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Show 2 INTRODUCTION The glass industry in the United States is rep~rtedly ihe fourth largest industrial (, ergy consumer. The majority of the glass -- representing container, flat, pressed, and blown -- is produced in relatively large (100 to 1000 ton/day) regenerative glass tanks, which operate continuously for up to 10 years. The glass container segment alone accou ts for about two-thirds of the total glass produ ed and uses over 60 billion cubic feet of natural gas per year. Regenerative glass melters use extre:nely high combustion air temperatures (1000° to 1300°C) to improve production rate, product qual~LY, and furnace thermal efficiency. Furnace and flame temperatures -- and, consequentl ,NO generation - are quite high. NOx emissions of over 3000 vppm· (12 to 15 lb NOx/ton of glass prodpced) are not uncommon (1,2) from natural gas-fired glass melters. Although there are currently no national regulations on NOx emissions in the United States, this could change in light of the 1990 Clean Air Act. On a regional basis, these emissions are restricted in certain areas - the most stringent being in Southern California. The South Coast Air Quality Management District currently restricts the NOx emissions from glass melters to 4.0 lb/ton of glass produced (3). Even stricter regulations are now being implemented for this region requiring NOx reduction to below 0.6 lb/ton in the year 2003. The glass industry, in general, has been able to reduce NOx to levels approaching the current regulations through relatively simple combustion modification techniques developed ea lier (2,4) by IGT and CTI with funding support from GRI and SoCalGas and by increasing the electric boost, as well as the percent of cullet in the feed. Some melters have been switched to fuel oil to control NOx' Fuel oil does offer somewhat lower NOx emissions, but at the expense of additional SOx and particulate emissions, higher fuel system operating costs, and other operating problems. Furthermore, the presence of vanadium and sulfur and the higher crown temperatures that result from oil firing somewhat reduces the furnace service life (5). The high levels of electric boost currently used are also not desirable because of increased energy costs and reduced furnace service life. There is, therefore, a need to develop advanced cost-effective 10w-NOx technologies for retrofit to natural gas-fired regenerative glass melters. POTENTIAL NOx REDUCTION TECHNIQUES During combustion in high-temperature furnaces, NOx is essentially formed by 1) thermal oxidation of nitrogen in combustion air (thermal NOx) and 2) oxidation of chemically bound nitrogen in fuel (fuel NOx)' Thermal NOx depends upon the time-temperature history of the flame and increases with increasing residence time and with increasing peak flame temperatures. Both thermal and fuel NOx also increase with increasing oxygen availability in the high-temperature zone. Natural gas does not contain any chemically bound nitrogen, and the NOx formed during natural gas combustion is essentially thermal NOx' Some NOx can be formed, however, from nitrogen contained in the batch. To reduce NOx formation during natural gas combustion, therefore, both the peak flame temperatures and the oxygen availability must be reduced. Many different modification approaches for reducing NOx formation in natural gas combustion have been used, investigated, or proposed. All emission values are corrected to 0% 02· (P-(II),) \ , 194M- _' i.doc |
