Study On Energy-saving And Dynamic Characteristics Of TDI Phosphoric Reactive Distillation

In this paper,Aspen Plus and Aspen Dynamics simulation software were used to study the simulation optimization and dynamic control of TDI phosgenation reactive distillation process.The conventional reactive distillation?CRD?was further improved by using reactive distillation dividing-wall column?RD-DWC?,and then the steady-state simulation optimization and dynamic control strategy were studied for the different reactive distillation dividing-wall column structures.Based on the selection of reaction kinetics and thermodynamics of this process,Aspen Plus was used to establish a mathematical model that could describe the process.The process was simulated and optimized with the minimum annual cost TAC as the optimal objective,subsequently,the sequential iterative optimization search method was used to optimize TAC and the optimal process parameters were obtained finally.On this basis,the dynamic characteristics of this process were studied,and then the control effects of the two feasible control schemes under different disturbances were investigated respectively.The results show that both two dynamic control schemes were designed reasonably,and could effectively control the disturbances of composition and flow rate±10%.During the simulation and optimization of CRD process,it was found that the requirement of HCl content in the side stream phosgene made the reflux rate of the column not less than a certain value,which limited the further reduction of energy consumption.A new process of reactive distillation dividing-wall column was proposed for this reason.The rectifying section of side stream phosgene was added inside the dividing-wall column,which could greatly reduce the reflux rate,thus saving energy.Considering the energy saving and safety,two dividing-wall column structures were presented,that was reactive distillation dividing-wall column?RD-DWC?and non inter-reboiler reactive dividing-wall distillation?NIR-RD-DWC?.The economic optimization for the two structures,that the optimal equipment parameters and process conditions were obtained.The results show that the TAC of RD-DWC and NIR-RD-DWC process was 1.8863×10⁶/(USD·a^-1)and1.6614×10⁶/(USD·a^-1)respectively.And compared with the CRD process,the TAC and energy consumption of RD-DWC process reduced 10.365%and 11.132%respectively;the TAC and energy consumption of NIR-RD-DWC process reduced 47.704%and50.878%respectively.In the aspect of dynamic control,the control schemes of two dividing-wall column structures were studied,and the respective control schemes was presented.The results show that the stability of product quality and operation could be achieved when the±10%disturbances of feed composition and flow rate.Finally,the steady-state economy and dynamic controllability of different processes were compared.According to the comprehensive comparison result that the NIR-RD-DWC process had great advantages in both economy and controllability.