Hydrocyclones belong to an important group of equipments designed to solid-liquid or liquid-liquid separation in a centrifugal field. It is possible to adapt a hydrocyclone to the accomplishment of several industrial activities depending on the geometrical relations among its main dimensions. The operation and design of these devices are relatively simple; however, the flow inside them is very complex and its prediction is very difficult. For that reason, most models that are used to predict hydrocyclone performance are empirical ones. The objective of this work was to study the influence of geometric variables in the performance of hydrocyclones, using CFD and response surface techniques. The obtained results show that it was possible to find an optimum hydrocyclone design, that is, geometric relationships that lead to Euler number and cut size in minimum levels.Les hdrocyclones appartiennentà un groupe important d'équipements conçus pour la séparation solide-liquide ou liquide-liquide dans un champ centrifuge. Il est possible d'adapter un hydrocycloneà la réalisation de plusieurs activités industrielles selon les relations géométriques dans ses dimensions principales. Le fonctionnement et la conception de ces dispositifs sont relativement simples; cependant, leur circulation interne est très complexe et sa prédiction est très difficile. Pour cette raison, la plupart des modèles utilisés pour prédire le rendement des hydrocyclones sont des modèles empiriques. L'objectif de ce travailétait d'étudier l'influence des variables géométriques sur le rendement des hydrocyclones en utilisant une DFN et des techniques de surface de réponse. Les résultats obtenus indiquent qu'ilétait possible de trouver une conception d'hydrocyclones optimale, c.-à-d. les relations géométriques qui mènent au nombre d'Euler età la mesure fixeà des niveaux minimaux.
The present work analyzed aspects of the fluid dynamics of the conventional concurrent dryer equipped with lifting flights and their influence on the performance of a rotary dryer. The drying of granulated fertilizers (GTSP) in a conventional concurrent rotary dryer was experimentally investigated and compared with a modified configuration known as the roto-aerated dryer. The main feature of this new dryer is the presence of an aerated system consisting of a central pipe (encased in the drum) from which a series of mini-pipes lead hot air directly to the particle bed, flowing at the bottom (without flights). The results obtained confirm the superior performance of the roto-aerated dryer due to its more effective gas-particle contact.
Some fluid-dynamics aspects of a rotary dryer, operating with granular single superphosphate, were investigated experimentally and by coupled discrete element model–computational fluid dynamics (DEM–CFD) simulations. The experimental data of flight holdup and dynamic angle of repose in the upper half flights, at different angular positions, were successfully used to identify the best set of parameters for the spring–dashpot model used in DEM simulations. The smallest deviations from the experimental data were obtained in the simulation whose parameters values were elastic constant k = 400 N/m, friction coefficient μ f = 0.2, and restitution coefficient η = 0.2. The results have shown that the coupled DEM–CFD approach with the selected parameters has been suitable to predict the fluid dynamics behavior of the rotary dryer operating with granular single superphosphate.
In view of the constant search for new sources of renewable energy, the particulate agro-industrial waste reuse emerges as an advantageous alternative. However, despite the advantages of using the biomass as an energy source, there is still strong resistance as the large-scale replacement of petroleum products due to the lack of scientifically proven efficient conversion technologies. In this context, the pyrolysis is presented as one of the most widely used thermal decomposition processes. The knowledge of aspects of chemical kinetics, thermodynamics these will, heat and mass transfer, are so important, since influence the quality of the product. This paper presents a kinetic study of slow pyrolysis of coffee grounds waste from dynamic thermogravimetric experiments (TG), using different powder catalysts. The primary thermal decomposition was described by the one-step reaction model, which considers a single global reaction. The kinetic parameters were estimated using nonlinear regression and the differential evolution method. The coffee ground waste was dried at 105°C for 24 hours. The sample in nature was analyzed at different heating rates, being 10, 15, 20, 30 and 50 K/min. In the catalytic pyrolysis, about 5% (w/w) of catalyst were added to the sample, at a heating rate of 30 K/min. The results show that the one-step model does not accurately represent the data of weight loss (TG) and its derivative (DTG), but can do an estimative of the activation energy reaction, and can show the differences caused by the catalysts. Although no one can say anything about the products formed with the addition of the catalyst, it would be necessary to micro-pyrolysis analysis, we can say the influence of the catalyst in the samples, based on the data obtained in thermogravimetric tests.
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