EFFICIENT USE OF AN INTERMEDIATE REBOILER OR CONDENSER IN A BINARY DISTILLATION

The impact of an intermediate reboiler or condenser on the distillatio n of ideal binary mixtures into pure product streams is studied using a simplified model. The advantage of heuristics derived from this stud y is that they can quickly tell a process engineer if an intermediate reboiler ol condenser is going to be effective in improving the effici ency and, of the two options, which one would be more effective. The h euristics simply states that if the actual fraction of liquid in a giv en feed is less than that with the maximum thermodynamic efficiency fo r distillation with no intermediate reboiler or condenser then an inte rmediate condenser not only substantially improves the thermodynamic e fficiency but is also more effective than an intermediate reboiler. An analogous heuristics exists for the intermediate reboiler when the fr action of liquid in the feed is greater than the optimum. Quick identi fication of cases that can achieve a substantial improvement in effici ency provides an incentive to search for the proper utilities needed f or the intermediate reboiler or condenser. When relatively pure feed s treams (concentration of either component greater than 90%) are distil led, the extremely low efficiencies of distillation can be remarkably improved by using an intermediate reboiler or condenser.