Marcelo Echegaray

Exergy Analyses of Onion Drying by Convection: Influence of Dryer Parameters on Performance

This research work is concerned in the exergy analysis of the continuous-convection drying of onion. The influence of temperature and air velocity was studied in terms of exergy parameters. The energy and exergy balances were carried out taking into account the onion drying chamber. Its behavior was analyzed based on exergy efficiency, exergy loss rate, exergetic improvement potential rate, and sustainability index. The exergy loss rates increase with the temperature and air velocity augmentation. Exergy loss rate is influenced by the drying air temperatures and velocities because the overall heat transfer coefficient varies with these operation conditions. On the other hand, the exergy efficiency increases with the air velocity augmentation. This behavior is due to the energy utilization was improved because the most amount of supplied energy was utilized for the moisture evaporation. However, the exergy efficiency decreases with the temperature augmentation due to the free moisture being lower, then, the moisture begins diffusing from the internal structure to the surface. The exergetic improvement potential rate values show that the exergy efficiency of onion drying process can be ameliorated. The sustainability index of the drying chamber varied from 1.9 to 5.1. To reduce the process environmental impact, the parameters must be modified in order to ameliorate the exergy efficiency of the process.

Pyrolysis and Combustion of Regional Agro-Industrial Wastes: Thermal Behavior and Kinetic Parameters Comparison

ABSTRACT The thermal decomposition of six regional agro-industrial wastes under inert and oxidative atmosphere at different heating rates was studied using thermogravimetric analysis. The kinetic parameters were calculated using the DAEM (distributed activation energy model) and FWO (Flynn–Wall–Ozawa) methods. The obtained thermogravimetric and differential thermogravimetric curves show similar shapes, considering the pyrolysis and combustion phenomena. Nevertheless, the biomass weight loss is slower and smaller under inert than oxidative atmosphere. The activation energy average values (E) in inert atmosphere for the active pyrolysis stage is about 133.90–275.57 kJ/mol and 136.51–261.10 kJ/mol for DAEM and FWO, respectively. The E average values for the devolatilization stage under oxidative atmosphere are about 104.11–125.73 kJ/mol and 108.40–128.81 kJ/mol using DAEM and FWO methods, respectively. The results calculated by FWO and DAEM methods show differences between activation energies for the same waste below 8%; thus, they were reliable and predictive in this study. The variation of E values with progressing conversion for two studied processes indicated the existence of a complex multi-step mechanism that occurs during the degradation process. Moreover, during the devolatilization stage of combustion, the lower value of E indicates that the combustion is produced in parallel to pyrolysis; the oxygen reacts with the remaining solid.

Pyrolysis kinetics of regional agro-industrial wastes using isoconversional methods

ABSTRACT The thermochemical conversion, under inert atmosphere, at high heating rate of agro-industrial wastes was studied using thermogravimetric analysis. Two reaction mechanisms were supposed: (a) The thermal solid decomposition is carried out through a single reaction; or (b) this occurs through several independent parallel reactions based on its main components. Kinetic isoconversional methods were applied to both proposed mechanisms. The best fit was obtained for the single-reaction models. Nevertheless, to study the influence of pseudocomponent decomposition in the global process, the kinetic behavior of each of them was analyzed. The R2 and D3 models represent the thermal decomposition of biomass wastes and their pseudocomponents. The first model supposes that the reactions tend at first order, and the second assumes that the diffusion is the predominant phenomenon. In all cases, the model with the best fit for the cellulose decomposition is the same for the single global reaction model. The enthalpy variations are positive, indicating that the reactions are endothermic. The entropy variations have negative values, signifying that these processes are slow. The Gibbs free energy variations exhibited positive values, revealing that the total system energy increased at the approach of the reagents and the formation of the activated complex.