Estudo experimental e de simulação computacional da secagem de sementes de mamão em leito de jorro

Abstract

Papaya and Formosa are widely cultivated in Brazil for their trade as fresh fruit, production of jellies, sweets, among others. In their processing there is generation of a large amount of seeds that are discarded. When it comes to sustainable development, the use of the seeds can contribute to it, since they can have great utility in pharmaceutical, food, and cosmetic industries, coming from the oil from the seeds because they have high added value thanks to the presence of fatty acids such as oleic, linoleic, stearic, and palmitic. However, this residue may contain high humidity, which contributes to its rapid degradation and, therefore, it is important that it goes through a drying stage. This operation can be performed in a spouted bed, equipment that stands out for its high rates of mass and heat transfer that contribute to a satisfactory reduction of particle humidity. In view of the above, the objective of this work was to perform characterization of papaya seeds with and without exotest and in natura and dried, experimentally investigate the drying of this material in a pilot unit of a spouted bed. In addition to establish empirical correlation for predicting the drying rate of papaya seed as a function of air velocity and temperature parameters, find the condition that favors drying among the conditions studied and perform computer simulations to investigate the characteristics of the flow inside the bed. Firstly, the physical characterization of papaya seeds was performed by obtaining the average Sauter diameter, sphericity, bulk and loose bulk density, bulk porosity, weight of one thousand seeds, moisture and angle of repose. After that, drying experiments were performed in a jet bed, varying the temperature in 40, 50 and 64 °C and air velocity in 21, 34 and 36 m/s. Furthermore, with the aid of Computational Fluid Dynamics (CFD) techniques, simulations of the flow inside the bed were performed. As results, the fresh papaya seeds without exotest presented higher porosity, lower humidity and better handling conditions and were used in the drying studies. This seed was classified according to the degree of flowability as being of good fluidity and according to the Geldart diagram as belonging to the particulate group D. The characteristic curve of the spouted bed presented behavior consistent with the typical pattern and allowed the identification of the minimum spouting velocity and minimum pressure drop of 22 m/s and 21 Pa, respectively. The computer simulations performed were able to represent the fluid dynamics of the seeds inside the bed. However, the experimental and simulated pressure drop values were not close. In addition, it was identified that higher values of temperature and velocity provide higher drying rates. In general, a satisfactory moisture removal of the seeds was achieved within the short operation time, besides obtaining a better understanding of the drying operation in a spouted bed provided by the experimental and simulated results.