锅炉风箱二次风流量分配对燃烧特性的影响

Influence of Secondary-Air-Box Air Distribution on the Combustion of a Utility Boiler

为了研究风箱二次风流量分配特性及其对锅炉燃烧特性的影响,在不同二次风风门开度工况下对一台600 MW超临界前后墙旋流对冲锅炉进行数值模拟。结果表明:在相同的二次风风门开度下,各燃烧器流量分配呈现出中间大、两边小的不均匀特性;随着二次分风风门开度减小,燃烧器流量分配不均匀特性逐渐增强,当二次风风门开度由100%减小到40%时,燃烧器之间的流量偏差系数由3.51%增加到6.17%;沿炉膛宽度方向,中心区域氧体积分数较高,两侧区域氧体积分数较低,靠近两侧墙燃烧器的煤粉未燃尽部分是锅炉煤粉未燃尽部分的主要来源;二次风流量分配不均匀性越大,飞灰含碳量、烟气中CO质量分数和炉膛出口NO_x质量分数越大;燃烧器流量分配不均,锅炉燃烧效率下降。

In order to study the flow distribution characteristics of the secondary air box burner and its impact on the combustion characteristics of the boiler,a 600 MW supercritical boiler with front and rear wall swirl hedging has been studied by numerical simulation under different secondary air damper opening conditions.The results show that with the same secondary-air(SA) opening,the SA distribution is non-uniform with the characteristics of more air into the middle burner and less air into the two-side burners.With reduced the SA opening,this non-uniform characteristics is enhanced.When the SA opening decreases from 100% to 40%,air distribution deviation coefficient increases from 3.51% to 6.17%.The oxygen volume fraction is high in the central zone and relatively low in two-side zones along the width direction of the furnace.The unburned carbon from the coal particles from the burners close to the side walls is the main source of the final unburned carbon.With reduced SA opening,the non-uniform characteristics of SA distribution is enhanced,resulting in the increased unburned carbon in fly ash,and increased CO and NO_x emissions.Based on the above,the non-uniform SA distribution has negative effect on the combustion of the boiler and reduce the combustion efficiency.