OCR Text |
Show in the evaluation. In the second series, combustion air preheated up to 400°F was used to classify only the EV burner performance. Results illustrating the effect of combustion air temperature on NOx emission for the EV burner levels are shown in Figure 4. As the air preheat level increases by 200°F, the NOx concentration roughly doubles. The level of increase in N O x will depend on the peak flame temperature. Therefore, if the combustion air preheat temperature does not increase the peak flame temperature beyond the critical value for N O x formation, the level of increase observed in Figure 4 will be lessened. Flue Gas Recirculation Another method to control flame temperature is FGR. For the purpose of this work, FGR is defined as the ratio of the mass of the recirculated flue gas to the mass of the combustion air. FCR FGR, % = x 100% Combustion Air The LNV™ burner was tested with flue gas recirculation when firing natural gas and light oil. Testing included two different thermal environments, with insulated and noninsulated walls. This series of tests examining thermal environment was done with the L N V ™ burner only. For both thermal environments with natural gas, the LNV™ burner achieved the following N O x with ambient air: • 90-95 ppm NOx without FGR • 41 p p m N O x with 12% FGR • 20 p p m N O x with 2 0 % FGR. As for No. 2 oil, with an insulated test environment the LNV™ burner achieved (corrected to 3 % 02): • 140 -150 ppm NOx without FGR • 120 p p m with N O x 12-14% FGR. and with an non-insulated test furnace, the LNV™ firing No. 2 oil burner achieved: • 95-110 ppm NOx without FGR • 72 p p m N O x with 12-14% FGR It is estimated that the thermal environment of a commercial boiler would represent a case somewhere between the fully insulated and cold-wall cases. Figure 5 illustrates the performance of the L N V ™ burner as a function of the extent of FGR. (Note, the No. 2 oil had a nitrogen content of 0.16 to 0.20 percent.) 9 IV-24 |