Study On The Optimization Of Flow Field Of Jet Pulp-mixing And The Interaction Mechanism Of Coal Slime And Collecting Agent

Flotation is the most widely applied and effective method in fine coal slime separation.Pulp-mixing is the origin of coal slime flotation and creates good initial conditions for flotation.The optimization of flow field of jet pulp-mixing and study on interaction mechanism of coal slime and collecting agent will provide basic theoretical support for selective regulation of pulp-mixing flow field.Jet pulp-mixing technology is studied systematically.The optimal interaction mechanism of coal slime and collecting agent in the optimized jet flow field is taken as the final research objective.Based on the theoretical calculation of fluid mechanics,the model design of jet pulp-mixing apparatus is completed.The core parameters and internal flow field of the apparatus are optimized comprehensively by numerical simulation.The laboratory physical model is made on the basis of optimized parameters.Laser particle velocimeter(PIV)is used to measure the actual flow field.And the theoretical analysis and calculation results are verified.The ideal jet pulp-mixing system is established.In jet pulp-mixing system,laser particle size analyzer is used to measure particle size dissociation of artificial mixed coal sample.SEM is used to observe the surface morphology of material before and after jet.EDS spectrometer is used to test the changes of elements in the material before and after jet.They are used to study the effect of leafing of jet flow field for mud minerals of the surface of coal particles.High-speed camera is used to capture the morphological evolution and entrainment phenomena of jet stream bundle.The effect of arrangement of ejector tube and the change of jet velocity of working fluid on the size distribution of the agent(bubble)is examined.The mechanism of agent(bubble)pulverization is explained.The effects of critical jet velocity of material suspension,mineral slurry concentration,jet height from the tank bottom,particle size composition and the bottom shapes of the tank on the material suspension capacity of the tank in jet pulp-mixing flow field are examined by sampling method.Absorbance test is used to optimize the feeding velocity of ejection liquid and the optimal circulation time of mineral slurry in the tank.Finally,the validation test of coal slime pulp-mixing is carried out in the physical model with the optimal parameters and the technical prototype of jet pulp-mixing of coal slime is put forward.The numerical simulation results of the structural parameters and flow field for jet apparatus show that area ratio,the nozzle-to-throat distance,the arrangement of suction tube,the length of throat tube and the nozzle exit velocity have significant effects on the ejection capacity and the mixing flow field of jet apparatus.The ejection capability of jet apparatus is higher and the mixing flow field is most favorable for diffusion and mixing of working fluid and ejection fluid when area ratio(a)is 1.96?3.24,the nozzle-to-throat distance(Le)is 0.3Dh?0.6Dh(Dh-diameter of throat tube),suction tube is directly opposite to the nozzle exit area(0-Le)and arranges symmetrically and the length of throat tube is more than 9Dz(Dz-diameter of nozzle).Both the working fluid and the ejection fluid can be mixed in throat tube with length greater than 9Dz under different nozzle exit velocities.Based on the optimized structural parameters and working parameters,a physical model test system is established to verify the numerical simulation results.PIV test system is used to capture flow field information in throat tube and tank.The results show the law of momentum and mass exchange between the working fluid and the ejection fluid in nozzle exit area and throat tube.The results also show that the structural and morphological evolution of jet stream bundle after entering the tank and the stirring range of jet stream bundle to ambient fluid.The design of the tank and the mechanism of jet stirring are clarified.Based on the above research results,laboratory test of jet pulp-mixing apparatus is carried out.The leafing rules of jet flow field for mud minerals of coal particles surface are studied.The results show that the clay minerals covered by the surface of coal slime with particle size below 0.5mm can be effectively removed by jet action.Clay minerals adhered to the surface of coal slime with particle size below 0.25mm have certain stability,so fine mud in folds and depressions is difficult to remove.Under the mechanism of jet stirring,the material suspension characteristics in tank indicate that the critical jet velocity of material suspension is in the range of 6 m/s to 9 m/s.When mineral slurry concentration is 140 g/L,jet height from the bottom of the tank is 150 mm,the content of fine material with particle size below 0.045 mm is 30%and the inclination angle of tank bottom is 10°,the cumulative concentration variance in tank is the smallest,which is most conducive to the suspension of materials.Absorbance test is used to study the optimal flow velocity of ejection fluid and the optimal circulation time of mineral slurry in tank.The results showed that air ejection velocity is 0.86 m/s,liquid ejection velocity is 0.13 m/s and circulation period of mineral slurry is more than 1.0 T,which are the most favorable for uniform mixing and full adsorption of agent and coal slurry.The effects of morphology and entrainment of jet stream bundle on dispersion and mixing of materials are studied.The analysis results of the high-speed dynamic camera show that the jet stream bundle has strong agglomeration in tank,which is not conducive to the full dispersion of material.The entrainment of edge of stream bundle for ambient fluid presents the morphology of vortex turbulence.The inner part of stream bundle has stronger shear crushing effect.More than 90%of bubbles formed by jet entrainment air are microbubble and are very stable within 1h.Bubble crushing rules are that the bubbles with particle size above 0.5 mm are mostly tearing and bursting and the bubbles with particle size below 0.3 mm collapse gradually,from big to small,until disappear.The test results of coal slime pulp-mixing with jet pulp-mixing apparatus show that the flotation improvement indexes of the coal slime with particle size of 0.5?0.25 mm and-0.075 mm increases significantly and recovery of combustible material of total cleaned coal increases after jet pulp-mixing.But the ash content of cleaned coal increases slightly.Based on the study results,two kinds of prototype of jet pulp-mixing technology are put forward.The amplification criterion of jet mixing apparatus is established and the structural parameters and working parameters of apparatus with different treatment quantities are calculated.Figure[134]table[36]Attached Table[55]reference[160].