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Show over the full firing range of the boiler and the N O x emissions are compared to the optimized baseline data. Over ten of these NOx reduction studies have been performed and a sampling of the results are provided in Table I. The greatest N O x reduction from the optimized baseline was 2 5 % from a single burner, field erected unit firing at 145 MBtu/hr. Most of the field erected boilers experienced significant N O x reductions from the optimized baseline with the use of rich-lean staged atomizer caps. However, the package boilers proved to be the most challenging application of staged caps with spray impingement on the boiler side walls limiting the degree to which the spray flame can be staged for N O x reduction. A typical set of emissions data are provided in Figure 6 from Boiler A in Table I. This boiler uses two burners, side by side, to produce up to 90,000 lb/hr of steam flow. The original atomizer equipment data shown in Figure 6A) illustrate the effects of optimization on N O x and C O emissions as combustion is improved through optimization of burner excess air. The N O x emissions increase with increasing firing rate to a maximum of 0.266 lb/MBtu N O x ( @ 3 % 0 2, dry) after the optimization. The emissions data for the best performing low N O x atomizer caps indicate significant emissions improvement over the entire operating range with a maximum N O x emission of 0.202 lb/MBtu. CONCLUSIONS AND OBSERVATIONS • Significant N O x emissions reductions for boilers firing residual fuel oil can be achieved through relatively inexpensive fuel spray modifications. • Fuel staging in residual fuel oil spray flames results in reductions of both thermal and fuel N O x . • Significant N O x reduction results are achieved in field erected boilers where generous furnace dimensions allow the increased flame volume of a highly staged residual oil flame. N O x reductions in package boilers with staged spray flames are inhibited due to flame impingement on the boiler walls. • Further research is required to determine the effects of droplet diameter on fuel N O x conversion in practical residual fuel oil fired boilers. Additional understanding of particulate reduction in low N O x residual oil flame is also required. ACKNOWLEDGMENTS The authors wish to acknowledge Coen service engineers Bill Bishop, B o b Kohnert, and Joe Harter for their diligent efforts in the acquisition of the field data. Also acknowledged is the kind and cooperative support received from the boiler room operators during the field trials. The efforts of Mark Clavelli and Kenneth Y. A h n in the management of the N O x reduction studies is gratefully acknowledged. Finally, the authors wish to acknowledge the efforts of Julie Webster in the preparation of this manuscript. |