| Energy-saving and ejection-decreasing, and a low carbon economy have become the mostimportant development trend in the modern paper industry. Waste paper recovery and utilizationcan save resources, and reduce environmental pollution. Using more and more waste paper inthe pulp and papermaking makes the impurity increase, and it seriously affects the screeningability and screening efficiency as well as increasing the screening energy consumption. Inorder to meet the development requirements of the high yield, high quality and low energyconsumption, the research in this paper focuses on screening mechanism and improvement ofthe key components of the pressure screen, and the achievements will promote the paperindustry in our country marching toward a low carbon economy.Based on the research of the key components of screener, the type and nature of the wastepaper pulp and the analysis of the pulp flow theory, pulp suspension motion characteristics wasresearched with the two-phase flow theory. Then, the screening process was simulated based onthe FLUENT software, the pulp motion state in the pressure screen was discussed, and it wasanalyzed that the key components of the pressure screen structure influences the simulationresults. What's more, different improvement schemes of the pressure screen corrugated surfacewas numerically simulated by using FLUENT software, and the influence of the corrugatedsurface on screening important mechanism were discussed pulp. Finally, the design idea ofpressure screen corrugated surface shape was established.The results were as follows:(1) Through the literature summary and the investigation in manufacturers, the inferencewas made that the researches of the pressure screen mainly focus on the improvement of therotor shape, the improvement of the screen holes and slots, the improvement of the screen platesurface shape, etc.(2) Pulp suspension is a multiphase mixture of water and pulp fibers, and belongs tonon-Newtonian fluid. Pulp flow can be assumed as a incompressible viscous flow, the phases offluid and particle can be both deemed as a continuum, and the mutual reaction of the fibers canbe ignored.(3) There are two primary methods of fiber separation in pressure screening: barrier andprobability screening. The best performance needs a high contaminant removal efficiency at alow reject rate. It was found that the passage ratio is determined by two factors:"wall effect" and "turning effect". In the engineering the realizable k-ε model is more used as simulating. Thesimulation is more accurate by using the realizable k-ε model for the turbulent flows with largevortexes.(4) Using FLUENT software to simulate screening process, the distribution of flow fieldinside the pressure screener was gotten. Pressure, velocity and turbulence intensity of the flowfield are related to and influenced by each other. From the numerical simulation,the pressuredistribution and pathlines of the pulp flow in the screening zone were obtained. By calculatingthe import and export flow, the production efficiency of accept pulp is80.58%.(5) Different improvement mechanisms and projects of the pressure screener's corrugatedslot shape were researched based on FLUENT software. The following conclusions wereobtained from the simulation that the vortex near the entrance of the slot is not good for theentrance of pulp fiber into the slot; the larger the screen slot chamfering angle was, thesmoother the fluid flow near the screen slot was; and under the optimal improvement of thecontoured slot, the passage ratio is the largest and can be increased by12.4%compared to thatof non-improvement before. Through analyzing and comparing the contour distribution of thescreen corrugated slot, it is clear that the static pressure is the minimum before the slot and itreaches the maximum after the slot. |
PDF Full Text Request