Research On Methods For Temperature Field Calculation And Leakage Fault Diagnosis Of Steam Trap In Steady Leakage Condition

Power plant valve leakage will reduce the overall efficiency of the whole generating units,or even may directly threaten maintenance staffs safety and operation safety of the unit.At present,there are a lot of diagnosis methods of valve leakage,but these methods have some limitations,it is very difficult to diagnose the leakage fault of the valve in complex environment of the coal-fired power plant. Therefore, there is an important theoretical value and good engineering application prospects to research the valve leakage fault based on drain pipe temperature field technology.When the valve leaks, tube wall temperature in front of the valve will change accordingly, so the valve before the tube wall temperature can be used as the diagnostic parameters for testing valve leakage.The detection method of valve leakage fault based on drain pipe temperature leak detection method is mainly studied by combing theoretical analysis,numerical simulation and experimental verification in this paper,and then a new method of power plant drain valve leakage is developed.First, the drain pipe in power plant is divided into multi-segment control body to establish the temperature field calculation model.Establishing the temperature field calculation model under different valve leakage conditions based on heat transfer theory of cylindrical wall pipe. Secondly, two diagnostic models to the valve does not leak and the leakage of the valve as the basis, and then the mathematic model was established,and abstracted the logic program diagram of tube wall temperature calculation program is needed,on the basis of this,write the front wall of the valve temperature calculation software.At the same time,in order to effectively solve the physical property parameters calculation of water vapor, In this paper,the state equation and the calculation precision of IAPWS-IF97 are analyzed, and finally chose the IAPWS-IF97 as the calculating formula of the physical parameters of water vapor,and then developed a calculation precision accurate drain pipe wall temperature calculation software.Finally,this paper explores a new method for thermal power plant steam drainvalve leakage diagnosis.There are two steps in this method to diagnose the faults of valveleakage.The first step for the qualitative diagnosis,through the drain pipe wall temperature calculation software to calculate tube wall temperature when valve does not leak. When the tube wall temperature measured value is lower than this temperature,this method can determine the valve does not leak.If above this temperature,the second step for quantitative diagnosis. Through the power drain pipe under different working condition of the valve leakage temperature field distribution of a large number of numerical simulation, it is concluded that hydrophobic and leakage of pipe wall temperature, pipe diameter, the change of the relationship between such factors as the insulation layer thickness. By adopting the method of mathematical modeling, the data obtained from the numerical simulation to synthesis quantitative calculation formula, using the calculation formula for the valve leakage quantitative diagnosis.