Numerical simulation of the effect of over-fire air on NOx formation in furnace

Numerical simulations were conducted for an 800MW ultra-supercritical utility boiler. The influences of over-fire air on distributions of temperature, oxygen concentration and NOx concentration were investigated. The results indicate that the using of OFA made a significant influence on parameters in the primary combustion zone. The temperature, oxygen concentration and NOx concentration all decreased here. In addition, Fuel NOx and Thermal NOx were analyzed individually. The formation of Fuel NOx was mainly affected by temperature and oxygen concentration. Thermal NOx increased dramatically with increasing temperature when the temperature exceeded a certain value. According to the result of simulation, the NOx concentration at furnace exit decreased 31.4% comparatively using OFA.