Optimization of fermenters for ethanol production: residence time analysis applying computational fluid dynamics

Abstract

The search for new ways to provide fuel for the society is a great challenge for scientists. An interesting alternative to petroleum-derived fuels is the ethanol produced from sugar cane. Brazil has an advantaged position in ethanol production, but the equipment used in the sugar cane plants, the fermenters, for example, still need efficiency improvements. The fermenter geometry has a great influence on the flow parameters and, consequently, in the chemical reactions involved in the fermentation process. It is necessary to ensure that the sugar cane juice remains enough time in the fermenter to complete the chemical reaction, but not more than the ideal time required, which can reduce the process efficiency. In this study, the influence of the geometry in the Residence Time Distribution (RTD) was analyzed by a computational tracer injection technique. Besides, twenty geometries were performed applying a univariate optimization process. Results show the inlet angle has the major influence in the flow and the optimum geometry for the continuous fermenter must have 22.5◦ for inlet angle and 120 cm for outlet tube height. Considering the fermenters large scales in sugarcane juice processing, the improvement proposed in the fermenter geometry can increase its efficiency and reduce environmental impacts.