Research On Steady And Dynamic Behaviors Of A Novel Heat Integration System With Divided Wall Column And Double-effect Distillation

Distillation is considered, by far, the most technically mature and widely used separation method, and will continue to occupy an irreplaceable role in the chemical and petrochemical industry. The main disadvantage of distillation process is its high-energy requirements. After the energy crisis and with the introduction of more strict environmental regulations, to develop more energy efficient structures becomes the prime consideration in the choice of the design alternatives. The divided wall column (DWC) and multi-effect distillation are two typical energy-saving technologies. DWC offers the possibility of both energy and capital cost savings, and the multi-effect distillation is also an improving energy efficiency technology.This dissertation studied a novel heat integration system employing both divided wall column and double-effect distillation (DDE), which was used to separate a multi-component mixture. Comparing with Double Column process (DC), DDE process can reduce energy consumption and waste water emission by 34.3% and by 20.2% separately, which is preferable in both energy consumption and water discharge. The contents of this dissertation include the steady simulations of this novel process and comparisons with other classic processes, the discussions of dynamical behaviors and controllability of DDE process, the weighing of control schemes, the comparing of closed-loop dynamical behaviors of different control schemes, the creative proposal of model predictive control scheme and the dynamical performances and effectiveness of different control schemes were investigated under typical disturbances. Studies of this dissertation can provide qualitative and quantitative guidance for the industrial applications of DDE process. The detailed research work and contributions of this dissertation are as follows:(1) The steady-state simulations of two classical processes and DDE process were completed using rigid non-linear model in the commercial simulation tools Aspen Plus. The energy consumption and core equipment parameters of different processes were compared. The economic efficiencies of three processes were studied using Aspen Process Economic Analyzer. The total project capital cost, utilities cost and payback period of different process were contrasted. (2) The dynamic model of DDE process was built in Aspen Dynamics. In order to get a more reliable and rigorous dynamic model, two rectifications of DWC model were considered according to the actual industrial operation. The detailed study of open-loop dynamic behavior about the feed stream and manipulating variables disturbances was discussed. The open-loop dynamic behavior characteristic of DDE process was summarized.(3) Degrees of freedom and process transfer matrixes of control schemes were analyzed, and four representative control schemes were investigated in comparison. The dynamic responses of temperature and composition control loops were studied in comparison, and the control effectiveness of four schemes against feed disturbance were analyzed.(4) In order to solve the defects of four representative control schemes, a model predictive control (MPC) scheme was proposed. Comparing with the representative control schemes, the MPC scheme gave the best performances of dynamic behavior. The results were verified by case studies.Finally, the conclusion of this dissertation was indicated and the direction for further research was provided.