Study On The Flow Behavior And Separation Mechanism Of Inline Cyclone Gas-liquid Separator

In the development of offshore oil and gas fields,the bulky gravity separation equipment often leads to a significant increase in development costs due to disadvantages such as heavy weight and difficulty in withstanding high pressure.The existing inline cyclone separation equipment has the advantages of high separation efficiency,compact and high-pressure resistance,but it cannot adapt to the fluctuation of inlet conditions.Therefore,an inline cyclone separator that can adapt to a wide range of inlet conditions is designed,and its internal flow characteristics and separation characteristics is investigated.The main findings are as follows.(1)A new inline cyclone gas-liquid separator is proposed and the corresponding design method is established.Combining the advantages of horizontal cyclone separator and vertical cyclone separator,a new inline cyclone gas-liquid separator which can adapt to a wide range of inlet conditions is designed by using a strong cyclone-weak cyclone in series.Using the theory of residence time of particles,the calculation methods of structural parameters of the primary horizontal separation section and the secondary vertical separation section of the inline cyclone gas-liquid separator are established respectively.(2)The experimental method of internal flow and separation performance of inline cyclone gas-liquid separator is established in this paper.Using transparent Plexiglas device,high-speed camera system,and digital image processing,we establish the method and experimental system studying the internal gas-liquid morphology of inline cyclonic gas-liquid separator.The experimental research system is built by using conventional gravity separation equipment as a benchmark and adopting the measure of separation before metering.Based on the experimental system,the performance evaluation method of the inline cyclone gas-liquid separator is proposed with the indicators of dehydration efficiency,degassing efficiency and pressure drop.(3)Numerical simulations of the inline cyclone separator are carried out using Eulerian multiphase flow and RSM turbulence models.The characteristics of tangential velocity,axial velocity and pressure distribution inside the inline cyclonic gas-liquid separator are obtained.The distribution of the flow field in the horizontal separation section has a high degree of symmetry,while that in the vertical separation section is slightly less symmetrical.The distribution of gas-liquid morphology in the inline cyclone separator under fixed working conditions is obtained.The effects of the changes of the working conditions such as the flow split and the inlet gas volume fraction on the gas-liquid morphology are studied.(4)The gas-liquid morphology inside the cyclonic flow pipe and inline cyclonic gas-liquid separator is investigated using visualization experimental methods.Within the cyclonic pipe,the critical superficial liquid velocity for the formation of rotating flow is 0.375 to 0.82 m/s when the superficial gas velocity of the inlet is<10 m/s.At inlet superficial gas velocities>10 m/s,the formation of rotating flow is almost independent of the superficial liquid velocity and geometric swirl number.At tangential velocity<0.5 m/s,the rotating flow gradually transforms into a stratified flow.At tangential velocity>0.5 m/s,the decay of the flow field affects the gas-liquid interface.According to the roughness,the rotating flow can be divided into the stage of entrained gas line,smooth gas-core stage,rough gas-core stage and gas-core diffusion stage.In the horizontal separation section,the gas core diameter increases with the increase of inlet liquid volume flowrate and the decrease of gas volume flowrate.The critical flow split of gas core tail crushing is obtained as 0.84,and the calculation model of gas core diameter is established.In the vertical separation section,the effects of gas and liquid volume flowrate on the variation and oscillation of the gas core diameter are studied.(5)An experimental study of the inline cyclone gas-liquid separator is conducted.The results show that the degassing efficiency increases with the increase of the standardized flow split(FS~*)and the dehydration efficiency decreases with the increase of FS~*for a certain inlet condition.The inline cyclone gas-liquid separator is able to adapt to a wide range of inlet conditions.In contrast,the horizontal separation section is key to its ability to accommodate variations in inlet gas volume fraction,but the pressure drop in the horizontal separation section is greater than that in the vertical separation section.(6)A separation mechanism model is developed for the designed inline cyclonic gas-liquid separator.The model contains droplets and bubble particle size distribution,critical separation particle size,gas-liquid shear entrainment,and gas core diameter.The developed separation efficiency prediction model is evaluated from qualitative and quantitative perspectives.The results show that the mechanism model can predict the separation performance of the inline cyclone separator accurately in the range of liquid volume flowrate from 5 to12 m~3/h and gas volume fraction from 0.1 to 0.8.