Emission Characteristics of CO and NO_{x from Opposed Firing Boiler in a 600 MW Supercritical Unit}

Emission characteristics of CO and NO_x from a 600 MW supercritical boiler with burners arranged in front and back walls were studied by both field experiment and numerical simulation. Results show that the CO concentration in the flue gas is within 500-2 500 mg/m³. The turning point of NO_x emission appears when the excess air coefficient α₁ is within 0.86-0.90 in main burning area, higher than the designed α₁ (0.80) for low NO_x emission, in which case the corresponding ratio of overfire air to secondary air is about 27%-32%. NO_x emission characteristics of the boiler are influenced by the design of its HT-NR3 burner for low NO_x emission, indicating a negative correlation to CO emission. At the load of 600 MW and a constant total air volume, the rise of overfire air ratio from 32% to 49% would result in a significant reduction of CO concentration and combustible contents in fly ash, but an increase of NO_x emission, when the influence of oxygen content on CO and NO_x emission weakens obviously, which may raise the possibility of high-temperature corrosion on side walls in the main burning area.