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Show COMBUSTION MEASUREMENTS IN AN INDUSTRIAL GAS FIRED ALUMINUM RECYCLING FURNACE 5_ Gas Temperature Gas temperatures were measured using a conventional, shielded, water-cooled suction pyrometers. A 1.7 in (43 m m ) outside diameter, 4.25 ft (1.3 m ) long, stainless steel water-cooled pyrometer with 4.7 in (12 cm) long double alumina radiation shields was used for the flue gas temperature measurements. A 2.5 in (63 m m ) outside diameter, 13 ft (4 m ) long, water-cooled pyrometer with 7 in (18 cm) long triple alumina radiation shields was used for the combustion space measurements. Gas suction for both small and large suction pyrometers was provided by a venturi pump that was attached to a 1 in (2.54 cm) pressure line at 80 psi (550 kPa). The thermocouple voltage was measured with a type-S, cold-junction compensator and amplifier using a hand-held voltmeter. A ninth-order polynomial was used to describe the thermocouple temperature as a function of the voltage output. The accuracy of the pyrometers is reported by the manufacturer to be ±8K when operated at the recommended gas flow rate. The pyrometers have a service temperature ceiling of approximately 3500°F (2200K). Wall Temperature Refractory wall temperature measurements were made using an Omega OS651 hand-held optical pyrometer with user-selectable emissivity. The instrument has a calibrated range of -20 to 2000°F with an accuracy of ±1%, with estimated accuracy of ± 5 % to 2400°F. These measurements were made immediately after the furnace door was lifted. Characterization of wall temperature drop during the time interval for dross removal was also made by making wall temperature measurements after the door was opened, and after some time. An emissivity of 0.8 was assumed in the measurement. Incident Radiant Flux A calibrated, water-cooled, hemispherical ellipsoidal radiometer was used to characterize wall incident radiant heat flux at each of the access hole locations. The radiometer consisted of a stainless steel, water-cooled jacket, 1.7 in (43 m m ) in diameter and 2 in (0.65 m ) long, encasing an inner signal wire tube with the detector head mounted in one end, and cooling water and signal lead connections at the opposite end. The hollow ellipsoidal cavity detector has a 0.12 in (3 m m ) diameter aperture at one focus, and a hemispherical sensing pellet at the other. The aperture and sensor head are centered at the foci of the ellipsoidal cavity, which is coated with a layer of polished gold. The ellipsoid is purged with dry nitrogen to prevent combustion products from fouling the highly reflective ellipsoidal cavity surface. The radiometer was calibrated by the manufacturer accurate to ± 5 % to radiant flux level of 95 Btu/hr/ft2 (300 k W / m ). Above this calibrated maximum the manufacturer indicates that the linear calibration curve can be extrapolated to calculate the radiative flux, although the extrapolated value would be below the true value of incident flux if not within the manufacturer-specified 5 % error. RESULTS AND DISCUSSION Exhaust Measurements Exhaust profile measurements of gas temperature and species concentrations were made for several furnace operating conditions. These settings included: (1) high-fire condition, which is the normal operating condition of the furnace; (2) low-fire condition, which is used when tapping the furnace or when the furnace roof temperature exceeds a predetermined maximum value; (3) high-fire, low-stoichiometry condition, selected to determine its impact on N O emissions; (4) high-fire, highest oxygen enrichment condition (without any manual valve changes); and (5) high-fire, air/fuel-burning condition. Each profile in these tests included six-point measurements in the approximately 4 ft (1.2 m ) square cross-section stack. The gas temperature and species concentration profiles were very flat in the stack (maximum variation from point to point less than 5%); therefore, only averaged values |
