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Show Coals are less effective reburning fuels in destroying NO than gaseous hydrocarbon fuels, since coal produces lower levels of hydrocarbon concentrations. Consequently, in coal reburning, NO + NHi reactions may dominate the destruction of NO in the reburn zone. Furthermore, low hydrocarbon concentrations in the reburn zone might explain the success of kinetic models that excluded NO reactions with CHi species, in describing NO profiles when coal was used as the reburning fuel8 • DATA ANALYSIS The detailed gas phase mechanism Il1VKIDIS COAl. ftDU&t PUMI. nJ!l. IlCi n • 0.90 IIAlULU. CAS IIAlULU. CAS + lIB) .ItuIfDIOUS CQAl. 0% • 1.41 • 1. 3% • 1100 eTfN eTfN eTfN ,... oNO ONO oNO o· 1000 OHCN OHCN OHCN ~ ANH, ANH, ANH, 0 g 7SO O~A~-~~~~~~~~~~~~ 0.0 0..4 0.. U 0.0 0..4 0.' U 0.0 004 0.1 U LI Rnid_ TIm... Residence nm... Ruldence r.me.. of Glarborg et al.(1986) was used as a basis Figure 4: Reburning: Effect of Reburning for identifying the reaction paths that were Fuel Type and Nitrogen Content. likely to be important and for the values of the kinetic rate coefficients that were used. The choice of the reactions was also based on the results of reburning tests, in which different primary and reburning fuels were usedlO. No adjustment of any rate coefficient was made and the analysis was based on known kinetic mechanisms taken from the literature, coupled with partial equilibrium assumptions. The destruction of NO was based on the reactions: NO + NHi --> N2 + products NO + CHi --> HCN + products i = 0,1,2 i = 0,1,2 The following partial equilibria were used to calculate NHi and CHi concentrations: NH· + OH = NH· 1 + H20 1 1- CHi + OH = CHi_l + H20 This yielded the following expression for NO decay: d(NO) = _ (NO)(NH3 )f1 - (NO)(CH4 )/2 dt 1 = 1,2,3 1 = 1,2,3,4 (1) (2) (3) Functions fi are in terms of temperature, OH and H20 concentrations, and represent the groupings of known elementary reaction rate constants and equilibrium constants. Expressions for functions fi and the values of the parameters are listed in Table I. The destruction rate of HCN was based on HCN + 0, HCN + OH reactions and the reversible reaction HCN + H < = > CN + H2. Pseudo steady state assumption was made for CN, combined with partial equilibrium for HCN + OH = CN + H20 and OH + OH = 0 + H20. 5 |