Low carbon biofuels and the New Brazilian National Biofuel Policy (RenovaBio): A case study for sugarcane mills and integrated sugarcane-microalgae biorefineries

Abstract

The newest endeavor by the Brazilian State for fostering bioenergy - the National Biofuel Policy, or simply RenovaBio - aims at establishing a mechanism for the commercialization of decarbonization credits linked to the carbon intensity of several biofuels. Under this horizon, this study evaluates the prospects for large-scale, integrated sugarcane-microalgae biorefineries in terms of their techno-economic and environmental feasibility, as well as the possible benefits brought by the RenovaBio program. Process integration was based on different energy and material vectors obtained from the sugarcane mill, especially the use of fermentation-derived CO2, CO2 in biogas, and vinasse as carbon sources for microalgae growth. Results show that the co-location of microalgae production with sugarcane mills leads to verticalized biorefineries currently behind in economic performance in comparison to conventional sugarcane mills due to an increase in both fixed and operational expenses. Anhydrous ethanol production costs remain in the range of US$ 0.36–0.42/L, below the market price of US$ 0.51/L. Integrating a microalgae facility with a sugarcane mill also helps to further improve the sustainability of anhydrous ethanol production: cradle-to-grave emissions of greenhouse gases fluctuate around 18 g CO2eq/MJ, a reduction of 15% in comparison to conventional sugarcane-based ethanol. Depending on the scenario, a reasonably-sized integrated biorefinery would be able to mitigate around 500 thousand t CO2eq/year when displacing gasoline with anhydrous ethanol. The analysis finally points out to integrated sugarcane-microalgae biorefineries becoming economically feasible at carbon prices as low as US$ 10/t CO2eq under the RenovaBio scheme.