Shortcut Methods for Multicomponent Batch Rectification

Shortcut methods for handling multicomponent batch distillation have been developed for the two cases of constant reflux and constant distillate composition (Diwekar and Mandhaven, 1991 Sundaram and Evans, 1993). Both methods avoid tedious stage-by-stage calculations of vapor and liquid compositions by employing the Fenske-Underwood-Gilliland (FUG) shortcut procedure for continuous distillation, described in Section 6.8, at succesive time steps. In essence, they treat batch distillation as a sequence of continuous, steady-state rectifications. As in the FUG method, no estimations of compositions or temperatures are made for intermediate stages. 

For preliminary studies of batch rectification of multicomponent mixtures, shortcut methods that assume constant molal overflow and negligible vapor and liquid holdup are useful. The method of Diwekar and Madhaven [Ind. Eng. Chem. Res., 30, 713 (1991)] can be used for constant reflux or constant overhead rate. The method of Sundaram and Evans [Ind. Eng. Chem. Res., 32, 511 (1993)] applies only to the case of constant remix, but is easy to apply. Both methods employ the Fenske-Uuderwood-GiUilaud (FUG) shortcut procedure at successive time steps. Thus, batch rectification is treated as a sequence of continuous, steady-state rectifications. 

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