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Sulfuric acid corrosion on the boiler's rear heating surface (economizer, air preheater) is called low-temperature corrosion because the flue gas and tube wall temperatures in the rear heating surface area are low. The sulfur in the fuel is burned to form sulfur dioxide (S+O2→SO2). The sulfur dioxide is further oxidized under the action of the catalyst to form sulfur trioxide (2SO2+O2→2SO3). SO3 and the water vapor in the flue gas generate sulfuric acid vapor. The presence of sulfuric acid vapor significantly increases the dew point of flue gas. For example, the partial pressure of water vapor in the flue gas of an oil furnace is about 0.008-0.014Mpa, and the corresponding thermodynamic dew point is 41-52°C. For example, when the concentration of sulfuric acid vapor in the flue gas is 10%, the dew point rises to 190°C. The preheater tube wall temperature is related to the flow rate and temperature of the flue gas and air, and is approximately equal to the average temperature of the flue gas and air. Since the air temperature in the lower part of the air preheater is low, the flue gas temperature in the lower part of the preheater is not high, and the wall temperature is often lower than the flue gas dew point. Sulfuric acid vapor will condense on the heating surface of the preheater, causing sulfuric acid corrosion. Low-temperature corrosion often occurs on the air preheater, but when the fuel contains high sulfur content and the excess air coefficient is large, resulting in a high SO3 content in the flue gas, a high dew point, and a low feed water temperature (such as the high-pressure feed water heater being disabled), low-temperature corrosion may also occur in the economizer tube. Please express your different opinions.