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Through 2009, Southern Company has invested about $7.5 billion in environmental
controls. We are planning to spend an additional $2.4 billion through 2012 to further reduce
emissions of nitrogen oxides, sulfur dioxide and mercury. Devices like SCRs, scrubbers and
baghouses require energy to operate. Typically, emission-control devices reduce generation by
about 2.5 percent.
Particulate matter and air quality research
Southern Company participates in data collection and research studies. Two leading studies, SEARCH and ARIES, have provided data to help establish causal relationships between chemicals in the air and their effects on people—and ultimately air quality standards to safeguard human health.
Scrubbers – sulfur dioxide removal
Emissions from burning coal contain sulfur dioxide. The scrubber sprays the combustion emissions with a water and limestone mixture. The sulfur dioxide reacts with the limestone to form gypsum, while water vapor rises out of the stack. The gypsum can be dried and sold for reuse in building materials, like wallboard. Scrubber gypsum is tested and typically purer than gypsum mined from the ground. Scrubbers remove up to 95 percent of the sulfur dioxide. At the end of 2009, Southern Company installed and is operating 19 scrubbers and plans to add 14 more.
How scrubbers work
A jet bubbling reactor is a type of scrubber. It can clean 95 percent of the sulfur dioxide left over from the coal in the flue gas. See how scrubbers work in our interactive demo at our educational site, Learning Power.
SCRs (Selective Catalytic Reduction systems) – nitrogen oxide removal
SCRs remove up to 85 percent of nitrogen oxides, another emission from burning coal. An SCR, or selective catalytic reduction system, adds ammonia to the gases 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 first SCRs was judged to be the best in the industry, according to a study by the Electric Power Research Institute. We have 15 operating SCRs with 10 more planned.
Baghouses – particulate removal
Baghouses collect flyash and other particulate matter. Baghouses work like vacuum cleaners, forcing the flue gas through filter bags, which collect more than 99 percent of the dust particles.
Mercury reduction research
Mercury emissions from power plants amount to the equivalent of about five grains of sand for every ton of coal used. Because of these tiny amounts, finding and capturing the mercury in power plant emissions is challenging. We have pioneered the first full-scale test of activated carbon injection into baghouses for mercury control at the nation's first test center for mercury emissions at Gulf Power's Plant Crist. The testing has not only been conducted for Southern Company but also for a variety of other companies, environmental research organizations and government scientists.
