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Show 3.0 ~ N 0 ~ U-') 2.0 +I C "'-' E a. a. > 0 1.0 z )( 0 Z 0.0 ~------________________________________ ~.o 0 o NOx • NO A CO 200 ~o Firing Rate, kW Figure 8. EFFECT OF FIRING RATE ON EMISSIONS N o .0 U~') E 2.0 aa.. > 600 o (.) distribution of the reactant flow in the combustion chamber. The location of the orifice directly determines the length of the combustion chamber and also brings flow recirculation into effect. Three different orifice sizes were tested. The ratios of the orifice diameters relative to that of the basic configuration were 0.82, 1.0, and 1.14. Because CO emissions are not critical to the present evaluation, only NOx emissions are presented for comparison between different configurations. Figure 9 presents NOx emissions obtained for different orifice sizes at different firing rates. It is obvious that the middle orifice size had the best performance in NOx reduction. An orifice that is too large cannot produce strong flow recirculation and mixing, but an orifice that is too small cannot produce strong flow recirculation either because the diameter of the recirculation zone is reduced. Furthermore, it would result in an increase in CO emissions because a portion of the reactant flow would have less residence time in the combustor. The effect of orifice location on NOx formation at different excess air operation is shown in Figure 10. The ratios of distance from the orifices to the nozzles were 0.9, 1.09, and 1 .15. Test results have demonstrated that the location of the exit orifice has no significant effect on NOx formation at relatively low excess air but a considerable effect at high excess air operation. Through the extensive parametric studies conducted at different combustor configurations and operating conditions, the optimized design of the ultra-low-emissions combustor can be specified for a commercial prototype. TECHNICAL EVALUATION A further technical evaluation of the present test combustor was conducted by comparing its performance to the existing commercial burners as well as a research prototype applied in direct-fired air heating. Based on available technical information, the best performing commercial gas-fired combustor applied in direct air heating is the "CXA" gas burner developed by Urquhart Engineering Company, Ltd., in the U.K1.10 The major design features of this burner include 11 |