Desenvolvimento de um secador tipo esteira circular assistido por aquecimento infravermelho para a secagem de bagaço de cana-de-açúcar

Abstract

Aiming to offer an alternative and efficient technology for drying biomass, an infrared IR) heating assisted-conveyor belt dryer was developed in this work. The initial stage of the project consisted in the identification of needs and analysis of possible configurations. After selecting the best setting, the project was detailed, through the mechanical e electrical dimensioning as well as of the suitable instrumentation for drying applications. Then, construction, assembly and operation of the prototype were carefully carried out. To evaluate the performance of the conveyor belt dryer an experimental study on the drying of sugarcane bagasse was conducted, since the process of moisture removal is essential to increase the energy potential of the aforementioned biomass. The bagasse of sugarcane (Saccharum Officinarum), final residue of sugarcane juice withdrawal, is one of the most used biomass raw materials in Brazil to produce energy. Samples of sugarcane bagasse with initial moisture content of 64,9 ± 0,5% w.t. were prepared and physically characterized. The thin-layer drying was conducted at IV source temperatures of 300, 400 e 500°C and conveyor belt speeds of 2,0, 3,5 e 5,0 rpm. Drying testes were also performed with the conveyor belt under static condition. During the drying process changes in the moisture content and temperature of the bagasse over time were evaluated, in order to study the kinetic behavior of the process. Its energy consumption was also measured. For a belt velocity of 2,0 rpm the time required for the sugarcane bagasse to reach a moisture content of, approximately, 0,05 at dry basis (d.b.),was 274, 154, and 90 min at temperatures of 300, 400 and 500°C, respectively. For the velocities of 3,5 and 5,0 rpm there were no significant differences in the obtained times. With the stationary belt it was found that the time required to reach a moisture content o 0.05 d.b. was approximately 116, 60 and 44 min, at temperatures of 300, 400 and 500°C, respectively. The values obtained for the effective moisture diffusivity ranged from 3,959x10- 11 to 4,012x10-10 m 2 /s. Five semiempirical equations were evaluated to represent the thin layer drying. The Midilli model was found to be the most suitable for describing the IR drying kinetics of sugarcane bagasse, presenting the best goodness-of-fit. From the analysis of variance (ANOVA) and the Pareto diagram with significance level of 5%, it was found that the only significant effect was the linear temperature term. The specific energy consumption ranged from 0,062 to 0,147 kWh/g of water. The highest efficiency for the moving belt was 35,93%, at the IV source temperature of 500°C and the conveyor belt speed of 2,0 rpm. Based on the results, the designed dryer was shown to be promising for the drying of sugarcane bagasse.