Effect of the Air Temperature on Combustion Characteristics and NOx Emissions from a 0.5 MW Pulverized Coal-Fired Furnace with Deep Air Staging

This paper evaluates the effect of the air temperature on the combustion characteristics and NOx formation in a 0.5 MW laboratory furnace fired by a pulverized coal swirl burner with deep air staging. The temperature and compositions of flue gas and fly ash in the primary zone and the second burnout zone were sampled and measured. The results show that air temperature in the deep air staging has a significant effect on the flame stability, emissions of NOx and unburnt carbon content in fly ash. When the air temperature is increased from 200 to 400 degrees C, in the primary zone (the stoichiometric ratio is 0.85), the ignition of flame is advanced, the flame stability improved significantly, the overall temperature level and combustion rate increased significantly, the CO concentration increased, the NOx concentration decreased significantly, and the carbon, hydrogen, and nitrogen release rates and the char burnout increased significantly. After the overfire air injection, in the second burnout zone, as the air temperature is increased, the NOx concentration decreased but the formation of NOx in the second burnout zone increased significantly, as well as the contribution of N species conversion to NOx. As the combustion reaction is completed, the final char burnout increased from 96.4 to 99.8%.