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Show Since all of these processes involve reactions between NO and nitrogen species in the temperature window between 1000-1350o K, there is some concern that N20 could be a product of the NOx reduction process. Kramlich, et ai, (1987, 1989) showed that there is a temperature window in the region from 1200 - 15000K for the formation and emission of N20 by the reaction of cyano species and NO, essentially the right hand path in Figure 1. This involves the formation of NCO which subsequently reacts with NO to form N20. OH + HNCO ~ NCO + H20 NCO + NO ~ N20 + CO Previously reported results with ammonia injection (Lyon, 1976; Muzio and Arand, 1976) Indicate that very little N20 Is formed during the reduction of NOx' This Is consistent with the path shown in Figure 1: the NH3 decomposes to NH, species, which in turn react with NO forming N2 as the primary product. Reported results with cyanuric acid injection «HNCO);> or isocyanic acid injection (HNCO) indicate N20 to be a major intermediate species and product (Siebers and Caton, 1988). The detailed reaction chemistry of urea (NH2CONH2) with NOx is not presently known. The actual reaction path is dependent on the urea decomposition products upon injection into high temperature combustion products, of which a number can be postulated. It has been suggested that the urea might decompose into NH3 and HNO (Caton and Siebers, 1988); this path is shown in Figure 1. If the urea decomposes to NH3 and HNCO, as suggested by the results of Caton and Siebers (1988), then the HNCO may ultimately lead to N20 formation. On the other hand, another decomposition path may be 2NH2 + CO, in which case little N20 would be expected as a product. OBJECTIVES AND APPROACH The specific objectives of work reported in this paper were to 1) determine the extent to which N20 is a by-product of selective non-catalytic NOx reduction processes and 2) determine the process parameters and underlying mechanisms leading to N20 emissions. 4 |
