Polypropylene Advanced Control And Grade Transition Technology Implementation In Lanzhou Petrochemical Company

The production of polypropylene is an extremely complex chemical process, with many variables, many disturbances, and serious coupling among variables. Production is mainly the occurrence of polymerization, the production process of strong nonlinear. These factors increase the difficulty of controlling the production process. Melt index is an important index in the process of polypropylene production. It needs precise control, which directly determines the quality of the product. But because there is no melt index online analyzer, the melt index is obtained by laboratory tests, from sampling to get the results usually need 2 hours, which brings a lot of uncertainty to the production. Especially when the large disturbance is encountered, the control of the production will not be brought to a lot of fluctuations, the serious impact on the production safety. According to melt index and other indicators can be divided into several grades of polypropylene, in the production process according to the needs of the market, to frequently adjust the production grade. At present, grade transition is by manual adjustment, complete the grade transition over time takes about 10 hours, the operator's labor intensity greatly. So the establishment of bulk polymerization mechanism model, the use of advanced control software, build melt index controller and soft measurement, melt index on-line measuring and closed-loop control, greatly improve the melt index control precision, bring economic benefits for the enterprise production. In the advanced process control system based on, according to the operator before the grade transition step, make the establishment and optimization of grade transition formula, realize automatic grade transition can greatly reduce the grade changeover time, reduce the transition material, bring economic benefits for enterprises, but also reduce the labor intensity of the operator.According to the polymerization reaction of polypropylene, the formula for calculating the concentration of each substance in the polymerization reaction is derived, and the mechanism model of the melt index is established, and the parameters of the model are identified by partial least square method and the validity of the model is tested by the model. To build advanced control system platform, through the Server OPC to establish the upper computer (Advanced Process Control System) and the next bit machine (DCS operating station) communication function, to achieve the advanced control system for the DCS system to read and write functions. DCS on the scene to do the functional configuration, the establishment of the control and soft sensor needs, the establishment of a logical protection function, so that the system has a key toremove the function. According to the operators of grade transition steps and two grade indicators and establish the grade transition formula, achieve grade transition automatically.