燃尽风对炉内流动和燃烧过程影响的数值模拟

燃尽风作为降低锅炉NOx排放浓度的一个措施已在我国得到逐步推广应用。应用数值模拟方法，对1台600MW对冲燃烧煤粉锅炉，在满负荷下燃尽风对炉内流动、燃烧和传热过程的影响开展了研究工作。应用混合分数／概率密度函数法模拟湍流燃烧，用P-1辐射模型开展辐射传热模拟，利用拉格朗日／欧拉法处理气固两相间的动量、质量和能量交换，对挥发份的析出采用单步反应模型，采用动力／扩散反应速率模型模拟煤粉颗粒的表面燃烧。研究发现：一方面，燃尽风的应用改善了炉内气流的充满情况，延迟了煤粉燃烧过程氧气的供应，加强了炉内的还原性气氛，降低了炉内最高火焰温度，有利于降低NOx排放浓度；但另一方面。燃尽风的应用将导致煤粉燃烧效率下降。

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 NO_x,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 600 MW boiler with cross firing,has been started.Mixture fracture/probability density functions are used to simulate turbulent combustion;a P-I 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 kinitics/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 NO_x.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.