Exergetic Analysis of the Biodiesel Production Process in a Biofuel Plant

This paper deals with the exergy analysis of the biodiesel production process from the binary mixture of soybean oil and beef tallow. The biodiesel is produced by transesterification of the methyl group and through basic catalysis. Thus, it was investigated the biofuel production process of a specific plant in the State of Minas Gerais, Brazil, characterizing the parameters of the main equipment and analyzing the raw material and by-products of the process and quantifying the mass and energy. The exergy analysis methodology followed the mass balance of each step, calculating irreversibility and exergetic balance and efficiency of the plant. The calculation of chemical exergy of the compounds of biomass from soybean oil and beef tallow, biodiesel, glycerol and free fatty acids was accomplished by raising the calorific value of the compounds by their chemical composition and mass percentage. Moreover, they were also calculated the specific irreversibility of methanol and process inputs, the irreversibility concerning electricity, mechanical work and steam. It was found that the useful exergy was 63.4%, however, considering that the glycerin can be sold as a final product and that some raw materials can be reused, the useful exergy of the system could be equal to 94.2%. The exergy efficiency of the plant is 71.7%, due to the irreversibility of the system. The exergy destroyed was 5.8% and could be minimized by changing variables such as temperature, reaction time and type of catalyst.