Reasons for wear/corrosion of the impeller in the secondary desulfurization circulation pump
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The impeller has been in use for 4 days and is severely worn. Used for ammonia-based desulfurization; the impeller is made of cast 316L. The medium inside the pump is sulfuric acid-An slurry with a solid content of 20% (in reality, due to the efficiency of electrostatic precipitators, the slurry contains a large amount of fine boiler ash, resulting in a solid content of 25–30%; this also affects the normal crystallization of sulfuric acid-An, leading to a higher density of the slurry, which may be a cause of wear). The slurry also contains small amounts of sulfurous acid-An and ammonium bisulfite ； The pH value is 5.0 (the actual pH value is 5.2; it is estimated that this has little impact). What could be the causes of wear? Material issue? Casting quality issues? Too high solid content? Impeller curvature design issue? It was worn out to look like that of a monk after just 4 days.
It is mainly caused by an excessively high solid content; the material should be replaced. How severe is the wear on the pump casing?
The cause of severe wear may be a combination of wear and corrosion. Wear can be caused by the formation of sulfuric acid crystals, but it is especially the dust particles present in the flue gas that pose a problem; these particles do not dissolve in the desulfurization solution, are quite hard, and cause significant wear on the pump casing and impellers； There are also other reasons for corrosion; during the desulfurization process, if the pH level is unstable, the sulfite ions present in sulfites can still cause slight corrosion to 316L steel. In particular, it is important to check whether there are chloride ions in the desulfurization solution. Generally, such solutions contain a certain amount of chloride ions due to those present in the flue gas, and these ions can cause significant corrosion to the austenitic 316L steel. Corrosion of 316L stainless steel during desulfurization has occurred in many desulfurization units; therefore, it is recommended to analyze the chloride ion content in the desulfurization solution in order to prevent excessive chloride levels from causing corrosion to 316L stainless steel.
Reply to 1# bruceshen113: If there are photos, I can help analyze the reasons in detail. According to the description, there are essentially three reasons: one is abrasion ； The second is cavitation ； Third is abrasion and cavitation. Firstly, the material choice was incorrect; austenitic stainless steel is not resistant to corrosion. Another reason is incorrect pump selection or inappropriate operating conditions.
It’s obvious there’s a problem with the material you’ve chosen; I suggest trying 17-4PH or using some other better wear-resistant material
It’s best to adjust the water quality; if that’s not possible, then the material of the impeller needs to be changed. 316L is not wear-resistant, and for corrosive environments, nickel-based tungsten carbide could be an option
In fact, for the slurry pumps used in ammonia-based desulfurization, 316L material should not be used as it is too corrosive; it is recommended to opt for engineering plastics instead, which can last around half a year