Optimization of Sampling Conditions to Minimize the Adverse Effect of Sulfur Dioxide on the Ability of the Ontario-Hydro Method to Accurately Distinguish the Chemical Forms of Mercury in Coal Flue Gas

Abstract

The goal of the work presented in this paper was the identification and quantification of various chemical forms of mercury in coal flue gas. To this end, bench-scale evaluations were carried out on the Ontario-Hydro Method to determine its capability to selectively isolate and retain various mercury species captured from flue gas streams containing moderate to high levels of sulfur dioxide (SO{sub 2}). Loss of mercury from the oxidized mercury capture solutions through chemical reduction by sulfur dioxide has been documented previously from both bench- and pilot- scale studies. Results from recent studies, giving further verification of this phenomenon with emphasis on optimization of sampling conditions to minimize this impediment to effective mercury speciation, are presented. All speciation methods utilizing impinger trains were configured in a similar manner. The impingers immediately down-stream of the heated sampling probe and filter box contained solutions intended to capture oxidized (ionic) mercury while impingers further down-stream of these contained acidic potassium pennanganate (KMnO{sub 4}). These latter solutions, having been shown by the EPA in their Method 101A validation studies to capture all forms of mercury, were utilized here to capture the remaining elemental mercury. The challenge was to develop, test and validate an oxidized mercury capture solution that would effectively capture and retain all of the oxidized mercury species while allowing 100% of the elemental mercury to pass through it and be captured down- stream in the KMnO{sub 4} impinger solutions. A schematic of the impinger train utilized in the Ontario-Hydro Method is shown in Figure 1. For oxidized mercury capture, this method utilizes a 1.0 molar potassium chloride (KCI) impinger solution, which we have shown to be effective in its ability to retain mercuric chloride solution spikes given the appropriate sampling conditions