Flow Field Analysis And Parameters Optimization Of Outward-Flow Pressure Screen

As the improving of paper quality requirements and increasing demand for the medium-to-high grade paper consumption in our country, pressure screen was used as screening equipment by most pulp and paper enterprises in recent years. The pressure screen was closed filter. Compared with other screening equipments, it has prominent advantages. The application of its use has gradually expanded to all kinds of pulp screening and waste paper pulping at present.Pulp screening was completed together both by the pressure difference of inside and outside of the screen cylinder and by the mechanical movement of the rotor and rotor wing. The flow characteristics of pulp and the screening effect was influenced by many factors, among which, the rotor speed, aperture scale, the clearance between rotor wing and screen cylinder was the main influence factors. To achieve an ideal filter effect, it was necessary to study the screening process and the change laws of main influence factors. This paper has mainly conducted the following work.According to the filtering theory of the pressure screen, the filter system of the F40type outward-flow pressure screen was designed. Through comparing with the traditional structure of rotor wing and the distribution of pressure, the rotor wing structure, which met the screen cylinder surface cleaning ability and exerted less resistance, was obtained. Based on the traditional structure of screen cylinder, a dilution water ring was added, which reduced the phenomenon of bottom densifying. And then the better performance and lower power consuming filter system was obtained.According to the basic flow equation, through comparing the turbulence numerical simulation method, the standard k-ε model was used. The reasonable assumption and simplification for the pulp was made. The mathematical model of pulp flowing was established, the boundary conditions was determined, and then the suitable method of dispersing model and calculating flow field was chose, which laid the theoretical foundation for the model’s simulation analysis.Through the simulation analysis of flow field of the rotor and rotor ring, the influence laws that the positive and negative pressure produced by the different ring speed exerted to the screen cylinder was obtained. And the suitable ring speed was obtained. Simulating the process of pulp flowing through the aperture, checking the vortex through the velocity and velocity vector distribution, the influence laws of the profile angle of the bar, the width of the aperture and the clearance between rotor wing and screen cylinder was obtained. The best technological parameter was obtained through analyze and comparing, which provided simple and feasible theoretical basis for the structure optimization of the outward-flow pressure screen and the choosing of operating parameters.