Análise comparativa entre a operação convencional e a com reversão de escoamento durante a secagem de alumina em leito fixo

Abstract

When sugar is added to a hot cup of coffee, the first action, almost intuitively before drinking, is to mix the drink so that it gets evenly sweetened. When preparing a cocktail, the most important stage is shaking the drink’s different ingredients. This action of mechanically mixing is very common. In larger scale, chemical reactors also adopt mechanical mixing systems to homogenize the processed material, ensuring uniformity to both the properties and the quality of the final product. In applications involving fixed bed, however, it is impossible to use mechanical mixers, due to the equipment’s nature. Instead, an alternative is to change the direction of the air flow from time to time. The bed’s homogenization during the drying process may be essential in some applications. The existence of significant internal gradients of moisture and temperature alike may make it unfeasible to use this kind of dryer depending on the application. In other words, this unwanted nonuniformity may result not only in a final product below the quality standards but also significant losses in subsequent operations. This happens, for example, in coffee processing during the roasting stage, in which beans with high moisture content may not pyrolyze and those with low humidity may roast. In this context, the objective of this work was to analyze the reduction of internal gradients during thick fixed bed alumina drying with the reversal technic, when compared to results that would be attained in the conventional operation. Numerical assays were carried out in MatLab® with a script developed by Particulate Systems Research Group of DEQ/UFSCar. The simulation results showed the effectiveness of the airflow reversal technique that allowed the reduction of moisture and temperature gradients of alumina.