Abstract: The big slag chunks were formed and fell off frequently in operation of Zouxian Power Plant ultra-supercritical boilers, and these caused some problems, such as the emergency door of the slag-off machine was opened by bulge force, the water seal lost, the negative pressure in furnace fluctuated, the temperature of flue gas rose, the superheating surface went up abnormally etc. The safety, stable operation of units was affected seriously. The reason of slagging in ultra-supercritical boiler was defined by analysis of fuel characteristics, boiler design, operation adjusting and others, and the relevant preventive measures were proposed according to the analysis.

Key words: ultra-supercritical boiler, slagging, reason analysis, measures