Determination of Hydrogen Halides and Halogen Emissions From Stationary Sources - Isokinetic Method
This method is applicable for determining emissions of hydrogen halides (HX) [HCl, HBr, and HF] and halogens (X2) [Cl2 and Br2 ] from sources controlled by wet scrubbers that emit acid particulate matter. This is an isokinetic sampling method.
Samples are collected isokinetically using a modified Method train consisting of a heated probe and filter, an optional cyclone, and a series of impingers. The filter is typically Teflon in a mat configuration. If the source temperature is above 210°C (410°F), a quartz filter can be used because the Teflon will begin to degrade at that temperature. The cyclone is optional and required if the stack gas is saturated with moisture, otherwise, the use is optional. A knockout impinger (for moisture) may be used which is placed prior to the series of impingers and filled with 50mL of 0.1N H2SO4. The 1st and 2nd impingers are filled with 100mL of 0.1N H2SO4. The 3rd and 4th impingers are filled with 100mL of 0.1N NaOH. A final impinger or drying tube contains contains 200-300g silica gel.
The filter collects particulate matter which includes the halide salts and is not typically recovered or analyzed. Note the methods calls for the use of a Teflon filter holder. New Teflon has been noted to release HF. Condition by heating any new Teflon filter holders prior to using them for sampling.
Please note, each sampling train will have two fractions. Typically, hydrogen halides (HCl, HBr, HF ) are analyzed from the acidic impinger fraction while halides (Cl2, Br2, etc.) are analyzed from the alkaline impinger fraction. Note that F2 cannot be determined using this method.
The contents of all impingers are measure for later determination of stack gas moisture. The contents of the H2SO4 impingers and knockout impinger are combined in a polyethylene bottle. The impingers, connecting glassware, and back half of the filter holder are rinsed with deionized water and combined with the impinger contents. The contents of the NaOH impingers are combined in a polyethylene bottle. The impingers and connecting glassware are rinsed with deionized water and combined with the impinger contents. Sodium thiosulfate must be added to the combined NaOH sample to ensure the complete reaction to the halide ion. An equivalent of 0.7 mg per ppm of halogen in dscf (dry standard cubic feet) of stack air is the amount to add as cited in the method. The silica gel can be weighed in the field to determine moisture content.
Each fraction (H2SO4 and NaOH) is analyzed by IC and each is analyzed in duplicate. Each measurement must agree within 5% of the mean value to be considered valid. Otherwise, the samples must be reanalyzed
(EPA 40CFR Part 60 Appendix A)