Optimization And Control Of Seperating Acetonitrilr/N-propanol Azeotropic System Using Special Distillation

It is difficult to separate the acetontrile and n-propanol azeotrope through traditional distillation. In this paper, the design and optimization of traditional extractive distillation, dividing-wall extractive distillation and pressure-swing distillation process was completed using Aspen Plus and Aspen Dynamics. As to the optimal process under particular distillation method, precise control structures were proposed respectively. The most suitable control structure was gained through analyzing the effectiveness.The sequential iterative optimization search method was adopted to get optimal parameters of the equipment and process in extractive distillation. According to the long recovery period, enormous fluctuation of purity and low sensitivity that appeared in the basic control structure, an improved control structure with QR/F and R/F proportional control was proposed to solve these problems. The result showed that the delay of sensitivity and purity fluctuation was dealt effectively. According to the temperature fluctuation, synergetic temperature control and pressure compensated temperature control shceme were applied in the advanced control structure. The optimal scheme proved steady control effectiveness obviously.Extractive dividing wall column was proposed based on the ED process. The double recycle sequential iterative method was firstly used in the optimization process. The composition control structure was applied in the EDWC which appeared a steady level of MeCN, while the purity of N-propanol did not recover to a stable level. Later, the VR/QR control with feed forward structure was proposed, the proportion of VR/QR was adjusted by the light component of side flow. The results indicated that product purity of N-propanol was achieved. Finally, the temperature-composition cascade control structure was proposed and appeared quite steady control effectiveness of purity and temperature.The feasibility of pressure swing distillation process was proposed based on the pressure sensitive of azoetrope. The “step-by-step forward” iterative search method was applied to minimize the TAC and got the optimal equipment parameters. The PSD with partial heat integration was proved the optimal scheme and the decrease of TAC wais 13.2% compared with no heat integration. According to the flaw of basic PSD contol structure, the Qx/F control with feed forward structure was proposed and appeared stable purity control effectiveness of MeCN. According to the purity deviation in low pressure column and pressure floating in high pressure column, pressure compensated temperature and temperature composition cascade control structure were used to improve the product purity. The results showed that this control structure coulde be used in globe control.Based on the extractive distillation process, the decrease of TAC was 7.94% in EDWC while 28.9% in PSD. When it came to control responses, pressure floating and long period were emerged in PSD. The fluctuation of product purity and temperature were appeared cause of composition controller made the system less of sensitive. In the controllability of EDC, the recover period was swift and the controllalibity was preferable. So the control structure of EDC could achieve the most effective dynamics responses.