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Show The tangentially-fired unit has burners in each corner forming a large rotating fireball. With GR-SI, these burners will be turned down to 80 percent of full load with all burners in service. Gas (20 percent of the total heat input) is injected through co-tangential ports immediately above the upper row of burners. Flue gas recirculation (FGR) is added to the natural gas to achieve rapid gas mixing and penetration. The gas injectors tilt along with the coal burners. The overfire air is also injected co-tangentially through four large ports. The injection velocity is low to minimize furnace flow disruption. At full load, the ideal temperature for Sorbent Injection occurs near the nose of the furnace; however, it occurs lower in the furnace as load is decreased. To accommodate the unit load range, two sets of sorbent injectors will be utilized. Ports along the front and side walls at the nose elevation will be used at near full load. At low load, the sorbent will be injected along with the overfire air. The cyclone fired unit has two cyclones on the front wall discharging into a "well" type secondary furnace. There is intense mixing in this zone due to the cyclone swirl. Above the well, the furnace expands sharply producing a large recirculation zone with most of the flow passing up along the rear wall. With GR-SI, both cyclones will be turned down uniformly to 80 percent capacity. The reburning gas (20 percent) and FGR will be injected just above the well from the rear wall. The overfire air will also be injected from the rear wall further up in the furnace. The ideal temperature for Sorbent Injection is at the entrance to the superheater in this unit. The flow patterns in this region are complex requiring a complex injector arrangement. A total of 10 injectors will be used on the front and side walls. The emission control performance of the GR-SI systems has been evaluated using EER's thermal, fluid flow, combustion and sulfation models. Both configurations are projected to meet the project goal of 60 percent NO~ emission cont ro 1 . A total SO reduct i on of 50 percent was the des i gn goa I • It is projected that this wi~l be achieved at Ca/S molar ratios in the range of 1.3 to 1.5. Gas Reburning - Low NOx Burners The Low NOx Burners wi 11 be direct replacements for the exi st i ng coal burners. No changes will be made to the burner arrangement and spacing. The Low NOx Burners will produce larger flames but will have little affect on the general furnace flow patterns. The GR system has been designed to take advantage of the flow patterns in the furnace. The overall arrangement is similar to that illustrated in Figure 2 except that the reburning fuel is injected from the rear wall. Since the furnace flow is primarily along the rear wall of the boiler immediately above the burners, inject i on from the rear wall is preferred. The GR- LNB system is projected to reduce NOx emissions by about 75 percent. Figure 4 is an isometric drawing of the Cherokee 3 boiler showing the preliminary arrangement of the major components. The carrier flue gas will be obtained from the existing flue gas recirculation system. However, a new 7 |
