Container and flat glass manufactures in the USA and EU are required to comply with new lower NO_x emissions limits as regulation becomes stricter. With modifications of the primary air combustion system such as the optimization of natural gas injection, most furnaces have been able to reduce No_x emissions and comply with current regulations. However, greater reduction (500 to 800 mg/Nm~3 at 8% O_2 dry) was shown to be difficult for many furnaces by the modifications of the fuel injectors alone. Combustion staging to reduce the stoichiometric ratio of the primary air flame by secondary oxidant injection at a strategic location of the furnace has shown significant reduction in No_x emissions in many furnaces. Praxair has developed the Oxygen Enhanced No_x Reduction (OENR) technology to further reduce No_x emissions and achieve No_x levels below 500 mg/Nm~3. A small amount of oxygen is injected near the exhaust ports within the furnace to burn out the remaining CO after optimizing the primary air flame. This paper presents a CFD study of the OENR technology and application examples to cross-fired and end-port furnaces. No_x emissions as low as 380 mg/Nm~3 at 8% O_2 dry flue gas conditions were achieved. Overall, OENR proved to be a cost effective technology, which significantly reduces No_x emissions while maintaining good glass quality and reducing fuel consumption.
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