Exergetic analysis of the integrated first- and second-generation ethanol production from sugarcane Reynaldo Palacios-Bereche a, * , Klever Joao Mosqueira-Salazar b , Marcelo Modesto a , Adriano V. Ensinas a , Silvia A. Nebra a, c , Luis M. Serra d , Miguel-Angel Lozano d a Centre of Engineering, Modelling and Social Sciences, Federal University of ABC (CECS/UFABC), Avenida dos Estados 5001, Santo André, SP 09210-580, Brazil b Mechanical Engineering School, University of Campinas, Cidade Universitária “Zeferino Vaz”, P.O. Box 6122,13083-970 Campinas, SP, Brazil c Interdisciplinary Centre of Energy Planning, University of Campinas (NIPE/UNICAMP), Cidade Universitária “Zeferino Vaz”, Rua Cora Coralina 330, P.O. Box 6166, Campinas, SP, Brazil d Departamento de Ingeniería Mecánica, Universidad de Zaragoza, C/ Maria de Luna 3, 50018 Zaragoza, Spain article info Article history: Received 30 November 2012 Received in revised form 13 April 2013 Accepted 10 May 2013 Available online xxx Keywords: Exergy Exergetic cost Sugarcane Ethanol Enzymatic hydrolysis abstract This study carried out an exergetic analysis of a proposed ethanol production scheme in which a new process e enzymatic hydrolysis of sugarcane bagasse e 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 35e37%. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The sugarcane industry is one of the most important economic sectors in Brazil, a position reached in large measure due to a high efficiency and competitiveness in the first-generation ethanol production process [1]. Nevertheless, the efficiency index and en- ergy balance can still be improved if a second-generation process, such as enzymatic hydrolysis of sugarcane bagasse and trash, is integrated into the conventional process. However, from an energy point of view, the introduction of bagasse hydrolysis can be a real challenge, because bagasse, the raw material in the new process, is a fuel in the current one. There are several studies in the literature evaluating the incor- poration of bagasse hydrolysis into current distilleries. CGEE (Center for Strategic Studies and Management in Science) [2] pro- duced a prospective study evaluating the ethanol production in- crease by means of an enzymatic hydrolysis process in projected scenarios for the years 2015 and 2025. Dias et al. [3] studied the incorporation of the organosolv hydrolysis process with diluted acid into the current ethanol production process. Dias et al. [4] also studied the incorporation of the ethanol production by enzymatic hydrolysis into the conventional process adopting different pre- treatments and producing biogas from pentose liquor. Walter and Ensinas [5] concluded a preliminary analysis of two technological routes for biofuel production from cellulosic materials (based on hydrolysis, and on gasification combined with the FischereTropsch conversion processes). Macrelli et al. [6] carried out a techno- economic evaluation of ethanol production by enzymatic hydroly- sis taking into account the production of biogas from pentose liquor and its use in boilers as fuel. Furlan et al. [7] carried out the modelling and simulation of the integrated first- and second- generation ethanol production process including the optimization of bagasse use. However, the efficiency of an integrated process should be evaluated in terms of its sustainability and use of energy resources. * Corresponding author. Tel.: þ55 11 49968215. E-mail addresses: reynaldo.palacios@ufabc.edu.br, reynaldopalaciosbe@ gmail.com (R. Palacios-Bereche), kjmosqueira@gmail.com (K.J. Mosqueira-Salazar), marcelo.modesto@ufabc.edu.br (M. Modesto), adriano.ensinas@ufabc.edu.br (A.V. Ensinas), silvia.nebra@pq.cnpq.br (S.A. Nebra), serra@unizar.es (L.M. Serra), miguel.lozano@unizar.es (M.-A. Lozano). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.05.010 Energy xxx (2013) 1e16 Please cite this article in press as: Palacios-Bereche R, et al., Exergetic analysis of the integrated first- and second-generation ethanol production from sugarcane, Energy (2013), http://dx.doi.org/10.1016/j.energy.2013.05.010