Process Design And Control Of A Reactive Double Dividing-wall Distillation Column

As the direct result of process intensification between reactive distillation column(RDC)and dividing-wall distillation column(DWDC),reactive dividing-wall distillation column(R-DWDC)can render much great potential of savings in capital investment and operating cost,but so far there is little research on process synthesis and design.In particular,the reactive single dividing-wall distillation column(R-SDWDC)is the dominant process configuration in the current study.Although the mass and energy coupling between reaction and separation operations is well coordinated,however,the mass and energy coupling between separation and separation operations is completely ignored,so R-SDWDC is not the optimal structure for process intensification.Based on this,we derived a reactive double dividing-wall distillation column(R-DDWDC),which can significantly improve the thermodynamic efficiency of the reaction separation process,in terms of savings in capital investment and operating cost compared with traditional reactive distillation column and R-SDWDC has obvious superiority.Although the reactive double-wall distillation column has high thermodynamic efficiency,its dynamics and control are rarely studied.Because of the complex structure and intense internal material and energy coupling of the R-DDWDC,its process dynamics and operation feasibility are more complicated.Therefore,the controllability and operation feasibility of the R-DDWDC are examined in this paper,with reference to the separation of an ideal quaternary reversible reaction with the most unfavorable ranking of relative volatilities,the feasibility and effectiveness of the proposed strategy are studied.(1)The open-loop and closed-loop controllability of the R-DDWDC is evaluated,and the influence of the complex process structure and operation mechanism of the R-DDWDC on the process flexibility and controllability is studied by analyzing the control channel and disturbance channel.The results show that R-DDWDC is characterized by severe nonlinearity and asymmetry,poor process controllability,and the strong matter-energy coupling between the internal reaction operation and the separation operation deteriorates the dynamic characteristics and controllability of the system.(2)Steady-state operation analysis of the R-DDWDC shows that the narrow operation range and complex dynamic characteristics of the R-DDWDC are caused by the inherent thermodynamic characteristics of the reactant system and the strong coupling between the reaction section and the dividing-wall section.These problems are difficult to be overcome by the design of the control system.Therefore,we propose to improve the operation feasibility of the R-DDWDC by increasing the vapor split ratio of the left dividing-wall in the process synthesis and design.The results show that the way increase the energy consumption of the system,but it can improve the operation feasibility of the R-DDWDC and obtain better dynamic control performance.(3)The operation rationality of the R-DDWDC is deeply studied from the temperature inferred control strategy.The three control methods of four-point single temperature control system,temperature plus temperature cascade control scheme,and temperature difference plus temperature cascade control scheme are evaluated under the disturbance of feed flow rate and composition.The results show that the latter reinforced temperature control scheme exhibits significant advantages in improving the operability of the R-DDWDC and suppressing the steady-state discrepancies.In the current study,the process dynamic performance and operation feasibility of the R-DDWDC are researched in depth,and it was revealed that the strong matter-energy coupling in the R-DDWDC is the root reason for its process complexity.Different methods are proposed and applied to greatly improve the dynamic performance and operability of the R-DDWDC,which is of universal significance to the study of other complex distillation systems.