Reduction and Control Technologies

Overview
Principles of NOx Reduction
Fuel Switching
Combustion Control
Flue Gas Treatment
Fuel Reburning
Choosing the Best NOx Technology for the Job
Summary and References

Principles of NOx Reduction

The actual mechanisms for NOx formation in a specific situation are dependent on the quantity of fuel bound nitrogen, if any, the temperature and stoichiometry of the flame zone, and residence time. Although the NOx formation mechanisms are different, both thermal and fuel NOx are promoted by rapid mixing of fuel and combustion air. Additionally, thermal NOx is greatly increased by increased residence time at high temperature.

Primary combustion modification controls for both thermal and fuel NOx typically rely on the following control strategies:

• Decrease primary flame zone O2 level:
  • Decreased overall O2 level
  • Controlled (delayed) mixing of fuel and air
  • Use of fuel-rich primary flame zone

• Decrease residence time at high temperature:
  • Decreased peak flame temperature:
    • Decreased adiabatic flame temperature through dilution
    • Decreased combustion intensity
    • Increased flame cooling
    • Controlled mixing of fuel and air
    • Use of fuel-rich primary flame zone