Real-Life Trial Of CO₂ Capture

A Wisconsin utility fired up an ammonia-based pilot project this week to capture and remove carbon dioxide from an operating coal-fueled power plant. If successful, the technology could be added to all coal or natural gas power plants to capture CO₂ for sequestration underground and potentially eliminate fossil-fuel-fired electric utilities as sources of atmospheric emissions of this greenhouse gas.

The pilot project is a partnership of Alstom, a France-based international construction and engineering firm; the nonprofit Electric Power Research Institute; and We Energies, a midwestern electric utility. The project involves a 1,210-MW power plant in Pleasant Prairie. The one-year trial will remove CO₂ from less than 1% of its flue gas waste stream. It is a catch-and-release experiment: The system will be monitored, but the CO₂ ultimately will be vented.

The pilot is a "critical step" to developing a cost-effective carbon capture technology to address global warming, "one of the most important environmental challenges facing utilities," notes Gale E. Klappa, chairman of We Energies. With 50% of U.S. electricity and 30% of CO₂ emissions coming from coal, he says, carbon capture technologies are essential to the future of energy and coal-related industries. A successful project will mean large profits. Some 30 companies are cosponsoring the Wisconsin trial.

To capture the CO₂, Alstom officials say, a chilled-ammonia approach that has been tried before-but only in laboratories-will be scaled up. Basically, flue gas temperature is lowered to 0–10 °C to put the system in the optimal range for the ammonium carbonate/bicarbonate system to form solids as chilled ammonium carbonate is introduced to the flue gas system.

"We want to form an ammonium bicarbonate crystal, which gives us greater carrying capacity for CO₂," explains Robert G. Hilton, director of business development for Alstom.

After the CO₂ is captured, Hilton says, the resulting mixture is then pumped to a regenerator. There it is heated to more than 100 °C, and the bicarbonate reverts to carbonate and to CO₂, which is concentrated under pressure. The intended result is a high-pressure, 90%-pure stream of CO₂ and the separation of ammonia for reuse.

The CO₂ capture system uses a lot of energy, and Alstom's target is to get the energy use of the collection system down to 20–25% of a plant's total output. If successful, Alstom predicts, the system will jack up the cost of electricity by 6 to 9 cents per kilowatt-hour-approximately doubling the current cost per kilowatt—hour.

Dow has also joined in the technology development process and is working with Alstom to develop an advanced amine-scrubbing technology.

Depending on results, the trial may grow. American Electric Power and Alstom plan to install the technology later this year at AEP's New Haven, W.Va., electric plant and in 2011 at an AEP power plant in Oologah, Okla. These programs will be larger and will actually sequester the CO₂.

But a Department of Energy review of Alstom's approach raised some questions about the technology, and DOE is not funding chilled-ammonia projects. Instead the agency supports a number of other solvent- and amine-based CO₂ removal technologies.

"There is so much we don't know about these technologies," Thomas Feeley, DOE technology manager, says. "Everybody is still low on the learning curve, and there are many opportunities for new technologies to be developed." But Feeley says he applauds the Wisconsin project.