The Effect Of Organic On Metal Corrosion In Cooling Water System In Urban Sewage Plants

At present,domestic and foreign thermal power plants have used the secondary biochemical effluent of a municipal sewage treatment plant as a make-up water for a circulating cooling water system.However,most thermal power plants use deep treatment of the effluent from the municipal wastewater treatment system and then reuse it in the circulating cooling water system.The effluent from the municipal wastewater treatment contains microorganism-undegraded organic matter and microbial metabolites organics,which have potential impacts on mineral scaling,microbial scaling,and metal corrosion in circulating cooling water systems.Based on the corrosion of organic matter in the effluent of municipal wastewater after being reused in a circulating cooling water system,the corrosion process and mechanism were studied in this paper by concentrating and separating the organics in the effluent from municipal wastewater treatment.Cooling water based on circulating cooling water systems tends to concentrate several times(4-8 times)during recycling.In this experiment,in order to investigate the effect of the effluent of urban sewage biochemical treatment on the corrosion behavior of carbon steel,stainless steel and brass under different concentration conditions,the actual water sample taken was concentrated at 55℃ to reach different concentration multiples.(2-5 times);In order to examine the influence of different organic substances separated on the corrosion behavior of carbon steel,stainless steel and brass,DAX-8 and XAD-4 resins were used to classify and separate the organic matter from the effluent of municipal wastewater biochemical treatment,and the hydrophobic alkaline organic substances,Hydrophobic acidic organics,weakly hydrophobic organics,and hydrophilic organics were separated.In this paper,the electrochemical corrosion behavior of metals from the effluent of municipal sewage under different concentration ratios and the different species of organics separated from the effluent of municipal wastewater are studied by using potentiodynamic polarization and electrochemical impedance spectroscopy.The main conclusions of this study are as follows:(1)The role and mechanism of organic matter of the effluent of municipal wastewater in the corrosion process of N80 and Q235 carbon steels.For N80 carbon steel,when the water sample contains hydrophobic acidic organic matter,hydrophobic alkaline organic matter,weak hydrophobic organic matter,and strictly hydrophilic organic matter,the diameter of the capacitive reactance arc is large,the reaction resistance is large,and the corrosion strength is weak;the corrosion rates are reduced by 27.6%,21.2%,15.2%,and 12.3%,respectively,relative to that of the control water sample,and the hydrophobic acidic organics have the strongest corrosion inhibition.For Q235 carbon steel,when the water sample contains hydrophobic acidic organic matter,hydrophobic alkaline organic matter,weak hydrophobic organic matter,and strictly hydrophilic organic matter,the diameter of the capacitive arc is large,the reaction resistance is large,and the corrosion intensity is weak;the corrosion rate are reduced by 27.6%,21.2%,15.2%,and 12.3%,respectively,relative to the corrosion rate of the control water samples,and the hydrophobic acid organics have the strongest corrosion inhibition.(2)The role and mechanism of organic matter of the effluent of municipal sewage in the corrosion process of 304 and 316 stainless steel.For 304 stainless steel,when the water sample contains hydrophobic alkaline organic matter,strict hydrophilic organic matter,weak hydrophobic organic matter and hydrophobic acidic organic matter,the diameter of capacitive arc is large,the reaction resistance is large,and the corrosion intensity is weak;the corrosion rates are reduced by 25.8%,10.7%,4.2%,and 3.8%respectively,relative to the corrosion rate of the control water samples,and the hydrophobic alkaline organics have the strongest corrosion inhibition effect.For 316 stainless steel,when the water sample contains hydrophobic acidic organic matter,hydrophobic alkaline organic matter,strictly hydrophilic organic matter,and weakly hydrophobic organic matter,the diameter of the capacitive reactance arc is large,the reaction resistance is large,and the corrosion intensity is weak;the corrosion rate are reduced by 46.4%,30.0%,28.4%,and 12.2%,respectively,relative to the corrosion rate of the control water samples,and the hydrophobic acidic organics have the strongest corrosion inhibition effect.(3)The role and mechanism of organic matter of the effluent of municipal sewage in the corrosion process of brass.When the water sample contains hydrophobic alkaline organic matter,hydrophobic acidic organic matter,weak hydrophobic organic matter,and strictly hydrophilic organic matter,the diameter of the capacitive arc is large,the reaction resistance is large,and the corrosion intensity is weak;the corrosion rate are reduced by 20.3%,19.2%,8.2%,and 7.5%respectively,relative to the corrosion rate of the control water sample,and the hydrophobic alkaline organic matter have the strongest corrosion inhibition effect.