Abstract: An experimental study to reduce the NOx emission is conducted in a 220 t/h tangential pulverized coal firing rectangle furnace, with a stereo-staged combustion technique combining horizontal bias combustion (HBC) burners and over fire air (OFA). The primary purpose of this work is to investigate the effects of HBC burners, distribution of secondary air and changing the ratio of OFA on the NOx emission, furnace temperature, and formation of CO and CO2. It is indicated that the combustion is enhanced and furthermore the NOx emission is reduced by 13% after utilizing the new HBC burners. The distribution of secondary air influences the NOx emission obviously, and the concentration of NOx emission decreases to 408 mg/m3 with reasonable distribution of secondary air. When the ratio of OFA is increased gradually from 0 to 0.21, 0.31 and 0.43, the concentrations of CO, CO2 and unburned carbon in fly ash do not change greatly, except the increase of O2 concentration at furnace exit. The temperature level of primary zone tends to lower as a whole, while the temperature level of over fire zone tends to rise at first and then to lower, and the . NOx emission concentration decreases continuously. The NOx emission concentration can decrease to 363 mg/m3 without the operation of tertiary air. The application of stereo-staged combustion technique can make the NOx emission concentration keep at below 450 mg/m3, and which provides an important technical basis for applying this new technique to the large capacity boiler.

Key words: Horizontal bias combustion burner, NOx emission, Over fire air, Pulverized coal boiler, Staged combustion technique