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Show low CO emissions of the RSB. The laboratory boiler was modified to allow the primary blower to pump flue gas into the air stream where together they mixed with the fuel. The amount of flue gas recirculated was controlled by an in-line damper on the FGR duct. The NOx and CO emissions results are shown in Figures 4 and 5, respectively. As with previous excess air data, NOx emissions are a strong function of the FGR level. Sub-9 ppm NOx emissions were achieved at FGR rates greater than 300/0. In general, burner operation was stable up to the highest FGR rates. At FGR rates above 300/0, burner stability was a problem. These results showed that FGR is an alternative for achieving sub-9 ppm NOx emissions. However, as previously discussed, using FGR as a NOx reduction technique carries significant efficiency and fan power penalties that we would prefer to avoid. This problem is most significant in package boilers, which have a high pressure drop through the boiler in order to minimize boiler size. 3.2 FIELD DEMONSTRATION Facility Description A 50,000 Ib/hr oil field steamer was used to conduct field tests. The radiant section of the boiler is cylindrical and 37 feet long with an inside diameter of 9.5 feet as illustrated in Figure 6. The watertubes make one pass through the radiant section and are 3 inches in diameter and arranged parallel to the centerline on 6-inch centers. The unit operated at a steam pressure of 1100 psig corresponding to a steam temperature of 550°F. The steamer was equipped with a Pyromat CSB30-4S0-30 burner element. The burner was cylindrical and 30 inches in diameter by 120 inches long. The burner was fully modulating and could fire up to full nameplate rating. 62.5 MMBtu/hr. The steamer fired on natural gas and/or casing collection gases. Casing collection gases are a low-Btu fuel composed of approximately 50% by volume methane and 50% carbon dioxide. The steamer was equipped with viewports on the front, side, and rear walls to view the burner. 8 |