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Show -5- (13) As far as possible, the ULN burner should be dimensioned so as to be easy to retrofit in place of existing burners. (14) As far as possible, gas and air pressure drop requirements should be similar to existing burner requirements. DESIGN SELECTION In an earlier paper (Ref 2), presented in October, 1980, a single stage, high excess air gas burner was described which produced 1 ppm NOx emissions. The success of this burner depends on keeping the maximum flame temperature as low as possible within flammability limits. At near limit conditions, the flame speed is low and if the flame is "chilled" before combustion is completed unacceptable aldehydes form. Although difficult, all the conflicting reqUirements were met and the 1 ppm NOx burner has been commerCially successful and is still available and in constant use today. This burner's main application has been in the European food and beverage industry directly drying ingredients for human consumption. The ULN burner described here is intended for wider industrial use and it was decided to develop the concept further, simplify the construction and test an alternate, FGR operation as a substitute for excess air. The new ULN burner design is shown in Figure 2. It is a gas/air premix, followed by two flame arrestors, one metal, one ceramic and a flame stabilizer. In addition, it is fitted with a flame scanner port, a pilot port and a heat sensor. EaUIPMENT Two prototype burners were manufactured and tested. The first has a maximum design heat liberation of 1.5 MM BTU/hr. The second is essentially four modules of the first, with a maximum heat liberation of 6 MM BTU/hr. The small, first burner was tested in a water cooled apparatus to establish the feasibility of the design concept. The larger second burner was tested in a refractory lined furnace shown in Figure 3. It is the testing of this larger burner that is discussed in this paper. PROTOTYPE BURNER TEST RESULTS Testing of a 6 MM BTU/hr ULN burner prototype was conducted in the Bloom Engineering/PCC laboratory from December, 1991 through February, 1992. The objective of these tests was to obtain emissions data at various excess air rates, confirm the ability of the burner to operate at the rated capacity, determine stability limits and turndown. This testing consisting of measurements taken at 46 different test pOints. The excess air rate was varied from 55 to 110% and the burner firing rate from 1.25 to 6 MM BTU/hr. Data collected included NOx, CO and THC plus temperatures and flows. Flame length, shape, noise level, and stability were also observed. |