TERNARY DISTILLATION SCHEMES WITH PARTIAL REBOILER OR PARTIAL CONDENSER

For the separation of a liquid ternary mixture ABC (A being the most v olatile and C the least volatile) into pure product streams, the possi bility to further improve the performance of a direct sequence by repl acing the total reboiler at the bottom of the first column receiving t he ternary feed with a partial reboiler is explored in detail. The use of a partial reboiler leads to four distinct configurations having pr ocess streams of different enthalpies or different compositions that c an be fed to the second column distilling B from C. At low to moderate values of relative volatilities (a approximately less than 5), any im provement 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 t o 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 re boiler leads to substantial improvement in the thermodynamic efficienc y, and it becomes thermodynamically more efficient to send a saturated liquid feed and a two-phase feed to the second column.