Over the next decade, Southern Company plans to install more than two dozen additional scrubbers, more than a dozen SCRs, and several baghouses at power plants throughout our service territory.
Scrubbers remove up to 95 percent of SO2
Emissions from burning coal contain sulfur dioxide. In a scrubber, we spray the combustion emissions with a water and limestone mixture. The sulfur dioxide reacts with the limestone to form gypsum, a reusable compound. The remaining water vapor rises out of the stack.
SCRs remove up to 85 percent of NOx
Another emission from burning coal is nitrogen oxide. An SCR, or selective catalytic reduction system, adds ammonia to the emissions exiting the boiler. A catalyzed chemical reaction breaks the nitrogen oxides down to harmless nitrogen and water. Catalytic converters in autos are similar devices. Performance of Southern Company's 13 SCRs was judged to be the best in the industry, according to a study by the Electric Power Research Institute.
Nitrogen Oxides
Nitrogen oxides form when gasoline, natural gas, coal, or oil is burned at high temperatures. Motor vehicles are the biggest source of NOx. Other sources include cement kilns, power plants, chemical facilities, and industrial boilers. NOx compounds, along with volatile organic compounds and sunlight, react in the atmosphere to form ozone. Ozone, a major component of smog, can cause respiratory problems at high concentrations. Ozone is regulated under the Clean Air Act.
Southern Company has reduced NOx emissions by 43 percent since 1990. By 2015, we forecast reductions of another 60 percent from today's levels using selective catalytic reduction and other technologies.
Click to enlarge and view as PDF. (Online charts updated through 2006.)