The Clean Smokestacks Act was signed into law by North Carolina Gov. Mike Easley in 2002 to reduce emissions from coal-fired power plants in the state. In November 2005, Progress Energy's Asheville Steam Electric Plant began operating the first “scrubber” installed under this landmark legislation. Progress Energy has also installed its first scrubber at the Roxboro Plant in Person County, N.C., and will be installing scrubbers every six months through 2009.

The questions and answers below provide more information about the Clean Smokestacks Act and the Asheville Plant's emissions reductions.

How does the Clean Smokestacks Act impact Progress Energy?
Progress Energy is investing between $1.1 billion and $1.4 billion in technologies to reduce emissions at its coal-fired plants in North Carolina.

What is the Asheville Plant doing to reduce emissions?
The Asheville Plant is an industry leader in implementing new technologies. The plant has installed scrubbers, which remove sulfur dioxide, and SCRs (selective catalytic reduction units) to remove nitrogen oxide emissions, on both coal-fired units at the plant. The last SCR was installed in spring 2007.

With these technologies, nitrogen oxide emissions are reduced by 93 percent, compared to 1996 levels, and sulfur dioxide emissions reduced by 93 percent, compared to 2001 levels. In addition, the N.C. Department of Environment and Natural Resources estimates that mercury emissions will drop by nearly two-thirds when Clean Smokestacks implementation statewide is complete in 2013.

How does a scrubber work?
As coal is burned in a power plant, it emits gases through the flue, or stack. Scrubbers work by taking this flue gas and passing it through a tower in which a water and limestone mixture is sprayed. The sulfur dioxide in the flue gas reacts with the limestone to produce gypsum, a useful additive to concrete or for the production of wallboard. The remaining water vapor rises from the stack.

How does an SCR work?
An SCR uses selective catalytic reduction to convert nitrogen oxides to nitrogen and water through a chemical reaction with ammonia. A similar type of SCR is a car's catalytic converter.

Don't those numbers exceed the requirements of the Clean Smokestacks legislation?
The legislation requires a reduction of at least 77 percent in nitrogen oxides by 2009 and a 73 percent drop in sulfur dioxide by 2013. Clean Smokestacks provided the flexibility for Progress Energy to make deeper cuts at some plants in our system, including Asheville.

What visible changes can we see at the plant as a result of these improvements?
People who drive by or live near the plant can see a 328-foot tall stack. The most noticeable change, however, is the visibility of water vapor rising from that stack.

Scrubbers work by spraying flue gas with a water and limestone mixture. The reaction produces gypsum, which is removed for other uses, and water vapor, which rises through the stack. In the past, there were barely visible emissions from the old stacks at the plant, but now people can see the water vapor. The visibility of the water vapor depends on the weather.

How large is the water vapor plume?
The size of the plume, which looks like a cloud, will depend on atmospheric conditions, particularly temperature and humidity. For example, cooler nighttime temperatures result in longer plumes.

Has traffic increased around the Asheville Plant because of these projects?
There are about 80 trucks per day entering and exiting the back gate of the plant, delivering coal and limestone and removing ash and gypsum (the scrubber byproducts) from the site.

Does the plume affect air traffic in and out of Asheville airport?
An analysis of the moisture plume indicates that for a very few hours per year, the plume may reach the approach path of the airport, but it is not expected to have any effect on airport operations. This analysis also indicates that the plume will not be near the vicinity of the airport approach path for the vast majority of the time. The scrubber plume is essentially a cloud, so even for those few hours per year that the plume may reach the approach path, for pilots, it will be similar to flying through clouds.