Desempenho da primeira e segunda lei da termodinâmica para o processo de desidratação de etanol: configurações convencionais e alternativas.

Abstract

This work investigates and compares four distillation configurations for the production of anhydrous ethanol. There are two conventional systems and two thermally coupled to a side rectifier, where the difference between each pair is the inclusion of a third separation column (concentrator). In order to verify which configuration is more efficient and with less energy demand, the first and second laws of thermodynamics were applied in order to carry out the energy and availability balance, respectively. In this way, the quantity and quality of the energy used were counted, in addition to the identification of the sources of irreversibilities of the processes. We compared the profiles of the availability balance (lost work, equivalent work and thermodynamic efficiency) and energy consumption for the four optimized systems with and without thermal integration. The analysis of thermodynamic efficiency according to the 2nd law was performed for the global process. The results suggest that the conventional configuration with three columns and thermal integration is the most exergetically sustainable process for the production of anhydrous ethanol. The thermally coupled configuration with two columns is the one with the lowest energy consumption. We carried out an analysis of the profile of exergetic losses in each column of the four configurations and we found that for all cases subject to optimization, after changes in the temperature and location of the supply of certain currents, it was possible to minimize loss of exergy and energy consumption. and maximize efficiency, being possible to affirm that the trinomial loss of exergy / energy consumption / thermodynamic efficiency has a direct correlation when the analysis is made within the same configuration. The main conclusion of this work is that it is only correct to correlate efficiency of the second law and energy consumption for the global process when also taking into account the variations in the function of availability and temperature of the hot source (reboiler) when comparing different separation processes.