Principles of Batch Distillation

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. 

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A detailed differential stepwise integration for a batch distillation with holdup can be made, but the time and effort involved are usually not justified by the value of the result. The method is useful in developing the principles of batch distillation with holdup. The following section will consider the basic differential equations which are helpful in obtaining a qualitative picture of the process. By an analysis similar to that for Eq. (14-1),... 

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