OCR Text |
Show Figure 8 shows photographs of the lifted flame at Ip=480 kW, A =1.1 and 1/J =0.36. Photograph (a) shows a side view of the flame with the test burner installed at the left. The flame initiates further downstream at roughly 400 mm from the burner plate, generating lifted blue flames, which are clearly distinct from stabilized flames. Photograph (b) shows a view from the back of the furnace. Three separate lifted blue flames are observed downstream of the slot-like air injection ports. The photographs clearly show the novel appearance of the lifted flame which enhances the self -induced EG R effect, thereby achieving the substantial reduction of N Ox. 4.4 Detailed flame measurements To gain a detailed understanding of the lifted flame and its remarkably low NOx emission characteristics, in-furnace detailed measurements were conducted. The measurements were conducted with Ip = 480 kW, A =1.1 and 1/J =0.36. Figure 9 shows a measured flow pattern in the test furnace. The flow pattern was measured by using the acetylene flame flow visualization method(2). A probe injecting a tiny amount of acetylene gas was placed in the furnace. Flow direction in the furnace was visualized by the movement of the acetylene flame. The probe clearly identified a main forward flow of the combustion air and two recirculating flows. On cross-section A across the air injection port, the combustion air creates a main forward flow slightly expanding towards the furnace wall. An external recirculation zone is observed down to about 300 mm from the burner in the area enclosed by the main forward flow and the furnace front and side walls. A remarkably large internal recirculation zone is observed on cross-section B, suggesting that a substantial amount of flue gas recirculates back to the burner zone. Figure 10 shows the temperature distribution in the test furnace, measured by a suction pyrometer. On cross-section A, a sudden increase in temperature is observed along the main forward flow at roughly 400 mm from the burner. The maximum temperature approaches 160SK at roughly 700 mm downstream from the burner. This sudden increase in temperature indicates the ignition of the lifted flame. Compared with that on cross-section A, the temperature distribution on cross-section B is relatively uniform. A high temperature region approaches very close to the burner zone. |