OCR Text |
Show Similarly, furnace N 0 X levels are shown along the length of the firebox in Figure 5c, and the 4 ft (1.2 m ) location slice is shown in greater detail in Figure 5d. Note that N 0 X levels are approximately 7-8 ppm along the furnace wall, and become 6-8 ppm across the complete furnace cross section at about the 20 foot (6.1 m) location. From this point on, little additional N O x is generated. In Figure 5e, methane concentration is shown as a function of radial position at the 4 foot (1.2 m) location. Note that the combustion reactions are nearing completion at approximately 4 inches (101 mm) above the burner surface. The well behaved distribution of the combustion reaction along the length of the burner, and in close proximity to the surface, is an important feature of the RSB. Alzeta Modeling Results Alzeta used an in-house plug flow code to model the thermal performance of the heater and the Alzeta P R O F code to model emissions. The well-behaved flow field around the R S B is conducive to this simple modeling. Alzeta plug flow results closely agree with the more rigorous C O M O model when comparing gas temperatures as shown in Table 1, where the average temperature at 4 foot (1.2 m ) intervals out to 16 feet (4.9 m ) agree to within 50-75 °F (10-24 °C). Results of the PROF NOx modeling show NOx emissions of 3 ppm, which is low relative to what was measured and what was predicted by C O M O . However, the model was used only to model the burner flame zone, and therefore only models NOx generated in the flame zone, which in this case was nominally 2.75 inches (70 m m) thick. Due to the large size of the firebox relative to the burner, additional NOx will be formed downstream of the flame, although at a lower rate. Therefore, it is reasonable to assume that the additional 3-4 ppm NOx that was measured and modeled by C O M O could be accounted for if P R O F modeling was extended further downstream. Of more interest are the results of PROF runs that model NOx emissions for two additional runs that have the same total dilution as the case described above, but which include flue gas as 25 percent to 40 percent of the total dilution, with excess air bringing the total dilution up to 60 percent. As was seen experimentally, the overall 7 |