Line of sight soot volume fraction measurements in air- and oxy-coal flames

Abstract

A two-color laser extinction method was used to collect measurements of soot volume fraction along a line of sight in air- and oxy-coal flames produced by two different burners. One was an Imjuiden block, variable swirl, 150kWth burner in the Burner Flow Reactor (BFR) at Brigham Young University. The second was a fixed-swirl vane (30°), 40kWth burner in the oxy-fuel combustor (OFC) at the University of Utah. In both burners, three stoichiometric ratios (SRs) and three oxygen volume fractions in the secondary oxidizer stream were investigated with measurements collected at three axial positions. In the OFC, two coals were investigated with simulated flue gas recirculation (FGR, O2 in CO2) and warm FGR. In the BFR, two coals were investigated, one with warm recycle (420°F) and the other with cold recycled flue gas. In the BFR, at high swirl (1.36), the flame was attached, and the amount of soot was found to correlate strongly with the secondary mass flow rate. Increasing flow rate produced shorter, more active flames and less soot indicating increased mixing. In the OFC, the flame was lifted. The air-fired flame was more lifted than the two oxy-fired flames (simulated FGR and warm FGR) and produced less soot. Soot for all flames decreased slightly with increased distance from the flame root where soot volume fraction was highest. The bituminous coal produced more soot than the sub-bituminous coal. Measured soot volume fractions ranged from 10 to 200×10−9. The data show that the local SR of the fuel rich region has a more significant impact than the overall SR and the type of oxidant (air, O2/FGR, or O2/CO2).