OCR Text |
Show OBSERVATIONS AND CONCLUSIONS Based on an analysis of the data collected the following observations and conclusions have been derived. 1. The flame length was sensitive to the size of grind of the coal and was significantly reduced as the size of grind diminished. The visual flame length was 60 cm (24 in.) for the finest coal, 90 cm (35 in.) for the middle grind, and 140 cm (55 in.) for the coarsest coal. 2. Flame length determined by carbon monoxide measurements (at 99% fuel consumed) showed good agreement between measured and visual flame lengths. However, the carbon monoxide profile along the furnace axis for the two finest coals, showed a sharp reduction in carbon monoxide concentration downstream of the flame end. For the coarsest coal, the carbon monoxide level remained relatively high until almost the end of the furnace (280 cm or 110 in. from the burner wall). 3. The fly ash analyses sampled on the furnace axis along the furnace length showed that 99.5% or greater carbon burnout occurred at 70 to 80 cm (28 to 31 in.) from the burner wall, for fine-ground coals, and at 180 to 190 cm (71 to 75 In.) for the coarser coal. The fly ash samples were not collected isokinetically so the results must be interpreted with care. 4. The combustion intensity achieved with the flame with the finest grind of coal was significantly higher than that with the coarser coal grind. The combustion intensities were determined to be about 0.8 X 106 kcal/hr-m3 (0.9 X 105 Btu/hr-ft3) for the finest coal, 0.6 X 106 kcal/hr-m3 (0.7 X 105 Btu/hr-ft3) for the middle size coal, and 0.35 X 106 kcal/hr-m3 (0.4 X 105 Btu/hr-ft3) for the coarsest coal. 5. Oxygen and carbon dioxide analyses along the furnace axis indicate some differences in the furnace and flame flow patterns. However, data collected are not sufficient to clearly interpret these differences. 6. The combustion gas temperatures measured confirm the more intense combustion that occurs as the size of grind is reduced. The combustion gas temperature along the furnace axis was highest near the burner wall, with a slow decline to the flue for fine-ground coals. For the coarsest grind, the combustion gas temperature was lowest near the burner wall, with rising gas temperature, until the middle of the furnaces. 7. The radiation heat flux and the overall amount of heat absorbed by the furnace load (water-cooling tubes) was considerably higher for fine-ground coals compared to the coarser coal. 44 |