Evaporation of Vinasse - Pilot Plant Investigation and Preliminary Process Design

Abstract

The large dependency of fossil fuel have made alternative fuel e.g. ethanol increasingly popular. However, very little research and few publications were found on the after-treatment of the effluent, named vinasse, from the sugar-cane based ethanol production. The vinasse is produced in large quantities, because of the high volume ratio 1:10-15 of ethanol to vinasse and has been labelled an increasing environmental problem in South America. In a new proposed treatment process for vinasse, evaporation is used to concentrate the vinasse to be able to combust it in a boiler. In this thesis an experimental investigation was conducted on a pilot plant on the evaporation of vinasse. It was found possible to evaporate vinasse to a high dry solid content of at least 70 %. A critical region of particle accumulation and fouling tendencies were established. The most important physical parameters, dry solid content, viscosity, boiling point elevation and the heat transfer coefficient, were closely monitored and assessed in the experiments. For some of the properties, correlations were established as a function of dry solid content and temperature. The heat transfer was tested on a general model used in falling film evaporation, which was proven to not be valid for vinasse. However, a correlation for the heat transfer was developed. Since vinasse’s chemical composition resembles black liquor, these two were compared in this work and it was found that vinasse has lower viscosity and boiling point elevation at the same dry solids content. Thus, the results of the physical properties show that vinasse has better heat transfer and heat economy than black liquor. Based on the results from the experiments, a preliminary process design of the evaporation plant was established.