Water vapor inhibits hydrogen sulfide detection in pulsed fluorescence sulfur monitors
2016
A. B. Bluhme | J. L. Ingemar | C. Meusinger | M. S. Johnson
The Thermo Scientific 450 Hydrogen Sulfide–Sulfur Dioxide Analyzer measures both hydrogen sulfide (H<sub>2</sub>S) and sulfur dioxide (SO<sub>2</sub>). Sulfur dioxide is measured by pulsed fluorescence, while H<sub>2</sub>S is converted to SO<sub>2</sub> with a molybdenum catalyst prior to detection. The 450 is widely used to measure ambient concentrations, e.g., for emissions monitoring and pollution control. An air stream with a constant H<sub>2</sub>S concentration was generated and the output of the analyzer recorded as a function of relative humidity (RH). The analyzer underreported H<sub>2</sub>S as soon as the relative humidity was increased. The fraction of undetected H<sub>2</sub>S increased from 8.3 at 5.3 % RH (294 K) to over 34 % at RH > 80 %. Hydrogen sulfide mole fractions of 573, 1142, and 5145 ppb were tested. The findings indicate that previous results obtained with instruments using similar catalysts should be re-evaluated to correct for interference from water vapor. It is suspected that water decreases the efficiency of the converter unit and thereby reduces the measured H<sub>2</sub>S concentration.
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