Anti-corrosion And Wear-resistant Coatings Application Of Stirrer's Impeller Remanufacturing In Absorption Tower In FGD System

The emission of SO2is the main cause of atmospheric pollution and acid rain intensification in our country. Flue gas desulfurization technology is the main way we adopt to control the emissions of SO2by coal-fired power plant. The stirrer in absorption tower is one of important parts in limestone/gypsum wetness FGD technology. But it costs so much and requires so high reliability that the maintenance has a significant impact on the entire desulfurization system. As the working medium, limestone or gypsum slurry, causes serious corrosion and cavitation erosion on the impeller during the operation, so does the high level of chloride ion. How to repair the damaged impeller and increase its service life in the actual working conditions has attracted extensive attention.In the paper, according to the structure, material, actual operating condition and failure mechanism of stirrer's impeller, micro-arc profile surfacing can be used to recover the dimensions and shapes; oxyacetylene flame spray fusing technology can also be used to prepare five kinds of Ni-based self-fluxing alloy and powder sprayed coating. Compare the base materials, and analyzed the anti-corrossion performance, by conducting anti-corrosion electrochemical test; studied the mechanism of cavitation erosion resistance, cavitation erosion resistance performance test, then the microstructure analysis were conducted after the cavitations erosion damage test using SEM.Experimental studies has shown that:the differences in performance between surfacing and base metal can be decreased by using duplex stainless steel covered electrode for surfacing during the manufacturing process of the impeller. Because of the less heat input and the higher bonding power of parent material and matrix, micro-arc profile surfacing is suitable for repairing the dimension and shape of the impeller.The research also has showen that:few potential differences between Ni55AMo, Ni45AMo and parent material, it is weak at the ability of forming the original battery, Ni55AMo has the low corrosion current density and the coating has strong anti-corrosion capacity by electrochemical corrosion to test five kinds of oxyacetylene flame spray fusing coating and the austenitic stainless steel, duplex stainless steel. The cavitation erosion resistance research in corrosive medium circumstance has showen that:Ni60, Ni46and Ni67has the higher cavitation erosion rate, and at the same time poor performance of the cavitation erosion resistance; WC particles peeling appeared in the coating of NiWC35when they lost the bond that relies on; the appearance of Ni55AMo shows less porosity and the best cavitation erosion resistance.Compared the morphology of microstructure of the five kinds spray fusing coating, Ni60, Ni46and Ni67have caused clear cavitations erosion pits and peeling. Silicon content in the alloy increased the hardness of the alloy welding layer with a significant drop in ductility and toughness with the increasingly use of boron; the coating of NiWC35has the clear pit and higher porosity, and the deeper peeling of the WC particles; the morphology of Ni55AMo after cavitation erosion unseen cavitation erosion pits and less porosity with symmetrical distributed grains, a lot of fine grain boundary, coating with higher toughness.Comprehensive research shows that:the spray fusing coating of Ni55AMo has excellent cavitation erosion resistance and anti-capitation performances, it's small microstructure has uniform distribution. So it is suitable in the process of duplex stainless steel stirrer's impeller anti-corrosion and wear-resisting treatment.