Double-effect distillation and thermal integration applied to the ethanol production process

Abstract

A double-effect distillation system allows a significant reduction in energy consumption, since the condensers and reboilers of different columns can be integrated thermally. To achieve this goal, some columns operate under a vacuum, while others operate close to atmospheric pressure. These pressure levels bring about different temperature levels, allowing energy recovery. Thus, the aim of this study is to assess the incorporation of double-effect distillation in ethanol production, and its impact on energy consumption and electricity surplus production in the cogeneration system. Moreover, because double-effect distillation and thermal integration involve an increase in equipment costs, an economic assessment was done. Several cases were evaluated and a thermal integration technique was applied, in order to integrate the overall process. The thermal integration study showed that it is possible to integrate the juice concentration step (multiple effect evaporation system) in the overall process without additional thermal consumption, through the selection of a suitable set of pressures in the evaporation system. The results showed a reduction in steam consumption of between 17% and 54%, in comparison with the Base Case. Regarding the electricity surplus, this increased by up to 22% when extraction–condensing steam turbines were adopted.