Wave Based Nonlinear Dynamic Modeling And Nonlinear Control Strategy Design For Energy-saving Distillation Processes

Energy saving technology has become a key point in the energy saving research area. Internal thermally coupled distillation has very high energy saving potential. Compared with conventional distillation columns it could save more than 30% energy. However, the complex nonlinear dynamic performance of internal thermally coupled distillation processes brings a great challenge to the control design. Traditional control strategies, like PID, internal model control and so on, could hardly control internal thermally coupled distillation processes, the control performance need more improvement. The strong asymmetric character, inverse response dynamic and ill condition performance make the efficiency of those ITCDiC control strategies reported in literature decreased seriously under high-purity control conditions, which is mainly because of the model mismatch of those models. As a result, many advanced control strategies could hardly improve the control performance. In the present work, Wave theory is exploited to low-order nonlinear modeling and nonlinear controller design of ITCDIC and ITCASC.The main work and contributions are summarized as follows:1. Pioneered in the Wave traveling disturbance pulse traveling analysis of ITCDIC, the development of natural wave velocity, shock wave velocity with varied molar flow rate and profile description function are carried out; a complete nonlinear wave dynamical model is then established; based on wave traveling analysis, the nonlinear dynamic performance like asymmetric and inverse response character are futher explored;2. Based on wave model of ITCDIC, three generic model control strategies, two improved general generic model control strategies are proposed, which well improve the model mismatch problem and robust performance, realize the multivariable decoupling function automatically. Specially, the proposed XGGMC control strategy realize the super high-purity control of ITCDIC with 99.999% product purity;3. The wave traveling phenomena and disturbance pulse traveling in ITCASC are explored, the natural wave velocity, shock wave velocity of ITCASC with varied molar flow rate are then developed, combined with which, the distinct nonlinear dynamic behavior like asymmetric and inverse response performance are explored for the first time;4. Based on the open-loop response analysis, PI control strategies, generic control strategy (GMC) and nonlinear model predictive control strategy (NMPC) of ITCASC are futher established. Detailed comparison research results show that NMPC present the best control performance, the control quality of generic model control deteriorate seriously in the regulatory control because of the model mismatch of the polynomial model. The two PI control strategies show that employing side extraction flow rate as a control variable could decrease the coupling relationship between the control loops efficiently, however the control quality of the Nitrogen concentration deteriorates seriously compared with the PI controller employing the pressure of rectifying section as a control variable.