Study Of Structure And Strength Of Screw Conveyor And Flow Field In Bowl Of Decanter Centrifuge

Decanter centrifuge is widely used centrifugal separation equipment with high efficiency, high degree of automation, large capacity, low operating costs and strong adaptability. However, theoretical study and strength design of decanter centrifuge is not so well-developed, which lead to some problems in the engineering application of the decanter centrifuge such as screw blade fracture, low separation efficiency, short service life. Moreover, the internal fluid flow of decanter centrifuge is still not very clear. Therefore, research on structure and strength of screw conveyor and flow field in bowl of decanter centrifuge is of considerable industrial application value and theoretical importance.Firstly in this dissertation, the normal pressure and frictional force acting on the screw conveyor were deduced by performing force analysis for the cake in the bowl. Parameter analysis and orthogonal designs were used to sort out major factors: slope angle of blade, screw blade thickness, screw blade height, cylinder outer radius and cylinder thickness are major factors affecting the strength of screw conveyor under the action of the centrifugal force, and screw blade thickness, screw blade height, pitch angle, cylinder outer radius and slope angle of blade are major factors under the action of the normal pressure and frictional force. It was shown that the strength of the conical conveyor varies with outer radius and is equivalent to that of the cylindrical conveyor of the same outer radius. By regressing the strength formulas for the cylindrical conveyor based on numerical calculations, the universal strength formulas for different types of blade can be obtained which can be used for engineering design.Secondly, to facilitate engineering design of decanter centrifuge, strength design software system of decanter centrifuge was developed by using visual programming language VB to pretreat the finite element software ANSYS. The system provides two selections including traditional calculation method and finite element calculation method, and is a fast and effective method for strength design of bowl and screw conveyor.Thirdly, in order to study internal fluid dynamic characteristics in bowl of decanter centrifuge, circumferential velocity of surface fluid in bowl was measured on a self-designed centrifuge fluid dynamics experiment platform. It was shown that the circumferential velocity lag of surface fluid increases with flow, and the circumferential velocity lag of surface fluid decreases with the angular velocity of bowl when fixing the screw velocity. Numerical simulation of fluid velocity in the bowl was carried out, and the influences of structural parameters and processing parameters on the circumferential velocity lag of fluid surface were investigated. Correlations for the axial velocity were given after sufficient parameter analysis. Moreover, numerical simulation in the presence of the screw conveyor was also performed and the results were compared with experimental measurements. Similarly by carrying out parameter analysis, correlations for the circumferential velocity lag of surface fluid were also obtained.In addition, a screw conveyor with an accelerating vane was proposed. The accelerating vane effectively accelerates the circumferential velocity of feed liquid, reduces disturbance of liquid pool and, thus, increases separation efficiency of the centrifuge.Finally, finite element analysis of bowl feed end head was performed under different working conditions, it was concluded that the design of bowl feed end head should be given full consideration to stress due to the centrifugal force and deformation induced by the reaction of both ends bearings.