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Abstract:Although in the last 40 years only sugarcane has been harnessed for the production of ethanol in Brazil, corn production has grown strongly in certain areas, and may serve as a supplementary feedstock for ethanol production in integrated plants during the sugarcane off-season. The aim of this study is to evaluate the environmental and energy performance of ethanol production from sugarcane, corn, and grain sorghum in a Flex Mill in the state of Mato Grosso, Brazil. A life cycle assessment was carried out to survey the production of ethanol from each individual feedstock, and the integration of two of these to increase production during a one-year period. Results indicate that the environmental and energy performance are greatly influenced by agricultural activities, highlighting the importance of sugarcane cultivation. Still, there was an increasing trend of Climate Change impacts, Human Toxicity (carcinogenic) and Ecotoxicity, as well as reduced impact of Photochemical Oxidant Formation and Energy Return on Investment (EROI) as the proportion of ethanol from starchy sources in integration scenarios increases.

When manual harvesting of sugarcane was discontinued in many regions of Brazil, interest in power generation by burning the bagasse and straw in cogeneration units rose. Exergy analysis is often applied to increase the thermodynamic yield of these plants by identifying irreversibility and work availability. Conversely, pressure for adopting clean energy requires these systems to be evaluated for suitable environmental performance. This study identified and discussed the thermodynamic and environmental effects of scaling up systems that operate according Rankine cycle with reheating. Ten scenarios have been designed considering different levels of steam pressure and addition rates of straw remaining in the sugarcane cultivation. The thermodynamic analysis revealed a 37% improvement in the exergy efficiency and 63% of increasing in power generation to raise the steam pressure from 20 to 100 bar. Moreover, the use of 50% of residual straw into units operating at 100 bar can more than double the amount of electricity exported. If addressed considering a life cycle perspective, the use of straw improves the environmental performance of the cogeneration for Climate Change and Particle Matter Formation but provides additional impacts in terms of Water and Fossil resources depletions.

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