PREFRACTIONATION TO REDUCE ENERGY-CONSUMPTION IN DISTILLATION WITHOUTCHANGING UTILITY TEMPERATURES

Distillation systems composed of a prefractionator and a main column a re introduced. The columns operate at different pressures, but the tem peratures of the utilities are the same as for a single column perform ing the same separation. The energy integration of the columns is real ized by condensing a vapor overhead from the prefractionator in an int ermediate reboiler located in the stripping section of the main column or by boiling a bottoms liquid from the prefractionator in an interme diate condenser place in the rectifying section of the main column. An alysis is performed to determine feasible regions of operational param eters and to minimize vapor flows. A detailed simulation example of th e benzene-toluene separation shows that for certain feed compositions it is possible to reduce energy requirements of a conventional binary distillation column by almost one-third using this new distillation sy stem. This savings is achieved without any change in the temperature o f the utilities used.