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

The present work was aimed at investigating particle size evolution during pulverized coal combustion in an O 2 /CO 2 atmosphere in comparison to that in an O 2 /N 2 atmosphere. Two narrow size fractions of a bituminous coal were devolatilized in N 2 and CO 2 and burned in O 2 /N 2 and O 2 /CO 2 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 CO 2 produces finer char particles than that in N 2 . It may have a consequence on particle size evolution and ash particle formation during char conversion. Combustion in an O 2 /CO 2 atmosphere generally generates more fine ash particles than burning in an O 2 /N 2 atmosphere at the same oxygen level. Increasing the O 2 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.