Control of Nitrogen Oxides. Forms of nitrogen. Nitrogen forms different oxides. NO and NO 2 are principal air pollution interests (NOx). N 2 O N 2 O 3 N 2 O 5 N 2 O 4 N 2 O 2. NO X and SO X : similarities. Emissions of Nitrogen oxides. Relatively higher contribution. Pros and cons.
Relatively higher contribution
Increase with T
Decrease with T
Reaction Rate is fast. Equilibrium is reached in about 0.3 s. Equilibrium conc. of NO is higher
Equilibrum conc of NO is low. Reaction rate is slow. Even at 30 th second it does not reach equilbrium
At high temperature flames, Zeldovich mechanism predictions are high in accuracy.
Forms due to carbon bearing radicals from the
CH+ N2HCN +N
NO in low temperature flames are prompt NO and
weekly depend on T.
Prompt NOx formation cannot be prevented in spite
of the temperature and oxygen amount adjustment.
NO increase by
The same principle as in staged air combustion technique
Since the flame will be physically longer, the hitting of the flame on furnace walls may cause problems like corrosion (aşınma )
The principle is the reduction of NOx to nitrogen and water by using NH2-X (mostly amonnia, NH3) or chemicals like urea.
30-50 % NOx reduction is achieved
Removal efficiencies reaching 99% have been observed
NOx emissions as low as 2 ppm can be observed when this technique is used together with other NOx control techniques
Since the regeneration must be done in oxygen-free medium, the gas flow in the column under regeneration is stopped.