OCR Text |
Show 10/79 Figure 9 compares emissions data collected with two different kiln-fuel injectors. The divergent nozzle provides for more rapid fuel/air mixing and thus a more intense flame with higher peak-flame temperatures. Again the higher air preheat temperatures also result in dramatically increased NO emissions and an increased sensitivity to excess air at successively higher air preheat levels. The curves for the divergent nozzle, however, do not increase as rapidly with excess air as the combination nozzle, suggesting that the divergent nozzle provides rapid enough fuel/air mixing to reduce the impact of oxygen level. Figure 10 shows the N0X emissions produced by the boiler burner using a straight nozzle fuel injector with natural gas as the fuel. The data show the effect of air preheat level and swirl. The NO emissions increase nearly exponentially with air preheat temperature. Figure 11 shows similar data for clean, ambient temperature Koppers- Totzek oxygen (KTO) fuel gas. This fuel gas has 285 Btu/SCF. The fuel injector diameter was increased to give the same fuel injection velocity as natural gas, however, the increased fuel mass flow results in an increased fuel injection momentum. The NO emissions for KTO are significantly higher than those seen for natural gas. This is because of the higher flame temperatures as evidenced by the higher adiabatic flame temperature of KTO. Figure 12 shows the data for clean, ambient temperature Winkler (WA) fuel gas on the boiler burner with a similar fuel injection velocity. WA is a 116 Btu/SCF fuel gas from an air blown gasifier. The WA emissions are significantly less than those of natural gas and do not show an exponential increase with air preheat temperature because of the low WA flame temperatures as predicted by the low adiabatic flame temperature. Staged combustion, where the air addition to the flame is divided to provide a fuel-rich zone in which combustion is initiated followed by one or more zones in which additional air is added to complete the burnup of the fuel, gives reduced thermal N0X 2 because the peak flame temperatures are minimized. This method of combustion, however, tends to produce long flames due to the delayed fuel/air mixing. 6-4 I N S T I T U T E OF GAS T E C H N O L O GY |