Design And Experimental Study Of Low-shear Tubular Dynamic Rotating Swirler

The tubular dynamic hydrocyclone has great application potential in the field of pre-dehydration of offshore oil platform due to its characteristics of high separation efficiency,large single-tube processing capacity and small volume.However,the traditional dynamic swirler,which uses a straight-blade structure,produces strong shear and turbulence during the swirling process,which easily causes dispersive oil droplets to be further sheared and emulsified.With the deterioration of the produced fluid and the gradual decrease in oil-water interfacial tension,the effect of the dispersed oil droplet breakup caused by this strong shear and turbulence has become a major limiting factor for the application and development of tubular dynamic hydrocyclones.In view of this,a design model of lowshear dynamic swirler(LSDRS)will be constructed to study the influence of operational parameters on the morphological changes of oil droplet and the distribution of internal flow field characteristics during the dynamic swirling process.This will help to master the theoretical basis for avoiding oil droplet shear emulsification during the dynamic swirling process,which will be of great significance for developing tubular dynamic swirling separation equipment.This study first constructed a design model for a LSDRS based on the relative motion relationship between the fluid and the swirler.The average relative error between the numerical simulation results and the experimental results was only 5%,which verified the accuracy of the selected numerical simulation method.Compared with the traditional straight blade swirler,the maximum shear stress is reduced by 74.6%,the peak value of turbulence energy dissipation rate is reduced by 68.5%,and the droplet size increment exceeds 1.6 times after using the LSDRS.An oil droplet morphology test evaluation system was designed and constructed.Particle Dynamic Analyzer(PDA)was used to measure the velocity field distribution,which verified the accuracy of the selected numerical simulation method.Then,by combining high-speed photography and numerical simulation,the influence range,backflow rate,droplet morphology changes,and particle size variations of anomalous flow caused by operating parameters during the dynamic swirling process were studied.The results showed that when the swirler ran near the design condition,the droplet breakage probability was less than 5%,the average droplet size was about 420μm,and the matching relationship between the operating parameters and the internal flow state of the experimental platform was established.Finally,the engineering prototype of the developed tubular dynamic hydrocyclone with a rated capacity of 5 m~3/h was tested in the field on an offshore oil production platform.During the experiment,the regression orthogonal method was used to carry out the experimental study on the influence of operating parameters on the separation performance of the equipment,and the optimal separation performance was taken as the optimization index.The optimal operating parameters of the tubular dynamic hydrocyclone engineering prototype were obtained as flow rate4.7m~3/h,speed 1200 rpm and split ratio 9.6%.Then,by combining the Euler-Euler multiphase flow model,the velocity field and phase distribution in the barrel were studied and analyzed to reveal the separation mechanism of the tubular dynamic hydrocyclone.The influence law of operating parameters on the separation performance,velocity field and phase distribution field of the engineering prototype was studied by combining field experiments and Euler-Euler multiphase flow model,thus revealing the influence mechanism of operating parameters on the oil phase discharge in the tubular dynamic hydrocyclone.The experimental results show that in the dynamic swirling,the pressure at the center of the separator barrel decreases with the increase of centrifugal force.The excessively low center pressure promotes the reverse flow at the center of the pipeline,thereby restricting the movement of the separated oil phase from the vicinity of the overflow pipe inlet towards the center of the pipeline.It can only enter the overflow pipe along the hub wall,and the accumulated unseparated oil phase gradually forms an oil ring.When the diameter of the oil ring exceeds the diameter of the overflow pipe,the separation efficiency drops sharply.Appropriate increase of shunt ratio(4%～13%)can prevent the oil phase from accumulating,speed up the oil phase discharge from the overflow pipe and improve the separation efficiency of the equipment.