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Show over a steel screen that acts as a support structure. The ceramic material is highly porous, such that the premixed gas and air pass through the ceramic matrix and combust in a thin combustion zone on the outer surface of the ceramic layer. Figure 1 shows the construction of a typical small CombuSlion Zone (1000· C) Radiant and Conveclive Energy Flux Fig. 1 - Ceramic fiber burner burner. For industrial burners, the screen structure is welded to end flanges to make up cylindrical burners of one or more segments or to a rectangular plenum for flat surface firing configurations. Figure 2 shows a typical cylindrical immersion tube burner. .. Exhaust Fig. 2 - Immersion tube burner The Pyrocore burner operates at a heat release rate per unit of burner surface are~ of 315 kW/m 2 (100,000 Btu/hr-ft ). Because the heat input is based on surface area, the burner is easily scalable. Burners ranging in size from 4.4 kW (15,000 Btu/hr) up to 293 kW (1 million Btu/hr) are commonly made using the same type of support structure and forming techniques. Cylindrical industrial burners of up to 2928 kW (10 million Btu/hr) as well as flat plate forms are currently being manufactured. The Pyrocore burner first drew attention for industrial uses under a contract from the U. S. Environmental Protection Agency. The objective of that contract was to develop low nitrogen oxide (NOx ) emission 268 combustors. One specific application where the burner appeared applicable was the firetube boiler. Following subscale tests under the EPA program, a pyrocore burner was retrofit in a 245 kW (25-hp) York-Shipley boiler and successfully operated on natural gas for over 1000 hours. NO emissions were reduced by approximat~ly 80 percent, with CO and hydrocarbon emissions at the same level as found with the conventional burner. Figure 3 shows typical emissions from the Pyrocore burner in boiler applications. (/) c 0 ~ C Q) u c 0 0 (/) c 0 in (/) E w 80 70 60 c5 C 50 Q) u <u Cl... 40 0 ro > E 30 Q. ~ CO 20 10 o 10 20 30 40 50 Excess Air (Percent) Fig. 3 - Fiber burner emissions characteristics 60 In addition to decreased NOx emissions, the pyrocore burner system operated at reduced excess air levels, resulting in a 1 to 2 percentage point increase in boiler efficiency, and was capable of being overfired by up to 20 percent without causing overheating of convective pass tube weldments at the end of the combustion chamber. To achieve scaleup to larger boilers, some changes to the burner were necessary. This early work brought the technology and its applicability to industrial uses to the attention of the Gas Research Institute. In a subsequent program sponsored by GRI, the burner was redesigned for fabrication and installation in segments, |