OCR Text |
Show tilt, % excess air, coal air/auxiliary air damper position variations, secondary air pressure variations, and boiler load. Only the effects of over-fire air, burner tilt, and % excess air were addre sed. The tests were performed in October and November in 1993. For the comparisons hown herein, measured NOx concentrations were taken to be principally NO. One test was performed to establish a baseline, with the top level of burners out of service, and no air injection through this level of burners. The burner tilts were operated at 0°. In the remaining tests, coal was still only injected in the three lower levels of burners, and the top level was used for injection of over-fire air. The tests which were simulated in this study are shown in Table II. Test I was conducted to determine the effects of over-fire air on NOx formation. In this test, the air and coal flow rates were the same as the baseline test, but only over-fire air was injected in the top level of burners, and all burners were operated at 0° tilt. Tests 2 and 3 were conducted to determine the effect of % excess air on NOx formation. As with previous tests, all burners were operated at 0° tilt. In Test 2, the air flows were increased to obtain approximately 1% increase in the exit 02 concentration. In Test 3, the air flows were decreased to obtain approximately I % decrease in the exit 02 concentration. Test 8 and 9 were conducted to determine the effect of burner tilt on NOx formation. In Test 8, the fuel nozzles were tilted upwards 22°, and in Test 9 the fuel nozzles were tilted downward 20°. Furnace Simulations Simulation of practical furnaces requires a large computational mesh to identify the processes occurring inside of these systems. The mesh used in the study discussed previously which compared profile measurements of temperatures, major species and pollutant concentrations, assumed symmetry of the furnace and used a grid with 122,500 (25x49xl00) computational cells. This is equivalent to a grid for the full boiler of 250,000 computational cells. Since only effluent values of NO pollutant measurements were available for this study, a smaller grid was used in this 5 |