OCR Text |
Show as baseline with burner directed horizontally and mounted 2 ft (0.610 m) above the glass bath. Case 4 with horizontal burners 1.3 ft (0.396 m) above glass surface was conducted to study the impact of burner elevation. In Case 5 finally, the O2 burners mounted at 2 ft were angled downwards towards the center-line of the fuy·nace. RESULTS AND DISCUSSION Air Case and Model Verification Results obtained for conventional air firing (Case 1) of the end-section are displayed in Figs. 5 through 8. Fig. 5 shows the relative mass flux distribution utilized in horizontal and vertical cross-sections of the furnace. The flow is characterized by a weak outer recirculation field surrounding the forward flow emerging from the firing port. The recirculation eddy extends over the whole furnace depth. Its strength was prescribed to be 1.0 times the inlet mass flow. However, previous experience with the zone model has shown that, in weak recirculating flows like in the current air case, the actual recirculation strength has only a weak effect on thermal performance provided bulk flow features are approximately simulated. Fig. 6 shows the distribu~ions of gas temperatures (F) predicted for air firing in a horizontal and in a vertical furnace cross-section through the flame as well as in a vertical cross-section located halfway between Port 5 and the bridge wall. The predicted flame extends over the whole furnace depth up to the flue gas port. This agrees with observations made in the actual furnace. It was observed that sooty flame tips extended inter~.i.tt~ntly into the opposite port. The mean g~s exit temperature predicted is 28510 F (1840 K). This is in good agreement with optical pyrometer measurements, which yielded averaged gas temperatures near the flue gas port of ca. 28570 F (1843 K) as seen from the regenerator observation ports. Fig. 7 shows the distribution of refractory temperatures (F) predicted for all walls of the furnace end-section for air firing. In this graph, as well as in all following graphs for air combustion, the display of the variables (i.e. the refractory temperatures in this case) is symmetrized with respect to the furnace axis. This approximately accounts for the complete firing cycle. Maximum refractory temperatures of 26840 F predicted for the furnace roof fall into the range of measured mean crown temperatures, which varied from 26500 F for the section of Port 1 to 28500 F for the end-section Port 5). The maximum roof refractory temperature of the non-symmetric prediction was 26940 F (1752 K). In comparing the model predictions with the 11 |