Nitrogen oxides (NOx) are pollutant gases produced by burning fossil fuels, motor-vehicle exhaust, decaying vegetation, and many industries. Although high levels of NOx are detrimental to human health, the main concern is their role in the production of ozone and acid rain.
Ozone is formed by a series of complex reactions involving other chemical substances, primarily NOx and volatile organic compounds. The most effective strategies in the Tennessee Valley for ozone reduction focus on the control of NOx emissions, since most volatile organic compounds in the region come from natural sources.
A large proportion of the Tennessee Valley’s NOx emissions are generated by human activity: automobiles, trucks, and other mobile sources produce about a third of the total NOx emissions, and fossil power plants produce 10 to 20 percent. NOx is also the second-largest human-generated source of excess acidity in rain, after sulfur dioxide.
NOx emissions at TVA coal fired plants
What TVA is doing about NOx emissions
TVA has reduced its emissions of nitrogen oxides by about 88 percent since 1995. At present, 58 of TVA’s 59 coal-fired units have combustion controls to reduce NOx. The 59th is an atmospheric fluidized bed combustion plant, which, by design, already operates with low NOx emissions
TVA also operates year round selective catalytic reduction (SCR) systems on 21 of its largest coal-fired units and selective noncatalytic reduction (SNCR) systems on 8 smaller units. SNCR includes a variant know has Higher Energy Reagent Technology (HERT). All five of TVA’s natural gas fired Combine Cycle Plants have SCRs to reduce nitrous oxide emissions.
TVA plans to continue a NOx emission reduction strategy that depends primarily on the installation of SCR systems. In August 2011, the TVA Board approved the installation of new SCRs at the Gallatin Fossil Plant by 2017.
TVA staff continue to look for better, more cost-effective ways to reduce emissions while continuing to supply reliable, affordable electricity and manage debt in the light of evolving emission reduction requirements.