Figure 4.10 Typical NOx and CO levels versus excess air. 0.9 1.0 1.1 1.2 1.3 1.4 Excess air factor vs CO and NOx Oxygen Control
In steam generators, oxygen trim can be added to control the excess oxygen levels. Too little oxygen increases CO formation, and too much can increase the NOx. Also, the boiler efficiency is impacted by the excess air levels as discussed in Chapter 3. The higher mass flow also affects the gas temperature distribution throughout the boiler and can affect the superheated steam temperature.