OCR Text |
Show IFRFDocNoK70/y/113 IJmuiden, April 1997 -9 AFRC Spring meeting 1997 Type II Swirled Secondary Air Sewage - - Coal Sewage Coal Swirled Secondary Air Type I Figure 3.5 Sewage Placement for Type II and Type 1 Flames 3.2.1 The effect of fuel ratio, fuel injection mode and burner operation on the NO^ emission level Injecting the sewage on the inside of the coal jet, Figure 3.5, created a type I flame and the devolatilisation of the sewage particles and subsequent flame propagation occuned under oxygen lean conditions. This resulted in reduced N O x emissions. In Figure 3.6, the effect of fuel ratio and sewage injection velocity is demonstrated with the highest levels of N O x being achieved with the high velocity sewage jet (87 m/s). This can be attributed to the reduced residence time of these sewage particles in the oxygen lean flame zone and further penetration through the LRZ. This resulted in an increase in flue gas N O x due to oxidation of these residual volatile nitrogen species at the tail end of the flame. For conditions where the sewage was injected at low velocity (19 m/s) entrainment and penetration was reduced resulting in lower N O x emissions as the ignition front proceeded in an oxygen lean environment from the outside of the coal jet to the inside of the sewage jet. cT V E X O z 2000 1750 1500 1250" 1000, 750 500 250 o c ^ - C T I -• • m i . i 1 10 20 i 30 Sewage (% ] • GB /(19nVs) o GB / (87 m/s) - • - M M /(19m/s) - a - MM / (87 m/s) I . I , 40 50 6 Figure 3.6 The Effect of Co-Firing Ratio on N O x for Type I Flames |