Development Of Speciation And Sampling Tools For Mercury In Flue Gas

EPA Grant Number: R827649C007
Subproject: this is subproject number 007 , established and managed by the Center Director under grant R827649
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Center for Air Toxic Metals® (CATM®)
Center Director: Groenewold, Gerald
Title: Development Of Speciation And Sampling Tools For Mercury In Flue Gas
Investigators: Thompson, Jeffrey S. , Schulz, Richard L.
Institution: University of North Dakota
EPA Project Officer: Chung, Serena
Project Period: October 15, 1999 through October 14, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Center for Air Toxic Metals (CATM) (1998) RFA Text |  Recipients Lists
Research Category: Targeted Research

Objective:

Work under this project focuses on the development of new or improved methods to measure various forms of mercury in flue gas. The effects of the particulate collection assembly and the probe design on mercury speciation have been reported and are significant. Consequently, a new probe design, which minimizes cool spots in the probe and particulate collection assembly, has been designed and is under testing. The collection and detection of mercury species using a cryogenic trap has been tested. The design and construction of a thermally controlled cryogenic trap is under way and will be followed by rigorous testing under flue gas conditions. The combination of these two efforts will improve the methods to speciate mercury in flue gas so that the effects of mercury speciation on collection efficiencies for both existing and new technologies will be possible.

The goal of this work is the development of an inexpensive, rapid, and reliable method for the sampling and determination of the primary chemical forms of mercury in flue gas streams produced by coal-fired utilities, gasification systems, and municipal waste incinerators. Specific project objectives are as follows:

  • Design, construction, and testing of a sample probe and particulate collection assembly with accurate temperature control for field work

  • Design, construction, and testing of a cryogenic trap and detection system for mercury speciation in flue gas
  • Approach:

    Probe and Particulate Collection Assembly

    The correct speciation of mercury requires that the mercury being measured be transported to the measuring device without altering its chemistry or concentration. Two factors that affect the transport of mercury are probe temperatures and particulate loading. CATM research is aimed at combining state-of-the-art heat tracing with new advances in insulation and probe design to produce a probe that will have as small of a temperature gradient as possible and to incorporate a particulate separation device to reduce the effects caused by fly ash. These two measures will help ensure that the mercury measurements are accurate for both speciation and total mercury.

    Cryogenic Trapping of Mercury for Speciation

    The collection and subsequent desorption of mercury, as both mercuric chloride and elemental mercury, have been accomplished by using a cryogenic trap. The separation from other flue gas components (SOx, NOx, CO2, etc.) will be attempted with the use of a thermally controlled cryogenic trap, currently under construction. The separation of the mercury species from the flue gas components is a big step toward the accurate analysis of mercury species because it eliminates the interferences that complicate methods for mercury detection. The separation of mercury species from each other and their detection will be accomplished with the use of conventional gas chromatography techniques and currently available detectors as necessary.

    Progress

    Probe and Particulate Collection Assembly

    The sampling probe has been built and tested at the bench-scale level with good results. Full-scale testing has revealed some small problems maintaining the temperature at the very last thermocouple on the sampling probe; this is partially due to the transition from the probe to the filter acting as a heat sink and partially due to problems maintaining the proper spacing of the heat trace lines at this transition. A modified probe has been built and is now ready for testing. Work, on incorporating the particulate removal device into the probe design, is under way and will soon be tested.

    Cryogenic Trapping of Mercury for Speciation

    The efficient trapping of mercury (elemental and mercuric chloride) has been accomplished with the use of a simple glass-packed trap. Initial tests were conducted using liquid nitrogen as a cooling source so that temperature was not a limiting factor. The detection of the mercury was accomplished with an atomic fluorescence detector for which the sensitivity is such that on-line instant detection of mercury was possible at relevant flue gas concentrations. The mercuric chloride was converted thermally to elemental mercury prior to detection. Following these initial experiments, a thermally controlled cryogenic trap was designed for use in testing the effect of temperature on collection efficiency and separation from other flue gas components. Construction of this trap is under way, and testing will begin shortly. The design of this trap includes an injection valve such that a clean carrier gas (helium) can be used for the desorption process. This should improve the sensitivity for mercury detection by atomic fluorescence by a factor of 50 to 100. In addition, the trap is designed with liquid nitrogen cooling with a thermostatically controlled valve to allow the separation of other flue gas components during the collection process.

    The testing of the trap will allow the temperature to be optimized for efficient collection of mercury species with maximum separation of other flue gas components. It is anticipated that the completed unit will be used for pilot-scale measurements of mercury species for verification of the method.

    Rationale:

    Current methods for mercury sampling and speciation for mercury (EPA Method 29) suffer from sampling effects, such as particulate partitioning and solution chemistry, that alter the chemical forms of mercury prior to detection. The development of alternative technologies for mercury sampling and analysis will eliminate these problems. This will allow the accurate determination of the chemical forms of mercury in flue gas. This is important for the ongoing development of control technologies as well as emission, transport, fate, and health-related issues.

    Supplemental Keywords:

    RFA, Scientific Discipline, Air, Toxics, Waste, Chemical Engineering, air toxics, Environmental Chemistry, HAPS, Incineration/Combustion, 33/50, Engineering, Chemistry, & Physics, Environmental Engineering, flue gas , mercury , mercury, coal fired utility boiler , sampling tools, mercury speciation, mercury speciation and sampling, speciation tools, mercury & mercury compounds, Mercury Compounds

    Progress and Final Reports:

  • 2000
  • 2001
  • Final

  • Main Center Abstract and Reports:

    R827649    Center for Air Toxic Metals® (CATM®)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827649C001 Development And Demonstration Of Trace Metals Database
    R827649C002 Nickel Speciation Of Residual Oil Ash
    R827649C003 Atmospheric Deposition: Air Toxics At Lake Superior
    R827649C004 Novel Approaches For Prevention And Control For Trace Metals
    R827649C005 Wet Scrubber System
    R827649C006 Technology Commercialization And Education
    R827649C007 Development Of Speciation And Sampling Tools For Mercury In Flue Gas
    R827649C008 Process Impacts On Trace Element Speciation
    R827649C009 Mercury Transformations in Coal Combustion Flue Gas
    R827649C010 Nickel, Chromium, and Arsenic Speciation of Ambient Particulate Matter in the Vicinity of an Oil-Fired Utility Boiler
    R827649C011 Transition Metal Speciation of Fossil Fuel Combustion Flue Gases
    R827649C012 Fundamental Study of the Impact of SCR on Mercury Speciation
    R827649C013 Development of Mercury Sampling and Analytical Techniques
    R827649C014 Longer-Term Testing of Continuous Mercury Monitors
    R827649C015 Long-Term Mercury Monitoring at North Dakota Power Plants
    R827649C016 Development of a Laser Absorption Continuous Mercury Monitor
    R827649C017 Development of Mercury Control Technologies
    R827649C018 Developing SCR Technology Options for Mercury Oxidation in Western Fuels
    R827649C019 Modeling Mercury Speciation in Coal Combustion Systems
    R827649C020 Stability of Mercury in Coal Combustion By-Products and Sorbents
    R827649C021 Mercury in Alternative Fuels
    R827649C022 Studies of Mercury Metabolism and Selenium Physiology