Numerical Simulation And Analysis Of The Separation Process In The Hydrocyclone

Hydrocyclone is an efficient separation device, in which the multiphase separation can be performed by the centrifugal force field. Because of its high separation efficiency and capacity for the multiphase flow system, hydrocyclone has been applied widely in mineral processing, chemical industry and biological engineering, representing a broad application prospect. In spite of the simple geometry of the hydrocyclone, the dynamics and mechanisms of fluid flow are extremely complicated, and the design and operation for the hydrocyclone separation need to be controlled more precisely. To keep the hydrocyclone running at the best performance, the multiphase flow field in the hydrocyclone should be clarified, and the effects of the parameters on the flow field should be understood very well.Based on the simulation of computational fluid dynamics (CFD), this paper presents a study for the gas-liquid and liquid-solid turbulent flow field in hydrocyclones. The RANS and the combined Reynolds Stress Model (RSM), the Volume of Fluid (VOF) model and Dispersed phase model (DPM) are used to describe the gas-liquid and liquid-solid flow field in a classic hydrocyclone with75mm diameter. By comparing the simulation results with the experimental data in the reference, the good qualitative agreements between the simulation results and experimental data can be found, that validates the reliability of the developed mathermetical model. The flow field in a hydrocyclone is measured using particle image velocimetry (PIV), good qualitative agreements between the simulated results and PIV data are presented. The developed model is deemed to be an adequate methodology for the investigation of the flow field in a hydrocyclone for the separation flow system.The formation and development of the flow field in the hydrocyclone are investigated by the simulation using the developed mathematical model, and the pressure distribution within the hydrocyclone is also reprensted. By analyzing the formation mechanism of air core in the hydrocyclone, it is found that the state of the air core is variational:The shape and diameter of air core, mainly on the cylinder section and spigot, are at a steady state, which do not vary with the time; But, at the same time, the high non-steady state is quarried from the part of the conical section, the shape and diameter of air core vary as soon as it forms. This paper also studies the effects of different inlet velocities on the state of air core. The simulated results show that the tangential velocity inside the hydrocyclone increases with the acceleration of inlet velocity, which results in the decrease of pressure at the central area and the increase of air core. But it has no influence on the air core’s state.The dimensions of body construction are also important factors to affect the separartion performance in the hydrocyclone. Based on the simulated results done using the deveopled the multi-phase mathematical model, the analysis of each geometrical dimension is made. This paper focuses on the effects of structural parameters on the flow field inside the hydrocyclone with140mm diameter. The flow features are represented in terms of flow field, pressure drop, split ratio and separation efficiency. The simulated results show that the diameter of vortex finder is the most important factor on the flow field. As a whole, the diameter of air core will increase with the increase of the vortex finder diameter. When the diameter of vortex finder is more than100millimetres, the air core will take up most of the hydrocyclone; the steady state of air core will get better with the increase of the vortex finder diameter. When the diameter of vortex finder is more than65millimetres, the whole air core is at a steady state, which does not vary with the time. The best separation efficiency can be achieved when the diameter of vortex finder is50millimetres. The effects of the diameters of inlet, vortex finder and spigot; the lengths of cylindrical part and vortex finder; cone angle of the hydrocyclone on separation efficiency have also been investigated.By analyzing the effect of atmospheric pressure on separation performance, it is found that the atmospheric pressure has great influence on the flow field and separation performance of hydrocyclone. It is found that the atmospheric pressure has an impact on the shape of air core formed in hydrocyclone, which results in the change of the flow field inside and near the air core, and the variation of velocity field inside the hydrocyclone leads to the difference of separation efficiency. Comparing three kinds of hydrocyclones with different body size, the atmospheric pressure has greater impact on the hydrocyclones with bigger diameter.Based on the research achievements of experiment and simulation, the two-stage hydrocyclone unit is designed and optimized for the separation of calcium sulfate (CaSO4) crystal in100,000tons/year KCl production line setup by QingHai Salt Lake Potash limited company. The online experimental data obtained with the optimized operating conditionds, indicate that the content of calcium sulfate in the product is greatly reduced, and industrial potassium chloride can be produced with a higher quality.