| OCR Text |
Show in the nozzle cone. This means more dissipation of ultraviolet rays by those particles, which causes less signal to the UV inlet port. Further carbon particles are burned down in the flame core but their short life influences dramatically on ultraviolet rays delivered to the scanner. This phenomenon has not occurred in the smaller size SER burners, probably due to the smaller volume of the combustion zone. As a result, the UV scanner was replaced with an IR scanner. It has given good results which was realized in a 7.5 volt stable signal. with only high excess air, the signal drops but is strong enough to be considered as an acceptable signal within the operational zone envelope. NOx emission data vs. tube average temperatures is represented in Fig.9. The highest NOx level (280ppm) is obtained in the 3.25" SER with ceramic radiant tubes. This is due to a higher volume of radiant flux which is formed on the surface. At the same heat flux, natural gas combustion produces only 160ppm of NOx. Butane combustion has the tendency to reduce NOx when the volume of combustion reaction increases. This is represented in Fig.9i there is NOx reduction from 280ppm for a 3.25" SER to 195ppm for a 4.5" SER, and further to 171ppm for a 6.0" SER. The excess air influence on NOx emission at the average tube temperature of approx. 930 - 9500 C is shown in Fig.10. Maximum NOx emission points are different with each burner size. The larger the radiant tube diameter and the higher the excess air level helps determine maximum NOx emission. For example, a 3.25" SER forms maximum NOx emission at approx 20% excess air, a 4.5 SER - 30%, 6.0" SER - 40%. Any decreases or increases in excess air from that point will lead to NOx emission reduction. The lower the excess air the lower temperature condition due to incomplete premix. with more excess air, the lower the temperature level due to the air ballast increase. -11- |
