循环流化床锅炉炉膛横向温度非均匀性模型研究

Modeling study on lateral temperature non-uniformity in CFB boiler furnace

随着循环流化床锅炉不断向大型化高参数发展,炉膛截面在尺度上已远超过化工领域的循环流化床反应装置,炉膛内运行参数的横向非均匀性问题愈发突出,尤其是横向温度偏差问题,严重影响锅炉汽水系统安全和高效运行。针对300 MW亚临界三分离器循环流化床锅炉燃烧系统建立二维整体小室模型,模型以分离器为回路单元将截面划分为3个并联的小室,包括炉内气固流动模型、密相区气固横向扩散模型、稀相区气固横向扩散模型、燃烧模型及传热模型等子模型。模型计算和实炉测试结果显示,炉膛宽度方向的温度分布存在明显的不均匀性,炉膛中间小室温度高于炉膛两侧小室,并且温度偏差沿床高方向一直存在。稀相区扩散系数的取值对温度横向分布有明显影响,根据模型计算和测试数据结果比较分析,稀相区的扩散系数取值应在0. 006～0. 010 m^2/s。密相区颗粒横向混合扩散作用强烈,改变各个给煤点给煤量分配时,局部浓度变化很快被强烈的横向混合扩散作用消除,因此炉膛横向温度分布受给煤量分布变化的影响较小,与测试结果一致。导致炉膛温度偏差的主要原因是两侧小室内水冷壁面积比中间小室多,使两侧小室温度偏低,通过调整炉内屏式受热面的布置位置,可有效改善温度分布不均的问题。

With the large-scale development of CFB boilers,the furnace cross-section has far exceeded the CFB reactor in the chemical industry.The lateral non-uniformity of boiler operating parameters,especially temperature,seriously affects the safety and efficient operation of boilers.Accordingly,a two-dimensional cell model is established for the combustion system of a 300 MW CFB boiler.The model divides the cross-section into three parallel cells.The model includes gas-solid fluidization model,lateral dispersion model,combustion model and heat transfer model.The calculation and test results show that the temperature distribution in the width direction is obvious non-uniform.The temperature of the intermediate circuit is higher than that of the sides.The dispersion coefficient of dilute region has a significant influence on the lateral temperature distribution.According to the model calculation and test data,the dispersion coefficient of dilute region should be in the range of 0.006-0.010 m^2 /s.In the dense bed,the lateral dispersion of particles is severe.When the coal flowrate of each coal feeding point is changed,the local concentration of coal is quickly eliminated by lateral mixing and dispersion.Therefore,the lateral temperature distribution of the furnace is less affected by the change of coal feeding distribution.The key point for the temperature deviation is that the water wall area of each cell on sides is larger than that of the middle one.By adjusting the arrangement of the screen heating surface in the furnace,the problem of uneven temperature distribution can be effectively improved.