Análise de sensibilidade paramétrica na modelagem da secagem de fertilizantes em secador rotatório

Abstract

Due to its high performance and great processing capacity, the rotary dryer has an important role in drying processes of various products. The rotary dryer is based in a cylindrical drum, slightly inclined in relation to the horizontal line that rotates in slow speed. The inner side of drum is equipped with flights that collect the solids on the bottom of the drum and are transported to an angular position where they fall as a raining curtain through a hot air stream. The modeling of the process was carried out by application of the mass and energy conservation equations to the fluid and particulate phases in infinitesimal element of volume of dryer. In a previous work at the Chemical Engineering School of the Federal University of Uberlândia-MG, it was developed a new model to describe the distributions of air s and fertilizer s humidity and temperature throughout the dryer, being validated with experimental data for granulated single superphosphate (SSPG). The comparison of results obtained from the model proposed by ARRUDA (2008) demonstrated a good agreement with the experimental data obtained from a small scale unit (diameter 0.3m and length 1.5m). However, the model proposed by ARRUDA (2008) demonstrated significant deviation when compared to experimental results obtained by FERNANDES (2008) in an industrial scale dryer (diameter 3.0m and length 30m), although these deviations were probably caused by measurements imprecision, false air (losses) assumptions and/or potential different behavior between the material used by ARRUDA (2008) and the one used by FERNANDES (2008). Aiming to improve the model s predictability, the main objective of this work was to analyze the influence of the following parameters: heat transfer coefficient, material drying rate and solid and air specific heat, through parametric sensitivity study using experimental design evaluated for solid moisture and temperature and air humidity and temperature responses, obtained by fertilizers drying model in rotary dryers countercurrent proposed by ARRUDA (2008). The variance analysis together with the surface plots demonstrated that each studied parameters has a statistic result, although in some results were observed a strong influence that features an important meaning in physical terms. The results obtained from the parametric analysis demonstrate the importance of knowing the most significant parameters in order to describe them accurately, which will contribute to aim in depth knowledge about the drying process enabling efficiency increase on already existent equipment and more accuracy on projects of new equipment.