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  STACK SAMPLING METHODS FOR HALOGENS AND HALOGEN ACIDS Larry D. Johnson Methods Branch, MD-44 Air Methods Research Division National Exposure Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 Presented At EPA/A&WMA International Symposium Measurement of Toxic and Related Air Pollutants Research Triangle Park, NC May 1996  STACK SAMPLING METHODS FOR HALOGENS AND HALOGEN ACIDS Larry D. Johnson Methods Branch, MD-44 Air Measurements Research Division National Exposure Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 ABSTRACT EPA Methods 26 and 26A and Proposed Methods 0050 and 005 1 are in widespread use for collection and quantitation of stationary source emissions of halogens and halogen acids from a variety of source types. Considerable research has been conducted in evaluation of these methods, but research information about the methods has not been published in one convenient summary and much of the technical community is unaware of its existence. This paper provides historical and scientific background for the EPA sampling methods in use today, along with some of their strengths and limitations. The primary evaluation studies are summarized, and publication references are given. The SW-846 Methods Manual versions of the procedures are compared with the versions from CFR40 part 60. Relatively new research work is summarized, along with recent changes in the methods, and critical operating factors. INTRODUCTION Sampling and quantitation of stack emissions from hazardous waste combustors and from boilers and industrial furnaces co-firing hazardous waste are required as part of the Resource Conservation and Recovery Act (RCRA) permitting process. Hydrochloric acid and chlorine are currently regulated, and consideration is being given to setting requirements for the similar bromine compounds. Hydrochloric acid emissions from municipal incinerators are regulated under the Clean Air Act and chlorine, hydrochloric acid, and hydrofluoric acid are listed among the 189 Hazardous Air Pollutants in the Clean Air Act Amendments of 1990 (CAAA). EPA’s Office of Research and Development has developed and evaluated two variations of the same sampling and analysis technology for measurement of halogens and halogen acids. The version using EPA Method 5 sampling hardware and many Method 5 procedures is shown in Figure 1. The sampling follows Method 5 isokinetic procedures with full stack traverse. HCl and other halogen acids are very water soluble, and sampling is often downstream of a scrubber where water droplets may occur. Because of their likely halogen acid content, the droplets must be collected isokinetically to avoid non- representative sampling. The isokinetic version of the sampling technology shown in Figure 1 corresponds to EPA Method 26A’ and Proposed EPA Method 00502, which will be described and discussed more fully later in this paper. A midget impinger train packaging of the same sampling technology, which may be used when isokinetic sampling is not required, corresponds to EPA Method 26l and Proposed EPA Method 005 1 2. Considerable research has been conducted in evaluation of these methods, but research information about the methods has not been published in one convenient summary and much of the technical community is unaware of its existence. A summary of the more important studies relative to these methods follows. The earliest work with a major influence on the EPA methods was reported in 1979 by Cheney and Fortune3. They investigated collection of HCl in NaOH solutions of several concentrations followed by four different titration procedures. A mercuric nitrate titration after collection in 0.1 M NaOH was ultimately recommended. Cheney and Fortune followed their earlier work with another study reported 2  in 19844. In the second study, they investigated reaction and sorption losses of HCl during sampling. Use of disc filters made of quartz was recommended to minimize losses to the filter material, and relatively high flow rates were recommended to minimize interactions with collected alkaline particulate material. Stern, et al. presented their work during 1983, and it appeared in print in 1 9845. They reported development and laboratory evaluation of a sampling and analysis system for collection and speciation of halogens and halogen acids. The sampling equipment was essentially the midget impinger version of that shown in Figure 1, but ion chromatography was chosen for the analysis because of its high selectivity, low detection limit, and multiple ion capability. Collection and quantitation of HCl(l30 ppm) and Cl, (19 ppm) were successful in the presence of 250 ppm SO, and 600 ppm NO,. It was demonstrated that dilute H,SO, was a superior collection medium for the halogen acids as compared to water. When water was used, some retention of the halogen compounds resulted, presumably from disproportionation reactions. The presence of the dilute acid suppressed these types of reactions and resulted in excellent speciation. Poor recovery was obtained with HBr (10 ppm). The authors speculated that the poor performance for HBr was due to sorption or line losses. The fact that virtually all of the HBr was collected in the first impinger would be consistent with that hypothesis, and would rule out poor impinger collection as the problem. The publications of DeWees, et a1.6 and Steinsberger and Margeson7 constitute the principal evaluation base for measurement of HCl and Cl, by Methods 26 and 26A and Proposed Methods 0050 and 005 1. The two publications are both reports of the same body of work. Building on the work of the previous authors, both laboratory evaluation and field testing were carried out. During the early phases of the investigation, the nonisokinetic midget impinger train received most of the attention, but the isokinetic sampler was worked into later experiments. Primary focus was on evaluation of the methodology for determination of HCl, but Cl, was studied as a potential interferant, and all indications were that the method was performing adequately for Cl, as well. During the laboratory phase of the project, a ruggedness test was conducted to evaluate the effect of six variables on HCl results. Within the ranges tested, the method was shown to be insensitive to low reagent volume, increased first impinger pH, longer sampling times, elevated impinger temperatures, higher sampling rate, and elevated Cl, levels up to 50 ppm. Earlier experiments showed that only a 3.4% positive bias was caused by 197 ppm of Cl, in a gas stream containing 221 ppm of HCl. The methodology was field tested using dynamic spiking of gaseous HCl standards and a test protocol similar to that later specified in Method 301, Field Validation of Emission Concentrations from Stationary Sources. Key conclusions of the field test were: 1. The precision of the method for HCl ranged from 0.24-0.49 ppm at flue gas HCl levels of 3.9 to 15.3 ppm. 2. The bias of the method was ~8% for HCI cylinder gases of 9.7 and 34.3 ppm. 3. The manual method agreed within 7% with a continuous HCl monitor based on gas filter correlation infrared spectroscopy (GFCXR). 4. Flue gas CO, absorption by alkaline impinger reagents was insignificant with either the midget impinger train or the Method 5 type train. 5. The midget impinger train and the Method 5 type train showed similar results at a flue gas HCl concentration of 2 1.2 ppm, but the Method 5 type train produced results with a negative bias of about 50% compared to the midget impinger train and the continuous monitor both of which averaged 4.8 ppm. The work of Steger et a1.8 was prompted by concern over three potential sources of error in Proposed Method 0050 and Method 26A. They investigated possible negative bias related to purging of the optional cyclone catch, negative bias at low ppm concentrations previously reported, and potential positive bias due to the presence of NH,Cl. Key findings were: 1. A negative bias at low HCl concentrations was confirmed. The bias was variable and seemed to correlate better with gas stream moisture content than with HCl concentration. Higher probe and filter temperatures were beneficial. 2. NH&l caused a positive bias under all test conditions by penetration of the filter as a vapor and subsequent interference in the analysis. Lower probe and filter temperatures were beneficial for this 3  interference, but detrimental from a sorption standpoint, as described above. 3. When high moisture levels force the use of the cyclone, a post-sampling cyclone purge is essential to drive any trapped HCI into the impinger catch. However, when the volume of aqueous solution in the cyclone exceeded 25 mL, the 45 minute purge required in Method 0050/26A was not sufficient to complete the task. Powell and Dithrich9 investigated the use of GFC/IR for monitoring of HCl emissions from cement kilns, in part duplicating the work of Steinsberger and Margeson’ and confirming the efficacy of the monitoring technology tested. Method 26 testing conducted simultaneously produced results for HCl compared to those from GFC/IR which ranged from being low by a factor of 2 to extremely low by a factor of 30. In subsequent laboratory studies HCl was spiked into Method 26 trains with and without probes and filters present. Recoveries were reasonably quantitative for the impingers-only, but were low by factors of 3 to 5 for the full train. The authors concluded that the train losses were due to condensation (sorption?) to train surfaces and to reaction of HCl with alkaline particulate material collected on the filter. Any losses which may have been due to these effects were no doubt exacerbated by the use of fiberglass filter material in direct violation of Method 26, which specifies quartz or fluorocarbon coated quartz filters. PRINCIPLES OF OPERATION EPA Air Test Method 26 and Method 26A are essentially the same as Proposed Method 005 1 and Proposed Method 0050, respectively. Methods 26 and 26A have been extended to deal with other halogens and halogen acids in addition to chlorine and chloride, but the principles of operation are still the same. The following description is worded in terms of sampling and analysis of HCl and Cl, with Proposed Method 0050, but it also applies to the other three methods and the other halogens and halogen acids. Method 0050 contains all of the elements necessary to cope with the usual multiphase mixture extracted from incinerator stacks. A heated glass or quartz probe and probe nozzle assembly is followed by a heated filter and a series of liquid filled impingers, which perform the dual role of cooler/condenser and sample collection medium. The usual gas moving and measuring hardware follows. It is a straightforward matter to collect HCl in either acidic, neutral, or basic solution, and to analyze for the resultant chloride ion with any one of dozens of determinative analysis techniques. The situation becomes more complex when the distinction must be made between HCI and chlorine and when the stack emissions contain chloride salts which might interfere with the analysis. One of the best ways to trap chlorine is by the use of dilute sodium hydroxide, but this produces a chloride ion as well as a hypochlorite ion. This confuses interpretation of the results if HCl and chlorine are both sampled. In Proposed Method 0050, the chloride salts are removed from the sample stream by the filter, while both HCl and chlorine pass through. Some glass fiber filters have sorbed unacceptable quantities of HCl, probably due to alkaline impurities on or in the glass surface. The filter specified for Proposed Method 0050 is a fluorocarbon polymer coated quartz material. Reports of inconsistent operating behavior of the coated filter have led to approval of quartz filters as an alternative. Uniform and adequate heating of the probe and the filter is essential when collecting HCl. Any trace of moisture condensation will result in removal of HCl from the gas stream, and a resulting low bias in the final data. This problem becomes even more serious at HCl concentrations in the low ppm range. Even dry probe and filter surfaces may sorb HCl if their temperature is too low. The filter support must be fluorocarbon polymer rather than fiitted glass, since the latter can remove significant amounts of HCl. If sufficient water is present in the sample stream to wet the filter, it will be necessary to include the optional cyclone for droplet removal. Inclusion of the cyclone complicates the sample recovery process later, so it should not be added unless necessary. Wetting of the filter is unacceptable, since it allows salt migration through the filter and possible contamination of the HCl collection elements. Once HCl and chlorine pass through the filter, the HCl is collected in the dilute sulfuric acid 4
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