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Show furnace) is inevitable. Good combustion is obtained by scaling down the coal particle size as much as practical. It was felt that the 44-50% through 200 mesh obtainable with our MPS-32 mill coupled with the use of hotter than normal secondary air (800°F versus 600°F) would work. This proved to be the case as previously shown in the pilot/field comparison of Table 2. The greater heat loss at the pilot-scale results in less turndown capability and tapping problems with coals at the high end of the B&W maximum recommended T 250 temperature. The T 250 temperature refers to the temperature at which the slag viscosity is 250 poise. Another challenge of the pilot-scale cyclone reburning work was the reburn burner design. Since downstream burners were needed, in-furnace flow was measured to select the number and location of the burners. Reburn burner design followed the same scaling criteria used for other pulverized coal burners - identical coal partical size and matching throat velocity. The need for mixing lower furnace gases and reburning zone fuel and air, as well as reburner fuel/air jet penetration in light of the lower pilot-scale furnace velocity, required extensive physical and numerical modeling to scale up the pilot-scale data. Jet and dispersion criteria based upon fundamental modeling similarities must be used. Before discussing the pilot-scale work and its comparison to full-scale, a brief review of the full-scale demonstration sites will be given . Demonstration Sites As stated earlier, the 10w-NOx cell and cyclone reburning programs evolved along similar lines. However, there are a number of differences between the low-NO cell burner x and cyclone reburning technology demonstration units. The size difference can be seen in Figure 6. The cyclone-fired unit (110 MWe) is 82 feet tall by 34 feet wide by 16 feet deep. The cell burner equipped unit (610 MWe) is 156 feet high by 63 feet wide by 39 feet deep. The test unit dimensions were listed previously. Boilers with cell burners are generally similar units. All are opposed-wall fired although the capacity ranges from 220 to 1300 MW. The 610 MWe Dayton Power and Light (DP&L) Stuart station is about average size. It is a universal pressure (3805 psig) design, has 24 burners, and is base loaded. A variety of eastern bituminous coals are frred. Cyclone-frred boilers were built in a variety of sizes, single and opposed wall frring modes, and fire eastern, western, or coal blends. The 110 MWe (Wisconsin Power and Light (WP&L) Nelson Dewey station is relatively small, but is base loaded, operates at relatively low pressure (1500 psi g), and has three 9-foot diameter cyclone furnaces. The demonstration coal frred is an eastern bituminous type. 5 |