US EPA 324 Vapor Phase Mercury Traps

By: Mark Robillard, Bob Cole, Bob Brunette, AnalytiX Volume 5 Article 5

US EPA 324 Vapor Phase Mercury Traps – Supelco is the exclusive supplier of innovative and economical FSTM™ trap technology from Frontier GeoSciences

Vice President, Research & Development, Supelco
Strategic Project Chemist, Supelco
Frontier GeoSciences

Introduction

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FSTMTM traps


US EPA Method 324 (40 CFR Part 75 Appendix K) is designed for short-term and continuous sampling of total mercury emissions in combustion flue gas streams. The method uses a specialized dry sorbent FSTM™ trap developed by Frontier GeoSciences, Inc. with cold vapor atomic fluorescence spectrometry (CVAFS) detection. Through a unique partnership, the combined expertise of Supelco and Frontier GeoSciences has been focused to offer rapid, sensitive, reliable and economical solu tions for short-term sampling and continuous monitoring of mercury in combustion flue gas.

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Mercury in the environment

The presence of mercury in the biosphere is an area of environmental concern. Although it occurs naturally, anthropogenic sources of mercury vapor in the atmos phere include coal-, oil- and natural gas-fired electric power plants, municipal solid waste incinerators, Hg retort facilities, Zn and Au smelters, chloro-alkali production and industrial boilers. According to the U.S. Environmental Protection Agency (EPA), coal-fired elec tric power plants are the largest source of humancaused mercury air emissions in the U.S., pumping an estimated 50 – 70 tons of mercury per year into the atmosphere. The U.S. regulations governing mercury emissions, including the Clean Air Mercury Rule (CAMR, 2005) and the Clean Air Interstate Rule (CAIR) issued by the EPA are to reduce mercury emissions from coalfired power plants. The CAMR reinforces the goal of the EPA’s Clean Air Interstate Rule (CAIR) which is to reduce mercury emissions in the US by nearly 70 percent at full implementation.

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Frontier GeoSciences and US EPA Method 324 (40 CFR Appendix K) for continuous Hg emissions monitoring

With the promulgation of the CAMR and the drawbacks inherent in existing Hg monitoring approaches, the EPA saw the need for a continuous monitoring method that was reliable, cost effective, accurate and provided more data points. Frontier GeoSciences developed and validated a novel mercury detection system based on a proprietary, chemically impregnated carbon sorbent and with key industry partners, developed a new field sampling method for continuous monitoring of mercury vapor. Because of Supelco’s expertise in manufacturing products for air monitoring applications, Frontier Geo Sciences collaborated with Supelco to pack their proprietary sorbent in specially designed glass tubes. The resulting mercury trap was given the trademark acronym FSTM for Flue Gas Sorbent Total Mercury. Besides the innovative sorbent, Frontier GeoSciences leveraged the sensitivity advantages of cold vapor atomic fluorescence spectroscopy (CVAFS) in analyzing the traps post-sampling. The newly legislated CAMR regulations that require continuous emissions monitoring popularized the FSTM technique and it became the underpinnings of the new EPA Method 324 (40 CFR Part 75 Appendix K).

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Principles of the FSTMTM method

Known volumes of flue gas are extracted from a duct through the FSTM trap containing the chemically impreg nated carbon. The FSTM trap is then acid digested and the resulting digest is analyzed by CVAFS detection as described in EPA Method 1631, Revision E. Mercury concentrations are determined on a mass basis and then combined with flue gas flow data (m3/min) to calculate the continuous mass emission rate of total vapor phase mercury. The analyte measured by this method is total vapor-phase mercury, which represents the sum of elemental and oxidized forms of mercury:

Hg (total) = PHg (particulate) + Hg(II) + Hg(0)

The innovations of FSTM technology have simplified two important application areas of mercury monitoring, making them much more practical and economically feasible:

  1. The initial assessment in order to understand the baseline of mercury behavior and emissions in a source is critical in order to enable cogent decision making for potential emission control measures. The FSTM traps permit rapid, sensitive and reliable multi-point measurement of total mercury in order to assess the behavior of mercury in existing air pollution control devices and develop the right mercury control strategy.
  2. The on-going, continuous emission monitoring role of the FSTM trap in EPA 324 is designed to measure weekly integrated continuous emissions from Hg sources. The FSTM traps permit sampling for as little as 15 minutes and up to 10 days per solid sorbent trap.

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FSTM trap features and benefits

The features of the FSTM traps include:

  • Each trap uniquely numbered for traceability and chain-of-custody purposes
  • High purity, chemically impregnated carbon adsorbent
  • Captures all species of gas phase mercury
  • Variable flow rate from 0.1 to 4.0 standard liters/min (SLPM)
  • Fast total mercury determination (5 to 15 L in 15 to 30 minutes)
  • No temperature constraints (ambient to 1000°F).
  • Highly standardized Hg blank on trap
  • Successfully intercompared to total mercury (THg) in coal-fired flue gas with Ontario Hydro, US EPA M29 and US EPA 101A

In addition, FSTM technology has the following bene fits over Ontario Hydro and EPA 101A techniques:

  • No hazardous chemicals, no HAZMAT shipping
  • World-wide tube availability through Sigma-Aldrich
  • Modern, highly-sensitive and fully validated analytical method (EPA 1631 employing CVAFS) gives 50- to 200-fold lower MDL than CVAAS method
  • Low Hg background (<1 ng/trap) permits small sample volumes
  • Short sample times allows more data points per unit time
  • Minimal tube sample train surface area means no Hg wall loss
  • No interference from SO2/NOX/ash
  • Very low overall cost, including materials, labor and analysis
  • Excellent field QA capability allows simultaneous field duplicates
  • Small equipment package

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Trap formats

FSTM traps are available in 2- and 3-bed formats designed for different environments, sampling times, volumes and flow rates. All tube formats can adsorb 5% or greater of their mass in mercury and have a detection limit of 0.005 μg/m3.

Short-term sampling traps allow for the collection of short-term samples with a dynamic range from 15 minutes up to 24 hours.

Continuous emission monitoring traps allows for a con tinuous emission monitoring approach with a dy na mic range from 24 hours up to 10 day integrated samples.

Indoor / ambient air monitoring traps have been approved by the National Environmental Laboratory Accreditation program (NELAP) and the US Department of Health. They are ideal for monitoring personnel exposure to indoor and outdoor mercury vapor using standard active air sampling devices.

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Conclusions

FSTM traps developed by Frontier GeoSciences in collaboration with Supelco/Sigma-Aldrich have been validated for use in EPA Method 324 (40 CFR Appendix K) for both short-term sampling and continuous monitoring of total mercury emissions from combustion sources. Using FSTM traps with CVAFS analysis greatly improves the ease-of-use and economy of routine mercury emissions testing. Measurements are accurate and precise, sampling techniques are simple, portable and easily adaptable to the conditions at each source. Compared to competing technologies, the FSTM traps have revolutionized mercury vapor monitoring.

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