Numerical Simulation And Performance Diagnosis Of Regenerative System Feed Water Heater In Power Plant

The existence of non-condensable gases and flash evaporation of feed water heater in regenerative system have always been a bottleneck in the safe operation of the heater,on the one hand,the complex structure of the heater is not tight,then air and other non-condensing gas leak into the heater,which seriously weaken the condensation heat transfer effect.On the other hand,the operation pressure mutation of heater under variable condition is easy to cause flash evaporation problem.The resulting gas-liquid two-phase flow causes more problems such as erosion corrosion,flow accelerated corrosion and vibration,and threatens the safety of the heater at all times.Therefore,the numerical simulation method is used to construct the internal characteristics of flash evaporation and non-condensing gas steam condensation model respectively,then to predict the corrosion position of gas-liquid two-phase flow in heater,and the simulation results are in good agreement with the experimental data and engineering practice.Key elements include:Aiming at the problem of wall condensation in the presence of non-condensable gases using Fluent,put forward using Eulerian wall film model coupling components are applied to solve the transport model,and then to fully satisfy the precision requirement of engineering application analysis from two aspects of grid model and boundary conditions to optimize the model set,then don’t condense gas mass fraction of inlet temperature and inlet velocity on the influence law of the non-condensable gases steam condensation for detailed analysis.The research shows that the liquid film thickness decreases with the increase of the mass fraction of non-condensable gas,and the condensation heat transfer coefficient changes very little when the vapor inlet is doped with 5% air.When the content of non-condensable gas,such as air,exceeds 20%,the condensation heat transfer coefficient decreases rapidly and finally reaches a plateau.With the increase of the inlet temperature from 80℃ to 140℃,the liquid film thickness on the condensation wall gradually increases,while the condensation heat transfer coefficient decreases with the increase of the inlet temperature.When inlet velocity v=5.5m/s,the maximum liquid film thickness is 4.396 e-4 m,and when the inlet velocity v=1.5m/s when the maximum liquid film thickness at 4.715 e-4 m,the thickness of liquid film and decreases as the inlet velocity and thus proves that the transport components based on Eulerian wall film model method of the liquid membrane containing no steam condensation problem of the feasibility of condensate gas,also in order to improve the condensate gas to provide the reference effect on condensation heat transfer.In order to obtain the internal characteristics that can accurately reflect the flash evaporation in the heater,the heater flash occurs within the internal characteristics of simplified model to trap and near the pipe as the research object,because of the flash evaporation phase transformation is the process of non-equilibrium thermodynamics,heater and mass transfer,intense and difficult to convergence here uses the unsteady calculation method on the basis of in-depth analysis of the pressure vaporization heat initial water temperature and water level height on the influence law of flash results show that compared with low entrance,high pressure inlet of flash happened more fully more obvious.The superheat of vaporization was simulated at 5K,15 K and 30 K,respectively,and it was found that the greater the superheat of vaporization,the faster and more intense flash evaporation occurred.The higher the initial temperature is,the better the external conditions are for the formation of the flash bubble.The change of initial water level has little influence on the rate of temperature reduction during flash evaporation,which provides a guiding idea for the operation optimization and structure design of non-flash heater,which provides guidance for the operation optimization and structural design of heaters without flash.Based on the above research,the simplified heater is simulated,and the main position of non-condensing gas and flash evaporation in the heater is predicted,combined with the power plant fault scene map to verify the erosion corrosion,flow acceleration corrosion and vibration noise of the heater,which was formed by gas-liquid two phase flow,then the structural optimization strategy and improvement measures are put forward to solve the problem.In order to help the power plant operators to find problems in time,the characteristic parameter changes of common faults in heaters are summarized and tabulated,then the heater performance diagnosis scheme is proposed,combining with the power plant safety instrumented system monitoring system to ensure the safe and economic operation of the heaters.