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Nitrogen Oxides

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 NO_x, 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, NO_x is composed of colourless nitric oxide (NO), and the reddish-brown and very toxic and reactive nitrogen dioxide (NO₂).

Other nitrogen oxides, such as nitrous oxide N₂O, are not regulated emissions.

Gas Turbines

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.

See also: Gas Turbine, Nitrogen, Nitrous Oxide, Oxygen, Toxic Emission.

Subjects: Chemistry Environmental