Otimização multiobjetivo da produção integrada de etanol de primeira e segunda geração e energia elétrica : aspectos ambientais e de processo
Abstract
Currently there is a growing increase in fuel consumption, but also an increased concern
about the end of fossil fuels and their environmental damage. In this scenario, secondgeneration
ethanol (E2G), produced from sugarcane bagasse, appears as an option to
increase the production of first generation ethanol (E1G), produced from sugarcane. The
aim of this study was to evaluate the production of ethanol, the generation of electricity,
CO2 emissions and vinasse into an E1G and E2G autonomous distillery through multiobjective
optimization. This assessment has been formulated in terms of multi-objective
optimization problems in virtual biorefinery modeled in EMSO (Environment for
Modeling, Simulation and Optimization). The modeling of closed water circuits, CO2
production in the boiler and in the fermenter, and the process of concentrating the juice
and vinasse streams through multiple-effect evaporators, and the multiobjective
optimization involving the production of E2G, electric energy and production of CO2 and
vinasse were performed. The modeled biorefinery processes 500,000 kg/h of sugarcane
and burns, in addition to bagasse, 35,000 kg/h of sugarcane straw. The multiple effect
evaporators for the broth concentration generated savings of around 18% in turbine
backpressure exhaust steam when compared to a process with a single effect. The
concentration of the vinasse through multiple-effect evaporators can cause a reduction in
flow rate of more than 70%. The obtained non-dominated solutions in multiobjective
optimization studies have shown a relationship among the production of ethanol, vinasse,
energy and CO2 as a function of the decision variables: bagasse fraction diverted to
produce E2G, and fraction of vinasse concentrated in multiple effect evaporators. Nondominated
solutions are in the bagasse fraction range from 0.01% to 50.09%, and vinasse
fraction comprises values greater than 14.09%. Among the solutions, ethanol flow was
between 35,730 kg/h and 41,633 kg/h. CO2 production can reach values above 187,000
kg/h considering the CO2 released in the fermenters and in the boiler. On the issue of
electricity generation, values above 83,000 kW can be reached. The results showed that
the methodology used was efficient and the proposed objectives have been met.