Marcos A.S. Barrozo

A study of particle motion in rotary dryer

The purpose of this work was to study the performance of a rotary dryer in relation to number of flights. In this work an equationing was proposed to calculate the area used by the solids in two-segment flights of with any angle between the segments. From this area, the flight holdup and the length of fall of the particles were calculated for different angle positions and the results obtained were compared to experimental values. The results show an increase in dryer efficiency with the increase in number of flights up to a limit value, for ideal operational conditions. The experimental data on average residence time were compared to results obtained by calculations using equations proposed in the literature. The equation proposed for predicting flight holdup and length of fall of particles generated very accurate estimations.

Effect of a Draft Tube on the Fluid Dynamics of a Spouted Bed: Experimental and CFD Studies

Knowledge about the gas and particle dynamics in spouted beds is important in the evaluation of particle circulation rates and the efficiency of gas-solid contacts. In this work, the mechanism of transition from a static bed to a spouted bed was numerically simulated using a Eulerian multiphase model. This model was applied to two distinct spouted bed geometries: a conventional device and a spouted bed with draft tube. The radial voidage and particle velocity profiles along the longitudinal position in the annular and spout regions were simulated for the geometries under study. The characteristic simulated curves were congruous with the experimental data.

A study of the fluid dynamics of the spouted bed using CFD

The spouted bed has been used in drying, granulation, catalytic polymerization, residue treatment and coating of several materials. Its success is attributed to its solids circulation characteristics and excellent gas-particle contact. In this work the pattern of solids and gas flows in a spouted bed was numerically simulated using a Eulerian multiphase model. The computational work was significantly reduced for axisymmetric gas-solids flows. The simulated velocity and voidage profiles were compared with results obtained in our laboratory (with a two-dimensional spouted bed using soybean seed) and by He et al. (1994) (with a cylindrical spouted bed and glass sphere). The simulated results showed good agreement with the experimental data for both geometries studied.

Modeling of Seed Coating in a Spouted Bed

In this work, a model based on population balance equations applied to perfect mixture domains has been employed to represent the coating of soybeans with fertilizer in a conical–cylindrical spouted bed. The results of the present model provided explicit equations for the coating mean and variance. The coating mass distribution function was validated against experimental data. The effect of operational time on the distributions was analyzed, showing that the coating uniformity can be improved by increasing the operating time.

Modeling of Fertilizer Drying in Roto-Aerated and Conventional Rotary Dryers

Conventional rotary dryers are equipped with flights placed parallel along the length of the shell to promote a rain of solids across the dryer section. In the roto-aerated dryer the hot air flows through the particles that run on the bottom of the drum through a series of mini-pipes and there is no cascading. This study analyzed heat and mass transfer modeling between the air and the fertilizer particles in conventional rotary and roto-aerated dryers, as well as the simulation results with the experimental data. A good agreement between the simulated and experimental results was obtained for the two rotary dryer configurations analyzed.

Experimental study and simulation of mass distribution of the covering layer of soybean seeds coated in a spouted bed

In previous work, it was observed that the covering of soybean seeds with bacteria and micronutrients enhances vigorous growth of the plant thereby avoiding use of ammoniacal fertilizers. In the spouted bed covering can be done by pulverization of the coater slurry on the soybean seeds using a pneumatic atomizer. The optimum thickness of the cover allows the fundamental gaseous interchanges for germination and provides the ideal conditions for bacterium activity. The objective of this work was to study the influence of the process variables on thickness of the cover. A simulation of the mass distribution of seeds was obtained using a population balance model. Through the results obtained the operational conditions under which the coating layer distribution were determined has the greatest uniformity.

Modeling and experimental study of hydrodynamic and drying characteristics of an industrial rotary dryer

The purpose of this work was to analyze the hydrodynamic and drying aspects of a rotary dryer used in a fertilizer industry. A set of equations to predict the solids holdup in the flights, the length of fall, the residence time of particles and the drying variables was evaluated by comparison to experimental measurements performed in an industrial rotary dryer of the Copebras Fertilizer Company, located in Catalao, state of Goias, Center-west of Brazil. Because of precise estimations, these equations may be used to design and predict the solids cascading behavior in industrial rotary dryers. Despite larger deviations, reaching 20%, the drying model can also be used for design calculations and process simulations.

Performance analysis and design of filtering hydrocyclones

The filtering hydrocyclone is a solid-liquid separation device patented by the Chemical Engineering Department at the Federal University of Uberlândia, which consists of a hydrocyclone whose conical section was replaced by a conical filtering wall. The objective of this work is to compare the performances of the filtering hydrocyclones designed by Bradley and by Rietema. The experimental results obtained with the filtering hydrocyclones under the same operational conditions as those used with the conventional device allow the conclusion that performance of the Bradley and Rietema types is significantly influenced by the filtering medium. Rietemas filtering hydrocyclones had a lower volumetric feed flowrate than the conventional device and Bradleys filtering hydrocyclones showed increases in this same variable. In both designs, overall efficiency was influenced by the underflow-to-throughput ratio.

Analysis of the influence of the filtering medium on the behaviour of the filtering hydrocyclone

Abstract The filtering hydrocyclone is a solid–liquid separation device patented by the Chemical Engineering Department of the Federal University of Uberlândia [M.A.S. Barrozo, J.J.R. Damasceno, Brazilian Patent No. 9001889, 1991.], which consists of a Bradleys cyclone whose conical section was replaced by a conical filtering wall. The objective of this work was to investigate the effects provoked by three different filtering media on the performance of that equipment. Within the limits of the region investigated — pressure drops in the range 88260–205940 N m−2 — these filtering hydrocyclones were compared to the conventional Bradleys hydrocyclone and displayed increases in both feed flowrates and reduced cut sizes. A dependence of the underflow-to-throughput ratios on the filtering medium resistance was also registered. Based on the experimental results, an explanatory mechanism for the phenomena observed as well as design equations accounting for the influence of the filtering medium resistance have been proposed, allowing the prediction of the performance of filtering hydrocyclones and providing a new alternative in terms of solid–liquid separation devices.

BAGASSE PYROLYSIS: A COMPARATIVE STUDY OF KINETIC MODELS

Thermogravimetric analysis was made of slow sugarcane bagasse pyrolysis. Several models of primary decomposition were tested and compared. Kinetic parameters were estimated using nonlinear regression and the differential evolution method. A one-step reaction model with first-order and n-order kinetics, a consecutive reaction model, and an independent parallel reaction model were employed in the modeling. The results show that the one-step model does not accurately represent the data of weight loss (TG) and its derivative (DTG). The consecutive reaction model yielded the expected activation energy results for the first two peaks corresponding to hemicellulose and cellulose, but inaccurate results for lignin. The independent parallel reaction model yielded the best results for the three subcomponents. The mass fraction of each subcomponent was estimated by the three independent parallel reaction models, showing values consistent with those reported in the literature.