Since acquiring the Potomac River Generating Station in 2000, Mirant has made several major improvements to minimize emissions and operate more cleanly. Potomac River — and our other three plants in the D.C. area — comply with operating permit emission limits. For example, our opacity — a measure of emissions leaving a smokestack — is less than five percent, compared to permitted limits of 20 percent.

Tim Martin, senior CEM technician, checks monitors on the rooftop of the Potomac River Generating Station.

We control NOx emissions through:

• Low NOx burners that inhibit NOx formation;
• Separated over-fire air (SOFA) systems that inhibit NOx formation;
• Modern computerized control systems to optimize combustion and minimize NOx formation; and
• Combustion tuning program.

We control particulate emissions through high-efficiency, “hot” and “cold” electrostatic precipitators capable of removing 99.7 percent of fly-ash. Each hot precipitator has a particulate collecting area equivalent to six acres. This is approximately three times larger than typical units of this type.

We control SO2 emissions through:

• Low-sulfur coal; and
• Trona injection, an innovative, patent-pending system developed by Mirant. Read more about trona»

Monitoring air quality

Air emissions are controlled and monitored using a Continuous Emissions Monitoring (CEM) system that monitors NOx, SO2, CO2 (carbon dioxide), CO (carbon monoxide) and opacity. Real-time data is collected and reported to the U.S. Environmental Protection Agency (EPA) and the Virginia Department of Environmental Quality (DEQ) on a quarterly basis.

In addition, the DEQ and the City of Alexandria Department of Transportation and Environmental Services conduct semi-annual inspections of the plant’s air quality equipment and record keeping.

More system-wide reductions coming

In 2004, Mirant Mid-Atlantic agreed with state and federal agencies to invest in equipment and technology to reduce NOx emissions from our four Mid-Atlantic plants — including Potomac River — by about 65 percent over seven years.

At the Potomac River plant we are using technology, including our new trona technology, to substantially reduce emissions and concentrations of SO2 and NOx. Most power plants have stacks that are often hundreds of feet high, so that emissions are dispersed over a large area. Our stacks are only 161 feet high — among the shortest for a coal-fired facility in the United States — because when the plant was built, there was some concern that higher stacks might endanger aircraft taking off and landing at National (now Reagan National) Airport. The Federal Aviation Administration (FAA) has given us permission to increase our stacks by 50 feet, which would still make them among the shortest but would disperse emissions over a much larger area and thereby benefit those living around the plant in Alexandria. Upon receiving final approval we will apply for the necessary permits to increase stack heights.

At our Morgantown station in Maryland, selective catalytic reduction (SCR) technology will be installed on both units, benefiting the greater D.C. metropolitan area. In addition, we plan to make a significant investment at our Maryland facilities to curb SO2 emissions to comply with Maryland’s Healthy Air Act.