Grantee Research Project Results
Final Report: Mercury Transformations in Coal Combustion Flue Gas
EPA Grant Number: R827649C009Subproject: this is subproject number 009 , 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: Mercury Transformations in Coal Combustion Flue Gas
Investigators: Pavlish, John H. , Benson, Steven A. , Galbreath, Kevin C. , Timpe, Ronald C. , Zygarlicke, Christopher J. , Hassett, David J. , Holmes, Michael J. , Miller, Stanley J. , Laudal, Dennis L. , Olson, Edwin S. , Thompson, Jeffrey S. , Heebink, Loreal V. , Ralston, Nicholas V.C. , Mibeck, Blaise , Kong, Lingbu
Institution: University of North Dakota
EPA Project Officer: Chung, Serena
Project Period: October 15, 1999 through October 14, 2004
RFA: Center for Air Toxic Metals (CATM) (1998) RFA Text | Recipients Lists
Research Category: Targeted Research
Objective:
The objective of this research project was to address air toxic trace element emissions, which have become a matter of worldwide concern as well as a regulatory issue in the United States. The specific objective of this research project was to develop and disseminate critical information on air toxic metal compounds to support development and implementation of pollution prevention and control strategies that will reduce effectively air toxic metal emissions and releases to the environment.
Summary/Accomplishments (Outputs/Outcomes):
Mercury has been targeted by the U.S. Environmental Protection Agency for further study with respect to its association with coal and power plant emissions. The speciation of mercury in coal combustion flue gas is important for devising control strategies, especially in light of pending mercury regulations. This research investigated the effects of flue gas components on mercury speciation.
A 7 kW (42 MJ/hr) combustion system, hereafter referred to as the conversion and environmental process simulator (CEPS), was designed and constructed to test the effects of fuel type and combustion conditions on air toxic metal transformations, emissions, and control. In initial tests on subbituminous coal flue gas, conversion of Hg0 was not detected at either 400° or 275°C, but at 150°C the rate of Hg2+(g) and Hg0 conversion to Hg(p) could be measured as a function of residence time. Significant mercury transformation of Hg0 to Hg(p) also was observed at higher temperatures of 440°–878°C when 200 ppmv HCl was injected into the combustion zone. Analysis of aerodynamically classified particulate and vapor-phase species from the CEPS indicated that the partitioning of arsenic, nickel, lead, selenium, and mercury between ash particulate and gaseous combustion byproducts generally was consistent with results from most other bench- and pilot-scale combustion systems in the literature.
CEPS tests on bituminous and subbituminous coals indicated significant differences in trace element volatility and speciation, depending on coal type and combustion conditions. In general, trace element concentrations were enriched in the smaller size range (< 2.5 μm), which potentially is most harmful to respiratory health. In coal, arsenic, chromium, and nickel occurred in large mineral grains in an Illinois No. 6 bituminous test coal but were associated with organic macerals and fine-grained minerals in subbituminous test coals. Concentrations of antimony, arsenic, cadmium, lead, nickel, vanadium, and zinc all increased with decreasing particle size in fly ash from an Illinois coal, suggesting volatility and surface deposition. Arsenic and chromium in fly ash from a subbituminous coal were distributed more uniformly. Low-NOx combustion conditions promoted vaporization and surface deposition. Analysis of chemical species in fly ash less than 2.5 μm by X-ray absorption fine-structure (XAFS) spectroscopy indicated As5O4-containing phases for both coal ranks, with Ca3(AsO4)2 as the dominant species for subbituminous coal. The ratio of Cr6+ to Cr3+ was higher for subbituminous coal, possibly as a result of the higher concentration of oxygen functional groups in low-rank coal. Both coal ranks exhibited similar NiO-containing species, possibly ferrite spinel. Combustion conditions did not appear to affect arsenic, chromium, or nickel speciation. Mercury in all cases partitioned primarily to the gas fraction.
In CEPS tests on Pittsburgh No. 8 bituminous coal from the Blacksville Mine, the addition of sufficient fly ash to double the ash content did not affect significantly the partitioning of selenium and mercury between the solid and gaseous phases. The increased fly ash did, however, promote oxidation of Hg0, possibly because of the catalytic effect of iron species.
Bench-scale investigations using synthetic flue gas indicate that NO, NO2, hematite (α-Fe2O3), and maghemite (γ-Fe2O3) promote the conversion of gaseous elemental mercury (Hg0) to gaseous oxidized mercury (Hg2+) and/or particle-associated mercury (Hg[p]) in simulated coal combustion flue gases.
Extensive tests on different coals and various simulated flue gas compositions point to complex interactions between mercury, chlorine, iron species, and calcium.
Kinetic experiments designed to obtain quantitative data on the time-temperature oxidation of Hg0 were performed in an entrained-flow reactor using a slipstream of subbituminous coal flue gas.
Solids from wet scrubbers were studied as part of a separate larger project on mercury emissions at coal-fired plants in North Dakota. The scrubbers at these plants effectively removed oxidized mercury, but total mercury removal was only about 20 percent owing to the presence of mercury, primarily as Hg0, in the entering flue gas. Separation and analysis of the solid and liquid phases in the scrubber sludge indicated that the mercury was partitioned to the solid phase. Leaching tests on the solids indicated that the mercury was not leachable.
Supplemental Keywords:
air, air quality, analysis, control, emissions, environment, hazardous, measurement, mercury, metals, modeling, pollutants, pollution, sampling, species, toxic, transformations,, RFA, Air, Scientific Discipline, Waste, Toxics, Chemical Engineering, Chemistry, HAPS, Environmental Chemistry, 33/50, Engineering, Chemistry, & Physics, Incineration/Combustion, air toxics, Environmental Engineering, mercury & mercury compounds, flue gases, mercury , mercury speciation, Mercury Compounds, coal fired utility boiler , mercury speciation and sampling, flue gas , sampling toolsRelevant Websites:
http://www.undeerc.org Exit
http://www.undeerc.org/catm/index.html Exit
Progress and Final Reports:
Original AbstractMain 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
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.