Effects of combined application of OFA and horizontal bias burner on NO_x emission characteristics

An experimental investigation to reduce the NO_x emission during burning bituminous coal has been carried out in a 220 t/h tangential pulverized coal firing rectangle furnace, with a technique combining horizontal bias combustion (HBC) burners in the primary zone and retrofitted seperated over fire air (SOFA) nozzles above the tertiary air. The influences of SOFA on NO_x emission and unburned carbon in fly ash were experimentally studied. Results show that the amount of NO_x emission is decreased to less than 450 mg/m³ adopting the suitable arrangement of OFA, when the time equals 0.32 s as the fuel flows from top primary air to OFA, and reasonable distribution of secondary air, when the excess air coefficient equals 0.85. The unburned carbon content in fly ash is as low as 1.6%-2% at the same time. Adjusting the distribution of secondary air can also improve the tube temperature distribution of superheater.