Simulation Study On Optimization Of Rotating Structure For Lignin Recovery By Dynamic Staggered Flow Membrane Filtration Of Black Liquor

Pulp and paper black liquor contains a large amount of recoverable lignin.Among many recovery methods,membrane technology to concentrate pulp and paper black liquor and retain lignin with uniform molecular weight distribution has received attention and favor from experts in the paper industry,but membrane contamination during the separation process has become a bottleneck that restricts the efficient and economic recovery of lignin.In this paper,three different rotational structures are used to change the membrane surface hydrodynamics,and increase the membrane surface shear force to reduce particle deposition and improve the filtration flux,so as to alleviate the membrane contamination problem and fundamentally improve the lignin recovery efficiency.The paper focuses on theoretical,simulation and experimental aspects to compare the shear force generated by three rotating structures on the membrane surface,and to obtain the optimal rotating structure for the pressure field of rotating components,membrane surface shear force,flow field structure and power under different structures,so as to provide data support and theoretical basis for the research and application of dynamic mis-flow membrane lignin separation.(1)Firstly,the theoretical analysis of the thesis establishes the lignin particle force equilibrium model in black liquor and analyzes the influencing factors of filtration flux.The analysis shows that: in the dynamic staggered flow filtration device,the magnitude of shear force is an important factor affecting the filtration flux,the higher the shear force,the higher the filtration flux and vice versa;while the shape and size of the rotating structure,the speed of the components and the pressure difference across the membrane are important factors affecting the magnitude and distribution of the shear force values on the membrane surface,based on which the analysis objective of the shear force field on the membrane surface is established.(2)Secondly,numerical models of three structures,vane type,propeller type and disk type,were designed and established.The process of black liquor recovery of lignin by using CFD software fluid simulation of the three rotating structures,the pressure field of the rotating parts of the three structures,the shear field of the membrane surface,the flow field structure and the device power were analyzed,and the pressure field distribution and numerical law,the shear field distribution and numerical law,the flow field macro structure and the device power characteristics of the three different structures were summarized,and the results of the flow field simulation of the three rotating structures were compared,and it was concluded that The blade structure is the most suitable structure among the three structures.(3)Finally,this thesis focuses on analyzing the distribution law of shear force on the membrane surface of the blade-type structure,and obtaining the lignin particle distribution law by numerical calculation,and observing the coupling of particle distribution and shear force field.Experiments on lignin retention by dynamic blade-staggered flow membrane separation of pulping black liquor were carried out,and the simulation data were compared with the experimental results,thus verifying the validity of the numerical results.The aim of this thesis is to increase the membrane filtration flux during the separation of lignin by optimizing the rotating components to increase the membrane surface shear,ensuring ideal filtration conditions of low cake and high flux,thus obtaining lignin with uniform molecular weight and few contaminants.