Oscillating combustion technology (OCT) offers a low-cost retrofit method to reduce NOx emissions and increase furnace efficiency.
Combustion under conditions of an excess air level near stoichiometric concentrations of fuel and oxygen results in maximum flame temperature and high levels of NOx emissions. However, NOx formation is sensitive to temperature and oxygen concentration1-2, so either a fuel-rich or fuel-lean flame generates less NOx than a stoichiometric flame (figure 1). Stoichiometric combustion can be avoided by using oscillating combustion, which creates alternating NOx-retarding fuel-rich and fuel-lean zones within a flame. The patented technique involves forced oscillation of the fuel flow rate to the burner. Heat is removed from the zones before they mix, reducing overall peak flame temperature, and, thus, reducing NOx formation. Heat transfer from the flame to the load increases due to the more luminous fuel-rich zones and the breakup of the thermal boundary layer. The technology3-6 can be applied with ambient air, preheated air, enriched air, and oxygen based combustion.