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Show Measured CO levels at the stack during the baseline tests were less than 30 ppm and no apparent increase during the reburning tests was observed. In summary, reburning had a minimal impact on the CO emission levels, but a moderate increase in unburned carbon. Pilot-Scale Furnace Temperature Profile. SBS furnace temperatures were measured during both baseline and reburning phases to detennine the technology's potential effect on temperature profiles. Figure 5 illusb'ates the furnace exit gas temperatures (FEGn under various operating conditions. With reburning, no FGR, and maintaining a constant 6-million Btulhr furnace heat input, FEGT increased from the baseline by approximately 40·F. However, when 10% FGR was added to the reburning system, a temperature quenching phenomena occurred, resulting in a 50·F FEGT drop from baseline. A 50·F variation in FEGT is considered to have a minimal (if any) impact to boiler perfonnance. At4.5-million Btu/hr, FEGT increases of up to 10(tF were observed; this is not a major concern for low-load operation in full-scale boilers. Corrosion Potential in the Reburn Zone. Since the reburn zone must be operated under substoichiomettic conditions, corrosion potential within this region was investigated. By operating the cyclone in an excess air mode, most (if not all) of the sulfur from the coal in the main combustion zone is converted to S02. Due to the reducing atmosphere in the reburning zone, H2S may evolve. High concenb'ations of H2S can be conducive to an increased rate of tube corrosion. Numerous H2S measurements were perfonned within the upper furnace region with and without reburning. No H2S was detected in the SBS during baseline conditions. Local H2S levels increased up to 200 ppm during reburning operation. Maximum H2S concentrations were observed between the two 2.4 2.3 INDIANA LAMAR COAL reburning burner flames and lower H2S levels were measured near the boiler walls (12 to 16 ppm). Due to minimum contact of H2S with the boiler walls, no major boiler corrosion via H2S would be predicted for the full-scale retrofit However, the corrosion rate in the reburn zone is expected to be a sttong function of coal sulfur content and boiler type, and site-specific analysis is required for future rettofit applications. Reburning burner(s) must be properly designed to prevent flame impingement with the boiler walls and will be discussed in detail later in this paper. Others. The potential impacts of reburning on electrostatic precipitator (ESP) perfonnance, N20 emissions, fll'eside deposition, and reburning burner detector were studied, but are not included in this paper due to space limitations. Mixing Evaluation. Effective mixing between the reburn fuel and cyclone gases is needed to obtain acceptable NOx reduction. In addition, good mixing between OF A and reburn zone gases is necessary to avoid unacceptable unburned combustible losses. Furnace flow patterns and mixing perfonnance were evaluated by in-furnace probing as well as three-dimensional mathematical simulation of the baseline and reburning flow conditions in the SBS. The B&W FORCE numerical flow model solves the governing equations for conservation of mass and momentum to predict the three-dimensional turbulent flow in the furnace. Velocity predictions for the SBS were compared with velocity measurements at four elevations in the furnace. The predictions were in general agreement with the data. The predicted flow patterns are shown in Figure 6. The direction of the flow is indicated by the arrows; the length of the arrows is proportional to the magnitude of 6-MIWON BTUIHR 2.2 Cl 2.1 2 Vi 1.9 0 z eCn( 1.8 :::) 0 E 1.7 E 1.6 t- O w 1.5 ~ 1.4 1.3 1.2 1.1 2 Rgure 5. Pilot-Scale Furnace Exit G,s Terr.-ratu,. ... x ~t 0 l{~ C x EI iJ 4.5-MILUON BTUlHR ~MIWON BTUIHR 4.s-MIWON BTUIHR BASEUNE (NO REBURNlNG) REBURNING 3 5 o )( + v 5 |