| Due to the polymer,alkali and surfactant in the chemical flooding wastewater,the emulsification degree of oil droplets in the water is increased,the floating rate is reduced,and the suspension is stable,the treatment difficulty of chemical flooding wastewater is increased,and the oil-water separation efficiency of in-service sedimentation technology is low.In this paper,based on Fluent fluid dynamics simulation,dynamic parameters such as gas holdup and liquid phase circulation velocity in loaded coalesce flotation column were analyzed,as well as backmixing between two stages and inside the same stage of flotation column.The influence of baffle position and length on flow field was simulated,and the influence law of gas phase and liquid phase flow field under different apparent gas velocity conditions was studied.The oil content and particle size distribution were determined by coalescing test,and the coalescing properties of PVC,PU,PA,SS（polyvinyl chloride,polyurethane,nylon,stainless steel）were investigated,the microscopic mechanism of oil droplet coalescing was explored,and the influencing factors of coalescing efficiency were analyzed.Based on the response surface method,the interaction between oil removal rate and hydraulic residence time,flow shear force,surfactant concentration and polymer concentration was analyzed.The optimum conditions of coalescence test were optimized according to response equation and response surface diagram.Field tests were conducted to investigate the treatment effect of loading coalesce flotation column under different working conditions（hydraulic residence time,dissolved gas mode and stage）,and to compare the oil-water separation efficiency of the two-stage sedimentation process and the loading coalesce flotation column process in the oilfield,and to verify the stability of the operation of the loaded coalesce flotation column under the condition of fluctuating water quality of chemical flooding wastewater.The efficiency equation and flotation kinetics equation of loaded coalesced flotation column are established.The simulation results show that the backmixing between the two stages can be effectively prevented by setting the baffle.When the apparent gas velocity is 2.5 cm/s,the local radial velocity of the bubble in a single stage is more consistent,and the backmixing degree is lighter.When the apparent gas velocity is 2.5 cm/s,the baffle with a length of 40mm is better.The height of baffle has little effect on the hydromechanical properties of flotation column,but it should avoid the situation that baffle is too high or too low.When the apparent gas velocity is 2.5 cm/s,the gas holdup is 11.2%.Under this condition,the operation effect of flotation column is the best.Therefore,the apparent gas velocity of the field test was 2.5 cm/s,and the gas holdup was set at 11.2%.It provides guidance for the design and operation of subsequent flotation column.The results of coalescing test show that the oil-water separation efficiency of the coalescing materials is compared with PVC>PU>PA>SS.The particle size of the oil droplet increases before and after coalescence,and the change of the particle size of the oil droplet is mainly achieved through the wetting and collision coalescence of the coalescence material and the gravitational sedimentation caused by the difference of oil and water density in the separation device.Under the combined influence of the response surface,the optimal removal rate is as follows:hydraulic retention time A is 87.0 min,flow shear force B is 187.0r/min,surfactant concentration C is 27.0 mg/L,polymer concentration D is 475.0 mg/L.Under these conditions,the removal rate predicted by the model is 99.1%.The experimental results are close to those predicted by the model.Field tests show that the average removal rates of oil content are 76.5%,84.2%,92.8%and 93.1%when the hydraulic residence time is 5.0,8.0,10.0 and 15.0 h,respectively.The method of dissolved gas+aeration is 14.7%higher than that of dissolved gas only,and increasing aeration can improve the oil-water separation efficiency.After secondary treatment,the removal rate of oil content increased by 15.1%compared with that of primary treatment,but the increment of oil-water separation efficiency gradually decreased and the column height increased.Comparison of oil-water separation efficiency of coalescing materials PVC>PU>PA>SS>Not loaded.The results show that under the conditions of loading PVC,hydraulic residence time of10.0 h,apparent gas velocity of 2.5 cm/s,gas holdup of 11.2%and continuous aeration,the average oil content removal rate is 82.6%,which is 34.8%higher than that of the field two-stage sedimentation process.After continuous stability test,most of the data showed that the oil content of treated water samples did not exceed 100 mg/L,and the average removal rate of oil content reached 83.8%.The loading coalescence flotation column,which combines coalescence technology and air flotation separation,has the advantages of strong adaptability to water quality fluctuation,low operating cost and good treatment effect,and is suitable for the treatment of chemical flooding wastewater.The efficiency equation of loading coalescated flotation column is as follows:R=1-1+0.6107*Tsvtvi+vp-1.the flotation dynamic equation is （?）.The reasons for the improvement of oil-water separation efficiency are as follows:firstly,the polymerization material provides a relatively static floating environment for bubbles,reduces the desorption of large oil droplets,and increases the residence time of oil droplets in the flotation column;Second,the dense axial distribution of the coalescent material can reduce the bubble rise rate,increase the oil droplet size,and improve the bubble-oil droplet adhesion probability. |
