Co-combustão em leito fluidizado de carvão mineral com bagaço de cana-de-açúcar e casca de nabo forrageiro: avaliação fluidodinâmica e das emissões atmosféricas

Abstract

Currently, the electricity generation is heavily dependent on fossil fuels, which emit large amounts of greenhouse gases (GHG) such as CO2, CO, NOx and SO2. One of the alternatives to reduce the emission of these gases and to insert renewable resources in the energy matrix is the use of biomass as substitute or associated with fossil fuels, like coal. In some countries, the fluidized bed technology has been used to associate biomass with coal in the generation of thermal energy. However, a step prior to its implementation on an industrial scale consists on the evaluation of the fluid dynamics behavior and the impact of the biomass on the atmospheric emissions in the process of co-combustion with coal. In this work, the minimum fluidization velocity of mineral coal and biomass mixtures was evaluated in three fluidized bed reactors with different scales and geometries. Mixtures of coal from the Candiota mine in Rio Grande do Sul were used, with two distinct regional biomasses: sugarcane bagasse and Raphanus Sativus L. husks, in proportions of 10%, 30% and 50% of volume. The biomasses were also characterized by different techniques that included heat value, immediate and elementary analysis, being possible to observe similar values of heat value between the biomasses 20,150 kJ / kg and 17,100 kJ / kg and the ash contents were of 4.88% and 3.56% for sugarcane bagasse and Raphanus Sativus L. husks, respectively, ash values are considered relatively low. To evaluate the impact of biomass combustion on atmospheric emissions, combustion tests were carried out on a bench unit with continuous NOx and SO2 emission monitoring. It was verified that the release of SO2 is high in the combustion of coal (164 ppm). It is possible to obtain lower amounts in the combustion of the Raphanus Sativus L. husks (23 ppm) and, mainly, with the cane bagasse (3 ppm). The results were promising for pilot-scale evaluation of the process, in order to technically and economically evaluate the process of co-combustion of these biomass residues in an industrial unit.