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Show 7 In Figure 8, results are shown for the methane runs at 1370K initial temperature. Best agreement in this case is obtained by using the modified rate for the reaction N20 + OH -> N2 + H02, and by increasing the free radical content of the inlet jet. Chemical equilibrium computations indicate OH = 20 ppmv and H-atom = 10-3 ppmv. When these values are increased by 10-fold, much better agreement is obtained between the model and the experiment for the low values of IFR. At this condition the methane oxidation is weak and produces very little free radical. At the higher values of IFR (as well as for the H 2 afterbuming cases of Figures 5, 6, and 7), the afterbuming process is the major source of the free radical concentrations, and thus, the 10-fold increase in the inlet jet free radical concentration has little effect on the predicted N20. The modeling indicates that the reaction responsible for the destruction of N20 in our experiments is N20 + H -> N2 + OH. 6. CONCLUSIONS Results have been shown for the afterburning destruction of nitrous oxide in a stirred reactor operated at short residence times (nominally 2ms). Under these conditions free radical destruction is predominant. Modeling strongly suggests that the reaction responsible for this is N20 + H -> N2 + OH. Further, modeling indicates that the experimental results are consistent with the new rate suggested for N20 + OH -> N2 + H02 (Glarborg et al., 1993), which significantly weakens the effect of this reaction. The good agreement obtained between the model and the experiments suggests that engineering modeling based on this chemistry can be used with confidence to design practical afterburners for maximum N20 destruction. Optimization of an afterburner design would involve use of the free radical reduction of the N20 in the early part of the afterburning flame, followed by thermal destruction in the downstream stages of the afterburning reactor, where the free radical concentrations approach equilibrium levels. References Amand, L-E. and Leckner, B. (1992), "Influence of Air Supply on the Emissions of NO and N20 from a Circulating Fluidized Bed Boiler," Twenty-Fourth Symposium (International) on Combustion/The Combustion Institute, pp. 1407-1414. Glarborg, P., Johnsson, 1. E., and Dam-Johansen, K. (1993), "Kinetics of Nitrous Oxide Decomposition," Combust. and Flame, in press. Gustavsson, L. and Leckner, B. (1992), Reduction of N20 from Combustion in Circulating Fluidized Beds with Afterburning of Gas," Report, Nordic Gas Technology Centre, IWrsholm, Denmark. |