Ternary distillation schemes with partial reboiler or partial condenser

For the separation of a liquid ternary mixture ABC (A being the most volatile and C the least volatile) into pure product streams, the possibility to further improve the performance of a direct sequence by replacing the total reboiler at the bottom of the first column receiving the ternary feed with a partial reboiler is explored in detail. The use of a partial reboiler leads to four distinct configurations having process streams of different enthalpies or different compositions that can be fed to the second column distilling B from C. At low to moderate values of relative volatilities (a approximately less than 5), any improvement in the thermodynamic efficiency due to the partial reboiler is small. However, the configuration with two saturated liquid feeds, of different compositions, to the second column can potentially lead to a small (up to 10%) reduction in the heat duty of the second column. At reasonably high values of relative volatility of B with respect to C (alpha(B) approximately greater than 10), the use of the partial reboiler leads to substantial improvement in the thermodynamic efficiency, and it becomes thermodynamically more efficient to send a saturated liquid feed and a two-phase feed to the second column.