Safety Design Of Distributed Control System For A PVC Production Process

PVC is short for Polyvinyl Chloride, which is widely used in the world as a general-purpose synthetic resin material. The production capacity of PVC is a significant reflection of a country’s industrialization. Now, the automation control of PVC production processes has come true, and the application of DCS (Distributed Control System) is a main means to achieve automation in PVC production. To ensure safe and reliable operation in PVC production, reasonable and safe design of the DCS application system is a crucial research issue. However, little research has been done on safety design of the DCS application projects at present. From the start point of safety design of DCS systems, based on the project with70cubic meters polymerizers and120thousand tons per year of PVC supporting devices, this thesis analyzed and designed the distributed control systems of the project.The main work of the thesis is shown as follows:Firstly, the structure and characteristics of SUPCON ECS-700DCS control system were introduced, and the DCS system selection basics were analyzed from the viewpoint of safety requirements. Based on the platform of ECS-700, the overall design was given, which includes hardware configuration, redundancy implementation, configuration and serial communication.Secondly, taking electrical system safety of the control room into consideration, factors affecting the reliability and safety of DCS systems were listed, and the electrical improvement and design is given responding to the requirements of operational environment, grounding design, power supply, and signal isolation.Finally, the control schemes and control programs were presented based on control safety principle. The security mechanism of the batch control software programming was analyzed, the detailed design of batch control program was shown for PVC batch production process, which includes sequential control of reactants feeding, termination feeding and discharging. A warm-water calculation function module was designed to achieve temperature set points. To precisely control the reaction temperature of the polymerizers, which is crucial for the polymerization process to ensure the quality of the products and the safety of devices, a unified control scheme was proposed, which comprises of single-loop control of the inner fender temperature, and cascade temperature control of the tank temperature, complemented with interlock start of the control systems. Such strategies help to improve the security of control systems, but also a bright spot in the design of the control scheme.