Research On Advanced Control Strategies Of High-purity Internal Thermally Coupled Distillation Columns

Distillation is one of the most important operation units in chemical and petroleum industries. And distillation columns producing high purity products also become more and more important owing to the growing demands of such products and the requirement of waste reduction, and have been one of the keys for the development of domestic chemical industries.Internal thermally coupled distillation column (ITCDIC) has long been regarded as a promising energy-efficient distillation column that has the potential for drastically reducing energy consumption. However, it has not yet been widely applied to industrial applications. One difficulty that preventing the process from being commercialized is the operational difficulties due to the nonlinearity, complex dynamics and interacting nature of the process, especially for the high purity ITCDIC. That poses control problem with the system. In this work, the advanced process control schemes for high purity ITCDIC are explored, and hopefully, one or several of them will give great performance, and help this new technology be industrialized.The main work and contributions are listed as follows:1. The progress and current status of dynamic and control researches of high purity distillation are summarized. The progress and current research status of internal thermally coupled distillation column (ITCDIC) are summarized.2. A generic model control (ARGMC) system for high purity ITCDIC is presented and performance evaluation shows its effectiveness of overcoming the process nonlinearities.3. A dynamic model control (DMC) system for high purity ITCDIC is derived. The results show that as a typical model predictive controller, DMC can realize the set-point tracing but the dynamic performance is not that good.4. The control design of adaptive generalized predictive control (GPC) system for high purity ITCDIC is given. After introducing the basic algorithms, the detailed performance is demonstrated, and shows that adaptive GPC gives great performance for high purity ITCDIC.5. To overcome system's strong nonlinearity, and also consider the transition control problem, a nonlinear model predictive control (NMPC) system based on first-principle model and using dynamic programming is proposed for high purity ITCDIC. The research shows the proposed NMPC controller gives out great performance both in the servo control and regulatory control, and also can deal with dramatic set-point change like from 0.999 (high purity) to 0.9999 (extremely high purity).