Second Law analysis of large-scale sugarcane-ethanol biorefineries with alternative distillation schemes: Bioenergy carbon capture scenario

Abstract

Distillation is one of the most used separation techniques, despite its high heat demand and low thermodynamic efficiency. Although new distillation schemes have been developed for ethanol-water separation, most of them prescribe expensive sub-atmospheric columns. On the other hand, heat-integrated distillation columns allow significant steam savings since thermally integrated condenser/reboiler of different columns share the same heat duty. In this work, three innovative distillation schemes for large-scale sugarcane-ethanol biorefineries are analyzed aiming at less energy-intense processes, higher thermodynamic efficiencies and steam savings. Ethanol production, power production through bagasse-fired cogeneration, thermodynamic efficiency, heat demand, water usage, steam demand, carbon dioxide intake, and potential of bioenergy with carbon capture and storage are assessed for technical and thermodynamic comparisons of distillations schemes. Results of carbon emissions go beyond the biorefinery boundaries and include sugarcane supply-chain emissions. It is shown that heat-integrated distillation schemes promote huge steam savings compared to conventional ethanol distillation. Distillation Scheme No.2 – with five heat-integrated columns – showed highest steam savings of 63% relative to conventional distillation, while distillation Scheme No.3, prescribing an innovative Petlyuk column for bioethanol distillation, attained the highest thermodynamic efficiency (11.1%) outperforming distillation Schemes No.1 and No.2 (7.65% and 7.03%, respectively). Sankey diagrams express results of carbon dioxide equivalent flows, lost bioenergy with carbon capture and storage potential, water flow and equivalent power flows via the Second Law of Thermodynamics.