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Show matter content and a higher portion of the nitrogen in the volatile matter. Under unstaged conditions, the volatile nitrogen species would be eff~ciently converted to NOx and result in high NOx values for Scotts Branch coal. However, under optimized conditions the volatile nitrogen species will be reduced in an oxygen lean environment to result in Scotts Branch having the lowest staged NOx emissions. 4.2 Burner B - Air Staged Precombustor Burner Figure 15 shows the relationship between NOx emissions and "effective" precombustor residence time, Tp, for a range of precombustor stoichiometries, SR1, firing Scotts Branch coal. "Effective" precombustor residence time was calculated assuming plug flow within the precombustor. At constant Tp, NOx emissions increase as SR1 increases. This would be expected as increased precombustor stoichiometry increases 02 availability for the volatile nitrogen species and thus promotes NOx formation. Increasing Tp resulted in reduced NOx emissions for all precombustor stoichiometries. Figure 15 also shows the effect of mixing rate between the devolatilised products and combustion air. At SR1 = 0.8, reduced mixing rate, in terms of increased MR, can be seen to promote lower NOx values. Figure 16 shows the relationship between NOx emission and burnout for all experimental flames studied for Scotts Branch coal. As can be seen, the ASPB performed significantly better than the externally air staged burner. Figure 17 shows the relationship between NOx and burnout for Heinrich Robert coal. Similarly to the AASB, no improvement on the externally air staged burner was realised for this coal. 5 CONCLUSIONS Two internally air staged burners have been evaluated for NOx reduction potential firing two coals. The design strategy for Burner A, the Aerodynamically Air Staged Burner, was promotion of devolatilisation within the IRZto encourage volatile nitrogen species decomposition to N2. This burner was tested with two modes of coal injection, and the optimised performance is summarised below. Burner-Injector Coal NOx Tx (ppm, 0% 02 ) (% ) AASB-annular Scotts Branch 320 98.0 AASB-oblique Scotts Branch 240 98.5 AASB-annular Heinrich Robert 520 98.0 10 |