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Show INTRODUCTION In 1988, IGT completed a fairly comprehensive survey of industrial burner manufacturers for the u. S. Army Construction Engineering Research Laboratory (1). The objective was to identify state-of-the-art lowNOx/ high-efficiency burners for field testing on the u.s. Army's firetube boilers. The results indicated that there was little emphasis on developing 10w-NOx burners. Only 6 of the 104 manufacturers surveyed claimed NOx levels below 50 ppm, and only one claimed NOx levels close to 40 ppm. None of the 10w-NOx burners had been developed specifically for, or were tested on, firetube boilers; the NOx emission levels given were only manufacturers' estimates with no actual backup data. With emission regulations becoming more and more stringent, the emphasis appears to be changing. For example, a recent article, "New Developments in Boiler Technology" states that "lowering NOx emission levels is a major aim of boiler manufacturers today" (2). As stated in the article, the strictest regulations are being employed by California's South Coast Air Quality Management District, which is now requiring NOx levels below 35 ppm (0% 02) for all boilers at or above 2 X 106 Btu/h. Other states are also expected to adopt similar NOx emission regulations. Limits on carbon monoxide (CO) and total hydrocarbon (THC) emissions may also be forthcoming with even stricter NOx emission limits. While the industry is focusing on developing burners to meet the current and near future regulations, IGT is looking ahead. We anticipate that NOx limits in the vicinity of 10 ppm may be required in the future or near future. IGT has long recognized the need for low-emission burners for boilers and fluid heaters; as a result, we conducted an evaluation to identify the most promising NOx control techniques for natural gas - fired boilers. The techniques were to b~ cost-effective and provide low CO and THC emissions while minimizing any decrease in boiler capacity or thermal efficiency and any increase in electricity consumption or other operating costs. The results of this study show that the best NOx control methods are - • Enhanced heat transfer from the flame • Internal combustion products recirculation • ruel/combustion air premixing • Combustion air staging • Fuel staging. With proper application, the above techniques could provide significant NOx reductions with equal or improved thermal efficiency and combustible emissions. For even greater NOx reduction, one or more of the above techniques could be combined with the following: |