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Show Luminous flames are defined as flames which, as a result of their containing small solid particles, radiate over a continuous spectrum. All the fuels used to heat glass tanks create different amounts of soot . Fuel-oil, with a much greater carbon/hydrogen ratio, burns with a strongly luminous flame. Natural gas, on the other hand displays an interesting versatility; it can be burnt not only with a clean blue non-luminous flame, but also with considerable luminosity by artificially seeding it with some concentration of soot particles. Hein [1] has shown that the type, size, and number of these particles vary widely. In the case of diffusion flames they are small particles of soot, each 0.01 to 0.05 mm in diameter, but agglomerated into flock-like clusters of 100-1000 particles. Hein' s data [1] are reproduced here in Figure 1, which shows flame gas temperatures, solid (carbon particles) content, and intensity of radiation of flames from different fuels and as a function of the distance from the burner. The soot content of oil varies between 2-40 g/m3 (at N.T.P.), whereas the natural gas soot content rarely exceeds beyond 5 g/m3 (at N.T.P). The flame temperature is high at the start of the oil flame and at the end of the gas flame. The temperature distribution in the oil flame is directly related to its high soot content and in turn its higher emissivity. Non-luminous gas flames have overall emissivity of about 0.2, whereas an emissivity of 0.6 is common in oil flames. OBJECTIVE Combustion Tec, Inc. (CTI) with the assistance from Southern California Gas Company (SCGC) and Institute of Gas Technology (IGT) is currently working on the development of oxylnatural gas "cracker" as applied to glass melting furnaces to reduce NOx emissions. The cracker is designed to add soot to the natural gas flame to increase the flame emissivity and thus simultaneously increasing heat transfer, glass production rate, and thermal efficiency, while lowering the peak flame temperatures and NOx emissions. The overall objective of the cracker is to reduce NOx emissions from the current achievable levels of 5.5 lb NOx per ton of glass pulled or approximately 1100 ppm on an air free basis (as required in the Southern California area) to 3.5 lb NOx per ton of glass pulled or approximately 700 ppm on an air free basis (a 35% reduction). The current regulation for new furnace construction is now 4.0 lb NOx per ton of glass production. The cracker utilizes a unique method of oxidant and fuel mixing to control the flame length and foster the formation of soot particles. It is expected that the adiabatic flame temperature and furnace wall temperatures have a significant effect on NOx emissions. As verified by Abbasi et al. [2,3] that each 100°F increase in either adiabatic flame temperature or furnace wall temperature increased NOx emissions by 20% to 25% . The proposed cracker will enhance the luminosity of a natural gas flame by seeding the natural gas with the desired soot concentration. The design soot concentration is set at 0.0025 lb carbon per cubic feet of natural gas supplied as a fuel to the furnace. Strictly on the weight basis, it is expected that approximately 8% of the fuel will -2- |
