OCR Text |
Show individual burner nozzles, arranged in a three-by-four matrix, that inject coal and primary air downward from the roof into the furnace. Secondary air is introduced around the burners nozzles through a duct arrangement shown in Fig. 3. Prior to development of the gas reburn system, two key modifications were made to the Elrama Unit 2 furnace by Energy Systems Associates (ESA) and DLC to achieve lower NOx and CO emissions. The first involved introduction of a parallel separated overfire air (SOFA) system that effectively provides air staging capability by diverting up to 3 0 % of the secondary air from the immediate vicinity of the coal nozzles. This SOFA system, shown in Fig. 3. is comprised of two independent SOFA ducts that allow biasing between the front and rear SOFA injection nozzles to control the staging. The separated overfire air from the SOFA nozzles is injected downward and nearly parallel to the coal and secondary air inflows to provide better staging control over the boiler load range. The second modification involved fuel redistribution by blocking one quarter of the coal injection nozzles, thus increasing the coal flow through the remaining nozzles. Since the primary goal was to reduce NOx formation in the boiler, the blocked nozzles are generally in the rearmost row of each burner block as shown in Fig. 2. This provides for better separation between the coal and the SOFA air, thus increasing the effectiveness of staging achieved with the SOFA system. This modification was also made to reduce CO emissions, and for this reason certain other coal injection nozzles that were identified as consistently producing high C O emissions were blocked. Subsequent to these modifications, and prior to the simulations described here, a natural gas injection system for overall fuel-lean gas reburning was designed and installed on the boiler by ESA and DLE in collaboration with the Gas Research Institute (GR1). Design of the system was done largely on the basis of partial furnace t t B4(SJ-38) B-Furnace P B6 (SJ-38) B 3 (SJ-38) (SJ-50) B2 Division Wall A-Furnace (SJ-38) A 4 (SJ-38) A 6 (SJ-38) (SJ-50) B5 B1 A3 (SJ-50) A1 (SJ<38) A5 (SJ-50) A2 1 Figure 4. Natural gas injector locations for the fuel-lean gas reburn system at Elrama Unit 2, showing locations of the six injectors in the furnace front wall (bottom) and six additional injectors in the sidewalls. |