考虑辐射强度沿截面方向减弱的炉内传热公式

分析了以2个平行平面辐射换热公式作为蒸汽锅炉炉内火焰对四周水冷壁进行辐射传热计算的基本公式,该式是在炉膛截面各处温度相同、从炉膛中心到四周水冷壁平面不发生辐射强度任何减弱的前提下获得的,因此,计算偏差在所难免.假设炉膛为横截面积和高度与近似矩形立方体的炉膛横截面积和高度相同的当量圆柱体,以辐射强度沿射线行程变化的能量方程,推导出一维(横截面的径向)的辐射能在从炉膛中心向四周壁面传递时因火焰介质的吸收、自身辐射和散射作用造成的辐射强度的减弱,并在此基础上推导出考虑了辐射能沿截面方向从炉膛中心向四周壁面减弱后的炉内辐射传热公式.分析了所得公式的特点和适用性.所提出的公式和现有某些计算方法,对大型煤粉电站锅炉燃用含灰量不同的3种典型烟煤时分别进行了炉膛出口烟温的计算,并进行了比较,分析了这些方法存在的不足.

Study on radiation heat transfer in boiler furnaces by taking radiant intensity attenuation in cross section into consideration

Using the radiation heat transfer formula between two infinite parallel plates as the basic method to calculate the radiation heat transfer from the furnace flame to the surrounded furnace water wall of steam boilers is analyzed in this paper.Since the basic condition assumes the flame temperature to be uniform elsewhere in the cross section of the furnace and without any attenuation of radiation intensity from the furnace central line to the surrounded water wall,the deviation of the calculation results is unavoidable. The calculation formula of furnace radiation heat transfer in the 1973-normative method of pre-Russia has the same necessary condition as that of two infinite parallel plate formula.Assuming that the boiler furnace is cylindrical with the identity of the cross sectional area and the height,based on the radiant energy transfer equation mentioned by Robert Siegel,and taking account of the medium Absorption,emission and scattering along the path of the radiation ray,the one dimensional equation of the radiation intensity attenuation from the furnace centre to the surrounded water wall has been derived in this paper,and furthermore, the radiation heat transfer calculation formula for the furnace flame of pulverized-coal steam boilers has been obtained.The characteristics of the obtained formula and its suitability for the radiation heat transfer calculation of steam boilers furnaces are analyzed.The obtained formula has been used to calculate the furnace exit flue gas temperature for the modern power plant boilers burned with different ash contents of three typical bituminous coals and the results are compared with those of some other calculation methods and the comment on the relevant calculation methods is made.