Comparison through energy, exergy and economic analyses of two alternatives for the energy exploitation of vinasse

The vinasse, effluent generated in the distillation step of the ethanol production process, has polluting characteristics and is generated in large amounts, making its disposition problematic and costly. The present study addresses the vinasse problem through a comparison between two alternatives for the energy use of it: i) vinasse concentration and subsequent incineration of concentrated vinasse; and ii) vinasse anaerobic biodigestion. A simulation of a base case; namely, a conventional sugar and ethanol production process, was performed using the Aspen Plus® software. The comparison was carried out through energy, exergy and economic analyses. The energy analysis evaluates the impacts of these technologies in the cogeneration system, while the exergy analysis comprises the calculation of irreversibilities and exergy efficiencies. Finally, the economic analysis includes the calculation of costs and revenues of each alternative, in order to evaluate their feasibility. Additionally, a sensitivity analysis was performed. Results show that energy and exergy efficiencies are in the same range for both alternatives; however, the economic assessment indicated the vinasse incineration as the best alternative for the assumed conditions.