Multicomponent distillation tray towers

Open-loop behavior of multicomponent distillation may be studied by solving modifications of the multicomponent equations of Distefano [Am. Inst. Chem. Eng. J., 14, 190 (1968)] as presented in the subsection Batch Distillation. One frequent modification is to include an equation, such as the Francis weir formula, to relate liquid holdup on a tray to liquid flow rate leaving the tray. Applications to azeotropic-distillation towers are particularly interesting because, as discussed by and ihustrated in the Following example from Prokopalds and Seider... 

Multicomponent distillation, 393 absorption factor method, 398 azeotropic, 420-426 bubblepoint (BP) method, 406-409 computer program references. 404 concentration profiles, 394 distribution of non-kevs. 395 Edmister method, 398,399 extractive, 412, 417-422 feed tray location, 397 free variables, number of 395 Lewis-Matheson method 404 MESH eauations. 405-407 molecular, 425-427 nomenclature, 405 number of theoretical trays, 397 packed towers, 433-439 petroleum, 411-415 reflux, minimum, 397 reflux, operating, 397 SC (simultaneous correction) method, 408-411... 

The concepts NTU and HTU are defined only for binary distillations and the transfer of a single substance in absorption or stripping. Since most processes of industrial interest involve multicomponents, the HETS of packed towers is the more useful concept, and may be evaluated readily from test data and tray calculations. 

A rigorous fractionation tower program has been developed with several features that broaden its applicability far beyond the capabilities of existing commercially available distillation tower simulation programs. In addition to the usual features of most modern multicomponent fractionation programs, the individual component material balances and the enthalpy balance written for each tray have been modified so that the resulting computer program is able to simulate ... 

The concept of a super-fractionation tray is important when separating products, if either the top or bottom product consists of a multicomponent mixture. For example, if we are fractionating only a mixture of propane and isobutane, the super-fractionation concept would not be significant. However, if the product consisted of a mixture of ethane, propane, and isobutane (i.e., C2S, C3S, and C4S) and the overhead condenser was a partial condenser (see Fig. 41.1), then the partial condenser would serve as a super-fractionation stage. The partial condenser would contribute far more to fractionation than any of the other stages in the upper portion of the distillation tower. 

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