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Show INTRODUCTION There are approximately 125,000 gas-fired firetube boilers in the 600 to 3,200 MJ/hr (0.6 to 3 million Btu/hr) firing range in the United States. An additional 3,000 new units are sold annually. These boilers produce about 150 ppmv N0x at 15 percent excess air, making gas-fired firetube boilers the 26th largest NO source in the U.S., accounting for one percent of the total A N0X produced. In addition, firetube boilers are usually located in population centers where their effect on air quality is greater than the inventory percentage would indicate. In the interest of improving air quality, the Environmental Protection Agency has funded the development of low NO burners for retrofit into existing boiler designs. The program approach was to select a burner concept that met the needs of firetube boiler users, test the feasibility of the concept, identify a suitable burner material, test the burner concept in a subscale facility, and, finally, demonstrate the concept as a retrofit burner in a commercial size firetube boiler. These aspects of the program are described in the following sections. CONCEPT SELECTION During the first year of the program, three low NO burner concepts were considered for firetube boilers: 1. Fiber matrix burner 2. Staged catalytic burner 3. Single stage catalyst with flue gas recirculation The fiber matrix burner was selected for further development because it requires few changes to the conventional boiler system. In comparison, staging introduces undesirable hardware complexities, and flue gas recirculation requires additional blowers that increase cost. The fiber matrix burner is a single stage concept that can operate near stoichiometric with low NO and A without flue gas recirculation, does not require preheat to operate with natural gas, and can potentially burn liquid fuels (with combustion air preheat). The last characteristic is important in the current marketplace, 3-3 |