Research On Multi-stage Cage Type Choke Valve Of Ultra-high Pressure Natural Gas Wellhead

For ultra-high pressure natural gas wells,in order to transport natural gas from the wellhead to the main network,it must be throttled and depressurized with a pressure regulating device.The cage type choke valve is a common choke and pressure regulating device for ultra-high pressure gas wells,so that the gas flow pressure at the wellhead reaches the pressure of the gas pipeline network.For gas wells with wellhead pressure exceeding100 MPa,many choke valves are required.As the working environment of the throttle valve is getting worse and worse,the loss and damage of the valve core and other materials are becoming more and more serious,and the cage type throttle valve mainly relies on imports,which is expensive,has a long procurement cycle and is inconvenient to maintain.Therefore,while satisfying the throttling and pressure reduction,the problems such as reducing the number of throttle valves used,increasing the pressure drop ratio,reducing the degree of erosion damage,and shortening the lifting life need to be solved urgently.This paper mainly studies from five aspects:1.Theoretical study of fluid flow in cage type throttle valve.By studying the relevant contents of fluid mechanics and thermodynamics,and taking the small hole throttling theory as the condition,the state equation of the compressible fluid flow of a single small hole is deduced.The relationship between fluid velocity,density,cross-sectional area,diameter and length of small holes and pressure difference between inlet and outlet is discussed.Next,the principle and calculation method of multi-stage throttling are deduced.2.Structural research of multi-stage cage type throttle valve.Avoid the turbulent disturbance of the high-speed airflow of the valve core,so that the fluid flow inside the valve core is smooth.The relationship between the flow area and the opening of the small holes of various valve cores is compared and analyzed,and the number of small holes and the arrangement of small holes are determined.According to the principle of multi-stage throttling,the number of layers of the spool sleeve and the internal structure of the spool are designed,and three different multi-stage throttling spool structures are proposed.Next,the whole valve body is structurally designed.3.Research on the flow field of different spool structures of multi-stage cage type throttle valve.Numerical simulation of fluid is carried out for four different structures proposed A,B,C and D,the influence of physical parameters of fluid in four different spool structures is analyzed,and the throttling effect of different spool structures is compared.The obtained(third structure)C structure valve core has a good throttling effect.4.Research on erosion wear and structure optimization of multi-stage cage type throttle valve spool.Combined with the erosion and wear of gas-solid two-phase flow particles in the throttle valve,the position and degree of easy erosion of the valve core are obtained by comparing different opening degrees and particle sizes optimization.5.Research on temperature field of multi-stage cage type throttle valve.Through the calculation of the internal temperature field of the throttle valve spool,it is proved that the valve core structure proposed in this paper can withstand the maximum pressure difference.If this range is exceeded,the "ice block" effect will occur inside the throttle valve,that is,the internal temperature is low at 273K.