Numerical Simulation Of The Effect Of Over-Fire Air On Flow And Combustion In Furnaces

The use of over-fire air as a means of reducing the concentration of NON, emitted by boiler, has gradually got popularized in China. A numerical simulation study on the effect of over-fire air on flow, combustion and heat transfer, during full capacity operation of a pulverized coal fired 600MW boiler with cross firing, has been started. Mixture fracture/probability density functions are used to simulate turbulent combustion; a P-1 radiation model is used for simulating radiation heat transfer, the Langrange/Euler's method is used for dealing with momentum, mass and energy exchange between the solid and the gas phase; the single rate model for devolatilization and the kinetics/diffusion limited combustion model for simulating surface combustion of pulverized coal particles. Study results indicate that over-fire air helps the current to spread wider in the furnace, delays the introduction of oxygen during the combustion process; the reducing atmosphere in the furnace gets boosted, and the maximal flame temperature is reduced, which helps to reduce the concentration of emitted NOR. But on the other hand, the use of over-fire air reduces the combustion efficiency of pulverized coal, Figs 5, Tables 2 and Refs 8.