USEPA Method 15

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Hydrogen Sulfide, Carbonyl Sulfide and Carbon Disulfide from Stationary Sources – USEPA Method 15

USEPA Method 15 applies to the determination of emissions of reduced sulfur compounds from tail gas control units of sulfur recovery plants, H₂S in fuel gas for fuel gas combustion devices, and where specified in other applicable subparts of the regulations.

A gas sample is extracted from the emission source and diluted with clean dry air (if necessary). Sulfur dioxide is removed using a wet scrubber. An aliquot of the diluted sample is then analyzed for CS₂, COS, and H₂S by GC/FPD.

The method uses the principle of gas chromatographic (GC) separation and flame photometric detection (FPD).

Moisture condensation in the sample delivery system, the analytical column, or the FPD burner block causes losses or interferences. This potential is eliminated by heating the probe, filter box, and connections, and by maintaining the SO₂ scrubber in an ice water bath. Moisture is removed in the SO2 scrubber and heating the sample beyond this point is not necessary provided the ambient temperature is above 0 °C (32 °F)

Alternatively, moisture may be eliminated by heating the sample line, and by conditioning the sample with dry dilution air to lower its dew point below the operating temperature of the GC/FPD analytical system prior to analysis.

CO and CO₂ have substantial desensitizing effects on the FPD even after 9:1 dilution. (Acceptable systems must demonstrate that they have eliminated this interference by some procedure such as eluting CO and CO₂ before any of the sulfur compounds to be measured.) Compliance with this requirement is demonstrated by submitting chromatograms of calibration gases with and without CO₂ in the diluent gas.

The condensation of sulfur vapor in the sampling system leads to blockage of the particulate filter. This problem is minimized by observing the filter for buildup and changing as needed.

SO₂ is not a specific interferent but is present in such large amounts that it cannot be effectively separated from the other compounds of interest. The SO₂ scrubber described in this method effectively removes SO₂ from the sample, although alkali mist in the emissions of some control devices causes a rapid increase in the SO₂ scrubber pH, resulting in low sample recoveries. Replacing the SO₂ scrubber contents after each run minimizes the chances of interference in these cases.

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Last Update: October 25, 2006