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Show increases with temperature, high-temperature applications such as calcining, heat treating, metal processing, and metal and glass melting generate very significant N O x emissions. A key GRI goal is to develop a high-temperature burner that achieves N O x levels below 100 p p m without compromising performance. With GRI sponsorship, a team composed of Arthur D. Little, Hauck Manufacturing Company, and the Massachusetts Institute of Technology are developing a staged air recirculating burner (StAR) that can meet required N O x levels with no loss of efficiency. Under intensive testing, the StAR burner produced N O x levels of less than 50 ppm while using combustion air preheated to 1500°F. A comparable commercial low-NOx burner produced levels of 180 ppm. Field evaluation is currently underway at a titanium forging plant in California. Other tests at aluminum manufacturing and steel forging plants are planned. GRI is also developing an advanced burner concept with Altex Technologies, Inc. At the prototype stage, the burner operates at air preheat temperatures of 1500°F and uses internal flue gas recirculation and staged combustion to keep N O x levels below 100 ppm. Its flame and heat transfer characteristics are equal to commercially available burners, and it provides excellent flame stability. Many high-temperature processes use indirect heating systems. Ceramic single-ended radiant tube burners developed for GRI by Eclipse Inc. and Pyronics, Inc., are now widely used. T o meet the challenges of the 1990s, GRI and Pyronics are developing enhanced low-NOx versions of these products. The first units are scheduled for field testing in late 1993. Low-Temperature Heating. Drying, and Curing Applications In low-temperature applications, natural gas burners offer cost savings over electric resistance heating. While the N O x emissions of existing gas burners in this group are already low, further reductions without loss of efficiency will most likely be needed to meet anticipated regulations while maintaining a competitive edge. Productivity and product quality are also important in these applications. Natural gas infrared heating is a proven low-NOx technology for many drying and curing applications. N O x levels are reduced because about 40 percent of the heat of combustion is converted to radiant energy as the flames impinge on the ceramic or metallic heating element. This quenching effect holds flame temperatures below the threshold of substantial N O x 4 r-i |
