OCR Text |
Show As can be seen, the NOx emission from these burners is low compared to the 168 ppm allowed by EPA for large gas-fired boilers. NOx emission decreases sharply with increasing excess oxygen for the K926 and K976 burners due to the reduced flame temperature. With the exception of the ULNx, using secondary air raises NOx emission. The burners with a flat block have a lower emission than those with the cup- type block. Staging reduces NOx emission from the ULNx despite its use of secondary air. Also, the secondary air provides higher capacity in a smaller burner with less sensitivity to fuel composition changes. Further, its emission decreases with decreasing excess air which results in higher firebox efficiency. Conclusions The measurements reported here show that burners can be designed that will meet the most stringent NOx emission regulations now or soon to be in force. Further, there is little or no loss of thermal efficiency or increase of investment cost. -4 - |