A Study On Corrosion Mechanism Of Iron In A Ammonia Desulphurization System And Its Corrosion Inhibitor

Ammonia Desulphurization Technology has been developed for several decades, and it is one of wet desulphurization technologies. Its working principle is that ammonia water is used for desulfurizer reduce SO2 content then ammonia is translated to(NH4)2SO3, and finally(NH4)2SO3will be oxidized to(NH4)2SO4 by air.Due to the high efficiency of desulphurization, it has extensive applications in industries. On the other hand, the technology involves the complicated physical and chemical process, the complex installation and extended structure, the long operation period, the poor accessibility, and its corrosion prevention is being widely paid attention to by more and more people. It is important to choose appropriate ways of corrosion prevention and develop high effective corrosion inhibitor at a low price for ammonia desulphurization systems. The main content of the thesis is described as follows.(1)The practical ammonia desulphurization solution was sampled from a plant of Wuhan Iron and Steel Group Company and analyzed to understand its composition. It was confirmed to be a weakly acidic corrosive solution with high salinity. The main corrosive ingredients were analysed by ionic chromatography, spectrophotometry and other methods. The experimental results indicated that content of Cl- was 95.3g/L, content of F- was 0.463g/L, content of NO3- was 3.46g/L, content of SO42- was 215.18 g/L, and the pH of the ammonia desulphurization solution is 4.3.(2)The mechanism and characteristics of metal corrosion was studied by polarization curves, static weight loss method and dynamic weight loss method in the ammonium sulfate solutions, in order to explore the impact of temperature, stirring speed, oxygen exposure, ammonium sulfate concentration, amount of crystallization and the main composition of corrosion on corrosion of the carbon steel. The result of the study indicated that the temperature, stirring speed, oxygen exposure and the content of NO3- can have remarkable effect on the corrosion of A3 carbon steel.(3)According to the study of the corrosion mechanism of carbon steel in the ammonium sulfate solutions, a corrosion inhibitor was developed by polarization technique, static weight loss method and dynamic weight loss method in the different simulated solutions and the actual ammonia desulphurization solution. The best formula is octadecylamine: thiourea: mercaptobenzothiazole(mass ratio)=5:12:3, which provided a corrosion inhibitory efficiency as high as 85.0% in the actual ammonia desulphurization solution.