Exergy assessment and techno-economic optimization of bioethanol production routes

Currently, electricity generation and second-generation ethanol production from lignocellulosic feedstocks represent technological alternatives in the bioenergy sector. Nevertheless, the introduction of new production processes denotes a real challenge due to the complexity and diversity of the pathways that can be evaluated. In addition, there are economic and environmental factors that must be considered during the development and consolidation of these new configurations. Accordingly, this paper presents a methodology to perform the exergy and exergo-environmental analysis, and ranking of sugarcane-based biorefineries. The proposed models assessed the Conventional (Route 1), Biochemical (Route 2), and Thermochemical (Route 3) pathways using simulation programs and mathematical tools to simulate the ethanol production and electricity generation. Furthermore, the process integration and different uses for the surplus bagasse were studied, aiming at the optimizing and ranking of routes. The results indicated optimal settings that allowed the routes ranking in terms of the renewability exergy index "lambda". In this context, the biochemical pathway (Route 2) presented the maximum exergy efficiency, therefore the lowest average unitary exergy cost of the evaluated platforms. This system that promoted an increase of 22% and 45% in the ethanol production, when compared to Route 1 and Route 3, respectively. Besides, the thermochemical pathway (Route 3) presented the configuration with the highest power generation rate. Concerning the environmental impact results, it was found that the most sustainable configuration was Route 2, which presented the lowest overall CO2 emissions rates (131.45 gCO(2)/MJ products).