Line of Sight Soot Measurements In Staged and Unstaged Air and Oxy-Coal Flames

Line of Sight Soot Measurements in Staged and Unstaged Air and Oxy-Coal Flames

Curtis Stimpson, Trevor Blanc, and Dale R. Tree

Brigham Young University

Will Morris and Yost Wend

University of Utah

Andrew Fry

Reaction Engineering Incorporated

Oxycombustion is a technology that has the potential to enable the capture of CO₂ produced coal-fired boilers. Oxy-coal combustion is expected to change the temperature and heat transfer characteristics of coal flames. Radiation is the principle mode of heat transfer and is typically dominated by soot. Soot concentration has been measured by an in-situ, line-of-sight extinction method at three axial locations from the burner in a 40 kW_th, down-fired, pulverized coal, reactor. The oxy-fuel combustor (OFC) located at the University of Utah, can be fired with air, O₂/CO₂, and O₂ with flue gas recycle (FGR). Soot measurements were taken with two coals, a PRB sub-bituminous and Skyline, lignite coal. The oxidizer was staged with S.R = 0.9 and 1.0 in the near burner zone followed by burnout oxidizer or unstaged with S.R. = 1.09-1.17 in the near burner zone. For Skyline coal, soot concentration was typically highest at the root of the flame near the burner and decreased with distance from the flame. For the PRB coal, soot concentrations was highest in the center of the flame. Soot concentration increased with decreasing stoichiometric ratio in the near burner zone. For a fixed axial location and S.R., soot was highest with air as an oxidizer. Oxidizer with O₂ in FGR O₂ in CO₂ produced similar amounts of soot. Peak soot volume fractions at the flame root were on the order of 1.5x10^-7 and 5.0 x10^-8 at the flame tip.