Exergetic analysis of the integrated first- and second-generation ethanol production from sugarcane

• The integrated first- and second-generation ethanol production from sugarcane.
• Two technologies for glucose liquor concentration: evaporation and membrane systems.
• An exergy and exergetic cost assessment.

This study carried out an exergetic analysis of a proposed ethanol production scheme in which a new process – enzymatic hydrolysis of sugarcane bagasse – is integrated into the conventional process. Seven cases were evaluated, among them a conventional ethanol production plant without hydrolysis, a conventional plant combined with hydrolysis and hydrolysate concentration by evaporation, and a conventional plant combined with hydrolysis and hydrolysate concentration by the membrane system. Process simulations were performed to evaluate mass and energy balances, adopting the pre-treatment of sugarcane bagasse by steam explosion, and including an integrated cogeneration system. It was assumed that sugarcane trash and lignin cake, a hydrolysis residue, are available as supplementary fuel. The exergies of streams involved in the process were calculated, along with their exergetic cost. For the conventional process, in which ethanol and surplus electricity are the major products, a second-law efficiency of 28% was found. In the integrated process, with biogas as an additional product, a higher performance in resources management was achieved, with values in the range of 35–37%.