Comparison of Particle Size Evolution during Pulverized Coal Combustion in O₂/CO₂ and O₂/N₂ Atmospheres

Abstract

The present work was aimed at investigating particle size evolution during pulverized coal combustion in an O2/CO2 atmosphere in comparison to that in an O2/N2 atmosphere. Two narrow size fractions of a bituminous coal were devolatilized in N2 and CO2 and burned in O2/N2 and O2/CO2 atmospheres in a high-temperature drop-tube furnace. The resulting chars and residual ashes as well as the parent coals were characterized with scanning-electron-microscopy-based image analysis to quantify particle size distributions, which were systematically compared. The results show that devolatilization in CO2 produces finer char particles than that in N2. It may have a consequence on particle size evolution and ash particle formation during char conversion. Combustion in an O2/CO2 atmosphere generally generates more fine ash particles than burning in an O2/N2 atmosphere at the same oxygen level. Increasing the O2 concentration decreases the amount of the fine ash particles in both atmospheres. The results also show that changing gas atmospheres has a greater influence on the evolution of the particle size distribution during the combustion of the larger coal size fraction.