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Show substoichiometrically and thereby scavenge the high excess oxygen levels which exist in many stokers rather than contribute to excess air losses. The burner was equipped with two gas spuds: a radial injection spud for operation at high loads, such as warmup, where rapid mixing is needed to avoid long flames; and an axial injection spud for lower loads where deep flame penetration is required. The burners were positioned 6 feet above the grate. This elevation is high enough to avoid overheating the grate and seals during startup, and to avoid interference with the overfire air which could kick up ash from the grate. This elevation is low enough to permit burnout and effective heat removal from the gas flame and to avoid overheating superheater tubes. Computational fluid dynamics was used by Coen to help select burner location and evaluate effects of the gas flame on overall furnace performance. These results are presented in a companion paper at the symposium (3). RESULTS The boiler was brought back on line july 6, 1995, using gas for warmup. After a period of validation of the new coal automatic Gontrol system installed during the retrofit, the unit was cofired with gas on August 4, and has been cofired for the majority of the time since. The boiler was tested with and without gas co firing to determine incremental performance effects and quantify benefits. Testing included: • Continuous emissions monitoring for 4 months of 02, CO, CO2, NOx' S02 • Furnace probing for temperature, velocity, and 02' CO, NOx • Particulate sampling upstream and downstream of the electrostatic precipitator (ESP) • Solids sampling of coal, bottom ash, mechanical collector ash, and ESP hopper ash • Thermocouple monitoring on the surface of 12 superheater tubes 13 |
