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Mercury Oxidization in Dielectric Barrier Discharge Plasma System Zongyuan Chen,† Deenal P. Mannava, and V. K. Mathur* Department of Chemical Engineering, UniVersity of New Hampshire, Durham, New Hampshire 03824
The pronounced volatility of elemental mercury (Hg0) and some of its compounds, coupled with their extreme toxicity, makes these substances extremely hazardous. Conversion of Hg0 to HgO would significantly enhance mercury removal from flue gases. This investigation is focused on studying the effect of some of the constituents such as O2, H2O, CO2, and NOx present in flue gases on elemental mercury oxidation in a dielectric barrier discharge (DBD) reactor. The results show that Hg vapors (6 ppbv) in a stream of 0.1% O2 and N2 are effectively oxidized at the energy density of up to 114 J/L. Hg conversion of over 80% is achieved when present in a gas mixture of 8% O2, 2% H2O, and 10% CO2 in N2 balance. The presence of NOx enhanced mercury oxidation in the DBD reactor. The oxidation chemistry is discussed. Studies show that Hg can be simultaneously removed along with the other two major pollutants, NOx and SO2, in one DBD reactor followed by a wet scrubber system. This avoids the need of three techniques for the removal of major gaseous pollutants from coal-fired power plants. 1. Introduction In the past decade, the emission of toxic elements from human activities has become a matter of great public concern. Hg, As, Se, and Cd typically volatilize during a combustion process1 and are not easily caught with conventional air-pollution control techniques. In addition, there is no pollution-prevention technique that may be available in the foreseeable future that can prevent the emissions of these trace elements. These trace elements pose an additional scientific challenge because they are present at only ppb levels in a large gas stream. Mercury, in particular, has attracted significant attention because of its high volatility, toxicity, and potential threat to human health.2 Presence of mercury in the environment is due to natural and human (anthropogenic) activities. The major emitters of mercury to the air include coal-fired electric utilities, municipal waste combustors (MWCs), medical waste incinerators (MWIs), and chemical industries such as chlor-alkali and cement plants. Petroleum processing leads to waste byproducts and air discharges that also contain mercury. The first three major emitters account for ∼75% of the United States’s total annual Hg emission of 158 tons. Three main forms of mercury emissions are particle-associated mercury, gaseous divalent mercury (Hg2+), and elemental mercury vapor (Hg0). Studies1,3,4 have shown that mercury emission from a combustion process, especially sub-bituminous coal or lignite, is mostly in the state of elemental mercury vapor (Hg0). There are two major differences in flue gases from coal-fired electric utilities and MWIs/MWCs, namely, mercury concentration and flue gas flow rate. The concentration of total mercury in the flue gas from typical coal-fired electric utilities ranges from 50 µg/ Nm3 (1-5 ppbv), while it is usually several orders of magnitude higher in flue gases from MWIs/MWCs. Considerable studies have been conducted regarding mercury control in emissions from coal-fired electric utilities.5-8 Conventional adsorption techniques such as sorbent injection have long been studied as potential methods for mercury control in utility flue gas. Most present studies are focused on screening * All correspondence should be addressed to this author. E-mail:
[email protected]. † Present address: School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
commercial activated carbons and other materials as sorbents. At this time, activated carbons have the best potential as sorbents. Elemental mercury and HgCl2 are often targeted to be adsorbed on various sorbents. The high carbon-to-mercury weight ratios (3000:1 to 100 000:1) and difficulties in sorbent regeneration result in the unacceptably high cost of using activated carbon as a sorbent.8 The factors that limit the application of conventional mercury adsorption processes include extremely low mercury concentrations, different speciation, waste gas residence time, and high-temperature effects. Studies have been conducted for developing cost-effective alternatives to activated carbon. Recently, Boren et al.9 reported quite encouraging pilot test results on mercury removal using multipollutant Palhman Process technology. The sorbents are hybrid types of manganese dioxides and can be regenerated. Another novel approach was demonstrated using UV light to realize photochemical removal of mercury from flue gas.10,11 In this approach, UV light initiates ozone formation and elemental mercury reacts with ozone forming HgO, which can be easily captured by downstream processes. The use of nonthermal plasma has been investigated for the oxidation of NOx, SO2, and hazardous organic chemicals, leading to some very promising results. However, there is very little research work reported for the use of nonthermal plasma for the oxidation of trace elements emitted from utility plants, smelters, foundries, chlor-alkali plants, etc. An electrical discharge is a phenomenon wherein free electrons are produced and accelerated under the influence of an electric field. Through collisions with molecules in the gas, electrons cause excitation, ionization, electron multiplication, and formation of atoms and compounds that give an electrical discharge its unique chemical environment and make it a powerful tool for chemical processing. Dielectric barrier discharge (DBD) is such an electrical technique where electrical breakdowns can be classified as a nonequilibrium discharge, also called nonthermal plasma. Although it is reported that e-beam appears to be more energy effective than electrical discharge methods,13 the high cost and radiation hazard associated with e-beam pose a challenge. In addition, another major hurdle is to keep clean the window that allows high-energy electrons to pass from the generation section to the gas stream under treatment, because the window cleanliness is critical to maintaining energy efficiency. We chose DBD
10.1021/ie0603666 CCC: $33.50 © 2006 American Chemical Society Published on Web 07/18/2006
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Figure 1. Schematic diagram of benchtop system.
since its power source is relatively cheaper. There are excellent publications on the mechanistic understanding of electrical discharge, electron distribution, and other properties of plasma.12-14 In our approach, a dielectric is placed between two electrodes, allowing a barrier discharge to occur through which the gases are made to flow. We have successfully applied this DBD technique in our laboratory for the oxidation of NOx and SO2 and the decomposition of freons.15-18 The key steps involve electroimpact dissociation of O2 forming metastable oxygen atoms which react with most NO, forming NO2. NO2 then interacts with OH resulting from electroimpact dissociation of H2O, producing byproduct nitric acid (HNO3). SO2 is partially oxidized into SO3, forming sulfuric acid (H2SO4). A literature review reveals that this technique has been also used for the oxidation of chlorobenzene, trichloroethylene, formaldehyde, etc.19-21 Some workers have investigated the use of DBD for the reaction of methane with carbon dioxide to form more valuable chemicals.22 McLarnon and co-workers23,24 reported a reduction in mercury concentration in a DBD reactor. Helfritch and Feldman25 studied the use of corona discharge for the oxidation of elemental mercury. To our best knowledge, however, no systematic study on mercury oxidation by DBD has been done so far. The present study has investigated the DBD technique to oxidize elemental mercury, Hg0, to HgO. The basic premise of this approach is that Hg0 in vapor form cannot be easily removed in an absorption tower, whereas HgO as a particulate is amiable to water scrubbing. Synergetic effects of the presence of O2, CO2, NOx, and H2O in the simulated gaseous mixture are also investigated, because these chemical compounds are usually present in flue gases. The chemistry of mercury oxidation is discussed. 2. Experimental Apparatus and Procedures A schematic diagram of the benchtop reactor system for this investigation is shown in Figure 1. It consists of a DBD reactor with power supply, gas mixture supply, and analytical instrumentation. A brief description of the main equipment and the procedures used to obtain experimental results are presented below. Details are available elsewhere.16,17,26 DBD Reactor with Power Supply. The reactor geometry to initiate a barrier discharge in a gas space containing simulated
flue gas is one of concentric cylinders. The center and outer cylinders are a solid stainless steel rod (o.d., 3 mm) and stainless steel tube (i.d., 23 mm), respectively. Each of these serves as an electrode, while the outer cylinder also serves as the pressure boundary. A high voltage (up to 25 kV, AC) is applied between the electrodes, with the outer electrode (tube) at ground potential for safety reasons. Two quartz tubes are installed adjacent to the electrodes for producing a barrier discharge. The length of the reactor tube is 1 ft (0.305 m). Discharge Energy Measurement. Power consumption in the DBD reactor is estimated using the voltage and current traces recorded and stored with the help of an oscilloscope. By multiplying the corresponding current and voltage values at the same phase angle, a curve of point power is obtained and averaged to give the discharge power. An on-line computer reads the values recorded by the oscilloscope and calculates the discharge power. The voltage and current signals are taken from the second circuit of the transformer, where there are some inefficiencies including transformer, inductors, and resistances. However, these inefficiencies are negligible compared to discharge power consumption. Gas Mixture Supply. The gas supply section is illustrated below the DBD reactor in Figure 1. Simulated flue gas is prepared using cylinders of N2, NO, O2, CO2, etc. Hastings model ST and 200H mass flow meters are used to measure the flow rates of dry gases from each of the cylinders. Water vapor is added to the gas stream by passing the nitrogen stream through a copper bubbler containing water. The tubing used throughout the system is either stainless steel or Teflon to minimize the adsorption on the walls of any of the products from the DBD reactor. Heating tapes are used to preheat the gas stream and prevent H2O condensation before it enters the DBD reactor. A mercury generation system is developed in our laboratory to provide trace mercury vapor of desired concentration to the inlet gas stream. It consists of three stainless steel cylindrical containers and a water bath with temperature control within (0.2 °C. The first cylinder contains liquid mercury. Nitrogen is passed over the liquid mercury. Saturated mercury vapor in nitrogen is carried through the following two equilibrium cylinders for achieving a constant concentration of mercury vapor in nitrogen stream (20 SCCM). This stream is mixed with the pure nitrogen stream of 2 SLM, diluting mercury concentration by 100 times. Typically, one-tenth of the mixture is added to the gas stream prepared from gas cylinders. Preconditioning of Sample Gases. Sample gases are subjected to preconditioning before reaching analyzers. The preconditioning section consists of wet chemistry absorbers, moisture trap, and furnace. The effect of NO on the mercury analyzer is to be avoided. An acidified ferrous sulfate (FeSO4) solution of 0.1 M is used to absorb any nitric oxide (NO) by bubbling the gas stream exiting the DBD reactor through a bubbler filled with 450 mL of acidified FeSO4 solution. In addition, an acidified sodium sulfite (Na2SO3) solution of 0.1 M is also used to absorb nitric oxide (NO2) in the gas stream. The moisture trap is packed with glass wool and maintained at -5 °C. HgO formed during the experiments is trapped by reactor walls, outlet tubing walls, and, finally, the glass wool. A furnace (680 °C) is installed downstream of the moisture trap to decompose ozone and NO2 and minimize their effect on mercury analysis. Analytical Instrumentation. The analytical work is to measure concentrations of inlet and outlet gas streams. Several commercial gas analyzers are used on-line. An affordable Jerome 431-X mercury analyzer (Arizona Instrument, Arizona)
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Figure 2. Effect of 0.1% O2 on oxidation of mercury.
is used to measure the concentration of elemental mercury. This instrument detects only elemental mercury and is unaffected by interference common to UV analyzers. With its gold film sensor, it can detect mercury in the range of 0.003-0.999 mg/ m3 (0.3-10 ppbv) in just 13 s. The reported accuracy is about (5%. A Thermo-Electron model 10A/R Chemiluminescent NO-NO2-NOx analyzer is used to measure the NO and NOx. A Nova model 375 portable combustion analyzer is used to measure the O2, CO2, and CO concentrations in the gas stream. A traceable hygrometer (VWR) with probe is used to measure the humidity of the gas stream.
Figure 3. Effect of energy density on Hg conversion.
3. Experimental Results and Discussion Experiments are conducted on mercury oxidation in the DBD reactor under controlled conditions. Conversion of mercury vapor is measured in terms of inlet and outlet Hg vapor concentrations as follows,
Conversion (%) )
Cinlet - Coutlet × 100 Cinlet
(1)
where Cinlet ) concentration of inlet Hg vapor (mg/m3) and Coutlet ) concentration of outlet Hg vapor (mg/m3). Energy density is the power deposited into 1 L of gas mixture at standard conditions (J/L), i.e., discharge power divided by total gas flow rate. Energy density is used in this study because its concept is simple and direct. The frequency used is 150 Hz.17 The DBD reactor is maintained around room temperature by circulating water from a water bath. Hg oxidation with Low-Concentration O2. Low concentration of 0.1% O2 is used to minimize ozone formation in the plasma reactor and to study its effect on Hg conversion. The concentration of Hg vapor in the outlet stream of the plasma reactor is measured and illustrated in Figure 2. A N2-O2 stream with 0.073 mg(Hg)/m3 is passed through the plasma reactor without power. When a voltage of 21.2 kV at 150 Hz is applied to the reactor, outlet Hg concentration drops to ∼0 mg/m3. Hg concentration restores to the feed level of 0.073 mg/m3 when power is turned off. It is found that 0.1% O2 in the inlet N2 gas stream through the plasma is adequate to oxidize almost all mercury vapors, which can be removed in a downstream scrubber. The following oxidation reactions are proposed to occur in the plasma reactor:
Hg + O f HgO
(2)
Hg + O3 f HgO + O2
(3)
Figure 4. Effect of water vapor on the oxidation of mercury: total flow rate 1000 mL/min, 0.055 mg (Hg)/m3, 1% H2O, N2 balance, 150 Hz, energy density 240 J/L, room temperature.
Effect of Energy Density on Mercury Conversion. Energy input is regarded as a key parameter for a barrier discharge reactor, since it has a strong effect on reactions inside the reactor. A gas stream is passed through the plasma reactor with 0.061 mg/m3 Hg, 0.1% O2, and N2 balance. An energy input of 86 J/L produced the initial discharge, resulting in 45% Hg conversion (Figure 3). The Hg conversion is found to be ∼100% at the energy density of 114 J/L. In general, a higher energy density results in a higher Hg conversion into HgO. Effect of Water on Mercury Conversion. The effect of H2O on Hg oxidation in the DBD reactor is shown in Figure 4. An energy density of 240 J/L is continuously maintained in the reactor. Bubbling a part of or the total gas stream, as needed, through water provides water vapor in the gas stream. The concentration of water vapor in the gas stream is maintained at 1%. Partial oxidation of Hg occurs. The average conversion of Hg is ∼18%. Fluctuations in the exit mercury concentration are observed. The following reactions are possible:
H2O + e f OH + H + e
(4)
Hg + 2OH f Hg(OH)2
(5)
It is known that OH‚ radicals are formed in the DBD reactor. These radicals react with mercury to form mercury(I) hydroxide (Hg2)2(OH)2 and mercury(II) hydroxide Hg(OH)2. The hydroxides are easily decomposed at room temperature. As stated earlier, the gases, after exiting the reactor, pass through the
Ind. Eng. Chem. Res., Vol. 45, No. 17, 2006 6053
Figure 5. Outlet Hg concentration in the presence of both O2 and H2O
Figure 7. Effect of coexisting O2, H2O, and CO2 on Hg conversion at energy density of 240 J/L.
Figure 6. Effect of CO2 on oxidation of mercury: total flow rate 1000 mL/min, 10% CO2, N2 balance. 150 Hz, energy density 300 J/L, room temperature.
heater in the preconditioning system. The mercury compounds, when exposed to higher temperatures, are more likely to decompose back to Hg, and thus, fluctuations are observed. Effect of Coexisting O2 and Water on Mercury Conversion. The effect of coexisting O2 and H2O on mercury oxidation is investigated with a gas mixture of 8% O2, 2% H2O, and 0.040 mg/m3 Hg. The energy density is 240 J/L. Figure 5 shows that the outlet Hg is measured to be 0.040 mg/m3, equal to inlet concentration before power is turned on. When power is on, the outlet Hg concentration is found to be zero. The outlet Hg concentration goes back to inlet level when power is turned off. Elemental Hg can be almost fully oxidized in the presence of O2 and water vapors. Effect of CO2 on Mercury Conversion. A gas mixture of 10% CO2 and N2 is passed through the plasma reactor to investigate the effect of CO2 on Hg conversion. High concentration (up to 700 ppm) of CO can be formed from CO2 decomposition in the plasma reactor when inlet gas contains 10% CO2 in N2.17 At the energy density of 300 J/L (21 kV and 150 Hz), 0.085 mg/m3 Hg present in the 10% CO2 and N2 stream shows a conversion of ∼65%. Figure 6 shows the operating conditions and the results. The following reactions may account for Hg conversion:
CO2 + e f CO + O + e
(6)
O + Hg f HgO
(2)
A N2 stream containing 1% CO is found to cause no interference in the mercury analysis.
Figure 8. Hg conversion in the presence of NO or NO2 as a function of inlet Hg concentration.
Effect of Coexisting O2, H2O, and CO2 on Mercury Conversion. A gas mixture of 8%O2, 2% H2O, 10% CO2, 0.060 mg/m3 Hg, and N2 is passed through the plasma reactor to investigate any synergetic effect of gas components on Hg conversion. With plasma power of 240 J/L, outlet mercury concentration is found to be ∼0.010 mg/m3 (Figure 7), showing 80% of inlet Hg is oxidized in the plasma reactor. It can be concluded that the synergetic effect of the three main components, O2, H2O, and CO2, present in flue gases on Hg conversion is favorable. Effect of NO/NO2 on Mercury Conversion. A gas mixture of Hg vapor and 100 ppm NO in N2 is passed through the plasma to investigate the effect of NO on Hg conversion. The total flow rate is 1000 SCCM. A much higher energy of 660 J/L is applied to the plasma reactor to decompose NO and prevent its possible interference in Hg analyzer. 100 ppm NO2 is also used individually to study its effect on Hg oxidation under the same experimental conditions. Shown in Figure 8 is the Hg conversion as a function of inlet Hg concentration. With inlet NO concentration of 100 ppm, Hg conversion is increased from 45 to 75% as inlet Hg concentration is increased from 0.042 to 0.106 mg/m3. However, a conversion of 81-86% is achieved for the inlet 100 ppm NO2 under the same operating conditions. This is because more O radicals produced via dissociation of NO2 (as compared to NO) are available for Hg oxidation, resulting in higher Hg conversion via reactions 7 and 2. The presence of relatively sufficient amounts of oxygen
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offsets the effect of low concentration of Hg in the gas, resulting in a stable high conversion.
NO2 + N f N2 + 2O
(7)
O + Hg f HgO
(2)
Chemistry of Mercury Oxidation under DBD Plasma Conditions. The chemistry and kinetics of atmospheric Hg oxidation have been well-studied by Hall27 and Pal and Ariya.28 However, the chemistry of Hg oxidation under DBD plasma conditions is very different from oxidation in a combustion process or under atmospheric conditions and is not wellunderstood. A characteristic feature of the nonthermal plasma is its high electron temperature (10 000 to 100 000 K), while the gas temperature can remain close to room temperature.22 The gaseous reactions in plasma can be very complex involving energetic electrons, ions, metastable neutral compounds, etc., resulting in tens of reactions. In our DBD plasma reactor, there are various species including Hg, O, O2, O3, N2, etc. that can react in several ways.29 The main reactions for Hg oxidation in this study can be summarized as follows:
O2 + e f O(3P) + O(1D) + e
(8)
O(1D) + O2 f 3O(3P)
(9)
O + O 2 f O3
(10)
Hg + O f HgO
(2)
Hg + O3 f HgO + O2
(3)
Hg + 1/2O2 f HgO
(11)
Overall reaction:
In the presence of water vapor, formation of O3 is suppressed. O3 may be just an intermediate during the barrier discharge process. The metastable O atom probably plays a key role in oxidizing elemental Hg into HgO. It is worth mentioning that mercury chlorination is generally regarded as a dominant mechanism for mercury transformation during and after coal combustion.30-32 Future study with DBD should consider the effect of chlorine species on mercury removal. Cost Comparison. The present study will potentially lead to the development of a cost-effective technology for mercury control, especially when the plasma technique can be simultaneously used for controlling other pollutants, such as NOx and SO2, also present in flue gases. A barrier discharge system not only converts pollutants to more manageable forms, it is also potentially less expensive and easier to operate than currently available abatement technologies because it is a low-temperature and ambient-pressure operation. Sargent and Lundy, LLC, and AmerenUE have made detailed cost estimates for the removal of NOx and SO2 using the barrier discharge ECO integrated process.21,22 On the basis of a 510 MW unit, it is reported that ECO is substantially less expensive than conventional technology for multipollutant control (NOx, SO2, Hg, and fine particulate matter), i.e., a levelized cost of 8.9 $/MWh compared to $11.7/MWh. Encouraged by the potential cost savings, a commercial demonstration unit treating a 50 MWe flue gas slipstream has been constructed at FirstEnergy’s Burger Power Plant near Shadyside, Ohio.33 It is currently
in operation. Since the technology controls multiple pollutants, there are no separate cost numbers available for Hg removal only. It will not be out-of-line to state that Hg removal in the same operation does not add significantly to the process cost. In contrast to the above cost saving, an estimated cost for mercury removal using activated carbon injection may exceed $3 million in annual carbon usage for a 500-MW coal-fired power plant.8 4. Conclusions DBD plasma technique can be used to oxidize up to 80% mercury present in a simulated gas mixture of 8% O2, 2% H2O, 10% CO2, and balance N2. The presence of NO/NO2 favors Hg oxidation under the experimental conditions of this study. Power consumption is a key parameter in reactor performance and must be minimized for commercial operation. About 100% conversion of elemental mercury to HgO has been achieved at the energy level of 114 J/L. We propose that the dominant oxidation reaction is Hg + O f HgO under the DBD plasma conditions. Our past and present studies show that Hg can be simultaneously removed along with the other two pollutants, NOx and SO2, in one barrier discharge reactor followed by a wet scrubber system. This avoids the need of three techniques for the removal of major gaseous pollutants from coal-fired power plants and, therefore, leads to a considerably cost-effective solution to the flue gas pollution. Acknowledgment The authors are thankful to U.S. Department of Energy for partially supporting this work, Grant No. DE-FG26-01NT41289, February 2003. Z.C. and D.P.M. are thankful to the Department of Chemical Engineering, University of New Hampshire, for financial support. Literature Cited (1) Bool, L.; Helble, J. A Laboratory Study of the Partitioning of Trace Elements during Pulverized Coal Combustion. Energy Fuels, 1995, 9, 880. (2) U.S. Environmental Protection Agency. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating UnitssFinal Report to Congress; EPA-453/R-98-004; Office of Air Quality Planning and Standards: Research Triangle Park, NC, 1998.. (3) Laudal, D.; Pavlish, J.; Graves, J.; Stockdill, D. Mercury Mass Balances: A Case Study of Two North Dakota Power Plants. J. Air Waste Manage. Assoc. 2000, 50, 1798. (4) Pavlish, J. H.; Sondreal, E. A.; Mann, M. D.; Olson, E. S.; Galbreath, K. C.; Laudal, D. L.; Benson, S. A. State Review of Mercury Control Options for Coal-Fired Power Plants. Fuel Process. Technol. 2003, 82 (23), 89. (5) Krishnan, S.; Gullett, B.; Jozewicz, W. Mercury Control in Municipal Waste Combustors and Coal-Fired Utilities. EnViron. Prog. 1997, 16 (1), 47. (6) Huang, H.; Wu, J.; Livengood, C. Development of Dry Control Technology for Emissions of Mercury in Flue Gas. Hazard. Waste Hazard. Mater. 1996, 13 (1), 107. (7) Galbereath, K.; Zygarlicke, C. Mercury Speciation in Coal Combustion and Gasification Flue Gases. EnViron. Sci. Technol. 1996, 30 (8), 2421. (8) Meserole, F.; Chang, R.; Carey, T.; Machac, J.; Richardson, C. Modeling Mercury Removal by Sorbent Injection. J. Air Waste Manage. Assoc. 1999, 49, 694. (9) Boren, R. M.; Hammel, C. F.; Harris, L. E.; Bleckinger, M. R. Pilot Test Result from EnviroScrub Technologies Multi-pollutant Pahlman Process Technology for NOx, SO2, and Mercury. Presented at Combined Power Plant Air Pollutant Control Mega Symposium, sponsored by EPRI, U.S. EPA, U.S. DOE-NETL, and the AWMA, Washington, DC, Aug 30-Sept 2, 2004. (10) McLarnon, C. R.; Granite, E. J.; Pennline, H. W. Initial Testing of Photochemical Oxidation for Elemental Mercury Removal from Subbituminous Flue Gas Streams. Presented at Combined Power Plant Air Pollutant
Ind. Eng. Chem. Res., Vol. 45, No. 17, 2006 6055 Control Mega Symposium, sponsored by EPRI, U.S. EPA, U.S. DOENETL, and the AWMA, Washington, DC, Aug 30-Sept 2, 2004. (11) Granite, E.; Pennline, H. Photochemical Removal of Mercury from Flue Gas. Ind. Eng. Chem. Res. 2002, 41, 5470. (12) Eliasson, B.; Kogelschatz, U. Modeling and Applications of Silent Discharge Plasmas. IEEE Trans. Plasma Sci. 1991, 19 (2), 309. (13) Penetrante, B.; Hsiao, M.; Kuthi, A.; Burkhart, C.; Bayless, J. Basic Energy Efficiency of Plasma Production in Electrical Discharge and Electron Beam Reactors, Presented at Symposium on Non-Thermal Plasma Technology for Air Contaminant Control, Tokyo, Japan, Nov 1, 1996. (14) Luo, J.; Suib, S.; Marquez, M.; Hayashi, Y.; Matsumoto, H. Decomposition of NOx with Low-Temperature Plasma at Atmospheric Pressure: Neat and in the Presence of Oxidants, Water, and Carbon Dioxide. J. Phys. Chem. A 1998, 102, 7954. (15) Breault, R.; McLarnon, C. Mathur, V. Reaction Kinetics for Flue Gas Treatment of NOx. In Non-Thermal Plasma Techniques for Pollution Control; Penetrante, B. M., Schultheis, S. E., Eds.; NATO ASI Series, Volume 34, Part B: Electron Beam and Electrical Discharge Processing; Springer-Verlag: Berlin, 1993; pp 239-256. (16) Chen, Z.; Mathur, V. Non-Thermal Plasma for Gaseous Pollution Control. Ind. Eng. Chem. Res. 2002, 41 (9), 2082. (17) (17)Chen, Z.; Mathur, V. Nonthermal Plasma Electrocatalytic Reduction of Nitrogen Oxide. Ind. Eng. Chem. Res. 2003, 42 (26), 6682. (18) McLarnon, C.; Mathur, V. Nitrogen Oxide Decomposition by Barrier Discharge. Ind. Eng. Chem. Res. 2000, 39 (8), 2779. (19) Snyder, H.; Anderson, G. Effect of air and oxygen content on the dielectric barrier discharge decomposition of chlorobenzene. IEEE Trans. Plasma Sci. 1998, 26 (6), 1695-1699. (20) Evans, D.; Rosocha, L.; Anderson, G.; Coogan, J.; Kushner, M. Plasma Remediation of Trichloroethylene in Silent Discharge Plasmas. J. Appl. Phys. 1993, 74 (9), 5378. (21) Storch, D.; Kushner, M. Destruction Mechanisms for Formaldehyde in Atmospheric Pressure Low-Temperature Plasmas. J. Appl. Phys. 1993, 73 (1), 51. (22) Eliasson, B.; Liu, C.; Kogelschatz, U. Direct Conversion of Methane and Carbon Dioxide to Higher Hydrocarbons Using Catalytic DielectricBarrier Discharges With Zeolites. Ind. Eng. Chem. Res. 2000, 39 (5), 1221.
(23) McLarnon, C.; Jones, M. Electro-Catalytic Oxidation Process for Multi-Pollutant Control at FirstEnergy’s R. E. Burger Generating Station. Proceedings of Electric Power 2000 Conference in Cincinnati 2000. (24) Boyle, P.; Steen, D.; Dovale, A. J. Commercial Demonstration of ECO Multi-Pollutant Control Technology. Presented at Power-Gen International 2003, Las Vegas, NV, Dec 9-11, 2003. (25) Helfritch, D.; Feldman, P. Coal Combustion Mercury Control by Means of Corona Discharge. Proceedings of IEEE International Conference on Plasma Science, Monterey, CA, June 20-24, 1999. (26) Mannava, P. C. D. Mercury Remediation by Dielectric Barrier Discharge. Master’s Thesis, University of New Hampshire, Durham, NH, Sept 2004. (27) Hall, B. The Gas-Phase Oxidation of Mercury by Ozone. Water, Air, Soil Pollut. 1995, 80, 301. (28) Pal, B.; Ariya, P. A. Studies of Ozone Initiated Reactions of Gaseous Mercury: Kinetics, Product Studies, and Atmospheric Implications. Phys. Chem. Chem. Phys. 2004, 6 (3), 572. (29) McLarnon, C. R.; Granite, E. J.; Pennline, H. W. The PCO Process for Photochemical Removal of Mercury from Flue Gas. Fuel Process. Technol. 2005, 87, 85. (30) Galbreath, K. C.; Zygarlicke, C. J. Mercury Transformations in Coal Combustion Flue Gas. Fuel Process. Technol. 2000, 65, 289. (31) Sliger, R. N.; Kramlich, J. C.; Marinov, N. M. Towards the Development of a Chemical Kinetic Model for the Homogeneous Oxidation of Mercury by Chlorine Species. Fuel Process. Technol. 2000, 65, 423. (32) Senior, C. L.; Sarofim, A. F.; Zeng, T. F.; Helble, J. J.; MamaniPaco, R. Gas-Phase Transformations of Mercury in Coal-Fired Power Plants. Fuel Process. Technol. 2000, 63 (2-3), 197. (33) Duncan, J. A Tale of Two Processes. Power 2004, 50.
ReceiVed for reView March 24, 2006 ReVised manuscript receiVed May 30, 2006 Accepted June 9, 2006 IE0603666
