How to reduce NOx

* Combustion Modifications
Reducing the flame temperature at the peak combustion area will mean reduction of NOx formation. This is the most effective method to control NOx and Fluidized Bed Combustion which maintains low temperature (850-950 oC) combusiton area is proven to be the best method to combat NOx problem.

* Flue gas treatmen
Flue gas treatment to remove NOx is useful in cases in which higher removal efficiencies are required than can be achieved with combustion control. Selective Catalytic Reduction (SCR) is the most advanced and effective method for reducing NOx emmissions. In selective catalytic reduction, the NOx species are reduced by NH3, ultimately to N2 gas. The predominant reactions are;

4NO+ 4NH3 + O2 -- 4N2 + 6H2O
2NO2 + 4NH3 + O2 -- 3N2 + 6H2O

Ammonia is vaporized and injected down ｓｔeam from the boiler feed water preheater as shown in the figure below.