Multiobjective optimization of economic and environmental performance of Fischer-Tropsch biofuels production integrated to sugarcane biorefineries

Abstract

The mitigation of greenhouse gas (GHG) emissions is a subject of high importance at a global level. The expansion of advanced liquid biofuels use can contribute to increase the sustainable bioenergy deployment while reducing GHG emissions in comparison to fossil fuels. In this study, the economic and environmental performance of a biorefinery involving biomass gasification followed by Fischer-Tropsch (FT) liquid biofuels production associated to sugarcane value chain is explored through a multiobjective optimization approach. The biorefinery configurations investigated include different biomass combinations, and the possibility of integrating the thermochemical processes to a first-generation ethanol distillery or operating it as a stand-alone plant. Different biomass mix considering conventional sugarcane, energy-cane and eucalyptus are considered in the optimization strategy. A Design of Experiments with a second-order polynomial regression technique is used to fit a metamodel from detailed and high-fidelity spreadsheet-based process models. Internal Rate of Return and avoided GHG emissions per agricultural land occupation are used as objective functions. The Pareto-optimal curves show the best performance possibilities and allows to identify the most suitable biorefinery configurations. Results indicate there is an economic benefit from the integration between the thermochemical process and conventional first-generation ethanol mills. An increase in cane and eucalyptus processing capacities tends to improve the economic performance due to the gain of scale. A higher proportion of energy-cane processed leads to better environmental performance as it reduces both the GHG emissions and the demand for agricultural land. In contrast, a greater share of energy-cane present trade-offs on the economic performance in the integrated biorefinery caused by the higher energy demand and lower ethanol production, but a minor effect is observed on the stand-alone configuration.