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Show EXPERIMENTAL PROCEDURE AND RESULTS Preheat, Start-Up, and Operation The furnace was preheated by firing natural gas at 2 X 106 Btu/hr at 20% excess air for 48 hours. Natural gas was also fired whenever the coal feed was off. To ignite the coal, natural gas was simultaneously fired with the coal at the onset of coal feedings and was shut off when the coal was ignited. First, the flame was examined visually for fuel pulsations and flame stability. After adjustments were made to optimize flame geometry and stability, the input conditions listed in Table 6 were set. For all tests, the firing rate for the fine-ground coal was 1.9 X 10& Btu/hr, and the excess air was near 20%, which would have 3.7% oxygen in the flue gas and a total flow of 25,000 SCF/hr of dry air. During this period, additional adjustments were made to the primary air and the secondary air. The goal of these adjustments was to achieve a good balance of minimum flame length with the desirable amount of excess air. After the desired conditions were reached, a detailed flue-gas analysis was taken to determine flue oxygen and to check for evidence of incomplete combustion in the form of carbon monoxide. If the C O levels were in the range of 100 to 200 ppm, the furnace was allowed to run long enough to achieve stability so that reliable data could be collected. After stability was reached, a complete gas analysis of the flue products was again taken. For some conditions, wall temperatures were also measured. For some conditions, particulate (ash) samples from the flue were also taken. Using the same procedure, the natural gas flame was studied prior to coal combustion at a similar firing rate and excess air level. These results were used as a baseline to compare the natural gas and fine-ground coal flames. During short periods, natural gas was used as a motivating media. During these periods, the natural gas/coal mixture (50/50 by heating value) flames were observed. The flames were stable and very similar to the coal flames. 16-25 |