Design And Application Research Of The Ethylene Compressor Control System

The ethylene compressor is a vital equipment for producing styrene through dehydrogenation of ethylbenzene, increasing the pressure of ethylene in the inlet and providing prerequisites for the following alkylation of benzene and ethylene and de-alkylation reaction. Its working conditions directly influence the operation and production of the whole set of styrene equipment. In order to guarantee the long-term and steady operation of the set and the equipment and eliminate the past set’s disadvantages of decentralized control, low-efficiency, and inconvenience, a safe and reliable control system is very important. The system includes the anti-surge, process adjustment, interlock protection, and controls of other aspects. Based on the ethylene compressor control system of ethylbenzene, this paper studies the condition that a large-scale chemical enterprise in Northeast China which sets up a styrene equipment of 0.32 million tons/year with consideration for demands for techniques and spot status. As for the anti-surge control, theorem is utilized to handle with the compressor and it breaks through the limitation of the traditional plans through characteristic curve method, therefore eliminating the influence of the inlet’s working conditions on the surge.As for the process control,advanced PID control is used and the integral separation and control of dead zone is introduced to make the adjustment more stable.As for the safety interlock, independent protection is added so that the security level increases. The systemmainly uses SIMENS S7-400PLC to constitute the hardware platform together with Pilz Security PLC and completes the internal and external communications through Modbus.As for the software, the system uses Simatic Step7 Program STL and FBD Language, configuring together with PONZ graphical software, making the advantages of various parts, and thus integrating to achieve the designed functions, such as control methods and safety interlock. The system works well in service, meeting the need for the set’s sufficient and reliable operation and ensuring the production safety. Meanwhile, the system has intuitive functions and clear structure, easy to adjust and maintain. It has a positive reference for the company’s future newequipment and production optimization.