循环流化床外置换热器壁温偏差改进措施

Improvements of non-uniform distribution of tube wall temperatures in circulating fluidized bed boiler’s external heat exchangers

为了解决660 MW超超临界循环流化床锅炉外置换热器中受热面的壁温偏差问题,通过数值计算,复现600 MW超临界循环流化床锅炉外置换热器壁温分布,并将该方法应用到相同尺寸的超超临界循环流化床锅炉外置换热器壁温计算中.通过对边壁区域3片管屏工质节流,从工质侧解决超超临界循环流化床锅炉外置换热器壁温偏差问题,使受热面计算壁温偏差控制在30℃以内,实现受热面管材安全运行.通过冷态试验,发现颗粒侧传热系数沿外置换热器宽度方向呈现马鞍形的双峰分布,传热系数最大值出现在距离边壁约0.2倍宽度范围内,通过调整边壁区域气体速度可以提高该区域的传热系数,为运行过程减缓局部偏差提供参考.

A wall temperature distribution of the external heat exchanger of 600 MW supercritical circulating fluidized bed boiler was reproduced by numerical calculation, in order to solve the wall temperature deviation of the external heat exchanger of 660 MW ultra supercritical circulating fluidized bed boiler. The result was applied to the calculation of wall temperature of the same size external heat exchanger of ultra-supercritical circulating fluidized bed boiler. By throttling the working medium of three tube platens near side wall, the calculated wall temperature deviation of external heat exchanger of ultra-supercritical circulating fluidized bed boiler was solved. The wall temperature deviation of heating surface could be controlled within 30℃ to keep safe operation of heating surface tubes. Experimental results show that the heat transfer coefficient of the particle side presents a saddle shaped bimodal distribution along the width direction of the external heat exchanger, and the maximum value of the heat transfer coefficient appear at about 0.2 times width near the side wall. By adjusting the gas velocity in the side wall area, the heat transfer coefficient can be improved, so as to provide guidance for slowing down the local deviation in the operation process.