OCR Text |
Show 9000 ~7000 iO Qj a. Fuel: Birmingham Natural Gas Air: Oxygen 21 %, Nitrogen 79% ~6000 IQ) ~5000 u:: 300 500 700 900 1100 Preheated Air Temperature (oF) FIGURE 1 ADIABATIC FLAME TEMPERATURE AS A FUNCTION OF . EXCESS AIR AND PREHEATED AIR TEMPERATURE 9000 8000 ~ ~ Fuel: No. 6 Fuel Oil ~ 7000 iO Air: Oxygen 21 %, Nitrogen 79% Qj a. E6000 Q) IQ) ~ 5000 u::: 300 500 700 900 1100 1300 1500 Preheated Air Temperature (oF) FIGURE 2. ADIABATIC FLAME TEMPERATURE AS A FUNCTION OF EXCESS AIR AND PREHEAT AIR TEMPERATURE extremely high (in excess of 1.5% of the combustion products). Figure 6 shows the effect of oxygen enrichment on the equilibrium values of NOx with varying preheat temperatures. When the oxygen enrichment reaches 30% and higher, an anomally at low excess air (0-5%) seems to occur in that the equilibrium NO level at 2000°F preheat is less than at 1500°F. For higher levels of oxygen enrichment, these anomalous trends seem to continue but in a more pronounced fashion. The maxima in the equilibrium mole fraction of NO for these curves corresponds to a flame temperature of about 3225 K or 5165°F. To the right of this maxima, the mole fractions are less than at 5165°F. This behaviour 190 9000 <.J Legend --- 10% Excess Air 30% 02 in Combustion Air --- 0% Excess Air 21 % O2 in Combustion Air _ .• - 10% Excess Air ---21- %- 0-2 in- C-o-mb-ust-ion- A-ir ----------- -"~ 4000 _ .. _ .. -.. --.. _ .. _ .. - " Fuel: Coal (80.6%C, 2.4%Hz, (1) :0 ci 3000 5.9% °2, 5.2% H20 1.1% Sand 9.5% ASH) 2ooo L---L---~--~--~--~--~--~--~--~~ 100 300 500 700 900 1100 1300 1500 Preheated Air Temperature (oF) FIGURE 3. ADIABATIC FLAME TEMPERATURE AS A FUNCTION OF EXCESS AIR AND PREHEAT AIR TEMPERATURE 9000 [ 8000 ,." _ .... _.... ,.,. --........ ,.,."" 35% ~2.- _ -;::_ - ........ _-:=--.. 30% 0 2 - _ . _ ---;==-::::--..::::. - 25% O2 - _.---.--........._ . - ... .... .. ...-.. . ---.. ...-.. _ . - . - ' - 21°~o.Q2_·· - · · ...... .. ----....... .--. .. ---.. Birmingham Natural Gas 0% Excess Air 2000 L-~L-~--~---L--~--~--L---L-~~ 100 300 500 700 900 1100 1300 1500 Preheated Air Temperature (oF) FIGURE 4. STOICHIOMETRIC ADIABATIC FLAME TEMPERATURE AS A FUNCTION OF PREHEATED AIR TEMPERATURE AND % OXYGEN 40% O2 ENRICHMENT. has not been reported in the literature presumably because combustion with such high preheat temperatures and oxygen levels in air was not extensively studied before. A plausible explanation for this phenomena can be obtained by viewing a plot of the equilibrium constants versus temperature for the various chemical reactions considered in this study as shown in Figure 7. In Figure 7, one notes that at lower temperatures (higher values of l/T), the Kp value of the NO producing reaction is several orders of magnitude higher than those for other dissociating reactions. However, above 5165°F, the other dissociating reactions predominate over the NO formation reaction. The mole fractions of the com- |