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.
Sulfur Dioxide
Sulfur dioxide is released primarily from burning fuels like coal, oil, and diesel fuel. Because coal-fueled power plants, steel mills, refineries, pulp and paper mills, and nonferrous smelters combust large amounts of fuel, they tend to be at the top of the list for SO2 emissions. SO2 is regulated under the Clean Air Act because of concerns about health effects at high concentrations. SO2 also contributes to acid rain and limited outdoor visibility in some areas.
SO2 emissions are controlled by burning lower-sulfur fuels and by installing pollution-control devices called scrubbers.
Southern Company has reduced SO2 emissions by about 30 percent since 1990. By 2015, we forecast reductions of another 80 percent from current levels.
Click to enlarge and view as PDF. (Online charts updated through 2006.)