The temperature at which the water vapor in the industrial steam boiler starts to condense is called the dew point. The dew point is related to many factors. The higher the water vapor content in the flue gas, that is, the higher the partial pressure of water vapor, the higher the dew point. However, the thermodynamic dew point determined by the partial pressure of water vapor is low. For example, under normal circumstances, the partial pressure of water vapor in flue gas is about 0.08 to 0.14 absolute atmospheric pressure, and the corresponding thermodynamic dew point is 41. ~ 52 ° C.
The higher the sulfur content in the fuel, the higher the dew point.
Sulfur dioxide is generated during the combustion of sulfur in fuel, which is further oxidized to sulfur trioxide. Sulfur trioxide and water vapor in the flue gas generate sulfuric acid vapor, and the presence of sulfuric acid vapor greatly increases the dew point. For example, when the concentration of sulfuric acid vapor is 10%, the dew point is as high as 190 ° C. The higher the sulfur content in the fuel, the more SO2 is generated after combustion. The larger the excess air coefficient, the more SO2 is converted into SO3.
Different combustion methods and different fuels have different dew points even if the fuel contains the same sulfur content. The ash content in fuel oil is very small, and the ability of ash in the flue gas to adsorb sulfuric acid vapor is very weak. Therefore, even if the sulfur content is the same, the flue gas dew point of fuel oil is significantly higher than that of coal combustion, so the low temperature corrosion of the heating surface at the tail of the fuel industry steam boiler is much more serious than that of coal combustion.
