Treatment Of Produced Water From ASP Flooding Using Bicyclone Column Flotation Based On Chemical Demulsification

ASP?Alkaline/Surfactant/Polymer?flooding is an EOR technique that has been found to increase oil recovery rate by over 20%than that of water flooding,which kept oil production stable and enhanced oil recovery when main oil fields domestic have come into the high water-cut stage in the middle and late stage of oilfield development.However,the ASP flooding technique also has some disadvantages including large amount of produced water from ASP flooding and difficulties in treating the produced water,which limit its further application in the oilfield.Produced water from ASP flooding is a typical oil/water?O/W?emulsion with high phase stability,emulsification and viscosity.Also,the extremely high content of the micro oil droplets in this wastewater makes it difficult to achieve the oil/water separation.This also has become a challenge to both oil field development and environmental protection in the oilfield.The traditional oily wastewater treatment process could hardly meets the treatment requirements of produced water from ASP flooding.In order to improve the treatment of produced water from ASP flooding,a bicyclone flotation column was developed,and numerical simulation was performed for internal flow field of the bicyclone flotation column using Fluent software.The flow field distribution characteristics and separation mechanism of the bicyclone flotation column were investigated based on systematic test and mechanism analysis.A reversed demulsifier,polyether-polyquaternium was synthesized in this work.The processes of microwave assisted demulsification-bicyclone column flotation and colloidal gas aphrons and froth-bicyclone column flotation have been proposed for the treatment of produced water from ASP flooding.A technical system including demulsifier,equipment and processes have been developed,which provide theoretical guidance and technical support for the treatment of produced water from ASP flooding.This main research includes the following aspects:A prototype of bicyclone flotation column that integrates the flotation separation with cyclone separation was developed.This device combines both flotation separation and cyclone separation process which formed a compound gravity-centrifugal separation field.The numerical simulation and analysis of the bicyclone flotation column were carried out using ANSYS Fluent software.The velocity distribution and energy distribution characteristics of the bicyclone flotation column were obtained.The simulation results indicate that the tangential velocity distribution of the representative planes at different heights are similar and are axisymmetric distributed.The tangential velocity gradually increases to 0.908 m/s,and then decreases to zero from the side wall to the center along radial direction.The axial velocity direction is upward and outward near the side wall of column body,and the axial velocity direction is downward toward the center along the radial direction.The axial velocity of the representative planes at different heights in the bicyclone flotation column is smaller than the radial velocity and tangential velocity.The axial velocity increases to 0.032 m/s,and then decreases to zero from the side wall to the center along radial direction.The height with steady flow field that the flow field changes from turbulent flow to steady flow increases when the inlet velocity from the circular processing influent increases from 0.5 m/s to 2.0 m/s,and the zone of flotation separation decreases,which is unfavourable to the flotation separation.The height with steady flow field is 1100 mm when the inlet velocities from the circular processing influent are less than 1.0 m/s.The height with steady flow field is 1200mm when the inlet velocity from the circular processing influent increases to 2.0 m/s.The partial velocity of the fluid increases less at different heights when the inlet velocity from the circular processing influent increases from 0.5 m/s to 1.0 m/s.The tangential velocity of the representative planes increases rapidly at different heights.The turbulence intensity of the representative planes near the tangential inlets is high and the flow field enters a stable laminar flow state at the height of 1200 mm.The tangential velocity of the representative planes at different heights increases rapidly,while the radial velocity and axial velocity increases step by step when the inlet velocity from the circular processing influent increases from 1.0 m/s to 2.0 m/s.The turbulence dissipation rate and turbulence kinetic energy of the representative planes at different inlet velocity from the circular processing influent are symmetric distributed along the radial axis.At the height of 300 mm and 600 mm,the turbulence dissipation rate of the representative planes is high and turbulence kinetic energy is low near the tangential inlet.At the height of 400 mm and 800 mm,the turbulence dissipation rate varied from 0 to 0.78 m²/s³,and the maximum value of turbulence kinetic energy is 0.031 m²/s².The region with high turbulent kinetic energy also possesses low turbulence intensity and lossing energyl.Therefore,the simulation results show that an inlet velocity from the circular processing influent of 1.0 m/s is appropriate.A physical model of the bicyclone flotation separation process was established based on combined flotation separation and cyclonic separation,and the basic coupling process of cyclone and flotation was analyzed.This integrated separation lowers oil droplet size limit of separation and accelerates oil-water separation.The oil removal of the cyclonic section,the flotation section and the total oil removal of the bicyclone flotation column were analyzed,respectively.The oil removal of cyclonic separation,flotation separation and total oil removal of bicyclone flotation device were 80.4%,94.0%and 98.5%under the conditions of gas flow of 1.0 L/min,inlet velocity from the circular processing influent of 1.0 m/s and flotation time of 15 min.The residual oil content of effluent treated by bicyclone flotation,cyclone flotation and dissolved air flotation were 45.2 mg/L,53.5 mg/L and 70.4 mg/L,respectively.The oil removal of bicyclone flotation is superior to that of cyclone flotation and dissolved air flotation.The characteristics of oil removal kinetics show that the dynamic characteristics of oil droplets at micro scale indicate that rapidly approaches an equilibrium distribution of the oil droplet size along with the extended of separation process when the inlet velocity from the circular processing influent increase.The oil droplets with small diameter has larger superiority in numbers in the oily wastewater when the oil droplet diameter distribution reaches an equilibrium state.A modified silicone oil intermediate was obtained by using silicone oil containing hydrogen grafted with aepoxy ether and methyl ether.By nucleophilic addition reaction of epichlorohydrin with dibutylamine,Poly?2-hydroxypropyl dibutyltin ammonium chloride?were prepared,then the polyquaternium was obtained by alignmenting with an organic cross-linker of polyethylene polyamine.By an epoxide-opening reaction of modified silicone oil with polyquaternium,the reversed demulsifier polyether-polyquaternium was synthetized.The structure of the reversed demulsifier polyether-polyquaternium was characterized by means of FTIR and ¹HNMR.The effects of demulsification conditions on the demulsification performance of the reversed demulsifier polyether-polyquaternium were studied.The results indicate that under the appropriate demulsification conditions of demulsifier dosage of 100 mg/L,demulsifying time of 4 h and demulsifying temperature of 60 ^oC,the oil removal reaches 94.9%and the residual oil content in the wastewater is 25.8mg/L.The demulsification performance of the polyether-polyquaternium demulsifier was superior to that of the polyquaternium demulsifier.In order to improve the oil-water separation efficiency of produced water from ASP flooding which is characterized as a complex and highly stable system with fine size oil droplets,one new process combined microwave assisted demulsification and bicyclone column flotation has been developed.Firstly,the microwave assisted demulsification method was used to demulsifying of produced water from ASP flooding in this work,then the bicyclone flotation column was applied for the separation of oily wastewater.The demulsifying efficiency of chemical demulsifiers demulsification,microwave demulsification and microwave assisted chemical demulsifier demulsification were investigated.The operating parameters,such as inlet rate of the circular processing influent,feed flow of oily wastewater,gas flow and oily froth layer height were studied.The experimental results show that an oil removal of93.6%was achieved by using microwave assisted demulsifying,which is higher than that of demulsifier?6.6%?and microwave demulsification?25.5%?,respectively.An oil removal of 99.4%was obtained under the conditions of demulsifier dosage of 50mg/L,microwave power of 800 W,treating time of 120 s,inlet rate of the circular processing influent of 1.0 m/s,gas flow of 0.75 L/min,feed flow of 0.3 L/min and oily froth layer height of 10 cm.In order to further improve the separation efficiency of oily wastewater,the other new process that combined colloidal gas aphrons?CGA?and froth in bicyclone flotation column has been developed.The positively charged CGAs combined with the negatively charged oil droplets to form a oil droplet-bubble aggregates.Effects of the surfactant concentration,stirring speed and stirring time on the stability of CGA were discussed.The inlet rate of the circular processing influent,gas flow,feed flow and CGA flow were also investigated.The experimental results showed that the oil removal of 96.5%was obtained under the optimized conditions.The size D₅₀ of the residual oil droplets in effluent is characterized as 3.97?m.This dissertation contains 95 pictures,5 forms and 175 references.