| The quality of Polyacrylonitrile (PAN) precursors is not so good which is restricting the development of carbon fiber in china. The process of PAN spinning solution into nascent fibers is the very important part in fiber formation, and is also the source of various internal and external defect formation. These defects will lower the performance fo the nascent fibers and even the carbon fiber. Therefore, to obtain uniform and compact structure, fewer defects of the nascent fibers have very important significance to the preparation of high quality precursors and carbon fiber. And the process of coagulating bath is an important part in preparation of nascent fibers. So studying the process in the coagulating bath is essential.This paper analysed a radial concentration diffusion model of solvent and non solvent in fiber precursor based on Fick’s law and got the rule of concentration of solvent DMSO and non solvent water on the variation of time and radial coordinates. Then drawing up the change regulation of average concentration of solvent and non solvent on time. Further considering the influence of temperature on diffusion process of solvent and non solvent. The diffusion process quickened with the increase of temperature in a certain range. And it was manifested that diffusion coefficients increased with the increase of temperature.In the coagulation process of actual production, it need ensure the concentration in the coagulation bath constantly in order to obtain the high quality of the nascent fibers. However, concentration in the coagulation bath changes continuously because of the influence of double diffusion and other factors. Therefore it is needed adding water to the coagulation bath to offset the change of concentration. This paper established the water supplement-solvent concentration model based on the diffusion model. This model showed the relationship between water supplement and coagulation bath that changes of coagulation bath concentration would affect the double diffusion process of spinning dope and the double diffusion process would affect the coagulation bath concentration and water supplement in turn. So this was a process of dynamic equilibrium. The model established in this paper could simulate the change of solvent concentration with changing water in the actual production and also could control water supplement according to the relationship between them. Finally the solvent concentration in the coagulation bath would reach the stable set value.This paper established the model of controlled object in coagulation bath by using the diffusion model and the concentration model in coagulation bath, then simulated it in Matlab. Because the concentration in coagulation bath would affect the diffusion speed, thereby affect the amount of water, the process model of controlled object was nonlinear. This paper adopted PID controller to regulate the concentration. When existed external disturbance, the simulated concentration curves can be quickly returned to the given value of concentration in coagulation bath. Therefore, the control mode of water supplement feed-forward and concentration deviation feedback could realize that the concentration of coagulation bath was stable to a desired value. At the same time, this paper also established the temperature and concentration control model considering the influence of temperature on the diffusion process to stabilize the concentration of coagulation bath.This paper established control system of coagulation bath in actual production with PCS7and set up CFC charts and SFC chart in the engineer station which was connected to the automatic station, then configured the operator station, established the main screen of the coagulating bath process, created alarms of key variables and so on to simulate the controlling process in coagulation bath. This paper realized real-time communication between Matlab and PCS7through OPC protocol. The value of real-time simulation data in the model of Matlab can be delivered to the monitor pictures of WinCC to realize the simulation and presented animation of the production process. |
