Analysis of the Thermal Exploitation of the Vinasse from Sugarcane Ethanol Production through Different Configurations of an Organic Rankine Cycle

Abstract

The search for a reduction of the dependence on fossil fuels has made the use of low temperature thermal sources attractive to many companies that have chosen to install recovery systems to generate electricity. In Brazil, the main solution found for the disposal of vinasse, which is a liquid residue of the ethanol production process, is fertigation, but there are restrictions of dosages in the crop. The biodigestion of vinasse is also shown as an alternative, being a process of generating energy from the biogas produced. Despite presenting a wide range of benefits, the biogas production costs are not yet covered by the prices charged by the electric power concessionaires. The temperature of vinasse leaving the distillation is around 100 °C, and this residual heat can be used to produce electricity through an Organic Rankine Cycle (ORC). One of the major challenges in designing an ORC is the proper choice of working fluid for the operation. Although there are many options available for work fluids, there are also many restrictions in its selection. Thus, the main objective of this work is the study of the thermodynamic properties of the application of three different organic fluids (R22, R227ea and R124) in two configurations of the ORC for the utilization of residual heat from the vinasse resulting from the sugarcane ethanol production process, as well as the gain of power inserted to the power generation in a traditional Rankine Cycle used in sugarcane power plants. In general, the isentropic fluid R124 has an advantage among the other fluids for both of the configurations studied.