Research On The Effect Of Double Cascade Interference And Gas-Liquid Separation In Counter-Rotating Multiphase Pump

The Oil and gas mixed transport technology plays a very important role in the exploitation of marginal oil fields and the long distance transportation of deep-sea oil.As the core of oil and gas mixed transport technology,the spiral axial flow multiphase flow pump has the function of pump and compressor at the same time.In terms of structure,it has the characteristics of compact structure,light volume,large flow rate and strong sand resistance.Therefore,it can well transport the gas-liquid two-phase flow.But in the engineering application,the ordinary helical axial multiphase pump has many problems.For example: The efficiency is low in engineering application;When multistage connection,the length of oil-gas mixed transport system is longer;When the gas content is high,it is easy to produce gas-liquid separation in the pump,inducing Gas pockets-Gas blockage phenomenon and difficult to control.In order to improve the gas-liquid mixing capacity of multiphase flow pump,a contra-rotating multiphase pump is proposed.The pump replaces the diffuser with a rear reverse impeller,so it has better pressurization ability on the same length.And it is planned to use the contra-rotating cascade to suppress the gas-liquid separation in the flow field.In order to analyze the gas-liquid mixing transport capacity and the gas-liquid separation characteristics of the contra-rotating multiphase pump,the following research is carried out in this paper.Firstly,the internal flow characteristics of the counter-rotating multiphase pump were analyzed.Through the analysis of the external characteristic curve,it is found that the optimal working condition of the contra-rotating multiphase pump is shifted to the right.Compared with the traditional multiphase flow pump,it has better boosting capacity and more efficient zone.The two-phase flow regularity in the multiphase pump is revealed by analyzing the cascades at different blade heights.Secondly,the interference phenomenon of contra-rotating cascade is analyzed.The effect of axial clearance δ on cascade interference in contra-rotating multiphase pump is studied by taking entropy production rate and flow field distribution as objects.And the change of booster capacity caused by cascade interference is analyzed.It is found that the smaller the axial clearance of the impeller is,the more obvious the cascade interference phenomenon will be.And the existence of cascade interference will lead to the increase of flow loss in the pump.The cascade interference mainly occurs near the hub position.Finally,the gas-liquid separation phenomenon in the counter-rotating multiphase flow pump with different inlet gas content rates is analyzed.The impeller flow channel is divided into three flow surfaces: working surface,middle flow surface and back flow surface.Calculation of gas-liquid separation energy potential for each flow surface to analyze the gasliquid separation phenomenon in a counter-rotating multiphase pump.Then,the degree of gasliquid separation between the traditional multiphase flow pump and the contra-rotational multiphase flow pump is compared.The results show that the potential energy of gas-liquid separation well reflects the degree of gas-liquid separation.There are many reasons for the improvement of gas-liquid separation,such as pressure gradient difference between gas-liquid two phases,cascade interference,vortex,etc.These factors together determine the gas phase distribution law in the pump.The gas phase in the diffuser of traditional multiphase flow pump is serious.Compared with the traditional multiphase pump,the counter-rotating multiphase pump has better liquidity.