Total Reduced Sulfur Emissions from Stationary Sources – USEPA Method 16B

USEPA Method 16B is used to determine total reduced sulfur (TRS) emissions from recovery furnaces (boilers), lime kilns, and smelt dissolving tanks at kraft pulp mills, and from other sources when specified in an applicable subpart of the regulations.  The flue gas must contain at least 1 percent oxygen for complete oxidation of all TRS to sulfur dioxide (SO₂).
 
An integrated gas sample is extracted from the stack.  The SO₂ is removed selectively from the sample using a citrate buffer solution.  The TRS compounds are then thermally oxidized to SO₂ and analyzed as SO₂ by gas chromatography (GC) using flame photometric detection (FPD).
 
Reduced sulfur compounds other than those regulated by the emission standards, if present, are measured by this method.  Therefore, carbonyl sulfide, which is partially oxidized to SO₂ and is present in a lime kiln exit stack, is a positive interferant.
 
Particulate matter from the lime kiln stack gas (primarily calcium carbonate) causes a negative bias if it is allowed to enter the citrate scrubber.  The particulate matter causes the pH to rise and H₂S to be absorbed before oxidation.  Proper use of the particulate filter, described in USEPA Method 16A, eliminates this interference.
 
Carbon monoxide (CO) and carbon dioxide (CO₂) have substantial desensitizing effects on the FPD even after dilution.  Acceptable systems must demonstrate that they have eliminated this interference by some procedure such as eluting these compounds before the SO₂.  Compliance with this requirement is demonstrated by submitting chromatograms of calibration gases with and without CO₂ in diluent gas.  The CO₂ level is approximately 10 percent for the case with CO₂ present.  The two chromatograms should show agreement within the precision limits of the method.