OCR Text |
Show previous section that an equivalent enrichment in the middle range of oxygen purities m a y be the best economically, but the theoretical N O curve shows this m a y be the worst place to operate as far as N O x is concerned. 20 30 50 60 70 O, in Oxidizer (%) Figure 8. Adiabatic equilibrium N O vs. the 0 2 in the oxidizer (vol.%) where the balance of the oxidizer is N2, the fuel is C H 4, the combustion is at atmospheric pressure and stoichiometric conditions, and both the fuel and oxidizer are at atmospheric temperature. NEW BURNER DEVELOPMENT It has been shown that there may be some economic advantages for using an oxidizer with an equivalent purity between air and pure 02. A s was also shown, there are several ways this can be accomplished. A popular method in the secondary aluminum melting industry is to use the combination of air and higher purity 02. The original EZ-Fire burner design [11] is shown in Figure 9. This technology has typically been retrofitted to existing air/fuel burners by putting an oxy/fuel burner through the center of the air/fuel burner. In many cases, this can be done simply by removing the oil gun in the middle of a dual fuel burner and replacing it with an oxy/fuel burner. Besides the easy retrofittability of this technology, the customer also has the complete flexibility to turn the oxy/fuel burner on or off as needed. Commonly, the oxy/fuel is used during the initial part of the melting cycle when the charges of cold scrap aluminum are made. The oxy/fuel burner is then turned off during other parts of the cycle such as whenever the charge doors are opened for skimming, alloy testing, and alloy additions and also when the furnace is being tapped and only minimal heat is required to keep the bath at temperature. Although this burner design had lower N O x compared to other previous similar designs, the N O x was much higher than with air/fuel combustion. Depending on the specific operating conditions, laboratory N O x measurements on this design ranged from 0.4 to 2.0 lb NO2/106 Btu. 8 |