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Show effect on N O x due to this substitution is small relative to the accuracy of the test measurements. However, the overall effect on thermal efficiency due to the addition of flue gas can be significant, and it is this increase in thermal efficiency that drives the usage of F G R in industrial applications. The comparison of the 3 cases modeled using P R O F is presented as Table 2. 5. SUMMARY Tests of the R S B at the Chevron field site demonstrated: • Stable operation, at high dilution levels of excess air or flue gas • High efficiency, with stack 0 2 levels of nominally 3%, and F G R percentages ranging from 10 to 40 percent. • NOx emissions obtainable at any desired regulatory level, 9 ppm, 15 ppm or 30 ppm • CO emissions below the most severe regulatory limits of 50 ppm Boiler modeling performed by B & W and by Alzeta demonstrated that both the B & W C O M O model and the Alzeta plug flow model accurately model the thermal behavior of the test boiler. Both models could therefore be used to determine water tube arrangements and overall boiler size. In addition, the COMO model accurately models NOx emissions. While it is believed that the Alzeta P R O F model probably predicts N O x formation accurately in the flame zone, a significant percentage of the total N O x is generated outside of the flame zone. Therefore, the P R O F model predicted N O x emissions that were less than what was actually observed. However, P R O F modeling of N O x emissions from the R S B with and without F G R did show the same trends as observed experimentally. The key trend is that N O x varies primarily as a function of total dilution, with F G R and excess air being the two diluents used in these tests. Alzeta has three sites, in San Francisco, Pittsburgh, and Modesto, California, that were tested at sub 30 ppm N O x (corrected to 3 percent 02) and a site in Woodland, 8 |