OCR Text |
Show possibility of air infiltration. For most conditions, flue gas temperatures and wall temperatures were also measured. Particulate (ash) samples from the flue and from points along the flame axis were also taken. At the end of each trial ash slagging and fouling rates were examined. The furnace operating conditions and some results of the fine-ground coal combustion trials are listed in Tables 1 through 4. Five trials are listed using four particle sizes. For the first three coal trials presented, all data on combustion characteristics were collected; for the last two trials, only a limited amount of data were taken. The firing rate was low for the first trial (470 kW or 1.6 million Btu/hr) so the same coal size was retested in Trial 5 at a higher firing rate (700 kW or 2.4 million Btu/hr). The firing rate was initially determined by measuring the mass flow from the screwfeeder at atmospheric pressure, but during experiments this rate was found to be slightly changed. This may have been the result of variation in coal density or variation of the pressure in the screwfeeder. The primary air and combustion air flows along with the flue gas analyses were eventually used to verify the true firing rate. Table 2 gives the burner pressure of the secondary air for the first three trials using a water manometer, which agrees with the measured air flow. Flame lengths were determined visually by observing the luminous end of the flame through the doors on the furnace sidewall. The luminous end of the flame varied with particle size directly. The visual shape of the flame was roughly cylindrical with a conical tip at the nozzle. The photograph in Figure 13 shows the flame near the burner block during Trial 2. All coal flames became stable after 30 minutes of initial operation, but some residual low-frequency (approx. 0.5 to 1 cps) flame pulsation was observed. Tn Trials I and 5 (the finest coal) the flame pulsated the most; in Trial 3 (the coarsest coal), the flame pulsated least. This may be due to feeding the coal to the burner nozzle. A total of 12 metric tons (13 short tons) of coal was burned during the project. The firing time listed in Table 2 for each trial includes all tests, but not start-up or shutdown time when natural gas was added to the flame. 21 |