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Show air header, well upstream of the burner, to ensure complete mixing. High levels of oxygen enrichment were produced by adding N2 to high purity 02 in the proper proportions. The natural gas consisted of 96.6% CH4, 1.7% C2H6, 0.7% C02, 0.4% N2, 0.4% C3Ha and 0.2% other hydrocarbons. The gross heating value of the natural gas was 1034 Btu/ft3 . The I!pure" oxygen used for the tests was actually at least 99.5% 02 plus inerts such as argon and nitrogen. Nitric oxide was measured using a Beckman Model 865 NDIR Analyzer. All data has been corrected to 0% 02 in the flue. The furnace was warmed up for several hours before testing began. All reported results were produced under positive furnace pressures to isolate the NOx produced by the burners by excluding air infiltration. The burners were fired at each set of conditions for at least 30 minutes to ensure that steady-state conditions were achieved. Figures 3 and 4 show that the worst NOx is theoretically produced at about 60% oxygen in the oxidizer. The lowest NOx occurs at either low level {air} or high level enrichment (pure 02). Since most industrial processes are also run at these two extremes, the experimental work was divided accordingly. 1. Low Level 02 Enrichment A standard North American 4425-SA nozzle mix burner was used to study the effects of NOx at low levels of 02 enrichment. The burner consisted of a central fuel nozzle surrounded by eight symmetrically located oxidant nozzles as shown in Figure 6. Figure 6: North American 4425-8A burner. This burner was designed for 1 to 4 MMBtu/hr with air and natural gas. For firing rates between 1.5 and 2.5 MMBtu/hr in increments of 0.25 MMBtu/hr, there was no detectable dependence of NOx on firing rate. The visible flame length ranged from 3 to 5'. The furnace wall temperatures varied from 1500 to lS00u F. As shown in (I), two moles of 02 are required for each mole of CH4 for complete combustion. If we define stoichiometry as: stoichiometry = moles 02 moles CH4 1990 AFRC Symposium -6- { 3 } October 1990 |