Approximate Solutions at Total Reflux

The equations are presented first for conventional distillation columns and then for complex columns. 

For a column having a partial condenser the Fenske equation3 is given by 

After finding N by use of Eq. (2), the complete set of 6,/d/s are found through the use of Eq. (1). Then the total distillate rate at total reflux is found by solving the overall component-material balances for dit and summing all components to give 

Suppose that the purity specifications are taken to be XD l and xB h. In general D and B are not determined by the specification of these two mole fractions except for the case of a binary mixture. To apply Fenske s equation to determine 

The above expressions contain two unknowns, bh/dh and N. Use of the above expressions for d, and bt permits the two expressions given by Eq. (6) to be restated in functional form in terms of the two unknowns as follows 

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