OCR Text |
Show burner block is used. No maintenance problems have been experienced. Burner Emission Performance NOx emission data for the burners are shown in Figures 3 and 4. On the figures, the P and S after K976 refer to primary and secondary air, respectively. Figure 3 shows NOx emission versus flue temperature with residual oxygen in the combustion products held constant at 2.1% which corresponds to 10% excess air. Figure 4 shows the effect of residual oxygen at a constant firebox temperature of 2282"F. NOx emission decreases sharply with increasing excess oxygen for the K976 burner due to the reduced flame temperature. Using secondary air raises NOx emission. Fuel staging produces the lowest NOx emission. Further, its emission decreases with decreasing excess air permitting higher firebox efficiency along with reduced NOx. It was surprising to see that NOx emission from the larger staged combustion burner, the K988M, was lower than from the smaller one, the K988. They are quite similar with the principal difference being a factor of two in size. The data shown is for natural gas but process off gases are often used as the fuel. We have seen that olefins and higher molecular weight hydrocarbons increase NOx. Hydrogen increased NOx for the single-stage burners, but reduced NOx with the staged combustion burner. These effects are at least partially explainable in terms of flame temperature and the effectiveness of the fuel to entrain air by the jet-pump principle. The influence of hydrogen cannot be fully explained in this way, however. Conclusions The measurements reported here show that burners can be designed that will meet the most stringent NOx emission regulations now or soon to be in force with no loss of thermal efficiency. -5- IV-23 |