Techno-Economic Evaluation and GHG Emission Assessment of Different Options for Vinasse Treatment and Disposal Aiming at Reducing Transport Expenses and Its Energy Use

Abstract

The vinasse is a polluting effluent generated in large quantities in the ethanol production process, whose disposition is problematic and costly. In this work, the vinasse problem is addressed through a comparison between four alternatives for treating it with energy recovery: (i) concentration in an evaporator system until 25 Brix for volume reduction (CONC); (ii) concentration in an evaporator system until 65 Brix, with subsequent incineration of concentrated vinasse (CONC + INC); (iii) anaerobic biodigestion (BIOD); and anaerobic biodigestion and digestate treatment by membranes (BIOD + MEM). The techno-economic assessment is performed through mass and energy balances, evaluating two configurations of the cogeneration system: considering back-pressure (BPST) and condensing-extraction (CEST) steam turbines, in combination with an economic feasibility evaluation. Furthermore, an evaluation of GHG emission was performed in each case. The BIOD + MEM and CONC cases promoted a significant reduction in effluent volume (53% and 82.8% respectively), while the CONC + INC case practically eliminated the disposal expenses of this effluent. Regarding the cogeneration system, the BIOD case presented the highest bagasse surplus (59.9 kg/t cane) for the BPTS configuration, while the CONC + INC case presented the highest electricity surplus (89.7 kWh/t cane) for the CEST configuration. As for the economic assessment, the cases CONC with BPST, and CONC + INC for both BPTS and CEST presented economic feasibility, while the GHG emission assessment indicates that the BIOD case with BPST is the option with the lowest emissions. A sensitivity analysis was also performed to evaluate eventual variations in market and operating conditions.