Working Process Analysis And Optimal Design Of Filter Press

Filter press,as an indispensable solid-liquid separation equipment,has a long history of application and had already been used in chemical industry production in the early 18th century.With the advantages of stable performance,simple structure,safe and convenient operation and high efficiency etc,nowadays it has been applied extensively in various industries including environment protection industry,medicine industry,food industry,mining industry and chemical industry.With the rapid development of industrial technology and the continuously raising requirements on environmental protection,new opportunities have been opened up for the development of filter press and new requirements have also been put up on the service performance including filtering performance and anti-fatigue performance of the filter press.Although in recent years,the functions of filter presses have become increasingly diversified and its work efficiency has also been improved,the flow condition of the slurry in the filter chamber,the process of particle phase depositing into cake,spatial distribution and time evolution characteristics of pressure are all difficult to directly monitor as the filter chamber composed of the pressed filter boards is totally-enclosed structure.Besides,the service state of the filter plate and the mechanism of the geometric structure of the filter plate influencing the slurry flow and particle phase deposition into cake remain unclear.Overall,due to the complex deformation of the filter press during service process under the direct effect of pressing force,gravity and squeezing force and the difficult direct test on the complex press distribution in the filter chamber,it’s full of challenges to analyze the service state of the filter press and conduct optimal design.Aiming at the above-mentioned key core common technical problems,according to the training objective "training innovative leading talents in engineering technology field for large-scale or key enterprises" in the Ph.D.students of advanced manufacturing majors directed training plan of Shandong University and combining the actual production status of the enterprise in which the author worked during the Ph.D.period,this paper conducted systematic research and optimal design on the service process of the filter process by taking the 1250-type chamber filter press in large production and sales volume as the research object and integrating the application of Computational Fluid Dynamics(CFD),Finite Element Analysis(FEA)of structural mechanics,fatigue analysis and topology optimization.Firstly,the CFD method was used to numerically analyze the law of slurry flow and particle phase deposition in the continuous filter chamber.Secondly,the FEA method was used to numerically simulate the service state of the filter plate and the rack during the filter pressing process and the FBG sensing technology was applied to conduct real time on-line monitoring on the evolution characteristics of the stress-strain during service of the rack,then the fatigue analysis method was used to conduct research on the fatigue state of the filter press rack.Finally,according to the topology optimization theory,the topology optimization design of the key rack components including the keep plate and the oil cylinder base was conducted.For the research on the slurry flow and the deposition of particle phase into cake in the filtration process,this paper adopted fluid dynamics software Ansys Fluent and User Defined Function(UDF)to build the CFD model for slurry flow and particle deposition analysis based on Euler Multiphase Flow Theory.Firstly,the filter pressing dehydration process of iron ore powder in the chamber filter press was taken as the research object.Based on the analysis of the actual working process of the filter press,the Eulerian multi-phase flow theory and its interphase momentum exchange coefficient model and shear stress model of solid phase involved in the CFD analysis of the filter pressing process were systematically studied and the mathematical model suitable for research object of this paper was determined;With the key geometric structures including the feed inlet,the water outlet,the support point of the filter cloth and the support platform being comprehensively considered,the analysis on the influence of the head-flow characteristics of the special slurry pump for the filter press on the feed boundary was conducted,and the geometric model with complete structural elements and multiple continuous filter chambers and conforming to the actual production was established;Based on the head-flow characteristic curve of the slurry pump,the feed inlet boundary conditions that could reflect the characteristics of the slurry pump was defined with the UDF method to make the flow of the filter pressing feed be changed according to the characteristic curve of the slurry pump and the flow resistance of the system,which not only ensured that the CFD analysis results conform to the actual situation,but also prevented excessive pressure or flow rate from appearing during the CFD analysis;Then,according to the flow characteristics of the slurry in the filter chamber and the geometric characteristics of the filter plate,the geometric model of the filter plate was reasonably cut and simplified,which greatly improved the quality of the mesh,thus enhancing significantly the efficiency of CFD analysis on the basis of ensuring the calculation accuracy and making the CFD analysis of the filter pressing process in the multiple filter chambers feasible.Finally,the CFD analysis model of the filter pressing process with reliable theoretical model,accurate geometric model,reasonable boundary conditions and analytical feasibility was established.On the basis of the established CFD analysis model,the numerical modelling of the flow laws of slurry in the filter chambers,the laws of particle phase deposition and cake formation,the laws of pressure distribution in the filter chambers were conducted,and the influences of the particle density and the characteristics of the feed pump on the filter pressing process were studied.The result showed that the deposition of particles was affected by both the drag force between the liquid particle phases and the true density of the particles;When the true density of the partrticles was large or the drag force between the two phases was small,the flow of the particles was mainly affected by their own inertia,and the flow of liquid phase had a small effect on the movement of the particles;When the true density of the particles was small or the drag force between the two phases was large,the movement of the particles was mainly affected by the flow of the liquid phase.The feed pump with higher rated flow shortened the filter pressing cycle to a certain extent,and at the same time led to a substantial increase in the energy consumption during the filter pressing process.The filter pressing technological parameters should be designed comprehensively according to the material characteristics such as particle density,and attention should be paid to both the required filter pressing cycle and economic cost when selecting the feed pump.For the research on the working status of the filter plate,the analysis model of filter plate working status was established with the Abaqus/CAE 2019 finite element software.With the 1250 type chamber filter plate being taken as the research object and the data of pressure distribution changing with time obtained from the CFD analysis of the filter press process being imported as the pressure load in the point cloud form,the working state analysis model of four filter plates during the filter pressing of the slurry at normal temperature was established,;On the basis of the above model,corresponding thermal convection boundaries were respectively applied to the interfaces between the filter plates and the slurry and that between the filter plates and air,and the working state analysis model of the filter plate during the high-temperature slurry filtering process was established with the thermal-mechanical coupling analysis method in Abaqus.Then,the working states of the filter plates under the action of the slurry at normal and high temperatures were simulated,respectively.The result showed that under the operating conditions at normal temperature the stress distribution and deformation of the filter plates during the filter pressing process were mainly affected by the pressures of the slurry and filter cake in the filter chambers and the strength of the existing filter plates could well meet the requirements of filter pressing;Under the operating conditions at high temperature,the limited thermal expansion was generated on the filter plate due to uneven temperature distribution,thus causing the great thermal stress which replaced the pressure in the filter chambers and became the main factor affecting the stress distribution and deformation of the filter plate.Therefore,for designing a filter plate used for slurry filtering at high temperature,enhancing the heat transfer performance of the filter plate should be considered emphatically to reduce the unevenness of the temperature distribution.For the research on the working state of the rack,the rack of a certain type of chamber filter press equipped with the 1250 type filter plates was taken as the research object,and the working state analysis model of rack was established with the Abaqus/CAE 2019 finite element software,including the assembly analysis model of the girder,thrust plate and oil cylinder base and the independent analysis model of the keep plate.The numerical analysis on the stress distribution and deformation of each rack component under normal working state and occasional overshoot loads was conducted.The result showed that,in addition to the tension stress concentration exceeding the material yield strength in the eave tile connection area of the girder and the middle edge of the upper and lower frame of the thrust plate,and the compression stress concentration exceeding the material yield strength in the contact area between the oil cylinder base and the eave tile,the overall stress level of the five main components of the filter press remained relatively low.Then,the real-time online monitoring experiment on the rack working process was conducted with the self-made substrate FBG strain sensor of composite material.The result showed that:the substrate FBG strain sensor of composite material attached to the surface of the rack could accurately monitor the evolution of the strain of rack along with the loading force,and there was a good linear correlation between them,with a linear correlation coefficient above 0.99.The comparison between the experimental test data and the finite element simulation data showed that the experimental results were in good agreement with the simulated results under the same loading pressure at the same test points,and thus the established finite element model and simulation calculation results were reliable.Finally,based on the finite element simulation results of the rack in normal service state,the fatigue analysis of the rack in normal working state was carried out with FE-Safe 2019 fatigue analysis software.The result showed that the currently designed rack had high fatigue strength and could fully meet the normal working cycle of 10 million times.Both the results of finite element analysis and fatigue analysis showed that there was a large space for the optimization design of the current filter press structure.For the research on the topology optimization design of rack,with Tosca 2019 topology optimization software,the topology optimization model of the key components of the rack including the oil cylinder base and the keep plate was established and the topology optimization design was carried out.With Abaqus/CAE 2019 and FE-Safe 2019,the numerical analysis on the working state and fatigue performance of the optimally designed oil cylinder base and keep plate was conducted once again.After being optimally designed,the material of the keep plate and the oil cylinder base could be fully utilized,with weighing less by 39%and 28%respectively and each filter press saving 467 kg of steel;the optimized oil cylinder base and keep plate could still fully meet the normal working cycles of ten million times and occasional overshoot loads.In conclusion,this paper had conducted a comprehensive and systematic analysis on the working process of the filter press,and revealed the laws of slurry flow and particle phase deposition as well as the working characteristics of the filter plates and the rack during the filter pressing process,then carried out on-line monitoring,fatigue analysis and topology optimization design of the rack,having changed the status quo that the enterprise where the author worked had overly been relying on experience but lacking theoretical guidance for many years,and provided the theoretical basis for the collaborative optimization of filter pressing technology,filter plates and rack structures.