Study On Enhanced Oil-water Separation By Non-equilibrium Plasma

Polymer flooding technology is widely used in oil fields.The polymer commonly used in polymer flooding and oil recovery technology is polyacrylamide（PAM）.Therefore,while using this technology to improve crude oil recovery,there will also be a large number of high concentration PAM solution in polymer containing oily water,and PAM solution belongs to viscoelastic fluid,which makes the viscosity of polymer containing oily sewage high,which is an important factor leading to the difficulty of oil-water separation of polymer containing oily sewage.In order to improve the effect of oil-water separation of oily wastewater containing polymer,the viscosity of oily wastewater containing polymer must be reduced.In this paper,the geometric model is established by COMSOL numerical simulation software,the boundary conditions are set as normal temperature and a standard atmospheric pressure,and the free triangular mesh is used for subdivision.In the process of numerical simulation,the level set method is selected to study and analyze the rise and reservoir fusion process of multiple oil droplets in PAM solution,mainly analyzing the changes of oil droplet volume fraction,oil droplet coalescence and floating velocity and pressure around oil droplets.In order to study the effect of non-equilibrium plasma on oil-water separation of oily wastewater containing polymer,a double glass dielectric barrier discharge reactor with water cooling function was designed.The non-equilibrium plasma discharge experiment was carried out through the device.The voltage,PAM solution concentration and time were changed,and AC/Mn+Ti O₂ catalyst and activated alumina were addedγ-Al₂O₃ catalyst was used to analyze the effects of these factors on the viscosity of PAM solution.Environmental scanning electron microscopy（ESEM）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）were used to characterize PAM solution and catalyst particles before and after discharge.Considering whether plasma discharge can strengthen oil-water separation and reduce the difficulty of oil-water separation of polymer containing oily wastewater,the change of oil content in simulated polymer containing oily wastewater is measured at the same time of discharge experiment,so as to study the change law of oil content and the effect of oil-water separation.The following conclusions are obtained:（1）The change of oil droplet viscosity has no obvious effect on the volume fraction.The coalescence and floating velocity of oil droplets are greatly affected by the viscosity of oil droplets.With the increase of the viscosity of oil droplets,the coalescence and floating velocity gradually decrease.When the viscosity of oil droplets is 0.1Pa·s,the coalescence time of oil droplets is 8s,and the time of oil droplets hitting the water reservoir is 20s,which takes the shortest time.When the viscosity is 0.5Pa·s,the time required for oil droplet coalescence is the longest,up to 14s.The change of oil drop viscosity has little effect on the pressure.The pressure distribution is mainly related to the height.With the increase of height,the pressure decreases linearly;（2）With the increase of discharge voltage,the generation of strong oxide is accelerated and the effect of discharge is enhanced.The solution viscosity decreases gradually with the increase of discharge time.Generally,the PAM viscosity decreases to the lowest at 20～30min,which is basically consistent with that of water.With the increase of the initial concentration of the solution,the viscosity of the solution decreases less in the same time;（3）With the increase of discharge voltage,the viscosity of simulated oily wastewater containing polymer decreases faster,which is more conducive to oil-water separation.When the voltage is 16k V,the effect of reducing the oil content of the solution after discharge for 30min is general.When the voltage is 19 k V and 20k V,the oil content of the solution decreases rapidly,and the effect of oil-water separation is obvious.The oil content of simulated oily wastewater with polymer has a great influence on the effect of oil-water separation.When the initial concentration increases to30mg/L,the oil-water separation effect becomes worse,which is not conducive to the experiment;（4）Adding catalyst can effectively improve the reaction speed and efficiency,up to 10%～15%,and the solution viscosity decreases faster.The change of the initial concentration of the solution will also affect its viscosity reduction efficiency.When the concentration is 1g/L,the viscosity reduction efficiency is the highest,and the viscosity reduction efficiency decreases with the increase of the concentration;（5）After discharge for 30min,AC/Mn+Ti O₂ catalyst andγ-The element composition of Al₂O₃ catalyst,the microstructure and functional groups of PAM have not changed much,indicating that PAM solution has not been degraded during discharge.The main reason for the decrease of its viscosity is that the discharge leads to the curling of PAM macromolecular chain and the weakening of intermolecular winding ability.