Numerical Simulation Study Of New Hydrocyclone

Hydrocyclone is widely used in mineral processing industry due to its simple structure,small footprint,large capacity and good separation efficiency.In the field of coal beneficiation,hydrocyclone is mainly used for low-cost sorting,coarse coal slurry classification and slurry concentration.In industrial practice,it was found that a coal processing plant applied the traditional hydrocyclone to pre-demuding the coarse coal slurry sorting feed,and found that the bottom flow was more serious,which seriously affected the ash content of the coarse coal,resulting in the system "back ash".In this thesis,a series of numerical simulations were carried out to explore the influence of cyclone structure parameters and operation parameters on the effect of bottom-flow entrainment by taking the actual demand of the site and the hydrocyclone with secondary flushing structure developed by the subject group in the early stage as the background,and the research conclusions were verified through industrial tests.In this thesis,we first use Reynolds Stress Model(RSM)to calculate fluid turbulence,and capture the gas-liquid two-phase interface boundary with multiphase flow model VOF(Volume of Fluid)and mixture model Mixture,on top of which we use Mixture mixture model to calculate the discrete phase.Numerical simulations of the gas-liquid flow field were carried out for the classic 75 mm hydrocyclone,and the results were compared with the Hsieh test results to initially verify the reliability of the model.On the basis of model validation,a simulation study was conducted on φ750mm hydrocyclone to investigate the effects of cyclone structure parameters and operation parameters on the internal pressure,velocity,air column diameter,classification efficiency and bottom flow entrainment of hydrocyclone.The effect of adding secondary flushing water to the hydrocyclone on improving the classification size of the hydrocyclone was demonstrated by comparing the results of the initial numerical tests: the addition of secondary flushing water structure made the internal pressure of the cyclone increase,the velocity increase,the diameter of the air column increase,the classification size increase from 0.126 mm to 0.170 mm,and the bottom flow entrainment fines rate decrease from 21.95% to 18.25%.For the newly developed large hydrocyclone,the influence of its structure parameters and operation parameters on the internal flow field of the cyclone was investigated,focusing on the number of secondary flushing water inlet,overflow port diameter,bottom flow port diameter(including the combination of overflow port diameter and bottom flow port diameter),the influence of secondary flushing water flow and inlet flow ratio on internal pressure,velocity,air column diameter,classification particle size and bottom flow pinch thinness.The results of the study showed that the number of secondary flushing water outlets did not have a significant effect on the flow field.Different from the traditional cyclone classification theory,the change of overflow diameter has less effect on the bottom flow distribution rate,but the overflow diameter is too large to increase the diversion ratio and the proportion of secondary liquid flow.As the diameter of bottom flow port decreases,the diameter of air column decreases.When the bottom flow port is 100 mm and the overflow port is295 mm,the classification particle size reaches the highest 0.238 mm and the corresponding bottom flow pinch fine is also the lowest 14.5%.In terms of the influence of operating parameters,when the ratio of secondary rinse water flow rate to feed flow rate is 1:8.6,the classifying particle size is the highest and the bottom flow is the lowest.The industrial test results of φ750mm secondary flushing water type hydrocyclone show that: under the smooth operation of the system,the secondary flushing water type hydrocyclone has less bottom flow entrapment rate compared with the original hydrocyclone,and there is no overflow running coarse phenomenon.Taking the bottom flow-0.2mm particle content required by the coal washing plant as the standard,when the fines content in the feed is 49.3%,the original hydrocyclone bottom flow entrainment fines is 39.4%,and the minimum of 21.7% for the secondary flushing water type hydrocyclone.The flow ratio of the new cyclone with the lowest bottom flow entrainment rate is close to the numerical simulation results,which further verifies the reliability of the mathematical simulation.