Energetic-environmental assessment of a scenario for Brazilian cellulosic ethanol
Highlights
► A Brazilian Biorefinery scenario producing cellulosic ethanol is assessed through an energetic-environmental approach. ► Energy, emergy, ecological rucksack and gas emissions indices were calculated. ► Biorefinery's ethanol productivity is much higher than first-generation ethanol plants. ► High ethanol productivity demands a high energetic-environmental cost. ► A trade-off exists and a systemic view should be considered by decision makers.
Introduction
Petroleum, natural gas and coal comprise about 87% of primary energy consumption worldwide (World Oil Outlook, 2010). This high demand considerably reduces the natural stocks and has been projected to be on the decline due to scarcity during next decade; this phenomenon is called Peak Oil and characterized by high energetic and economic cost to make oil available (Campbell and Laherrére, 1998; Cleveland, 2005). Since the energetic issue is an urgent and real problem, and since that energy market affects globally the political-monetary balance, alternative energy sources to fossil fuels are considered extremely important for governments, scientists and entrepreneurs worldwide. Other resources are also crucial to society, for example fresh water, agricultural lands and food (Meadows et al., 2004; Hall and Day, 2009; MEA, 2005), but their importance has not yet garnered as much attention as fossil fuel and climate change.
Considering that world energy demand is predicted to increase by 40% (from a 2010's consumption of 230 million barrels of oil equivalent to 323 millions in 2030 World Oil Outlook, 2010), some biofuels are being considered part of the answer to move to a low carbon-emitting fuel for transportation. Nevertheless, there are several technological routes and raw material available for biofuel production and the characteristics of a specific route should never be generalized to any biofuel, because it depends on how and where it is produced. Brazil is recognized as a huge producer of first generation sugarcane ethanol, reaching 28 billion liters in 2008/2009 (UNICA, 2011), corresponding to 12% of all liquid fuel used for transportation in Brazil (Balanço Energético Nacional, 2011). To reach that high sugarcane production, 6.7 Mha of land using conventional agriculture were required (UNICA, 2011).
Large-scale ethanol production and its expansion are being criticized by some researchers based on arguments related to net energy output, biofuel versus food competition for land, water consumption in ethanol production, labor quality during harvest season, among others (Santa Barbara, 2007; Giampietro and Mayumi, 2009; among others). Trying to overcome these criticisms and to be well received by society, scientists are conducting research aimed at producing ethanol from lignocellulosic material, called as second generation ethanol. This production process maximizes waste reduction through the closed-industries concept, i.e. material and energy previously considered as by-products by one process are fed back to other processes as raw materials. This approach resulted on the Zero Emission definition (Gravitis et al., 2008), the concept that will be applied to the new ethanol plants, Biorefineries.1
The concept of biomass refining has been a subject of discussion for more than 25 years motivated by potential for enhanced energy security, climate change mitigation, and rural economic development (Laser et al., 2009). Biomass energy and material recovery is maximized when a Biorefinery approach is considered, because many technological processes are jointly applied (Cherubini and Ulgiati, 2010). Different Biorefinery pathways, from feedstock to products, can be established according to the different types of feedstock, conversion technologies and products. Generally, the two technological routes are bio-chemical (enzymatic hydrolysis, and fermentation) and thermo-chemical (gasification). The choice about one route rather than the other depends on several aspects including political, economic, social, raw material availability, market for products, infra-structure, land and water availability, and so on. There is much time before a Biorefinery will be installed in Brazil and, in practical terms, Seabra et al. (2010) argues that for the Brazilian case there is a possibility to use sugarcane residues2 to produce more ethanol in adjacent plants of sugarcane mills already installed.
An assessment of different aspects of a Biorefinery is mandatory for a better decision about which technological route should be chosen, verifying their strengths and weaknesses. In this sense, several papers are being published about technological and economic aspects of Biorefineries (Laser et al., 2009; Cherubini and Ulgiati, 2010; Luo et al., 2010; among others). On the other hand, the energetic-environmental issues are rarely discussed, and when they are considered, often only the Energy Return on Investment (EROI) index and the amount of CO2 released to atmosphere are calculated. The technological and economic aspects are important, but to get a sustainable production, socio-politics and energetic-environmental issues are fundamental. Focusing on this last topic, the following doubt arises: Does the new second generation ethanol plant envisaged for Brazil have better energetic-environmental performance than the current first generation ethanol plant?
The Sustainability Multi-criteria Multi-scale Assessment (SUMMA) approach (Ulgiati et al., 2006) has been proposed as an alternative evaluation technique assessing the energetic-environmental performance of products and processes. This approach aims to use different methodologies with their own rules and meanings, avoiding the generation of one over-simplified final indicator. Moreover, the SUMMA allows decision makers to have access to a range of indicators showing different aspects of the system instead just one or two, supporting the choice for one or the other technological route for Biorefinery.
The objective of this work is to assess, through a multi-criteria approach, the energetic-environmental performance of a Biorefinery scenario in Brazil. Four main methodologies are used: Embodied Energy Analysis, Ecological Rucksack, Emergy Accounting and Gas Emission Inventory. Data for first generation large-scale ethanol and also for the Integrated Systems of Food, Energy and Environmental Services (IFEES) production calculated by Agostinho and Ortega (2012) are used for comparison.
Section snippets
Biorefinery scenario
One of the main aspects for the future development of Biorefineries is the efficient production of transportation liquid biofuels. This is explained due to the increase of energy demand in the transportation sector, and the demand for renewable fuels, which can only be produced from biomass (Cherubini and Ulgiati, 2010). This is a crucial point, because currently only liquid fuel for transportation (ethanol) is considered in almost all energy discussions in Brazil, i.e. ethanol production is
Biorefinery in Brazil: a scenario approach
The main characteristics of the Biorefinery scenario previously shown on Fig. 1 are presented on Table 1. Raw data are average values from Macedo et al. (2008), Pereira and Ortega (2010) and Seabra et al. (2010). An ethanol plant producing only ethanol (instead ethanol and sugar as usual) was considered in this study; this approach does not influence the study because the ethanol and sugar production involves processes clearly distinguished, with specific equipment and energy use. Table 1 shows
Conclusions
Considering the methodologies and assumptions of this work, the follow conclusions can be drawn:
- (a)
Regarding total systems production – The Biorefinery is able to produce 1.57 times more ethanol than Conventional Ethanol Plants (CEP) and 40 times more than IFEES. Moreover, its electricity production is 2.58 times higher than CEP. On the other hand, IFEES also produces food, wood, compost and environmental services instead only ethanol.
- (b)
Regarding the energetic-environmental performance for a system
Acknowledgements
Feni Agostinho is grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, process number 2009/51705-9) for granting the Post-Doctoral scholarship that helped make this work possible. Special thanks to Brandon Winfrey for his work on English language revision.
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