Dennis L. Laudal

Effects of flue gas constituents on mercury speciation

Beginning with the 1990 Clean Air Act Amendments, there has been considerable interest in mercury emissions from coal-fired power plants. This past year, the U.S. Environmental Protection Agency (EPA) issued both the Mercury Study Report to Congress and the Study of Hazardous Air Pollutant Emissions from Electric Utility Steam-Generating Units, which make clear that EPA views mercury in the environment as a serious issue and that coal-fired utilities are a major source of mercury. For the past 4 years, EPRI and the U.S. Department of Energy (DOE) have funded research on mercury measurement, control, and chemistry at the Energy and Environmental Research Center (EERC). The primary goal of bench-scale work was to determine what flue gas constituents affect mercury speciation, specifically how mercury speciation affects measurement methods and the ability of mercury sorbents to absorb mercury. A bench-scale test rig was designed and built to simulate flue gas conditions. The baseline simulated flue gas consisted of O2, CO2, H2O, and N2. Other flue gas constituents tested include SO2, HCl, NO, NO2, HF, Cl2, and fly ash. The mercury was delivered to system as either elemental mercury (Hg0) or mercury(II) chloride (HgCl2) via temperature-controlled permeation tubes. EERC bench-scale data clearly show that the type of fly ash is important in determining mercury speciation in flue gas streams. Not surprisingly, there appear to be a number of interactions between various flue gas constituents that affect mercury speciation. Depending on concentration, there is clearly an interaction between NO–NO2 and fly ash, and it is possible that the interaction may be related to the ratio of NO:NO2. However, it has been shown that when NO–NO2 is tested without fly ash, there is no conversion of Hg0 to Hg2+. Bench-scale tests clearly show that the chemistry of mercury is very complex and that more research is needed to understand what is occurring. However, it is equally clear that the development of effective mercury sorbents and the ability to accurately model mercury speciation are dependent on understanding mercury chemistry, thermodynamics, and kinetics.

Heterogeneous oxidation of mercury in simulated post combustion conditions

Heterogeneous mercury oxidation was studied by exposing whole fly ash samples and magnetic, nonmagnetic, and size-classified fly ash fractions to elemental mercury vapor in simulated flue gas streams. Fly ash from sub-bituminous Wyodak–Anderson PRB coal and bituminous Blacksville coal were used. Scanning electron microscopy, X-ray diffraction, thermogravimetric analyses, and BET N2 isothermal sorption analyses were performed to characterize the fly ash samples. Mercury speciation downstream from the ash was determined using the Ontario Hydro method. Results showed that the presence of fly ash was critical for mercury oxidation, and the surface area of the ash appears to be an important parameter. However, for a given fly ash, there were generally no major differences in catalytic oxidation potential between different fly ash fractions. This includes fractions enriched in unburned carbon and iron oxides. The presence of NO2, HCl, and SO2 resulted in greater levels of mercury oxidation, while NO inhibited mercury oxidation. The gas matrix affected mercury oxidation more than the fly ash composition.

Mercury mass balances: a case study of two North Dakota power plants.

ABSTRACT The Energy & Environmental Research Center (EERC) conducted a mercury-sampling program to provide data on the quantity and forms of Hg emitted and on the Hg removal efficiency of the existing air pollution control devices at two North Dakota power plants—Milton R. Young Station and Coal Creek Station. Minnkota Power Cooperative, Great River Energy, the North Dakota Industrial Commission, and EPRI funded the project. The primary objective was to obtain accurate measurements of Hg released from each plant, as verified by a material balance. A secondary objective was to evaluate the ability of a mercury continuous emission monitor (CEM) to measure total Hg at the stack. At both plants, speciated Hg measurements were made at the inlets and outlets of both the electrostatic precipi-tators (ESPs) and the flue gas desulfurization (FGD) systems. A Semtech Hg 2000 (Semtech Metallurgy AB) mercury CEM was used to measure the total Hg emissions at the stack in real time. Using these measurements and plant data, the measured Hg concentrations in the coal, FGD slurries, and ESP ash, a Hg mass flow rate was calculated at each sampling location. Excellent Hg mass balances were obtained (±15%). It was also found that the Hg was mostly in the elemental phase (~90%), and the small amount of oxidized Hg that was generated was removed by the FGD systems. Insignificant amounts of particulate-bound Hg were measured at both plants. However, 10-20% of the elemental Hg measured prior to the ESP was converted to oxidized Hg across the ESP. The data show that, at these facilities, almost all of the Hg generated is being emitted into the atmosphere as elemental Hg. Local or regional deposition of the Hg emitted from these plants is not a concern. However, the Hg does become part of the global Hg burden in the atmosphere. Also, the evidence appears to indicate that elemental Hg is more difficult to remove from flue gas than oxidized Hg is.

LONG-TERM DEMONSTRATION OF SORBENT ENHANCEMENT ADDITIVE TECHNOLOGY FOR MERCURY CONTROL

Long-term demonstration tests of advanced sorbent enhancement additive (SEA) technologies have been completed at five coal-fired power plants. The targeted removal rate was 90% from baseline conditions at all five stations. The plants included Hawthorn Unit 5, Mill Creek Unit 4, San Miguel Unit 1, Centralia Unit 2, and Hoot Lake Unit 2. The materials tested included powdered activated carbon, treated carbon, scrubber additives, and SEAs. In only one case (San Miguel) was >90% removal not attainable. The reemission of mercury from the scrubber at this facility prevented >90% capture.

EFFECTS OF FLY ASH ON MERCURY OXIDATION DURING POST COMBUSTION CONDITIONS

Tests were performed in simulated flue gas streams using two fly ash samples from the electrostatic precipitators of two full-scale utility boilers. One fly ash was derived from a Powder River Basin (PRB) coal, while the other was derived from Blacksville coal (Pittsburgh No. 8 seam). The tests were performed at temperatures of 120 and 180 C under different gas compositions. Elemental mercury (Hg) streams were injected into the simulated flue gas and passed over filters (housed in a convection oven) loaded with fly ash. The Ontario Hydro method was used to determine the total amount of Hg passing through the filter as well as the percentages of elemental and oxidized Hg collected. Results indicated that substantial amounts of Hg oxidation did not occur with either fly ash, regardless of the temperature used for testing. When oxidation was observed, the magnitude of the oxidation was comparable between the two fly ashes. These results suggest that the gas matrix may be more important than the ash components with respect to the distribution of Hg species observed in gaseous effluents at coal-fired power plants.

Issues associated with the use of activated carbon for mercury control in cement kilns

Mercury is a known neurological toxin that the U.S. Environmental Protection Agency (EPA) regulates under the National Emission Standards for Hazardous Air Pollutants (NESHAP) for municipal waste incinerators and medical waste incinerators. Although later vacated by the courts, mercury regulations were also promulgated for coal-fired utilities. Under the existing and proposed NESHAP for the portland cement industry, EPA is proposing to regulate mercury for the portland cement industry for both new and existing cement plants. A substantial body of information has been generated in the coal-fired boiler industry for activated carbon injection control systems. Utilizing this knowledge base and the limited data from the cement industry, issues and opportunities for activated carbon injection to control mercury from cement kilns will be discussed.

Mercury Information Clearinghouse

The Canadian Electricity Association (CEA) identified a need and contracted the Energy & Environmental Research Center (EERC) to create and maintain an information clearinghouse on global research and development activities related to mercury emissions from coal-fired electric utilities. With the support of CEA, the Center for Air Toxic Metals{reg_sign} (CATM{reg_sign}) Affiliates, and the U.S. Department of Energy (DOE), the EERC developed comprehensive quarterly information updates that provide a detailed assessment of developments in the various areas of mercury monitoring, control, policy, and research. A total of eight topical reports were completed and are summarized and updated in this final CEA quarterly report. The original quarterly reports can be viewed at the CEA Web site (www.ceamercuryprogram.ca). In addition to a comprehensive update of previous mercury-related topics, a review of results from the CEA Mercury Program is provided. Members of Canadas coal-fired electricity generation sector (ATCO Power, EPCOR, Manitoba Hydro, New Brunswick Power, Nova Scotia Power Inc., Ontario Power Generation, SaskPower, and TransAlta) and CEA, have compiled an extensive database of information from stack-, coal-, and ash-sampling activities. Data from this effort are also available at the CEA Web site and have provided critical information for establishing and reviewing a mercury standard for Canada that is protective of environment and public health and is cost-effective. Specific goals outlined for the CEA mercury program included the following: (1) Improve emission inventories and develop management options through an intensive 2-year coal-, ash-, and stack-sampling program; (2) Promote effective stack testing through the development of guidance material and the support of on-site training on the Ontario Hydro method for employees, government representatives, and contractors on an as-needed basis; (3) Strengthen laboratory analytical capabilities through analysis and quality assurance programs; and (4) Create and maintain an information clearinghouse to ensure that all parties can keep informed on global mercury research and development activities.

PILOT-SCALE EVALUATION OF THE IMPACT OF SELECTIVE CATALYTIC REDUCTION FOR NOx ON MERCURY SPECIATION

Full-scale tests in Europe and bench-scale tests in the United States have indicated that the catalyst, normally vanadium/titanium metal oxide, used in the selective catalytic reduction (SCR) of NO{sub x}, may promote the formation of Hg{sup 2+} and/or particulate-bound mercury (Hg{sub p}). To investigate the impact of SCR on mercury speciation, pilot-scale screening tests were conducted at the Energy & Environmental Research Center. The primary research goal was to determine whether the catalyst or the injection of ammonia in a representative SCR system promotes the conversion of Hg{sup 0} to Hg{sup 2+} and/or Hg{sub p} and, if so, which coal types and parameters (e.g., rank and chemical composition) affect the degree of conversion. Four different coals, three eastern bituminous coals and a Powder River Basin (PRB) subbituminous coal, were tested. Three tests were conducted for each coal: (1) baseline, (2) NH{sub 3} injection, and (3) SCR of NO{sub x}. Speciated mercury, ammonia slip, SO{sub 3}, and chloride measurements were made to determine the effect the SCR reactor had on mercury speciation. It appears that the impact of SCR of NO{sub x} on mercury speciation is coal-dependent. Although there were several confounding factors such as temperature and ammonia concentrations in the flue gas, two of the eastern bituminous coals showed substantial increases in Hg{sub p} at the inlet to the ESP after passing through an SCR reactor. The PRB coal showed little if any change due to the presence of the SCR. Apparently, the effects of the SCR reactor are related to the chloride, sulfur and, possibly, the calcium content of the coal. It is clear that additional work needs to be done at the full-scale level.

Mercury Emission Monitoring for the Cement Industry

In March 2005, the U.S. Environmental Protection Agency (EPA) promulgated the Clean Air Mercury Rule (CAMR), the first rule ever to restrict mercury emissions from coal-fired power plants. Because the rule is designed to be a cap-and-trade program, mercury measurement is an important component. As a result, substantial effort and resources have been invested in developing mercury measurement protocols both in terms of continuous mercury measurement for compliance purposes and reference methods for conducting relative accuracy test audits (RATAs). Although utilities are the largest source of anthropogenic mercury, they are not the only source. EPA has announced mercury emission standards for new cement kilns but currently exempts existing facilities. Many states are also reviewing the potential of reducing mercury from other sources such as metals smelting, waste-to-energy facilities, and the cement industry. In the manufacture of cement, four raw materials are necessary: limestone, shale, clay, and iron slag. Of these four raw materials, three (limestone, shale, clay) are generally mined on-site, with only the iron slag being imported. To provide the energy required for the processing of the kiln feed in the pyroprocess, a typical plant can use coal, natural gas, used oil, tire-derived fuels, and/or other refuse-derived fuels. A potential source of mercury can be from either the raw materials or the fuel used during the cement- manufacturing process.

Subtask 4.24 - Field Evaluation of Novel Approach for Obtaining Metal Emission Data

Over the past two decades, emissions of mercury, nonmercury metals, and acid gases from energy generation and chemical production have increasingly become an environmental concern. On February 16, 2012, the U.S. Environmental Protection Agency (EPA) promulgated the Mercury and Air Toxics Standards (MATS) to reduce mercury, nonmercury metals, and HCl emissions from coal-fired power plants. The current reference methods for trace metals and halogens are wet-chemistry methods, EPA Method (M) 29 and M26A, respectively. As a possible alternative to EPA M29 and M26A, the Energy & Environmental Research Center (EERC) has developed a novel multielement sorbent trap (ME-ST) method to be used to sample for trace elements and/or halogens. Testing was conducted at three different power plants, and the results show that for halogens, the ME-ST halogen (ME-ST-H) method did not show any significant bias compared to EPA M26A and appears to be a potential candidate to serve as an alternative to the reference method. For metals, the ME-ST metals (ME-ST-M) method offers a lower detection limit compared to EPA M29 and generally produced comparable data for Sb, As, Be, Cd, Co, Hg, and Se. Both the ME-ST-M and M29 had problems associated with high blanks for Ni, Pb, Cr, and Mn. Although this problem has been greatly reduced through improved trap design and material selection, additional research is still needed to explore possible longer sampling durations and/or selection of lower background materials before the ME-ST-M can be considered as a potential alternative method for all the trace metals listed in MATS.