Several air-polluting gases composed of nitrogen and oxygen which play an important role in the formation of photochemical smog. Nitrogen oxides are collectively referred to as NOx, where x represents a changing proportion of oxygen to nitrogen.
Internal combustion engines are significant contributors to the worldwide nitrogen oxide emissions. For the purpose of emission regulations, NOx is composed of colourless nitric oxide (NO), and the reddish-brown and very toxic and reactive nitrogen dioxide (NO2). Sometimes defined as Thermal NOx
Other nitrogen oxides, such as nitrous oxide N2O, are not regulated emissions.
NOx Emissions from Stationary Gas Turbines:
- The level of NOx emissions varies for different fuels.
- In the case of thermal NOx , this level increases with flame temperature.
- For gaseous fuels, the constituents in the gas can significantly affect NOx emissions levels.
- Hydrocarbons with molecular weights higher than that of methane burn at higher flame temperatures and as a result can increase NOx emissions greater than 50%.
- Gas fuels that contain significant inert gases, such as CO2, generally produce lower NOx emissions.
- Hydrogen burns with a higher flame temperature and so gases with significant amounts of hydrogen result in higher NOx.
- Ambient conditions affect NOx production:
- Increasing humidity reduces flame temperature as it has a quenching effect and so reduces NOx.
- At high humidity levels and low ambient temperatures, NOx emissions increase with increasing temperature.
- at high humidity levels and ambient temperatures above 10°C NOx emissions decrease with increasing temperature.
- NOx production levels increase with increases in ambient pressure.
"Alternative Control Techniques Document - NOx Emissions from Stationary Gas Turbines", U. S. ENVIRONMENTAL PROTECTION AGENCY, EPA-453/R-93-007