Avaliação da co-combustão de carvão mineral com serragem de eucalipto em leito fluidizado borbulhante

Abstract

It is estimated that coal will remain, for the next few years, the main input to produce electricity. Thus, there is a need to study its co-combustion with biomass, a renewable and abundant fuel, to mitigate the environmental impacts caused by emissions of this fuel. This study aimed to analyze the effect of biomass content on the co-combustion of biomass and coal in a bubbling fluidized bed reactor in laboratory scale. The biomass used is eucalyptus sawdust from Rio Grande do Sul and the coal comes from a deposit in Colombia. The cold fluid dynamic behavior, the physical and thermal characteristics of the particles, the operational conditions of the reactor, as well as the emissions of CO, CO2, NO and SO2 gases were evaluated. It was possible to observe that the minimum fluidization velocity increased as higher biomass ratios were added to the mixture. Chemical and thermal analyzes of coal identified a low ash content (approximately 7%) and a high calorific value (28.1 MJ/kg). The temperatures inside the bed remained stable, between 800 and 900 °C, for all mixtures and excess air analyzed. The addition of biomass to the mixture, in proportions of 10 and 25% by mass, increased the average bed temperature due to the rapid devolatilization of the biomass volatile content verified in the TGA tests. In the freeboard region, temperature fluctuations were observed, mainly in the mixture with 25% of biomass. The addition of 10 and 25% of biomass proved favorable for CO emissions for most of the reasons tested. The addition of 10% biomass promoted a better efficiency of the combustion process, and this fact was observed based on the CO2 emission closer to the ideal. As for the NO and SO2 gases, the addition of biomass resulted in a slight reduction in emissions when compared to the singular burning of coal, which can be explained by the lower content of N and S elements present in the biomass.