Efficiency multicomponent distillation

Uses of Oldershaw columns to less conventional systems and applications were described by Fair, Reeves, and Seibert [Topical Conference on Distillation, AIChE Spring Meeting, New Orleans, p. 27 (March 10-14, 2002)]. The applications described include scale-up in the absence of good VLE, steam stripping efficiencies, individual component efficiencies in multicomponent distillation, determining component behavior in azeotropic separation, and foam testing. 

The fact that component efficiencies in multicomponent systems are unbounded means that the arithmetic average of the component Murphree efficiencies is useless as a measure of the performance of a multicomponent distillation process. Taylor, Baur, and Krishna [AIChE J., 50, 3134 (2004)] proposed the following efficiency for multicomponent systems ... 

These interaction phenomena have been discussed above in the context of ternary gas diffusion but are typical of the general multicomponent case. The practical implications of these interaction phenomena include such interesting possibilities as negative Murphree point efficiencies in multicomponent distillation as we shall see later (Chapter 13). 

It is interesting to note that the thermodynamic factors cancel out of Eqs. 8.8.19 and 8.8.20. The elimination of the thermodynamic factors will prove particularly useful in the estimation of transfer efficiencies in multicomponent distillation (Section 12.3). 

Two different approaches have evolved for the simulation and design of multicomponent distillation columns. The conventional approach is through the use of an equilibrium stage model together with methods for estimating the tray efficiency. This approach is discussed in Chapter 13. An alternative approach based on direct use of matrix models of multicomponent mass transfer is developed in Chapter 14. This nonequilibrium stage model is also applicable, with only minor modification, to gas absorption and liquid-liquid extraction and to operations in trayed or packed columns. 

Aittamaa, J., Estimating Multicomponent Plate Efficiencies in Distillation, Kem.-Kemi, 8, 295-300,... 

Chan, H., Tray Efficiencies for Multicomponent Distillation Columns, Ph.D. Thesis in Chemical Engineering, The University of Texas at Austin, TX, 1983. 

Chapter 12 presents models of mass transfer on distillation trays. This material is used to develop procedures for the estimation of point and tray efficiencies in multicomponent distillation in Chapter 13. Chapter 14 uses the material of Chapter 12 in quite a different way in an alternative approach to the simulation and design of distillation and absorption columns that has been termed the nonequilibrium stage model. This model is applicable to liquid-liquid extraction with very little modification. Chapter 15 considers the design of mixed vapor condensers. 

Understand the difference between the equilibrium-efficiency approach and the rate-based approach to multicomponent distillation problems. 

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