The influence of feed molar flow rate on key streams properties and duties in ethanol-water azeotropic distillation process

Abstract

Investigation on the influence of near azeotropic feed molar flow rate on properties of key streams connecting main process units of an  ethanol-water azeotropic distillation pilot processis presented. The heterogeneous azeotropic distillation model with cyclohexane  entrainer was configured in Aspen Plus® V10 commercial simulation software. Property analysis and prediction of plant’s  performancewere achieved using Non-Random Two Liquid Redlich-Kwong thermodynamic model. Both residual curve maps and ternary  diagrams were used to determineseparation possibility and presence of ethanol-water azeotrope in the formed ternary mixtureduring  distillation synthesis. The process convergence was addressed using flowsheet convergence and balance node. Distillation of ethanol- water azeotropic mixture was simulated at constant recycle ratio (R = 5), numberof stages (N = 12) and pressure (P = 1 atm). Data  obtained were analysed in MS Excel 2013. Results showed that simultaneous increase ofmolar flow rate of the near azeotropic feed and  feed ethanol concentration improves ethanol purity but results in retrograde phenomenon which may humper plant’s performance and  increase stream flow rates and therefore increase energy duties. The condenser duty of the main column wasaround 90.94% higher than  the recycle column’scondenser duty. Also, reboiler duty of the main column were nearly 90.25% higher than the recycle column’s reboiler  duty.It was concluded that setting 18 to 20 kmol/h feed molar flow rate enhances higher energy efficiency and improves ethanol  product purity. Careful distillation synthesis and plant’s monitoring are recommended to improve ethanol-water azeotropic  distillation plant’s performance and address retrograde phenomena.