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Show In the United States, testing includes research and application work by Exxon (up to 30 MMBtu/hr) , similar work by KVB (up to 5 MMBtu/hr) funded by EPPvI and Exxon, and one commercial demonstration on a 50 MMBtu/hr steam (6) generator for tertiary oil recovery. 2.2.3 Application Application of Thermal DeNOx requires access to the flue gas for NH injection and residence time for reaction at or near the optimum temperature. The optimum temperature is 1700 °F to 1800 °F for injection of ammonia only, and 1400 °F to 1700 °F for injection of appropriate quantities of hydrogen with the ammonia. Figure 5 presents a schematic of a Thermal DeNOx system. Accurate temperature measurements at tentative injection locations along the gas flow path are required to select an injection location. Since an injector piping grid must be installed, this selection must correspond to a location where space is physically available between tube banks. Typically, such space exists for soot blower lanes, inspection lanes, and divisions between heat transfer sections (superheater, reheater, etc.). It must also be considered that the temperature at a tentative location, e.g., after the superheater, will vary with unit load. Temperature may also vary spatially across the injection plane due to temperature nonuniformity in the combustion zone and vary with time due to short-term fluctuations in flame length. Such temperature variations may adversely affect the NO reduction efficiency unless design provisions are made to adapt to the existing^conditions. Temperature variation is one of the difficulties which results in lower NOx reduction efficiencies in field applications than are achieved under laboratory conditions. A residence time of 0.1 sec or more at the optimum reaction temperature after mixing of the flue gas and ammonia is desirable. In addition to time in the cavity, some credit for residence time can be taken for the time between when the flue gas reenters the tube banks and when it is cooled to 1400 °F. The decrease in NOx reduction effectiveness as the temperature drops must be considered when predicting performance of a candidate system. Exxon has developed procedures for such predictions. 4-18 P-233 |