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Show COMBUSTION MEASUREMENTS IN AN INDUSTRIAL GAS FIRED ALUMINUM RECYCLING FURNACE 16 CONCLUSIONS The objective of the work reported here was to characterize the combustion performance in a natural-gas-fired, oxygen-enriched, aluminum recycling furnace. Measurements of gas temperature and species concentration (02, C O , N O , and C02) were made in the exhaust of the furnace. Gas temperature, species concentration, wall incident radiant heat flux, and furnace wall temperature were made in the combustion. Stack measurements in this furnace included five operating conditions, i.e., normal high and low firing, high fire with only air as the oxidizing agent, high fire low stoichiometry, and high fire with the highest possible oxygen enrichment. Combustion space measurements were only made for the baseline, high-fire operating condition. Average exhaust gas temperatures varied between a low of 1560"F (1121K) and a high of 2280°F (1523K) for the conditions of low fire and highest oxygen enrichment, respectively. Furthermore, the differences in exhaust gas temperature for the high-fire conditions were not significant. Changes in furnace stoichiometry were important in controlling the overall N O production. The highest N O level (3509 ppmvd) was observed for the normal high-fire condition when the temperatures were high in the furnace and there was enough excess oxygen available (more than 1 0 % excess). A significant reduction in N O production (from 3509 to 1390 ppmvd) was observed when the stoichiometry was reduced (from 2.22 to 2.01). Only a small increase in N O levels was observed for the case of the highest oxygen enrichment which had an excess air of about 5% based on the plant settings. Values of C O concentrations of 10,820 and 7700 ppmvd were measured with oxygen excess values of 0.5 and 5%, respectively. As one would expect, the flow structure is very complex in this highly three-dimensional combustion configuration. Steep temperature gradients were observed in the combustion space, with levels exceeding the service ceiling of the type S thermocouple used in the suction pyrometer. 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. Distinct peaks in the O z concentration profiles suggest independent flame structures early in the reaction. Further downstream the flames appear to have merged. N O profiles in the combustion space indicate high concentrations in locations where the oxygen concentrations and gas temperatures were high. Peak values of 8000 ppmvd were detected in the flame region. C O concentrations reached values as high as 10 vol% earlier in the flame at the initial stages of combustion and C 0 2 values were largest in locations where combustion is complete as indicated by the low values of C O concentrations. Wall radiant heat flux measurements revealed a nearly constant heat flux of 140 Btu/hr/ft2 (442 W/m2). ACKNOWLEDGMENTS The support of the Roth Brothers Smelting Corporation personnel is gratefully acknowledged, with particular thanks to Neal Schwartz, Robert Hubbert, and John Sessler. Financial support of the project was provided by Air Products and Chemicals, Inc., and the U.S. Department of Energy. The help of student assistants Jacob Peart and Raj Dubey is also gratefully acknowledged. |
