Fuel Processing Technology (v.90, #11)
Editorial Board (IFC).
Preface to the AQVI special issue of fuel processing technologies entitled: Air quality VI: Mercury, trace elements, SO3, particulate matter, and greenhouse gases by John H. Pavlish (1327-1332).
Selenium's importance in regulatory issues regarding mercury by Laura J. Raymond; Nicholas V.C. Ralston (1333-1338).
Current seafood safety and health risk assessment criteria use mercury concentrations as their sole basis. This unfortunate limitation omits consideration of selenium, an essential trace element that appears to be the primary molecular target of mercury toxicity. Although selenium has been recognized for decades as a means of counteracting mercury toxicity, its effects have often been overlooked or misunderstood. Experimental animal studies have demonstrated that increasing concentrations of selenium throughout the normal dietary range increasingly counteracts methylmercury toxicity. Dietary concentrations of selenium that are slightly less than the average amount present in ocean fish have been shown to completely prevent the onset of toxic symptoms of mercury toxicity, while animals fed lesser amounts of selenium rapidly sickened and died. Dietary selenium from a variety of sources including ocean fish such as tuna, swordfish, menhaden, and rockfish has been shown to counteract mercury toxicity. Since ocean fish are among the richest sources of dietary selenium, it is important to include selenium concentration measurements in future mercury risk assessments and seafood safety criteria. Mercury:selenium molar ratios in blood provide far more consistent and physiologically meaningful risk assessments. Comprehensive seafood safety criteria such as the Selenium Health Benefit Value enable clear differentiation between seafoods that are safe and those that are hazardous for human consumption. Use of parameters that integrate mercury–selenium relationships also make it easy to understand the differences between the findings of maternal mercury exposure studies that have been performed in New Zealand, the Faroes, the Seychelles, and the United Kingdom. Development of criteria for evaluating mercury–selenium interactions will enhance environmental protection and improve public safety.
Keywords: Mercury; Methylmercury; Selenium; Fish; Seafood; Health;
Alberta mercury regulation for coal-fired power plants by Prasad Valupadas (1339-1342).
Alberta stakeholders, through the Province's Clean Air Strategic Alliance (CASA), identified mercury as the pollutant of highest priority for control from coal-fired power plants. Working with CASA, the Province finalized a new Mercury Emission from Coal-Fired Power Plants Regulation [Mercury Emissions From Coal-fired Power Plants Regulation, March 2006, Alberta Regulation 34/2006, Alberta Queen's Printer, Regulation may be found at http://www.gov.ab.ca/qp.] . The regulation places the province at the forefront of controlling mercury emissions from the sector on a global level by driving actions to reduce mercury emissions from existing coal-fired power plants in the province by at least 50% by 2010. Requirements also include continuous improvement provisions for further mercury reductions beyond 2010 based on technology advancement over the next 10 years. This paper summarises the regulation, the work the province undertook at the provincial and national level in its development, and status of implementation actions.
Conducting a RATA of continuous mercury monitors using EPA Method 30B by Dennis L. Laudal (1343-1347).
In June 2005, the U.S. Environmental Protection Agency (EPA) finalized the Clean Air Mercury Rule (CAMR). As part of the rule, all coal-fired power plants were required to do continuous mercury measurements. Although CAMR has now been vacated by the courts, based on discussion with the EPA, it is expected that the mercury measurement requirements as written will be part of any future mercury regulations. This paper focuses on the process for certifying a continuous mercury monitor and conducting a relative accuracy test audit using EPA Method 30B. Based on the experience gained at the Energy & Environmental Research Center, a number of recommendations for conducting a RATA are provided.
Keywords: Continuous mercury monitor (CMM); Mercury; Relative accuracy test audit (RATA); EPA Method 30B;
Fate of trace element haps when applying mercury control technologies by Carolyn M. Nyberg; Jeffrey S. Thompson; Ye Zhuang; John H. Pavlish; Lynn Brickett; Sara Pletcher (1348-1353).
During the past several years, and particularly since the Clean Air Mercury Rule (CAMR) was promulgated in June of 2005, the electric utility industry, product vendors, and the research community have been working diligently to develop and test Hg control strategies for a variety of coal types and plant configurations. Some of these strategies include sorbent injection and chemical additives designed to increase mercury capture efficiency in particulate control devices. These strategies have the potential to impact the fate of other inorganic hazardous air pollutants (HAPs), which typically include As, Be, Cd, Cr, Co, Mn, Ni, Pb, Se, and Sb. To evaluate this impact, flue gas samples using EPA Method 29, along with representative coal and ash samples, were collected during recent pilot-scale and field test projects that were evaluating Hg control technologies. These test programs included a range of fuel types with varying trace element concentrations, along with different combustion systems and particulate control devices. The results show that the majority of the trace element HAPs are associated with the particulate matter in the flue gas, except for Se. However, for five of the six projects, Se partitioning was shifted to the particulate phase and total emissions reduced when Hg control technologies were applied.
Keywords: HAPs; Trace elements; Mercury control; Coal;
Mercury wet deposition and coal-fired power station contributions: An Australian study by Upma Dutt; Peter F. Nelson; Anthony L. Morrison; Vladimir Strezov (1354-1359).
Regions that have large coal-fired power station regions may be prone to elevated mercury (Hg) deposition fluxes. Total mercury (THg) in daily rainfall samples at a near-field sampling site (Hunter Valley) and a far-field station (Sydney) has been monitored in this study employing ultra-clean sampling techniques and Cold Vapour Atomic Fluorescence Spectrometry (CVAFS) analysis.Measurements of THg range from 0.9 to 16.5 and from 1.2 to 18.9 ng/L for the far-field and near-field sites respectively. Average daily THg wet deposition fluxes were 49.9 and 79.8 ng/m2 for the far and near-field sites respectively. A two-sample t-test reveals the near-field site to have higher rainfall mercury (significant at the 95% level) and deposition fluxes.At the far-field site, lower Hg deposition occurs during the cooler months, while the Hunter Valley site has higher winter deposition. It is believed that the higher winter values near-field may be due to the combined impact of prevailing wind direction and high pollutant build up brought on by lower mixing height.Based on this study, the first in the Southern Hemisphere, we conclude that rainfall THg concentrations and Hg wet deposition fluxes at the two sites are comparable to rural sites in North America.
Keywords: Australia; Coal-fired power stations; Mercury wet deposition flux;
New developments in the theory and modeling of mercury oxidation and binding on activated carbons in flue gas by Edwin S. Olson; Alexander Azenkeng; Jason D. Laumb; Robert R. Jensen; Steven A. Benson; Mark R. Hoffmann (1360-1363).
Recent advances in the mechanistic understanding of mercury oxidation on a carbon surface in flue gas are reviewed in this paper. Theoretical calculations were performed to determine whether the energetics are feasible for a proposed detailed model for oxidative addition of elemental mercury on a carbon edge structure. The results of the calculation show that mercury complexation with a carbenium ion formed at a zigzag edge carbon has a small positive ΔG, but attack of chloride on the complex will proceed with negative ΔG. The energetics rule out a direct covalent bond formation between mercury and the carbenium ion. Alternative concerted reaction models and double-charged models for the mechanism are also feasible but have not yet been computed.
Keywords: Mercury capture model; Mercury oxidation model; Mercury oxidation mechanism; Mercury oxidation calculation;
HgCl2 sorption on lignite activated carbon: Analysis of fixed-bed results by Blaise A.F. Mibeck; Edwin S. Olson; Stanley J. Miller (1364-1371).
Factors that influence kinetic reactivity and equilibrium between elemental mercury, carbon, and flue gas components have been the focus of numerous studies. This study pertains to recent bench-scale fixed-bed tests in which activated carbon was exposed to HgCl2 in a flue gas composition typical of an unscrubbed eastern bituminous coal. Results are discussed in light of a refined binding site model based on the zigzag carbene structures recently proposed for electronic states at the edges of the carbon graphene layers.
Keywords: Carbon; Mercury; Flue gas interactions; Oxidized mercury control; Sorbent;
Interpreting enhanced Hg oxidation with Br addition at Plant Miller by Stephen Niksa; Chitralkumar V. Naik; Mark S. Berry; Larry Monroe (1372-1377).
This paper introduces the first detailed reaction mechanisms for Br/Hg chemistry in flue gas, and interprets the Hg oxidation performance across a broad range of Br injection rates in recent field tests at Plant Miller. Homogeneous chemistry with Br species is much faster than with Cl species because the Br atom concentrations at the furnace exit are three to four orders of magnitude greater. The dominant channels with Br are analogous to those for Cl, whereby a Br atom partially oxidizes Hg0 into HgBr which is then oxidized into HgBr2 by Br2. Mercury also oxidizes heterogeneously on unburned carbon (UBC) with Br species. This mechanism is also analogous to the surface mechanism for Cl species, except that (i) Hg0 adsorption is faster on brominated sites and (ii) the high Br atom concentrations promote recombination reactions which maintain very low surface coverages of Hg/Br species. Hence, Br addition does not promote the production of particulate-Hg. Catalytic Hg0 oxidation on SCR monoliths by Br species is more than 40 times faster than by Cl species and follows a similar mechanism. For all Br loadings over 10 ppmw in the field tests, essentially all Hg0 entering the SCR was oxidized.
Keywords: Mercury emissions; Emissions production; Reaction mechanisms; Bromine;
Mercury control testing in a pulverized lignite-fired system by Steven A. Benson; John H. Pavlish; Michael J. Holmes; Charlene R. Crocker; Kevin C. Galbreath; Ye Zhaung (1378-1387).
The Energy & Environmental Research Center (EERC) is evaluating and developing advanced and innovative concepts for controlling Hg emissions from North Dakota lignite-fired power plants with the goal of achieving 50%–90% Hg removal at one-half to three-fourths the current estimated costs. Pilot-scale tests were performed to evaluate potential sorbents and fuel additives for removing Hg from North Dakota lignite (Freedom and Center Mines) combustion flue gases. The Hg sorbents and Hg0 oxidation and sorbent enhancement additives were evaluated separately, and most were also tested in combination. A 580 MJ/h (550,000 Btu/h) pulverized coal combustion system was used to conduct sorbent injections and/or lignite additive additions upstream of three particulate control devices (PCDs): 1) an electrostatic precipitator (ESP), 2) a spray dryer and fabric filter, and 3) a retrofit advanced hybrid particulate collector (AHPC) filter (an ESP followed by an AHPC filter). ASTM International Method D6784-02 (Ontario Hydro method) and continuous Hg monitors were used to measure Hg species concentrations across the control devices. The effects of sorbent injection and coal additive addition rates on Hg removal were evaluated for each PCD option. The effects of continuous injection and batch addition of sorbents on the Hg removal performance of the ESP/AHPC filter system were also investigated. Increasing injection and additive rates and improving contact between the sorbents and flue gases generally promoted Hg capture. Most of the coal additives tested significantly enhanced PCD Hg removal, especially in the presence of a sorbent.
Keywords: Mercury; Emission control; Activated carbon; Sorbents; Coal additives; Mercury speciation;
An update on DOE's Phase II and Phase III mercury control technology R&D program by Thomas J. Feeley; Andrew P. Jones; Lynn A. Brickett; B. Andrew O'Palko; Charles E. Miller; James T. Murphy (1388-1391).
The U.S. Department of Energy's National Energy Technology Laboratory, under the Office of Fossil Energy's Innovations for Existing Plants Program, carried out a comprehensive Hg research and development program for coal-fired power generation facilities since the mid-1990s. Working collaboratively with the U.S. Environmental Protection Agency, the Electric Power Research Institute, power plant operators, state and local agencies, and a host of research organizations and academic institutions, the Program identified the major factors that affect mercury speciation and capture in coal combustion flue gas and funneled this knowledge into the development of a suite of mercury control technologies for the diverse fleet of U.S. coal-fired power plants. The high performance observed during full-scale field testing has given coal-fired power plant operators the confidence to begin deploying technology. As of March 2009, more than 130 full-scale activated carbon injection systems have been ordered by the U.S. coal-fired power generators. These contracts include both new and retrofit installations and represent over 55 GW of coal-based electric generating capacity.
Keywords: Mercury capture; Activated carbon injection; Chemically-treated; Calcium bromide; Oxidation; Commercialization;
Sorbent injection into a slipstream baghouse for mercury control: Project summary by Jeffrey S. Thompson; John H. Pavlish; Lucinda L. Hamre; Melanie D. Jensen; David Smith; Steve Podwin; Lynn A. Brickett (1392-1399).
A project led by the Energy and Environmental Research Center to test and demonstrate sorbent injection as a cost-effective mercury control technology for utilities burning lignites has shown effective mercury capture under a range of operating conditions. Screening, parametric, and long-term tests were carried out at a slipstream facility representing an electrostatic precipitator–activated carbon injection–fabric filter configuration (called a TOXECON™ in the United States). Screening tests of sorbent injection evaluated nine different sorbents, including both treated and standard activated carbon, to compare mercury capture as a function of sorbent injection rate. Parametric tests evaluated several variables including air-to-cloth (A/C) ratio, flue gas temperature, cleaning frequency, and dust loading to determine the effect on mercury control and systems operation. Long-term tests (approximately 2 months in duration) evaluated the sustainability of systems operation.The screening tests identified four sorbents that achieved greater than 90% mercury capture. Longer-term tests demonstrated mercury capture of 82% at sorbent injection rates of about 2–2.5 lb/Macf. Ash loading and A/C ratio affected the operation of the fabric filter. At lower ash loadings, A/C ratios as high as 6 ft/min could be sustained while operating with conventional bags, but higher ash loadings required the use of high-permeability bags to overcome pressure drop issues.
Keywords: Electrostatic precipitator–fabric filter; Trace elements; Continuous mercury monitor; Sorbent injection; Mercury; Mercury control;
TOXECON clean coal demonstration for mercury and multi-pollutant control at the Presque Isle Power Plant by Steven Derenne; Paul Sartorelli; Jean Bustard; Robin Stewart; Sharon Sjostrom; Paul Johnson; Michael McMillian; Fred Sudhoff; Ramsay Chang (1400-1405).
We Energies and DOE, under a Clean Coal Power Initiative program, are working together to design, install, evaluate and demonstrate the EPRI-patented TOXECON™ air pollution control process as an integrated emissions control system for mercury and particulate matter from three 90 MW units at the Presque Isle Power Plant located in Marquette, Michigan.The process involves the injection of activated carbon between the existing particulate collector and a fabric filter installed downstream. The sorbent collects mercury that is then removed from the flue gas using the baghouse. The project has also recently investigated SO2 and NOx control using sorbent injection. Demonstration of TOXECON™ began in February 2006 and is scheduled to continue through early 2009. This paper will discuss balance of plant issues encountered during start-up in 2006 as well as ongoing issues. Mercury removal results from optimization and long-term testing will be presented as well as current efforts in SO2 and NOx trim control.
Keywords: Coal; Mercury removal; Sorbent injection; Activated carbon; TOXECON;
Evaluation of low ash impact sorbent injection technologies for mercury control at a Texas lignite/PRB fired power plant by Katherine Dombrowski; Carl Richardson; Jackie Padilla; Kevin Fisher; Tom Campbell; Ramsay Chang; Craig Eckberg; John Hudspeth; Andrew O'Palko; Sara Pletcher (1406-1411).
A sorbent injection test program was carried out at NRG Texas Power LLC's (NRG) Limestone Electric Generating Station (LMS). LMS fires a 30/70 blend of Powder River Basin (PRB) and Texas Lignite, and is equipped with a cold-side electrostatic precipitator (ESP) and wet scrubber. The plant markets its fly ash for beneficial use, so development of a low ash impact mercury control technology is important to the economics of implementing a mercury control system. In addition to standard activated carbon injection, two different low ash impact mercury control technologies were evaluated in parametric tests: low ash impact sorbents and Toxecon™ II. The parametric ACI test program conducted at LMS demonstrated that high (>90%) levels of mercury removal could be achieved with carbon sorbents. The Toxecon™ II design used at LMS did not provide for as high a mercury removal as injection upstream of the ESP, likely due to poor coverage of the cross-sectional area of the ESP. Limited concrete testing was performed with simulated ash/carbon mixtures. As expected, the amount of air-entraining additive required increased with increasing carbon content in the ash. However, it appeared that small amounts of non-passivated carbon may be acceptable in fly ash for concrete use.
Keywords: Activated carbon injection; Mercury control; Fly ash; Toxecon™ II; Sorbent; Electrostatic precipitator;
First full-scale demonstration of mercury control in Alberta by Terry Brown; Vitali Lissianski (1412-1418).
Alberta electricity companies, TransAlta, ATCO, and EPCOR, teamed with GE Energy to conduct full-scale evaluation of sorbent injection in Sundance Unit 5 operated by TransAlta. Sundance Unit 5 fires a Western Canadian sub-bituminous coal and is equipped with cold-side ESP for PM control. Goals of the program were to evaluate: (1) the ability of achieving 70% or greater mercury reduction using activated carbon injection in long-term tests (30 days), (2) the effect of sorbent injection on ESP performance and opacity in long-term testing, and (3) the effects of combustion conditions on “natural” mercury removal in fly ash.DARCO Hg-LH was injected upstream of ESP at average injection rate of 2.1 lb/MMacf and achieved an average mercury removal of 80%. During the test, the sorbent injection rate was varied from 0.55 lb/MMacf to 8 lb/MMacf with mercury removals from 65% to > 95%. The continuous 30-day DARCO Hg-LH injection testing demonstrated that 70% mercury removal could be achieved at DARCO Hg-LH injection rate of 1.2 lb/MMacf.Tests were conducted to optimize combustion conditions to improve “native” mercury capture in the fly ash. Testing demonstrated that combustion conditions that resulted in reduction of NO x emissions also corresponded to reduced mercury emission. Mercury emissions were reduced by up to 50% and NO x emissions by up to 35% from baseline levels as a result of changes in the way Unit 5 operated. Integration of sorbent injection with combustion conditions reduced requirements for sorbent injection by 20–30%.Testing has demonstrated that sorbent injection did not have an effect on opacity and ESP performance.
Keywords: Mercury; Sub-bituminous coal; Activated carbon; Sundance 5; Cold ESPs;
Influence of SO3 on mercury removal with activated carbon: Full-scale results by Sharon Sjostrom; Martin Dillon; Brian Donnelly; Jean Bustard; Greg Filippelli; Rob Glesmann; Tom Orscheln; Steve Wahlert; Ramsay Chang; Andrew O'Palko (1419-1423).
Activated carbon injection is considered one of the most cost-effective options for mercury control at PRB-fired power plants. However, roughly 30% of sites firing PRB coal use SO3 for flue gas conditioning. The presence of SO3 in flue gas can decrease mercury capture by activated carbon, sometimes dramatically. Overcoming activated carbon performance limitations caused by SO3 conditioning for units with this configuration is essential to enable these plants to cost-effectively meet pending mercury emission regulations. Ameren's Labadie Unit 2 fires PRB coal and uses SO3 to enhance particulate capture in the electrostatic precipitator (ESP). Full-scale sorbent injection tests at Labadie were conducted from 2005–2007. Six sorbents were tested at SO3 injection concentrations ranging from 0 to 10.7 ppm. Sorbent performance was evaluated at two injection locations (the air preheater (APH) inlet and outlet). Native mercury capture on fly ash was typically less than 15%. When the mercury sorbents were injected downstream of the air preheater, the SO3 concentration resulted in a decrease in mercury capture from 85% (no SO3 injection) to 17% (SO3 injection set at 10.7 ppm). Mercury sorbents were more effective when injected upstream of the air preheater. With the SO3 system off, mercury removal increased from 75% when injecting 5.1 lb/MMacf of brominated carbon at the APH outlet, compared to 95% when injecting at the inlet. With the SO3 system on, test results indicated an increase from about 30% injecting at the outlet to 58% injecting at the inlet. Tests evaluating the ADA-ES patented onsite milling process showed that 85% mercury capture was achieved injecting 4 lb/MMacf of milled activated carbon compared to a requirement of 10 lb/MMacf to achieve the same removal using as-received carbon, representing a 60% reduction in activated carbon consumption. No changes in opacity, APH and ESP performance, or other balance-of-plant effects were observed in these tests.
Keywords: Coal; SO3; Hg; Activated carbon injection;
Fabric filter bag investigation following field testing of sorbent injection for mercury control at TXU's Big Brown Station by John H. Pavlish; Jeffrey S. Thompson; Christopher L. Martin; Lucinda L. Hamre; Robert Wiemuth; Sara Pletcher (1424-1429).
Field testing of mercury control sorbent injection options with a TOXECON™ configuration has been completed at TXU's Big Brown Station. Mercury control results at Big Brown were promising and have been previously reported. However, the high air-to-cloth ratio of operations at this unit results in significant differential pressure, and thus there was little operating margin before differential pressure limits were encountered, especially at high loads. This limited the use of sorbent injection as the added material contributes to the overall differential pressure. After field testing, the residual differential pressure across the test fabric filter module had increased relative to baseline conditions to the point that the plant performed a filter change of the test module several months ahead of schedule. An investigation was conducted on pre- and posttest filter samples from the test module and a parallel nontest module to examine the effect of activated carbon injection. Analysis of the samples indicates an increase in residual dust embedded in the filters which appears to explain the low fabric permeabilities. The long-term increase in differential pressure did not appear to be associated with activated carbon injection, but instead was due to a gradual buildup of embedded material on the filters that was not cleaned away by the pulse cleaning system. The injected activated carbon appeared to behave like additional fly ash in terms of baghouse differential pressure but did not appear to accelerate the buildup of residual material.
Keywords: TOXECON; Mercury control; Filter analysis; Activated carbon injection;
Activated carbon for mercury control: Implications for fly ash management by Debra F. Pflughoeft-Hassett; David J. Hassett; Tera D. Buckley; Loreal V. Heebink; John H. Pavlish (1430-1434).
As more utilities begin to use activated carbon injection (ACI) for mercury control, the potential for the presence of elevated concentrations of mercury, other air toxic elements, and activated carbon to impact fly ash management needs to be evaluated. Several Energy & Environmental Research Center (EERC) projects have allowed the collection of comparative baseline fly ash samples and associated fly ash–activated carbon (AC) samples from full-scale demonstrations of ACI for mercury emission control. These samples were evaluated for mercury and air toxic element content and mobility and for performance criteria to facilitate a better understanding of the impact of these components to specific utilization applications, including use as a mineral admixture in concrete. These data are compared with published data from samples collected at similar large-scale mercury emission control tests.The data presented are in agreement with previous results from the EERC, the U.S. Environmental Protection Agency, and elsewhere that mercury associated with fly ash is stable and unlikely to be released under most management conditions. Additionally, this paper will discuss the potential for fly ash–AC samples to be used as a mineral admixture in concrete and other large-volume use applications.
Keywords: Carbon; Mercury; Fly ash;