Analysis of the Gaseous Emissions and the Residues Generated under Oxy-fuel Combustion of Biomasses in a Drop Tube Furnace (DTF)

Abstract

Some environmental problems are caused by pollutants from thermoelectric plants, mainly by burning fossil fuels. Alternatives for reducing such emissions are discussed worldwide and using green fuels is a promising way. Five biomasses (pine sawdust, sugarcane bagasse, coffee and rice husks and tucumã seeds) were evaluated for application as feedstock in thermochemical processes. Particular attention is devoted to the residues and emissions (CO, CO2, SO2 and NO) produced by biomasses burning in a Drop Tube Furnace (DTF). Oxy-combustion (CO2/O2:60/40%) experiments were performed and emissions monitored continuously. Thermal analysis, scanning electron microscopy, and energy dispersive spectroscopy were used to characterize in natura biomasses and residues after oxy-fuel combustion. CO2 emissions ranged between 34 and 60 mg Nm-3 g-1. Sugarcane bagasse showed the lowest emissions of CO2 and NO (34 and 21 mg Nm-3            g-1, respectively) and highest O2-consumption (≈ 32%), while tucumã seed and pine sawdust samples provided the lowest values of CO and SO2 (345 and 5 mg Nm-3 g-1, respectively). TG/DTG curves of the residues compared to the in natura samples aided in diagnosing the performance of the oxy-combustion in a DTF. Organic matter remaining in residues (from 3 to 92%) showed clearly that efficiency of the thermal process varies with biomass-type used. Chemical composition of the residues showed different proportions of inorganic elements (Si, K and Ca) and trace elements (Na, Fe, Cu, S, P, Ma and Cl), demonstrating that individual behavior is an effect of the biomass properties diversity, influencing directly the burning process. The knowledge of some trends is important for the understanding that generalizations of processes cannot be applied when different biomasses are used in thermal processes.