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Show The fuel temperature was increased to 490°F, the firing rate was reduced to 1.9 X 106 Btu/h, and again moisture was added. The flame was stable up to 11.3% moisture in the fuel which represents a heating value of 50 Btu/SCF. The fuel temperature was then slowly reduced. The flame lifted off at a fuel temperature of 350°F. N0X REDUCTION TESTS At the nominal firing conditions, the N0X emissions for the average heating value gas were about 500 ppm or 1.1 lb per 10" Btu fuel. This value was considered relatively high and it was decided to test combustion modifications for reducing the N0X emissions. The relatively high N0X levels were anticipated for these low-Btu gases because of the high fuel nitrogen content, and provisions for testing combustion air staging and fuel staging were included in the original combustor design. Both of these techniques are widely used for N0X reduction. Combustion Air Staging The first N0X reduction method tested was combustion air staging. The major portion of combustion air was injected normally through the axial and the radial ports near the front wall and the remaining air (up to 30%) was introduced through two tangential ports about 4-1/2 feet from the front wall. At the nominal firing conditions air staging with up to 30% air in the second stage did not have a significant effect on the N0X emissions. It was felt that, at these conditions, the temperature and residence time in the first stage were not high enough to effectively convert the fuel NH3 to molecular nitrogen. Increasing the first stage temperature by eliminating moisture in the fuel, and increasing the air and fuel temperatures to 1000°F and 530°F, respectively, resulted in a 35% reduction in N0X with 15% to 30% of the combustion air introduced in the second stage. Further increasing the first stage temperature by adding natural gas to the fuel, however, did not show any additional improvements in N0X» This was probably because of the reduced first stage residence times that resulted from the higher firing rates. Figure 13 shows the N0X emissions within the combustor during one of the air staging tests. Whereas the N0X concentrations along the axis were relatively uniform, the N0X concentrations along the combustor wall peaked at the 5.7.21. I N S T I T U T E OF GAS T E C H N O L O GY |