| As a new type of gas flotation hydrocyclone equipment,the multiphase vortex mixer utilizes the rotating flow field to promote the collision and adhesion between oil drops and the gas bubbles in the flow field,forming stable oil drop-bubble adhesion particles for use in the air flotation separation.In this paper,CFD numerical simulation technology,with consideration given to PBM model and DPM model,is used to study the flow field distribution features of the mixer under aerated and non-aerated conditions.Analysis has been done systematically regarding the influences of the inlet velocity v,the inflation pressure P and the inflation time T as well as the diameter Dw and the number of the vortex channel in the structural parameters on the flow field distribution features of the mixer.Finally,based on the separation law and features of the single-stage mixer,the industrial multi-stage series mixer is designed,with the flow field distribution features of each stage mixer being analyzed.The main conclusions are as follows:Under aerated conditions,the enhancement of flow field effectively restrains the formation of regional circulation flow,while the enhancement of axial and radial velocity fields promote the migration and diffusion of oil drops and bubbles,which increases the collision and adhesion efficiency of oil drops and bubbles.The bubble diameter is mainly distributed in 170μm-250μm by the cyclone flow field effect of the mixer,with the bubble content being up to 70.95%under the particle size,and the gas carrying rate at the outlet up to 19.77%,indicating that the mixed fluid carries a large number of microbubbles after the mixing and separation.The increase of the inlet velocity promotes the collision contact between the oil particles and the bubbles,meanwhile,the shear fracture of dispersed particles is enhanced by the increase of tangential velocity field.When the inlet velocity is v=15m/s,the content of bubble particles with the particle size distribution between100-250μm is as high as 93%,with the bubble diameter being small and the distribution highly concentrated.With the increase of the inflation pressure,the gas holdup of the flow field increases gradually.When the inflation pressure reaches P≥0.4MPa,the bubble content in the flow field is too high,which leads to the bubble collision and burst,causing the flow field disturbance.When the inflation pressure is0.3MPa,the gas holdup of the flow field is 21.67%,with the bubble particle size being mainly distributed between 170-320μm and the bubble content being 88.86%under the particle size,where the number of oil droplets with the particle size≥300μm is the greatest in the flow field.With the increase of the inflation time,the shear breakup effect of the bubbles in the flow field is strengthened continuously,resulting in the decrease of bubble diameters.When the inflation time is T=4s,with the increase of the gas holdup,the number of bubbles in the flow field increases tremendously,resulting in the collision and aggregation between the bubbles,and the particle size of bubbles with a diameter of Dair>400μm increases,which is not conducive to the air flotation reaction.The results show that the best inlet velocity is v=15m/s,with the optimal inflation pressure being P=0.3MPa,and the best inflation time T=3s.By reducing the diameter and the number of the vortex tubes,the mixing energy in the mixer flow field can be enhanced,which effectively weakens the formation of circulation flow.Meanwhile,the enhancement of both the tangential velocity and the axial velocity strengthens the coalescence and breakup of the dispersed particles in the flow field.Under the effect of the mixer,when the diameter of the vortex tube Dw=6mm,a large number of bubbles with a diameter of Dair<100μm are produced in the flow field,accounting for 65.59%of the total number of bubbles.Meanwhile,the number of oil droplets with a diameter of Doil>400μm is increased by 8%.When the number of vortex channels in each group is 6,the bubbles are mainly distributed between 30μm-170μm,with the number of bubbles under this particle size accounts for 81.3%of the total number of bubbles.Compared with other conditions,the number of bubbles under this particle size becomes at least 50%higher.Therefore,the optimal diameter of vortex tube is 6mm,with the optimal number of vortex tubes in each group being 6.The numerical simulation of the industrial multistage serial mixer shows that the flow field distribution of the first stage mixer is approximately the same as that of the single stage mixer.On the one hand,through the flow field of the second and third stage mixers,the bubbles in the formed adherent particles grow larger,thus forming the adherent structure with a lower density.On the other hand,the change of the flow field leads to the increase of the particle size of oil drop without adhesive structure formation,and therefore is easier to have effective collision and adhesion in the second stage and third stage mixers.The results of the research indicate that the separation efficiency of the effluent can be increased by 18%with three-stage serial mixer. |
