Structure Optimization Of Multistage Cyclone Flotation Device For Oily Water Treatment

With the deepening of oilfield development,the water content of produced liquid is increasing and the emulsification is serious.The existing water treatment technology has the problems of low treatment efficiency and high cost.Cyclone flotation technology has good separation performance for oily sewage with small oil-water density difference,but it has problems such as incompact structure,low inlet oil content,and large dependence on chemicals,which limit its further application.In this paper,through theoretical analysis,numerical simulation and experimental research,a new multi-stage cyclone flotation structure is proposed,and its structure optimization and separation characteristics are studied.The main research contents and conclusions are as follows.Based on the principle of cyclone flotation,a new type of multi-stage cyclone flotation device is designed.Based on flow field distribution and flotation efficiency,the structural parameters such as height-diameter ratio,guide vane position,guide vane spiral angle,guide vane width,distribution pipe number and distribution pipe diameter are optimized.Studies show that increasing the height to diameter ratio is beneficial to the bubble rise,but increases the volume of the equipment;The position of the guide vane is raised,the bubble residence time in the swirling zone is shortened,which is not conducive to the bubble rising;With the increase of guide blade width,the distribution area of swirl flow field first increases and then decreases,and the bubble distribution gradually concentrates;Increasing the spiral angle of guide vane and the number of distribution pipes can slow down the axial and circumferential attenuation rate of swirl field and enhance the uniformity of flow field distribution,which is beneficial to improve the separation performance.Based on the simulated and optimized cyclone flotation structure,an experimental prototype is designed and manufactured,and the influence of the structural parameters of the prototype on the separation performance is studied.The results show that the separation efficiency of this stage is about 50%of that of the previous stage for each additional stage.The position H₁/H=0.5 is the equilibrium position between the cyclone flotation area and the static buffer zone,and the separation efficiency is the highest at this time.The suitable cyclone intensity at the outlet of the water distribution pipe is within 13.70～20.75 and has a certain universality.The operating parameters are studied,and the results show that with the increase of treatment capacity,the separation efficiency first increases and then decreases.When the treatment capacity is 1.3 m³·h^-1,the corresponding residence time of each stage is 70 s,and the separation efficiency is the highest.With the increase of diversion ratio,the separation efficiency gradually increases but the increase decreases.Considering the difficulty of reprocessing the oil spill phase,the optimal diversion ratio is determined to be 0.08;With the increase of oil concentration in sewage,the required air intake increases,but it is difficult to reach the optimal value when the oil concentration at the inlet exceeds 1000 mg·L^-1 due to the restriction of dissolved air in water.The smaller the bubble size and the larger the oil droplet size,the higher the separation efficiency of the device.Considering the smaller the bubble size and the higher the manufacturing cost,it is recommended that the bubble size d₅₀ should be controlled below 35.7μm in actual production.With the increase of polyaluminium chloride concentration,the separation efficiency gradually increased but decreased.When the inlet oil concentration is 500 mg·L^-1 and polyaluminium chloride concentration is 25 mg·L^-1,the separation efficiency reachs 95.55%,which indicats that the synergistic effect of bubbles and reagents could significantly enhance the separation effect of cyclone flotation.Combined with the simulation and experimental results,the operating parameters of the swirl air floatation were given,and the intake volume and bubble size could be reasonably selected according to the oil concentration of the inlet liquid and the particle size distribution of the oil droplets.The design criterion of multistage rotary air flotation device is determined.