Analysis Of High Temperature Corrosion Of Spiral Waterwall Tubes In A Coal-fired(Ultra)Supercritical Boiler

At present,the main power generation of our country is thermal power,and large capacity and high parameter(ultra)supercritical thermal power unit is still the main development direction of the thermal power generating,its main steam pressure and temperature is high,which can greatly improve the thermal efficiency and economic efficiency,at the same time,the temperature in the furnace can reach 1600? during the operation of the(ultra)supercritical boiler,the water wall temperature is much higher than subcritical units,(ultra)supercritical boiler water wall high temperature corrosion phenomenon occurred frequently,therefore,the conditions of high temperature corrosion are very important to avoid the accidents caused by.high temperature corrosion.High temperature corrosion of the water wall in the burner region of the(ultra)supercritical boiler has been a major hidden danger for the safe operation of power station.The two units studied in this paper such as Lingwu 1060MW ultra supercritical boiler and Xinxiang 660MW supercritical boiler on the side wall all happened severe high temperature corrosion and the reduction of wall thickness was serious.In the preamble described the concept and development of ultra supercritical units,listed the details about the occurrence of high temperature corrosion of(ultra)supercritical boiler,discussed the mechanism,influencing factors and preventive measures which associated with high temperature corrosion of boiler water wall,then analysed the corroded water wall tubes and laboratory test to verify the conclusion.The area of high temperature corrosion of(Ultra)supercritical boiler water wall is using spiral wound membrane tube,it is observed that the surface of the corroded water wall tube covered with a layer of unburned ash,at the same time,the corrosion degree of different parts of single corroded water wall tube is great difference,the corrosion which water tubes covered with a layer of ash is most serious,the average reduction about 3.6mm,the arc wall is etched into a plane,the corrosion degree of water wall not covered by unburned coal ash is much lighter,the average reduction about 2.4mm.In this paper,analysis the high temperature corrosion samples,using visual,electron microscopy,energy spectrum and X ray diffraction analysis method for detection and analysis,analysis of the causes,infer the reasons for this phenomenon are unburned coal ash on the pipe heated released[S]is much corrosive will aggravate corrosion,and[S]under high temperature can cause oxide film cracking,detective carbon deposition at the crevices,the carrburzing behavior must lead to the decrease of the tube properties.The measure for reducing high temperature corrosion was conducted by decreasing the pulverized coal concentration of primary air by 20%in the burner region close to the side wall,the volume fraction of O2 basically above 2%and the volume fraction of CO below 1.5%,the reducing atmosphere was signficiantly improved and the thermal efficiency of the boiler was not affected.