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Show flue gas and across the ductwork of an SCR or SNCR system); (c) it is portable; and (d) it is relatively inexpensive. The initial prototype system developed in this Phase I research effort , for use in a field investigation, is a two-tube, annular heated probe with a high-temperature stainless steel (type 316) reactor . Sample gas from the exhaust duct is directed through the probe and diverted into two separate lines that are heat traced to prevent moisture condensation (which could subsequently remove NH3 from the sample gas). One of the lines consists of a gas conditioning system (for NH3/H20 removal) and a chemiluminescent NOx analyzer. This analyzer is used to monitor the NOx (only) levels in the sample gas . It is equipped with a low-temperature, molybdenum converter to minimize oxidization of any NH3 that may escape the gas conditioner. Sample gas that is transferred to the second line initially passes through the NH3 oxidation reactor, then a gas conditioner for moisture removal (and temperature reduction), and is finally sent to the NOx analyzer that contains a standard supply stainless steel converter . The second analyzer is for measuring the NOx formed in the reactor from the oxidation of NH3 present in the flue gas and the NOx already present in the sample gas. NH3 concentrations are determined continuously from the difference between the two analyzer readings. (Note: For semi-continuous measurements, a single gas conditioner/NOx analyzer could be used, with measurements made by intermittently switching the gas sampled between the two lines.) BACKGROUND To help define design parameters for the probe prototype, a literature review was conducted which focused on NH3 oxidation and measurement of NH3 via chemiluminescence as it relates to the applications of interest in this study, i.e . , measurement of NH3 and NOx both at high and low levels (upstream and downstream of an SCR catalyst or SNCR reaction zone) , and where relative concentrations vary greatly (NH3 injection/maldistribution) . The review indicated that conversion efficiencies up to 100 percent have been achieved at temperatures greater than 920 K for NH3/air mixtures using stainless steel converters in commercially available chemiluminescence analyzers. 3-6 As discussed below, previous measurements involving NH3/air mixtures by chemiluminescence have been generally successful to varying degrees; however, no information on direct application of this measurement technique for troubleshooting SCR or SNCR systems was identified in the literature review . NH3 Measurement Technique In recent years, chemiluminescent analysis has been widely used for determining NOx concentrations. The reaction with ozone in the chemiluminescent detector is specific for NO. To measure total NOx ' a converter is utilized to dissociate any N02 present to NO, which can then be detected according to the following: lmo/148 3 |