By eddy-dissipation(ED) model

the mixed combustion characteristics of a 600 MW unit coal-fired boiler which co-burning ventilation air methane(VAM) was numerically studied. The influence of the VAM's volume fraction on combustion characteristics and NO_x generation characteristics were researched. The results show that

with an in increase in the VAM's volume fraction

the average temperature of main burner region decreases by 30 K at most

however

the scope of decrease is not obvious. Meanwhile

the average temperature above the main burner region increases at first and then decreases. With an increase in volume fraction of methane

the oxygen concentration in furnace cross-section decreases and the production of CO rises. After the VAM is added

with an increase in the methane's volume fraction

the NO_x mass concentration around the burner area of C/D/E/F layer increases

while that around the burner area of A/B layer reduces

by 253.21 mg/m~3 at most. When the VAM with methane's volume fraction of 1.5% is added into the furnace

the NO_x concentration at the furnace outlet decreases from 569.64 mg/m~3 to 519.24 mg/m~3

by 8.85%. The numerical simulation indicates that adding VAM into the furnace not only contributes to saving resources and protecting the environment

but also helps reducing the emission of NO_x.