Research And Management System Development On Corrosion Product Migratioly In The Steam-water Cycle System Of Power Plant

The continuous improvement of the capacity and parameters of coal-fired generating units put forward higher requirements on the safety and life management of the steam-water cycle system pipeline materials.Low temperature corrosion,deposition of corrosion products,high temperature corrosion and the oxide exfoliation are impact factors of the safety and life of pipelines,which belong to the migration process of corrosion products.In order to realize the scientific management of the information of corrosion products migration,this paper described the process of corrosion product migration and developed the assessment system:First of all,in order to make the migration mechanism of the corrosion products in the steam-water cycle system clearer,the migration process and impact factors are systematically analyzed.Low temperature corrosion,weight gain of high temperature corrosion,deposition of corrosion products and oxide exfoliation are broadly defined as a migration behaviors of corrosion products.These behaviors are controlled by a variety of factors,including the basic parameters of the boiler,the water quality parameters and the operating parameters.The basic parameters of the boiler include the parameters of the flow components,water chemical treatment,water quality standards,material types,wall roughness,shape and size.Boiler water quality parameters include pH,temperature,pressure,flow rate,dissolved oxygen concentration,iron concentration and corrosion product particle diameter.Boiler operating parameters include units load,load fluctuation frequency,load range and wall temperature.Then,in order to realize the prediction of the migration process of corrosion products,a mathematic prediction model based on cyclic characteristics of steam-water cycle system needs to be established.The analysis shown that the typical supercritical power plant steam-water cycle system has the characteristics of parallel cross cycle,which adds complexity to the migration process of corrosion products.The basic mathematics models of the migration of corrosion products,in each flow components and between each flow components,have internal relationships which determined by water cycle characteristics in steam-water cycle system.The parameters are reclassified by further analysis,a mathematical model of corrosion product migration is established by mass conservation principle and mass transfer principle.At the same time,the generation and deposition of the corrosion products are calculated,the deposition proportion of corrosion products in the heating surface of boiler is between 10%-45%,the calculation results of generation and deposition of the corrosion products are compared with the actual test results,which can be used as reference for the design of the migration system of corrosion products.In addition,in order to make scientific management of the information of corrosion products migration possible,the monitoring mechanism of the corrosion products migration process was analyzed based on the analysis of the influencing factors and the mathematical models of the corrosion products migration process.Based on the widely used DCS system in the power plant,the assessment system of corrosion products migration information in the steam-water cycle system was designed,including data acquisition type optimization,data application function design and interface design.The design of assessment system will provide a theoretical reference for the safety and life evaluation of the pipelines of power plant as well as protection strategies and evaluation of prediction effects of the pipelines safety and life management in the future.