Research On Corrosion Protection Of Inner Cooling Water System In Generator

Generator is the heart of the power plants. The quality of inner cooling water can cause effect to the safty of power plants. Corrosion product in inner cooling water system can deposit on hollow copper conductor. It can cause temperature increase of copper conductor. The over high temperature can lead to insulation damage and can cause serious stopping accident. Conventional copper corrosion inhibition methods cann't be used directly in inner cooling water system of gnerator because that inner cooling water is running in a high-pressure electric environments. Synchronous control of conductivity and pH value is the technical problem in corrosion inhibition of inner cooling water system.This paper comprehensively described operation state and problems of inner cooling water system, and analyzed the corrosion features of inner cooling water system. Thermodynamics and electrochemical theory were used to analyze the influence of the contain of carbon dioxide in air to pH value and conductivity of inner cooling water and the relationship of pH value and limit concentration of copper ion. Corrosion control principle of inner cooling water system was put forward. Static corrosion tests show that temperature, pH value, basifier species, the contain of dissolved oxygen can exert an influence on corrosion of no.2 industrially pure copper. Some key problems in alkalescence treatment in inner cooling water system such as resin type, resin ratio, system reform were studied in this paper. The main conclusions are as follows:Carbon dioxide can exert remarkable influnce to pH value and conductivity of inner cooling water system. The dissolution of carbon dioxide in inner cooling water can make pH value of inner cooling water decrease greatly. It can lets hollow copper conductor in corrosion area.The pH value of water have tremendous influence to copper content in water. The relationship of pH change value and decrease rate of limit concentration of Cu2+ can expressed as mathematics type as follows: i pHipHpH[Cu²]_i/[Cu²⁺]₀=10⁽-2(ph_i-ph₀)=10^-2Δph. It is an effective methods to enhance pH value to higher than 7.2 to inhibt the corrosion of copper. It can control the concentration of copper ions below 20μg/L.In the allowance of operation temperature range, the higher of the temperature, the easier to form passivation membrane on the copper surface, which is benefit to copper anticorrosion. In the pH range of 6.4⁹.0, copper ions concentration is decreased with the increase of pH value. As the pH value is higher than 9.5, the change of copper ions concentration is opposite. In alkalescence condition, the inhibition effect to copper corrosion of sodium hydroxide is better than that of ammonia. In the same pH value, the conductivity of the experimental solution is smaller when choosing sodium hydroxide as basifier. Copper corrosion speed is relatively small when the the content of dissolved oxygen in demineralized water is extremely high or extremely low. Copper corossion is most serious when the content of dissolved oxygen is in subsaturation condition.Alkalescence treatment device can release sodium hydroxide slowly and effectively by ion exchange, and keep alkalescence of inner cooling water. Conductivity, pH value and the concentration of copper ions of inner cooling water can reach standard simultaneously. Simulation experiment shows that alkalescence treatment is easy for operation, secure and reliable.Dow monosphere resin havs larger volume exchange capacity and better heat resistance. Water conductivity of effluent is lower. Thus, Dow monosphere resin is a ideal inner resin to treat inner cooling water. Alkalescence recycling treatment device can adjust pH value of inner cooling water system to 7.51⁸.40 while ratio of Na-pretreateated resin and H-pretreateated resin is 2:1. It can inhibit the corrosion of hollow copper conductor effectively.