Research On The Characteristics In Flow Path Tapered Axial-Flow Multiphase Pump

The axial-flow multiphase pump is used as a key equipment in the oil and gas mixing system because it can reduce pipeline distribution equipment and save cost in oil field exploitation.In this study,aiming at improving the hydraulic performance and stability of the multiphase pump,the theoretical design and numerical simulation are combined to optimize the structural parameters of the YQH-100 axial-flow multiphase pump.The main contents are as follows: Firstly,exploring the influence of the inlet angle of the diffusers on the hydraulic performance of the multiphase pump;Secondly,on the basis of the optimal diffusers inlet angle,the existing multiphase pump was improved on the flow channel,and the flow path tapered multiphase pump was proposed and optimized.Details as follows:1.Aiming at the problem of uneven flow at the static and dynamic junction of the original multiphase pump compression unit,the pump's supercharging and efficiency improvement under the design conditions are optimized.Three kinds of diffusers with different inlet angles were designed.The steady-state analysis of the single-stage compression unit is carried out under different gas volume fraction.When the inlet angle is increased,the inlet flow rate of the diffusers is reduced,and the starting point of the low-speed degassing zone on the back of the blade moves toward the inlet.The supercharging capacity,gas-liquid mixing capacity and efficiency of the multiphase pump are first increased and then decreased.The pressure on the impeller outlet is reduced,the pressure distribution is relatively uniform,but the average pressure is lower.The smaller inlet angle leads to increased displacement between the blades,and the flow area is reduced,and flow rate and pressure non-uniformity are increased at the static and dynamic junctions.It is concluded that the compression unit with the diffusers inlet angle of 15°/19° has the best performance,and its efficiency is increased by 1.7% compared with the original model.2.For the gas-liquid separation phenomenon of multiphase pump at high gas volume fraction,refering to the internal structure of the compressor,the three-stage multiphase pump was improved to a tapered flow path,and designed three different average channel heights on this basis.By comparing the steady-state calculation results under different gas volume fraction,it is concluded that with the increase of the gas volume fraction,the efficiency of the original model is gradually reduced,and the efficiency of the flow path tapered multiphase pump is first decreased and then increased.It shows that compared with the original model,the improved model improves pump performance when conveying high gas volume fraction gas-liquid mixed medium.For the improved model,as the average flow path height decreases,the static pressure of the impeller blade working face is more uniform,and the number and area of the high gas-bearing zone in the flow channel gradually decrease,reflecting the external characteristics as mixed.The pump's supercharging capacity is reduced,but the gas-liquid mixing capacity is enhanced,and the flow separation loss is reduced,which makes the efficiency of the multiphase pump increase.Considering comprehensively: when the average flow channel height is 55 mm,the flow path tapered multiphase pump has better overall performance.3.In order to study the transient characteristics of multiphase pump,the transient calculation of the optimized model is based on the steady state calculation.The pressure fluctuation analysis of each model shows that the main frequency of the pressure fluctuation in the impeller is one times the leaf frequency.The pressure fluctuation in the impeller is mainly affected by the impeller rotation and the number of impeller blades;the pressure fluctuation of the impeller inlet and outlet is mainly concentrated in the middle and low frequency,and there is also obvious pressure fluctuation in the middle of the impeller at the high frequency.According to the analysis of the force of each model impeller,in the one rotation period,the axial force of the impeller appears four fluctuation periods,and the radial force of the impeller shows eight fluctuation periods,indicating that the fluctuation period of the axial force and radial force of the impeller is related to the number of blades.With the decrease of the average flow path height,the axial force of the impeller is also reduced,but the radial force is increased.Considering comprehensively,when the average flow channel height is 55 mm,the flow path tapered multiphase pump has better transient characteristics.The analysis of the impeller force of the improved flow-path tapered multiphase pump at different gas volume fraction shows that the axial force,the radial force and its fluctuation amplitude are negatively correlated with the gas volume fraction.This study improves the performance of existing multiphase pump,and provides an important theoretical reference for optimizing the hydraulic design of multiphase pump,ensuring the stability of multiphase pump operation under high gas volume fraction and studying the vibration characteristics of the pump.