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Show ADVANCED MATERIALS DEVELOPMENT FOR RADIANT TUBE APPLICATIONS Winston W. Liang, Matthew E. Schreiner Gas Research Institute Chicago, Illinois, USA Abstract Gas Research Institute, GRI, is supporting the development of innovative advances in the state-of-the-art for natural gas-fired industrial process heating and melting equipment. The industrial Utilization Research Department of GRI is currently planning to fund multiple projects for the development of systems capable of providing furnace temperatures in the range of 1100 to 14500C (2000 to 26000 F). These systems will be required to provide a minimum peak heat flux of 91 kW/m2 (200 Btu/Hr/In 2) within this temperature range) in order to effectively compete with comparable electric resistance heating technology. To remain cost competitive with electricity these systems must be at least 65% efficient to take advantage of the existing electricity to natural gas price ratio. System first cost and required maintenance costs must also be competitive with existing gas-fired systems and comparable electrically heated systems. The basic components of an advanced indirect gas-fired heating system include burners, heat transfer surface, and heat recovery equipment. GRI has identified the most critical of these components to be radiant tubes, which provide the required heat transfer surface, and house the combustion flame and its oxidizing by-products. This paper attempts to review state-of-the-art and emerging advanced materials including high temperature alloys, monolithic ceramics and fiber-reinforced ceramic matrix composites. A series of development projects involving ceramic and composite materials, and component development for radiant tube applications will be discussed. 305 MANY INDUSTRIAL PROCESSES REQUIRE a method for heating products to a working temperature of 800 to 14500C (1500 to 26000 F). Advances in natural gas combustion equipment have been developed in response to an industrywide need to lower costs through efficiency and productivity improvements. Such improvements will allow natural gas to effectively compete with alternate energy sources. New natural gas burner systems must enhance the premium qualities of natural gas while meeting or surpassing the advantages of other fuels. Industry currently utilizes direct-fired and indirect fired burner types. Direct-firing burners discharge the products of combustion, as well as heat, directly into the process environment or onto the workpiece. In contrast, combustion with indirect-fired burners takes place within a tube or other enclosure; transferring heat through the walls of the enclosure to the process environment. The radiant-tube burner is one common type of indirect-fired burner used in processes where the presence of combustion products would contaminate or otherwise degrade the material being processed. STATE-OF-THE-ART METALLIC RADIANT TUBE TECHNOLOGY Until recently, radiant-tube applications have been limited to process temperatures below 10000C (19000 F), thus limiting both heating rates and process productivity. This limitation stems predominantly from the properties of the metallic materials of construction. Where nickel based superalloy materials are currently used as key system components; 11000C (20000F) appears to be the maximum temperature for safe, continuous operation. At process temperatures above 10000C (19000 F) most indirect-fired processes employ electric resistance heating elements as the heat source. Development of a |