Staged combustion

Primary air (70-90%) is mixed with the fuel, producing a relatively low temperature, oxygen-deficient, fuel-rich zone, leading to only moderate amounts of NOx being formed.

The location of the injection ports and the mixing of over-fire air is critical to maintaining efficient combustion.

This technique is currently used in 116 pulverized coal-fired units on a total capacity of 50 gigawatt electrical (GWe) as a standalone measure.

It is used in combination with other primary measures for NOx control in 175 coal-fired units on a total capacity of 53 GWe.

Air staged supply also leverages a simple configuration and is applicable in small-scale combustion.

[4] The technique involves shutting off the fuel flow from one burner or more to create fuel-rich and fuel-lean zones, achieving some NOx emission control (10%).