Research On Methods And Standard For Diagnosing Drain Valve Inner Leakage Faults In Thermal Power Plant During Operation

As for the thermal generator set,drainage valve leakage will result in serious risks for the equipment safety as well as a low power generation efficiency.At present,although many means have been applied to the detection of valve leakage,no expected results have been reached due to the deteriorating working environment related to valve in thermal power plant with an especially difficult discovery for the leakage in the early stage.Therefore,in order to detect tiny leakage of drain valve in the early stage,a new method for detecting valve leakage has been received with the adoption of theoretical analysis,numerical simulation and engineering fieldtesting based on the distribution of drain pipe temperature field;meanwhile,on this basis,standard used for valve leakage diagnosis has been drafted.At first,typical drainage system model is obtained,a heat transfer model of multi-layer cylinder pipe wall based on infinite by deep research on the drainage system of thermal power plant are established,and thus mathematical model for calculating the temperature of drainage pipe wall has been established under two states of non-leakage and leakage valve.As a result,calculation process of pipe wall temperature can be reached under leakage and non-leakage states with the program logic design of the calculation process,and then the calculation software can be developed for calculating drainage pipe wall temperature with the help of MATLAB.With the aid of this software,pipe surface temperature calculation software used on the front water wall of the water globe valve was designed.Functions like the calculation of water and steam physical parameters,and parameter calculation of infinitesimal pipe working medium and calculation of heat transfer of pipeline were implemented through this software.In addition,based on the massive calculation for the temperature of drain pipe of infinitesimal section by the developed software,two diagnosis methods have been withdrawn for detecting the drainage valve leakage,which are temperature and temperature difference.Then factors affecting the two diagnosis indicators above have been analyzed by single variable method,which are environmental temperature,structural parameters of the pipe,steam parameter of the leakage as well as the leakage rate of steam flow.Through the analysis,correlation between pipe wall temperature and above factors has been established,which provides calculation method for the threshold of drainage valve regarding leakage and non-leakage diagnosis.Therefore,a field test platform which is suitable for the diagnosis method has been established to evaluate the distributions of pipe wall temperature field as well as the accuracy of diagnosis method.At the end,based on theoretical and test research,it conductsthe research on the standardization of drainage valve leakage based on temperature field diagnosis,including five parts such as employment range of the diagnosis standard,normative citation,terminology,detection technology and rules as well as process requirements and detection process.which can provide the basis for field test hydrophobic valve leakage.