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Show high temperature, indirect firing burner system is appropriately used. The objective of GRI's advanced indirect gas-fired heating system program is to develop a system that is capable of operating at furnace temperatures in the range of 1100 to 14500C (2000-26000 F). This system will be required to provide a minimum peak heat flux of 95 kW/ (30,000 Btu/Hr./Ft 2) within this temperature range, in order to effectively compete with comparable electric resistance heating technology. The overall performance goals are summarized in Table 3 as compared to a metallic state-of-the-art system. Table 3 Stale-ol·Ihe-Ar1 Versus Emerging Technology: INDIRECT GAS·FIRED HEATING SYSTEMS SOA ....... 1 Me .. 1 FumlCe Tempeqlu,., ·F 1,400 - 1,900 (Mo.) Furnace efficiency (Recupereled), % 40-65 Heel Flu., Blulhr tt' 6,000 - 8,000 ( ..... ) lUbe ute, Yur 0.5-3 Goal C.,.mIc 1,900 - 2,600 70-85 20,000 - 30,000 MInimum 2 Materials technology is advancing to the point where monolithic ceramics and ceramic matrix composites capable of operating at temperatures up to 30000 F (See Figure 2), can b~ competitive with or superior to superalloys as radiant tube materials in high temperature furnaces. To achieve the system performance goals (Table 3)for these applications, high temperature advanced burners and high effectiveness heat exchangers must be properly integrated with the ceramic tubular component in the combustion system. The most critical of the components within these systems are clearly the radiant tubes. 840 NO 480 400 320 240 1110 110 Figure 2 STRENGTH-TO-DENSITY RATIO VERSUS ® "C Of' TEMPERATURE a/f' - 10" ... t.,. _----~=::::::::==~11e 700 1,2'2 800 1,852 1,100 2,012 1,300 2,312 14 12 10 e e 4 The design requirements for radiant tubes in advanced gas fired heating system applications have been identified as follows: o Thermal conductivity in the 2200-2800oF range which will insure 95 kw/m2 (30,000 Btu/hr. ft. 2) heat flux o Physical and mechanical properties which will insure structural stability at temperatures up to 15000C (28000 F) o Good thermal shock resistance to 307 withstand normal furnace cycling and occasional forced air cooling o Reasonably thin walls (1/16 to 3/8 in.) to minimize the temperature gradiant through the tube wall o Compatibility with products of combustion and furnace environments at operating temperature up to 28000F (e.g. endothermic or H2/N2 atmosphere) o Impermeable to gas (to 10 torr vacuum) o Life cycle cost equivalent to or better than metallic tube In consideration of these requirements and the environmental conditions to which the radiant tubes will be exposed, ceramic based materials are well suited for application as radiant tubes in these advanced indirect heating systems . The most likely configurations for ceramic radiant tube heating systems are: o Straight tube o Single Ended Tube o "U" Tube as described in Figures 3, 4 and 5. Figure 3 OPEN-ENDED RADIANT TUBE FIGURE 4 SINGLE-ENDED RADIANT TUBE FIGURE 5 U-SHAPED RADIANT TUBE |