2017 International Conference on Electronic, Control, Automation and Mechanical Engineering (ECAME 2017) ISBN:

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1 2017 International Conference on Electronic, Control, Automation and Mechanical Engineering (ECAME 2017) ISBN: Exergetic Analysis between a First-Generation Bioethanol Production Plant and a Second-Generation Plant Coupled to Conventional Process Marcus MARI 1, João MARI 1, Maykon FERREIRA 1, Wagner CONCEIÇÃO 1 and Cid ANDRADE 2,* 1 Mechanical Engineering Department, State University of Maringa, Colombo Avenue 5790, Maringa, Parana, Brazil 2 Chemical Engineering Department, State University of Maringa, Colombo Avenue 5790, Maringa, Parana, Brazil Keywords: Sugarcane, Bioethanol, Exergy. *Corresponding author Abstract. Large consumption of non-renewable fuels in the world has strongly encouraged the search for biofuels, due to inevitable shortage of fossil energy sources and catastrophic problems generated by their use. Under these circumstances the so called second generation biofuel production has been highlighted, where lignocellulosic materials such as sugarcane bagasse are used to produce bioethanol, unlike the traditional first-generation process, whose feedstock is sugarcane. Therefore, this work aimed to perform a comparative exergetic analysis between first and second-generation bioethanol production processes, in order to evaluate from the exergetic point of view, which of these processes is the most feasible. It was found an overall exergetic efficiency of % for the exclusively first-generation plant, whereas for the integrated plant, it was obtained %. In this way, insertion of new stages in production process, required by the second generation, has caused consequently an increase of irreversibilities and losses. Introduction Much effort has been done to develop and produce larger quantities of biofuels due to the irreversible problems caused to environment by the use of fossil fuels. One of the main advantages of using renewable sources to produce biofuels is the exploration of natural sources, which are geographically more distributed than fossil sources. Moreover, this bioenergy produced provides independence and security to the energy supply [1]. Bioethanol production plants from sugarcane are one of the most important industries to Brazilian economy [2,3] and have been producing ethanol in large scale for more than 30 years, due to an incentive program called as ProÁlcool [4,5]. First generation process consists in convert sugarcane juice in ethanol, where bagasse and trash collected from the cane field are burnt into boilers to produce steam and electricity to supply the process demand, besides of that, it is also possible to sell the surplus electricity to the grid [6]. On the other hand, second generation process produce ethanol from sugarcane bagasse, which is a lignocelulosic material that does not compete with food crops [7] and has some advantages such as large quantity of feedstock, low price and reduction of CO 2 emissions [8]. Nevertheless, it is required more sophisticated equipments and processes, as well as bigger investments in comparison with the conventional process [1]. Thus, the aim of this study is to carry out a global exergetic analysis between a first-generation bioethanol production plant and a second generation bioethanol production plant integrated to the traditional process. 407

2 Description of the Process Both cases evaluated in this work was based on study of [3], in which bioethanol production plants were modeled and simulated according to actual and experimental data, as well as data collected from the literature. Table 1 shows the basic characteristics of the plants, common to both cases. First Generation Process Table 1. Basic characteristics of the plants. Crushing rate [t of cane/h] 500 Season operation hours [h/year] 4000 Bagasse production [kg/t of cane] 277 Sugarcane trash processed [kg/ t of cane] 78 The first-generation bioethanol production plant was divided into 10 subsystems, as can be seen in Fig. 1. A control volume was defined involving all subsystems, where some inputs are required by the processes, obtaining as a result some outputs. Second Generation Process Figure 1. Control volume of first generation process. For this case, the bioethanol production plant was divided into 13 subsystems, in which 3 new subsystems were added in relation to the conventional first generation, representing the second-generation process. This new process consists of five main steps: biomass pre-treatment, cellulose hydrolysis, hexose fermentation, separation and effluents treatment [9]. The most used methods for each step were utilized, such as steam explosion for pre-treatment [6,7,10,11], enzymatic hydrolysis of cellulose [6,7,10,11,12,13,14], and concentration of glucose liquor by means of a multiple effect evaporation system [6,15,16,17,18]. Furthermore, pentose liquor, a hydrolysis by-product was biodigested in an upflow anaerobic sludge blanket reactor (UASB) to produce biogas, as in [6,19,20]. Fig. 2 shows the integrated process of first and second generation, in which a control volume was defined involving all subsystems. 408

3 Figure 2. Control volume of integrated first and second-generation processes. Global Exergetic Analysis Exergetic analysis is a powerful tool to identify causes, locations, types and magnitudes of thermodynamic losses in processes [21]. To perform a global exergetic analysis was necessary to find the exergy of each input and output of the process, shown in Fig.1 and Fig. 2. The sugarcane exergy was calculated by the sum of exergies of its components, sugarcane juice and bagasse. The sugarcane juice was evaluated as a sucrose-water solution, as in [3,22]. On the other hand, it was used a particular analysis proposed by [23] to calculate the exergy of bagasse and trash. The second-grade alcohol and anhydrous ethanol were considered as an ethanol-water solution, and their exergy were calculated following the procedure reported in [24]. Exergy of biogas was obtained from [3]. For the flows with organic constituents, such as vinhasse and phlegmasse, an organic-water solution was considered to determine their exergies [3]. Exergies of chemical inputs, such as calcium oxide, sulfhuric acid and sulfur dioxide were obtained considering the standard chemical exergy of pure components provided by [23]. Finally, for enzymes, its exergy was calculated according to the technical fuels procedure reported in [23]. The surplus electricity for the first-generation plant was kw, whereas for the integrated plant, it was generated a surplus electricity of kw [3]. Exergetic Efficiency Global exergetic efficiency was determined according to Eq. 1 [3,25], which relates the exergy of outputs and inputs of system. Ɛ 1 Results and Discussion Table 2 and 3 show the flows description for the first and second case, respectively, where the exergies were calculated according to the methodologies described previously. Table 2. Description of first generation process flows. Flows [kg/s] T [ C] [kj/kg] [kw] Sugarcane Surplus bagasse Trash Second-grade alcohol Vinhasse

4 Phlegmasse Anhydrous ethanol Makeup water Calcium oxide Sulphuric acid Water withdrawal Table 3. Description of flows for integrated first and second-generation process. Flows [kg/s] T [ C] [kj/kg] [kw] Sugarcane Trash Second-grade alcohol Vinhasse Phlegmasse Anhydrous ethanol Makeup water Calcium oxide Sulphuric acid Sulfur dioxide Water withdrawal Flows [kg/s] T [ C] [kj/kg] [kw] Biogas Enzyme Considering all inputs and outputs that cross the control volume, it was reached an exergetic efficiency of % for the first-generation bioethanol production plant, whereas for the second generation bioethanol production plant coupled to conventional process was obtained %. Conclusion Evaluating the found results for exergetic efficiency, it can be concluded that from the exergetic point of view, the first-generation bioethanol production plant is more feasible than the integrated process. The second-generation production plant requires inclusion of new steps, such as biomass pre-treatment and enzymatic hydrolysis. Thus, insertion of these processes inevitably caused an increase of inefficiencies, irreversibilities and losses, contributing to the efficiency reduction. However, not only an exergetic analysis should be used to define the best bioethanol production process, but also economic, political, social and environmental aspects must be analyzed. Acknowledgement This work has been realized with support of Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) - Brazil. References [1] P.S. Nigam, A. Singh, Production of liquid biofuels from renewable resources, Prog. Energ. Combust. 37 (2011) [2] A.V. Ensinas, M. Modesto, S.A. Nebra, L. Serra, Reduction of irreversibility generation in sugar and ethanol production from sugarcane, Energy. 34 (2009) [3] R. Palacios-Bereche, K.J. Mosqueira-Salazar, M. Modesto, A.V. Ensinas, S.A. Nebra, L.M. Serra, M. Lozano, Exergetic analysis of the integrated first- and second-generation ethanol production from sugarcane, Energy. 62 (2013) [4] C.R. Soccol, L.P.S. Vandenberghe, A.B.P. Medeiros, S.G. Karp, M. Buckeridge, L.P. Ramos, A.P. Pitarelo, V. Ferreira-Leitão, L.M.F. Gottschalk, M.A. Ferrara, E.P.S. Bon, L.M.P. Moraes, J.A. 410

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