White Water Recovery Mechanism Simulation And Control System Design For Multi-Disc Filter

A large amount of white water is discharged during the papermaking process.The white water contains materials such as fibers and fillers.Direct discharge it not only causes waste of fiber and water resources,increases production costs,but also pollutes water resources and damages the environment.As a white water recycling equipment,the multi-disc filter has been widely used in recent years due to its compact structure,small floor space,no need to add chemicals,no“secondary pollution”to water,and easy maintenance.However,the domestic multi-disc filter has the disadvantages of low efficiency of white water recovery and low automation,which restricts its popularization and application.With the support of shaanxi science and technology coordination innovation project(2016KTCQ01-35),this paper research on application technology about white water recovery mechanism and control system for multi-disc filter,based on the multi-disc filter distributed control system project of a paper mill in baoding hebei province.Analyzed the influence factors of the white water recovery efficiency of the filter,designed the control system of the white water recovery system,and received good application results.The main work of the thesis can be summarized as follows.I.Analysis of influence factors of multi-disc filter's white water recovery efficiencyEstablished water quality of the filtrate and white water treatment capacity as the evaluation index of recovery efficiency according to the actual process conditions,mechanical structure and working mechanism of the multi-disc filter.The effects of concentration of mixed white water,liquid level of tank,pulp beating degree,installation height,spindle speed and distribution valve angle,mesh on white water recovery efficiency are analyzed by controlled variable method.Finally,establish concentration of mixed white water and liquid level of tank as main influence factors.II.Numerical simulation of influence factors of white water recovery process of multi-disc filterIn order to numerical simulation the effects of influence factors of white water recovery efficiency,using the computational fluid dynamics as the theoretical basis,and using ANSYS Fluent as the software platform.The spherical fiber model was used to characterize the fibers in white water.The porous media model was used to characterize the filter cake on the surface of the filter disc.Finally,set the corresponding initial conditions and carry out the numerical simulation.The simulation results show that the concentration of mixed white water affects the water quality of the white water recovery process,and the tank liquid level affects the white water recovery capacity of the filter per unit time.III.Control system design for multi-disc filterDesigned the control system for multi-disc filter according to the white water recovery process and the influence factors of white water recovery efficiency.In order to solve the problem of the concentration of mixed white water so low that can not be detected,the flow ratio control method was used to adjust the concentration of mixed white water.To improve the liquid level control accuracy of the filter tank,a fuzzy self-tuning particle swarm optimization algorithm was proposed to tunning the PID parameter.At the same time,the control method of the accessory equipment as well as the start-stop sequence and chain logic of all the equipments are designed to improve the automation level of the white water recovery process.IV.Control system implementation for multi-disc filter based on PCS 7development platformThe network architecture design,hardware selection,measurement and control point statistics,control system module configuration,control program writing,human-machine interface rendering and advanced optimization algorithm implementation are completed to implement the control system,under the circumstance of using SIEMENS S7-400 PLC as the control hardware and PCS 7as the development platform.The system has been operated on the multi-disc filter white water recovery system.The control system has been operated on a multi-disc filter in a paper mill in baoding,hebei province.The operation results shows that the liquid level control range is improved from 84%~94%to 86%~90%,and improved the liquid level control accuracy from 6.82%to 2.27%.The white water treatment capacity is increased from 450m~3/h to 540m~3/h,the white water recovery capacity increased20%,saving fiber and water effectively as well as reducing pollution of water resources the economic benefits and environmental protection value are significant.