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Show be expected to attain higher levels of NOx reduction. Fuel nitrogen can also have an impact on reburning effectiveness since the addition of more reactive nitrogen species to the reburning zone can influence the fmal emissions levels attained. Generally, fuel nitrogen content becomes more critical at lower initial NO It levels. The distribution of nitrogen in the volatile matter and char is also important, since nitrogen species released with the volatile matter have more opportunity to be reduced to molecular nitrogen. During burnout, nitrogen in the char can be oxidized, or it can play a role in heterogeneous NO reduction6• x In the practical application of coal reburning, there are concerns about the impacts of the process on carbon burnout and slagging and fouling in the reburning zone. The impacts of coal properties on these parameters are expected to be coal and boiler specific. Test Results The screening studies tests were conducted in a 1.0 MMBtuIhr down-frred furnace. A schematic of the reactor is shown in Figure 1. To evaluate the test coals on a consistent basis, the primary fuel was natural gas fired at 800,000 Btulhr with ten percent excess air. The initial NOx emissions from the primary flame (NOp ) were controlled at 400 ppm (dry, corrected to 3%O). The reburning coals were all injected at an initial temperature of approximately 2630°F. Nitrogen was used as the transport carrier for the coal. Overfire air was injected downstream of the reburning fuel to bring the overall furnace stoichiometry up to 20 percent excess air. The overfrre air injection location was set to provide a rebum zone residence time of approximately 350 milliseconds. The thennal profile in the furnace was set to provide a quench rate in the reburning zone of approximately 350°F per second. Ten coals were selected from a data base of commercially available Canadian coals using a methodology where the coals were rank;ed according to their NO It reduction potential, slagging potential, carbon burnout potential, and then according to their relative usage. By ranking the coals in this fashion, it was possible to identify tens coals for the screening tests. The properties of the test coals selected for testing are summarized in Table 1. Each of the coals shown in Table 1 were tested over a range of reburn stoichiometric ratios (SR~ ) between 0.8 to 1.0. The results of these tests are summarized in Figure 2. Also shown in this figure are the results of using natural gas as a reburning fuel. With the exception of Coal C, each of the coals 4 |