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Show EFFECT OP TRACB COMBUSTION SPECIES ON SNCa PERFORMANCE INTRODUCTION A number of technologies are available to control NOx emissions from fossil fueled power plants including flue gas recirculation, staged combustion, and ~elective £atalytic ~eduction with ammonia (SCR). Another option is ~elective non-£atalytic ~eduction (SNCR) with ammonia or urea (1,2). However, the SNCR process, which has many attractive features, does have several disadvantages. One drawback is the relatively narrow temperature "window" over which the process is effective. Another potential disadvantage is the emission, at least under some operating conditions, of undesirable byproducts such as NH3 or CO. Emissions of byproduct N20 during SNCR operation have also been noted (3). More recently, it has been observed that the presence of small amounts of CO can lead to significantly increased levels of N20 when using urea (4). Results of a series of laboratory tests to address the issue of N20 production in the presence of CO using ammonia and urea as the reducing reagents are presented in the sections which follow. The effect of CO on removal efficiency, peak NH3' and final CO levels is also discussed. PROCESS DESCRIPTION Conceptually, application of the SNCR process to power plants is quite simple. An aqueous solution of reagent is injected into, and mixed with, the flue gas at the correct temperature. After the mixing has been completed, the reagent then reacts selectively to remove the NOx • In practical applications, however, the process (and the equipment required) can be much more complicated due to non-uniformities in velocity, temperature, and NOx concentration at the point of injection. In addition, the location where the effective process temperature range physically occurs depends on a number of operating factors including load, type of fuel fired, and length of time on a particular fuel. These factors often lead to multiple levels of injection and/or use of additives to accommodate the shifts in temperature. PILOT SCALE TEST FACILITY A schematic of the pilot-scale facility used for the current tests is shown in Figure 1. The pilot scale combustor fires natural gas doped with NH3 to control the initial NOx level. The combustion section is water cooled and partially refractory lined. The test section is refractory lined, 15 cm in diameter and 240 cm long. At the firing rates used for these tests, the residence time in the test section is nominally 0.5 seconds; the temperature drop along the test section is nominally 2500 C/sec (4500 F/sec). The SNCR solutions were injected into the combustion products at the combustor throat through a small air assist atomizer above the test section. The atomizer was fabricated into a water cooled holder. The atomizer was located at the center of the throat with the spray directed downward (i.e., co-flowing with the combustion products). The solutions were pumped with variable speed per- 3 |