Simultaneous Optimization Of Complex Distillation Systems With A New Pseudo-Transient Continuation Model

In Chemical industry,in order to separate special mixture or save energy,complex distillation systems,such as extractive distillation and thermally coupled distillation,are common.However,due to difficult convergence and integer optimization problems,simultaneous optimization of complex distillation systems based on equilibrium stage model is difficult.The objective of this work is to develop a framework for the simultaneous optimization of stage numbers,feed locations and operation variables in complex distillation systems based on rigorous distillation model.For the simultaneous optimization of process systems,because of the easy access to automatic and symbolic differentiation,Equation-Oriented method is advantageous.However,when the rigorous equilibrium stage model is adopted,poor convergence performance impeded the wide application of Equation-Oriented method in the simultaneous optimization of complex distillation systems.For the sake of resolving this problem,a simple pseudo-transient continuation(PTC)distillation model was proposed in this work.This model was based on the dynamic simulation of distillation columns but with a suitable and simple pseudo hold-up correlation,which leaded to an easy to solve and well-posed differential algebraic equation(DAE)system.When the DAE system integrates to the steady state,it would have the same results with the equilibrium stage model.A series of simulation cases of distillation systems in different complex levels demonstrated the robustness of the PTC distillation model.Furthermore,in order to avoid the introduction of integer variables,bypass efficiency was incorporated in the developed PTC distillation model.This method avoided the intractable and time-consuming integer optimization problem,and got the physically realizable integer-stage numbers solution at the same time.The model developed in this work could be applied to the simultaneous optimization of various complex distillation systems,i.e.,it was general.Several optimization cases of complex distillation systems validated the effectiveness and generality.Among these cases,for the first time,a highly complex pressure-swing distillation process with heat integration and a ternary partially thermally coupled extractive distillation process were optimized.