OCR Text |
Show needed. However, the flames shortened and moved closer to the burner as the coal was ground finer. A preliminary investigation was performed by IGT on the combustion characteristics of a fine-ground coal flame in a previous study. This flame was compared with a natural gas flame and a standard pulverized coal flame. A Pittsburgh No. 8 bituminous coal was ground to 99.9% less than 37 microns. One-half of the mass of the coal had particle sizes less than about 8.5 microns. The coal was fired using a boiler burner with various fuel nozzles in a research furnace modified to simulate an oil-fired boiler furnace at a rate of about 2 million Btu/hr with 20% excess air. The flame was evaluated by visual length and stability. The combustion air temperature and percent of primary air were varied with different nozzles to maintain visual flames from 35 to 45 cm in length. Carbon monoxide and unburned carbon in the fly ash were measured along the furnace axis to substantiate the visual observations of the flame length. The natural gas flame was visually the same shape and 10 cm long, and the standard pulverized coal flame was from 190 to 230 cm long. Short runs were done burning a natural gas/fine-ground coal mixture. In these cases, the visual flame length was very close to the flame length of fine-ground coal combustion. Gulf States Utilities Co., Babcock & Wilcox Co., and Stone & Webster Engineering Corp. in 1981 initiated a test and demonstration program to investigate the feasibility of burning ultrafine pulverized coal in boilers currently burning oil or g a s ^ . The results of ashing in the laboratory furnace showed that the ash particles from the micronized coal were much smaller than those from the conventional pulverized coal and the micronized coal ash particles did not appreciably agglomerate in the combustion zone. The reduction Ln ash deposition on convective tubes and effectiveness of the soot blowing when burning micronized coal was also shown on their pilot scale furance. The previous background indicates that fine-ground coal can reduce flame lengths, increase heat-release rates in the flame, reduce the combustion volume necessary for a given thermal input, and reduce 4 |