Structure Optimization And Performance Study Of Axial Flow Oil-water Separator

At present,most oilfields have entered high water cut stage.Water cuts of oil-well produced fluid are generally above 85%.With the improvement of water cut,the load of the existing processing equipment in oilfield increases and the economic benefit of oilfield decreases.Therefore,an axial flow oil-water separator was proposed for the processing of high-water-cut crude oil.Compared with the traditional oil-water hydrocyclone separator,the separator has advantages of compact structure,high efficiency and low pressure drop.The geometric model of the axial oil-water separator was established based on the swirl separation theory.The numerical simulation software FLUENT was used to study the fluid field inside the separator with RSM turbulence model and Mixture model.The distribution rules of velocity field,pressure field and concentration field was studied.The effect of physical parameters on separation performance was obtained with the change of oil viscosity,oil density and inlet oil concentration.At the same time,the influence of the split ratio on separation performance was also studied.The main structures were simulated and optimized for the initial separator model.The result shows that the increase of swirl chamber length and overflow tube diameter can enhance oil-water separation efficiency.However,both of them have a critical value.The insertion depth of overflow tube can not be too large,otherwise the mixture will be discharged directly without enough time to separate.Increasing the width and length of slits appropriately can reduce oil concentration pressure drop of underflow outlet.The pressure drop changes less as the slit length increases.Reducing the vane outlet angle or increasing the vane wrap angle can enhance swirl intensity and improve the separation efficiency as the pressure drop enlarges significantly.The separation efficiency can be enhanced obviously with the number of blades changing from 2 to 3.There is little effect on separation efficiency as the pressure drop increases when increasing the number of blades from 3 continuously.The experimental loop was established which set the prototype of separator as the core to carry out indoor experimental study.The study shows that the small inlet flow can cause the swirl intensity to reduce and the mixture to separate uncompletely as the large flow can cause oil droplets to shear and break and the emulsification to enhance.Therefore,an optimal inlet flow exists for the separator.The separation increases with the decrease of inlet oil concentration and the pressure drop changes little which is consistent with simulation results.The pressure drop increases with the decrease of vane outlet angle.The vane outlet angle has larger effect on pressure drop with larger inlet flow velocity.The influence order and degree of all factors on separation efficiency,overflow pressure drop and underflow pressure drop were obtained according to the orthogonal experiment analysis.The prediction model of efficiency and pressure drop was established with the stepwise regression analysis.The model was verified and the average errors of separation efficiency,overflow pressure drop and underflow pressure drop are 10.02%,6.68% and10.13% which are within the allowed scope of the engineering.The prediction model provides a reliable basis for the design of the design,optimization and prediction of the axial oil-water separator.