Scaling the Low Swirl Burner from 15 kW to 600 kW

The lean premixed low swirl burner (LSB) concept has been successful scaled to input powers of up to 600 kW. Using a constant velocity approach, the design of a large capacity LSB (10.16 cm ID) is a linear scaled-up version of a smaller LSB (5.28 cm ID) developed previously for smaller water heaters of up to 18 kW. The operating regimes of the large burner have been investigated and found to be stable over an input power range from 100 to 600 kW. These tests demonstrate the validity of using the constant velocity approach in scaling the LSB. The non-dimensional swirl number for the larger LSB is constant for the input power range we have investigated. However, it is higher than that of the smaller burner. This is attributed to the fact that the swirl rate does not scale with velocity, instead, it scales with the residence time of the swirl air within the burner's exit tube. The NOx, CO and UHC emissions of the large LSB were investigated in a furnace simulator and compared to those of a small LSB operating in a burner evaluation facility. The test matrix was limited to <}> = 0.8 (25% excess air) at various input powers. The results showed that the NOx emissions of both the large and the small LSBs average about 14 ppm (3% O2) over the entire input power range of 15 to 600 kW. Therefore, NOx emissions from the LSB is independent of burner size and combustion chamber geometry. On the other hand, the CO and UHC emission showed a strong dependence on burner chamber coupling. Both sets of data showed that a minimum input power is needed in order to keep CO emission below 25 ppm (corrected to 3% O2) and UHC concentrations at the undetectable level. When operating above the minimum input power, the performance of the LSB is very encouraging. With NOx at 14 ppm, CO at 25 ppm, and UHC at an undetectable level, the LSB should be a prime candidate for use in natural-gas furnaces and boilers.