Study On Multiphase Interactions And Motion Characteristics In The Oil Removal Process By Gas Flotation And Cyclonic Separation

This article proposes and designs a new type of three-phase gas-liquid-solid mixing device based on the gas flotation technology and vortex technology to solve the problem of oil-water separation in offshore oilfields.The key factor determining the oil-water separation effect is the agglomeration and interaction between bubbles,oil droplets,and flocs.The addition of the vortex field changes the collision and adhesion process between the three,and this article analyzes the motion characteristics and interaction mechanisms of bubbles,oil droplets,and flocs in the vortex field through experiments and simulation methods.During the theoretical research phase,the basic viewpoints of gas flotation and vortex mechanism were expounded,and various ways in which the vortex field affects collision and adhesion were proposed.It was concluded that centrifugal collision and inertial separation act on the collision process,liquid discharge adhesion acts on the adhesion process,and emulsification dissipation acts on the detachment process.This provides a theoretical basis for the impact of vortex characteristics,wastewater characteristics,and bubble and oil droplet size on gas flotation vortex performance.The impact of the vortex field on gas flotation mainly manifests in the collision process rather than the adhesion process,and the size of bubbles and oil droplets is the basic factor determining the adhesion performance.The vortex field can only adjust the turbulent environment of adhesion and has a weaker impact than the impact of particle size.Using Fluent numerical simulation technology,a simplified mixer model was established,and the changes in the flow field inside the mixer under different inlet velocities were analyzed using the RNG k-ε turbulence model and the VOF model.The axial,radial,and tangential velocity distributions of characteristic sections at different heights were compared and analyzed.The discrete phase particle model(DPM)was used to track the motion of oil droplets in the mixing field.The velocity in the vortex region of the mixer inner cylinder showed a circular distribution,with the maximum tangential velocity near the wall and the smaller the tangential velocity value closer to the middle area,showing a significant velocity gradient.The impact of the vortex action on oil droplets was simplified into the influence of density(the number of oil droplets per unit volume)and particle size.The particle size and density of oil droplets affect the residence time in the mixer inner cylinder,which is beneficial to the contact between oil droplets and bubbles.However,when the residence time is too long,it can cause difficulty in discharging oil droplets,which negatively affects the separation efficiency of the mixer.Therefore,the particle size and density of oil droplets affect the separation efficiency of the mixer.Based on high-speed photography and image processing technology,the article studies the influence of rotational speed(0-1000 r/min)of the flow field and wastewater characteristics(bubble size,oil concentration,and floc shape)on gas flotation performance.It is found that different rotational speed conditions have a significant effect on the single-phase motion characteristics of bubbles,oil droplets,and flocs in the vortex field and their size.In the gas flotation process,the influence of the vortex field on the residence time of bubbles in water is significant.A rotational speed of 400 r/min can increase the residence time of bubbles in water by 240%,increasing the probability of collision between bubbles and oil droplets.However,an excessively strong vortex field can enhance the agglomeration effect between bubbles,resulting in the decrease of separation efficiency of the mixer.