Ethanol and Sugar Production from Sugarcane

The process under analysis comprises four major sections: (1) Pretreatment; (2) Sugar Production; (3) Fermentation; and (4) Distillation.

Pretreatment. The sugarcane is milled to extract its juice. The sugarcane bagasse – solid residue from the milling – is directed to a cogeneration unit, where it is burned for steam and electricity generation. The juice is neutralized with lime in an agitated vessel and sent for clarification in a flocculator and decanter. The resulting clarified juice has a part sent to the evaporation process for raw sugar production, while the other part undergoes the fermentation process for Ethanol production.

Sugar Production. Treated cane juice is sent to multiple-effect evaporators to adjust the sugar concentration before crystallization. The concentrated cane juice goes through vacuum calandrias, cooling crystallizers, and centrifuges, producing two final streams: raw sugar and molasses. The raw sugar is dried and then stored in a warehouse, while molasses is filtered and sent as a substrate for fermentation process aimed at Ethanol production.

Fermentation. The molasses and treated cane juice are directed to the parallel batch fermenters, where the sugar will be fermented to produce Ethanol by adding yeast in a controlled temperature. The gases obtained in fermenters, mainly containing carbon dioxide, are sent to a scrubber to recover Ethanol. To separate the yeast biomass from the broth, centrifuges are used, and the recovered yeast returns to the fermenters after an acid treatment.

Distillation. At the end of fermentation, the concentration of Ethanol in the wine is about 10 vol%. To achieve the desired 93 wt% Ethanol, the wine passes through a concentration column, where most of water is separated by the bottom. An Ethanol/water mixture is withdrawn as a side stream. The Ethanol stream is then conducted to a rectifying column where Hydrous Ethanol (93 wt%) is obtained as distillate.