MULTIEFFECT DISTILLATION PROCESSES

Twenty-three different multieffect distillation systems are considered with detailed calculations for 19 variants and 2 single-column base c ases. A new method for balancing columns by varying the feed rate of a n additional feed stream is introduced. Schemes are compared on the ba sis of dimensionless energy use, separation volume per mole of feed, a nd heat-transfer area per mole of feed. For liquid feeds with excess l ess volatile component and relative volatility of 4.0 a multieffect sy stem with a stripping column and a balanced fractionation column looke d attractive. If energy savings are very important, a third effect (a balanced stripping column) looks attractive. For high-pressure vapor f eeds with excess less volatile component a single column with the vapo r feed as the energy source in the reboiler should be considered. High -concentration high-pressure vapor feeds can be processed with no ener gy cost in a high-pressure enriching column at the high pressure conne cted by forward feed to a low-pressure fractionating column. In all of these applications the use of multieffect distillation can lead to si gnificant energy savings with modest increases in capital investment. Heuristics are presented to rapidly devise a feasible system.