Características de fluidização de misturas binárias contendo casca residual de mandioca e areia

Abstract

The better management of natural resources has become a global agenda and in recent years there is a global trend towards an increase in the use of renewable energy sources. In this context, the conversion of biomass into energy has grown in importance, in order to replace the demand for fossil fuels, as well as to diversify energy sources. Cassava (Manihot esculenta Crantz) is one of the most prominent temporary crops in Brazil, with more than 18.1 million tons produced in 2021. All this productivity generates waste that most often does not have proper disposal. Among solid residues, the cassava peel represents a valuable source of biomass for the production of bioenergy due to its lignocellulosic characteristics. Fluidized bed technology appears as a potential alternative, both for drying as biomass pre-treatment, in order to reduce its high moisture content, and for thermochemical conversion processes. This technology, by promoting an intense mixing between the particles and the fluid, intensifies the rates of heat and mass transfer, and of conversion. To assist in the fluidization of different biomasses, inert particles have been commonly used. Therefore, given the scarcity of information in the literature on the application of the fluidized bed technique for the processing of residual cassava husk, the objective of this work was to investigate the fluid dynamic behavior of single components and binary mixtures containing biomass particles from cassava peel and sand particles in fluidized bed. The fluid dynamic tests were carried out in a typical fluidized bed with air at room temperature, binary mixtures of 1.29 mm biomass with sand of 1.29 mm and 0.93 mm, following a 33 factorial design, in order to evaluate the effects of the bed aspect ratio L/D (1, 1.5 and 2), of the volumetric fraction (25%, 50% and 75%) and of the moisture content of the biomass (10%, 42.5% and 75% b.u.), in addition to influence of the inert particle diameter on the fluidization parameters. Pressure drop and velocity data were measured using an U-tube differential manometer and an anemometer, respectively. The results for the binary mixtures showed that the bed aspect ratio influenced the behavior of the incipient and complete fluidization velocities. The moisture of the particles significantly affected all velocities, including the minimum fluidization, mainly as the volumetric proportion of biomass and the bed aspect ratio increased. The proportion of biomass affected moist and dried biomass in different ways and the velocities generally increased for the larger diameter inert. The slugging phenomenon seen for pure biomass beds did not occur with the binary mixtures, indicating an improvement in the fluidization quality of the mixture with the use of sand as inert, in line with the angle of repose data obtained. Based on the fluid dynamic analysis carried out, the most suitable operating conditions to obtain greater fluidization quality and stability, both for drying the wet cassava peel (75% b.u.) and for the thermochemical conversion processes of the dehydrated biomass (10% b.u.), were those using the binary mixture with the sand having the smallest particle diameter (0.93 mm), with 75% volumetric fraction of biomass and L/D ratio of 1.5. For perspectives of studies resulting from this line of research, there is the definition of the optimal operating conditions to increase the thermal efficiency of a fluidized bed dryer, having as reference the fluid dynamic data determined here, in addition to the application of cassava peel and quartz sand in a fluidized bed reactor.