Research On Operating Characteristics Of Spring-loaded Safety Valve Under High Temperature Steam Conditions

Safety valves are important accessories to pressure vessels,and they play a vital role in over-pressure protection.The valve that uses steam as medium usually works under very harsh condition,where its operating characteristics are easily affected by high temperature,yet there is no systematic way to quantify such effect.For high temperature steam safety valves,many researchers tend to adopt normal temperature and high pressure air instead of high temperature and high pressure steam in their experiments,and thus the correctness of their conclusions needs to be further verified.In view of the above problems,this dissertation combines the methodology of CFD numerical simulation and theoretical analysis to do the research work in the following three aspects.The specific content and conclusions are:1.A three dimensional simulation model is established according to the actual structure and size of an A48Y-40 spring-loaded steam safety valve.For different working conditions,ANSYS FLUENT is used to calculate the temperature fields formed on the safety valve.Results show that the temperature field on the safety valve remains similar with different medium and ambient temperature.The general rule of the temperature distribution on the valve is obtained via in-depth analysis,and it provides a basis for studying the influence of high temperature on the valve's performance.2.Since the set pressure deviation caused by high temperature is difficult to be quantified,a method of set-pressure-correction for engineering application is proposed.First the spring stiffness and compression distance should be corrected based on the temperature distribution formed on the valve,and then these data are used to calculate the actual set pressure under high temperature conditions.3.During the CFD simulation of steady discharge process with different superheated steam,real property data that collected from IPAWS-IF97 are used.Comparing the simulated results with those calculated by standard document formulas,a good consistency between them can be expected.Then use the same technology to study flow features and discharge capacity of the valve at different lift heights.It turns out the discharge capacity did not reach its maximum when the lift is 0.25 of throat diameter.In order to make full use of the safety valve's capacity,it is recommended to set the maximum lift height to 0.34 times its throat diameter,correspond to that,a series of overheating correction coefficients are also provided.Another group of simulations are carried out to find the judgement fomulas in standard document have some limitations,so simulation and experimental data are better basis to determine if the flow is in critical state.