Influence of overfire air rate of the two‐channel overfire air on flow and combustion characteristics in a 600‐MWe boiler.

To solve the problem of high NOx emission of 600‐MWe boilers in power plants, we established a cold gas–solid modeling testbed scaled by 1:5 for two‐channel overfire air (OFA). A phase‐Doppler anemometer was used to measure the characteristics of the outlet flow field of the two‐channel OFA under different OFA rates. We also verified the industrial feasibility of this testbed under loads of 300 and 600 MWe. The influence of the OFA rate on the divergence angle of the outlet jet was small: When the OFA rate was increased from 15% to 35%, the divergence angle only increased by 2.2°. The attenuation of the axial velocity of the outlet jet increases with increasing OFA rate. For OFA rates of 15% and 25%, the jet penetration depth was between 1.5d and 2.5d (where d is the cone diameter of the OFA model in the cold‐flow experiments). When the OFA rate was 35%, the jet penetration depth was between 2.5d and 3.5d. The jet maintained about 17% O2 concentration at 1.4 m (about 11d) in the furnace under different boiler loads, and the concentration of emitted NOx increased with decreasing load. Based on these findings, we propose the use of two‐stage OFA: The jet at the outlet of the first‐stage OFA ports should have a larger jet‐divergence angle, and the other stage should have a larger jet‐penetration depth to realize full mixing with the flue gas and to ensure high burnout and low NOx emission. [ABSTRACT FROM AUTHOR]