NOx Emission Characteristics of a Self-recirculation Type Tubular Flame Burner

Abstract

With use of the ejector effect of tangentially injected high-velocity gas streams, a self-recirculation type tubular flame burner has been newly designed and its NOx emission characteristics have been determined. The burner has eight tangential injectors, each of which a recirculation pass is connected. The extent of recirculation of the burned gas is varied by changing the number of the recirculation path opened. Results show that with an increase of the number of the recirculation path opened, the NOx emission is decreased. For the stoichiometric premixed combustion, the NOx concentration without recirculation is 84 ppm, which is reduced to 46 ppm when all the eight recirculation passes are opened. For the stoichiometric rapidly-mixed combustion, in which methane is injected through two injectors while air is injected through any of the other six injectors, the NOx concentration without recirculation is 75 ppm, which is reduced to 31 ppm for the other six recirculation paths opened. This value is further reduced to 9 ppm at an overall equivalence ratio of 0.8 (the air excess ratio of 1.25). The temperature distribution is determined along the burner axis and it is found that with an increase of the number of the recirculation path opened, the high temperature zone shrinks and its distribution is flattened below 1200°C for premixed and rapidly-mixed combustion. This suppression of high temperature zone may lead to significant reduction of NOx emission in the present burner.