OCR Text |
Show concentrations were taken at the first measured point in the fuel rich zone. The initial value of OH in the rebum zone was estimated using measured NO decay rates from gaseous flame data only (natural gas + NH3 primary flame and natural gas reburning) and solving Equations 3 and 9 for OH concentration. The calculated values were then correlated as a function of temperature, which gave the following expression: (OH)initial = (OH)equil x 1.65 x lOS exp (18745 IT) The initial value of OH in the fuel rich zone of air staging was taken at equilibrium. In all cases, an equilibrium assumption was made for the initial OH concentration at fuel rich zone inlet temperatures above 1520 K. It should be emphasized that, unlike the analysis of Bose and Wendt6 , the use of empirical estimates of OH was restricted to the calculation of an initial condition for OH rates. The decay in OH concentration was calculated using the kinetic rate (Equation 9), solved simultaneously with Equations 3 and 6-9. Figure 5 shows a comparison between measured and predicted nitrogenous species profiles in the reburn zone for three natural gas reburning experiments, in which the primary fuel was natural gas doped with varying amounts of NH3• This allowed the variation of the primary NO concentration entering the rebum zone. The symbols represent measured values of nitrogenous species, on a wet basis, and the curves are model predictions. Only measured values of CH4, H2, H20 and N2 are used in the prediction of nitrogenous species profiles in the reburn zone. In general, there is good agreement between measurements and predictions over a wide range of primary NO levels (33-715 ppm). . Figure 6 shows the effect .. 00 ~ 1100 f MOO ... 1200 E Q. Q. ,,; lOO ] 200 Q. In Z X 100 o ILUVIAI. c;,u IDDIIIUC:. PUZL UCI SI. • 0." ~ ~ ~ !lOp • 7U '1M ." • 160 '1M lOp • )) ,,. \ r:t.SJ • .o 0 ~ 0 0 0 6-=6- '~6 A' ....· 6 ,,'6'·'6 ~~~ 0.0 0... 0.1 U 0.0 0... o.a U 0.0 0.. 0.1 U II Re.ldence nm... Residence TIme., Ruldenel nm .. s o -"'r" III ......... ICI • lIoo __ .. n) -PrMict" 10 -.rMicc .. ICI -PrMicCM n) Figure 5: Reburning Profiles- Measurements and Predictions. temperature n mo I predictions, where natural gas reburning experiments of different temperature environments are examined. Bituminous coal was the primary fuel in both cases. The model predicted nitrogenous species values well, at different temperature profiles in the rebum zone. However, the model failed to account for the rapid decay in HCN at high temperatures. Comparisons between model predictions and experimental measurements for all the natural gas reburning experiments of this study are shown in Figure 7, where each nitrogenous species is examined separately. The scatter of the predictions does not indicate bias with ~espect to a prim ry fuel type (coal or gas flame), or a certain range of values for 8 |