Projeto, construção e avaliação da performance de um secador solar híbrido para a secagem de entrecasca de mandioca

Abstract

The cassava inner bark is a starch-rich residue, which allows its application in several areas. It also has great potential for the production of biofuels, such as bio-oil, biogas or biochar. However, the proper use of this biomass is hindered due to its high moisture content, thus requiring drying as a pre-treatment operation. Despite numerous studies on the drying of different types of biomass, information regarding cassava peel is scarce in the literature. In the search for efficient drying technologies that can add value to cassava processing waste at competitive costs, solar drying emerges as a green, sustainable and economically viable technology. Within this context, the objective of this work was to construct and evaluate the performance of a solar dryer operating in active and indirect modes, as well as in a hybrid mode, where forced convection of air heated by solar energy is combined with infrared radiation (IR) for drying cassava inner bark. The performance of the dryer was analyzed in terms of the drying kinetics of the biomass and the efficiencies of the solar collector and the drying process itself. Two air velocities, 1.3 and 3.7 m/s, were used in both operating modes. In the hybrid mode, the power of the infrared radiation source was 50 W. During the experiments, solar irradiation intensity, collector temperature, air temperatures, and relative humidities along the dryer, as well as biomass mass and temperature, were measured. The collector temperature, air temperatures and relative humidities showed consistent values, following the behavior of solar irradiation. The forced airflow over a corrugated aluminum absorber plate promoted an increase in air temperature between 5.2 and 13.7°C, with the highest heating observed at 1.3 m/s, although the collector efficiency and drying rate were lower. The use of infrared radiation as an auxiliary heating source reduced drying time but increased energy consumption, leading to lower efficiency in the hybrid drying mode. Thus, in terms of cost and efficiency, the best performance of the developed solar dryer was achieved in the indirect-active mode, with an air velocity of 3.7 m/s, where a target moisture content of approximately 15% (wet basis) was reached in 260 minutes of drying, with an efficiency of 10.5%.