| With the continuous development of oilfield,water content of produced fluid in oilfield increases continuously year by year,and the subsequent difficulty and cost of processing oily wastewater also increase gradually.How to realize oil-water separation economically and efficiently has become a major problem to be urgently solved by petroleum industry at home and abroad.The traditional coalescence separation technology has high processing cost and discontinuous problems in oil-water separation,while the hydrocyclone is difficult to ensure the separation efficient of small oil droplets.To study oil droplets' shear,collision deformation and types and affecting factors of coalescence in vortex flow field to further understand the influences of oil droplets coalescence on separation properties is of great significance in both revealing the mechanism of hydraulic coalescence and separation in hydrocyclone and guiding the design of an efficient and feasible coalescence-enhanced de-oiling hydrocyclone.An experimental system for observing the motion and deformation characteristics of oil droplets in a vortex field driven by a magnetic rotor is constructed by means of high-speed camera technology.The images of oil droplets in vortex flow filed are convolutional calculated by using Sobel gradient operator to complete the contour recognition of oil droplet movement,deformation and coalescence process.Oil droplets collision forms and process are analyzed and represented such as coalescence,rebound,extrusion deformation,drawing separation,and so on.A nonlinear model for oil droplets non-affine deformation by collision is established.The static equilibrium inertia force and Weber number in the process of oil droplet deformation are derived.The deformation and weber number of oil droplets are used as assessment index to analyze the coalescence critical condition of oil droplets in vortex flow field.Particle image velocimetry technology is used to measure target flow field velocity and calibrate the relation between the velocity of the rotor and the velocity of fluid,and the relation formula for the radius of the vortex field and the velocity of fluid is obtained.The oil droplets particle size measurement system without shearing failure is designed,and the influence of rotation velocity,the oil concentration,and shearing time on droplets size distribution were obtained.Different oil droplets' radial sedimentation time and velocity are analyzed based on theoretical analysis and numerical simulation,and the influence of droplets size on radial sedimentation time and velocity is gained.Taking two different hydrocyclones with axial and tangential inlets as the research object,oil droplets' migration trajectory and separation characteristic in hydrocyclones are carried out by using Euler-Lagrange numerical model,and influence laws of oil droplets size and migration trajectory on separation efficiency are obtained.Based on coalescence mechanism and hydraulic cyclone separation theory,a new oil-water separator consisting of the hydraulic coalescer and hydrocyclone is designed.The CFD-PBM numerical simulation of oil droplets breakage and coalescence and separation characteristic in coalescence hydrocyclone is carried out,and the distribution characteristics of velocity,concentration,particle size,and motion characteristic in coalescence hydrocyclone are obtained.The oil droplets coalescence and breakage positions in hydrocyclone are identified,and the influence laws of split ratio and entrance flow rate on oil droplets particle distribution are gained.Mathematical model of coalescence efficiency is established to evaluate coalescer performance.The Plackett-Burman experimental design method is used to screen the significant factors of structural parameters which influence coalescence efficiency.Based on orthogonal experiment design method,the center points of structural parameters for response surface are gained.Response surface method is adopted to build the second-order models for structural parameters and coalescence efficiency and pressure loss.The optimal structure parameters are decided by the relationship equation.Regression-orthogonal method is used to establish the regression equation between oil concentration,interfacial tension,inlet velocity,water viscosity and coalescence efficiency.Significance of the regression is analyzed to verify the accuracy of the equation.Coalescence hydrocyclone fluid model is established to analyze the velocity field,oil concentration,oil droplets size distribution,and oil droplets motion characteristic in the coalescence hydrocyclone by numerical simulation.The influence laws of split ratio and inlet flow rate on coalescence hydrocyclone separation efficiency are obtained by numerical simulation.Coalescence and separation performance experiment system is introduced to evaluate the hydrocyclone separation efficiency and the coalescer performance.Meanwhile HSV and microscopy are applied to observe the oil droplets coalescence process in coalescer,and the oil droplets size distribution in coalescer inlet and outlet in the different condition are analyzed by Mastersizer 2000.The results show that the separation efficiency of coalescence hydrocyclone is higner than hydrocyclone in different split ratio and inlet flow rate.The small oil droplets in the coaleser can be coalesced efficiently in different operation conditions.The experimental results validate the accuracy of numerical simulation and the rationality of separator design.Finally separation performance experiments are carried out by manufacturing lipophilic and hydrophobic coating on coalescence inner part to increase the oil droplets collision probabilities,so as to further improve the separation efficiency of coalescence hydrocycnoe. |
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