Simultaneous Control of Hg0, SO2, and NOx by Novel Oxidized Calcium-Based Sorbents

Abstract

Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents leads to a significant improvement in elemental Hg vapor (Hg⁰), SO₂, and NO_x removal from simulated flue gases. In the study presented here, two classes of Ca-based sorbents (hydrated limes and silicate compounds) were investigated. A number of oxidizing additives at different concentrations were used in the Ca-based sorbent production process. The Hg⁰, SO₂, and NO_x capture capacities of these oxidant-enriched sorbents were evaluated and compared to those of a commercially available activated carbon in bench-scale, fixed-bed, and fluid-bed systems. Calcium-based sorbents prepared with two oxidants, designated C and M, exhibited Hg⁰ sorp-tion capacities (~100 μg/g) comparable to that of the activated carbon; they showed far superior SO₂ and NO_x sorption capacities. Preliminary cost estimates for the process utilizing these novel sorbents indicate potential for substantial lowering of control costs, as compared with other processes currently used or considered for control of Hg⁰, SO₂, and NO_x emissions from coal-fired boilers. The implications of these findings toward development of multipollutant control technologies and planned pilot and field evaluations of more promising multipollutant sorbents are summarily discussed.     

Pore structure effects on Ca-based sorbent sulfation capacity at medium temperatures: activated carbon as sorbent/catalyst support

The reaction between three different Ca-based sorbents and SO2 were studied in a medium temperature range (473-773 K). The largest SO2 capture was found with Ca(OH)2 at 773 K, 126.31 mg SO2 x g Ca(OH)2(-1), and the influence of SO2 concentration on the sorbent utilization was observed. Investigations of the internal porous structure of Ca-based sorbents showed that the initial reaction rate was controlled by the surface area, and once the sulfated products were produced, pore structure dominated. To increase the surface area of Ca-based sorbents available to interact with and retain SO2, one kind of CaO/ activated carbon (AC) sorbent/catalyst was prepared to study the effect of AC on the dispersion of Ca-based materials. The results indicated that the Ca-based material dispersed on high-surface-area AC had more capacities for SO2 than unsupported Ca-based sorbents. The initial reaction rates of the reaction between SO2 and Ca-based sorbents and the prepared CaO/AC sorbents/catalysts were measured. Results showed that the reaction rate apparently increased with the presence of AC. It was concluded that CaO/AC was the active material in the desulfurization reaction. AC acting as the support can play a role to supply O2 to increase the affinity to SO2. Moreover, when AC is acting as a support, the surface oxygen functional group formed on the surface of AC can serve as a new site for SO2 adsorption.     

Low Concentration Mercury Sorption Mechanisms and Control by Calcium-Based Sorbents: Application in Coal-Fired Processes

ABSTRACT

The capture of elemental mercury (Hg⁰) and mercuric chloride (HgCl₂) by three types of calcium (Ca)-based sor-bents was examined in this bench-scale study under conditions prevalent in coal-fired utilities. Ca-based sorbent performances were compared with that of an activated carbon. Hg⁰ capture of about 40% (nearly half that of the activated carbon) was achieved by two of the Ca-based sorbents. The presence of sulfur dioxide (SO₂) in the simulated coal combustion flue gas enhanced the Hg⁰ capture from about 10 to 40%. Increasing the temperature in the range of 65-100 °C also caused an increase in the Hg⁰ capture by the two Ca-based sorbents. Mercuric chloride (HgCl₂) capture exhibited a totally different pattern. The presence of SO₂ inhibited the HgCl₂ capture by Ca-based sorbents from about 25 to less than 10%. Increasing the temperature in the studied range also caused a decrease in HgCl₂ capture. Upon further pilot-scale confirmations, the results obtained in this bench-scale study can be used to design and manufacture more cost-effective mercury sorbents to replace conventional sorbents already in use in mercury control.     

Surface compositions of carbon sorbents exposed to simulated low-rank coal flue gases

Bench-scale testing of elemental mercury (Hg0) sorption on selected activated carbon sorbents was conducted to develop a better understanding of the interaction among the sorbent, flue gas constituents, and Hg0. The results of the fixed-bed testing under simulated lignite combustion flue gas composition for activated carbons showed some initial breakthrough followed by increased mercury (Hg) capture for up to approximately 4.8 hr. After breakthrough, the Hg in the effluent stream was primarily in an oxidized form (>90%). Aliquots of selected activated carbons were exposed to simulated flue gas containing Hg0 vapor for varying time intervals to explore surface chemistry changes as the initial breakthrough, Hg capture, and oxidation occurred. The samples were analyzed by X-ray photoelectron spectroscopy to determine changes in the abundance and forms of sulfur, chlorine, oxygen, and nitrogen moieties as a result of interactions of flue gas components on the activated carbon surface during the sorption process. The data are best explained by a competition between the bound hydrogen chloride (HCl) and increasing sulfur [S(VI)] for a basic carbon binding site. Because loss of HCl is also coincident with Hg breakthrough or loss of the divalent Hg ion (Hg2+), the competition of Hg2+ with S(VI) on the basic carbon site is also implied. Thus, the role of the acid gases in Hg capture and release can be explained.     

Pore Structure Effects on Ca-Based Sorbent Sulfation Capacity at Medium Temperatures: Activated Carbon as Sorbent/Catalyst Support

Abstract

The reaction between three different Ca-based sorbents and SO₂ were studied in a medium temperature range (473–773 K). The largest SO₂ capture was found with Ca(OH)₂ at 773 K, 126.31 mg SO₂?g Ca(OH)₂ ^?1, and the influence of SO₂ concentration on the sorbent utilization was observed. Investigations of the internal porous structure of Ca-based sorbents showed that the initial reaction rate was controlled by the surface area, and once the sul-fated products were produced, pore structure dominated. To increase the surface area of Ca-based sorbents available to interact with and retain SO₂, one kind of CaO/activated carbon (AC) sorbent/catalyst was prepared to study the effect of AC on the dispersion of Ca-based materials. The results indicated that the Ca-based material dispersed on high-surface-area AC had more capacities for SO₂ than unsupported Ca-based sorbents. The initial reaction rates of the reaction between SO₂ and Ca-based sorbents and the prepared CaO/AC sorbents/cata-lysts were measured. Results showed that the reaction rate apparently increased with the presence of AC. It was concluded that CaO/AC was the active material in the des-ulfurization reaction. AC acting as the support can play a role to supply O₂ to increase the affinity to SO₂. Moreover, when AC is acting as a support, the surface oxygen functional group formed on the surface of AC can serve as a new site for SO₂ adsorption.     

Surface Compositions of Carbon Sorbents Exposed to Simulated Low-Rank Coal Flue Gases

Abstract

Bench-scale testing of elemental mercury (Hg⁰) sorption on selected activated carbon sorbents was conducted to develop a better understanding of the interaction among the sorbent, flue gas constituents, and Hg⁰. The results of the fixed-bed testing under simulated lignite combustion flue gas composition for activated carbons showed some initial breakthrough followed by increased mercury (Hg) capture for up to ～4.8 hr. After breakthrough, the Hg in the effluent stream was primarily in an oxidized form (>90%). Aliquots of selected activated carbons were exposed to simulated flue gas containing Hg⁰ vapor for varying time intervals to explore surface chemistry changes as the initial breakthrough, Hg capture, and oxidation occurred. The samples were analyzed by X-ray photoelectron spectroscopy to determine changes in the abundance and forms of sulfur, chlorine, oxygen, and nitrogen moieties as a result of interactions of flue gas components on the activated carbon surface during the sorption process. The data are best explained by a competition between the bound hydrogen chloride (HCl) and increasing sulfur [S(VI)] for a basic carbon binding site. Because loss of HCl is also coincident with Hg breakthrough or loss of the divalent Hg ion (Hg²⁺), the competition of Hg²⁺ with S(VI) on the basic carbon site is also implied. Thus, the role of the acid gases in Hg capture and release can be explained.     

Effect of solution pH on SO2, NO(x), and Hg removal from simulated coal combustion flue gas in an oxidant-enhanced wet scrubber

This paper presents a study on the simultaneous removal of SO2, NO(x) and Hg (both Hg0 and Hg2+) from a simulated flue gas by oxidant injection in a bench-simulated wet limestone scrubber for a wide range of slurry pH. The slurry pH strongly influenced the chemical mechanism in the scrubber and, therefore, affected pollutant removal. This paper also examines the potential ClO2(gas) reemission from a developed multipollutant scrubber at different slurry pHs. To better understand the chemical mechanisms at each slurry pH and to apply a mass balance to the process, detailed product ion analyses were performed for all experiments. Ion analysis covered three different chlorine species (chlorite, chloride, chlorate), sulfate, nitrite and nitrate. Different NO(x) removal efficiencies and mechanisms were found in acidic and alkaline pHs in the multipollutant scrubber. The acidic solution was favorable for NO and Hg0 oxidation, but increasing the slurry pH above 7.0 was disadvantageous for NO and Hg oxidation/removal. However the rate of NO(x) absorption (by percentage) was higher for the alkaline solution.     

Performance of Copper Chloride-Impregnated Sorbents on Mercury Vapor Control in an Entrained-Flow Reactor System

Abstract

An entrained-flow system has been designed and constructed to simulate in-flight mercury (Hg) capture by sorbent injection in ducts of coal-fired utility plants. The test conditions of 1.2-sec residence time, 140 °C gas temperature, 6.7 m/sec (22 ft/sec) gas velocity, and 0–0.24 g/m³ (0–15 lbs of sorbent per 1 million actual cubic feet of flue gas [lb/MMacf]) sorbent injection rates were chosen to simulate conditions in the ducts. Four kinds of sorbents were used in this study. Darco Hg-LH served as a benchmark sorbent with which Hg control capability of other sorbents could be compared. Also, Darco-FGD was used as a representative raw activated carbon sorbent. Two different copper chloride-impregnated sorbents were developed in our laboratory and tested in the entrained-flow system to examine the possibility of using these sorbents at coal-fired power plants. The test results showed that one of the copper chloride sorbents has remarkable elemental mercury (Hg⁰) oxidation capability, and the other sorbent demonstrated a better performance in Hg removal than Darco Hg-LH.     

Removing and recovering gas-phase elemental mercury by Cu(x)Co(3-x)O(4) (0.75< or = x < or =2.25) in the presence of sulphur compounds

The Hg(0) oxidation ability and reusability of Cu(x)Co(3-x)O(4) were investigated in an attempt to improve SO(2) anti-poisoning ability of metal oxide and produce more economic and effective sorbents for the control of Hg(0) emission from combustion processes. The influence of copper content on Cu(x)Co(3-x)O(4)'s (0.75< or = x < or =2.25) oxidation ability of Hg(0) in the presence of SO(2) was investigated. According to the X-ray diffraction, Brunauer-Emmett-Teller (BET) and mass balance analysis on mercury, we found that Cu(1.5)Co(1.5)O(4) showed the highest S(BET) and best Hg(0) oxidation ability. With continuous increase of x from 0.75 to 2.25, Cu(x)Co(3-x)O(4)'s SO(2) anti-poisoning ability increased. The analysis results of the X-ray photoelectron spectroscopy manifested that the adsorptive mercury species on spent Cu(1.5)Co(1.5)O(4) was HgO. The spent Cu(1.5)Co(1.5)O(4) could be regenerated by thermal decomposition at 673K and regenerated Cu(1.5)Co(1.5)O(4) showed higher Hg(0) oxidation ability due to Hg-doping. Regenerated enrichment Hg(0) was collected using activated carbon at an ambient temperature to eliminate the secondary pollution.     

The importance of the location of sodium chlorite application in a multipollutant flue gas cleaning system

In this study, removing sulfur dioxide (SO2), nitrogen oxides (NO(x)), and mercury (Hg) from simulated flue gas was investigated in two laboratory-sized bubbling reactors that simulated an oxidizing reactor (where the NO and Hg(0) oxidation reactions are expected to occur) and a wet limestone scrubber, respectively. A sodium chlorite solution was used as the oxidizing agent. The sodium chlorite solution was an effective additive that enhanced the NO(x), Hg, and SO2 capture from the flue gas. Furthermore, it was discovered that the location of the sodium chlorite application (before, in, or after the wet scrubber) greatly influences which pollutants are removed and the amount removed. This effect is related to the chemical conditions (pH, absence/presence of particular gases) that are present at different positions throughout the flue gas cleaning system profile. The research results indicated that there is a potential to achieve nearly zero SO2, NO(x), and Hg emissions (complete SO2, NO, and Hg removals and -90% of NO(x) absorption from initial values of 1500 ppmv of SO2, 200 ppmv of NO(x), and 206 microg/m3 of Hg(0)) from the flue gas when sodium chlorite was applied before the wet limestone scrubber. However applying the oxidizer after the wet limestone scrubber was the most effective configuration for Hg and NO(x) control for extremely low chlorite concentrations (below 0.002 M) and therefore appears to be the best configuration for Hg control or as an additional step in NO(x) recleaning (after other NO(x) control facilities). The multipollutant scrubber, into which the chlorite was injected simultaneously with the calcium carbonate slurry, appeared to be the least expensive solution (when consider only capital cost), but exhibited the lowest NO(x) absorption at -50%. The bench-scale test results presented can be used to develop performance predictions for a full- or pilot-scale multipollutant flue gas cleaning system equipped with wet flue gas desulfurization scrubber.     

Investigation of selective catalytic reduction impact on mercury speciation under simulated NOx emission control conditions

Selective catalytic reduction (SCR) technology increasingly is being applied for controlling emissions of nitrogen oxides (NOx) from coal-fired boilers. Some recent field and pilot studies suggest that the operation of SCR could affect the chemical form of mercury (Hg) in coal combustion flue gases. The speciation of Hg is an important factor influencing the control and environmental fate of Hg emissions from coal combustion. The vanadium and titanium oxides, used commonly in the vanadia-titania SCR catalyst for catalytic NOx reduction, promote the formation of oxidized mercury (Hg2+). The work reported in this paper focuses on the impact of SCR on elemental mercury (Hg0) oxidation. Bench-scale experiments were conducted to investigate Hg0 oxidation in the presence of simulated coal combustion flue gases and under SCR reaction conditions. Flue gas mixtures with different concentrations of hydrogen chloride (HCl) and sulfur dioxide (SO2) for simulating the combustion of bituminous coals and subbituminous coals were tested in these experiments. The effects of HCl and SO2 in the flue gases on Hg0 oxidation under SCR reaction conditions were studied. It was observed that HCl is the most critical flue gas component that causes conversion of Hg0 to Hg2+ under SCR reaction conditions. The importance of HCl for Hg0 oxidation found in the present study provides the scientific basis for the apparent coal-type dependence observed for Hg0 oxidation occurring across the SCR reactors in the field.     

Modifying sorbents in controlled release formulations to prevent herbicides pollution

The herbicides chloridazon and metribuzin, identified as groundwater pollutants, were incorporated in alginate-based granules to obtain controlled release properties. In this research the effect of incorporation of sorbents such as bentonite, anthracite and activated carbon in alginate basic formulation were not only studied on encapsulation efficiency but also on the release rate of herbicides which was studied using water release kinetic tests. In addition, sorption studies of herbicides with bentonite, anthracite and activated carbon were made. The kinetic experiments of chloridazon and metribuzin release in water have shown that the release rate is higher in metribuzin systems than in those prepared with chloridazon, which has lower water solubility. Besides, it can be deduced that the use of sorbents reduces the release rate of the chloridazon and metribuzin in comparison to the technical product and to the alginate formulation without sorbents. The highest decrease in release rate corresponds to the formulations prepared with activated carbon as a sorbent. The water uptake, permeability, and time taken for 50% of the active ingredient to be released into water, T(50), were calculated to compare the formulations. On the basis of a parameter of an empirical equation used to fit the herbicide release data, the release of chloridazon and metribuzin from the various formulations into water is controlled by a diffusion mechanism. Sorption capacity of the sorbents for chloridazon and metribuzin, ranging from 0.53mgkg(-1) for the metribuzin sorption on bentonite to 2.03x10(5)mgkg(-1) for the sorption of chloridazon on the activated carbon, was the most important factor modulating the herbicide release.     

非固定化和固定化啤酒酵母对Cd^2＋和Cu^2＋的吸附特性研究

对比了不同吸附剂对重金属的吸附效果,同时研究了啤酒酵母的固定化方法、菌体用量对吸附效果的影响、非同定化和固定化啤酒酵母吸附热力学特性。研究结果表明,非固定化死啤酒酵母对Cd^2＋的单位菌体吸附量是常用吸附剂活性炭的3倍;由1：3的海藻酸钠与碱处理啤酒酵母（w／w）制得的固定化颗粒吸附效果最好;菌体用量的增加会降低单位菌体对重金属的吸附量;啤酒酵母对重金属的吸附位点有限,Cd^2＋的实际最大吸附量为13．95mg／g,Cu^2＋为7．67μg／g。非固定化和固定化啤酒酵母对Cu^2＋和Cd^2＋的等温吸附过程均可用Linear方程、Langmuir方程和Freundlich方程来进行拟合,但非同定化啤酒酵母以Langmuir方程最优,其拟合计算的最大吸附量qmzxCd和qmxxCu分别为13．96mg／g和8．01mg／g;固定化啤酒酵母以Freundlich方程最优,实际最大吸附量Cd为75．41mg／g,Cu为66．58mg／g。     

Assessing sorbents for mercury control in coal-combustion flue gas

Sorbent injection for Hg control is one of the most promising technologies for reducing Hg emissions from power-generation facilities, particularly units that do not require wet scrubbers for SO2 control. Since 1992, EPRI has been assessing the performance of Hg sorbents in pilot-scale systems installed at full-scale facilities. The initial tests were conducted on a 5,000-acfm (142-m3/min) pilot baghouse. Screening potential sorbents at this scale required substantial resources for installation and operation and did not provide an opportunity to characterize sorbents over a wide temperature range. Data collected in the laboratory and in field tests indicate that sorbents are affected by flue gas composition and temperature. Tests carried out in actual flue gas at a number of power plants also have shown that sorbent performance can be site-specific. In addition, data collected at a field site often are different from data collected     

Biosorption of divalent Pb, Cd and Zn on aragonite and calcite mollusk shells

The potential of using mollusk shell powder in aragonite (razor clam shells, RCS) and calcite phase (oyster shells, OS) to remove Pb²⁺, Cd²⁺ and Zn²⁺ from contaminated water was investigated. Both biogenic sorbents displayed very high sorption capacities for the three metals except for Cd on OS. XRD, SEM and XPS results demonstrated that surface precipitation leading to crystal growth took place during sorption. Calcite OS displayed a remarkably higher sorption capacity to Pb than aragonite RCS, while the opposite was observed for Cd. However, both sorbents displayed similar sorption capacities to Zn. These could be due to the different extent of matching in crystal lattice between the metal bearing precipitate and the substrates. The initial pH of the solution, sorbent’s dosage and grain size affected the removal efficiency of the heavy meals significantly, while the organic matter in mollusk shells affected the removal efficiency to a lesser extent.     

Experimental design methodology for the preparation of carbonaceous sorbents from sewage sludge by chemical activation--application to air and water treatments

The objective of this study is to optimize experimental conditions of sorbent preparation from sewage sludge using experimental design methodology. Series of carbonaceous sorbents have been prepared by chemical activation with sulfuric acid. The sorbents produced were characterized, and their properties (surface chemistry, porous and adsorptive properties) were analyzed as a function of the experimental conditions (impregnation ratio, activation temperature and time). Carbonaceous sorbents developed from sludge allow copper ion, phenol and dyes (Acid Red 18 and Basic Violet 4) to be removed from aqueous solution as well as VOC from gas phase. Indeed, according to experimental conditions, copper adsorption capacity varies from 77 to 83 mg g(-1), phenol adsorption capacity varies between 41 and 53 mg g(-1) and VOC adsorption capacities (acetone and toluene) range from 12 to 54 mg g(-1). Each response has been described by a second-order model that was found to be appropriate to predict most of the responses in every experimental region. The most influential factors on each experimental design response have been identified. Regions in which optimum values of each factor were achieved for preparation of activated carbons suitable for use in wastewater and gas treatments have been determined using response surfaces methodology. In order to have a high mass yield and to minimize the energetic cost of the process, the following optimal conditions, 1.5 g of H2SO4 g(-1) of sludge, 700 degrees C and 145 min are more appropriate for use of activated carbon from sludge in water and gas treatments.     

Economics of an integrated approach to control SO2, NOX,HCl, and particulate emissions from power plants

An integrated approach for the simultaneous reduction of major combustion-generated pollutants from power plants is presented along with a simplified economic analysis. With this technology, the synergistic effects of high-temperature sorbent/coal or sorbent/natural gas injection and high-temperature flue gas filtration are exploited. Calcium-based (or Na-based, etc.) sorbents are sprayed in the post-flame zone of a furnace, where they react with S- and Cl-containing gases to form stable salts of Ca (or Na, etc.). The partially reacted sorbent is then collected in a high-temperature ceramic filter, which is placed downstream of the sorbent injection point, where it further reacts for a prolonged period of time. With this technique, both the likelihood of contact and the length of time of contact between the solid sorbent particles and the gaseous pollutants increase, because reaction takes place both in the furnace upstream of the filter and inside the filter itself. Hence, the sorbent utilization increases significantly. Several pollutants, such as SO2, H2S, HCl, and particulate (soot, ash, and tar), may be partially removed from the effluent. The organic content of the sorbents (or blends) also pyrolyzes and reduces NOx. Unburned carbon in the ash may be completely oxidized in the filter. The filter is cleaned periodically with aerodynamic regeneration (back pulsing) without interrupting furnace operation. The effectiveness of this technique has been shown in laboratory-scale experiments using either rather costly carboxylic salts of Ca or low- to moderate-cost blends of limestone, lime, or sodium bicarbonate with coal fines. Injection occurred in the furnace at 1150 degrees C, while the filter was maintained at 600 degrees C. Results showed that 65 or 40% SO2 removal was obtained with calcium formate or a limestone/coal blend, respectively, at an entering calcium-to-sulfur molar ratio of 2. A sodium bicarbonate/coal blend resulted in 78% SO2 removal at a sodium-to-sulfur molar ratio of 2. HCl removal efficiencies have been shown to be higher than those for SO2. NOx reductions of 40% have been observed with a fuel (coal)-to-air equivalence ratio, phi, around 2. The filter has been shown to be 97-99% efficient in removing PM2.5 particulates. Calculations herein show that this integrated sorbent/filter method is cost-effective, in comparison with current technologies, on both capital cost ($/kW) and levelized cost ($/ton pollutant removed) bases, if a limestone/coal mixture is used as the sorbent for fossil fuel plants. Capital costs for the filter/sorbent combination are estimated to be in the range of $61-$105/kW for a new plant. Because current technologies are designed for removing one pollutant at a time, both their cost and space requirements are higher than those of this integrated technique. At the minimum projected removal efficiencies for HCl/SO2/NOx of about 40%, the levelized costs are projected to be $203-$261/ton of combined pollutant SO2/HCl/NOx and particulates removed from coal-fired power plants.     

Thermodynamic behaviour of sodium and calcium based sorbents in the emission control of waste incinerators

The dry treatment of flue gas produced by incineration processes is discussed thermodynamically. The study investigates the theoretical limits achieved by sodium and calcium based sorbents in the removal of the pollutant species HCl, NOx and SO2. Calculations were performed varying the temperature and the molar ratio between the amount of the injected alkaline sorbent and the content of the pollutant gaseous species in the flue gas. Results show that sodium cation based sorbents are more efficient than calcium based ones in the whole investigated temperature range (100-600 degrees C). The higher effectiveness of sodium based sorbents is particularly remarkable towards hydrogen chloride, whose concentration can always be reduced below the values set by the environmental regulations. Possible improvements in the treatment efficiency of combustion fumes obtainable with sodium based sorbents can be mainly summarised in a lower concentration of HCl in the treated gas and in a partial reduction of NOx concentration.     

A pilot study of mercury liberation and capture from coal-fired power plant fly ash

The coal-fired electric utility generation industry has been identified as the largest anthropogenic source of mercury (Hg) emissions in the United States. One of the promising techniques for Hg removal from flue gas is activated carbon injection (ACI). The aim of this project was to liberate Hg bound to fly ash and activated carbon after ACI and provide high-quality coal combustion products for use in construction materials. Both bench- and pilot-scale tests were conducted to liberate Hg using a thermal desorption process. The results indicated that up to 90% of the Hg could be liberated from the fly ash or fly-ash-and-activated-carbon mixture using a pilot-scale apparatus (air slide) at 538 degrees C with a very short retention time (less than 1 min). Scanning electron microscope (SEM) evaluation indicated no significant change in fly ash carbon particle morphology following the thermal treatment. Fly ash particles collected in the baghouse of the pilot-scale apparatus were smaller in size than those collected at the exit of the air slide. A similar trend was observed in carbon particles separated from the fly ash using froth flotation. The results of this study suggest a means for power plants to reduce the level of Hg in coal-combustion products and potentially recycle activated carbon while maintaining the resale value of fly ash. This technology is in the process of being patented.     

Development of outcome-based, multipollutant mobile source indicators

Multipollutant indicators of mobile source impacts are developed from readily available CO, NOx, and elemental carbon (EC) data for use in air quality and epidemiologic analysis. Two types of outcome-based Integrated Mobile Source Indicators (IMSI) are assessed. The first is derived from analysis of emissions of EC, CO, and NOx such that pollutant concentrations are mixed and weighted based on emission ratios for both gasoline and diesel vehicles. The emission-based indicators (IMSI(EB)) capture the impact of mobile sources on air quality estimated from receptor models and their uncertainty is comparable to measurement and source apportionment uncertainties. The IMSI(EB) have larger correlation between two different receptor sites impacted by traffic than single pollutants, suggesting they are better indicators of the local impact ofmobile sources. A sensitivity analysis of fractions of pollutants in a two-pollutant mixture and the inclusion in an epidemiologic model is conducted to develop a second set of indicators based on health outcomes. The health-based indicators (IMSI(HB)) are weighted combinations of CO, NOx, and EC pairs that have the lowest P value in their association with cardiovascular disease emergency department visits, possibly due to their better spatial representativeness. These outcome-based, multipollutant indicators can provide support for the setting of multipollutant air quality standards and other air quality management activities.