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Show 3.0 ...-.. N 0 ~ &0 -~ 2.0 0 '-" E a. a. > 0 1.0 z x 0 Z 0.0 FIRING RATE: 322 kW o NOx • NO IJ. CO 50 60 70 80 Excess Air, ,; Figure 7. EFFECT OF EXCESS AIR ON EMISSIONS 90 N o 10.0 &~0 E a. .0 c.. > o <.> 12 to 60 kW. Then the main burner was started up at 60 kW to replace the flame stabilizer until it reached a firing rate of about 240 kW. The flame stabilizer was operating at 18 to 41 kW when the main burner was firing above 240 kW. Thus, an overall turndown as high as 40: 1 was achieved by combined operation of the main burner (with 8:1 turndown) and the flame stabilizer (with 5:1 turndown). The maximum firing rate of the present test burner was limited by emission requirements, whereas the minimum firing rates for both the main burner and the stabilizer were restricted by the adjusting limits of the variable-discharge nozzle as well as the control devices (valves and flow-rate orifices). Figure 8 presents test results of NO, NOx, and CO emissions versus firing rate for a typical configuration. When the main burner was operated within an overall firing rate of 60 to 500 kW, NOx emissions constantly increased from 0.3 to 1.0 vppm, with most of the contribution from NO. This occurred because the combustion temperature increased with increasing firing rate as a result of the decrease in the maximum excess air for flame stabilization as the firing rate was increased. It was found that the maximum excess air was decreased from 110% to 67% with an increase in the firing rate from 60 to 500 kW because flame stabilization at high excess air operation deteriorated when the axial velocity of the reactant flow increased. At very low load, NOx emissions increased slightly because the flame stabilizer was operated alone. CO emissions from the combustor increased constantly from 1 to 3.6 vppm with increasing firing rate because of a corresponding decrease in residence time of the reactant flow in the combustor. Again, N02 emissions determined by the difference between NOx and NO values were very low (0.1 to 0.4 vppm) over the full range of firing rates. Test data have demonstrated that the test burner can operate stably at 40: 1 turndown with NOx emissions from 0.3 to 1 vppm and CO emissions from 1 to 3.6 vppm. In all tests, N02 was less than 40% of overall NOx. Effect of Main Burner Configuration The major features of the combustor configuration are diameter and location of the exit orifice. The size of the orifice has a significant effect on the ICPR and residence-time 10 |