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Show 8 CulletlBatch Preheating: Reduces energy requirement for melting in the furnace, increases furnace thermal efficiency, and increases specific production rate. These techniques should be fairly effective in moderate (~5%) NOx reduction. The challenge, however, is to develop a preheating system that can operate effectively and reliably. Two types of preheaters - one using the heat in the flue gases for culletlbatch preheating and the other separately gas-fired for cullet preheating - have been developed by SORG (11) and GRI (12). Post-Combustion Techniques NOx can also be reduced by post-combustion techniques that involve chemical reduction of NO x through the use of a reagent or by process modifications. Specific post-combustion methods include -- Gas Reburning: Adding natural gas to exhaust gases to form afuel-rich mixture that promotes NOx destruction and then burning this mixture in air at lower temperatures to complete combustion. This method has been tested by Pilkington showing significant NOx reduction. Pilkington injected additional natural gas near the exhaust port for the reburning reactions followed by secondary air downstream of the regenerator for CO burnout. Again, as with Pilkington's air staging approach, this method results in an efficiency loss. A different version of gas reburning is currently being evaluated by GRI. Selective Noncatalytic Reduction (SNCR) (3): Dry injection of ammonia or slurried urea into the flue gas at temperatures of 870° to 1040°C (1600° to 1900° F). Selective noncatalytic reduction has been applied to several glass melters in California By combined injection ofNH3 and hydrogen as the reducing gas to expand the operating window from 700° to 1040°C (1300° to 1900°F), NOx reductions of over 500/0 are reported on both a float glass and a fiberglass melter. This approach, however, is quite expensive [adding up to 300/0 to the energy costs (11)]; involves pressurized storage of a toxic gas; and could result in ammonia slip. A typical NOx reduction with this approach can be expected to be about 30%. Selective Catalytic Reduction (SCR): Dry injection .of ammonia into the flue gases at 260° to 430°C (500° to 800°F) in the presence of a catalyst. Selective catalytic reduction can reduce the NOx to very low levels by as much as 75%; however, it is high in both capital and operating costs. Although it is successfully being used in some other countries, it is not currently used in the United States. Wet Scrubbing: Wet scrubbing offlue gases with an aqueous solution of a reagent, generally water or a mild alkali. Similarly, wet scrubbing of flue gases is high in both capital and operating costs and, consequently, not used in the United States for combustion-generated NOx reduction. This approach is, however, very popular in the chemical industry, where NOx concentrations could be in the 10,000-vppm range. ADVANCED NOx CONTROL TECHNIQUE CURRENTLY UNDER DEVELOPMENT As discussed, the container glass industry in California, in general, has been able to meet the current regional regulations of 5.5 Ib/ton by applying the relatively simple first-generation combustion modification technologies developed and commercialized earlier, namely, low excess-air firing and flame-shape adjustments, and in some cases, together with increased electric boost and cullet usage. For (P-002\1194Maui.doc |