Corrosion of the afterfan in the wet flue gas desulfurization process
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Our company’s wet flue gas desulfurization system features a flue gas inlet temperature of ≤50°C; the flue gas is directly subjected to alkaline absorption in the first, second, and third desulfurization towers. The third tower is equipped with two layers of mist removal devices. After passing through the absorption towers, the flue gas enters the exhaust fan and is then discharged through the chimney. The design specifies that the SO2 content in the exhaust gas should be ≤100 mg/Nm3; during operation, monitoring shows that environmental standards are met, and the actual sulfur content in the exhaust gas is likely even lower than the specified value. The current problem is corrosion of the relay fan; the back cap, shaft, and flexible connectors are all severely corroded. They have been replaced twice, and significant corrosion has also occurred on the fan’s casing and bottom. Fan material: spindle 40Cr, casing 316L, impeller 316L, air inlet 316L, bearing housing HT250, back cap carbon steel, flexible connector 304 stainless steel. During operation, the fan leaks water, and there is a lot of mist at the chimney outlet. Given the current materials used for fans, what causes this type of corrosion? Is it dew point corrosion? What are the solutions?
You guessed right; it’s dew point corrosion. The temperature is too low. Solutions: 1. Place the fan in front, ahead of the desulfurization tower. 2. Add a heat exchanger after desulfurization. 3. It’s a bit difficult to replace the material. 40Cr is mainly wear-resistant, but it cannot withstand corrosion under such conditions; carbon steel is even less capable of withstanding it, and 304 is only slightly better.
But the concentration of sulfur dioxide in our exhaust gases is already very low; can it still cause dew point corrosion?
There is a type of anti-corrosion coating material that can solve your corrosion problems, and it’s not expensive. Specific in-person communication.
If, as the original poster says, there is a large amount of water mist in the exhaust gases and the fans drip water, it indicates that there are also significant issues with the efficiency of foam removal in these exhaust gases. So, for the two-layer demisting devices in the three-level tower design mentioned by the poster, what demisting technologies and structures are used for these two layers? Have the reasons for the poor demisting capacity and demisting effect been analyzed?