OCR Text |
Show 8. The slag and ash deposition tests demonstrated the reduction in slag and ash deposition rate on convective tube passes when burning the finer coal particle sizes. These tests were conducted at relatively high (1300°C or 2370°F) flue gas temperature entering the convective passes of the probe and with heat transfer surface temperatures from 340°C (640°F) to 590°C (1090°F). The deposition rates were 63.5, 105.9, and 284 grams per hour (0.14, 0.23 and 0.63 pounds per hour), respectively, for the finest to the coarsest coal. Depositions from the fine-ground coals were also easier to remove. A bimodal coal tested showed the deposition rate of 109.4 grams per hour (0.24 pounds per hour), which is close to the rate from the middle size coal. However, the bimodal coal produced a hard black slag on the rear convective tubes that was difficult to remove. 9. Slag and ash deposits were found in the burner throat, on the burner wall, and on the furnace cooling tubes. These may be either eliminated or minimized by developing a better burner and nozzle design for fine-ground coal firing. 10. Feeding and pneumatic transport of very finely ground coal proved to be more difficult than with coarser coal. Although even coal ground to 99.9% below 15.8 um was successfully transported in this program, it was not easily achieved and the feeding and transport system could be further improved. 11. No relationship was found between coal particle size and NO emissions. Acknowledgment We wish to acknowledge Mr. James D. Hickerson and Mr. Harry Ritz of the Pittsburgh Energy Technology Center and our colleagues of IGT's Industrial Energy Utilization Group for their contributions in conducting this study. 45 |