关键词: 精馏过程, 控制图, 统计过程控制, 工程过程控制

Abstract: Distillation is the most widely used separation technology in the chemical industry, and its high energy consumption has been a major concern. Traditional distillation process control usually focuses on controlled variables, such as tower top and bottom temperature. Engineering process control (EPC) on the operating variables can maintain the control output in a given range. In real-time production, regulation of EPC might cause shifts in the mean value of the manipulation variables, and energy waste might occur when both the cold and hot utilities increase spontaneously. Under carbon peaking and carbon neutrality, it is important to seek an accurate monitoring/control strategy to realize the energy-saving operation of the distillation processes. This work proposes to combine statistical process control (SPC) and EPC, i.e., SPC charts are introduced to determine the disturbance scenario as well as EPC is adopted to control the process. According to the analysis of SPC charts, the interference source could be identified, which might assist in the control decision on EPC. To demonstrate the monitoring effect, a benzene separation column is taken as a case study where decoupling control is implemented for temperature disturbance rejection. Then, step and slope disturbances are introduced into the system to locate or predict shifts of the manipulated/control variables, afterwards, root cause analysis is implemented. The simulation results show that while EPC could maintain tower temperature within a specific range for a relatively long period, SPC might suggest abnormal working status, which would cause unnecessary consumption of energy. The results show that combining EPC and SPC could effectively enhance the understanding of the process run-away conditions, and assist reduce the unnecessary energy consumption of the distillation process.

Key words: Distillation process, Control charts, Statistical process control, Engineering process control