Dimensionamento, construção e avaliação de um secador de leito fluidizado para secagem de produtos vegetais

Abstract

Drying equipment designed for agricultural products, known as dryers, are built in different models, airflows and operating modes, aiming at process efficiency and maintaining product quality during and after drying. Fluidized bed drying has been highlighted due to the good contact between gas-solid, attractive costs and high rates of particle recirculation, heat and mass transfer, and also as an alternative potential for compact and efficient equipment for drying. The objective was to design, build and evaluate a fluidized bed dryer regarding its efficiency in the yield and drying time of vegetable chips, as well as to determine and model the drying kinetics of sweet potato chips at different slice thicknesses and temperatures. Drying process and fit the best mathematical model that represents the behavior of the experimental data. The relevant design parameters for the fluidized bed dryer sizing were determined, such as chip sphericity, minimum fluidization velocity, terminal velocity, optimal velocity, bed volume and area, bed pressure drop, distributor pressure drop, orifice fluid velocity and number of orifices. After assembling all the necessary parts and equipment, the chips were dried. The experiment was carried out in a completely randomized design (DIC) in a 2x4 factorial scheme (slice thickness x drying temperature), with three replications. The slice thicknesses evaluated were 0.0012 and 0.0024 m and the drying temperatures 40, 50, 60 and 70 ±1 °C. The mathematical models tested to predict drying kinetics were: Diffusion Approximation, Two-Term, Two-Term Exponential, Henderson and Pabis, Henderson and Modified Pabis, Logarithmic, Midilli, Newton, Page, Thompson and Verma. The mathematical modeling was developed in Statistica 12.0 software. The evaluation tests of the prototype of a fluidized bed dryer for drying sweet potato chips showed that its use is advantageous and promising. Among the mathematical models analyzed, the modified Henderson and Pabis model presented the best statistical fit to the experimental data of drying kinetics under the conditions evaluated. For drying sweet potato chips, it can be concluded that this process is feasible at the temperatures studied, the drying time being inversely proportional to the temperature. The thickness of the slices is a determining factor in reducing the drying time of sweet potato chips regardless of the temperature analyzed, and the thickness of 0.0012 m promoted a drying of the product with a shorter period of time. The best combination of variables obtained by factorial design for drying sweet potato chips in a fluidized bed dryer is with a temperature of 70°C and a slice thickness of 0.0012 m.