Determination of Total Reduced Sulfur emissions from stationary sources (impinger technique)
This method is applicable for the determination of emissions of Total Reduced Sulfur emissions (TRS) from recovery boilers, lime kilns, and smelt dissolving tanks at kraft pulp mills, reduced sulfur emissions (hydrogen sulfide, carbonyl sulfide, carbon disulfide) from sulfur recovery units at onshore natural gas porcessing facilities, and other sources that are covered in applicable regulations. Samples are analyzed by barium-thorium titration as in EPA Method 6.
Sulfur reacts with metal and can bias results, therefore, all components of the sampling train need to be Teflon or Teflon lined. Components of the sampling train include a probe, filter, three SO2 scrubbers (impingers) in series and a series of four impingers. The first two SO2 scrubbers are filled with a citrate buffer solution and the third left empty. The citrate buffer solution should be replaced after each run as these scrubbers selectively remove SO2 from the flue gas. The first two impingers following the SO2 scrubbers should contain a 3% hydrogen peroxide solution, the third impinger is empty and the fourth impinger contains silica gel.
Note that the flue gas must contain at least 1% oxygen for complete oxidation of all TRS to SO2. TRS is then thermally oxidized to SO2 which is collected in the hydrogen peroxide impingers as sulfate ion. When sampling is completed, the hydrogen peroxide contents for each sample run are combined in a polyethylene bottle, the impingers are rinsed with water which is combined with the impinger contents and sent to the laboratory for analysis.
The oxidation process is non-discriminating and will oxidize other reduced sulfur compounds that are present in the gas. These compounds will also be converted to SO2 and cause a positive bias in the results. The Teflon filter in the sampling train is needed to remove the particulates which can cause a bias in the sample results.
(EPA 40CFR Part 60 Appendix A)