| OCR Text |
Show radiation heat transfer from the higher concentration of radiating species (H20 , C02)' Although the results of these tests were excellent, development of the cyclonic combustion approach was impeded until recently because - 1. Limited demand existed for a burner with <20 ppm NOx 2. Industry was reluctant to accept the premixed burner. We believe that these impediments no longer exist. Proper employment of fuel/air premixing is now accepted (e. g., Alzeta fiber burner, Takuma ceramic burner, IGT/Maxon burner, GE gas turbine combustor, other porous burners, etc.), and, considering the relatively long life of boilers, customers for new boilers as well as retrofit burners may require performance that would meet foreseeable future regulations on NOx and combustible emissions. 40-hp TEST BURNER The l6-inch-diameter 40-hp burner and its combustion chamber were designed to provide a wide variability in critical operating parameters. The test burner is water-cooled and refractory-lined to provide extreme flexibility and durability. The combustion chamber for the initial tests was also water-cooled and refractory-lined. Figure 2 shows the test arrangement. The first series of tests with this arrangement were carried out to determine the size and location of the internal refractory-orifice; the number, size, and orientation of the fuel/air injectors; and its firing capabilities. Figures 3 and 4 show the results at selected test conditions. Figure 3 illustrates the variation in 02, CO, and temperature (measured using a suction pyrometer) across the combustion chamber at distances of about 14, 21, and 33 inches from the burner lid. The data show that, even at 14 inches from -the burner lid, the maximum 02 concentration variation across the chamber was only 0.5%, and combustion was over 99.5% complete (~2000 ppm CO remaining). The level of CO was higher at the higher firing rate, as was the uniformi ty in 02 and CO concentrations. The drop in the combustion products temperature near the axis is caused by internal recirculation of relatively cold products of combustion, which helps decrease the peak flame temperatures and, consequently, NOx formation. Figure 4 shows the effect of firing rate on NOx and CO emissions at the combustion chamber exit. The co emissions level increased nearly threefold at the high firing rate because of the lower residence time; however, it was still well below 50 ppm. The NOx level, on the other hand, actually decreased with the increasing firing rate even though the temperature inside the combustor increased slightly. The decrease in NOx is believed to be caused by the significant decrease in residence times at the high combustion temperatures as well as greater internal recirculation. |
