The effect of reflux ratio and feed thermal conditions on ethanol-water distillation process performance

Abstract

Demand for ethanol has increased globally due to the need for energy and consumer chemicals, necessitating use of distillation to  concentrate dilute sources. This paper presents the effect of reflux ratio, number of stages, feed thermal conditions (FTCs), feed composition (XF), and feed plate location on the performance of a normal distillation column separating ethanol-water mixtures ranging  between 0.1 and 0.6 mol/mol. The model was created using Aspen Plus® Software. The FTCs studied include: feed at room temperature  (FRT), partially vaporized feed (PVF), feed at its boiling point (FBP), superheated vapor (SHV) and feed at dew-point (FDP). The  performance factors studied were: distillate composition (XD), reboiler and condenser duties. The axial profiles of temperature and  ethanol concentration in the liquid across the column revealed stronger dependence on XF in the stripping section and on feed plate  location. Increasing reflux ratio increased distillate composition, reboiler and condenser duties. Increasing feed composition increased  distillate composition and lowered reboiler and condenser duties depending on the FTCs. Locating the feed plate further down the  column increased the distillate composition. The QR was highest for FRT while QC values were highest for FTC and SHV. The FBP led to  minimum energy demands for both QR and QC. To minimize energy, switch all FTCs to FBP was recommended, with highest savings  observed for switching from FRT to FBP.