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Show flue gas stream through a distribution grid. Uniform distribution of NH3 in the flue gas stream is essential to achieve optimum NOz reduction while maintaining low NH3 slip. It is particularly critical in gas turbine SCR applications, where the NOx levels are low and stringent NOx emissions limits have to be met; generally in conjunction with NH3 slip limits. This is also true for boiler SNCR applications typically characterized by nonuniform flow and NOx profiles, making design and operation of the ammonia injection grid (AIG) a key component of the SCR and SNCR technologies. Currently, field measurement tools neces sary for start-up, optimization, and modification of an AIG are somewha t limited. 1 •2 Commercially available systems for the continuous sampling and analysis of NH3 are generally large, not portable , and expensive for use as a diagnostic tool in the field. Therefore, Radian Corporation has initiated an R&D program to develop a continuous NH3 monitoring probe system for use as a field diagnostic tool in optimizing the performance of and troubleshooting SCR and SNCR operations . Phase I of this three-phase program focused on the following activities : (a) reviewing current literature on NH3 measurement by chemiluminescence via NH3 oxidation to NO, and efficiency of conversion on. catalytic materials ; (b) defining preliminary design parameters for a Phase I probe prototype using readily available catalytic materials (i.e., stainless steel) ; and (c) conducting field trials using the probe prototype. During the characterization of the laboratory reactor system, a critical need arose to quickly implement the probe in the field as a diagnostic tool for AIG tuning (NH3 distribution/redesign as required), forcing the initial field check-out of the probe prototype to be conducted before the laboratory reactor system study was complete. This paper discusses the design and construction of the Phase I prototype system, testing in the laboratory, and initial field check-out . In Phase II, emphasis will be placed on completing the laboratory study , investigating alternative catalytic materials/preparation, determining effects of moisture and NOx ' and evaluating catalyst life . Design improvements will be made to the probe prototype based on Phase I field trials and also to facilitate sampling streams containing fly ash, S03, etc . Phase III of the program will involve demonstrating the modified probe design on an SNCR system . CONTINUOUS NH3 MONITORING PROBE SYSTEM DESIGN The prototype probe system design, which allows simultaneous measurement of NH3 and NOz , is based on two components : (1) a sample probe with an NH3 oxidation reactor, and (2) chemiluminescent NOz analyzers (see Figure 1). The principles underlying the prototype design have been implemented previously by several researchers to measure NH3 and NOz concentrations (as described in the following section). However, the prototype design presented in this paper is unique in that: (a) it allows rapid determination of NH3 (and NOx ) concentration profiles while simultaneously measuring temperature and velocity gradients across an exhaust duct; (b) it can be used as an effective diagnostic tool in optimizing the performance of and troubleshooting SCR and SNCR systems (particularly in evaluating NH3 injection, NOz , velocity, and temperature profiles within the lmo/148 2 |
