| OCR Text |
Show The burner has also been tested in the flue gas recirculation mode. Here, a portion of the products of combustion are returned to the burner. This allows the burner to be operated at lower excess oxygen levels in applications where thermal efficiency is of prime importance (e.g boilers). It also enables the burner to be used in VOC thermal oxidation applications where the waste gas contains a reduced oxygen concentration. An example of this condition is described below. Figure 6 shows expected NOx emissions versus flue gas recirculation rate (or % 02 in waste gas) at a fixed 3 % 02 in the products of combustion. APPLICATIONS Five applications of this burner to thermal oxidation of actual waste gases are described below. In all five cases expected NOx emissions are in the range of 4 - 6 ppmv . The first application is shown on Figure 7 . Here, a tank vent, blanketed with an inert gas (nitrogen) to prevent premature ignition, is vented to the thermal oxidizer. In this particular case, the vent gas contains hexane at a concentration is 0.25 %. Even though the burner is firing at 100 % excess air, the oxygen content of the products of combustion is less than 4 % because combustion of the hexane portion of the vent gas consumes a large portion of the excess oxygen. Thus, this design produces low NOx emissions without sacrificing fuel economy. The second application is shown on Figure 8. In this case, the waste gas is an air stream contaminated with methanol and toluene. Part is supplied directly to the burner to supply oxygen for auxiliary fuel combustion and part injected downstream of the burner. Even though the burner flame temperature is 2200 F the oxidizer exit temperature is 1500 F due to the moderating effect of the waste gas injected downstream of the burner. The third application is shown on Figure 9. Waste gas from a chemical reactor Absorber Off-Gas (AOG) is thermally oxidized and the heat generated used to produce steam. In this case the waste gas does not contain sufficient oxygen to support combustion. With the addition of a small amount of ambient air this gas can be used as vitiated combustion air through the burner. This simulates flue gas recirculation and produces the same low NOx levels. V-30 6 |
