Combustion Measurements in an Industrial Gas Fired Aluminum Recycling Furnace

The objective of the work reported here was to characterized the pre-rebuilt combustion performance in the natural-gas-fired, partially oxygen-enriched, aluminum recycling furnace (Furnace 8) operated by Roth Brothers Smelting Corporation in Syracuse, New York. Measurements of gas temperature and species concentration (02, CO, NO , and C02) were made in the exhaust of the furnace. Local gas temperature, species concentration, incident wall radiant flux and furnace wall temperature measurements were also made in the combustion space. Average exhaust gas temperatures varied between a low of 1558°F (1121K) and a high of 2281°F (1523K) for the conditions of low-fire and highest oxygen enrichment, respectively. It was observed that changes in furnace stoichiometry were important in controlling the overall NO production. The highest NO level (3509 ppmvd) was observed for the normal high-fire condition when the temperatures were high in the furnace and there was enough excess air available (more than 10% excess). A significant reduction in NO production (from 3509 to 1390 ppmvd) was observed when the stoichiometry was reduced. Values of CO concentrations of 10,820 and 7700 ppmvd were measured in the stack with oxygen excess values of 0.5 and 5%, respectively. Temperatures in the combustion space very quickly reached the service ceiling of the type S thermocouple used in the suction pyrometer (3500°F), which prevented full profiles in all access holes available. Oxygen concentration profiles indicate that typically early in the centerline of the jet flames the concentrations are higher. NO 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. CO concentrations reached values as high as 10 vol% earlier in the flame at the initial stages of combustion and C02 values were largest in locations where combustion is complete as indicated by the correspondingly low values of CO concentrations. Nearconstant values of wall radiative heat fluxes were measured of 140.5 Btu/h/ft^2 (443 W/m^2).