Combustion Aerodynamics of a Pulverized-Coal, Low NOx Swirl Burner: Influence of Flow Types on NOx Emissions

The combustion aerodynamics of a pulverized-coal, 10w-NOx swirl burner firing an industrial boiler were determined experimentally. Measurements of gas temperature, velocity, particle speed and number density were used to classify the flow type for two different swirl numbers (2.1 and 1.9). The swirl number was changed by adjusting the damper settings on the three combustion air streams of the burner. The measurements indicated that a flame based on Type II flow was associated with the high swirl number (2.1), which produced a high combustion efficiency (98%) and high NOx emissions (700 ppm at 3% 02). The lower swirl number (1.9) produced a Type III flow, which resulted in a flame with high combustion efficiency (97%) and lower NOx emissions (380 ppm at 3% 02). Therefore, a 10% change in the overall swirl number for this burner in the specified boiler, resulted in a major change in the flame type and a significant change in NOx emissions. Lower NOx emissions emanated from the Type III flow.