Distillation column design system factors

The knowledge of the occurrence of azeotropic points in binary and higher systems is of special importance for the design of distillation processes. The number of theoretical stages of a distillation column required for the separation depends on the separation factor i.e. the ratio of the 7< -factors (7required separation factor can be calculated with the following simplified relation (Reference 1) ... 

The quality of the design of a distillation column by solving the MESH equations mainly depends on the accuracy of the K-factors (separation factors) [1]. Using one of the -models given in Table 5.6 these values can be calculated for the system to be separated, if the binary parameters are available. However, for the proper design binary parameters have to be used which describe the fC-factors resp. separation factors ctij of the system to be separated over the entire composition and temperature range considered reliably. 

Among the various types of systems, the flowsheet could have either one or two columns. The TACs varied by a factor of 7.5, the energy costs changed by a factor of 8, and the number of trays in the reactive distillation column ranged from 11 to 96. Physical explanations for the effects of combined reaction/sepaiation were given. Heuristics were provided to evaluate potential difficulties in reactive distillation design. 

Depending on the tray geometry (diameter, weir height, downcomer design, etc.) in trayed columns or on the type of packing in packed columns, a certain amount of liquid is retained within the column as liquid holdup. An additional amount of liquid holdup is associated with the condenser assembly. The remaining space within the distillation system contains the vapor holdup. In continuous columns, holdup is usually not a factor since it does not affect the separation as long as the column operates at steady state. 

In Section 11.1 the importance of reliable -model parameters for the synthesis and design of extractive distillation processes is demonstrated for the separation of cyclohexane from benzene using NMP as entrainer. Furthermore for the system acetone-water it is shown how default values can lead to poor separation factors or even not existing azeotropic points at the top of the column (x acetone 1) ... 

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