Modelling of a Brazilian ethanol plant: impact of the bagasse use and the ethanol dehydration on energy efficiency and sustainability

Abstract

Ethanol has a large share in Brazilian primary energy consumption and plays a significant role in the mitigation of the emissions from combustion engines, as national regulations advance towards increasing anhydrous ethanol content in gasoline or by the direct use of hydrated ethanol as fuel. A simulation of a sugarcane ethanol plant with a regular yield of 85.3 L of ethanol per ton of cane was carried out. The investigated process starts from the cultivation of sugarcane to the production of hydrated and/or anhydrous ethanol. The study considered that bagasse can be either burnt for cogeneration or used as feedstock for the enzymatic hydrolysis system. Additionally, alternative energy sources (such as natural gas (NG) burnt in a boiler or electricity from the Brazilian National Interconnected System (NIS)) are considered in order to cover the domestic demand in cases where biomass lacked for energy purposes. Net energy ratio (NER), fossil energy ratio (FER) and total CO 2 emission were modelled through central composite designs to assess scenarios in which the fraction of bagasse sent to hydrolysis (x 1) and hydrated ethanol sent to dehydration (x 2) both varied between 0 and 100%. The application of statistical tools (ANOVA, Student's t test and R 2) showed that x 1 caused significant variations on the investigated parameters, while x 2 proportioned mild effects. NER varied in the range 0.795-0.984, with an optimal value being found at (x 1 , x 2) equal to (81.82, 0) and (36.67, 0) when the system is coupled to NIS and a NG boiler, respectively. FER was verified as high as 11.910 with energy from NIS to produce hydrated ethanol with maximal cogeneration from the bagasse. It diminished to 3, when around 40% of bagasse is sent to enzymatic hydrolysis instead for the cogeneration system and NG complements the domestic demand.

Determining regions for installing flex-biomass sugar-ethanol plants: a multicriteria approach for location

“…The sugar-ethanol sector in Brazil is electrically self-sufficient, as it generates electricity from bagasse and still sells the surplus to distribution concessionaires (Furlan et al, 2012;Castiñeiras & Pradelle, 2020;Dias et al, 2015). In the U.S. experience, they recur to fossil sources and the power grid to attend to heat and electrical demands in the ethanol conversion (Shapouri et al, 2003).…”

“…If the residue does not meet the cogeneration of energy for the continuous production of sugar and alcohol, we must consider the location of energy sources among the locational criteria. In addition, it is necessary to consider the possibility of increasing the production of second-generation ethanol from bagasse (Bechara et al, 2018;Castiñeiras & Pradelle, 2020;Palacios-Bereche et al, 2018). The technology is not yet extensively employed in the Brazilian industry (Castiñeiras & Pradelle, 2020), but a venture such as a flex plant must remain operating in the same location for several years.…”

“…In addition, it is necessary to consider the possibility of increasing the production of second-generation ethanol from bagasse (Bechara et al, 2018;Castiñeiras & Pradelle, 2020;Palacios-Bereche et al, 2018). The technology is not yet extensively employed in the Brazilian industry (Castiñeiras & Pradelle, 2020), but a venture such as a flex plant must remain operating in the same location for several years. Furlanetto et al (2020) evidenced the complexity of the Brazilian taxation system.…”

Análise Técnica, Econômica E Ambiental De Usinas Termelétricas Alimentadas Por Biomassa Residual Operando Com Ciclos Combinados Híbridos

“…Por sua vez, esse bagaço pode ser utilizado em diversas outras aplicações, como para aumentar a geração de eletricidade na usina ou produzir etanol de segunda geração [64]. Por exemplo, Castiñeiras e Pradelle [80] simularam uma típica usina brasileira de etanol, considerando tanto a utilização do excedente de bagaço no sistema de cogeração quanto o aumento da produção de etanol de segunda geração.…”