meant to provide basic science data, not to advocate ocean carbon storage. "Down the line, people are going to want to do this," he said, "and it's better that our policy makers have some scientific evidence."

More advanced concepts could offer less controversial options. Scientists at Los Alamos National Laboratory in New Mexico have designed a coal-burning power plant that releases no carbon dioxide at all. Instead, a stream of pure carbon dioxide from the plant is mixed with magnesium silicate, a chemical reaction that produces solid rocks and locks up the carbon for eons. A small pilot plant could be built within five years.

Mr. Herzog said that when he started his carbon storage research in the early 1990's, others regarded it to be on the scientific fringe.

"It's not going to be the silver bullet," Mr. Herzog said. "There are no silver bullets." But, he added: "It's very encouraging that this type of mitigation path is now being taken seriously at the highest levels of government. It's hard to believe a president of the United States is sort of endorsing this as a viable option."