Análise termodinâmica do uso adicional do palhiço da cana-de-açúcar à queima do bagaço no sistema de cogeração de uma usina sucroenergética

Abstract

In a reality of potential energy crisis in the country and search for sustainable alternatives in the generation of energy, bioelectricity emerges as an important solution for this market and has as highlight the sugar-alcohol sector. Sugarcane straw appears as an additional energy potential of biomass fuel in addition to the traditional use of bagasse in power cogeneration plants, due to the current environmental policies applied to the sugar-alcohol sector, which propose the prohibition of the practice of burning of the cane fields and result in tons of this biomass left in the field during harvesting. In this context, this work proposes a thermodynamic research study aiming at the use of sugarcane straw in the generation of surplus electric energy in a sugarcane plant installed and operating in the city of Dourados, MS, based on data from productivity of the 2016/2017 crop. In the analysis the thermodynamic properties were maintained for each control volume delimited, as well as the thermal demand of the industrial process and the internal consumption of electric power of the plant. The results point to a 130% increase in the generation of surplus electric energy with the insertion of burning of the straw to the bagasse in the steam generation cycle when compared to the current plant. However, there was a considerable reduction in overall cycle efficiency by the First Law of Thermodynamics as a function of the large condensate flow in the extraction-condensation turbine. The greatest irreversibilities in the cogeneration system configurations are evidenced in the boilers, whereby losses occur from the release of heat by the fuel in the combustion process. Evaluating the overall efficiency of the cycle by the Second Law, the proposed configuration presented a better use of the maximum available exergy potential of the fuels.