| OCR Text |
Show AFRC - 1996 Int. Symposium Baltimore September 30 - October 2 1996 Page 10 of 14 The minimum NOx production, limited by blow-off, achievable with an undiluted 'standard' gas/air-mixture at ambient temperature was 14 g/GJ. From figure 5, it may be observed that significantly lower NOx emissions « < 10 gIG!) have been achieved from the combustion of natural gas/air/flue-gas mixtures at an elevated temperature. This demonstrates the potential to reach lower NOx emissions using a higher initial mixture temperature. It is interesting to notice that stable flames with an air factor above 1.5 only have been obtained with mixtures with an oxygen level of 16% and a temperature of 420°C. This is in agreement with the flame velocity calculations, see figure 2. At a temperature of 420°C, a fuel percentage of approximately 4.5 % is required which corresponds with an overall air factor of about 1.6. In figure 6, the NOx production in the flame tube has been presented as a function of the adiabatic flame temperature. --<...3.. . -0'" c:: .9 U ::l ~ e Cl... x 0 z 120 100 80 60 40 20 o 1200 )( a .. 0 • 0 i V 0 ., o .0 0# I- • .~ .. II> ~ ~ .,...". 1300 1400 1500 1600 1700 1800 1900 Ad iabatic flame temperature 1)(19~ 02 ; 20·C a 1 6~ 02 ; 100 ·C .'4~ 02 ; 370'C ·14~ 02 ; 500'C .12~ 02; 360 'C I Figure 6: Experimental data on HOx production. Same data as used in figure s. CARS-measurements of temperature in similar flames (Mokhov and Levinsky, 1996) have shown that the flame temperature, in the absence of heat transfer to the burner, reaches its adiabatic value. The adiabatic flame temperatures have been calculated using an enthalpy balance. It may be concluded that, within the experimental range considered, the NOx production correlates very well with the adiabatic flame temperature. |
