Análise da modelagem, simulação e otimização da secagem em leito deslizante com escoamentos paralelos

Abstract

The Brazilian soybean production increases every year, and its stored in safe places so as to meet future demands, or unsuccessful crops. The drying process must reduce the moisture content and maintain the physical and physiological qualities (seeds fissures, germination and vigor), especially when the objetive is to replant. The technique of sliding bed proves to be a safe alternative for the maintenance of seed quality and reduction of moisture in less time. The literature presents several studies on differents configurations of flow between the solid and fluid, and the operating variables that influence the quality of soybean seeds. Empirical functions are used to represent the germination, vigor and non-fissured seeds indices as functions of drying variables, which are: the interstitial air velocity, inlet air inlet temperature, solids flow rate and inlet relative humidity. Another method to reduce the damage on the soybean seed is to divide the bed of the dryer in stages, generating a multi-stage dryer. The mathematical model that describes the transfer of mass and energy in sliding bed dryers are widely reported in the literature. Associated with this model, the equations of the quality indices, in addition to the constitutive equations for the coefficient of heat transfer between the two phases, the drying kinetics and equilibrium moisture content in the solid material. The modeling and simulation of the models presented in the literature need to be better studied. To this end, this thesis examine the modeling, simulation and optimization of energy and mass transfer between air and soybean seeds in parallel flow sliding bed, searching for satisfactory conditions that promote the maintenance of seed quality and better removal rates moisture. In addition, the modeling sought to improve the agreement between the models used and the experimental data obtained in the literature. The mathematical model generated five general models, which proposed the change in physicochemical properties (Cpf , Cpv, Cpl and Cps) constants or not, variation of the porosity of the bed and the velocity profile, and these have provided important data for the analysis of the drying model. According to the simulations, the results showed agreement in relation to those models that considered the property of the solid specific heat (Cps) constant. This property was represented by an equation that was a function of moisture from the solids, whereas other properties were explicit functions of temperature. Overall, it was observed that the physico-chemical profile and porosity influence the velocity profiles of humidity and temperature of the solid and fluid for all experiments, confirming that the assumptions made in each model generates significant changes in drying results. The computational fluid dynamics proved to be of great help to verify the effect of wall profiles of porosity and fluid velocity, confirming that the assumption of flat velocity profile of fluid phase in twophase model is not valid in the range of air analysis. Regarding the study of the quality of soybean seeds, and index of germination, vigor and seeds without cracking and drying performance, it was observed that the strategy to transform a conventional sliding bed dryer on a multi-stage dryer is proved quite satisfactory in relation to the elevation of the potential for drying and maintaining the quality of seeds. The study of optimization of the dryer through the technique of Differential Evolution, obtained optimum operational conditions that maximize the quality indices or the removal of moisture. Thus, this thesis has generated data from simulation and optimization that can be used to improve the models already presented in the literature and thus provide for the construction and improvement of dryers, and optimal experimental conditions to study the sliding bed drying.