Abstract
Abstract The large-scale production of bioethanol fuel requires energy demanding distillation steps to concentrate the diluted streams from the fermentation step and to overcome the presence of the ethanol-water azeotrope. The conventional separation sequence consists of three distillation columns performing several tasks with high energy penalties: preconcentration distillation (PDC), extractive distillation (EDC) and solvent recovery (SRC) columns. Remarkable, almost all papers on this topic focus on the azeotropic separation only, while neglecting the pre-concentration step. Usually, the ethanol concentration in the first distillate stream is arbitrarily considered close to the azeotropic composition. While the energy usage in the PDC increases as the distillate composition gets closer to the azeotrope, the energy requirements in the EDC-SRC units decreases as the feed to EDC becomes richer in ethanol – and the other way around. This paper addresses this key trade-off of the distillate composition – a fundamental issue that was not studied before. Aspen Plus simulations were used to investigate how this parameter affects the energy usage and investment costs of the complete system. This issue applies in any other methods using a pre-concentration column (e.g. extractive and azeotropic distillation). The optimal economics is reached at a distillate concentration of 91.0 %wt ethanol, where the specific energy use is only 2.11 kWh (7,596 kJ) per kg ethanol.
Published Version
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