Assessment of the physical–chemical properties of residues and emissions generated by biomass combustion under N2/O2 and CO2/O2 atmospheres in a Drop Tube Furnace (DTF)

Abstract

This study evaluated the gases CO, CO2, NO and SO2 emitted from five in natura Brazilian biomasses: pine sawdust, sugarcane bagasse, coffee and rice husks, tucuma seed and the residues generated when these biomasses were applied to combustion atmospheres (N2/O2: 80/20%) and oxy-fuel combustion (CO2/O2: 80/20%) in a Drop Tube Furnace. The in natura samples and residues were evaluated by TG/DTG (thermogravimetry/derivative thermogravimetry), SEM images (scanning electron microscopy) and EDS analysis (energy-dispersive spectroscopy). The SEM images revealed some of the main morphological differences in the in natura materials. However, for the residues under both atmospheres, a large part of the lignocellulosic matrix was degraded, indicating the good efficiency of the thermal process. The TG/DTG curves for the in natura samples and residues for both thermal processes enabled the quantification of the contents of remaining moisture, total organic materials consumed and ashes produced. The emissions for both atmospheres ranged between 90 and 6200 mg Nm−3 g−1 for CO, 5 and 210 mg Nm−3 g−1 for CO2, 10 and 170 mg Nm−3 g−1 for NO and 25 and 870 mg Nm−3 g−1 for SO2 and are directly related to the chemical composition of the lignocellulosic materials, oxidizing atmospheres and furnace conditions. The O2 consumption (6–77 mg Nm−3 g−1) inside the furnace for the oxidizing atmospheres and different biomasses exhibited an 80% CO2 > 80% N2 trend. The chemical composition (EDS) for the in natura samples and residues under both atmospheres revealed different proportions of organic, inorganic and metallic elements in the samples and that the individual behavior of the biomass is a consequence of the diversity of its properties.