OCR Text |
Show Results and Discussions When the axial air flow rate was set at 250 L/min,the CO emission is high near the burner and decrease with axial distance. But, NOx and NO emission lncreases with axial distance before L/D=8 from burner; within this distance, the NO or NOx emission is inverse proportional to CO concentration (as shown in Fig.4) [5],[6]. Under this operation condition, the length of flame is about 80-100 cm where higher flame temperature causes higher NO/NO x emissions. After L/D=8 (maximum flame temperature), the NO/NO x emissions will decrease with axial distance. (1) The Influence on CO Emission In Fig.5 , at initial stage the CO emission will increase with increasing radial air flow rate and then decrease at fixed equivalence ratio. The peak of CO emission values will decrease with increasing the equivalence ratio. After the peak CO emission will be the lowest at equivalence ratio=0.9, radial air flow=450 L/min. It means we could get lower CO emission by adjusting the radial air rate at lower equivalent ratio. At fixed axial air flow, CO emission will decrease with radial air flow. The more excess axial air and radial air flow causes better fuel/air mixing and will have lower CO emission. (2) The Effect of Changing Radial or Axial Air At ¢ -1=1.0 the NOx emissions in the stack will increase from 42ppm to 56ppm with increasing radial air flow rate from 200 L/min to 350 L/min. Increasing the radial air flow rate will increase the fuel/air mixing rate, which means nitrogen atom has more chances to react with. oxygens. Fig.7 also shows NO and NOx emissions will reach maximum values at ¢ -1=1.0 [7]. While radial air flow rate reaching 450 L/min, the NOx emissions in the stack will drop to 45 ppm. (3) The Effect of Adding Cooling Water Local flame temperature will reduce by adding cooling water [4]. At L/D=5 (75 cm from burner) nitrogen oxides reduc~d about 9.2%, and at L/D=8 (120' em from burner) nitrogen oxides reduced about 16.7% at fixed 300 L/min radial air rate (Fig.8). Similarly, at L/D=5 nitrogen oxides reduced about 11%, and at L/D=8 nitrogen oxides reduced about 22% at fixed 350 L/min radial air rate. Thus, adding cooling water without staged air at L/D=8 could lower nitrogen oxides formation. |