The term NOx, or nitrogen oxides, refers to the reactive gases that are formed through the combustion process. Nitrogen oxides are formed when fuels such as coal, natural gas, or even waste/trash are burned at high temperatures.
The 1990 amendments to the Clean Air Act were created specifically to address NOx emissions. These NOx emissions have been directly associated with environmental issues including acid rain, ground level ozone and atmospheric ozone depletion.
Ammonia Application in DeNOx
Ammonia, both anhydrous and aqua, is injected in the DeNOx or de-nitrification process to reduce the NOx and convert it into nitrogen and water, allowing for a cleaner emission through the stack.
The emissions control systems that are primarily in use today to facilitate the DeNOx process are Selective Catalytic Reduction; commonly know as SCR, and Selective Non-Catalytic Reduction, or SNCR.
The Selective Catalytic Reduction process uses ammonia to reduce NOx by injecting it into flue gases while passing over a catalyst. Extremely high levels of NOx reduction, typically around 90 percent are accomplished in this manner. SCR systems are in use at power plants, high pressure boiler refractory with exhaust, chemical manufacturing plants, and some steel mills and crude oil refineries.
The Selective Non-Catalytic Reduction process relies on ammonia injection into hot flue gas streams to react with the NOx at high temperatures. The NOx reduction varies with technologies and fuels that are burned, but typically a 50-70 percent reduction rate is achieved.