OCR Text |
Show I.Heat transfer, Flame and Wall Temperatures. Figure 7 shows changes in the heat flux to the furnace floor for varying oxygen addition and for firing rates of 80%, 90% and 100%. It can be seen that the heat flux increased with the oxygen enrichment, most noticeably for the full firing rate. The increase of the heat flux, about 10%, is more evident with the lance air on, shown in Figure 8. Stronger trends can be observed in changes of the roof maximum temperature, shown in Figure 9. This temperature increased for all firing rates with the largest increase at 80% firing rate. The furnace floor in the single burner combustion chamber is comprised of eleven water-cooled panels. By measuring of the water flow rate and change of water temperature across each panel the heat flux density to the floor can be determined. Next four figures, Fig.10, 11, 12 and 13, show the distribution of the heat flux into the floor based on individual panels data. Figures 10 and 11 contrast no oxygen and 6% oxygen addition cases at 90% firing rate. The distribution pattern remained unchanged however, for the 6% case higher values of the flux are present close to the burner face. In both cases the maximum fluxes were recorded in the upper right quadrant of the floor, where the exit from the combustion chamber is located. There is a dramatic change in the distribution pattern for the operation with the lance air on, for both the atmospheric air, Figure 12 and the 6 % oxygen enriched air, Figure 13. The high heat fluxes are present on larger portion of the floor however, there is no flame signiture in the close vicinity of the burner face. The 6% oxygen addition case shows again substantial increase of the heat flux near the exit form the combustion chamber. The next two figures, Fig.14 and 15, illustrate results of the flame temperature measurements for the four cases described above. As it was pointed before there was only a modest increase in the heat transfer to the floor. The temperature profiles shown in Figures 14 and 15 indicate flame temperature increases of about 100°C. This should have resulted, all other parameters being the same, in about 30% increase in the total heat transfer. One needs to remember however, that data shown in the Figures 14 and 15 are local, the flame centerline temperatures. Having this in mind, the 10% ; increase of the total heat flux to the floor is well justified. 2. Nitrogen Oxides. Prior to testing with oxygen enriched combustion air series of runs with atmospheric air was performed. This was to establish the baseline performace of the burner. In order to test the burner for NOx production levels with varying temperature of combustion air, the floor of the furnace was covered with a layer of refractory material. The results, for 100% firing rate, are shown in Figure 16. As expected there is an increase of the NOx , about 25%, with the increasing combustion air temperature. More importantly however, the measured NOx levels do indeed allow to classify this burner as the low NOx burner. Figure 17 shows temperature profiles at the flame centerline. The temperatures here are much higher then those disscussed before, since the combustion chamber is now close 4 |