Technical-Economic Assessment of Different Biogas Upgrading Routes from Vinasse Anaerobic Digestion in the Brazilian Bioethanol Industry

Energy xxx (2016) 1e13

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Technical-economic assessment of different biogas upgrading routes from vinasse anaerobic digestion in the Brazilian bioethanol industry

* Rodrigo Marcelo Leme , Joaquim E.A. Seabra

Faculdade de Engenharia Mecanica,^ Universidade Estadual de Campinas (Unicamp), Rua Mendeleyev, 200, CEP 13083-860, Cidade Universitaria "Zeferino Vaz" Barao~ Geraldo - Campinas, SP, Brazil article info abstract

Article history: This paper presents a technical-economic assessment of biomethane production from vinasse in the Received 4 March 2016 Brazilian bioethanol industry, considering ﬁve technological routes of biogas upgrading. The technologies Received in revised form assessed were pressure water scrubbing, organic-physical scrubbing, amine scrubbing, membrane sep- 26 October 2016 aration and pressure swing adsorption. The biomethane costs of the ﬁve technological routes overlapped Accepted 7 November 2016 in the range between R$30/GJ (US$13/GJ ) and R$34/GJ (US$14/GJ ), which indicates a Available online xxx HHV HHV HHV HHV certain equivalence of the options. Those costs were comparable to the prices of potential alternative fuels at 2014 prices, such as the Bolivian natural gas, priced at R$20/GJ (US$8/GJ); imported LNG, at R$31/ Keywords: Vinasse GJ (US$13/GJ); and diesel, at R$42/GJ (US$18/GJ). The effects of scale on biomethane cost were also Biomethane assessed and pointed out that the likely minimum scale for vinasse-to-biomethane projects aiming at Biogas diesel substitution would be at sugarcane mills with a minimum capacity of producing 87 million liters of Biogas upgrading ethanol per season, whereas if the aim were to target natural gas markets, 174 million liters of ethanol Anaerobic digestion per season would likely be the minimum capacity for competitive prices. © 2016 Elsevier Ltd. All rights reserved.

1. Introduction nutrients for sugarcane production in Brazil [2,3]. Nevertheless, there is still debate as to whether further treatment and control of The sugarcane industry is one of the most relevant in the Bra- fertirrigation should be required. Notwithstanding the alleged zilian economy. The industry boasts more than 350 sugarcane mills, benefits of vinasse fertirrigation and the lack of evidence of envi- mostly located in the South of the country, that processed 630 ronmental impacts, there is little scientific research available in the million tonnes of sugarcane in the 2014/2015 harvesting season, literature that effectively investigates the potential detrimental placing the country amongst the top producers of fuel ethanol in effects of fertirrigation in the environment in the long term [4,5]. the world [1]. In Brazil, ethanol is produced through the fermen- Based on extensive literature research, Fuess e Garcia [5] state that tation of sugars obtained from the sugarcane. As in other fermen- the main adverse effects of vinasse fertirrigation on the soil that tative routes, a main production waste, known as vinasse or stillage, should be further investigated are salinization; aquifer contami- results. Vinasse is a liquid of dark color and strong smell, with high nation by salts; organic overloading; reduction of soil oxygen; organic content and high polluting potential, produced at a ratio of contamination by chemical species, such as nitrates, chlorides, lead, 12 L of vinasse for each liter of ethanol. An estimated 336 billion copper and zinc; and acidification. liters of vinasse must have been produced during the 2014/2015 Given the benefits of fertirrigation on nutrients recycling and its harvesting season. potential of environmental damage due to overuse, it is reasonable The vast majority of the vinasse is disposed directly in the that further options be investigated for vinasse pre-treatment and sugarcane field, without prior treatment, in an operation referred use. Harnessing its energetic potential, which can be tapped by to as “fertirrigation” (a combination of fertilization and irrigation). anaerobic digestion, is one of them. Fertirrigation associated to the use of other residues from sugar- Anaerobic digestion results in a double-dividend as it not only cane processing are important elements in the recycling of reduces the polluting potential of vinasse, due to organic matter removal, but also produces biogas. Tapping the energetic potential of vinasse would represent gains between 0.83 MJ and 2.33 MJ per * Corresponding author. liter of ethanol, which represents improvements between 4% and E-mail address: [email protected] (R.M. Leme). 10% in the energy yield of a bioethanol distillery [6]. The energetic http://dx.doi.org/10.1016/j.energy.2016.11.029 0360-5442/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Leme RM, Seabra JEA, Technical-economic assessment of different biogas upgrading routes from vinasse anaerobic digestion in the Brazilian bioethanol industry, Energy (2016), http://dx.doi.org/10.1016/j.energy.2016.11.029 2 R.M. Leme, J.E.A. Seabra / Energy xxx (2016) 1e13 potential of vinasse remains mostly unexplored though, as reported about 50% of the fermentable sugars are destined for sugar pro- by Ref. [7]. There is only a handful of sugarcane mills in Brazil that duction); or a mill with the capacity of processing 2 million tonnes produce biogas from vinasse and many of those tried it on a pilot of sugarcane per season, if the distillery is autonomous. Those are scale. Therefore, it is worth to further the research on options to relatively typical installations amongst the modern mills in Brazil. promote for the development of vinasse anaerobic digestion and That project size results in a nominal biomethane production close the biogas industry in the ethanol distilleries. to 3000 Nm3/h. Most of the literature published so far on the topic focused It has been assumed that all the vinasse produced by the sug- mainly on its use for electricity generation such as in Refs. [8e11]. arcane mill was processed for biomethane production, as per the There is a lack of studies exploring the use of vinasse for bio- quality standards defined by the Brazilian legislation, for injection methane production. For instance, Moraes et al. [12] assess in a nearby natural gas grid at a pressure of 20 bar(g). The assess- different applications of biogas, including electricity generation, ment considered the five technological routes for biogas upgrading and concludes that the use of biogas for diesel replacement would as presented before, namely, amine scrubbing, organic-physical be the most economically attractive alternative. The authors scrubbing, pressure water scrubbing, membrane separation and conclude that biogas could replace up to 40% of the annual diesel pressure swing adsorption. demand in the agricultural operations of the sugarcane mill. Bud- The technical-economic assessment was undertaken by firstly zianowski et al. [13] report that the high subsidies to biogas-based defining a conceptual process flow diagram for each biogas electricity in Europe have promoted the development of biogas upgrading route; then estimating the corresponding mass and technology towards combined heat and power systems, in spite of energy balances; and finally calculating the unit cost of bio- the greater economic benefits that biomethane would offer in many methane, for the five biogas upgrading technologies. cases. The input data used in the assessment was obtained from in- Given the lack of in-depth studies of vinasse-to-biomethane terviews with technology providers, sugarcane mill operators, projects in the literature that cover the whole, integrated process biogas upgrading plant operators, and from the literature. When- from both technical and economic standpoints, the present paper ever information was lacking, the expert judgement of the authors assesses the unit cost of biomethane of five different technological was used to fill data gaps. Generic process flow diagrams; perfor- routes of biogas upgrading in the Brazilian bioethanol industry. The mance parameters; and mass and energy balances obtained during paper presents a detailed technical assessment and estimates the the interviews were used for the technical assessment and process unit cost of biomethane considering the whole, integrated process, design. Process integration was made by the authors and resulted in including vinasse collection in the sugarcane mill, its anaerobic the overall mass and energy balances that generated the informa- digestion, raw biogas H2S removal, biogas upgrading and bio- tion on investment and consumables that were later used for the methane dispatch to the natural gas grid. The technologies assessed economic assessment. Prices quotations were obtained also from were pressure water scrubbing, organic-physical scrubbing, amine the interviews for the main process equipment and consumables. scrubbing, membrane separation and pressure swing adsorption. The economic assessment was accomplished by calculating the equivalent uniform annual cost (EUAC) of the plant, which was then used to determine the unit cost of biomethane in energy terms. 2. Materials and methods

The technical-economic assessment was undertaken at an 3. Technical assessment and process design example vinasse-to-biomethane project. The project was chosen at a distillery with the capacity of producing 174 million liters of The conceptual process flow used for each of the biogas bioethanol per season. That figure translates into a sugarcane mill upgrading routes is slightly different due to their specific re- with the capacity of processing 4 million tonnes of sugarcane per quirements, as it will be explained along the following sections. season, if the distillery is annexed to a sugar factory (assuming that However, the generic process flow diagram presented in Fig. 1

Fig. 1. Generic process ﬂow diagram.