The Optimization And Dynamic Control Of Extractive Distillation Process With Two Columns To Separate Toluene-methanol-water

Toluene,methanol and water mixture forms two different azeotropes at atmospheric: the homogeneous azeotrope of toluene-methanol with minimum boiling point and the heterogeneous azeotrope of toluene-water with minimum boiling point,however,the conventional separation method cannot separate this ternary azeotropic mixture efficiently.This paper developed an extractive distillation process that with two columns and decanter to separate this ternary azeotrope by studing the characteristic in the three components,meanwhile,the economy and dynamic control strategy were analyzed in this paper.With the help of flowsheet simulation software Aspen Plus,this paper inspected the Vapor-Liquid equilibrium data and Liquid-Liquid equilibrium data,and the model of UNIQUAC was selected as the thermodynamic model finaly.This paper put forward a new way of entrainer selecting and derived the computational formula by exploying the relationship between the relative volatility of the light-heavy component and the relative volatility of heavy component-entrainer with total annual cost(TAC).Based on the sequential iterative optimization procedure of traditional extractive distillation and the tool of Extractive Distillation Optimization Software(EDOS),this paper optimized all the flowsheets and obtained the optimal parameters with the minimal TAC.Finaly,the energy cost of the extractive distillation process with two columns and decanter is 3.07 MW and the TAC is 1070346$/y.Compored with the traditional extractive distillation process with three columns,the extractive distillation process with two columns and decanter exhabits obviously advantages in energy savings and TAC reduction.Based on the process,this paper explored a further energy efficient scheme to separate the ternary azeotropic system:(1)The extractive distillation process with a side stream;(2)The extractive distillation process with thermal coupling;(3)The extractive distillation process with heat integration;After the rigorous flowsheet simulation and optimization,the results show that the processes with heat integration perform better than the processes with a side-stream or thermal coupling on energy savings and TAC reduction.In the process of the extractive distillation with heat integration,the process with two columns feed streams preheating can can save energy consumption by up to 27.69 % and reduce the TAC by 21.36 %.With the help of the flowsheet simulation software Aspen Plus Dynamic,this paper explored the dynamic control strategy of the extractive distillation process with two columns and decanter under the optimal parameters.Control structure of two columns extractive distillation process using decanter with fixed reflux ratio(CS1),process with fixed R/F ratio(CS2),and process with fixed Q/F ratio(CS3)are all can not resist the composition disturbance of the feed stream.In the proposed control structure(CS4),the temperature controller of extractive distillation column was replaced by a proportional controller.The control structure(CS5)can efficiently control the process when the flowrates of the entrainer increased from 80kmol/h to 85kmol/h.Therefor,it can dramaticly enhance the dynamic control effect by increasing the solvent content slightly.