OCR Text |
Show D. Marlow and T. S. Norton times for a constant reactor temperature of 1700 K. The smallest time, 't ~ 10-4 s, represents the approximate residence time in a flame front, while the largest time, 't = 10.1 s, is about the residence time in a turbine combustor. Three cases were considered: (1) methane-air combustion with no nitrogenated species in the reactants (Fig. 1), (2) methane-air combustion with 1000 ppm V NO in the reactants (Fig. 2), and (3) methane-air combustion with 1000 ppm V NH3 in the reactants (Fig. 3). The first two cases are identical to those considered by Glarborg et al. (1992) and are only reproduced here to show that no accuracy has been lost in expanding the mechanism. The third case is meant to represent syn gas combustion with a typical NH3 level from a gasifier. The agreement is generally very good for all cases and mechanisms considered. The excellent agreement obs~rved between the reduced and skeletal mechanisms for all conditions suggests that the steady-state and partial-equilibrium assumptions applied to create the reduced mechanism are sound. The largest discrepancies observed are those for the detailed and skeletal mechanisms at fuel-rich conditions where ~ chemistry and reactions between nitrogenated species become more important. A small part of the discrepancy is caused by small changes in the elementary rate coefficients which were previously introduced by Glarborg. As Fig. 3 suggests, no major NH3 pathway appears to have been neglected. Nor do any of the added reactions affect the agreement observed by Glarborg et al. (Figs. 1 and 2). Figures 4, 5, and 6 show tests of the same three cases for varying reactor temperature (1300 K to 2000 K) at a fixed residence time of 10.1 s. The agreement is generally the same as that observed in Figs. 1,2, and 3, with the largest discrepancy observed for fuel-rich, low-temperature combustion. Again, most of the discrepancy observed arises from the neglect of Cl chemistry in the skeletal mechanism. v. Summary A reduced mechanism has been created to model syn-gas combustion with NH3 present in the reactants. The mechanism contains rates for 10 non-steady-state species (CH .. , Hl, °1, CO, H10, H, COl' Nl, NO, HCN, and NH3)' as well as a partial equilibrium relation for one species (OH), and steady-state relations for 18 species (0, CH3, 3CH1, 'CH1, CH10H, C~O, CH, HCO, C, H01, CN, NCO, NH, N, N10, NHl, NNlL HNO). The reduced mechanism is based on a skeletal mechanism containing 96 reactions which were chosen to model hydrocarbon oxidation and nitrogen chemistry with an emphasis on correct prediction of radical concentrations. All performance calculations were executed for a perfectly stirred reactor. Three cases were considered: (1) methane-air combustion with no nitrogenated species in the reactants, (2) methane-air combustion with 1000 ppm V NO in the reactants, and (3) methane-air combustion with 1000 ppm V NH3 in the reactants. Both the reduced and skeletal mechanism calculations agree very well with calculations using a detailed mechanism for a range of reactor residence 12 |