NOVEL ENERGY-SAVING METHOD OF RECTIFICATION

Abstract

The conventional rectification method to separate and purify chemical mixtures has the disadvantage of being an energy-intensive unit operation. The innovative method proposed in this article employs vapor and liquid recycles to the trays that in turn reduce the reflux rate and vapor boil-up rate, resulting in energy reduction without compromising the separations.

These findings were supported with examples of ethanol-water and butane- pentane system separations. With ethanol-water system, the experiments were conducted without overhead liquid recycle and using 16 and 5 vapor recycles. The energy saved was found to be 25–35% for 16 recycles and 20–30% for 5 recycles. Butane-pentane system was chosen as an example of industrial use of the proposed method. A liquid overhead reflux ratio of 0.5 (L/D) was used with vapor recycles, compared to a reflux ratio of 1.25 for the conventional separation without vapor recycles. This resulted in 30–35% saving in energy while giving the same productivity of the column. Butane-pentane separation was also simulated using a commercial process simulator (ASPEN^©PLUS).

Keywords:

• Rectification
• Distillation
• Vapor and liquid recycles
• Energy saving

Notes

Feed flow: 30,000 kg/hr, distillate: 17,850 kg/hr, Bottom: 12,150 kg/hr, feed composition, NC₄: 59.2 (wt%), NC₅: 40.8 (wt%), no. of trays = 31 (excluding reboiler and condenser).

Reduction in energy consumption = ((11,022.3 − 7,508.9)/11,022.3) × 100 = 32%.

Reduction in energy consumption = ((10,390 − 6,746.85)/10,390) × 100 = 35%.