Discussing the issue of corrosion caused by low-temperature, humid flue gas in boiler plants

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In boiler equipment, low-temperature corrosion is generally associated with air preheater tubes and condensers. The factors contributing to a high corrosion rate are mainly the sulfur content in the fuel, the high dew point temperature of the acidic components in the flue gases, and the moisture content in the fuel and air used for combustion. On the cooler metal surfaces of the boiler air preheater, the emission of condensed acid particles from the chimney is the main cause of recurrent low-temperature corrosion. Larger particles in the emissions (100 mesh or larger) generally adhere to the metal surface near the stack. Since these particles are inherently acidic, they can initiate corrosive electrochemical reactions on solid surfaces. Engines and boilers that use sulfur-containing fuels generally inevitably face this problem. Sulfur reacts with oxygen and is first converted into sulfur dioxide (SO2), which may further lead to the formation of sulfur trioxide (SO3) in the next stage. The oxidation reaction is as follows: (SO2) + O2 = 2(SO3). Due to its high reactivity, sulfur trioxide gas readily combines with water at temperatures below the dew point to form sulfuric acid.