Refinery Flue Gas Dew Point Corrosion Threat To Production Equipment Problem Response And Solution

Flue gas dew point corrosion is a serious problem faced by refineries. In the refining process, a variety of fuels such as natural gas, waste gas, liquefied petroleum gas, naphtha and fuel oil are burned through thermal processes. Most of them contain sulfides such as H2S, mercaptans and thiophenes, which are easily converted into SOx in the combustion chamber. Especially SO2, and a part of it (usually 2-4%) is further oxidized to SO3. When the flue gas is cooled below the acid dew point, SO3 condenses with water vapor to produce sulfuric acid: SO3 (g) + H2O (g) -> H2SO4 (l). The acid dew point temperature depends on the concentration of sulfides in the flue gas and is usually in the range of 100-150℃.

Sulfuric acid is extremely corrosive and has a serious impact on the surface of equipment. For example, when the local temperature of the cold surface of the metal air preheater drops below the acid dew point, sulfuric acid begins to condense, accelerating the corrosion rate of the plates and tubes. This corrosion phenomenon is called cold spot corrosion. Initially, this degradation may not be noticeable, but over time, increased corrosion can lead to leaks in the equipment that can cause a short circuit between the combustion air and the flue gas. This reduces recovery efficiency and increases power consumption of the combustion air fan, which in turn leads to energy loss. Once the combustion air fan is stretched to its limits, these leaks will significantly affect production efficiency.

Although the overall temperature of the flue gas is maintained at 250°C, the so-called cold spot phenomenon still occurs due to the cooler ambient air on the other side of the air preheater. This overcooling causes the temperature of the flue gas side surface to drop below the acid dew point. Different levels of sulfur content in the fuel will increase the severity of cold spot flue gas dew point corrosion. Increased sulfur content leads to an increase in acid dew point. Even if the refinery sets a goal of maintaining 10-20°C above the typical acid dew point, fluctuations in the sulfur content of the fuel may cause sulfuric acid to condense during sulfur peaks, thereby exacerbating the damage to equipment integrity and reducing the overall performance of the plant.

Therefore, effective management and reduction of flue gas dew point corrosion is critical for refineries. The use of appropriate protective measures and monitoring technologies, such as the use of high temperature flue gas acid dew point meters, measuring the dew point temperature of sulfuric acid, and optimizing process parameters can significantly reduce the adverse effects of corrosion and maintain the long-term stable operation of the equipment.