Design Of Control And Interlock Systems Of An Ethylene Oxide Unit

Ethylene oxide (EO), also known as ethylene oxide, is an important chemical products, second only to polyethylene in downstream derivatives in ethylene industry. As an important intermediate for organic synthesis, it is used mainly for the production of ethylene glycol, also in the production of ethanolamines, ethers, non-ionic surface active agent. EO/PEO device is characterized by a long and complex process, and its operating conditions change frequently, with wide variety of materials, including oxygen, flammable, explosive, corrosive media, and there are high temperature, low temperature, high-pressure conditions, the reliability of the automatic control system, high security requirements. Therefore, the design of the automatic control and monitonng system for EO production unit plays an important role in improving the level of automation, ensuring safety of the production process, and smoothing operation.In this thesis, the basic flow sheet of EO production unit and the control requirements of the plant are described. The technologically advanced and reliable Distributed Control System (DCS) and Safety Instrumented System (SIS) are adopted for process control and equipment monitoring design, where DCS is mainly applied for process control, including a variety of advanced control strategies, such as three elements control system for boiler level. The SIS system is used for interlock protection of the entire device, its system hardware is designed with redundancy to improve system stability. The SIS system includes oxygen mixing station (OMS) and compressor. Once meets the interlock conditions, it will rapidly interlock stoping devices and equipment to ensure safe and reliable operation. SIS interlock system not only has a protective effect, but also has the retrospective and accident cause analysis capabilities after interlocking action, in order to analyze reasons for stopping, eliminate hazards and reduce the number of stops, improve continuously operating cycle, and enhance economic efficiency.The control and interlock systems have been put into operation, which are proven to be stable and reliable, and have achieved the desired production control requirements and interlock protection results.