Ethanol production from sugar cane: Comparison of juice cane extractions systems - Mill and diffuser - Through exergetic cost analysis

The sugar and ethanol production is one of the most important economical activities in Brazil, mainly due its high efficiency and competitiveness. The ethanol production is done by several steps: juice extraction, treatment, fermentation and distillation. The juice extraction and treatment is a common operation of both industries sugar and alcohol. The process begins with the sugar cane juice extraction, usually done by devices namely mills, where the cane is compressed between big cylinders for the separation of the juice from the bagasse. Recently, another juice extraction system named diffuser was introduced in some sugar and alcohol factories. On diffusers, after sugar cane preparation stage, done with knives and shredders, it passes through a bed, where the juice is separated from bagasse by the addition of imbibition water and steam, in a lixiviation process. This study evaluates these two juice extraction systems, performing an exergetic cost analysis. The total production plant is treated, considering the most important process sections: cogeneration, extraction and distillation and their products: electric energy, cane juice and hydrated ethanol, respectively. The results of exergetic efficiency, irreversibility generation and unitary exergetic cost of products are analyzed and compared.