An instrument was developed for the detection of NH3 in flue gas, exploiting a fortuitous spectral overlap between the ν2aQ(6,6) absorption line of NH3 and the R (18) emission line of the isotopic 13C16O2 laser. The system was developed for use with De–NOx processes, which convert harmful nitric oxides generated in utility and industrial furnaces into harmless nitrogen and water vapor by injection of NH3. The instrument detects unreacted NH3 in the flue gas down to concentrations of a few ppm with an accuracy of ∼10%. It can serve as an environmental monitor and as part of a feedback control system to adjust the upstream NH3 injection to the desired rate.
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