Comprehensive Analysis Of The Oxide-skin Exfoliation In Large Capacity Supercritical Pressure Once-through Boiler

With the fast development of our country electric power construction, the newly-built units gradually orient to large capacity and high parameters. Supercritical and ultra-supercritical units will become leading electric power units in our country. However, parameters of units become higher, the metals'oxide-skin issue will bring about more outstanding effects on operation of boiler and turbine.This article presents a comprehensive analysis on issue of oxide-skin on boiler metal heating surface, and mainly covers formation mechanism of oxide-skin. Effecting factors of exfoliation of oxide-skin, effects on operation of boiler and turbine arising from exfoliation of oxide-skin and how to prevent the SPE (solid particle erosion) problem of turbine throughout part from exfoliation of oxide-skin, etc.This article, based on exfoliation of oxide-skin of the boiler of Guohua Taicang power plant, conducts a comprehensive analysis on reasons of overheat of superheater and reheater, and provides an improved plan on resolving overheat problem. But,based on the analysis of the oxide-skin thickness, it found that the thickness of the oxide-skin is not the conclusive factor that causes oxide-skin produces exfoliation.In addition, based on analysis conducted on variation of main steam temperature in the process of units' startup, it is found that temperature control is not well during the frequent start-up occur because lack of supercritical boiler's operating character. It leads to temperature rising rate is fast and main steam temperature and superheater tube temperature vary too fast.Based on combustion adjustment, overheat of heating surface relieved through optimization of startup procedures, boiler tube failure due to exfoliation of oxide-skin is eliminated and safe and stable operation of units are assured.