Capturing the carbon dioxide that wafts up the smokestack after burning coal (or any other fossil fuel) has been identified by everyone from President Obama to the United Nations Intergovernmental Panel on Climate Change as a critical technology to help keep the lights on while combating climate change. And now there has been yet another successful demonstration that the technology to capture that CO₂ from flue gas might actually work: chilled ammonia can capture more than 88 percent of the greenhouse gas before it goes up the smokestack.

Alstom Power and We Energies have released preliminary data on their carbon capture pilot project at Pleasant Prairie, Wisc. The pilot plant, set up to siphon the CO₂ from a small stream of the total flue gas using chilled ammonia, not only captured most of the CO2, it captured it in a more than 99 percent pure form, according to Robert Hilton, vice president of power technologies and government affairs at Alstom, which is important for any future storage or industrial reuse. "We can [capture] 90 percent [of the CO₂] and do it consistently," he notes. "We've done over 90 percent at times."

So far the project has run some 4,600 hours continuously without issue and captured some 18,000 tons of CO₂ over the last year.

Because this was just a demonstration project, Alstom didn’t do anything with the CO₂, which in the future would either be sold to industrial users for carbonated beverages or oil recovery or pumped deep underground for permanent storage. Alstom just re-released the CO₂ right back up the smokestack with the other flue gas.

A similar demonstration project using Alstom's chilled ammonia at AEP's Mountaineer power plant in West Virginia this fall aims to be the first to put together the full package. "It really will be the first plant that will take flue gas from a coal-burning power plant, clean it, remove the CO₂, compress it and inject it in a true sequestration at 8,300 feet deep," Hilton says. "It's the first time that will be done anywhere in the world."

Following that test and others, the company plans to have the chilled ammonia technology available for sale by 2015.

Of course, employing such technology uses up much of the energy produced by burning the coal in the first place. Although Alstom declined to give exact figures, Hilton claimed the process used up less than 25 percent of the electricity produced: "We expect chilled ammonia to be in the low 20s."

In other words, capturing that CO₂ will cost between $50 and $90 per metric ton, though Hilton believes that scaling up the process and refining it will reduce that cost to as little as $20 per metric ton of CO₂. That could make such carbon capture and storage a cheap alternative for avoiding CO₂ emissions under any regulatory scheme to fight global warming, such as the cap-and-trade proposal currently being debated in Congress.

The company is also developing amine scrubbers as well as pilot projects in Europe of so-called oxyfuel combustion—burning coal in pure oxygen to create flue gas of nearly pure CO₂.

The reason to pursue multiple technologies, Hilton says, is because they can be added on to existing plants—either by replacing the boiler in the case of oxyfuel or adding processes to the back-end in the case of amine and ammonia. And that may be the key to halting the CO₂ emissions from power plants driving climate change. As Hilton says: "You can't make any of the goals [for emission reductions] anybody's proposed without doing the existing fleet."

Credit: Courtesy of We Energies