Influence Of Cyclone Separator Height And Diameter On Performance And Flow Field

Cyclone separator is a common gas-solid multiphase flow separation equipment.It has a simple structure,no moving parts,and can operate normally under harsh environments such as high temperature,high pressure,and high dust loading.It is widely used in energy,chemical,environment and many other fields.Improving the separation efficiency and reducing the pressure drop are always the goals pursued in the research and development of the cyclone separator technology.The excellent performance of the cyclone separator depends on the appropriate structure size.Optimizing the structure size of the separator is one of the ways to improve the performance.In this thesis,the height and diameter of cyclone separator are studied by experiment and numerical simulation.It is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height.However,an exceeded height increase could result in a dramatical drop in separation efficiency.In this study,experimental and computational fluid dynamics（CFD）simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop.Generally,the optimal cyclone height should be closely related to the natural vortex length.While,when the vortex end contracts into the separation space in the cyclone with an exceeded height,severe back-mixing of particles always occurs,which will result in the decrease of separation efficiency.Herein,it is found that when an apex cone is installed at the dust outlet,the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile,the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency.In addition,it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.The cylinder diameter of cyclone separator can affect both separation efficiency and pressure drop.Experimental and computational fluid dynamics simulation results show that there is a maximum efficiency cylinder diameter when Q_in and V_in are constant,and the pressure drop of the separator decreases with the increase of cylinder diameter.Numerical simulation was used to analyze the internal flow field of cyclone separator with the change of cylinder diameter.The results show that the back-mixing escape of particles is based on the balance between the amount of back-mixing at the dust outlet and the secondary separation capacity of cyclone separator.When the diameter of the cylinder is small,the secondary separation capacity is strong,but the tail end of the vortex is located near the dust outlet,resulting in a large number of particles back-mixing,resulting in a decrease in efficiency.With the increase of cylinder diameter,the natural vortex length of cyclone separator increases continuously.Compared with the separator with cyclone cylinder diameter,the particle back-mixing at the dust outlet is less,but the secondary separation capacity is greatly weakened,and the separation efficiency will also decrease.When the diameter of cylinder is small,the short circuit escape of particles is mainly affected by the volume flow of“lip leakage”flow,while when the diameter of cylinder is large,it is mainly affected by the particle concentration at the entrance.