The Characteristic Of H₂S High-temperature Corrosion Studies On Supercritical Boiler's Water Wall

According to the National“Thirteenth Five-Year Plan for Power Development”,by 2020,the proportion of thermal power will still be as high as 60%.As environmental protection issues have received more and more attention,the improvement of efficient and clean thermal power has become the direction of China's power development.The supercritical unit has unparalleled advantages,higher thermal efficiency than traditional units,lower coal consumption,less nitrogen oxide emissions and higher desulfurization rate.In the background of deteriorating environment and less resources,the advantages of supercritical units are enormous.Although supercritical units have great advantages in improving thermal efficiency and reducing pollutant emissions,they have their own limitations and shortcomings.Due to its large capacity and high parameters,it directly leads to an increase in the temperature of the supercritical boiler's water wall,and due to the application of low-nitrogen technology,the reducing atmosphere near the water wall of the supercritical boiler is aggravated,so the frequency of high-temperature corrosion phenomenon's occurrence in the supercritical unit is getting higher and higher.In this paper,the high-temperature corrosion characteristics of supercritical boiler water wall are studied.Four representative supercritical boiler water wall materials are selected.The high-temperature corrosion experiment is carried out in the laboratory by simulating atmospheric conditions and temperature conditions.The composition is H₂S,CO,O₂ and N₂.The concentrations of CO,O₂ and N₂ are the same under different working conditions,and the concentrations of H₂S are 0.08%,0.1%and 0.3%.The temperature conditions were 350^°C,400^°C and 500^°C,respectively.The quality change analysis and wall thickness reduction analysis were performed on the samples after corrosion.The microstructure of the sample was observed by SEM,the phase composition and elemental composition of the sample were determined by XRD and EDS.The effects of H₂S concentration and temperature on high temperature corrosion and the strength of four materials against high-temperature corrosion will be explored.The results show that,when the corrosion temperature is at 500°C,the corrosion weight gain of H₂S concentration at 0.1%is about 1.3 times that of H₂S concentration at 0.08%.When H₂S concentration is at 0.3%,the corrosion weight gain is about 6 times that of 0.08%,the increase of corrosion weight gain is greater than the increase of hydrogen sulfide concentration,and with the increase of H₂S concentration,this trend is getting stronger.The change in the reduction of wall thickness is not very sensitive to the response to changes in H₂S concentration.There is a linear relationship between them.Under the different corrosion time gradients at the same atmospheric conditions,the corrosion weight gain of the four materials at temperature of 400^°C is about 1.7times that at 350^°C.The corrosion of four materials at temperature of 500^°C is about 7times that of 350^°C.It indicates that the larger the value reached after the temperature rises,the greater the amount of change in corrosion weight gain.Corrosion temperature has a great influence on wall thickness reduction.When the temperature is lower than350^°C,high temperature corrosion may occur,but the reduction of wall thickness may not occur.When the corrosion time exceeds 60h,the order of the ability of four material samples resisting high temperature corrosion will maintain a stable trend.The order from weak to strong is:SA-213T12,SA-210A1,15CrMoG and 12Cr1MoVG.And the difference of the ability of four materials samples resisting high-temperature corrosion is getting larger.