Optimization Design And Dynamic Control Of Extractive Distillation Process With Intermediate-Boiling Entrainer

Extractive distillation is one of the effective separation technologies for separating azeotropic mixtures.Heavy entrainer with high boiling point is widely used in extractive distillation,which causes large consumption of high-temperature utilities.Using intermediate entrainer whose boiling point is between the boiling points of binary azeotrope can avoid the use of high-temperature utilities.In this paper,the steady-state design and dynamic control of double column extractive distillation(DCED)sequence,single column side-stream extractive distillation(SC-SSED)and single-column extractive distillation with internally circulated intermediate-boiling entrainer(ICSCED)are studied.The DCED with intermediate-boiling entrainer can be designed into direct distillation sequence(DDS)and indirect distillation sequence(IDS).The steady-state optimization design results show that DDS and IDS have similar energy consumption,but DDS has a greater number of stages,so IDS has lower total annual cost(TAC).In order to further reduce energy consumption,the SC-SSED process with low concentration of intermediate-boiling entrainer is designed.The process only includes one side-stream extractive distillation column,which realizes the efficient separation of binary azeotrope.Based on the analysis of liquid and vapor flowrate profiles in SCSSED process,IC-SCED configuration is proposed,which avoids the side stream withdrawal and external circulation of the entrainer,and realizes extraction through the conversion of the entrainer between vapor and liquid stream in the column.In order to realize the design of this kind of process,a two-column model is proposed in this paper.The optimization results show that IC-SCED process has higher separation efficiency and lower TAC.Compared with DDS,it can save 35.42% equipment investment cost and 44.45% operation cost,and TAC can be reduced by 40.32%.In this paper,the dynamic control of IDS,SC-SSED and IC-SCED process are studied.The effective control structures are proposed and good control effects are obtained.Because of the simplicity of IC-SCED configuration,the effective control can be achieved without the use of complex control structure.