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The following are project highlights from research performed through CATM during 2004.
Mercury Transformations in Coal Combustion Flue Gas
The EERC is performing critical fundamental research to understand mechanisms responsible for conversion of mercury to other chemical species within combustion flue gas. Salts were cofired with low-acid gas coals in low amounts, which caused elemental mercury to be converted to oxidized gaseous species and/or particle-associated phases.
Unburned carbon from two full-scale utility boiler fly ashes, one high in mercury and the other low, is being concentrated using separation methods. The chemical composition, morphology, and microstructure of the individual unburned carbon particles will be determined using a host of analytical techniques including x-ray photoelectron spectroscopy (XPS). Surface morphology and chemistry of the carbon particles are being evaluated in order to find correlations between carbon characteristics and mercury capture.
Sulfur species in unburned carbon from coal or tire rubber are being explored as possible reaction sites for oxidizing and stabilizing gaseous mercury. Chemical additives will be investigated in combination with tetrasulfide flue gas injection to determine the impact on mercury oxidation and capture.
Bench-scale flue gas simulation was used to study the effects of SO3, SO2, and HCl on mercury oxidation across a selective catalytic reduction (SCR) catalyst. Tests using subbituminous and bituminous ash conditioning showed no conversion of Hg0 to an oxidized form across the SCR catalyst unless HCl was added. SO2 and SO3 alone had little effect. SO3 enhanced oxidization of Hg0, but SO2 hindered the reaction. Oxidation of Hg0 was lessened by the absence of ammonium, but still significant. Ammonium addition without the acid gases had no effect on Hg0 oxidation.
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Development of easer-Based Mercury Continuous Emission Monitor
An apparatus has been assembled for developing a laser-based method for measuring elemental mercury. A diode laser tuned to 407.784 nm has been used with a mercury lamp at 253.7 nm to induce fluorescence at 546 nm in elemental mercury. At this time, modification of the apparatus and more preliminary data are needed before a minimal detection limit can be determined. Instrumentation developed in this area could impact research requiring small, low-power measurement techniques for high-speed mercury determination.
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Methods to Improve Measurement of Mercury and Chlorine in Combustion Flue Gases
The EERC is striving to improve the mercury measurement results obtained with impinger-based methods, such as ASTM International (American Society for Testing and Materials) Method D6784-02 (Ontario Hydro), and continuous mercury monitors (CMM) (e.g., Semtech Hg 2000, PS Analytical [PSA] Sir Galahad, Tekran) by investigating two potential sources of analytical bias: 1) the removal of CO2 from flue gas by a SnCl2-NaOH solution and
2) the mercury-fly ash interactions that occur on filter medium (i.e., glass fibers) which promote the formation of Hg1+, 2+ and/or particle-associated mercury forms (Hg[p]), thus negatively biasing Hg0 measurements. The EERC is also striving to use infrared spectroscopy combined with chiller and NafionŽ gas-drying systems and a Cl2 to HCl conversion system to quantify Cl2 and HCl in coal combustion flue gas and other gas streams on a nearly continuous basis.
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Development of an Oxidized Mercury Spiking System
To determine conditioning and conversion system biases, an oxidized mercury-spiking system is being developed. This system will enable CMM operators to detect and troubleshoot biases and provide researchers with an indication of CMM performance.
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Development of Mercury Control Technologies
Based on health, emissions, and scientific data, EPA and the Canadian Council of Ministers of the Environment (CCME) have determined that the amount of mercury emitted from utility power plants should be reduced. On March 15, 2005, EPA released the Clean Air Mercury Rule (CAMR) for utility mercury regulations. With promulgation of mercury regulations, improvements in mercury control options and reductions in costs are extremely important and the primary focus of this project.
Sorbent injection is the most mature technology for reducing mercury emissions. Based on current projections, the amount of sorbent needed to serve the U.S. market is expected to be very large. Sorbents can be either injected as a powder or used in fixed or moving beds. The low concentrations of mercury in flue gases from coal-fired systems and high fractions of the mercury emitted in elemental form from many coals result in a low reactivity between activated carbon and mercury. New methods are being developed to increase this reactivity in order to minimize changes required for the utility systems and to reduce costs associated with capital equipment and carbon injection. In addition, research continues on development of control options to optimize use of pollution control equipment available on scrubbed systems.
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Modeling Mercury Speciation in Coal Combustion Systems and Interactions on Activated Carbon
A fundamental model framework has been established that incorporates a homogeneous gaseous reaction mechanism relevant to mercury species and a heterogeneous mercury-particulate interaction mechanism. This model has shown promising predictions of mercury capture by particulates as well as gaseous split between elemental mercury and oxidized mercury. With the newly integrated model, coal composition including mineral size and composition, bulk ash composition, mercury level, and chlorine level is utilized to predict the fraction of particulate, elemental, and oxidized mercury. The model was used to predict mercury speciation as a function of flue gas temperature and chlorine additive levels. The model-predicted mercury species are reasonably close to the measured mercury species in flue gas of Caballo coal fired in the PTC with and without CaCl2 addition.
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Developing SCR Technology Options for Mercury Oxidation in Western Fuels
The project was initiated to evaluate the ability of used and new SCR catalysts as well as the use of additives to enhance oxidation The first catalyst to be tested is manufactured by Haldor Topsoe. A second set of tests will be conducted on several new formulations developed in cooperation with Haldor Topsoe. This past year's work focused on further developing a finalized research plan for the project and finalizing the contractual agreement with Haldor Topsoe.
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Development of a Laser Absorption Continuous Mercury Monitor
Experiments are being prepared in which two-photo frequency-modulation spectroscopy measurements are made of mercury in a closed cell. This has included the procurement of major pieces of equipment such as the diode laser system and an optical spectrum analyzer. Other equipment that has been acquired include a Tektronix oscilloscope, a LeCroy digital storage data acquisition system, Horiba imaging spectra-photometer, and various other hardware. Results using this instrument will become available over the next year.
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Investigation of Mercury and Carbon-Based Sorbent Reaction Mechanisms
This project is just beginning as of the end of 2004. It will build on the previous CATM research of mercury capture on carbon-based sorbents, focusing on the effects of halogen pretreatment of sorbent surfaces on mercury capture. The overall goal of the project is improve the mercury capture efficiency of carbon-based sorbents through a better understanding of mercury-sorbent reaction mechanisms. This work will mainly be accomplished in 2005.
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Mercury in Alternative Fuels
As the United States and other countries investigate ways to use renewable fuels, the content of mercury in various biomass sources must be evaluated. Previous research indicated that some plant and woody materials took up more significant amounts of mercury than others. During the course of this project, various alternative fuels were collected, air-dried, and analyzed for residual moisture and mercury concentration and compared to a National Institute for Standards and Technology (NIST) biomass standard. The biomass samples were collected in rural areas at least 50 miles from the nearest power plant in Iowa, Minnesota, North Dakota, and Wisconsin. Cattail, a plant that has been discussed for cocombustion with coal, had the highest mercury concentration of all samples analyzed.
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Mercury Metabolism and Selenium Physiology Studies
Studies on the interaction between dietary mercury and selenium are extremely important in order to contribute to the understanding of risk factors, as well as possible factors that could mediate the harm done by ingestion of mercury. Well-known studies of the Faroe and Seychelles Islands and the Minamata region leave much to be explained.
This year's study confirms previous CATM research that exposure to mercury can result in sequestration of selenium within cells of vulnerable organs. At high dietary-mercury concentrations, formation of these insoluble mercury selenides may result in diversion of selenium from selenoprotein synthesis and diminishment of selenoenzyme activities. However, a diet that is rich in selenium mediates these effects. If one considers that saltwater fish is an extremely rich source of selenium, has many beneficial health effects, and is one of the lowest-cost sources of protein in the world, these studies do not support the claim that ocean fish should be eliminated from the diet of pregnant women or children.
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Mercury and Air Toxic Element Impacts of Coal Combustion By-Product Disposal and Utilization
The second year of a 3-year effort is nearing completion. This effort is focused on the evaluation of coal combustion by-products (CCBs) for their potential to release mercury and other air toxic elements under different controlled laboratory conditions and will investigate the release of these same air toxic elements in select disposal and utilization field settings to understand the impact of various emission control technologies. Results through Year 2 were used to determine if mercury release from CCBs, both as currently produced and as produced with mercury and other emission controls in place, will potentially impact CCB management practices. Preliminary conclusions can be summarized as follows:
| • | Analysis of the carbon forms data revealed that samples with anisotropic or isotropic coke as the dominant carbon form also had the higher mercury content. Those samples also generally contained activated carbon from mercury emission control. |
| • | No correlation has been observed between total mercury and leachable mercury. |
| • | Most samples of CCBs act as mercury sinks in ambient-temperature vapor-phase release experiments. |
| • | Elevated temperature release experiments showed that mercury generally released at temperatures greater than 200°C. |
| • | Organomercury compounds were present in leachates from microbiological experiments. |
| • | Some vapor-phase mercury from microbiological experiments showed evidence of methylation. |
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Technology Commercialization, Education, and Publication
To facilitate the transfer of technical information produced by CATM, several communication vehicles are used, including participation in both domestic and international conferences, symposia, workshops, and other educational programs; annual meetings and peer review; quarterly reports on topical issues related to mercury through a collaborative project funded by CATM Affiliates, DOE, and the Canadian Electricity Association (CEA); and the publication of a semiannual newsletter. In addition, the CATM Director and staff provide input into various public forums during the year to assist in the development of venues of technology transfer that may not be directly funded by CATM.
The EERC, through CATM, EPA, and DOE, has organized and sponsored four conferences on Air Quality: Mercury, Trace Elements, and Particulate Matter, held in 1998, 2000, 2002, and 2003. The first two conferences were held in Tysons Corner, McLean, Virginia. In 2002 and 2003, the third and fourth conferences were held in Arlington, Virginia. Air Quality V: Mercury, Trace Elements, SO3, and Particulate Matter is scheduled to be held in September 19-21, 2005 in Arlington, Virginia. The Air Quality conference is a forum for reviewing the current state of air toxic science and policy on pollutants, mercury, trace elements, SO3, and particulate matter in the environment.
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The CATM Web page has been maintained throughout the year and can be accessed at www.undeerc.org/catm. Copies of the CATM Newsletter and topical reports to the CEA are available and can be accessed via the CATM Web page for download and distribution.
2006 CATM Highlights
2005 CATM Highlights
2003 CATM Highlights |
