Development, Process Modeling And Optimization Of Ultrafiltration System Enhanced With Complex Physical Fields For Concentration And Separation

This dissertation deals with the scaling-up design and process optimization of an ultrafiltration (UF) system enhanced with complex physical fields. In the investigation, the flow filed in the membrane module, a key component of the UF system, was researched, and the structure of the membrane module was analyzed. Then, by reasonably optimize the whole procedure and each process unit, an automatic UF system enhanced with complex physical fields was developed, which is of multiple UF loops and is effective in separating and purifying functional bioactive compounds. Thus, the key scientific and technological problems in the development of the system were solved, and some key technologies for the industrial and large-scale application of the UF system were obtained. The main research and results are as follows:1. Structure analysis of UF membrane module based on CFD simulationBy introducing the Computational Fluid Dynamics (CFD) method, a newly-developed method of process simulation, in the scaling-up of the membrane module, the flow field in the chamber of both the laboratory-scale and the pilot membrane modules were simulated with FLUENT. The simulation was performed for different materials in not only Laminer but also turbulent flow states, form which the variation rules of the flow field in the chamber were straightly and objectively revealed, and the feasibility of the equal-proportion scaling-up of the module chamber was verified. Then, some measures to enhance the flow and improve the flow uniformity were presented, such as amplifying the inlet/outlet diameter, setting a diversion port and fixing a corrugated plate. All these avoid the degradation of UF performance of the membrane module resulting from the size scaling-up. Moreover, with the combination of the similar amplification and the physical-field enhancement, a pilot membrane module was successfully designed based on a reasonable structure analysis.2. Research on the whole machine of the pilot UF system enhanced with complex physical fieldsBy fully considering the objective requirements of UF in industry, the technical process and operation procedure were determined and optimized, the process units were designed and integrated, and the unit equipment was designed or selected. Afterwards, a pilot UF system was investigated. The system consists of a crude filtration loop, two ultrafiltration loops, a cleaning loop and a heat-exchange loop, and possesses excellent operation flexibility because it can simultaneously perform multi-stage or separately perform a single-stage ultrafiltration/filtration. And, it is simple and optimal in structure due to the adoption of three-way valves for loop switching.3. Automatic control of the pilot UF system enhanced with complex physical fieldsIn order to accurately control the pilot UF system with multiple inputs and outputs, a multi-layer distributed control architecture was constructed. By analyzing the architecture, the hardware subsystem of the control system was designed, which adopted an industrial personal computer (IPC) as the host computer and a SIEMENS S7-200 PLC as the main controller. As for the system software, the initialization, main-cycle control and human-computer interaction modules were all developed in Kunlun MGCS configuration environment, and the incremental digital PI control of flowrate and temperature was analyzed, with the corresponding control software being programmed. The adoption and implementation of incremental digital PI overcome the shortcomings of the traditional simulated PI control in food and light chemistry fields and improve the speed and accuracy of parameter control. Thus, the developed control system successfully implements the automatic and high-accuracy control of UF parameters and process.4. Ultrafiltration of pumpkin polysaccharides enhanced with complex physical fields and corresponding dynamic modelingSome UF experiments were carried out by using the developed pilot UF system for the concentration of pumpkin polysaccharides (PP) with or without physical-field enhancement, by which the effects of UF parameters on the membrane flux were analyzed, and the enhancement of ultrasonic and high-voltage pulse electric fields on the UF was revealed. Based on the experimental results, a dynamic model considering several UF parameters was established by means of Matlab simulation. The model is of high accuracy, with an average relative error of 6.36%, and it provides guidance to the quantitative analysis of the relationship between the UF parameters and the performance indexes.5. Fuzzy evaluation of UF parameters and fuzzy optimization of process schemeIn order to correctly evaluate the UF parameters, the theory of layered fuzzy optimization was introduced to perform a linear regression analysis of the experimental results, and a regression analysis model for the UF parameters was established and the corresponding fuzzy evaluation program was presented. Thus, the UF parameters can be correctly evaluated. Moreover, by introducing a fuzzy correlation degree in the selection of process scheme, a model to optimize the process scheme was set up. All these lay a foundation for the selection and optimization of UF parameters and process scheme in large-scale production.