Chemical & engineering aspects of low NOx concentration

Two new requirements for low NOx emission from industrial combustion installations are explained. One, which is directed against a previously unsuspected and dangerous form of contamination of certain food-stuffs, calls for a NOx concentration not exceeding 1 ppm at the burner mouth; and the other is a special case of environmental protection in the United States, resulting from greatly accelerated activity in the application of special methods of recovery of indigenous oil. Background mechanisms of NO formation and their reaction rates are reviewed, and the methods of sub-stoichiometric combustion, staged combustion, high excess air combustion, recirculation, interstage cooling and enhanced flame radiation are examined as possible means of producing the recurred low concentrations of NOx. Burner designs capable of meeting both requirements are described.