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Selective Catalytic Reduction

Selective catalytic reduction (SCR) technology is a proven and effective method to reduce nitrogen oxides (NOx) emissions from coal-fired power plants.

How does selective catalytic reduction technology work?

During the combustion process, the nitrogen that is present naturally in the coal, and the nitrogen and oxygen present in the combustion air combine to form NOx.  Prior to being released to the atmosphere, the exhaust gas is passed through a large catalyst where the NOx reacts with the catalyst and anhydrous ammonia and is converted to nitrogen and water. Selective catalytic reduction removes between 80 and 90 percent of the NOx that is in the exhaust gas of a coal-fired power plant.

Why reduce NOx emissions?

Nitrogen oxides in the atmosphere contribute to ground-level ozone.  Nitrogen oxides also undergo complicated reactions in the atmosphere to form fine particles.  These fine particles are referred to as secondary particles because they aren’t emitted directly into the atmosphere.

What is ground level ozone?

Ground level ozone is formed on hot, sunny days by complex chemical reactions between NOx and volatile organic compounds (VOCs). Nitrogen oxides are released into the air from the burning of fossil fuels such as gasoline, oil and coal. The primary manmade sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fossil fuels. In the U.S., motor vehicles are the largest source category for NOx emissions. Motor vehicles, gasoline vapors and chemical solvents are some of the major sources of the VOCs that contribute to ground-level ozone formation. Vegetation can be a significant source of VOCs.

What has Duke Energy done to address safety or environmental concerns associated with using selective catalytic reduction technology?

Anhydrous ammonia is a compressed, liquefied gas which is typically stored on at the power plant where it is used. It has the potential to become hazardous if released to the environment. To ensure the safety of our employees, the environment and the public, we have a comprehensive safety and emergency response plan at every station that stores anhydrous ammonia, to be put into action in the unlikely event of an accidental release. In addition, all of Duke Energy’s anhydrous ammonia systems are designed with redundant safety features and systems (leak detection, automatic shutoff valves, etc.) to further reduce the risk of an accidental release. Other sectors that use anhydrous ammonia include agriculture, chemical and pharmaceutical manufacturing, water and wastewater treatment, pulp and paper, and many more.