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Show - 3 - the NOx reduction possible in the reburn zone under rapid mlXmg conditions. The process conditions in the two experiments were matched in order to compare NOx and TVFN concentrations. The flow patterns in both experiments were modelled using a tmite difference code to partially quantify the mixing rates. 2.1 Description of the Furnace Experiments The furnace experiments were conducted in the IFRF Furnace No.1, Figure 2. This furnace has a 2x2 m square cross-section and is 6.25 m long. To separate the primary and reburn combustion zones, a 0.65 m diameter by 2.8 m long precombustor was installed on the front of the furnace. Primary combustion products were generated in the precombustor using a 2 MW swirling flow coal burner. At the design conditions, the primary zone residence time was estimated to be 0.3 s. The reburning zone was located in the front section of Furnace No. 1 up to 1.8 m axial distance and was separated from the tertiary combustion zone using two refractory choke walls centered at 0.9 and 1.65 m axial distance. These chokes were intended to split the large external recirculation zone at the front of the furnace and prevent excessive recirculation of tertiary air into the reburn zone. The two chokes had circular openings of 1 m and 1.35 m diameter which approximately matched the predicted flow contour of an expanding jet in a contmed chamber [8]. Reburn fuel was injected through four moveable water cooled guns. The guns were situated around the circumference of the precombustor and were angled in wards converging on the centerline of the furnace at 1.5 m axial distance. By moving the guns, reburn fuel could be injected up to 1 m into the reburn zone. Tertiary air could be injected at 1.9, 2.3, 3.5 and 4.5 m axial distance. The air was injected on the furnace centerline and directed radially outwards at an angle of 75° to the forward flow with a velocity of 20-60 m/s. Heat was extracted from the flame through the four water-cooled tertiary air pipes and six cooling loops, located on the outer circumference of the furnace. rebu-n zone reoomlng cooling injec tors pipes r------- ~~~~:iiiiiiiiiiiiii---~""S---"""'--""" __ / ~~========~---:------=!!;111~"" -- I / I I I I I I I I primary coal r;::::::::-- + air first tertiary air _---'-'~2 rebum cool + air bLrnOUt zone / I / I I I 3 I. tertiary air Injectors second tertiary air -.L __ ---J a 2 3 I. 5 6 axial dis tance (m) Figure 2: Arrangement of Furnace No.1 for the furnace experiments |