Scientists know how to return carbon dioxide to the earth, but nothing may come of it

ALBANY — Would you be willing to double the amount you pay for electricity if doing so would remove carbon dioxide from emissions generated by coal-fired power plants?

Researchers at the National Energy Technology Laboratory-

Albany have proven that carbon sequestration — pulling carbon dioxide out of the air and returning it to the earth — will work through several methods, but they doubt anything will come of it on a national scale unless federal regulations are enacted concerning fossil fuel greenhouse gas levels.

The level of carbon dioxide in the atmosphere has risen from 280 parts per million before the industrial age to more than 375 parts per million today, scientists agree. Increased use of fossil fuels is believed by some to be the cause of that increase.

Cathy Summers, research program leader, and geologist Bill

O’Connor, have spent several years studying ways to capture carbon dioxide that some scientists believe contributes to global warming because it traps energy from the sun.

“Our research has focused on converting carbon dioxide from coal-fired power plants into a solid or slurry solution and keeping it out of the atmosphere,” O’Connor said.

To be successful, the Department of Energy believes carbon sequestration techniques must meet these criteria:

• Be effective and cost-competitive.

• Provide stable, long-term storage.

• Be environmentally benign.

The goal is to develop cost-effective technology in the next 10 to 15 years.

Why is such research so important?

“The United States is the Saudi Arabia of the coal world,” O’Connor said.

The United States sits on a huge reserve of coal. In fact, a recent study suggests there’s enough coal to support 100 gigawatts of new electricity generation,

2.6 million barrels per day of refined liquid products and 4 trillion feet of natural gas production.

U.S. energy consumption is expected to increase by 27 percent through 2030. Some believe coal is the answer to that need, but removing carbon dioxide from emissions would be necessary from an environmental standpoint.

O’Connor said there are several methods of storage that can be applied, although each would bear its own additional costs to consumers.

Those applications include:

• Injecting carbon dioxide into the ocean, at about 3,000 meters deep on the ocean floor. At this depth, the carbon dioxide would be a liquid denser than water, and it is believed that it would form a relatively stable pool.

• Carbon dioxide has been injected into a saline aquifer beneath the ocean floor of the North Sea, off the coast of Norway, for several years. Carbon dioxide is separated from natural gas at the off-shore well head, then re-injected. This method could provide the best assurance for the long-term storage of carbon dioxide, but is somewhat unique to this location.

• Carbon dioxide has been injected into depleted oil reservoirs for decades, a method for enhanced oil recovery that results in much of the carbon dioxide remaining in the reservoir. This technology could be used to a greater degree, but would likely provide a limited potential for sequestration.

• Coal bed methane injection of carbon dioxide. The carbon dioxide could be injected into unmineable coal seams, where it would displace the methane which could be recovered in production wells.

• In-ground injection into saline aquifer zones. “This means non potable water,” O’Connor said. “There is a huge capacity for this in the middle of the United States, which is also where more coal-fired power plants exist.”

• Mineralization. This would require capturing the carbon dioxide (all methods of sequestration require a capture step first) and mixing it into a slurry of ground up minerals. The minerals react with the carbon dioxide and when the water is removed, a solid carbonate product is produced. O’Connor said there have been more than 600 autoclave tests concerning mineral sequestration undertaken at the research center. A filter press is used for solid/liquid separation and the solids are dried.

A value added benefit from the mineral carbonation process could also be the development of materials from the recovered carbon dioxide and slurry minerals. Those materials might be used in a diverse range of products such as ceiling tiles.

However, the vast majority of the carbonate product would likely be used to reclaim the silicate mineral mine that supplied the minerals to react with the carbon dioxide.

One of the methods of storage being researched would be in saline aquifers in basalt rock flows, O’Connor said. The individual layers are about 30 meters thick, and in some locations the total thickness of the multiple flows is more than 1,000 meters. Carbon dioxide could be injected into the porous sections and trapped by the solid layers.

There is a huge area of the Pacific Northwest where basalt formations are present, but the best potential may be in central Washington and northeastern Oregon.

O’Connor said a 1.3 gigawatt coal-fired power plant produces about 24,000 tons of carbon dioxide per day. So, it would take a huge quantity (up to 70,000 tons per day) of minerals to supply the process. This would require a large open pit mine for each plant.

A process evaluation indicated that cost could be as much as $2 billion for one mineral carbonation plant sized for the 1.3 gigawatt coal-fired power plant, but this cost could be greatly reduced if a flow-through reactor was used. This would allow the use of less expensive, narrow diameter pipes rather than large diameter high pressure tank reactors.

At this time, the researchers estimate the mineral carbonation step in the carbon sequestration process would add about eight cents per kilowatt hour to consumers’ electrical bills. Carbon dioxide capture and transportation would further add to this cost.

Current mineral carbonation systems would cost about $53 per ton of carbon dioxide sequestered, plus another $25 per ton in energy used. The goal is to develop systems that would be effective for about $10 per ton.

Based on these economic factors, mineral carbonation may best be suited to niche applications, such as the remediation of industrial solid wastes or asbestos mine tailings. Much of the cost involved in any of the sequestration processes would come from actually capturing the carbon dioxide from the power plant exhaust stream.

“A key part of our research has focused on whether the process could be accomplished with off-the-shelf equipment at a cost that’s comparable to other carbon dioxide transfer systems,” Summers said. “We believe it can.”

The researchers also said there’s a natural way to sequester carbon nn by planting trees. Young trees, those less than 50 years old, pull carbon dioxide from the air and put out oxygen, through photosynthesis.

“A 50-year-old Douglas fir appears to be at its peak in terms of carbon sequestration,” O’Connor said. “On the other hand, an old-growth tree that’s growing very slowly, doesn’t do a very good job of it.”

Logs decaying on the forest floor actually release carbon dioxide into the atmosphere.

Alex Paul can be reached at alex.paul@lee.net or 812-6076.

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