Energy supply design for the integrated production of 1G + 2G ethanol from sugarcane

Abstract

The full renewable energy production of the Brazilian sugarcane industry involves, besides ethanol production, the use of bagasse and straw. The bagasse is burned in mills for cogeneration and any surplus bioelectricity is sold to the grid. While 40% of the straw must be left for soil protection, 60% could be used for cogeneration. This study evaluated the energy integration of first-generation (1G) and second-generation (2G) ethanol operations and the resulting surplus energy. The work used experimental and published data of higher calorific values of these residues as well of lignin, a solid process stream. The C5 stream from the hydrothermal pretreatment was considered for methane generation. A sensitivity analysis was used to evaluate three integrated scenarios for 1G + 2G ethanol and surplus energy production: In scenario (A) the gradual allocation, up to 100% bagasse, for 2G ethanol would increase the ethanol volume by 29% and surplus energy, from lignin and methane burning, by 10%, compared to total bagasse burning. In scenario (B), where 50% straw would be set for burning, the gradual allocation up to 100% bagasse for 2G ethanol would keep the same ethanol increase by 29%; however, surplus energy would be increased by 16% of that expected from total bagasse burning. In scenario (C), where 50% bagasse would be set for 2G ethanol and straw burning would be gradually increased, up to 60%, the ethanol volume would increase by 14%, and surplus energy would be increased by 64% of that expected for total bagasse burning.