Waste-to-energy facilities are subject to standards that are among the most stringent in the world. Under the Clean Air Act, more than $1 billion was invested in upgrades to air quality control systems at America’s waste-to-energy facilities. The results were so dramatic that the U.S. Environmental Protection Agency wrote that the “upgrading of the emissions control systems of large combustors to exceed the requirements of the Clean Air Act Section 129 standards is an impressive accomplishment.” In addition to combustion controls, waste-to-energy facilities employ sophisticated air quality control equipment.
- A “Selective Non-Catalytic Reduction” or “SNCR” converts nitrogen oxides – a cause of urban smog – to harmless nitrogen by spraying ammonia or urea into the hot furnace.
- A “scrubber” sprays a mixture of lime and water into the hot exhaust gases. The lime neutralizes acid gases, just as a gardener uses lime to neutralize acidic soil. Scrubbing also can improve the capture of heavy metals such as mercury in the exhaust gases.
- A “carbon Injection” system blows powdered carbon into the exhaust gas to absorb mercury. Carbon injection also reduces emissions of trace organics such as dioxins.
- A “bag house” works like a giant vacuum cleaner with hundreds of fabric filter bags that clean the air of soot, smoke and metals.
As a result of the controls employed at these plants, dramatic reductions in emissions have been achieved, leading EPA to conclude that waste-to-energy generates electricity with “less environmental impact than almost any other source of electricity.”
|Pollutant||1990 Emissions||2005 Emissions||Percent Reduction|
|CDD/CDF, TEQ basis*||4,400 g/yr||15.0 g/yr||99+%|
|Mercury||57 tons/yr||2.3 tons/yr||96%|
|Cadmium||9.6 tons/yr||0.4 tons/yr||96%|
|Lead||170 tons/yr||5.5 tons/yr||97%|
|Particulate Matter||18,600 tons/yr||780 tons/yr||96%|
|HCI||57,400 tons/yr||3,200 tons/yr||94%|
|SO2||38,300 tons/yr||4,600 tons/yr||88%|
|NOx||64,900 tons/yr||49,500 tons/yr||24%|
|*dioxin/furan emissions in units of toxic equivalent quantity (TEQ), using 1989 NATO toxicity factors|