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Coal fueled the Industrial Revolution and the global expansion of electrification in the 20(th) century. In the 21st century, coal use has declined in North America and Europe, but continues to increase in Asia. Coal contains many of the elements of the Periodic Table, in percent-levels or in trace amounts (ppm, ppb). The impact of many of these elements on the environment via air and water discharges from coal-fired plants has been studied with decades of research on their chemical transformations within combustion systems and on their fates upon reintroduction into the environment. The transformations of the trace elements present in coal burned during combustion can be categorized as thermal volatilizations from the coal in the furnace; thermal decomposition of trace element compounds inside the coal; encapsulation inside ash structures through high-temperature vitrification; oxidation of the trace elements with the myriad species contained in flue gas through gas phase (homogeneous) reactions or catalytic (gas-solid) reactions; adsorption and/or reactions with active sites on entrained fly ash particulates contained in the flue gas; and absorption into solutions. These transformations can, in many cases, impact the fraction of these trace elements that are removed by various pollution control devices compared to the fraction released into the environment. The sampling and measurement of trace elements, in the inlet coal, outlet flue gas, aqueous scrubber solutions, and ash matrices, represents a significant challenge. This review focuses on the behavior of trace elements in industrial coal combustion systems with an emphasis on what has been learned over the past century uniquely related to the use of coal in boilers for electricity and heat production. Key accomplishments in measurement, modeling and control of trace element emissions in coal-fired systems are highlighted.

Using a 1-MWe slipstream pilot plant, solid-sorbent-based post-combustion CO2 capture was tested at a coal-fired power plant. Results from pilot testing were used to develop a preliminary full-scale commercial design. The sorbent selected for pilot-scale evaluation during this project consisted of an ion-exchange resin that incorporated amines covalently bonded to the substrate. A unique temperature-swing-absorption (TSA) process was developed that incorporated a three-stage fluidized-bed adsorber integrated with a single-stage fluidized-bed regenerator. Overall, following start-up and commissioning challenges that are often associated with first-of-a-kind pilots, the pilot plant operated as designed and expected, with a few key exceptions. The two primary exceptions were associated with: (i) handling characteristics of the sorbent, which were sufficiently different at operating temperature than at ambient temperature when design specifications were established with lab-scale testing; and (ii) CO2 adsorption in the transport line between the regenerator and adsorber that preloaded the sorbent with CO2 prior to entering the adsorber. Results from the pilot programme demonstrate that solid-sorbent-based post-combustion capture can be utilized to achieve 90% CO2 capture from coal-fired power plants.

Selenium has unique fate and transport through a coal-fired power plant because of high vapor pressures of oxide (SeO2) in flue gas. This study was done at full-scale on a 900 MW coal-fired power plant with electrostatic precipitator (ESP) and wet flue gas desulfurization (FGD) scrubber. The first objective was to quantify the partitioning of selenium between gas and condensed phases at the scrubber inlet and outlet. The second objective was to determine the effect of scrubber operation conditions (pH, mass transfer, SO2 removal) on Se removal in both particulate and vapor phases. During part of the testing, hydrated lime (calcium hydroxide) was injected upstream of the scrubber. Gas-phase selenium and particulate-bound selenium were measured as a function of particle size at the inlet and outlet of the scrubber. The total (both phases) removal of Se across the scrubber averaged 61%, and was enhanced when hydrated lime sorbent was injected. There was evidence of gas-to-particle conversion of selenium across the scrubber, based on the dependence of selenium concentration on particle diameter downstream of the scrubber and on thermodynamic calculations.

The analysis of gas-phase mercury speciation in combustion gases containing bromine and SO2 was studied using a commercial mercury analyzer coupled with several different wet conditioning systems; ...

Oxidized mercury species may be formed in combustion systems through gas-phase reactions between elemental mercury and halogens, such as chorine or bromine. This study examines how bromine and chlorine species affect mercury oxidation in the gas phase. Experiments were conducted in a bench-scale, laminar, methane-fired (300 W), quartz-lined reactor, in which gas composition (HCl, HBr, NOx, and SO2) was varied. In the experiments, the postcombustion gases were quenched from the flame temperature to about 350 °C and then speciated mercury was measured using a wet conditioning system and continuous emission monitor (CEM). Bromine was shown to be much more effective in the postflame, homogeneous oxidation of mercury than chlorine, on an equivalent molar basis. The addition of NO to the flame (up to 400 ppmv) had no impact on mercury oxidation by chlorine or bromine. The addition of SO2 had no effect on mercury oxidation by chlorine at SO2 concentrations below about 400 ppmv; some increase in mercury oxidation...

Ash deposition is still an unresolved problem when retrofitting existing air-fired coal power plants to oxy-fuel combustion. Experimental data are quite necessary for mechanism validation and model development. This work was designed to obtain laboratory combustor data on ash and deposits from oxy-coal combustion, and to explore the effects of oxy-firing on their formation. Two bituminous coals (Utah coal and Illinois coal) and one sub-bituminous coal (PRB coal) were burned on a down-fired combustor under both oxy- and air-firing. Two oxy-fired cases, i.e., 27 vol% O2/73 vol% CO2 and 32 vol% O2/68 vol% CO2, were selected to match the radiation flux and the adiabatic flame temperature of air combustion, respectively. Once-through CO2 was used to simulate fully cleaned recycled flue gas. The flue gas excess oxygen was fixed at 3 vol%. For each case, both size-segregated fly ash and bulk fly ash samples were obtained. Simultaneously, ash deposits were collected on an especially designed un-cooled deposition probe. Ash particle size distributions and chemical composition of all samples were characterized. Data showed that oxy-firing had insignificant impacts on the tri-modal ash particle size distributions and composition size distributions in the size range studied. Bulk ash compositions also showed no significant differences between oxy- and air-firing, except for slightly higher sulfur contents in some oxy-fired ashes. The oxy-fired deposits were thicker than those from air-firing, suggesting enhanced ash deposition rates in oxy-firing. Oxy-firing also had apparent impacts on the deposit composition, especially for those components (e.g., CaO, Fe2O3, SO3, etc.) that could contribute significantly to ash deposition. Based on these results, aerodynamic changes in gas flow and changes in combustion temperature seemed more important than chemical changes of ash particles in determining deposit behavior during oxy-coal combustion.

The behavior of Se during coal combustion is different from other trace metals because of the high degree of vaporization and high vapor pressures of the oxide (SeO 2 ) in coal flue gas. In a coal-fired boiler, these gaseous oxides are absorbed on the fly ash surface in the convective section by a chemical reaction. The composition of the fly ash (and of the parent coal) as well as the time–temperature history in the boiler therefore influences the formation of selenium compounds on the surface of the fly ash. A model was created for interactions between selenium and fly ash post-combustion. The reaction mechanism assumed that iron reacts with selenium at temperatures above 1200 °C and that calcium reacts with selenium at temperatures less than 800 °C. The model also included competing reactions of SO 2 with calcium and iron in the ash. Predicted selenium distributions in fly ash (concentration versus particle size) were compared against measurements from pilot-scale experiments for combustion of six coals, four bituminous and two low-rank coals. The model predicted the selenium distribution in the fly ash from the pilot-scale experiments reasonably well for six coals of different compositions.

Activated carbon adsorbs mercury from combustion flue gas, and this is exploited for the control of mercury emissions from coal-fired boilers and incinerators. The reaction pathway for the adsorption of mercury on activated carbon appears to be complex. The form of mercury that is adsorbed on activated carbon is likewise unknown. Experiments were carried out on vaporization of mercury compounds on non-treated, non-halogenated activated carbon in order to identify characteristics of the mercury compound adsorbed on the carbon and to assess the thermal stability of mercury once adsorbed. In these experiments, a solid material was heated in a boat in flowing air in the Ohio Lumex pyrolysis furnace. As the temperature of the boat was ramped up, the amount of mercury transferred to the gas was measured. A transient heat-transfer model was developed and coupled with a mercury vaporization model to predict, respectively, the heat-up and evolution of mercury from samples in the pyrolysis furnace. The model was able to reproduce the trends in the experimental observations, particularly the location of the peaks. The activation energy of mercury desorption in the model was used to distinguish between two different mercury species. The model also illustrated the effect of the thermal profile on mercury evolution in the pyrolysis furnace.

The U.S. Environmental Protection Agency has proposed to regulate emissions of air mercury from Portland cement kilns. Understanding the behavior of mercury within cement kilns will help operators of Portland cement kilns to devise methods for accurate measurement of mercury emissions and for reducing mercury emissions when regulations are imposed. A transient model for mercury behavior was developed and benchmarked with a comprehensive data set on the dynamic behavior of mercury in a Portland cement kiln reported by the German Research Institute of the Cement Industry. The model was able to reproduce key features of the transient behavior, including spikes in the exhaust gas concentration during the period when the plant switched from the raw mill on-line to the raw mill off-line; the high concentration of mercury in the electrostatic precipitator (ESP) dust; and the weekly transients resulting from operation over weekends with the raw mill on-line.

Lunar in situ resource utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery processes (pyrolysis, gas-solid reactions, gas-liquid or three-phase reactions and desorption) require thermal energy at temperatures from 1,000 K to 2,500 K . Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures 1,200 K–1,800 K . For these materials, process applications or solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing an innovative solar power system in which solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper, we will review our work on the development of the solar thermal power system and its application to a lunar ISRU process.

Incinerators that process mercury-containing feedstocks need to remove mercury from the flue gas with sufficient efficiency to meet regulations for mercury emissions from the stack. Equipment designed to remove other pollutants, such as acid gases and particulate matter, can remove mercury as well, under certain conditions. Acid gas scrubbers, designed to remove compounds such as HCl and SO2, can remove mercury, when the latter is found in the flue gas in an oxidized form. There is a growing body of evidence that mercury, once absorbed into the scrubbing solution, can be reduced back to the nonsoluble elemental form, resulting in little net capture of mercury. Dissolved sulfur compounds in the scrubbing solution play an important role in the reduction of absorbed mercury. In this paper, the mechanisms for mercury capture and release in scrubbing solutions are presented. Conditions that promote or inhibit retention of mercury in scrubbers are discussed, as well as the use of additives to improve mercury re...

X-ray absorption fine structure spectroscopy has been used to determine directly the oxidation states and speciation of selenium and arsenic in 10 fly ash samples collected from full-scale utility plants. Such information is needed to assess the health risk posed by these elements in fly ash and to understand their behavior during combustion and in fly ash disposal options, such as sequestration in tailings ponds. Selenium is found predominantly as Se(IV) in selenite (SeO3(2-)) species, whereas arsenic is found predominantly as As(V) in arsenate (AsO4(3-)) species. Two distinct types of selenite and arsenate spectra were observed depending upon whether the fly ash was derived from eastern U.S. bituminous (Fe-rich) coals or from western subbituminous or lignite (Ca-rich) coals. Similar spectral details were observed for both arsenic and selenium in the two different types of fly ash, suggesting that the postcombustion behavior and capture of both of these elements are likely controlled by the same dominant element or phase in each type of fly ash.

This paper presents a mercury oxidation data set suitable for validation of fundamental kinetic models of mercury chemistry and for mechanism development. Experimental facilities include a mercury reactor fitted with a 300-W, quartz-glass burner and a quartz reaction chamber. While operated with a temperature profile representative of a typical boiler, a residence time of 6 s was achieved. Participating reacting species (chlorine, mercury) were introduced through the burner to produce a radical pool representative of real combustion systems. Speciated mercury measurements were performed using a Tekran 2537A Analyzer coupled with a conditioning system. Homogeneous mercury reactions involving chlorine have been investigated under two different temperature profiles producing quench rates of −210 K/s and −440 K/s. The larger quench rate produced 52% greater total oxidation than the lower quench at chlorine concentrations of 200 ppm. The effect of reactor surface area on oxidation was also investigated. The quartz surfaces interacted with mercury only in the presence of chlorine and their overall effect was to weakly inhibit oxidation. The extent of oxidation was predicted using a detailed kinetic model. The model predicted the effects of quench rate and chlorine concentration shown in experimentation.

Vapor-phase arsenic in coal combustion flue gas causes deactivation of the catalysts used in selective catalytic reduction (SCR) systems for NO x control. A one-dimensional model has been developed to predict the behavior of arsenic in the postcombustion region of a coal-fired boiler as a function of gas residence time. The purpose of the model is to calculate the partitioning of arsenic between the vapor phase from volatilization and arsenic on the ash particles due to surface reaction and/or condensation at temperatures characteristic of SCR systems. The model accounts for heterogeneous condensation of arsenic on the fly ash, as well as surface reaction for two regimes: (1) the free molecular regime (submicrometer ash particles) and (2) the continuum regime (supermicrometer ash particles). All gas properties are computed as functions of gas temperature, pressure, and composition, which are allowed to vary. The arsenic model can be used to calculate the impact of coal composition on vapor-phase arsenic at SCR inlet temperatures, which will help utilities better manage coal quality and increase catalyst lifetimes on units operating with SCR. The arsenic model has been developed and implemented and was tested against experimental data for several coals.

The proportion of Hg in coal feedstock that is emitted by stack gases of utility power stations is a complex function of coal chemistry and properties, combustion conditions, and the positioning and type of air pollution control devices employed. Mercury in bituminous coal is found primarily within Fe-sulfides, whereas lower rank coal tends to have a greater proportion of organic-bound Hg. Preparation of bituminous coal to reduce S generally reduces input Hg relative to in-ground concentrations, but the amount of this reduction varies according to the fraction of Hg in sulfides and the efficiency of sulfide removal. The mode of occurrence of Hg in coal does not directly affect the speciation of Hg in the combustion flue gas. However, other constituents in the coal, notably Cl and S, and the combustion characteristics of the coal, influence the species of Hg that are formed in the flue gas and enter air pollution control devices. The formation of gaseous oxidized Hg or particulate-bound Hg occurs post-combustion; these forms of Hg can be in part captured in the air pollution control devices that exist on coal-fired boilers, without modification. For a given coal type, the capture efficiency of Hg by pollution control systems varies according to type of device and the conditions of its deployment. For bituminous coal, on average, more than 60% of Hg in flue gas is captured by fabric filter (FF) and flue-gas desulfurization (FGD) systems. Key variables affecting performance for Hg control include Cl and S content of the coal, the positioning (hot side vs. cold side) of the system, and the amount of unburned C in coal ash. Knowledge of coal quality parameters and their effect on the performance of air pollution control devices allows optimization of Hg capture co-benefit.

Preface INTRODUCTION FATE OF MERCURY IN THE ENVIRONMENT REGULATIONS US Regulations International Regulations and Trends TRACE ELEMENTS IN COAL MERCURY MEASUREMENT IN COAL GAS Continuous Emission Monitors Batch Methods: Impingers and Sorbent Traps MERCURY CHEMISTRY IN COAL UTILIZATION SYSTEMS AND AIR POLLUTION CONTROL DEVICES Combustion Systems Gasification Systems Cement Kilns RESEARCH PROGRAMS IN THE US USDOE Program EPA Research Program EPRI Program MERCURY CONTROL PROCESSES USING EXISTING TECHNOLOGY Scrubbers Fuel and Flue Gas Additives Catalysts for the Oxidation of Mercury Combustion Modification MERCURY CONTROL PROCESSES USING SORBENTS Introduction to Carbon Sorbents for Pollution Control Sorbent Manufacture and Characterization Activated Carbon Injection Halogenated Carbons Concrete-Compatible Activated Carbons Non-Carbon Sorbents Sorbents for Gasification Process FATE OF MERCURY IN COAL COMBUSTION RESIDUES MODELING OF MERCURY CHEMISTRY IN AIR POLLUTION CONTROL DEVICES Mercury-Carbon Surface Chemistry Fundamental Models System-Level Models FURTHER READING

Emissions of mercury to the environment, in particular air emissions, are of increasing concern in the United States. The U.S. EPA has surveyed sources of mercury emissions, and coal-fired power plants were found to discharge the largest amount of mercury into the atmosphere as compared to other man-made sources. In December 2000, the U.S. EPA made a determination to regulate mercury emissions from coal-fired electric utility boilers. Compliance with the as-yet-to-be-determined regulations may necessitate additional air-pollution control devices being installed at utility power plants.There is a considerable amount of data in the literature showing that high levels of mercury removal can occur in existing control devices. Particulate control devices such as electrostatic precipitators and fabric filters are capable of removing mercury, but the level of removal is highly variable, depending on coal type, boiler configuration, mercury speciation in flue gas, and operating conditions in the control device. T...

With impending regulation of mercury from coal-fired power plants, it is important to concentrate efforts on the most mature retrofit control technologies. Injection of powdered activated carbon (PAC) has been deemed the most mature technology, but has until recently only been demonstrated in bench- and pilot-scale experiments. This paper presents some of the results from a field evaluation program of sorbent injection upstream of existing particulate control devices (PCDs). An important component of the field demonstration program is to characterize the fly ash that results from injection of PAC upstream of a baghouse or electrostatic precipitator (ESP). Leaching analyses were performed on fly ash collected during two different field demonstrations; one fly ash was derived from bituminous coal and the other from a subbituminous coal. Several widely accepted leaching methods were used in order to assess the stability of the ash by-product in landfill situations; other ash characterization tests were also used in the study. Little or no detectable Hg was leached as a result of the various leaching protocols. The subbituminous ash conformed to the ASTM C-618 standard for Class C fly ash, but did not pass the Foam Index Test that is also required for sale of this ash for use in concrete formulation.

A review is presented of data obtained by X-ray absorption fine structure (XAFS) spectroscopy on the speciation of mercury captured on a variety of sorbent materials from simulated combustion flue gases at low temperatures (

Sixteen different fly ash samples, generated from both pilot-scale and full-scale combustion systems, were exposed to a simulated flue gas containing either elemental mercury or HgCl2 in a bench-scale reactor system at the Energy and Environmental Research Center to evaluate the interactions and determine the effects of temperature, mercury species, and ash type on adsorption of mercury and oxidation of elemental mercury. The fly ash samples were characterized for surface area, loss on ignition, and forms of iron in the ash. While many of the ash samples oxidized elemental mercury, not all of the samples that oxidized mercury also captured elemental mercury. However, no capture of elemental mercury was observed without accompanying oxidation. Generally, oxidation of elemental mercury increased with increasing amount of magnetite in the ash. However, one high-carbon subbituminous ash with no magnetite showed considerable mercury oxidation that may have been due to unburned carbon. Surface area as well as the nature of the surface appeared to be important for oxidation and adsorption of elemental mercury. The capacity of the ash samples for HgCl2 was similar to that for elemental mercury. There was a good correlation between the capacity for HgCl2 and the surface area; capacity decreased with increasing temperature.

Accumulation of toxic trace elements generated by coal-fired power stations presents a serious threat to the environment. Field testing and laboratory studies have revealed the existence of trace elements in submicron particles emitted from power stations. Arsenic, selenium, and antimony are present in the submicron particles presumably via a vaporization-condensation pathway although the volatilities of these elements are very different. Previous explanations include the volatility and the forms of occurrence of elements in coals. Based on well-controlled experimental studies for selected coals, this paper establishes the first quantitative physicochemical model for vaporization of arsenic, selenium, and antimony during coal pyrolysis and combustion. Advanced characterization methods found that the three elements are associated with pyrites in the coals burned for this study. The vaporization processes for these three elements consist of three consecutive processes: transport of molecules or atoms through the bulk pyrite liquid (melt) to the melt/gas interface, vaporization of elements at the surface of melts, and transport of molecules/atoms through the pores of the char to the atmosphere. The controlling step for vaporization of arsenic is diffusion through the melt. Diffusion processes in the melt and within the char pores together determine the vaporization rates for selenium and antimony.

The emissions of trace elements and mercury from stationary combustion sources are determined by the occurrence of these elements in fuels, the transformation of the elements into vapor and particles in furnaces, and the ability of the vapors and particles to penetrate the air pollution control devices (APCDs). For electrostatic precipitators (ESPs), in use at greater than 90% of coal-fired utility boilers in the US, the preferential escape of particles is in the 0.1–1.0 μm size. The major source of particles in this size range is the vaporization and condensation of the inorganic constituents in the parent fuel. Potentially toxic elements, although mainly confined to the particulate phase, may therefore show enhanced release to the environment as a result of preferential condensation on the surface of submicron particulate matter. Surface reaction with larger fly ash particles can reduce these emissions by redistributing the trace elements away from the difficult-to-capture submicron particulate. In contrast, mercury is the most volatile of the trace elements in coal and its escape is near complete when the mercury is in the elemental vapor form. Mercury emissions may be mitigated, however, by transformation to mercuric chloride, more readily captured either in scrubbers or by collection in the particulate form. In this paper, we present our recent research developments contributing to an improved understanding of the relative importance of factors determining trace element emissions. Significant progress that has been made in understanding and quantifying each of the processes governing the transformation of the inorganic constituents of fuels leading to promising results on the prediction of emissions given detailed characterization of fuels, the combustion conditions to which they are exposed, and the characteristics of APCDs.

Both surface and groundwater are threatened by buried waste at a number of sites because of subsurface plumes containing dense non‐aqueous phase liquids (DNAPLs), hazardous metals, and radionuclides. In this work, a novel process is explored which represents an enhancement to thermal extraction methods as well as a mobile system that is suitable for remediation of remote sites. Solar radiation is collected by modular concentrators which transfer the concentrated solar radiation to an optical waveguide (OW) transmission line consisting of low‐loss optical fibers. The OW line transmits the high intensity solar radiation to the contaminated site where the solar flux is injected into the soil for thermally enhanced soil vapor extraction (SVE). The organic compounds driven out of the soil go through off‐gas treatment. A small prototype was constructed and used to heat soil contaminated with trichloroethylene (TCE). The thermal efficiency of the solar SVE process conducted using the small scale experim...

Trace elements in coal have diverse modes of occurrence that will greatly influence their behavior in many coal utilization processes. Mode of occurrence is important in determining the partitioning during coal cleaning by conventional processes, the susceptibility to oxidation upon exposure to air, as well as the changes in physical properties upon heating. In this study, three complementary methods were used to determine the concentrations and chemical states of trace elements in pulverized samples of four US coals: Pittsburgh, Illinois No. 6, Elkhorn and Hazard, and Wyodak coals. Neutron Activation Analysis (NAA) was used to measure the absolute concentration of elements in the parent coals and in the size- and density-fractionated samples. Chemical leaching and X-ray absorption fine structure (XAFS) spectroscopy were used to provide information on the form of occurrence of an element in the parent coals. The composition differences between size-segregated coal samples of different density mainly reflect the large density difference between minerals, especially pyrite, and the organic portion of the coal. The heavy density fractions are therefore enriched in pyrite and the elements associated with pyrite, as also shown by the leaching and XAFS methods. Nearly all the As is associated with pyrite in the three bituminous coals studied. The sub-bituminous coal has a very low content of pyrite and arsenic; in this coal arsenic appears to be primarily organically associated. Selenium is mainly associated with pyrite in the bituminous coal samples. In two bituminous coal samples, zinc is mostly in the form of ZnS or associated with pyrite, whereas it appears to be associated with other minerals in the other two coals. Zinc is also the only trace element studied that is significantly more concentrated in the smaller (45 to 63 μm) coal particles.

Trace metal emissions from coal-fired power plants are largely associated with the fly ash. The work reported here is part of a larger effort to develop a fundamental model for transformation of trace metals in coal to air toxic emissions from coal-fired power plants. Because the time-temperature history of the combustion gases determines the condensation behavior of gaseous species, experimental study of these phenomena require a realistic post-combustion environment. Pilot-scale combustion of a Powder River Basin coal was conducted using realistic post-combustion conditions. Trace element distributions were measured in the submicron fly ash at the inlet to an electrostatic precipitator. Flame temperature had a dramatic impact on the amount of certain trace elements such as As and Se in the submicron ash, indicating that these elements vaporize during the combustion process. The amount of vaporization was not sensitive to coal grind. There is evidence for the reaction of As and Se vapors with the large (supermicron) ash in the post-combustion flue gas via a surface reaction. The correlation between arsenic and calcium in the ash suggests the formation of calcium arsenate. No such correlation was observed between selenium and calcium.

Because mercury enters the food chain primarily through atmospheric deposition, exposure models require accurate information about mercury emission rates and mercury speciation from point sources. Since coal-fired power plants represent a significant fraction of the anthropogenic emissions of mercury into the atmosphere, the speciation of mercury in coal-fired power plant flue gas is currently an active topic of research. We have demonstrated that the assumption of gas-phase equilibrium for mercury-containing species in coal-fired power plant exhaust is not valid at temperatures below approximately 800 K (500°C). Chlorine-containing species have been shown to be the most important for oxidation of elemental mercury in the post-combustion gases. The conversion of HCl to Cl2 in the flue gas of a coal-fired power plant is kinetically limited. Kinetic calculations of the homogeneous oxidation of elemental mercury by chlorine-containing species were carried out using global reactions from the literature. The levels of mercury oxidation, while of comparable magnitude to field observations, are still below the 40% to 80% oxidation typically observed in field measurements.

Small-scale combustion experiments were conducted to study the vaporization of trace elements during the combustion of pulverized coal. The combustion process was sampled at high temperatures (1423 K) corresponding to in-flame conditions. Rapid quenching and dilution of the combustion products were followed by a cascade impactor to collect size-segregated ash samples. Based on the comparison of concentrations of refractory elements in size-segregated ash with their bulk concentrations, we conclude that the ash having diameters less than approximately 0.4 micrometers represents the material which vaporizes during combustion in our combustion furnace. Good mass balance closure (90% to 140%) was obtained overall for ash in the sampling system. The volatile elements As, Sb, Se, and Zn showed mass balance closures significantly less than 100%. Thermochemical equilibrium predictions reported in the literature indicate that these elements should be completely volatile in the flame, although As is predicted to form condensed calcium arsenate at the sampling temperature in our system. Little chromium was found in the vaporization mode in our experiments. The uniformly low volatility of chromium suggests that chromium may react with oxides in the bulk ash. An upper bound on the amount of the more volatile elements which vaporized was computed. This upper bound accounted for the amount of the element in the finest ash and the material “losses” indicated by the mass balance closure. The results of these experiments suggest almost complete vaporization of certain trace elements (Se, Zn) from coal combustion in the flame zone, in accordance with theoretical equilibrium predictions. Other elements (As, Sb) appeared considerably less volatile and may react with constituents in the bulk ash at combustion temperatures.

Data suggest that coal-fired power plants are a significant source of atmospheric mercury. Predicting emissions of mercury and the speciation of mercury in combustion emissions cannot be done without a fundamental understanding of the chemical reactions of mercury in flue gas. In this work, chars generated from three coals were used as sorbent material for both elemental mercury and mercuric chloride. The temperature of the source as well as the char sorbent was carefully controlled at either 343 or 433 K (70 or 160°C). When exposed to a synthetic flue gas consisting of O2, H2O, CO2, and N2, both Hg0 and HgCl2 were adsorbed by coal char. The rank of the coal seemed to have a large effect on the adsorption of Hg0, but not on adsorption of HgCl2. The bituminous chars adsorbed similar amounts of Hg0, while the sub-bituminous char adsorbed almost an order of magnitude less. The amount of Hg0 adsorbed did not appear to be correlated with the sulfur content of the char. The rank dependence suggests that some other characteristic of the char, for example, pore structure or surface functional groups may be important for adsorption of elemental mercury. Adsorption of HgCl2 was higher by a factor of two for the bituminous chars and 50 times higher for the sub-bituminous char. The adsorption of HgCl2 showed less differences as a function of coal rank and a better agreement among all chars with respect to char surface area. This suggests that adsorption of HgCl2 on char may be by a physical adsorption process and, therefore, char surface area would be a good indicator of capacity for HgCl2.

A new technology for monitoring airborne heavy metals on aerosols and particulates based on spark-induced breakdown spectroscopy (SIBS) was evaluated at a joint U.S. Environmental Protection Agency (EPA)/U.S. Department of Energy test at the rotary kiln incinerator simulator (RKIS) facility at EPA/Research Triangle Park, NC, in September 1997. The instrument was configured to measure lead and chromium in a simulated combustion flue gas in real time and in situ at target levels of 15 and 75 micrograms/dry standard cubic meters. Actual metal concentrations were measured during the tests using EPA Reference Method (RM) 29. The SIBS technology detected both lead and chromium at the low- and high-level concentrations. Additionally, the hardware performed without failure for more than 100 hr of operation and acquired data for 100% of the RM tests. The chromium data were well correlated with concentration increases resulting from duct operations and pressure fluctuations that are known to entrain dust.

The sorption of mercury, as Hg0 and HgCl2, in a synthetic flue gas (SFG) by three activated carbons has been examined by XAFS spectroscopy. The three carbons consisted of a sulfur-activated carbon, an iodine-activated carbon, and an activated carbon derived from lignite. In addition to mercury, the occurrence and behavior of sulfur, chlorine, calcium, and iodine were also examined by XAFS spectroscopy. These other elements were present either as activating species on the carbons or as reactive components (SO2, HCl) in the SFG. The XAFS results showed that each type of activated carbon behaves differently with respect to sorption of mercury and other species from the SFG. For the iodine- and sulfur-activated carbons, the XAFS data confirm that it is the activating element (I or S) that forms a sorption complex with mercury. However, the activated carbon from lignite exhibited a more variable behavior that reflected the conditions of the experiments, in particular whether HCl or HgCl2 was present in the SFG...

Electric utilities are under pressure to reduce emissions and increase efficiency, and this means that coal-fired power plants must meet new challenges such as switching to coals for which the units were not designed. Ash deposition in coal-fired power plants reduces heat transfer and can cause the plant to be shut down. Ash deposits on convective heat transfer surfaces are generally removed mechanically by soot-blowers. On-line cleaning is practical as long as the ash deposits are not highly sintered. The sintering behavior of deposits is complex and depends on flue gas temperature, ash particle size, and ash composition. In this paper, a method is presented for estimating, for a specific coal, the maximum flue gas inlet temperature that allows the convective heat exchanger to be cleaned using conventional means. The calculation was carried out for conditions that represent the steam superheater section of a conventional pulverized coal-fired power plant, and the results are consistent with observations ...

Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO2, NO(x), particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional "stack" and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO2 processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests.Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.

The control of mercury in the air emissions from coal-fired power plants is an on-going challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous- and anthracite-rank coals. The chemistry of the feed coal and the resulting composition of the flue gas enhances Hg capture by fly ash carbons. This is particularly evident in the correlation of feed coal Cl content to Hg oxidation to HgCl2, enhancing Hg capture. Acid gases, including HCl and H2SO4 and the combination of HCl and NO2, in the flue gas can enhance the oxidation of Hg. In this presentation, we discuss the transport of Hg through the boiler and pollution control systems, the mechanisms of Hg oxidation, and the parameters controlling Hg capture by coal-derived fly ash carbons.

Oxidized mercury species may be formed in combustion systems through gas-phase reactions between elemental mercury and halogens, such as chorine or bromine. This study examines how bromine species affect mercury oxidation in the gas phase and examines the effects of mixtures of bromine and chlorine on extents of oxidation. Experiments were conducted in a bench-scale, laminar flow, methane-fired (300 W), quartz-lined reactor in which gas composition (HCl, HBr, NO{sub x}, SO{sub 2}) and temperature profile were varied. In the experiments, the post-combustion gases were quenched from flame temperatures to about 350 C, and then speciated mercury was measured using a wet conditioning system and continuous emissions monitor (CEM). Supporting kinetic calculations were performed and compared with measured levels of oxidation. A significant portion of this report is devoted to sample conditioning as part of the mercury analysis system. In combustion systems with significant amounts of Br{sub 2} in the flue gas, the impinger solutions used to speciate mercury may be biased and care must be taken in interpreting mercury oxidation results. The stannous chloride solution used in the CEM conditioning system to convert all mercury to total mercury did not provide complete conversion of oxidized mercury to elemental, when bromine was added to the combustion system, resulting in a low bias for the total mercury measurement. The use of a hydroxylamine hydrochloride and sodium hydroxide solution instead of stannous chloride showed a significant improvement in the measurement of total mercury. Bromine was shown to be much more effective in the post-flame, homogeneous oxidation of mercury than chlorine, on an equivalent molar basis. Addition of NO to the flame (up to 400 ppmv) had no impact on mercury oxidation by chlorine or bromine. Addition of SO{sub 2} had no effect on mercury oxidation by chlorine at SO{sub 2} concentrations below about 400 ppmv; some increase in mercury oxidation was observed at SO{sub 2} concentrations of 400 ppmv and higher. In contrast, SO{sub 2} concentrations as low as 50 ppmv significantly reduced mercury oxidation by bromine, this reduction could be due to both gas and liquid phase interactions between SO{sub 2} and oxidized mercury species. The simultaneous presence of chlorine and bromine in the flue gas resulted in a slight increase in mercury oxidation above that obtained with bromine alone, the extent of the observed increase is proportional to the chlorine concentration. The results of this study can be used to understand the relative importance of gas-phase mercury oxidation by bromine and chlorine in combustion systems. Two temperature profiles were tested: a low quench (210 K/s) and a high quench (440 K/s). For chlorine the effects of quench rate were slight and hard to characterize with confidence. Oxidation with bromine proved sensitive to quench rate with significantly more oxidation at the lower rate. The data generated in this program are the first homogeneous laboratory-scale data on bromine-induced oxidation of mercury in a combustion system. Five Hg-Cl and three Hg-Br mechanisms, some published and others under development, were evaluated and compared to the new data. The Hg-halogen mechanisms were combined with submechanisms from Reaction Engineering International for NO{sub x}, SO{sub x}, and hydrocarbons. The homogeneous kinetics under-predicted the levels of mercury oxidation observed in full-scale systems. This shortcoming can be corrected by including heterogeneous kinetics in the model calculations.

A fundamental study encompassing measurement and prediction of ash deposit initiation was conducted under conditions representative of coal-fired boilers. Laboratory experiments were performed with four bituminous coals to determine the ash collection and adhesion efficiencies due to inertial deposition. Measurements of the ash particle size distribution and composition as well as the deposit composition were made. An ash deposition model was developed based on a new viscosity model relevant to silicate glass with viscosities in the 10 5 to 10 7 Pa·s range in combination with crystallinity criterion for iron and calcium-rich particles. At long furnace residence times, the collection efficiency and deposit composition were predicted successfully for all four coals by using a critical viscosity of 10 5 Pa·s and assuming iron to be predominantly in the +3 oxidation state. At short residence times, the assumption of the +2 oxidation state for iron appears to be appropriate for these coals.

Gas-phase reactions between elemental mercury and chlorine are a possible pathway to producing oxidized mercury species such as mercuric chloride in combustion systems. This study examines the effect of the chemistry of a commonly used sample conditioning system on apparent and actual levels of mercury oxidation in a methane-fired, 0.3 kW, quartz-lined reactor in which gas composition (HCl, Cl2, NOx, SO2) and quench rate were varied. The sample conditioning system included two impingers in parallel: one containing an aqueous solution of KCl to trap HgCl2, and one containing an aqueous solution of SnCl2 to reduce HgCl2 to elemental mercury (Hg0). Gas-phase concentrations of Cl2 as low as 1.5 ppmv were sufficient to oxidize a significant fraction of the elemental mercury in the KCl impinger via the hypochlorite ion. Furthermore, these low, but interfering levels of Cl2 appeared to persist in flue gases from several doped rapidly mixed flames with varied post flame temperature quench rates. The addition of 0.5 wt% sodium thiosulfate to the KCl solution completely prevented the oxidation from occurring in the impinger. The addition of thiosulfate did not inhibit the KCl impinger's ability to capture HgCl2. The effectiveness of the thiosulfate was unchanged by NO or SO2. These results bring into question laboratory scale experimental data on mercury oxidation where wet chemistry was used to partition metallic and oxidized mercury without the presence of sufficient levels of SO2.

A kinetic model for predicting the amount of mercury (Hg) oxidation across selective catalytic reduction (SCR) systems in coal–fired power plants was developed and tested. The model incorporated the effects of diffusion within the porous SCR catalyst and the competition between ammonia and Hg for active sites on the catalyst. Laboratory data on Hg oxidation in simulated flue gas and slipstream data on Hg oxidation in flue gas from power plants were modeled. The model provided good fits to the data for eight different catalysts, both plate and monolith, across a temperature range of 280–420 °C, with space velocities varying from 1900 to 5000 hr–1. Space velocity, temperature, hydrochloric acid content of the flue gas, ratio of ammonia to nitric oxide, and catalyst design all affected Hg oxidation across the SCR catalyst. The model can be used to predict the impact of coal properties, catalyst design, and operating conditions on Hg oxidation across SCRs.

The objective of this project is to understand the importance of and the contribution of gas-phase and solid-phase coal constituents in the mercury oxidation reactions. The project involves both experimental and modeling efforts. The team is comprised of the University of Utah, Reaction Engineering International, and the University of Connecticut. The objective is to determine the experimental parameters of importance in the homogeneous and heterogeneous oxidation reactions; validate models; and, improve existing models. Parameters to be studied include HCl, NO{sub x}, and SO{sub 2} concentrations, ash constituents, and temperature. This report summarizes Year 2 results for the experimental and modeling tasks. Experiments in the mercury reactor are underway and interesting results suggested that a more comprehensive look at catalyzed surface reactions was needed. Therefore, much of the work has focused on the heterogeneous reactions. In addition, various chemical kinetic models have been explored in an attempt to explain some discrepancies between this modeling effort and others.

Lunar In‐Situ Resource Utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery process (pyrolysis, gas‐solid reactions, gas‐liquid or three‐phase reactions and desorption) requires thermal energy at temperatures from 1000 K to 2500 K. Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures 1200 K ∼ 1800 K. For these materials process applications, solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing a innovative solar power system in which solar radiation is collected by the concentrator which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper we will present the recent progress of the solar thermal power source being developed at PSI, and discuss potential applications of the system to Lunar ISRU processes.

The objective of this project is to understand the importance of and the contribution of gas-phase and solid-phase coal constituents in the mercury oxidation reactions. The project involves two experimental scales and a modeling effort. The team is comprised of University of Utah, Reaction Engineering International, and University of Connecticut. The objective is to determine the experimental parameters of importance in the homogeneous and heterogeneous oxidation reactions; validate models; and, improve existing models. Parameters to be studies include HCl, NOx, and SO{sub 2} concentrations, ash constituents, and temperature. This report summarizes Year 1 results for the experimental and modeling tasks. Experiments in the drop tube are just beginning and a new, speciated mercury analyzer is up and running. A preliminary assessment has been made for the drop tube experiments using the existing model of gas-phase kinetics.

In this paper we describe our progress toward creating a process workbench for performing virtual simulations of DOE Vision 21 energyplex systems. The workbench provides a framework for incorporating a full complement of models, ranging from simple heat/mass balance reactor models that run in minutes to detailed models that can require several hours to execute. Provided herein is an overview of a process workbench for a conventional PC power plant developed during the past year and our current efforts at developing a workbench for a gasifier based energyplex configuration.Copyright © 2002 by ASME

The final program review meeting of Phase II was held on June 22 in Salt Lake City. The goals of the meeting were to present work in progress and to identify the remaining critical experiments or analyses, particularly those involving collaboration among various groups. The information presented at the meeting is summarized in this report. Remaining fixed bed, bench-scale experiments at EERC were discussed. There are more ash samples which can be run. Of particular interest are high carbon ash samples to be generated by the University of Arizona this summer and some ash-derived sorbents that EERC has evaluated on a different program. The use of separation techniques (electrostatic or magnetic) was also discussed as a way to understand the active components in the ash with respect to mercury. XAFS analysis of leached and unleached ash samples from the University of Arizona was given a high priority. In order to better understand the fixed bed test results, CCSEM and Moessbauer analyses of those ash samples need to be completed. Utah plans to analyze the ash from the single particle combustion experiments for those major elements not measured by INAA. USGS must still complete mercury analyses on the whole coals and leaching residues. Priorities for further work at the SHRIMP-RG facility include arsenic on ash surfaces and mercury in sulfide minerals. Moessbauer analyses of coal samples from the University of Utah were completed; samples from the top and bottom layers of containers of five different coals showed little oxidation of pyrite in the top relative to the bottom except for Wyodak.

The Clean Air Act Amendments of 1990 identify a number of hazardous air pollutants (HAPs) as candidates for regulation. Should regulations be imposed on HAP emissions from coal-fired power plants, a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion will be needed. With support from the Federal Energy Technology Center (FETC), the Electric Power Research Institute, and VTT (Finland), Physical Sciences Inc. (PSI) has teamed with researchers from USGS, MIT, the University of Arizona (UA), the University of Kentucky (UK), the University of Connecticut (UC), the University of Utah (UU) and the University of North Dakota Energy and Environmental Research Center (EERC) to develop a broadly applicable emissions model useful to regulators and utility planners. The new Toxics Partitioning Engineering Model (ToPEM) will be applicable to all combustion conditions including new fuels and coal blends, low-NOx combustion systems, and new power generation plants. Development of ToPEM will be based on PSI's existing Engineering Model for Ash Formation (EMAF). This report covers the reporting period from 1 July 1999 to 30 September 1999. During this period the MIT INAA procedures were revised to improve the quality of the analytical results. Two steps have been taken to reduce the analytical errors. A new nitric acid leaching procedure, modified from ASTM procedure D2492, section 7.3.1 for determination of pyritic sulfur, was developed by USGS and validated. To date, analytical results have been returned for all but the last complete round of the four-step leaching procedure. USGS analysts in Denver have halted development of the cold vapor atomic fluorescence technique for mercury analysis procedure in favor of a new direct analyzer for Hg that the USGS is in the process of acquiring. Since early June, emphasis at USGS has been placed on microanalysis of clay minerals in project coals in preparation for use of the Stanford/USGS SHRIMP RG Ion Microprobe during August 1999. The SHRIMP-RG data confirm that Cr is present at concentrations of about 20 to 120 ppm, just below the electron microprobe detection limits (100 to 200 ppm), as suspected from Phase 1 microprobe work and previous studies of clay mineral separates. The University of Utah has started trial runs on the drop tube furnace to ensure that the gas analysis system is working properly and that the flow pattern within the furnace is laminar and direct. A third set of ASTM samples will be prepared at the University of Utah for the Phase 1 and Phase 2 coals. This time the INAA counting time will be optimized for the elements in which the authors are interested, guided by the results from the first two samples. The iodated charcoal which was used by MIT for vapor phase Hg collection was tested to see whether it collected other vapor phase metals. A second set of tests were performed at PSI using the entrained flow reactor (EFR). The University of Arizona's pilot-scale downflow laboratory combustion furnace was used to test the partitioning of toxic metals in the baseline experiments for the Phase 2 North Dakota lignite and the Pittsburgh seam bituminous coal at baghouse inlet sampling conditions. In addition, baseline data were collected on combustion of the Phase 1 Kentucky Elkhorn/Hazard bituminous coal. Emphasis at the University of Kentucky was placed on (1) collection of new Hg XAFS data for various sorbents, and (2) on collection of XAFS and other data for arsenic, sulfur, chromium and selenium in two baseline ash samples from the University of Arizona combustion unit. A preliminary interpretation of the mercury data is given in this report. Revision was made to the matrix for the initial experiments on mercury-ash interactions to be conducted at EERC. The overall goal of this effort is to collect data which will allow one to model the interactions of mercury and fly ash (specifically, adsorption of Hg{sup 0} and Hg{sup +2} and oxidation of Hg{sup 0}) in the air heater and particulate control device of a coal-fired power plant. The simple mass balance model for emissions of mercury from coal-fired power plants was revised to further test the current understanding of mercury transformations in flue gas. Improvements were made to the model for major element vaporization. The method for predicting vaporization of major elements predicts the total amount vaporized within a factor of two.

The Clean Air Act Amendments of 1990 identify a number of hazardous air pollutants (HAPs) as candidates for regulation. Should regulations be imposed on HAP emissions from coal-fired power plants, a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion will be needed. Over the past decade, a large database identifying the partitioning and emitted concentrations of several toxic metals on the list of HAPs has been developed. Laboratory data have also been generated to help define the general behavior of several elements in combustion systems. These data have been used to develop empirical and probabalistic models to predict emissions of trace metals from coal-fired power plants. While useful for providing average emissions of toxic species, these empirically based models fail when extrapolated beyond their supporting database. This represents a critical gap; over the coming decades, new fuels and combustion systems will play an increasing role in our nation's power generation system. For example, new fuels, such as coal blends or beneficiated fuels, new operating conditions, such as low-NO burners or staged combustion, or new power x systems, for example, those being developed under the DoE sponsored Combustion 2000 programs and integrated gasification combined cycle (IGCC) systems, are all expected to play a role in power generation in the next century. The need for new predictive tools is not limited to new combustion systems, however. Existing combustion systems may have to employ controls for HAPs, should regulations be imposed. Testing of new control methods, at pilot and full scale, is expensive. A sound under-standing of the chemical transformations of both organic and inorganic HAPs will promote the development of new control methods in a cost-effective manner. To ensure that coal-fired power generation proceeds in an environmentally benign fashion, methods for the prediction and control of toxic species in a broad range of coal fired systems must be developed.

The Clean Air Act Amendments of 1990 identify a number of hazardous air pollutants (HAPs) as candidates for regulation. Should regulations be imposed on HAP emissions from coal-fired power plants, a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion will be needed. With support from the Federal Energy Technology Center (FETC), the Electric Power Research Institute, and VTT (Finland), Physical Sciences Inc. (PSI) has teamed with researchers from USGS, the Massachusetts Institute of Technology (MIT), the University of Arizona (UA), the University of Kentucky (UK), the University of Connecticut (UC), the University of Utah (W) and the University of North Dakota Energy and Environmental Research Center (EERC) to develop a broadly applicable emissions model useful to regulators and utility planners. The new Toxics Partitioning Engineering Model (ToPEM) will be applicable to all combustion conditions including new fuels and coal blends, low-NO{sub x} combustion systems, and new power generation plants. Development of ToPEM will be based on PSI's existing Engineering Model for Ash Formation (EMAF). This report covers the reporting period from the submission of the draft Phase 1 Final Report through the end of June, 1998. During this period two of the three Phase 2 coals were procured and pulverized samples were distributed to team members. Analysis of Phase 1 X-Ray Absorption Fine Structure (XAFS) data, particularly of mercury in sorbent samples, continued. An improved method for identifying mercury compounds on sorbents was developed, leading to a clearer understanding of forms of mercury in char and sorbents exposed to flue gas. Additional analysis of Phase 1 large scale combustion data was performed to investigate mechanistic information related to the fate of the radionuclides Cs, Th, and Co. Modeling work for this period was focused on building and testing a sub-model for vaporization of major elements during combustion.

The Clean Air Act Amendments of 1990 identify a number of hazardous air pollutants (HAPs) as candidates for regulation. Should regulations be imposed on HAP emissions from coal-fired power plants, a sound understanding of the fundamental principles controlling the formation and partitioning of toxic species during coal combustion will be needed. With support from the Federal Energy Technology Center (FETC), the Electric Power Research Institute, and VTT (Finland), Physical Sciences Inc. (PSI) has teamed with researchers from USGS, MIT, the University of Arizona (UA), the University of Kentucky (UKy), the University of Connecticut, and Princeton University to develop a broadly applicable emissions model useful to regulators and utility planners. The new Toxics Partitioning Engineering Model (ToPEM) will be applicable to all combustion conditions including new fuels and coal blends, low-NOx combustion systems, and new power generation plants. Development of ToPEM will be based on PSI`s existing Engineering Model for Ash Formation (EMAF). During the past quarter the final program coal, from the Wyodak seam in the Powder River Basin, was acquired and distributed. Extensive coal characterization and laboratory work is underway to develop and test new sub-models. Coal characterization in the past quarter included direct identification of the modes of occurrence of various trace inorganic species in coal and ash using unique analytical techniques such as XAFS analysis and selective leaching. Combustion testing of the bituminous coals continued and additional data were obtained on trace element vaporization in the combustion zone. Studies of post-combustion trace element transformations, such as mercury speciation in the flue gas, were also begun in the last quarter.