Corrosion and Fouling Reasons of Low Temperature Heating Surface on Flue Gas Side of Waste Heat Boiler in a Power Plant

The corrosion and fouling phenomenon in the low temperature section of the flue gas side of a waste heat boiler seriously affected the safe operation and heat transfer efficiency of the boiler. The morphology and composition of the solid attachments on gas side heating surface of module 6 to module 8 in the waste heat boiler were studied by solution analysis, scanning electron microscopy, energy dispersive spectrum and X-ray diffraction. The corrosion mechanism of the heating surface was analyzed. The results show that the the solid attachments were strong acidic and mainly contained three elements of Fe, S and O, and the main components were iron sulfate compounds and iron oxides. According to the concentration of SO₃ in the flue gas and the partial pressure of water vapor, the acid dew point temperature of the waste heat boiler flue gas was estimated to be 150-176 ℃. The leeward side surface of module 6 and module 8 had been accumulated with sulfate compounds, showing the characteristics of sulfuric acid corrosion. Other areas were characterized by acid wet flue gas corrosion, and yellow flake corrosion products existed on their surfaces. Corrosion control recommendations were proposed based on the current status of the waste heat boiler.