Raise the minimum wall temperature of heat pipes to prevent low-temperature corrosion

Raise the minimum wall temperature of heat pipes to prevent low-temperature corrosion

Use chemical cleaning agents to clean the dust, or use blowing and mechanical methods to remove the dust on the surface of the pipe [3]. These two methods are only carried out after the accumulation of dust is generated, which has a lag effect.

3. Dew point corrosion of heat pipes

3.1 Production mechanism

When a heat pipe heat exchanger is used in low-temperature flue gas, the heat pipes of the heat exchanger often suffer from low-temperature dew point corrosion. Sometimes, even at normal exhaust temperatures, there is low-temperature dew point corrosion in the last few rows of heat pipes on the exhaust outlet side (without a pre heater). According to heat transfer theory, the temperature of the flue gas sidewall is mainly related to the temperature, heat transfer coefficient, and heat transfer area of the cold and hot fluids. It is directly proportional to the temperature, heat transfer coefficient, area of the hot fluid, and the temperature of the cold fluid, while inversely proportional to the heat transfer coefficient and area of the cold fluid. When the heat transfer coefficient and heat transfer area on the cold and hot sides are basically constant, when the cold flow temperature is low, the wall temperature on the flue gas side may be below the dew point temperature and dew point corrosion may occur.

3.2 Countermeasures

3.2.1 Control smoke exhaust temperature [4]

Reasonably determine the exhaust temperature based on the dew point temperature of the flue gas. Generally, the exhaust temperature should be 20-30 ℃ higher than the dew point temperature. In addition, when there is a significant difference in ambient temperature between winter and summer, different exhaust temperatures should be controlled, and the exhaust temperature in winter should be appropriately increased.

3.2.2 Adding a pre heater

Adding a pre heater can increase the temperature of air entering the preheater, effectively preventing dew point corrosion [5,6]. 3.2.3 Set up bypass air channels. When the flue gas temperature or ambient temperature is low, corresponding bypass channels can be set up to mix some of the heat exchanged air into cold air to increase the inlet temperature of the air.

3.2.4 Adjusting structural parameters

By adjusting the structural parameters of the cold and hot ends, the minimum wall temperature of the heat pipe can be increased to prevent low-temperature corrosion. Among the structural parameters, the changes in the length of the cold and hot ends are the most sensitive to changes in wall temperature, but the length of the hot end cannot be increased too much, otherwise it will cause an increase in the temperature of the outlet flue gas, a decrease in the heat transfer capacity of a single heat pipe, and an increase in the air side flow resistance. Currently, the most commonly used method is to adjust the height and spacing of the fins. In the adjustment of structural parameters, it is recommended to change a certain parameter on both the cold and hot sides simultaneously. This way, the wall temperature changes quickly, and the heat transfer of a single row of heat pipes remains basically unchanged. The original heat transfer performance can be ensured without adding more pipe rows. When there is not much difference between the wall temperature and dew point temperature, priority should be given to selecting fin height or spacing as temperature control parameters; When there is a significant difference between the wall temperature and dew point temperature, the cold end length should be selected as the temperature adjustment parameter or multiple adjustments should be made simultaneously.

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