Experimental investigation of NO reburning during oxy-coal burner staging

This study presents an investigation into the impact of varied burner staging environments on an oxy-fuel flame and the rate of the NO formation and destruction processes. The experimental data was extracted from the use of a 250 kWth down-fired combustion test facility with a scaled-down model of an industrial low-NOx burner (LNB). Two oxy-coal combustion regimes were investigated by varying a fixed flow of oxidant between the secondary and tertiary registers, so as to impact the stoichiometry in the fuel-rich region and flame structure, and using various NO recycling regimes, to test the impact of these different burner configurations on NO reburning. The data was collected by monitoring key emissions in the flue gas and in the flame, as well as temperatures throughout the furnace and the unburned carbon content of the ash. A detailed investigation encompassing the impact of secondary oxidant proportion for different oxidants on NO emissions, together with the quantification of recycled NO destruction, is discussed. This investigation finds that 85 % to 95 % of the recycled NO is destroyed at a range of burner configurations using OF 27 and OF 30 at 170 kWth. In addition to this, NO formation and carbon burnout are found to be significantly affected with changing burner configurations. Further to this, OF 30 flames appear to be more sensitive to burner configuration than OF 27 flames with regards to both NO formation and destruction, possibly due to the decreased density of the OF 30 oxidant. Radial profiles of two burner configurations at OF 27 and OF 30, as well as an axial profile of two burner configurations at OF 30, are analysed. The profiles appear to show that burner staging aids in controlling the products of NO reburning, hence maximising the destruction of recycled NO.