Abstract: There are some problems existing in operation of ultra supercritical unit, which include that the cleanness of watersteam is poor, the scaling speed is higher, the pressure difference of the boiler increases faster and others. The factors influencing on corrosion and scaling of the unit were analyzed. The operation condition of chemical water system was optimized with certain aim. The unit feed water treatment mode had been changed from the reducing fullvolatile treatment mode with adding ammonia and hydrazine to the oxidizing fullvolatile treatment mode with adding only ammonia, which can eliminate some negative influences partly and is helpful for safe and economical operation of the unit.

Key words: ultra supercritical unit, operation condition of chemical water system, optimization, corrosion, scaling