A column with a partial reboiler and a partial condenser operates at \(400.0 \mathrm{kPa}\). The saturated liquid feed flow rate is \(200.0 \mathrm{kmol} / \mathrm{h}\) and is \(22.0 \mathrm{~mol} \%\) ethane, \(47.0 \mathrm{~mol} \%\) propane, and \(31.0 \mathrm{~mol} \% \mathrm{n}\)-butane. Recover \(97.0 \%\) of the ethane in distillate and \(99.0 \%\) of the propane in bottoms. Reflux is a saturated liquid and \(\mathrm{L}_{0} / \mathrm{D}=3.0\). Find the optimum feed stage and the total number of equilibrium contacts required. Assume CMO, and use DePriester charts or Eq. (2-28). Use of a spreadsheet to do dew-point calculations is highly recommended.

Equation 2-28

In K = a/T + a/T + a + a In p+ a2/p + : T2' T6 pl ap3/p