Study On Depressurization Flow Characteristics And Erosion Law Of High-pressure Differential Multi-layer Sleeve Regulating Valve Under Cavitation

As a typical representative of high parameter special regulating valve for nuclear power and coal chemical industry,the multi-layer sleeve regulating valve has variable application conditions and complex structure.High temperature,high pressure,high flow rate,solid particles and other harsh conditions put forward new requirements for the performance of the regulating valve,which seriously affects the service life of the equipment and poses a major challenge to the safety of production.The clarification of the depressurization flow characteristics and erosion law in multi-layer sleeve regulating valve under cavitation effect can alleviate these problems to a certain extent and help to improve the design theory system of special valves for severe service conditions.In this paper,a new high-pressure differential multi-layer sleeve regulating valve in nuclear power main feedwater and coal direct liquefaction systems is used as the research object to carry out the analysis of the depressurization flow characteristics and erosion law of the regulating valve under cavitation effect: the influence of the working parameters and structural parameters on the depressurization flow characteristics and cavitation in the nuclear power main feedwater regulating valve is studied.The inner connection between the working parameters and particle properties and the depressurization flow characteristics and erosion law and cavitation effect in the coal liquefaction liquid-controlled regulating valve is clarified.Suggestions to prevent cavitation and particle erosion are made according to the numerical simulation results.The main research content and findings include five parts:(1)For the use of multi-layer sleeve regulating valve in two typical applications,a comprehensive numerical model of the depressurization flow characteristics and erosion law of the regulating valve under cavitation effect is constructed,and the failure mechanism of the regulating valve under the two operating conditions was predicted.A set of experimental device for the depressurization flow characteristics of multi-layer sleeve regulating valve was built and several experiments were conducted.The measured results under different experimental conditions match with the numerical simulation of the pressure drop law of the fluid in the regulating valve.(2)The effects of different opening degrees and differential inlet and outlet pressures on the depressurization flow characteristics and cavitation of the nuclear power main feedwater regulating valve are analyzed.When the regulating valve is kept fully open,the fluid velocity in the sleeve at each level is maintained at approximately82 m/s and each level of the sleeve provides a pressure drop of 2-3.5 MPa,which has the most ideal pressure reduction effect.Three cavitation locations exist in the regulating valve: at the inner wall surface of the third stage sleeve in the fourth throttle orifice flow path,at the seat throttle orifice flow path and at the corner of the regulating valve outlet flow path.(3)The influence of structural parameters and external pressure characteristics of multi-layer sleeve on the cavitation inside the regulating valve used in nuclear power main feedwater system was investigated.The cavitation effect can be suppressed to a certain extent by adopting the stepwise increase of sleeve diameter,appropriately reducing the thickness of the third sleeve,appropriately decreasing the orifice diameter of the valve seat flow path and increasing the outlet pressure of the regulating valve to0.7 MPa and above,so as to prevent cavitation failure.(4)Numerical simulations of the depressurization flow characteristics and erosion law of coal liquefaction liquid-controlled regulating valve under cavitation effect were carried out.The locations of severe erosion mainly appear around the flow path of the small hole near the sleeve,and the fluid pressure,velocity and turbulent energy changes in the sleeve at all levels are relatively uniform under the large opening operation of the regulating valve.The maximum erosion rate of the regulating valve increases with the increase of particle diameter and then decreases,and the increase of particle mass flow rate leads to the increase and then decrease of the maximum erosion rate in the valve,and the change of opening degree leads to the maximum erosion rate in the valve alternately in different inner wall surfaces.(5)The increase in particle mass flow rate and the decrease in opening leads to a reduction in the volume of the vapor phase inside the valve,with a reduction of more than 20% at the valve seat and more than 6% at the inner wall surface of the third stage sleeve,and the change of particle size has almost no effect on cavitation in the valve.In order to effectively prevent cavitation and erosion failure of the valve,it is recommended that the valve be maintained at as large an opening as possible,reducing the amount of time it is operated at a small opening.The innovative work of this paper is: The influence mechanisms of the sleeve flow path diameter,sleeve thickness and the diameter of the small orifice flow path at the valve seat on the cavitation effect inside the nuclear power main feedwater regulating valve are analyzed,and the theoretical basis for the optimization of the regulating valve structure design is laid.The influence of the inherent properties of the particles in the valve and the opening degree of the regulating valve on the cavitation effect and wear law in the valve is clarified,and recommendations are made for the use of the regulating valve based on the prevention of cavitation effect.