In the operation process of SG2080/25.4-M969 type boilers for ultra-supercritical units no.3 and no.4 in Guohua Cangdong Power Generation Co Ltd

owing to frequent overrun of the tube-wall temperature in final-stage superheater

the temperature of superheated steam in said two boilers can't reach the designed values.Taking boiler no.4 as the object of study

the causes leading to frequent overrun of tube-wall temperature in final-stage superheater have been tesed

it shows that the main cause resulting in frequent overrun of the left-side tube-wall metall's temperature is the non-uniform temperature field at the left-side in the horizontal flue duct.Through adjustment of the air distribution mode

the difference value between the left-side superheated steam temperature and the highest tube-wall metall temperature has been reduced

enhancing the operation value of the left-side superheated steam temperature.Moreover

cacellation of differential pressure control mode for boiler-windbox has been recommended

the open-degree of secondary air gate being maintained at a relative stable level in a certain load range

so as to obtain a stable flue gas temperture field and stable speed field distribution.After the said adjustment

the temperature of fianl-stage superheater in boiler no.3 and no.4 can close to or reach the designed value in operation.