| OCR Text |
Show NOx emission in preheat mode (ie., 100% air into the annular air duct) is about 90 ppm and decreases drastically when FDI air distribution ratio exceeds 20 %. NOx approached a minimum value when the FDI ratio is 80-100%. 4.2 NOZZLE ARRANGEMENT Two burner configurations were compared in order to optimize the arrangement of air and gas injectors. Fig. 6 shows the two types of burner configuration tested. For type A configuration the gas nozzle was located in the center surrounded by 6 air nozzles. For type B configuration, by contrast, the air injector was located in the center surrounded by 6 gas injectors. The velocities of the air and gas were maintained constant for both configuration (heat input 1.7MW air ratio 1.05 furnace temperature 1300°C preheated air 650t ). NOx level from type A is 34ppm(11 %02) while 40ppm NOx is obtained with type B. This observation indicates th~ importance of arrangement of the air nozzles. The air jet has a major role in creating self-induced FGR since the air was one order higher magnitude of momentum flux compared with the gas jet. If the air jet which dominates the entrainment of the combustion products is split as in type A configuration, the total surface area of the air jets which is essential for entrainment is increased. Thus more entrainment of the combustion products can be expected for type A, resulting in a lower NOx level than type B. (A) Center Gas Nozzle Outside Air Nozzles , (B) Center Air Nozzle Outside Gas Nozzles Input 1,700kW Air Ratio 1.05 Ta 650°C Tf 1,300°C Gas Velocity m/s Air Velocity m/s NOx ppm (02=110/0) NOx Ratio 0/0 100 120 34 85 100 120 40 100 Ffg. 6 Effect of nozzle arrangements on NOx emission 7 |
