Influence Of Mixture And Separation Requirements On Optimal Configuration For Ternary Distillation

Distillation is the most mature and reliable separate operation in chemical process industries.However,distillation is also a high energy consumption and low thermodynamic efficiency process.Therefore,the energy saving of distillation is widely concerned,and a variety of energy-saving technologies continuously emerging,such as heat-integration and thermally coupled distillation system,etc.However,for separating a multicomponent mixture by distillation,there exist enormous possible flow sheet structures that can fulfill a specified separation task.But,the costs of these distillation systems are usually very different.How to find effectively,systematically the one having the lowest energy consumption,or the lowest total annual cost(TAC)among all the alternatives constitutes a veritable problem of Process Systems Engineering.At the same time,it brings up another critical problem,that is how mixture,feeding conditions and separation requirements impact on the selection of optimal distillation structure.The purpose of this paper is to show the impact of the feed composition,physical properties of the components,and the separation requirement(products' purity specifications)on the selection of the most economic distillation schemes for ternary separation.In the present work,rigorous simulation is carried out to investigate and compare the total annual costs(TAC)of a number of promising distillation configurations,including simple columns sequences with or without heat-integration,complex column with side-rectifier or side-stripper,and fully thermally coupled(or dividing-wall column(DWC)).We select six ternary mixtures with different ESI(Ease of Separation Index)for our tests,then for each of the ternary mixtures of different feed compositions,the best distillation scheme is selected.Based on the best selections,the triangle map of a feed composition is divided into different areas,in each of which the optimal distillation scheme is identical.And we also use the ESI and the product purities as variables,and show how separation requirement influence on the selection of the most economic distillation schemes.The analysis and the results show that the ESI,feed composition and separation requirements all have strong influence on the selection of the optimal distillation configuration.Based on the results of the analysis,influential factors for selecting the best distillation scheme for separating ternary mixtures are discussed.