Abstract
The loss in the quality of energy throughout any process can be assessed by the thermodynamics magnitude related to its entropic performance—the exergy. This indicator has been suggested as an environmental index, as an alternative to life cycle assessment (LCA), which is a classic tool for this purpose. This study assesses the potential of coupling the life cycle approach and exergy in a bioenergy supply chain environmental performance characterization, examining two scenarios in the sugarcane agroindustry. The first one, the reference scenario, is a classical production, and the second includes the returning of a portion of residual biomass from the plant, in the form of biochar, to agricultural soil. The use of biochar engendered an increase in sugarcane productivities and a reduction of nitrous oxide emissions. These changes resulted in scenarios 1 and 2, reducing the exergy destroyed from 390 to 355 MJ/MJ ethanol (9.0%) and decreasing the greenhouse gases emissions (GHG) from 11.8 to 11.0 g CO2-equivalent/MJ ethanol (6.8%). The latter represents an improvement in the use of carbon. A sensitivity analysis showed that the effect of changing productivity was quite significant: The exergy showed a sensitivity of −0.49, and in total emissions, this figure was slightly lower, at −0.41. By changing the emissions of N2O in the soil, the sensitivity of exergy was almost null, and the total emissions were 0.077.
Highlights
Since the beginning of the 20th century, the world’s population has increased more than four-fold, increasing from 1.7 to 7 billion inhabitants
In order to allow for the development of this new industrial model, it is necessary to quantify the environmental impacts related to any processes, enabling a comparison of possible corrections, in which exergy can be of use
In addition to presenting biochar as an industrial waste that has positive results when returned to the soil, with an increased productivity and reduction of nitrous oxide emissions in the soil, this study showed that, using the system, it is possible to perform a coupling between CEENE and air pollution in the form of greenhouse gases, where the ratio of these quantities is represented by the Y function
Summary
Since the beginning of the 20th century, the world’s population has increased more than four-fold, increasing from 1.7 to 7 billion inhabitants. There was a 100-fold increase in industrial production and a 50-fold increase in fossil fuel consumption, reaching 10,700 MTOE (million tons of oil equivalent) in 2016 [1]. A new model has emerged, which is economically and socially feasible, as well as environmentally sustainable. In order to allow for the development of this new industrial model, it is necessary to quantify the environmental impacts related to any processes, enabling a comparison of possible corrections, in which exergy can be of use. The use of the exergetic method, which, according to Kotas [3], is a relatively new alternative thermodynamic analysis based on the concept of exergy, is loosely defined as a universal measure of the work potential or quality of different forms of energy in relation
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