煤粉锅炉二次风挡板及喷口阻力特性数值计算

Numerical Calculation of Resistance Characteristics of Secondary Air Baffle and Nozzle of Pulverized Coal Boiler

【目的】优化锅炉二次风量调节是提高锅炉经济性的常见手段,能降低CO_(2)和NO_(x)排放,减少环境污染,助力我国早日实现“碳达峰”和“碳中和”目标。在此基础上,提出一种便于工业应用的监测和调控四角切圆锅炉燃烧器喷口的二次风的方法,帮助电厂提高四角切圆锅炉二次风量调节的准确性。【方法】根据某电厂350 MW四角切圆锅炉的二次风管道结构特性和燃烧器的结构特点,采用冷态数值模拟,对挡板入口到燃烧器喷口建立局部几何模型,采用ICEM-CFD划分网格,通过FLUENT进行流场数值计算,以挡板开度为唯一变量,得到挡板不同开度下的喷口和挡板的阻力系数,进而获得热态运行中挡板开度与流量的精准对应关系。【结果】通过计算得到的不同挡板开度下的阻力系数,可绘制出挡板及喷口的阻力特性曲线,发现该曲线的变化趋势有明显的区间分布,通过对比分析可得到二次风挡板调节流量特性较好的有效行程区。通过分析挡板和喷口阻力在不同挡板开度下的占比情况,发现在挡板的有效行程区内,喷口的局部阻力不可忽视。以挡板开度为100%时的阻力系数作为喷口的阻力系数,以此为基准可得到挡板单独的阻力特性曲线,对比得到两种挡板的调节特性异同。【结论】所提方法的计算结果可以为调节挡板开度,控制热态运行时二次风量的分布提供参考。

[Purposes]Optimizing the boiler secondary air volume regulation is a common means to improve the boiler economy,it could reduce CO_(2) and NO_(x) emissions,reduce environmental pollution,help China to achieve the goal of carbon emission peak and carbon neutrality as soon as possible.On this basis a method of monitoring and regulating the secondary air of burner nozzle of quadrate tangential boiler was presented,which was conve⁃nient for industrial application,and helped to improve the accuracy of secondary air volume regulation of quad⁃rate tangential boiler.[Methods]According to the structural characteristics of the secondary air duct and burner of a 350 MW tangentially fired boiler in a power plant,the cold numerical simulation was used to establish a lo⁃cal geometric model from the baffle inlet to the burner nozzle,the grid was divided by ICEM-CFB,the flow field was numerically calculated by fluent,and the resistance coefficients of the nozzle and baffle under different baffle openings were obtained with the baffle opening as the only variable.Then the accurate corresponding rela⁃tionship between opening and flow in hot operation was obtained.[Findings]Through the calculated resistance coefficient under different baffle opening,the resistance characteristic curve of baffle and nozzle was drawn.It was found that,the change trend of the curve had obvious interval distribution.Through comparative analysis,the effective stroke area with good flow regulation characteristics of secondary air baffle could be obtained.By analyzing the proportion of baffle and nozzle resistance under different baffle opening,it was found that the local resistance of nozzle could not be ignored in the effective stroke area of baffle.Taking the resistance coefficient of 100%of the baffle opening as the resistance coefficient of the nozzle,as the benchmark,the separate resistance characteristic curve of the baffle could be obtained,and the similarities and differences of the adjustment charac⁃teristics of the two baffle could be compared.[Conclusions]The calculation results of the proposed method could provide a reference for adjusting the opening of baffle to control the distribution of secondary air volume in hot operation.