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Show Tangentially Fired Boilers It is well known that, for boilers without N0X control, tangentially fired boilers generally produce lower N0X emissions than other firing methods; however, pilot scale data on the lowest achievable N0X levels for tangential boilers are not available • In view of the pilot scale performance of the low N0X burner for wall fired boilers, a study has been initiated to generate that data, A pilot scale furnace will be used to study tangential firing at 0.5 to 1.0 thermal MW. Examination of the design approach and pictures of the fireball of a tangential unit suggests that at least two phenomena need to be studied. First, the characteristic flame originating from each fuel injection elevation strongly resembles the axial diffusion flames studied by Heap, i.e., an axial fuel jet completely surrounded by a flame sheet. This configuration was shown to produce lower N0X levels than more highly mixed swirl burners. It could be postulated that this factor accounts for the differences observed in practical boilers; however, a second possibility must also be considered. It can be argued from available photographs of a tangential fireball that, within a short distance, the flame from each corner begins to interact with other flames. It is well known that N0X can be partially reduced on passage through a flame front. It has also been shown that NO added to the combustion air of a lean residual oil flame could be reduced by up to 35 percent. If the N0X formed in one flame of a tangential unit is processed by another flame front, a similar reduction of N0X might occur. It is obvious these two possibilities are not independent phenomena. The research program is structured to examine the effects of both initial fuel/air mixing and flame interactions independent of the entire fireball. The results will then be used to define experiments for the tangential configuration of the pilot scale furnace. Although the individual flame in a tangential boiler may be compared to an axial diffusion flame from a circular symmetric swirl burner, there are some potentially important differences. The axial diffusion flame studied by Heap and others has the central fuel jet completely surrounded by combustion 3-29 29 |