New alternatives for the fermentation process in the ethanol production from sugarcane:extractive and low temperature fermentation

摘要

Ethanol is produced in large scale from sugarcane in Brazil by fermentation of sugars and distillation.This is currently considered the most efficient biofuel technology,leading to significant reduction on greenhouse gases emissions.However,some improvements in the process can be introduced in order to reduce the steam consumption.In current distilleries,a significant fraction of the energy consumption occurs in the purification step – distillation and dehydration-since conventional fermentation systems employed in the industry require low substrate concentration,thus producing wine with low ethanol content(around 8.5 °GL),which must be distilled,consequently with high energy consumption.In this study,alternatives to the conventional fermentation processes employed in the industry are assessed,in the context of a large scale sugarcane autonomous distillery,through computer simulation.These new alternatives are: low temperature fermentation and vacuum extractive fermentation.The aim of this study is to assess the incorporation of these alternative fermentation processes,evaluating the impacts in ethanol production,energy consumption and surplus electricity produced in the cogeneration system.Simulations of the complete ethanol production process,including these alternative technologies were carried out using the Aspen Plus software.Several cases were evaluated,taking into account different cooling technologies,which include vapour compression refrigeration systems and absorption refrigeration systems.A thermal integration technique was applied.Results shown that the ethanol production increases between 3.3％and 4.8％and a reduction in steam consumption of up to 36％.About the surplus electricity,the reduction in steam consumption promotes a reduction in surplus electricity when a steam cycle with backpressure steam turbines is adopted,however,a surplus electricity of 85 kWh/t of cane can be achieved when condensing – extracting steam turbines are used.