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Show COMBUSTION MEASUREMENTS IN AN INDUSTRIAL G A S FIRED A L U M I N U M RECYCLING FURNACE 10 Combustion Space Measurements Detailed profiles of gas concentration, limited profiles of gas temperature, and wall incident radiant heat flux in the combustion space were also measured for the normal, high-fire operating condition. As explained before, these measurements were obtained through the access insert mounted in the furnace door as illustrated in Fig. 2. Figures 6 through 10 show the results for the profiles of gas temperature, 02, N O , C O , and C 0 2 concentrations, respectively. Included in each of these five figures is a top-view schematic (drawn to scale) of one half of the furnace showing the relative position of the profiles with respect to important features in the combustion space. As one would expect, the flow structure is very complex in this highly three-dimensional combustion configuration. Interpretation of these experimental results can certainly be enhanced if accompanied by numerical simulations of the flow field in this furnace. In an attempt to aid in the understanding of this complex flow structure, Fig. 2 illustrates the probe locations relative to burner vectoring. Not only are all burners vectored downward by 10°, but the two exterior burners (burners 1 and 4) are also vectored towards the furnace centerline by 7°. Temperatures in the combustion space very quickly reached the service ceiling of the type S thermocouple used in the suction pyrometer [3500°F (2200K)] as the probe moved in the direction of the flames as indicated by the large temperature gradients shown in Fig. 6. Typically, the gas temperature increased rather quickly from around 2240°F (1500K) to 3500°F (2200K) in regions close to the flame. Profiles at access holes 3, 4, and 5 were not possible because the high temperature environment in the final measurement position in hole 2 caused the ceramic radiation shields to melt and collapse, eventually fusing the tip and the thermocouple wire, making the suction pyrometer inoperable. The furnace back wall temperature was measured through the access door with a hand-held optical pyrometer assuming a furnace refractory emissivity of 0.8 during a period when the furnace door was open for dross removal. Immediately after opening the door the wall was measured to be 2461 °F (1623K). After 46 min the wall temperature in the same location had dropped to 2300°F (1533K). The highest 0 2 concentrations were observed in the profiles of holes 2 and 3, where the probe traversed oxygen-rich, unreacted streams in the flames (see Fig. 2). The quite distinct peaks in the 0 2 concentration profiles maybe seen in Fig. 7 for hole 1 coinciding with burners 1 and 2, suggesting independent flame structures early in the reaction, which can be further complicated by the existence of a possible recirculation flow present below the burners. By hole 2, the flames appear to have merged. The oxygen concentrations in the combustion products are low (penetration distances 3 and 6 ft for holes 4 and 5). Although close to the exhaust flow at positions greater than 7 ft the oxygen concentrations were high (between 2 and 3.5 vol% for holes 2, 3, 4, and 5). N O profiles (Fig. 8) indicate high concentrations in locations where the oxygen concentrations and gas temperatures were high. A peak value of 8000 ppmvd were detected in the flame region in hole 2. C O concentrations reached values as high as 12 vol% early in the flame during the initial stages of combustion (Fig. 9), and C 0 2 values were largest in locations where combustion is complete (Fig. 10) as indicated by the correspondingly low values of C O concentrations. It is also interesting to note that of all species measured, C 0 2 profiles exhibited the least spatial variation. Wall radiant heat flux measurements through the five access holes are summarized in Table 2. The incident flux measured varied between 139 and 141 Btu/hr/ft2 (438 and 446 W/m2) with an average value of 140 Btu/hr/ft2 (443 W / m 2). Table 2. Measured incident radiant flux at the wall for each access hole. Hole: Inc. Rad. Flux, Btu/hr/fr (W/m2): 1 139 (438) 2 141 (444) 3 141 (446) 4 140 (441) 5 141 (446) |