Separation Mechanism And Experimental Research On Air-injected Liquid-liquid Hydrocyclones

With the applications of polymer-flooding technology in oilfields,oilfield produced water normally contains certain amount of polymer,which makes wastewater have the characteristics of high viscosity,small oil droplet,severe emulsification,and then difficult for treatment.Traditional hydrocyclone has lower efficiency for treating this kind of wastewater.In this dissertation,inner flow fields of air-injected hydrocyclones are theoretical analyzed.Based on that,flow field characteristic analysis is finished by using Fluent soft pack focus on hydrocyclones.Laboratory and oilfield experiments are carried out.The geometric and operating parameters of air-injected liquid-liquid hydrocyclones are optimized so as to realize high efficient wastewater treatment.Related theories such as strong swirling turbulent theory,multi-phase flow theory,and porous medium theory involved in air-injected hydrocyclones are first studied.Forcing situation of oil droplet or oil-gas compound body inside the flow field is analyzed.The functional mechanism of inner pressure field and velocity field on oil-water separation process inside hydrocyclones are discussed.A porous medium model is adopted to build the geometrical model of the air-injected hydrocyclone,and numerical simulation is carried out.Finite element models of hydrocyclones are established focus on conditions with no air-injection,big cone air-injection,whole air-injection and part air-injection of small cone.Flow field analysis is made;the distribution rules of inner pressure field and velocity field of hydrocyclones are obtained.It is shown that the distribution rules of pressure and velocity of air-injected hydrocyclones are familiar with those of traditional hydrocyclones(without air-injection).The concept of division region is proposed.Division region is a transitional area between upflow to the overflow outlet and downflow to the underflow outlet below locus of zero vertical velocity of hydrocyclones.The location of division region is influenced much by split ratio,while it has little relation to air-injection and its position.Based on simulation and analysis of hydrocyclone separation efficiency,and combining with lots of experimental results,it is shown that the separation efficiency of air-injected hydrocyclones is higher than traditional hydrocyclones.Higher efficiency can be obtained by injecting air through the nearby area of the division region.The changing rules of hydrocyclone separation efficiency with split ratio,gas-liquid ratio,overflow tube diameter,and air-injection position are studied by laboratory experiments,i.e.,with the rise of split ratio(or gas-liquid ratio),separation efficiency increases to a maximum value,and then drops down.It illustrates that a hydrocyclone has an optimum split ratio(or gas-liquid ratio)when geometric parameters and flowrate keep certain values.The optimum split ratio(or gas-liquid ratio)is different with the change of air-injection position.By comprehensive analysis of a large amount data,the parameters of split ratio,gas-liquid ratio,overflow tube diameter,air-injection position are optimized and higher separation efficiency is obtained.The results of numerical simulation and laboratory experiments are applied to oilfield polymer-flooding wastewater treatment.It shows that the separation efficiency of air-injected hydrocyclone is obviously higher than that of traditional hydrocyclone.By further study,it is found that the combination of first-stage air-injected hydrocyclone plus second-stage traditional hydrocyclone can obtain higher separation efficiency for polymer-flooding wastewater treatment.