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Show ~ '" ~ ~lf''\ ~t ~ '" ~ ~ ~ (NOXUN). There is a strong correlation of NOXUN with the VMIPfR data. This is expected since the volatile path to NOx has been found to be very efficient in fuel lean conditions. The %NVM values are also important, but to a lesser extent. It can be seen that trends that can not be justified on the basis of VMIPfR data can be explained by adding the effect of %NvM. However, VMIPfR is the predominant parameter. This predominance can be clearly seen by comparing the results of Rhein Braun and Scotts Branch coals on the AASB. The value of %NvM for Rhein Braun coal is less than half that of Scotts Branch coal, but the NOx emissions were about the same. This behaviour is the result of the larger VMIPfR value for Rhein Braun coal. Data relating to the effect of coal quality on the staged flames is presented in Table 4, below. For the EASB, the flames has a primary combustion zone with 0.5 of the stoichiometric air requirement. For the AASB, staging was accomplished by optimization of the burner operation as explained in the experimental section. Because of the method of burner optimization, the exact primary stoichiometric ratio is not known. Table 4: Staged NOx emissions Coal VMIPfR Peak Downs 34 Heinrich Roberts 44 Elk Creek 62 Scotts Branch 64 Hugo 39 Heinrich Roberts 44 Scotts Branch 64 Coal Valley 83 Rhein Braun 91 NOXUN VN s1'f(ft6Y 450 390 700 825 520 790 940 940 960 NOXST 51 fJr(,,Jf}> 350 200 500 450 350 530 360 490 490 %Reduction 46 62 32 62 33 33 62 48 49 Although correlation of the staged NOx emissions (NOXsT) with coal properties is possible, it is more difficult than with the NOxuN values. In general, the unstaged flames of coals with low VMIPFR values had low NOXST values. Also, the effect of %NvM can be seen. The notable exception to these trends is Heinrich Roberts coal with a relatively high NOX&T value for the AASB and a relatively low NOXsT value for the EASB. 8 |