Stack Sampling Methods for Halogens and Halogen Acids

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 nonrepresentative 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