Low NO<sub><i>x</i></sub> ammonia / methane combustion with highly preheated air in a furnace

In this study, attempts have been made to utilize ammonia in the industrial heating field, in which highly preheated air around 1000°C is used under high temperature atmosphere inside the furnace 1200°C. The high temperature inlet air and atmosphere are realized in the bench-scale furnace. Ammonia and methane in the fraction of 30%-NH3 and 70%-CH4 based on lower heating value, corresponding volumetric fraction of 55%-NH3 and 45%-CH4 is used as fuel under the fixed thermal input of 40-kW. On the furnace, the nozzle burner is installed in which fuel nozzles are installed inner side of the annular air nozzle, and furthermore, injection nozzles called “F2 nozzle” are installed on the top side of the furnace to inject NH3 separately from the air. To stabilize the combustion field, CH4 is injected from the burner for all cases. Results of exhaust gas measurements show that over 1000ppm of NOx is emitted for NH3 burner injection, however, in the case F2#1-NH3 injection from x = 0.3-m where x is the distance from the burner, NOx is drastically decreased to 464ppm even with high temperature inlet air and atmosphere. NOx concentration is further decreased by increasing the distance of the F2-NH3 nozzle from the air, then, NOx is reduced to 160ppm for F2#6-NH3 injection which is located at 3.3-m from the burner air. Furthermore, unburned NH3 and N2O are not detected for all cases of examined. As a result of species measurement inside the furnace for F2#6 NH3 injection case, it is found that the O2 concentration is significantly low at the upstream of NH3 injection position, thus, injecting NH3 into the low O2 concentration region is considered to be effective to reduce NOx even for NH3 combustion with high temperature inlet air and atmosphere.