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Show -3- equipment. In particular, the NOiNOx ratio can affect an SCR unit located downstream of the boiler. This paper will address these impacts. For a traditional vanadialtitania SeR catalyst, the primary overall reactions between NOx and NH3 are thought to be NH3 + NO + 1/4 O2 ~ N2 + 3/2 H20 8NH3 + 6N02 ~ 7 N2 + 12 H20 2NH3 + N02 + 1/2 O2 ~ 3/2 N2 + 3H20 (1 ) (2) (3) If NO is the primary component of NOx' Reaction 1 will dominate and the required NHiNOx stoichiometry will be one mole of NH3 per mole of NOx' As the amount of N02 increases, Reactions 2 and 3 will become important. In this case, the NH3 requirement will increase to a ratio of 1.33 to 2.0 moles of NH3 per mole of NOx' Odenbrand, et aI., (1986), found the stoichiometry to vary from 1.33 to 1.44 over the temperature range of 485 to 683°F, suggesting Reaction 2 dominates. In addition, the catalyst activity is also a function of the amount of N02 (Bosch and Jansen, 1988; Tuenter, et aI., 1991). During the current study, a bench-scale experiment was conducted to evaluate the performance of a commercial titanialvanadia catalyst with varying NO!NOx mixtures. Experimental Facility The experiments were conducted in a bench-scale SCR research facility at Fossil Energy Research Corp. The facility consists of a natural gas-fired combustor to generate the flue gas, followed by an SeR reactor. The bench-scale SeR catalyst evaluation facility is shown schematically in Figure 1. The combustor deSign permits a high degree of operational flexibility. During the current tests, the combustor was Qperated to produce combustion products with an oxygen content of 3% , typical of utility boiler operation. Anhydrous ammonia was injected into the natural gas to control the NO levels in the flue gas. A water-cooled jacket and a |