Mercury Removal From Simulated Coal-Fired Power Plant Flue Gas Using UV Irradiation And Silica-Titania Composites

MISSING IMAGE

Material Information

Title:
Mercury Removal From Simulated Coal-Fired Power Plant Flue Gas Using UV Irradiation And Silica-Titania Composites
Physical Description:
1 online resource (92 p.)
Language:
english
Creator:
Gruss,Alexander F
Publisher:
University of Florida
Place of Publication:
Gainesville, Fla.
Publication Date:

Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Environmental Engineering Sciences
Committee Chair:
Mazyck, David W
Committee Members:
Wu, Chang-Yu
Chadik, Paul A
Dempere, Luisa A

Subjects

Subjects / Keywords:
air -- coal -- flue -- gas -- mercury -- oxidation -- photocatalysis -- photolysis -- pollution -- removal
Environmental Engineering Sciences -- Dissertations, Academic -- UF
Genre:
Environmental Engineering Sciences thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract:
Mercury is listed as a hazardous air pollutant (HAP) because of its adverse health effects on humans. Without technologies that effectively remove mercury that is contained in the flue gas of coal combustion power plants, the long-term effects on the nation?s health could be catastrophic. This research builds on previous work to examine mercury removal at typical flue gas temperatures (up to 375?F), multiple flue gas components (SO2, NO2, HCl), and short contact times (0.3 - 2 s) by studying photocatalytic oxidation and capture of mercury by a silica-titania composite technology coated onto ceramic packing material. Experiments conducted under flue gas conditions showed little change in Hg removal performance when the temperature was increased from 275?F to 375?F. Both oxidation and adsorption seemed to be inhibited by moisture at 375?F, except when chlorine was present. Moisture had a significant detrimental effect on oxidation levels of mercury by UV alone, particularly at a wavelength of 254 nm.
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Alexander F Gruss.
Thesis:
Thesis (Ph.D.)--University of Florida, 2011.
Local:
Adviser: Mazyck, David W.

Record Information

Source Institution:
UFRGP
Rights Management:
Applicable rights reserved.
Classification:
lcc - LD1780 2011
System ID:
UFE0043294:00001


This item is only available as the following downloads:


Full Text

PAGE 1

1 MERCURY REMOVAL FROM SIMULATED COAL FIRED POWER PLANT FLUE GAS USING UV IRRADIATION AND SILICA TITANIA COMPOSITES By ALEXANDER F GRUSS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011

PAGE 2

2 2011 Alexander F Gruss

PAGE 3

3 To everyone who has helped me along the way

PAGE 4

4 ACKNOWLEDGMENTS I would like to thank my parents, who have always been there for me. Whenever times get tough, I can count on their advice and support to help me get through any situation. I thank my sister for her friendship throughout the years. A special thank you to Amy Borello for making me laugh every day and for her support in everything I do. Without her this would have been a much different experience. I would also like to thank Dr. Mazyck for giving me the opportunity to work in his lab and experience small business technology commercialization. I have learned tremendous lessons that I will take with me throughout my business life. I thank my supervisory committee Dr. Amelia Dempere, Dr. Paul Chadik, and Dr. Chang Yu Wu for their guidance and suggestions. I am grateful for the advice, assistance and company of Rick Loftis and Dave Baun, who made working in the lab a more pleasant experience. Thanks go to Anna Casass for her guidance and help. I thank the membersof my research group, past and present for their support, especially Amy Borello, Heather Byrne, William Kostedt IV, and Jennifer Stokke.

PAGE 5

5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 8 ABSTRACT ................................................................................................................... 11 CHAPTER 1 INTRODUCTION .................................................................................................... 12 2 LITERATURE REVIEW .......................................................................................... 16 Photocatalysis ......................................................................................................... 16 Methods of Mercury Removal ................................................................................. 17 Silica Titania Composites ....................................................................................... 19 Mercury Oxidation ................................................................................................... 21 3 EXPERIMENTAL .................................................................................................... 23 STCP Production .................................................................................................... 23 Characterization ...................................................................................................... 23 Experimental Setup ................................................................................................ 24 Oxidation Studies ............................................................................................. 25 Flue Gas Simulation ......................................................................................... 26 Mercury Anal ysis .................................................................................................... 27 4 MERCURY OXIDATION BY UV ............................................................................. 30 Effect of Contact Time ............................................................................................ 30 Effect of Water Vapor and Temperature ................................................................. 31 Effect of UV ............................................................................................................. 33 Effect of Ozone ....................................................................................................... 33 Summary ................................................................................................................ 34 5 MERCURY VAPOR REMOVAL FROM BENCH SCALE SIMULATED FLUEGAS USING STCP ................................................................................................. 39 Baseline Experiments ............................................................................................. 40 Effect of NO2 ........................................................................................................... 40 Effect of SO2 ........................................................................................................... 41 Effect of HCl ............................................................................................................ 41

PAGE 6

6 Effect of Simulated Flue Gas .................................................................................. 42 Su mmary ................................................................................................................ 43 6 PILOT SCALE MERCURY REMOVAL USING STCP ............................................ 48 Materials and Methods ............................................................................................ 50 STCP Material Development ............................................................................ 50 Evaluation of Mercury Removal ........................................................................ 52 ScaledUp Evaluation of Mercury Removal from Simulated Flue Gas Using STCP ............................................................................................................ 53 Results and Discussion ........................................................................................... 53 STCP Material Development ............................................................................ 53 STCP Material Characterization ....................................................................... 55 XR D ........................................................................................................... 55 SEM Imaging ............................................................................................. 56 Hardness/Durability .................................................................................... 56 Pore size, pore volume, and surface area ................................................. 57 Simulated Flue Gas Benchscale Experiments ................................................ 57 4 ACFM Pilot Scale Data .................................................................................. 59 Competitive Analysis ........................................................................................ 60 Summary ................................................................................................................ 60 7 CONCLUSIONS ..................................................................................................... 69 APPENDIX: VOC REMOVAL BY STC PELLETS ......................................................... 72 Experimental ........................................................................................................... 74 Adsorption ........................................................................................................ 74 Regeneration .................................................................................................... 75 Results .................................................................................................................... 75 Adsorption Studies ........................................................................................... 75 Regeneration o f STC ........................................................................................ 76 Summary ................................................................................................................ 77 LIST OF REFERENCES ............................................................................................... 83 BIOGRAPHICAL SKETCH ............................................................................................ 92

PAGE 7

7 LIST OF TABLES Table page 5 1 Summary of results in % mercury removal. ........................................................ 43 5 2 Standard error of STCP results in % mercury removal. ...................................... 43 6 1 Coating recipes that were attempted during this study. ...................................... 61 6 2 Summary of durability test results. ...................................................................... 61 6 3 Characteristics of PEG and nonPEG packing. .................................................. 61 6 4 Competitive analysis of STCP versus two widely accepted commercial technologies for Hg removal from flue gas. ........................................................ 62

PAGE 8

8 LIST OF FIGURES Figure page 2 1 Schematic of band gap irradiation of a semiconductor particle .......................... 22 3 1 Test stand setup for mercury oxidation study ..................................................... 28 3 2 Test stand setup for STCP study ........................................................................ 29 3 3 Hg analysis setup with impingers and Zeeman .................................................. 29 4 1 Mercury oxidation by 254 nm UV at 300F and 26,000 ppmv WVC. .................. 35 4 2 Mercury oxidation by 185 nm UV at 300F and 26,000 ppmv WVC. .................. 35 4 3 Mercury oxidation vs water vapor concentration varying UV wavelength at ca. 80F. ................................................................................................................... 36 4 4 Mercury oxidation vs water concentration varying UV wavelength at 200 F. ..... 36 4 5 Mercury oxidation vs water concentration varying UV wavelength at 300F. ..... 37 4 6 Mercury oxidation by ozone vs water concentration at ca. 80F ........................ 37 4 7 Mercury oxidation by ozone vs water concentration at 200F ........................... 38 4 8 Mercury oxidation by ozone vs water concentration at 300F ........................... 38 5 1 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC. ................. 44 5 2 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2. ........................................................................................................... 44 5 3 Long term Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2. ......................................................................................... 45 5 4 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 350 ppmv SO2. ........................................................................................................... 45 5 5 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 100 ppmv H Cl. ........................................................................................................... 46 5 6 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 100 ppmv H Cl, 350 ppmv SO2. ................................................................................... 46 5 7 Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2, 100 ppmv H Cl, 350 ppmv S O2. .......................................................... 47

PAGE 9

9 5 8 Hg oxidation/removal using STCP at 375F and 197,000 ppmv WVC, 250 ppmv NO2, 100 ppmv H Cl, 350 ppmv SO2. .......................................................... 47 6 1 Test stand schematic for benchscale studiesfor evaluation of STCP for Hg removal from simulated flue gas. ........................................................................ 62 6 2 Schematic of 4 ACFM pilot scale reactor used for scaledup evaluation of STCP for Hg removal from simulated flue gas. ................................................... 63 6 3 UV transmission through a packed bed of various materials. ............................. 63 6 4 SEM imaging of PEG packing (5000X magnification). ........................................ 64 6 5 SEM imaging of nonPEG packing (5,000X magnification). ............................... 64 6 6 SEM imaging of used packing (5,000X magnification). ...................................... 6 5 6 7 375PEG STCP. ......... 65 6 8 375 PEG STCP, 100 ppm HCl. ...................................................................................................... 66 6 9 3754% relative humidity, nonPEG STCP, 100 ppm HCl, 350 ppm SO2. .............................................................................. 66 6 10 375 PEG STCP, 100 ppm HCl, 350 ppm SO2, 250 ppm NO2. ....................................................... 67 6 11 375 0 ppm SO2, 250 ppm NO2. Media: 3 mm by 5 mm cylindrical STC pellets (140 pore size, 12% TiO2). ............................................................................... 67 6 12 375 ppb Hg, 4% relative humidity, nonPEG STCP, 100 ppm HCl, 350 ppm SO2, 250 ppm NO2. ....................................................... 68 6 13 Results of 4 ACFM pilot scale evaluatio n of non PEG coated honeycomb at the following conditions: 375 or 200 sections defined earlier, 10 ppb Hg, 4% relative humidity, and 100 ppm HCl. ... 68 A 1 Experimental setup for toluene adsorption. ........................................................ 79 A 2 Experimental setup for ethanol adsorption. ........................................................ 79 A 3 Experimental setup for regeneration. .................................................................. 80 A 4 Toluene adsorption at 72 ft/min face velocity. ..................................................... 80 A 5 Toluene adsorption at 176 ft/min face velocity. ................................................... 81

PAGE 10

10 A 6 Toluene adsorption by virgin and regenerated STC pellets. Note that the virgin and regenerated pellets remove the same percentage of toluene at the last data point. .................................................................................................... 81 A 7 Ethanol removal before and after regeneration with sweep air. .......................... 82 A 8 Toluene removal after several regenerations with sweep air. ............................. 82

PAGE 11

11 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy MERCURY REMOVAL FROM SIMULATED COAL FIRED POWER PLANT FLUE GAS USING UV IRRADIATION AND SILICA TITANIA COMPOSITES By ALEXANDER F GRUSS August 2011 Chair: David Mazyck Major: Environmental Engineering Sciences Mercury is listed as a hazardous air p ollutant (HAP) because of its adverse health effects on humans. Without technologies that effectively remove mercury that is contained in the flue gas of coal combustion power plants, the long term effects on the nations health could be catastrophic. This research builds on previous work to examine mercury removal at typical flue gas temperatures (up to 375F ), multiple flue gas components (SO2, NO2, HCl), and short contact times (0.3 2 s) by studying photocatalytic oxidation and capture of mercury by a silicatitania composite technology coated onto ceramic packing material. Experiments conducted under flue gas conditions sho wed little change in Hg removal performance when the temperature was increased from 275F to 375 F Both oxidation and adsorption seemed to be inhibited by moisture at 375F except when chlorine was present. Moisture had a significant detrimental effect on oxidation levels of mercury by UV alone, particula rly at a wavelength of 254 nm.

PAGE 12

12 CHAPTER 1 INTRODUCTION In 2010, coal combustion accounted for almost half of the electricity supply (45%) in the US and is the predominant source of energy in the world (1). Coal fired power plants account for over one third of total US anthropogenic mercury emissions, making t hem the largest single source of mercury air emissions (2). Globally, almost two thirds of total anthropogenic mercury emissions in 2000 came from combustion of fossil fuels, of which coal combustion had a large share (3). Emission of certain gases from coal combustion power plants, such as nitrogen oxides (NOx) and sulfur dioxide (SO2) are regulated by the EPA (4, 5). However, mercury emissions from coal combustion power plants are currently not regulated. The 1990 Amendments to the Clean Air Act direct ed the Environmental Protection Agency (EPA) to study the health and environmental impacts of HAPs (6). The EPA found that mercury emitted into the atmosphere bioaccumulates in the environment and can cause impaired neurological development in fetuses, i nfants and children, as well as problems in the nervous system and gastrointestinal tract in adults (7), to name but a few adverse health effects. In 2000, the EPA announced its intent to regulate HAP emissions from coal and oil fired power plants. In M arch of 2005, EPA issued the Clean Air Mercury Rule (CAMR) to permanently cap and reduce mercury emissions from coal fired power plants. This rule made the US the first country in the world to regulate mercury emissions from utilities. While a federal court invalidated the CAMR in February of 2008, there is no doubt of the urgency to reduce our mercury emissions to the environment. Based on research conducted by the EPA, coal fired power plants emit 50 tons of mercury annually (8) It is important to de velop cost effective

PAGE 13

13 technologies that efficiently remove mercury from the flue gas of power plants to avoid significant harm to the long term health of the nation. The EPA has announced its intent to impose mercury emissions rules requiring power plants to reduce their mercury emissions by 91 percent (9). The annual cost to meet the new regulation will be approximately $11 billion in 2016. However, the public health benefits are estimated to be between $59 billion and $140 billion in 2016, much of it fr om avoiding premature deaths (10). Mercury is truly a global pollutant, as Hg0 has an atmospheric lifetime of ca. 12 years and can travel over great distances (11, 12). Mercury emitted from a coal combustion power plant in China can thus be deposited in the United States and vice versa. In this global context, mercury removal from coal combustion flue gas is especially important considering the total mercury emission from coal combustion in China: 302.87 tons in 1995 (13). The flue gas in coal combustion contains gases such as SO2, NOx, and chlorine as well as toxic metals such as arsenic, lead, selenium, thallium, and mercury, all of which have adverse effects on human health (14). While pollutant control devices such as flue gas desulfurization (FGD) s crubbers are used to remove SO2, and selective catalytic reactors (SCR) are used to remove NOx, heavy metals removal techniques from coal combustion power plants have yet to be implemented in a widespread manner in the United States. The current best avail able technology for mercury capture is activated carbon injection; however, it does have several limitations, such as weakened performance when exposed to sulfur species (SOx) in the flue gas and high operating cost (1518).

PAGE 14

14 This work focused on the optim ization of mercury removal under simulated flue gas conditions whereby flue gas components (NO2, SO2, and HCl), temperature, moisture, and contact time were chosen as the main parameters. Specifically, this research focused on the use of a photocatalytic m aterial, silica titania composite coated onto ceramic chemical tower packing material (STCP). Previous research involving UV irradiation of silicatitania composite (STC) in pellet form was conducted and was successfully shown to remove mercury from air ( 19, 20). The STCP material, which has a higher void space than STC pellets, was conceived as a way to improve the scalability of this technology for application in a power plant by reducing pressure drop through the reactor (i.e. tower packing has more void space than a fixed bed of pellets) minimizing the energy necessary to push the air stream through the system and thus decreasing operating and maintenance cost. A reactor cont aining the STCP material to oxidize and remove mercury could be inserted into the air stream of a power plant after the particulate control devices (fabric filter or electrostatic precipitator) and before the stack. In this fashion, the buildup of fly ash and other particulates would be mitigated. The treated air stream would t hen exit the power plant through the stack. With the goal of evaluating the STCP material for full scale application in mercury removal from coal combustion flue gas, the following hypotheses and objectives were identified. The following hypotheses were investigated in this study: Mercury oxidation could occur under UV irradiation alone at wavelengths lower than 365 nm, as wavelengths above that lack sufficient energy to oxidize mercury.

PAGE 15

15 STC in pellet form has been shown to oxidize and remove mercury succes sfully from air. Therefore, it is expected that the STCP is capable of oxidizing and removing mercury from simulated coal combustion flue gas at similar levels The STCP material would not be affected by catalyst poisoning from sulfur and NO2. The object ives of this work were as follows: S tudy of oxidation of Hg by UV alone. This ha s not been previously studied. Wavelengths of 365, 254, and 185 nm wer e examined for their ability to oxidize Hg while varying contact times in the reactor and moisture content in the air stream. Test performance of STCP under simulated flue gas conditions. Conduct long term experiments (> 200 hours) to evaluate the prolonged exposure of STCP to sulfur and NO2. Characterize STCP surface using various techniques (SEM, nitrogen adsorption isotherm, XRD). Perform durability tests on STCP.

PAGE 16

16 CHAPTER 2 LITERATURE REVIEW Photocatalysis Upon absorption of a photon with an energy ( hv ) greater than or equal to the semiconductors band gap energy, an electron/hole pair in the semiconductor is formed where an electron (e-) is promoted to the conduction band and leaves behind a hole (h+) in the valence band (Equation 21, Figure 21) (21, 22): TiO2 + hv TiO2 (eCB + hVB +) (2 1) These electron/hole pairs are able to generate heat when recombined or subsequently contribute in redox reactions. Excited electrons participate in reduction reactions of compounds adsorb ed to the semiconductor surface; however, they can also react with oxygen and via intermediate reactions create H2O2 and OH radicals that are known to be powerful oxidizers The formation of these compounds can be seen in Equations 22 through 27 (23) : TiO2(eCB -) + O2 TiO2 + O2 (2 2) O2 + H+ HO2 (2 3) HO2 + HO2 H2O2 + O2 (2 4) TiO2(eCB -) + H2O2 TiO2 + OH + OH(2 5) H2O2 + O2 OH + OH+ O2 (2 6) H2O2 + hv 2OH (2 7) It is also believed that the hole in the valence band contributes to oxidation of contaminants through the formation of OH radicals. This can be seen in Equations 28 and 29 (23) : TiO2(hVB +) + H2O TiO2 + OH + H+ (2 8)

PAGE 17

17 TiO2(hVB +) + OHTiO2 + OH (2 9) OH radicals can then oxidize organics as well as inorganics such as mercury to a final form of mercury oxide (24, 25) Methods of Mercury Removal Mercury is a d block element, in the gr oups 3 through 12 of periodic table known as transitional elements. It has an electronic structure that causes it to be unusually nonreactive compared to other metals (5d106s2 closed shell that is isoelectric to He), and especially difficult to oxidize wi thout the presence of strong oxidants such as Cl2 (26, 27) Mercury has three oxidation states, elemental (Hg0) and two ionic states ( Hg+ and Hg2+), and can also occur as particulate mercury (Hgp). Particularly in its elemental form, mercury remains in the atmosphere for an extended period of time, contributing to the global background concentration, while in its oxidized form s it can be associated with particles or occur as gases, and are more readily deposited (28) The oxidation state of mercury is difficult to predict ; i ts state is highly dependent on the type of coal burned, as well as the configuration of air pollution control devices (APCD) in a given plant (2933) For example, coals low in chlorine lead to a greater proportion of elemental merc ury (vs. oxidized). This form of mercury cannot be effectively captured in particulate control devices such as el ectrostatic precipitators (ESP) because it is present as a vapor in combustion systems. Nor can it be removed by flue gas desulfurization scr ubbers (FGD) because it is not very soluble in water (34) M uch work has been done to develop models that can predict mercury speciation in flue gas streams of various power plant configurations (33, 3540) and thus devise a removal technology that can be used throughout the electric utility industry (41) Fundamentally, two types of removal technologies exist: those based on adsorption

PAGE 18

18 alone and those that aim to convert all mercury in the air stream into the much more reactive and removable mercuric species by means of oxidation, with adsorption either simultaneously occurring or in a subsequent stage. The current maximum achievable control technology (MACT) is activated carbon injection (ACI). Powdered activated carbon is injected upstream of a particulate matter (PM) control device, such as a fabric filter, and adsorbs mercury. The contaminated carbon is then captured in the fabric filter and removed from the plant. Because it commingles with fly ash in the fabric filter and cannot be easily separated, the salability of the fly ash is adversely impacted, increasing the operating cost of ACI beyond just that of the material. Other sorbents such as c a lcium have been investigated, but have been found to be ineffective in removing elemental mercury (42). Gold and palladium catalysts have also been tested on benchscale, but in their current technical development are not suitable for combustion conditions for several reasons. Gold catalysts do not adsorb m ercury efficiently at temperatures higher than ca. 390F (43) and were found to desorb mercury above 930F (44) which can easily be achieved during a temperature excursion. Fouling is a definite issue with flue gas, which contains multiple corrosive constituents such as NO2, SO2, SO3, Cl2, and HCl. While less of a problem with gold, catalyst deactivation seemed more pronou nced with palladium catalysts (45, 46) While activated carbon can overcome the fouling issue by virtue of its short contact time wi th the flue gas, sorbents and catalysts that remain in contact with the gas stream for any significant period of time are exposed to the aforementioned corrosive constituents and fly ash that deposit on any and every surface

PAGE 19

19 (47). Similar problems were fo und to exist with selective catalytic reduction (SCR), normally used for NOx removal, when applied to mercury oxidation (48) While multipollutant controls, i.e. the combination of SCR, wet FGD and PM controls, are being implemented more and more in the U S and are already common in certain countries in Europe, and have an inherent mercury removal of 70% or more (31, 37), this is not an optimal approach for two reasons. First, the greater removal values were achieved by plants burning higher rank coals suc h as bituminous, which have a higher chlorine concentration and lower sulfur concentr ation than lower rank coals. Thus, the formation of mercuric oxide species by chlorine species is promoted post combustion (40) which can be captured in wet FGDs. Consequently, plants burning lower rank coals (subbituminous, lignite, or blends), will see lower removal rates because of a matrix with little chlori ne and/or high sulfur content (49) resulting in elemental mercury dominant in the air stream and little removal. Second, it is expected that future regulations will stipulate a mercury removal efficiency of at least 90% ( 10). In that scenario, ACI can easily become a major financial burden for electric utilities and consumers alike. Silica Titania Composit es The STC technol ogy was developed to treat VOCs. I n addition, it has also been found to be effective for mercury removal in a benchscale reactor and in chlor alkali facilities (19, 25, 5052). A STC system was developed that would oxidize and adsorb mer cu ry in one stage in a packed bed. A thorough description of STC synthesis can be found elsew here (53, 54) STC in the form of pellets was primarily used, with titanium dioxide (TiO2) used as the photooxidization component. Silica was chosen as the subs trate bec ause of its high

PAGE 20

2 0 surface area (53) While elemental mercury (Hg0) adsorbs onto the pellet surface, UV irradiation activates the titania; electronhole pairs are generated that can oxidize the adsorbed mercury. A lower volatile form is created, H gO, which is not as easily reentrained as Hg0. For these reasons, the composite was found to develop an enhanced adsorption capacity after periods of photocatalytic oxidation (25). Previous research investigated performance of STC under various conditions, such as relative humidity of the carrier gas, TiO2 loading, and fixed bed residence time (19, 20, 25, 55) A UV lamp with a nominal wavelength of 350 nm was cycled off and on (19) With UV initially off, mercury was loaded onto the pellets until the e ffluent reached 68% of the concentration of the influent, at which point the UV lamps were turned on. Hg removal of greater than 95% was observed during the UV on phase at low relative humidity (15%), while high moisture (greater than 75% RH) reduced adsorption capacity by occupying active sites on the adsorbent. A 13% TiO2 loading was found to be optimal based on current synthesis technology. These results were obtained at a temperature of 80F and with breathing grade air, mercury, and nitrogen as the balance gas making up the air stream. In a combustion system such as a coal fired power plant, tem peratures are much higher (> 250F ) and the air stream contains a multitude of gases (and particulate matter whic h was not investigated). At 250F under dr y conditions (i.e. no addition of moisture), removal efficiency during UV irradiation was greater than 95% for the clean gas, and was not affected when NO2, HCl, or SO2 were added (19) When water vapor was added (1.8% relative humidity) and with a temper ature of 250F UV irradiation significantly improved removal

PAGE 21

21 efficiency as compared to n o UV. When constituent gases w ere added, there was little change in Hg removal performance under UV irradiated conditions. The effect of water vapor was subsequently investigated with respect to adsorption, oxidation and reemission of the adsorbed mercury back into the air stream (55). At 150F moisture was found to inhibit both adsorption and photocatalytic oxidation, as well as promote reemission of adsorbed Hg0. It was found that continuous UV irradiation in humid air could either inhibit or promote Hg0 reemission, depending on the dominant reactions occurring on the STC surface: when photocatalytic oxidation of reemitted Hg0 was dominant, UV was an inhibitor, but as the hydrophilic surface attracted water vapor, which blocked the photooxidizing reagent TiO2, UV acted as a promoter for Hg0 reemission as the reduction of HgO to Hg0 dominated (55). It is clear that water vapor plays a key role in the removal of Hg from the air stream by affecting the dynamic equilibrium that exists between Hg adsorption and reemission. The STC material has been characterized in terms of its photocatalytic oxidation kinetics, and good agreement with the Langmuir Hinshelwood (LH) model was demonstrated (56) The rate of Hg0 oxidation increased as the influent concentration increased, and was greatest without addition of moisture This would appear to agree with previous research (19). Mercury O xidation The reaction occurring between mercury and oxygen in the presence of 253.7nm light is given by E quation 2 10 : (2 10)

PAGE 22

22 The reaction products are mercuric oxide as well as ozone, because Hg0 serves as a sensitizer for ozone formati on and ozone oxi dizes mercury (57). This has been shown to be a potential method of mercury removal from coal combustion flue gases (58, 59), and warrants further investigation. Figure 21. Schematic of band gap irradiation of a semiconductor particle

PAGE 23

23 CHAPTER 3 EXPERIMENTAL STCP Production STC was coated onto packing material (LPD KNIGHT CHEM Chemical Porcelain Packing) by preparing a silica suspension (50% Ludox colloidal silica, 50% DI water mixed with 3.5% TiO2 by weight), in which the packing material was dipped and then dried in an oven. The TiO2 used was commercially available Degussa P25. This coating procedure was repeated up to 22 times to produce a visually uniform coating and was tested for hardness and durability Polyethylene glycol (PEG) was added as a binding agent and compared to the former suspension, but no significant performance differences were observed. In addition, the coating was not noticeably thicker or more uniform with the solution c ontaining PEG. Characterization The STCP material was characterized using scanning electron microscopy (SEM). SEM functions by sending a stream of electrons (confined and focused by apertures and magnetic lenses into a monochromatic beam) towards a sample using a positive electrical potential. The resulting interactions between the electrons and the sample are detected and transformed into an image. A high vacuum SEM needs a very low pressure in the sample chamber (below 104 Pa) in order to function. T his reduces the number of collisions between the beam electrons and the molecules of the residual gas, thus minimizing noise in the image. The sample must either be inherently conductive or otherwise be coated with a conductive material to minimize chargi ng of the sample, conduct away heat from the sample during imaging, and increase the secondary electron yield of the sample.

PAGE 24

24 Another characterization technique employed in this research was gas adsorption isotherms using a Quantachrome NOVA 2200e (Boynton Beach, FL). Using the Brunauer, Emmett, and Teller (BET) method and classical Kelvin equation, the surface area, total pore volume, and pore size can be determined. A sample is exposed to nitrogen gas, which is added or removed from the sample chamber in finite volumes at carefully controlled pressures. The result is a data plot of the quantity of adsorbed gas versus the equilibrium pressure, the isotherm plot. Based on the plot and amount of adsorbed gas, the values of the aforementioned properties c an be calculated. X ray diffraction (XRD) is a technique used to identify crystalline materials by directing a focused X applied to determine the distances (d) between the planes of the atoms that mak e up ray beam is known and the angle of As the STCP is a mixture, XRD analysis can determine the proportion of different components. The degree of crystallinity can also be determined, which would make it useful in determining the proportion of anatase TiO2 on the surface of the STCP. Experimental Setup The experimental setups used to collect the mercury oxidation and removal data can be seen in Figures (31) and (32) Air from a compressed air tank (A irgas) is run through Pyrex tubing wrapped in heat tape and the temperature was controlled with a power controller and measured with thermocouples placed throughout the test stand Both gas flow rate and the flow rate of water into the system are controlled by rotameters (Aarlborg, various models). Flow rates were determined based on the desired contact time in the reactor and the target concentrations of the constituents.

PAGE 25

25 Mercury was introduced into the system by passing nitrogen gas over an elemental mercury containing bubbler in a heated w ater bath (maintained at 106 F ) to prevent fluctu ation in mercury delivery The water vapor concentration is controlled by injecting deionized (D I) water (18.1 M cm ) from a pressure vessel into the heated main line, w here it immediately vaporizes. The 100 m L Pyrex annular reactor with a quartz sleeve for UV irradiation is sufficiently spaced from the main line to allow mixing of the gas constituents to occur. The inside of the reactor is approximately 14 cm long and the quartz sleeve is 2.5 cm in diameter. There is a space of approximately 0.8 cm between the outside of the quartz sleeve and the inside of the reactor. The reactor, tubing leading to it, and the tubing following it, are all wrapped in heat tape to maintain constant temperatures in the test stand. Teflon tubing was used on all lines that were not Pyrex to avoid adsorption of mercury. Experiments were conducted at least twice to determine standard error, which is depicted by error bars in figures demonstrating mercury oxidation or removal experiments. Oxidation Studies Mercury oxidation by UV alone was examined initially to determine the benefit when compared with photocatalytic oxidation. Wavelengths of 365 nm, 254 nm, and 185 nm were chosen, the latter two were lower than the 365 nm wavelength ex amined in previous literature (56, 60) All lamps were germicidal and manufactured by Atlantic Ultraviolet Corporation. The ozone output of the 185 nm bulb was measured at the temperatures examined in this study using an ozone monitor (Teledyne Model 454). Using an ozone

PAGE 26

26 generator (Pacific Ozone Technology), that ozone dosage could then be applied to a mercury laden air stream in the absence of UV. Experiments could thus be conducted at the same contact times and moisture conditions as with the UV lamps. Flue Gas Simulation To simulate flue gas, individual flue gas components are added to the main line, prior to the heated section. The main air stream temperature was chosen similar to post ESP flue gas conditions, and experiments conducted at both 275 and 375F. Flue gas components selected include N O2, S O2, and HCl, and were selected based on their importance in the mercury oxidation/removal chemistry and occurrence in coal combustion s cenarios (31) While NO is the predominant form of NOx in actual flue gas, NO2 was chosen in this study, and was expected to decompose into a mixture of NO and NO2 when introduced into the heated main line, as NO2 decomposes above 300F (26). Concentrations of the flue gas components were chosen based on conversations with a lignite coal firing utility operator and their observed concentrations: 250 ppmv NO2, 350 ppmv SO2, and 100 ppmv HCl. SO2 and NO2 were introduced via gas tanks. Chlorine was introduced by mixing liquid HCl with water in the pressure vessel. Due to the nature of HCl, there are several chlorine species in the gas mixture, such as HCl, HO Cl and Cl2 (61 63). The mercury concentration was kept at around 10 ppb ( 9 0 3), which is similar to the concentrations observed under actual flu e gas conditions (41) To account for the fluctuation of the influent concentration (1015% around the target concentration), regular influent samples were taken during runs. A wavelength of 254 nm was used for STCP experiments after it was determined by experimentation that 185 nm did not offer significantly improved performance, while increasing energy costs, making it less economi cal in industrial application. Relative

PAGE 27

27 humidity was kept constant between temperatures at 4% RH as this is still within the range seen at coal combustion power plants. This translates into water vapor concentrations (WVC) of 43,000 ppmv for experiments conducted at 275F a nd 197,000 ppmv for the 375F experiments. Mercury Analysis A junction after the reactor (Figure s 3 1 and 3 2 ) allowed for the effluent air to be directed to the appropriate point of analysis, either an influent or an effluent measurement. T he excess air was exhausted to a carbon trap. The instrument used to measure mercury was an Ohio Lumex Zeeman Mercury Analyzer (RA 915+ ) hereafter called Zeeman, which measures gaseous elemental mercury in real time using the principle of atomic absorption spectrometry to detect and quantify mercury. The method of mercury analysis was the use of a Zeeman with chilled impingers in front of it to determine mercury speciation and remove the corrosive gases from the air stream, such as chlorine, NO2, and SO2 (Figure 33) Once the air stream was treated in the reactor it reaches a junction, where it can either be sent through an impinger train design to determine elemental mercury or an impinger train to determine total mercury concentration. Both impinger trains contai ned a NaOH impinger to remove corrosive gases (64). The elemental mercury train then followed the NaOH impinger with an impinger containing a KCl solution in order to remove oxidized mercury and thus only allowed elemental mercury through the Zeeman. The impinger train designed to measure total mercury had an impinger containing a SnCl2 solution, which reduced all oxidized mercury to elemental mercury, allowing the Zeeman to measure the total concentration of the mercury in the air stream. Prior to enter ing the Zeeman, both

PAGE 28

28 impinger trains pass the air stream through a condensation impinger to avoid condensation in the Zeeman. Mercury removal was calculated using total mercury concentrations and equation (3 1). Mercury oxidation was calculated using equation (32), whereby the total mercury concentration of the influent and the elemental mercury concentration of the effluent are measured. 100 ] [ ] [ ] [ = Removal Hg Influent total Effluent total Influent totalHg Hg Hg (3 1) (3 2) Figure 31. Test stand setup for mercury oxidation study

PAGE 29

29 Figure 32. Test stand setup for STCP study Figure 33. Hg analysis setup with impingers and Zeeman

PAGE 30

30 CHAPTER 4 MERCURY OXIDATION BY UV Several approaches exist to oxidize Hg0, either by nonthermal plasma (65), achieving mercury oxidation o f 59%; corona discharge (66), whereby an air stream is passed through a field of ionized gas and mercury oxidation of 86% is achievable; ozone (67), or UV irradiation (58, 59). UV irradiation as a means to oxidize mercury was studied at 254 nm with simulated flue gas, at temperatures between 80F and 350F (58), and focused on the effects of gas components (SO2, NO), as well as light intensity. The study found that mercury was most easily removed at temperatures below 300F and that NO negatively affected removal. A separate study of mercury oxidation at 100F and 280F also used 254 nm UV light and simulated flue gas (59). This study also found that a temperature increase and the presence of NO had negative effects on mercury oxidation. In both studies UV wavelength and water vapor concentration were not varied. Herein, the objective was to investigate UV wavelength, contact time, temperature, and water vapor concentration on mercury oxidation to understand the viability of this approach for applicatio n in mercury removal in a preFGD treatment system. Effect of Contact Time Contact time is an important design factor in designing flue gas purification systems, as a shorter contact time allows for a smaller reactor volume, keeping costs down. In this st udy, it was necessary to determine the minimum contact time required to achieve at least 91% mercury oxidation, as this is the mercury removal required by the United States Environmental Protection Agency (EPA) in announced future regulation (10) Contact times in the annular reactor in this study were varied from 0.3

PAGE 31

31 to 1.5 seconds, similar to those found in treatment systems of coal combustion power plants. Oxidation was expected to increase as the contact time increased, which was confirmed (Figures 4 1 and 4 2 ). Figure 4 1 shows mercury oxidation by the 254 nm UV bulb at 300F and a water vapor concentration (WVC) of 26,000 ppmv. Oxidation reached 86% at a 1.2 second contact time. At a UV wavelength of 185 nm and the same WVC and temperature (Figure 4 2 ), there was a greater level of mercury oxidation at contact times under one second than at the same contact times with 254 nm UV. However, mercury oxidation did not exceed 91% until a contact time of 1.2 seconds. The Reynolds numbers vary from 440 down to 90 for the 0.3 and 1.5 second contact times, respectively, indicating laminar flow. This might explain the low oxidation at the shorter contact times, as there may be a channeling effect causing a lower level of mixing in the annular reactor. Effect of Water Vapor and Temperature Flue gas conditions are subject to change, as the coal being burnt is a heterogeneous material, which can result in fluctuations in the concentration of water vapor in the air stream. Therefore, it was important to determin e the change in mercury oxidation by the UV bulbs as WVC was varied. When irradiated with 365 nm UV, oxidation was minimal over a range of temperatures and WVCs (Figures 4 3, 4 4, and 45 ), likely because it lacks sufficient energy to excite mercury electrons to the conduction band (68). Figure 43 shows Hg oxidation at 80F over three UV wavelengths and several WVCs at a contact time of 1.2 s. At that temperature t here is a clear difference between the performances of the 254 nm versus the 185 nm lamps, whereby the 185 nm lamp maintains a greater level

PAGE 32

32 of Hg oxidation over the range of WVCs. As the 185 nm lamp is ozoneproducing, it is possible that the ozone aids in Hg oxidation. There is a significant decline in oxidat ion for 185 nm UV with an increase in WVC, possibly due to the overabundance of water vapor, interacting with UV light. However, the decline is steeper than for 254 nm. The increased sensitivity of the 185 nm bulb to water vapor is possibly due to water vapor impeding ozone formation by the bulb (69). At a UV wavelength 254 nm, Hg oxidation shows an improvement as the wat er vapor concentration increased until about 14,000 ppmv (40% relative humidity), at which point oxidation drops s lightly. Here, wate r vapor aided in oxidation through formation of OH radicals by UV irradiation (70) while not inhibiting the interaction of the radicals with Hg0. These OH radicals are formed through the photolysis of water by UV irradiation. The radicals subsequently aid in the oxidation of mercury (71). As WVC further increased, the water vapor UV interaction negatively affects oxidation (Figures 43 and 45). In Figure 44, that point does not seem to have been reached, as mercury oxidation still increased at the highest WVC studied. Figures 4 4 and 4 5 show Hg oxidation at 1.2 s contact times and temperatures of 200F and 300F respectively. At both temperatures, UV 254 showed less oxidation at the very lowest WVC, but was clearly aided by the presence of water v apor as WVC increased likely due to the formation of OH radicals as discussed above. In fact, when comparing the oxidation at 26,000 ppmv WVC and 1.2 s contact time in Figure 4 1 with the oxidation at 3 ppmv WVC at the same contact time in Figure 4 5 ( d ata point with the lowest WVC ), mercury oxidation jumps from just below 40% at 3 ppmv to ca. 85% at 26,000 ppmv.

PAGE 33

33 Effect of UV This study varied UV wavelength to determine the advantage, in terms of mercury oxidation, a 185 nm bulb might have over a 254 nm bulb. At 200 F and 300 F UV wavelength has a clear effect on mercury oxidation rates only in the lower range of water vapor concentrations. In both Figure 4 4 and 4 5 Hg oxidation did not significantly change over the range of WVCs when utilizing the 185 nm UV lamp. While oxidation started out much higher than that of the 254 nm lamp at the low range of WVC, both lamps perform similarly at higher WVCs This is contrary to what would initially be expected, as ozone should provide for additional oxidation. However as previously discussed, water vapor can impede ozone formation by the185 nm bulb (69) rendering an ozoneproducing lamp no more useful than an ordinary UV lamp at high te mperatures and water vapor concentrations. At 300 F (Figure 4 5), 254 nm UV showed better oxidation compared to 200F likely due to the increased Brownian m otion inside the reactor which aids the interaction between OH radicals and Hg0. With both lamps a slight decrease in oxidation can be observed as WVC increased, as a consequence of the UV water vapor interaction. Effect of Ozone The 185 nm bulb produced very little ozone at 80F (0.01 0.03% by weight), therefore very little mercury oxidation was ex pected. Indeed, at that temperature, no detectable mercury oxidation by ozone alone occurred (Figure 46). At 200 F ozone generation by the 185 nm bulb was highest (0.40% by weight), and mercury oxidation by that dosage of ozone was almost complete (i.e., almost 100%, Figure 47). Ozone generation by the 185 nm bulb was lower at 300F (0.06% by weight), and resulted in

PAGE 34

34 9095% mercury oxidation by the corresponding ozone dosage (Figure 48). At both 200 and 300F these oxidation levels are higher than with the 185 nm bulb (Figures 44 and 45), suggesting interference between UV light and ozone, a phenomenon discussed in literature (55, 72, 73), in addition to the previously discussed effect of water vapor on ozone formation. Summary Oxidation of mercury at three UV wavelengths (365 nm, 254 nm and 185 nm) was investigated over a range of water vapor concentrations. Oxidation was higher with the 185 nm over the range of temperatures and water vapor concentrations than 254 nm, except at the highest WVCs and 200 and 300F There was no mercury oxidation with the 365 nm bulb in any conditions. With little water vapor in the air stream, oxidation at the 254 nm wavelength was low, but could be increased by an increase in water vapor concentration. Mercury oxidation at 185 nm was steadier over the range of water vapor concentrations tested, with decreasing levels of oxidation at the upper range of water vapor concentrations for all temperatures. Mercury oxidation of at least 90% was only achievable under c ertain scenarios under irradiation with 185 nm UV, where the water vapor concentrations were high enough to aid in the formation of OH radicals, but not so high as to impede ozone formation. This study demonstrated the variability of mercury oxidation under UV irradiation, as well as the efficacy of this method for removing mercury in conjunction with a capturing mechanism, such as a wet FGD scrubber.

PAGE 35

35 Figure 41. Mercury oxidation by 254 nm UV at 300F and 26,000 ppmv WVC. Figure 42. Mercury oxi dation by 185 nm UV at 300F and 26,000 ppmv WVC.

PAGE 36

36 Figure 43. Mercury oxidation vs water vapor concentration varying UV wavelength at ca. 80 F. Figure 44. Mercury oxidation vs water concentration varying UV wavelength at 200 F

PAGE 37

37 Figure 45. Mercury oxidation vs water concentration varying UV wavelength at 300F. Figure 46. Mercury oxidation by ozone vs water concentration at ca. 80F

PAGE 38

38 Figure 47. Mercury oxidation by ozone vs water concentration at 200F Figure 48. Mercury oxidation by ozone vs water concentration at 300F

PAGE 39

39 CHAPTER 5 MERCURY VAPOR REMOVAL FROM BENCH SCALE SIMULATED FLUEGAS USING STCP Currently, activated carbon injection is considered the most feasible technology by industry. However, a major drawback is the cost, as the injection rates to achieve high mercury removal performance can be very high and the mercury adsorption rate is dependent on flue gas conditions A different strategy is multi pollutant control, where technologies designed to remove other pollutants are utilized to additionally remove mercury and has been shown to be effective, in particular in systems with wet FGD scrubbers (41). This approach works well with highrank coals, such as eastern bituminous, where there is a higher percentage of mercury in oxidized form present in the flue gas due to the higher chlorine content of the coal. Oxidized mercury is more water soluble than elemental mercury (Hg0) and thus more easily removed by a wet FGD scrubber For low rank coal s, such as lignite or subbituminous, elemental mercury is the dominant species in the flue gas resulting in overall lower mercury removal efficiency from this approach. A recent approach is the use of catalytic technologies to oxidize and remove mercury f rom coal combustion flue gas (32, 74, 75). The photocatalytic STC technol ogy was developed to treat VOCs and in addition, it has also been found to be effective for mercury removal in a benchscale reactor and in chlor alkali facilities (19, 20, 25, 5052 55). In this study, silica titania coated packing (STCP) was developed, whereby the STC is coated onto ceramic chemical tower packing material. By reducing the surface area of hydrophilic silica in the STCP, it was thought this might reduce the effect of water vapor on the surface of the photocatalyst. Due to the materials higher void space

PAGE 40

40 (i.e. the space not occupied by the material), this also allows for a lower pressure drop through the reactor than the STC in pellet form and is thus economically more favorable. The goal of this study was to determine if the STCP is capable of oxidizing and removing mercury from sim ulated coal combustion flue gas with a performance similar to that of STC in pellet form In order to test this, performance under simulated flue gas conditions was tested. Baseline Experiments Baseline experiments were conducted in order to determine the mercury removal without the presence of the flue gas constituents NO2, SO2, and HCl (Figure 5 1 ). Water vapor concentration was 43,000 ppmv at 275F and 197,000 ppmv at 375F (4% relative humidity). As can be seen in Figure 5 1 mercury removal remains at a steady state over a significant period of time. Lab work has shown steady state removal even after 200 hours of continuous r untime. Data points for both 275 and 375F are shown (denoted as either 275 or 375 in the legend), with both no added water vapor (denoted as 0) and added water vapor equaling 4% relative humidity (denoted as 4). Addition of water vapor did not significantly affect mercury removal at 275F At 375 F however, there was a significant drop in mercury removal when water vapor was added. This is likely due to the significant increase in water content, which competes with mercury for adsorption onto the hydrophilic silica on the STCP surface. Effect of NO2 NO2 was added to the air stream to determine its effect on mercury oxidation and removal. Figure 5 2 shows data with 250 ppmv NO2 (all other conditions equal to the baseline). Compared to the baseline (80% removal), there is a slight reduction in mercury removal to ca. 78%. NO2 has been shown to enhance Hg oxidation on fly ash

PAGE 41

41 (76) however to a minor extent as compared to chlorine addition. Therefore, the slight decrease in removal might be due to conversion of NO2 to NO through UV irradiation, as NO has been shown to be an inhibitor of mercury remov al by scavenging OH* radicals (20) Additional data confirmed that even after considerable run time (> 200 hours), removal stayed at ca. 78% (Figure 5 3) Effect of SO2 No significant change in removal occurred when SO2 was added to the clean air stream, as can be seen in Figure 5 4 Whereas SOX species (SO2 and SO3) are adsorption inhibitors in activated carbon injection (38) STCP performance showed little change when exposed to SO2. This is possibly due to oxidization of SO2 into sulfuric acid by UV irradiation in the presence of oxygen and water vapor (77) Even SO2 that is adsorbed onto the STCP surface would not significantly affect mercury adsorption due to the higher adsorption capacity of the STCP material (300 mg Hg/g STC in pellet form; the STCP material has shown comparable adsorption over significant periods, i.e. 200 hours, demonstrating an adsorption capacity similar to that of the STC in pellet form). Adsorbed SO2 could also be photocatalytically oxidized at the STCP surface due to the presence of OH radicals (55) further extending the time until the STCP adsorption sites are exhausted. Effect of HCl Chlorine sp ecies are known oxidants (35, 78) and thus a high level of Hg oxi dation was expected. Figure 55 demonstrates mercury oxidation and removal with 100 ppmv HCl (all other conditions equal to the baseline) yielding ca. 90% mercury removal, which is a only a slight improvement in Hg removal compared to the baseline, although oxidation increased to almost 99%.

PAGE 42

42 As expected, an air stream with 100 ppmv HCl and 350 ppmv SO2 does not significantly impact STCP pe rformance, as seen in Figure 56 where Hg removal is ca. 8085%. Whi le the chlorine aids oxidation without SO2 present, it seems the SO2 is inhibiting Hg oxidation by reacting with HCl in the gas phase, possibly via formation of sulfur chlorine complexes, thereby reducing the availability of chl orine to oxidize mercury (43 79) This is confirmed by the lower Hg oxidation in Figure 56 as compared to Figure 55 Interestingly, when comparing experiments that contain chlorine with experiments that do not, there is a difference in the time before steady state mercury removal is reached. Figures 53 and 54 do not include chlorine in the air stream and an increase in mercury removal can be observed before steady state is reached. In contrast, Figures 55, 5 6, 5 7, and 58 show experiments containing mercury removal, and ste ady state is reached more quickly. In the absence of chlorine, this lag effect is likely due to the initial buildup of HgO on the STCP surface, which has a high affinity to elemental mercury, thus facilitating further mercury adsorption (20, 80) The pr esence of chlorine aids in the oxidation of mercury, overcoming the initial hurdle of forming HgO on the surface. Effect of Simulated Flue Gas In Figures 5 7 and 5 8 all constituents were added (NO2, SO2, and HCl) at 275F and 375 F respectively. Mercur y removal did not change significantly compared to the baseline, confirming the resiliency in performance of the coated material to the flue gas constituents tested. A summary of STCP results is provided in Table 5 1, where removal is given as the steady s tate mercury removal (in %) across replicate runs. As can be seen in Table

PAGE 43

43 5 2, results were replicable with a good degree of consistency thus yielding low standard errors across runs. Summary A novel photocatalytic silicatitania composite technology was tested under flue gas conditions. Removal rates of 85% were achieved under benchscale conditions simulating coal combustion flue gas. Temperature did not have a significant effect on removal performance under simulated flue gas conditions. At 375F water vapor had a negative effect on mercury removal. By introducing chlorine into the air stream, mercury removal performance improved to levels approximately equal to those at 275F. Overall, the technology is promising, but performance might be susceptible to fluctuations in chlorine levels in the flue gas. Research on minimum concentrations of chlorine required to counteract the negative effects of water vapor at high temperatures is necessary for future development as an option for full scale implem entation in coal combustion flue gas environments. Table 51. Summary of results in % mercury removal. Table 52. Standard error of STCP results in % mercury removal. Temp (F) No added water vapor 4% RH 4% RH, 250 ppm NO2 4% RH, 350 ppm SO2 4% RH, 100 ppm HCl 4% RH, SO2, HCl 4% RH, NO 2 SO2,HCl 275 75 80 78.5 80.5 87.5 82 85 375 90 55.5 49 48 89 80.5 84 Temp (F) No added water vapor 4% RH 4% RH, 250 ppm NO2 4% RH, 350 ppm SO2 4% RH, 100 ppm HCl 4% RH, SO2,HCl 4% RH, NO 2 SO2,HCl 275 0 2 0.5 2.5 0.5 2 1 375 5 1.5 5 2 1 1.5 1

PAGE 44

44 Figure 51. Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC. Figure 52. Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2.

PAGE 45

45 Figure 53. Long term Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2. Figure 54. Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 350 ppmv SO2.

PAGE 46

46 Figure 55. Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 100 ppmv HCl. Figure 56. Hg oxidat ion/removal using STCP at 275F and 43,000 ppmv WVC, 100 ppmv HCl, 350 ppmv SO2.

PAGE 47

47 Figure 57. Hg oxidation/removal using STCP at 275F and 43,000 ppmv WVC, 250 ppmv NO2, 100 ppmv HCl, 350 ppmv SO2. Figure 58. Hg oxidation/removal using STCP at 375F and 197,000 ppmv WVC, 250 ppmv NO2, 100 ppmv HCl, 350 ppmv SO2.

PAGE 48

48 CHAPTER 6 PILOT SCALE MERCURY REMOVAL USING STCP An important issue surrounding the use of coal for energy production is the control of hazardous pollutant emissions resulting from combustion. Emissions of mercury (Hg) are of particular concern for existing and proposed coal fired power plants. Hg is a widespread and persistent pollutant that accumulates in the environment and has contaminated bodies of water worldwide, particularly via deposition from the air. In the US approximately 5% to 10% of women of childbearing age are estimated to exceed federal exposure guidelines due to dietary intake of Hg contaminated fish (81) This exposure can lead to adverse neurological effects, particularly in the developing fetus and during early childhood. Recently, Hg has been linked to a cause of autism and ADHD in children (82). Activated carbon injection (ACI) is believed to be the most promising technology for near term mercury control, but its effectiveness under various conditions is still being investigated (83) Commercially available powdered activated car bon (PAC) has its limitations, resulting in poor Hg removal under certain conditions, unless impregnated with halogens, which substantially adds to cost. PAC is particularly ineffective in removing elemental Hg, and thus will struggle to achieve high levels of Hg removal in conditions where this Hg species is predominant (e.g., when burning lignite or powder river basin (PRB) coal). Although halogenation improves performance in these conditions, the release of halogens from the PAC has led to concerns about corrosion of equipment, emissions of halogens in the flue gas, and impact on the safety and usability of coal combustion by products (8486) Additionally, waste PAC accumulates in fly ash, a product of combustion commonly sold for the manufacturing of concrete and

PAGE 49

49 other materials, thus compromising this potential source of revenue generation. The goal of the research presented here was to develop a novel adsorbent packing coated with a silica titania photocatalyst (herein referred to as SilicaTitania Coated Packing, STCP) that can capture greater than 90% of Hg in flue gas with lower O&M costs than ACI. A n innovative silica titania composite (STC) material and process for Hg capture has been developed. This technology focuses on the combination of adsorption and photocatalytic oxidation for pollutant removal (25, 51, 80) The STC has demonstrated Hg capture orders of magnitude greater (300 mg/g) than achievable by PAC. Previous research efforts using STC have been completed successfully in the benc h scale and in a pilot scale study at a US chlor alkali facility (i.e., chemical manufacturing plant), leading to the design, fabrication, and installation of t wo full scale commercial units (51). In the current commercial application, the STC material is employed in a packed bed of STC pellets. A packed bed of STC pellets is well suited for treating flow rates on the order of 2000 ACFM or less, such as those found in the chlor alkali industry, and when sufficient pressure drop is available. However, when employing the technology for higher flow rates, such as those associated with coal fired boiler flue gas (greater than 100,000 ACFM), a reactor employing a packed bed of pellets may not be the best solution, since the associated pressure drop may be signi ficant. Recognizing this limitation, we have developed a durable material consisting of commercially available chemical tower packing that is coated with a thin film of STC, to be used in a fixed bed. This STCP has a large external surface area and high void space, which is expected to result in a significantly lower pressure drop (expected to be below 3 to 5 inches of water

PAGE 50

50 gauge (WG) depending on the void space of the packing material and residence time required for greater than 90% Hg capture) than that associated with a packed bed of STC pellets. This is an acceptable pressure drop range for full scale operations. The STCP technology would offer the power industry a robust and economical technology that does not negatively impact the balance of plant issues, does not compromise the salability of fly ash, and is capable of adsorbing all species of Hg; particularly the difficult to remove elemental Hg. Hence, the technology has application to all coal fired power plants, but is particularly well suited for those utilities that burn lignite or subbituminous coal (about 45% of the total US coal fired power plant capacity), which when combusted produce higher concentrations of elemental Hg compared to ionic Hg. The objectives of this work were to: (1) opt imize the design of the STCP to be used in coal fired power plant applications, (2) characterize the final product, (3) determine the effectiveness of the STCP for Hg removal from simulated flue gas, and (4) evaluate a scaled up version of the STCP in a sm all pilot reactor and compare the performance to benchscale results. Materials and Methods STCP Material Development The first step of the research consisted of the selection of commercially available chemical tower packing materials, and the evaluation o f coating procedures and formulations. With regards to packing material selection, it was important that the raw material of construction was resistant to high heat (e.g., greater than 200 retained the coating. The extent of transmission of UV lig ht through a packed bed of the material was also important, and thus was evaluated. This evaluation was carried out

PAGE 51

51 using a system consisting of a series of varying sized test boxes fabricated with Alzack aluminum, which reflects UV light. A 254 nm UV bulb was center mounted within an Alzack box, and the box was filled with packing. By use of a UV radiometer looking through various port holes on the box sides, intensity of UV radiation passing through the STCP bed was measured. The second step consis ted of coating procedure selection and recipe development. General research on costs associated with various coating methods previously used by the research team, including dip coating, impregnation, and chemical vapor deposition, led to the conclusion that dip coating would result in the lowest cost for full scale production. Thus this method was evaluated by directly dipping the selected packing in various silicatitania recipes. Various coats were applied as needed (up to 21 coats), with heating to 120 coats, to obtain a durable coating. After obtaining successful coatings (i.e., coatings that would not rub off and appeared uniform to the naked eye), two coated materials were selected, characterized for their physical properties via X Ray Diffraction (XRD), Scanning Electron Microscope (SEM) imaging and durability/hardness testing, and evaluated for Hg removal efficiency from a simulated flue gas under various conditions, as will be discussed below Durability testing consisted of using a rotator, whereby a known weight of each sample was placed in a glass vial, rotated at 3 RPM for four hours, and then reweighed after sieving to eliminate any powder produced from attrition of the coating. In addition, ASTM method D3363 (Standard Test Method for Film Hardness by Pencil Test) was used on both PEG and nonPEG coatings. This method consists of using a set of

PAGE 52

52 calibrated drawing leads (i.e., pencils of different hardness) to attempt to scratch or cut a coating surface by applying pr essure with the pencil at a 45 Evaluation of Mercury Removal This task involved the utilization of a labscale test bed (Figure 6 1) with simulated flue gas. The reactor system included a supply of elemental mercury vapor a mercury analyzer (Ohio Lumex Zeeman RA 915 + ), and appropriate appurtenances for measuring total Hg (i.e., elemental and oxidized Hg) via an analogous version of the Ontario Hydro Method (ASTM D678402). This modified version skips steps related to particulate matter, as there is no particulate matter present in this simulated flue gas. Hg laden air was introduced into the annular test reactor by passing nitrogen gas above liquid Hg in a reservoir. The t est reactor contained an influent and effluen t port and a UV lamp (254 nm, 12 W) encased by a quartz sleeve centered in its annulus. The reactor was randomly packed with STCP. Simulated flue gas containing varying concentrations of Hg, HCl, SO2, NO2, air and water vapor was passed through the packed reactor. Concentrations were controlled by varying flows with flow meters as presented in Figure 6 1. In the case of water vapor and HCl concentrations, these were controlled by the flow of a dilute HCl sol ution from a 4liter pressure vessel. Contact time was varied by adjusting the flow of carrier air and/or volume of STCP in the reactor (from 3 to 6 LPM). Temperature was varied and controlled via heat tape surrounding the gas feed lines and the reactor. The parameters controlled and verified included: (a) inlet and outlet total Hg concentrations measured using the online Hg analyzer and the Ontario Hydro Method for the duration of 24hour tests, (b) volumetric flow rate of air, (c) flow/concentration of

PAGE 53

53 various typical flue gas constituents, and (d) temperatures on the inlet and outlet controlled by heat tape and monitored by thermocouples. Scaled Up Evaluation of Mercury Removal from Simulated Flue Gas Using STCP A 4 ACFM (113 LPM) pilot reactor (schem atic shown in Figure 6 2) was built and evaluated in our laboratory using simulated flue gas and the optimal conditions determined in benchscale evaluations. Various flue gas constituents were added in the same way they were added in the benchscale experiments described above. Data analyses were also carried out as above. The reactor design was slightly different than the benchscale reactor design. The benchscale reactors were annular, with a quartz sleeve centered in the annulus where a UV lamp is h oused. The STCP material was packed around the quartz sleeve, and the test gas flowed upwards through the bed. The 4 ACFM pilot scale reactor consisted of two sections. The first section was a circular quartz tube. The lamp was placed outside of the qu artz tube, and the test gas flowed on the inside of the tube. The second section, downstream of the quartz/UV section, consisted of a ceramic honeycomb coated with the same recipe selected for small benchscale experiments. Preliminarily, this design was chosen with full scale commercialization in mind. The hypothesis was that a UV section without STCP could begin the oxidation of Hg while a slightly irradiated STCP section would complete the oxidation and remove the oxidized Hg. As proven later, this design was not ideal. Results and Discussion STCP Material Development The first step consisted of selecting the appropriate packing material based on temperature resistance (as indicated by manufacturer specifications) and UV

PAGE 54

54 transmission through the pac ked bed. Thus the transmission of UV through a packed bed of various uncoated packing materials was evaluated using the Alzack test system described above. Results are summarized in Figure 6 3 and include transmission through a packed bed of STC pellets for comparison. T here is better penetration through a packed bed of all packing materials when compared to penetration through the bed of STC, due to the higher void space of the packing. This will not only result in lower UV requirements in a full scale system, but also result in a lower pressure drop compared to a bed of pellets. Thus any of the tested materials would be better suited than the STC pellets for this application based on UV penetration character istics (at lamp spacing below 2 inches). Bas ed on temperature resistance characteristics, three materials were coated: (1) metal rings (Jaeger metal Raschig super rings, 50 mm, 98% void space), (2) 1 KochKnight HPC high porosity carrier saddle (67% void space), and (3) 1 LPD KNIGHT CHEM Chemica l Porcelain Packing (67% void space). However, the only material that was successfully coated was the Chemical Porcelain Packing, whereas all others resulted in coatings that could be easily wiped off and/or were uneven regardless of coating formulation. Packing materials were initially dip coated with powdered STC pellets suspended in a solvent and heated (to 120 solvent. However, these coatings easily rubbed off, and thus other coating recipes were devel oped (Table 6 1). These included various ratios of TiO2 (Degussa P25 and also titanium (IV) tetraisopropoxide (TTIP) used as a precursor) to water, plus an added silica source (Ludox colloidal silica). In addition, various additives were included that

PAGE 55

55 were expected to improve the coating quality (e.g., polyethylene glycol (PEG), methylcellulose, and powdered dispersible alumina (Dispal, Disperal)). STCP Material Characterization As Table 6 1 indicates, successful coatings were achieved with a combination of a 50% Ludox solution with 3.5% TiO2 (Degussa P25), with and without PEG. PEG coatings were successful with and without sonication. Since sonication would only lead to a higher energy requirement for material synthesis (and hence higher manu facturing cost), this was not included in the ultimately selected coating strategy. To analyze the impact of PEG on coating characteristics, two coating methods were characterized: (1) 3.5% TiO2, 50% Ludox, 50% water (hereon nonPEG) and (2) 1% PEG, 3.5 % TiO2, 50% Ludox, not sonicated (hereon PEG). The following analyses were carried out: (a) XRD, (b) SEM imaging: of both coatings plus imaging of STCP that had been used in simulated flue gas studies described ahead (hereon used), (c) hardness/durabi lity testing, (d) average pore size, (e) average pore volume, and (f) BET surface area. Results are summarized below. XRD XRD analyses to determine the ratio of anatase to rutile phase titania were originally proposed assuming there would be successful coatings using various titania precursors. However, the only successful coatings used Degussa P25 as the titania source, which has a known crystalline structure (4:1 anatase to rutile ratio). The analyses were completed and verified that there was a ratio o f anatase to rutile that was greater than 1 for three coated samples (PEG, nonPEG, and used).

PAGE 56

56 SEM Imaging In the PEG s ample (Figure 6 4) the deposition of coating is uneven, with layering. Most of the surface appears to be composed of platelets lying fl at, but with small quantities of amorphous deposits. The platelets are noncrystalline, probably resulting from cracking of the surface as the layers dried. The nanoporosity of the surface cannot be determined at these magnifications, but most of the pl atelet surface area is readily accessible. Cracking of platelets during drying provides very limited access to the internal structure on surfaces perpendicular to the faces. In the n onPEG sample (Figure 6 5), t he surface is again composed of layered plat elets. However, around 1020% of the surface area of the plates is covered by a thin layer of amorphous globules. The deposition pattern suggests flow of liquid on the surface, with rapid precipitation of solids during drying, which would not allow effec tive controlled growth patterns to develop. Whether or not the globules are interspersed between sequential layers of platelets cannot be determined from the available images. In the u sed sample (Figure 6 6) the used surface has substantial deposition of materials of form inconsistent with the virgin surface. Some of the new deposits appear to be crystalline. Some of them form clusters of platelets growing skew or perpendicular to the underlying surface, while others form stacks of smaller platelets (upper right corner). Hardness/Durability The durability of the PEG and nonPEG STCP were compared to that of STC pellets and uncoated ceramic tower packing. Results are summarized in Table 6 2. As the table indicates, there was a minimal amount of at trition during the rotation period in all cases, with the maximum attrition observed for the NonPEG sample.

PAGE 57

57 ASTM method D3363 (Standard Test Method for Film Hardness by Pencil Test) was used on both PEG and nonPEG coatings to determine film hardness. Th e test resulted in Gouge Hardness and Scratch Hardness of 6H for both the PEG and nonPEG coatings. This means that the hardest pencil tested did not scratch or cut either surface. Pore size, pore volume, and surface area The PEG and nonPEG samples were analyzed for pore size, pore volume, and surface area. The results can be found in Table 6 3. Simulated Flue Gas Bench scale Experiments Because the PEG and nonPEG coated materials had similar characteristics, it was deci ded to carry out the majority of benchscale evaluations using the nonPEG material. Based on preliminary work carried out with STC pellets, at least a 1 s contact time was required for high temperature, high relative humidity applications such as the coa l fired power plant flue gas application of interest here (e.g., lignitefired boiler). Thus, initial testing of the nonPEG material was initiated with a 2 s contact time. Through discussions with a lignitefired electric utility, test conditions were es tablished to represent those of where the technology could be applied. These included 375 350 ppmv of SO2, 250 ppmv of NOx, and 100 ppmv of HCl. Before testing these collectively, tests were performed without the presence of sulfur, NOx, and chlorine. In general, oxidation was very high throughout the 24hour period, and removal was greater than 90% for the majority of the duration, with a slight decrease to 87% in the final data point.

PAGE 58

58 Because different utilities will exhibit different flue gas temper atures and relative humidities, the testing environment was challenged by adding 4% relative humidity to the feed. In addition, as flue gas will have varying amounts of chloride present (depending on type of coal burned), HCl (100 ppmv) was incorporated i nto the simulated flue gas stream. Results are shown in Figure 6 8. It should be pointed out that 100 ppmv HCl is a relatively low concentration for flue gas. There was no significant difference in oxidation/removal when comparing Figure 6 7 to Figure 6 8 Sulfur compounds are known to negatively impact the performance of activated carbon. In flue gas conditions particularly, the presence of SO2/SO3 will be a challenge for activated carbon. Thus, SO2 (350 ppmv) was incorporated into the flue gas stream next to determine its effect on the STCP performance. As shown in Figure 6 9, excellent oxidation (92 99%) and removal (86 97%) were obtained when adding the challenging SO2 to the simulated flue gas stream. While the data appears to drop off, it is expected to remain steady above 80% for extended periods based on previous testing not discussed here. It should be pointed out that past studies with STC pellets have shown similar results with SO2 concentrations as high as 3500 ppmv. Ahead it will be d emonstrated that STC pellets and STCP perform very similarly, if not identically, under the conditions evaluated here. Nitrogen compounds are abundant in flue gas conditions, and may negatively impact some technologies, such as activated carbon. Thus, NO2 was incorporated into the simulated flue gas stream to determine its effect on the STCP performance. As Figure 6 10 indicates, NO2 does not negatively impact performance of the STCP. Oxidation ranged from 92 to 100% and removal ranged from 91 to 93%.

PAGE 59

59 In order to directly compare between the performance of the STCP and the STC, the work presented in Figure 6 10 was repeated under the same conditions (i.e., contact time, temperature, constituent concentration, and relative humidity), but using STC pellets rather than STCP. Results are summarized in Figure 6 11. As the Figure indicates, oxidation ranged from 92 to 100% and removal ranged from 89 to 99%. Although at times removal was higher than that observed with the STCP, performance is very similar. In order to attempt to decrease the 2 s contact time used for most of the experiments summarized above, a final run was completed at 375 humidity, 10 ppb Hg, 100 ppmv HCl, 350 ppmv SO2, and 250 ppmv NO2 but with a 1 s contact time. As Figur e 6 12 shows, oxidation varied from 90 to 97% and removal varied from 72 to 78%. This is a decline in removal when compared to that obtained with a 2 s contact time (Figure 6 11). 4 ACFM Pilot Scale Data To evaluate the scaleup potential of the STCP technology, a few experiments were carried out using a 4 ACFM (113 LPM) pilot reactor designed and fabricated for this purpose. The first experiment was carried out at 375 humidity and no added additional constituents, other than 100 ppmv HCl. The second was carried out at 200 constituents, other than 100 ppmv HCl. The second conditions were examined since the lower temperature is representative of flue gas after a wet scrubber, for example. As Figure 6 13 indicates, oxidation ranged from 70 to 76% and removal from 45 to 59% at 375

PAGE 60

60 74%. This diffe rence in performance when compared to benchscale tests is attributed to the difference in design. In the benchscale reactor design, the STCP is in direct contact with the UV lamp encased in a quartz sleeve. In the small pilot scale reactor, the only di rect UV/STCP contact occurs on the interface of the two sections described earlier (UV section followed by honeycomb section). Although it is known that 254 nm UV will oxidize elemental Hg, clearly the oxidation ability is much lower at 375 76%) t han that observed when incorporating UV plus STCP (greater than 90%). It is expected that a scaled up design with more irradiation of the STCP will result in greater oxidation and removal. Competitive Analysis Table 6 4 includes a summary of characteristi cs and costs of the STCP in comparison two of the most widely accepted technologies for Hg removal from coal fired utility flue gas. Cost estimates, which factor in capital and O&M costs, are based on a ten year cost analysis. Summary A durable and even s ilica titania coating can be obtained by dip coating ceramic chemical tower packing in a 3.5% TiO2, 50% Ludox (in water) solution. This coated packing, termed STCP, is as effective as the previously developed STC in oxidizing and removing Hg from simulate d flue gas, resulting in greater than 90% oxidation and removal in conditions typical of various flue gases from electric utilities. Flue gas components that generally affect performance with other technologies, such as ACI, did not negatively impact the STCPs Hg oxidation and removal efficiency. A 2 second contact time was the optimum determined in this study, which certainly leaves room for optimization.

PAGE 61

61 A major concern of most technologies considered for Hg control in coal fired power plants is t he effect of temperature. The data collected here at 375 promising, particularly because this temperature is in the upper range of temperatures expected in flue gas. A second concern is the fact that sulfur species poison most catalysts and sor bents. The data presented here would indicate that SO2 does not have a negative impact on performance. Table 61. Coating recipes that were attempted during this study Good coating recipes Bad coating recipes STC suspension 1% PEG, 3.5% TiO 2 50% Ludox, sonicated 0.1% TiO 2 water, sonicated 3.5% TiO 2 50% Ludox, 50% water 7% TiO 2 water, sonicated 1% PEG, 3.5% TiO 2 50% Ludox, not sonicated 1% TiO 2 sonicated 7% TiO 2 washed before coating 1% TiO 2 washed 1% PEG, 3.5% TiO 2 water, sonicated 25/75 high surface area TiO 2 water, TiO 2 3.5% TiO 2 100% Ludox 3.5% TiO 2 3.5% Dispal (alumina powder), water 3.5% TiO 2 3.5% Disperal (alumina powder), 50% water, 50% Ludox 1% methylcellulose, 3.5% TiO 2 50% Ludox, 50% water 1% methylcellulose, 3.5% TiO 2 100% water TTIP (titania precursor)/Degussa 0.5M TTIP 0.5M Table 62. Summary of durability test results. Type Starting Mass (g) Post Rotating Mass (g) Mass Loss (g) % Mass Loss Uncoated Ceramic 30.01 30.01 0 0% STC 30.051 29.9884 0.0626 0.21% PEG 30.14 30.07 0.07 0.23% NonPEG 30.02 29.89 0.13 0.43% Table 63. Characteristics of PEG and nonPEG packing. Material Parameter Avg. pore size () Pore volume (cc/g) BET surface area (m 2 /g) PEG 82.4 0.0234 11.4 Non PEG 73.3 0.0204 11.2

PAGE 62

62 Table 64. Competitive analysis of STCP versus two widely accepted commercial technologies for Hg removal from flue gas. Technology Silica Titania Coated Packing Activated Carbon Injection TOXECON Removes Hg YES Only if oxidized Only if oxidized Oxidizes Hg YES Only if halogen (e.g., bromine) present Only if halogen (e.g., bromine) present Unaffected by Sulfur YES NO NO Operation Packed Bed Injection/Removal Injection/Removal Material Life Estimated at 10 yrs Single use Single use Maintains Fly Ash Salability YES NO YES Average Annual Cost ($/year) 3,350 27,000 20,000 Figure 61. Test stand schematic for benchscale studies for evaluation of STCP for Hg removal from simulated flue gas.

PAGE 63

63 Figure 62. Schematic of 4 ACFM pilot scale reactor used for scaled up evaluation of STCP for Hg removal from simulated flue gas. Figure 63. UV transmission through a packed bed of various materials.

PAGE 64

64 Figure 64. SEM imaging of PEG packing (5000X magnification). Figure 65. SEM imaging of non PEG packing (5,000X magnification).

PAGE 65

65 Figure 66. SEM imaging of used packing (5,000X magnification) Figure 67. 375 e, 10 ppb Hg, no added humidity, nonPEG STCP.

PAGE 66

66 Figure 68. 375 non PEG STCP, 100 ppm HCl. Figure 69. 375 non PEG STCP, 100 ppm HCl, 350 ppm SO2.

PAGE 67

67 Figure 610. 375 ative humidity, nonPEG STCP, 100 ppm HCl, 350 ppm SO2, 250 ppm NO2. Figure 611. 375 350 ppm SO2, 250 ppm NO2. Media: 3 mm by 5 mm cylindrical STC pellets (140 pore size, 12% TiO2)

PAGE 68

68 Figure 612. 375 nonPEG STCP, 100 ppm HCl, 350 ppm SO2, 250 ppm NO2. Figure 613. Results of 4 ACFM pilot scale evaluation of nonPEG coated honeycomb at the following conditions: 375 or 200 1.2 s contact time in each of two sections defined earlier, 10 ppb Hg, 4% relative humidity, and 100 ppm HCl.

PAGE 69

69 CHAPTER 7 CONCLUSIONS Mercury oxidation by UV was studied at three UV wavelengths (365 nm, 254 nm and 185 nm) over a range of water vapor concentrations. Oxidation was higher with the 185 nm over the range of temperatures and water vapor concentrations than 254 nm. No mercury oxidation was detectable with the 365 nm bulb in any conditions. While lack of water vapor seemed to inhibit oxidation at the 254 nm wavelength, oxidation increased as water vapor concentration was increased. UV irradiation at 185 nm was steadier over the range of water vapor concentrations tested. As water vapor concentration was further increased, mercury oxidation seemed to be slightly inhibited under most test conditions. Based on its ability to oxidize mercury under conditions with a limited amount of water vapor present t his method is capable of removing mercury in conjunction with a capturing mechanism, such as a wet FGD scrubber under certain conditions The STCP material built on the STC technology to optimize pressure drop across the treatment system of a coal combustion flue gas. Chemical tower packing material was coated with a silicatitania suspension Removal rates of 85% were achieved under benchscale conditions simulating coal combustion flue gas. Temperature did not have a significant effect on removal performance under simulat ed flue gas conditions. At 375F water vapor had a negative effect on mercury removal. By introducing chlorine into the air stream, mercury removal performance improved to levels appr oximately equal to those at 275F Overall, the technology is promising, but performance might be susceptible to fluctuations in chlorine levels in the flue gas. It is also promising that performance at 375F under simulated flue gas conditions is still

PAGE 70

70 high, as that temperature is in the upper range of temperatures expected in flue gas. Finally, t he data presented here indicates that SO2 does not have a negative impact on performance, which is a drawback of other technologies employing catalysts Air phase VOC removal using STC pellets under UV irradiation was s tudied for application in aircraft cabin air purification. Pellets were smaller than in previous work involving STC in order to increase surface area of the STC material. The effectiveness of the STC technology for removal of VOCs for application in airc raft cabin air purification was successfully demonstrated, as it was able to effectively remove toluene and ethanol via adsorption alone. Regeneration with 254 nm UV plus sweep air was proven effective for aver age flight lengths (i.e., 4 hours ). When usi ng ethanol as the target pollutant, regeneration with 254 nm UV plus sweep air was proven effective for long haul flights, which indicates it would also be effective for shorter flights. The STC t echnology overcomes the limitations of typical PCO systems ( constant irradiation, poor mass transfer) The high surface area adsorbent also allows for the preferred operation of adsorption during flight and regeneration between flights. This mode of operation would not only achieve high levels of contaminant removal, but would also eliminate the possibility of releasing toxic intermediate oxidation by products into the air during flight. The STC/STCP material, both in pellet and coated forms, was successfully applied to both organic and inorganic pollutant control under various conditions. For application in both coal combustion flue gas mercury removal and aircraft cabin air purification, the fundamental silicatitania photocatalytic technology was adapted to fit the environmental conditions and shown to be technologically feasible.

PAGE 71

71 Recommendations for future w ork are listed below : Further investigation of water vapor interaction with STCP surface. Characterization of used STCP with environmental SEM. Further development of the STC technology for application in VO C treatment using a larger reactor and LED UV for improved energy efficiency. This work has made the following contributions to s cience: First to study oxidation of elemental mercury by UV alone at wavelengths of 254 nm and 185 nm at various temperatures and moisture levels. Developed STCP material as an improvement on the limitations of STC in pellet form, in particular the issue of pressure drop. Characterization of STCP material by XRD, SEM and nitrogen adsorption isotherm. Demonstrated the efficacy of the STCP material under benchscale and pilot scale simulated flue gas conditions at higher temperatures than in previous research. Demonstrated removal of VOCs (specifically toluene and ethanol) by STC pellets under UV irradiation.

PAGE 72

72 APPENDIX VOC REMOVAL BY STC PELLET S Volatile organic compounds (VOCs) are among the most abundant chemical compounds in indoor air, including aircraft cabin air, and may negatively impact human health. In fact, negative health effects experienced by pilots and flight c rews have led to numerous studies on what is termed aerotoxic syndrome (87) Symptoms of aerotoxic syndrome include headache, eye and nose irritation, cough, shortness of breath, chest tightness, increased heart rate, light headedness, dizziness, blurre d or tunnel vision, disorientation, confusion, memory impairment, shaking and tremors, loss of balance, vertigo, nausea, vomiting, seizures, and loss of consciousness. The airline and its support industry have been focused on the development of solutions that are more effective than traditional activated carbon filters, which must be replaced regularly when they reach their adsorption capacity. One promising solution is photocatalytic oxidation (PCO), which results in the chemical destruction of VOCs, but the concerns surrounding intermediate by products from incomplete oxidation have prevented this tec hnology from being implemented (88) A high surface area sorbent and photocatalyst, STC is used in this study which has been previously evaluated for remo val of VOCs and hazardous air pollutants (HAPs) from gases emi tted from pulp and paper mills (50, 89, 90), removal of synthetic organic compounds from gray water (91 93), mercury remova l from flue gas (19, 25, 80), mercury removal from caustic exhaust at c hlor alkali facilities (51), and pathogen deactivation (94) Due to the unique characteristics of the STC, the technology can be used to adsorb VOCs during flight (without UV), with regeneration (UV irradiation for destruction of sorbed VOCs) on the tarma c while the aircraft is prepared for its next voyage. A small volume of recirculated

PAGE 73

73 sweep air may assist with regeneration, followed by exhausting to the atmosphere. In this manner, passengers and flight crews would be protected during flight, and if pr oblematic intermediates are developed during regeneration, they can be vented to the atmosphere or to an onthe tarmac adsorbent bed. Complete "mineralization" of adsorbed VOCs to water and carbon dioxide during regeneration is the desired goal, to avoid any venting of VOCs. Although initial research presented here has focused on the development of the STC for aircraft cabin air purification, the technology can be extended for use in air revitalization and odor control in space exploration vehicles and ar chitectures. Additionally, a PCO system as described herein could contribute to the design of heating ventilation and air conditioning (HVAC) systems with lower energy requirements, resulting in significant energy savings. I n addition to improved air quality onboard aircraft, an improvement in fuel economy can be realized from removing VOCs via the proposed methodology. Aircraft engines are not just used to propel the plane. Because engines have a source of compressed air for fuel combustion, this is a convenient source for providing compressed air to the cabin. Thus, air is bled from the engines upstream of the combustion chamber to supply the cabin air conditioning system. This bleed air, which is not filtered, may become contaminated with hydraulic oils prior to reaching the cabin. Additionally, since taking this bleed air from the engine reduces the engines thrust capacity, it results in lower fuel efficiency. Some aircraft and engine manufacturers reduce the bleed air requirement by recirculating 50% of the cabin air, which results in an annual savings of about $60,000 per aircraft (95). Recirculated air is typically filtered. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) requires the use of HEPA

PAGE 74

74 filters f or recirculated air (96) HEPA filters will remove 99.97% of 0.3 m (or larger) particles, which includes some bacteria and viruses. Additionally, sorbent filters (e.g., activated carbon) are sometimes used for VOC and odor control. Because of their typ ically low adsorption capacity, these filters become ineffective quite rapidly, thus needing regular replacement even before manufacturer defined intervals (i.e., they reach 100% capacity at five to six months, and become ineffective before then). Better purification methodologies for recirculated air will reduce the need for bleed air, improving fuel economy even further. Technologies also capable of removing potential pollutants from engine bleed air would further increase air quality and reduce the con cerns of aerotoxic syndrome. Experimental Adsorption Adsorption experiments were carried out in glass flow through reactors with the setups shown in Figures A 1 and A 2. Figure A 1 shows the experimental setup for toluene adsorption runs. Figure A 2 shows the experimental setup for ethanol adsorption runs. The operation of both setups was similar. The contaminant laden air was mixed in line with air from a compressed cylinder to achieve the desired contaminant concentration. A bypass allowed for inf luent samples to be collected. The air then passed through the reactor, where the contaminants were adsorbed onto the STC material, after which effluent samples were collected. Toluene was analyzed via GC/MS with sample collection using a syringe with compound specific fiber. Ethanol was analyzed via GC/FID with sample collection using NCASIs Chill ed Impinger Method (97)

PAGE 75

75 The following parameters were varied: STC particle size Contact time Face velocity Influent VOC concentration Regeneration method Ra tio of adsorption duration to regeneration duration For adsorption studies, STC with a 30 pore size and 4% TiO2 loading were packed in a glass reactor. Contact time was varied by varying the volume of STC added to the reactor The use of reactors with different cross sectional areas resulted in variation in face velocity. Regeneration The STC material was regenerated by passing sweep air through the reactor while irradiating with 254 nm UV. The experimental setup can be seen in Figure A 3. Regenerati on times between 30 minutes and 2 hours were investigated. Results Adsorption Studies An experiment was run with 0.25 ppmv toluene, using 0.6 mm by 1.4 mm STC and a 0.1 s contact time at a 72 ft/min face velocity. As Figure A 4 indicates, toluene removal was greater than 81% throughout the 20h ou r adsorption period, with greater than 94% removal for at least 18 hours. In conversations with members of the airline industry it was determined that greater than 50% removal for 20 hours was the goal for long haul flights. Typical VOC concentrations in aircraft cabins range from 0.25 to 0.7 ppmv, with ethanol being the most concentrated VOC, which was how the influent VOC concentrations were chosen.

PAGE 76

76 The expected face velocity for a full scale system for this application, based on air flow rate and cross sectional area of currently used carbon filters, is 200 ft/min. Thus the impact of increasing the face velocity to 176 ft/min (as close to 200 ft/min as possible based on benchscale reactor dimensions) was studied and results are plotted in Figure A 5. The influent toluene concentration was 1 ppmv. Removal was greater than 93% for over eight hours and greater than 70% for 20 hours. Regeneration of S TC Figure A 6 shows the results of 4hour adsorption of toluene with an influent concentration of 0.75 ppmv, followed by 1hour regeneration with 254 nm UV and vented room temperature sweep air, followed by post regeneration 4hour adsorption of 0.75 ppmv t oluene. Adsorption performance was very similar between regenerated and virgin (i.e., unused) pellets. The final data point with virgin pellets cannot be seen in the graph because it is identical to that with regenerated pellets (i.e., 97.1%). Ethan ol is the most predominant organic pollutant in aircraft cabin air, particularly during food and beverage service. It was expected that if high removal of toluene were obtained during this study, high removal of ethanol would also be obtained. In order t o verify this, an experiment was carried out consisting of 20hour adsorption of 1 ppmv ethanol, followed by 2hour regeneration with 254 nm UV plus vented room temperature sweep air, followed by 20hour post regeneration adsorption of 1 ppmv ethanol. Res ults, which are summarized in Figure A 7, indicate that ethanol adsorption with virgin and regenerated pellets was greater than 93% for 20 hours. Additionally, there was only a slight deterioration in performance when comparing virgin and regenerated pell ets.

PAGE 77

77 Because a slight deterioration in performance was observed in several of the regeneration experiments with toluene, an experiment was carried out consisting of multiple cycles of adsorption followed by regeneration with 254 nm UV plus vented room temperature s weep air. A concentration of 0. 34 ppmv t oluene was used, with each adsorption cycle lasting two hours and each regeneration cycle lasting 30 minutes, plus a final regeneration period lasting four hours. As Figure A 8 indicates, there was some det erioration in performance as additional regeneration cycles progressed, although a final 4hour regeneration restored most of the STCs adsorption capacity. It should be noted that toluene is more challenging to adsorb and oxidize than other VOCs that are more predominant in aircraft cabins. Thus, although it is apparent that there may be some accumulation of toluene remaining on the STC at the end of each regeneration cycle, the more easily destructible VOCs, such as ethanol, which is abundant in aircraf t cabins, were expected to be fully oxidized to CO2 and water. Figure A 8, along with the superior data for ethanol (Figure A 7), which makes up about 85% of total VOC concentration in aircraft cabins, lead one to expect the STC technology to retain its high performance even after multiple regenerations in a real world scenario. Summary The effectiveness of the STC technology for removal of VOCs for application in aircraft cabin air purification was successfully demonstrated. It was determined that the ST C can effectively remove toluene and ethanol via adsorption alone. Regeneration with 254 nm UV plus sweep air was proven effective for average flight lengths (i.e., 4 hours ). When using ethanol as the target pollutant, regeneration with 254 nm UV plus

PAGE 78

78 sw eep air was proven effective for long haul flights, which indicates it would also be effective for shorter flights. Commercial systems employing photocatalysis for the removal of gas phase contaminants have limitations (88) Typical photocatalytic systems employ a thin film of titania (98, 99) which can be easily damaged and results in poor mass transfer of the pollutants to the catalyst. In addition, photocatalytic systems typically require constant UV irradiation, and may lead to incomplete oxidation of organic compounds, which is a major concern for aircraft cabin air purification. The STC technology overcomes these limitations of typical PCO systems. Not only is the catalyst trapped within a silica matrix rather than coated, but the high surf ace area adsorbent also allows for the preferred operation of adsorption during flight and regeneration between flights. This mode of operation would not only achieve high levels of contaminant removal, but would also eliminate the possibility of releasing toxic intermediate oxidation by products into the air during flight.

PAGE 79

79 Figure A 1. Experimental setup for toluene adsorption. Figure A 2. Experimental setup for ethanol adsorption.

PAGE 80

80 Figure A 3. Experimental setup for regeneration. Figure A 4. Toluene adsorption at 72 ft/min face velocity.

PAGE 81

81 Figure A 5. Toluene adsorption at 176 ft/min face velocity. Figure A 6. Toluene adsorption by virgin and regenerated STC pellets. Note that the virgin and regenerated pellets remove the same per centage of toluene at the last data point.

PAGE 82

82 Figure A 7. Ethanol removal before and after regeneration with sweep air. Figure A 8. Toluene removal after several regenerations with sweep air.

PAGE 83

83 LIST OF REFERENCES (1) H ankey, R.; Cassar, C.; Peterson, R.; Ha rris Russel, C.; Knaub Jr., J Electric Power Monthly 2011, March. Washington, D.C.: U.S. Energy Information Administration. (2) Pai, P.; Niemi, D.; Powers, B. A North American inventory of anthropogenic merc ury emissions Fuel Processing Technology. 2000, 6566, 101 115. (3) Pacyna, E. G.; Pacyna, J. M.; Steenhuisen, F.; Wilson, S. Global anthropogenic mercury emission inventory for 2000. Atmospheric Environment. 2006, 40, 4048 4063. (4) USEPA Nitrogen Dioxide Primary Standards 2011. http://www.epa.gov/ttn/ naaqs/standards/nox/s_nox_index.html. (5) USEPA Sulfur Dioxide Primary National Ambient Air Quality Standards 2011. http://www.epa.gov/ttn/naaqs/standards/so2/s_so2_index.html (6) S.1630 Clean Air Act Ammendments of 1990 Washington, D.C. 1990. (7) Study of Hazardous Air Pollutant Emisions From Electric Utility Steam Generating U nits Final Report to Congress Washington, D.C.: U.S. Government Printing Office. 1998. (8) Keating, M. H.; Bea uregard, D.; Benjey, W. G.; Driver, L.; Maxwell, W. H.; Peters, W. D. Mercury study r eport to congress V olume 2: An inventory of anthropogenic mercury emissions in the United S tates. 1997. EPA452/R 97004 (9) Wiatrowski, K EPA tightening mercury emissions rules 30 May, 2011. http://www2.Tbo.c om/news/news/2011/may/30/menewso6epa tighteningmercury emissions rules ar 233662/ (10) Power, S. EPA rule targets mercury pollution. March 17, 2011. http://online.wsj.com/article/SB100014240527487038997045762045838161328 32.html (11) Slemr, F.; Schuster, G.; Seiler, W. Distribution, speciation, and budget of atmospheric mercury. Journal of atmospheric chemistry. 1985, 3, 407434. (12) Lindqvist, O.; Rodhe, H. Atmospheric mercury a review. Tellus B. 1985, 37, 136159. (13) Wang, Q.; Shen, W.; Ma, Z. Estimation of Mercury Emission from Coal Combustion in China. Environmental Science & Technology. 2000, 34, 27112713.

PAGE 84

84 (14) Managing Coal Combustion Residues in Mines. Washington, D.C., The N ational Academics Press, 2006. (15) Scala, F. Simulation of mercury capture by activated carbon injection in incinerator flue gas. In duct removal. Environmental Science & Technology. 2001, 35, 4367 4372. (16) Jones, A. P.; Hoffmann, J. W.; Smith, D. N .; Feeley, T. J.; Murphy, J. T. DOE/NETL's phase II mercury control technology field testing program: Preliminary economic analysis of activated carbon injection. Environmental Science & Technology. 2007, 41, 13651371. (17) Huggins, F. E.; Yap, N.; Huffman, G. P.; Senior, C. L. XAFS characterization of mercury captured from combustion gases on sorbents at low temperatures. Fuel Processing Technology. 2003, 82, 167196. (18) Mercury Study Report to Congress Volume 5: Health Effects o f Mercury and Mercury Compounds Mercury study report to congress volume 5: Health effects of mercury and mercury compounds. 1997. (19) Pitoniak, E. Evaluation of nanostructured silicatitania composites in an adsorption/photocatalytic oxidation system for elemental mercury vapor control. Master of Engineering Thesis, University of Florida. 2004 (20) Li, Y.; Murphy, P.; Wu, C. Y. Removal of elemental mercury from simulated coal combustion flue gas using a SiO2TiO2 nanocomposite. Fuel Processing Technology. 2008, 89, 56757 3. (21) Robertson, P.; Bahnemann, D.; Robertson, J.; Wood, F. Photocatalytic detoxification of water and air. Environmental Photochemistry. 2005, 2, 367423. (22) Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W.Environmental applications of s emiconductor photocatalysis. Chemical Reviews. 1995, 95, 6996. (23) Al Ekabi, H.; Serpone, N. Kinetic Studies In Heterogeneous Photocatalysis. Photocatalytic Degradation of Chlorinated Phenols In Aerated Aqueous Solutions Over TiO2 Supported On A Glass Matrix. Journal of Physical Chemistry. 1988, 92, 57265731. (24) Wu, C. Y.; Lee, T. G.; Tyree, G.; Arar, E.; Biswas, P. Capture of Mercury in Combustion Systems by In Situ--Generated Titania Particles with UV Irradiation. Environmental Engineering Science. 1998, 15, 137 148. (25) Pitoniak, E.; Wu, C. Y.; Londeree, D.; Mazyck, D.; Bonzongo, J. C.; Powers, K.; Sigmund, W. Nanostructured silicagel doped with TiO2 for mercury vapor control. Journal of Nanoparticle Research. 2003, 5, 281 292.

PAGE 85

85 (26) Hall, B.; Schager, P.; Lindqvist, O. Chemical reactions of mercury in combustion flue gases. Water and Soil Pollution. 1991, 56, 3 14. (27) 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 Processing Technology. 2000, 6566, 423438. (28) Lindberg, S. E.; Stratton, W. J. Atmospheric mercury speciation: Concentrations and behavior of reactive gaseous mercury in ambient air. Environmental Science & Technology. 1998, 32, 49 57. (29) Cao, Y.; Chen, B.; Wu, J.; Cui, H.; Smith, J.; Chen, C.; Chu, P.; Pan, W. Study of Mercury Oxidation by a Selective Catalytic Reduction Catalyst in a Pilot Scale Slipstream Reactor at a Utility Boiler Burning Bituminous Coal. Energy & Fuels. 2007, 21, 145156. (30) Galbreath, K. C.; Zygarlicke, C. J. Mercury speciation in coal combustion and gasification flue gases. Environmental Science & Technology. 1996, 30, 24212426. (31) Kilgroe J. D.; Sedman, C. B. ; Srivastava, R. K. ; Ryan, J. V .; Lee, C. W.; Thornloe, S. A. Control of H g emissions from coal fired electric utility boilers: Interim report. 1997. EPA 600/R 01109 (32) Lee, S. J.; Seo, Y.; Jang, H.; Park, K.; Baek, J.; An, H.; So ng, K. Speciation and mass distribution of mercury in a bituminous coal fired power plant. Atmospheric Environment. 2006, 40, 2215 2224. (33) Niksa, S.; Fujiwara, N. Predicting extents of mercury oxidation in coal derived flue gases. Journal of the Air and Waste Management Association. 2005, 55, 930 939. (34) Clever, H. L.; Johnson, S. A.; Derrick, M. E. The solubility of mercury and some sparingly soluble mercury salts in water and aqueous electrolyte solutions. Journal of Physical and Chemical Reference Data. 1985, 14, 631. (35) Edwards, J. R.; Srivastava, R. K.; Kilgroe, J. D. A study of gas phase mercury speciation using detailed chemical kinetics. Journal of the Air & Waste Management Association. 2001, 51, 869877. (36) Fujiwara, N.; Fujita, Y. ; Tomura, K.; Moritomi, H.; Tuji, T.; Takasu, S.; Niksa, S. Mercury transformations in the exhausts from labscale coal flames. Fuel. 2002, 81, 20452052.

PAGE 86

86 (37) Meij, R.; Vredenbregt, L. H. J.; Winkel, H. T. The fate and behavior of mercury in coal fired power plants. Journal of the Air & Waste Management Association. 2002, 52, 912917. (38) Niksa, S.; Fujiwara, N. A predictive mechanism for mercury oxidation on selective catalytic reduction catalysts under coal derived flue gas. Journal of the Air and Waste Management Association. 2005, 55, 18661875. (39) Sable, S. P.; de Jong, W.; Spliethoff, H. Combined Homoand Heterogeneous Model for Mercury Speciation i n Pulverized Fuel Combustion Flue Gases. Energy & Fuels. 2008, 22, 321 330. (40) Senior, C. L.; Sarofim, A. F.; Zeng, T. F.; Helble, J. J.; Mamani Paco, R. Gas phase transformations of mercury in coal fired power plants. Fuel Processing Technology. 2000, 63, 197213. (41) Pavlish, J. H.; Sondreal, E. A.; Mann, M. D.; Olson, E. S.; Galbreath, K. C.; Laudal, D. L.; Benson, S. A Status review of mercury control options for coal fired power plants. Fuel Processing Technology. 2003, 82, 89 165. (42) Ghoris hi, S. B.; Sedman, C. B. Low concentration mercury sorption mechanisms and control by calcium based sorbents: Application in coal fired processes. Journal of the Air & Waste Management Association. 1998, 48, 1191 1198. (43) Zhao, Y. X.; Mann, M. D.; Olso n, E. S.; Pavlish, J. H.; Dunham, G. E. Effects of sulfur dioxide and nitric oxide on mercury oxidation and reduction under homogeneous conditions. Journal of the Air and Waste Management Association. 2006, 56, 628635. (44) Heebink, L. V.; Hassett, D. J Release of mercury vapor from coal combustion ash. Journsl of the Air and Waste Management Associstion. 2002, 52, 927930. (45) Hrdlicka, J. A.; Seames, W. S.; Mann, M. D.; Muggli, D. S.; Horabik, C. A. Mercury Oxidation in Flue Gas Using Gold and Palladium Catalysts on Fabric Filters. Environmental Science & Technology. 2008, 42, 66776682. (46) Presto, A. A.; Granite, E. J. Nob le Metal Catalysts for Mercury Oxidation in Utility Flue Gas: Gold, Palladium and Platinum Formulations. Platinum Metals Review. 2008, 52, 144154. (47) Jadhav, R .A.; Meyer, H. S.; Winecki, S.; Breault, R. W. Evaluation of nanocrystalline sorbents for m ercury removal from coal gasifier fuel gas. In The 2005 Annual Meeting. AIChE.. Cincinnati, OH. 2005.

PAGE 87

87 (48) Benson, S. A.; Laumb, J. D.; Crocker, C. R.; Pavlish, J. H. SCR catalyst performance in flue gases derived from subbituminous and lignite coals. Fu el Processing Technology. 2005, 86, 577613. (49) Cao, Y.; Duan, Y.; Kellie, S.; Li, L.; Xu, W.; Riley, J. T.; Pan, W. P.; Chu, P.; Mehta, A. K.; Carty, R. Impact of coal chlorine on mercury speciation and emission from a 100 MW utility boiler with cold side electrostatic precipitators and low NOx burners. Energy and Fuels. 2005, 19, 842 854. (50) Stokke, J. M.; Mazyck, D. W.; Wu, C. Y.; Sheahan, R. Photocatalytic oxidation of methanol using silicatitania composites in a packedbed reactor. Environment al Progress. 2006, 25, 312318. (51) Stokke, J. M.; Mazyck, D. W. Development of a regenerable system employing silica titania composites for the recovery of mercury from endbox exhaust at a chlor alkali facility. Journal of the Air and Waste Management Association. 2008, 58, 530537. (52) Gruss, A. F.; Casass, A. I.; Mazyck, D. W. VOC removal by novel regenerable silica titania sorbent and photocatalytic technology. In Proceedings from the 39th International Con ference on Environmental Systems. Savannah, Georgia. July, 2009. (53) Londere, D. J. Silicatitania composites for water treatment. Master of Engineering Thesis, University of Florida. 2002. (54) Powers, K. W. The development and characterization of s ol gel substrates for chemical and optical applications. PhD Dissertation, University of Florida. 1998. (55) Li, Y.; Lee, S. R.; Wu, C. Y. UV AbsorptionBased Measurements of Ozone and Mercury: An Investigation on Their Mutual Interferences. Aerosol and Air Quality Research. 2006, 6, 418429. (56) Li, Y.; Wu, C. Y. Kinetic study for photocatalytic oxidation of elemental mercury on a SiO2TiO2 nanocomposite. Environmental Engineering Science. 2007, 24, 312. (57) Dickinson, R. G.; Sherrill, M. S. Forma tion of ozone by optically excited mercury vapor. Proceedings of the National Academy of Sciences of the United States of America. 1926, 12, 175 178. (58) Granite, E. J.; Pennline, H. W. Photochemical removal of mercury from flue gas. Industrial & Engineering Chemistry Research. 2002, 41, 54705476. (59) Jia, L.; Dureau, R.; Ko, V.; Anthony, E. J. Oxidation of Mercury under Ultraviolet (UV) Irradiation. Energy & Fuels. 2010, 24, 43514356.

PAGE 88

88 (60) Lee, T. G.; Biswas, P.; Hedrick, E. Overall kinetics of h eterogeneous elemental mercury reactions on TiO2 sorbent particles with UV irradiation. Industrial & Engineering Chemistry Research. 2004, 43, 14111417. (61) Perry, R. H.; Green, D. W.; Maloney, J. O. Perry's Chemical Engineers' Handbook New York, McGraw Hill, 1984. (62) Lide, D. R. CRC Handbook of Chemistry and Physics, 20002001: A Ready Reference Book of Chemical and Physical Data. CRC press, 2000. (63) Dasent, W. E. Inorganic Energetics: An introduction. New York, Cambridge University Press, 198 2. (64) Cauch, B.; Silcox, G. D.; Lighty, J. S.; Wendt, J. O. L.; Fry, A.; Senior, C. L. Confounding Effects of Aqueous Phase Impinger Chemistry on Apparent Oxidation of Mercury in Flue Gases. Environ Sci. Technol. 2008, (65) Byun, Y.; Ko, K. B.; Cho, M.; Namkung, W.; Shin, D. N.; Lee, J. W.; Koh, D. J.; Kim, K. T. Oxidation of elemental mercury using atmospheric pressure nonthermal plasma. Chemosphere. 2008, 72, 652 658. (66) Ko, K. B.; Byun, Y.; Cho, M.; Namkung, W.; Hamil ton, I. P.; Shin, D. N.; Koh, D. J.; Kim, K. T. Pulsed corona discharge for oxidation of gaseous elemental mercury. Applied Physics Letters. 2008, 92, 251503251503. (67) Hall, B. The gas phase oxidation of elemental mercury by ozone. Water, Air, & Soil Pollution. 1995, 80, 301 315. (68) Fujishima, A.; Rao, T. N.; Tryk, D. A. Titanium dioxide photocatalysis. Journal of Photochemistry and Photobiology C: Photochemistry Reviews. 2000, 1, 1 21. (69) Lukes, P.; Appleton, A. T.; Locke, B. R. Hydrogen perox ide and ozone formation in hybrid gas liquid electrical discharge reactors. IEEE Transactions on Industry Applications. 2004, 40, 6067. (70) Caren, R. P.; Ekchian, J. A. Method for Using Hydroxyl Radical to Reduce Pollutants in the Exhaust Gases from th e Combustion of a Fuel. U.S. Patent 5,863,413, Jan 26, 1999. (71) Zhang, H.; Lindberg, S. E. Sunlight and iron (III) induced photochemical production of dissolved gaseous mercury in freshwater. Environmental Science & Technology. 2001, 35, 928935. (72) Grosjean, D.; Harrison, J. Response of chemiluminescence NOx analyzers and ultraviolet ozone analyzers to organic air pollutants. Environmental Science & Technology. 1985, 19, 862865.

PAGE 89

89 (73) Bader, H.; Sturzenegger, V.; Hoigne, J. Photometric method for the determination of low concentrations of hydrogen peroxide by the peroxidase catalyzed oxidation of N, N diethyl p phenylenediamine (DPD). Water Res. 1988, 22, 11091115. (74) Jeon, S. H.; Eom, Y.; Lee, T. G. Photocatalytic oxidation of gas phase elem ental mercury by nanotitanosilicate fibers. Chemosphere. 2008, 71, 969 974. (75) Li, J.; Yan, N.; Qu, Z.; Qiao, S.; Yang, S.; Guo, Y.; Liu, P.; Jia, J. Catalytic Oxidation of Elemental Mercury over the Modified Catalyst Mn/ Al2O3 at Lower Temperatures. Environmental Science & Technology. 2010, 44, 426 431. (76) Norton, G. A.; Yang, H.; Brown, R. C.; Laudal, D. L.; Dunham, G. E.; Erjavec, J. Heterogeneous oxidation of mercury in simulated post combustion conditions. Fuel. 2003, 82, 107 116. (77) Takahashi, K.; Kasahara, M.; Itoh, M. A kinetic model of sulfuric acid aerosol formation from photochemical oxidation of sulfur dioxide vapor. Journal of Aerosol Science. 1975, 6, 4555. (78) Byun, Y.; Cho, M.; Namkung, W.; Lee, K.; Koh, D. J.; Shin, D. N. Insight into the Unique Oxidation Chemistry of Elemental Mercury by ChlorineContaining Species: Experiment and Simulation. Environmental Science & Technology. 2010, 44, 16241629. (79) Och iai, R.; Uddin, M. A.; Sasaoka, E.; Wu, S. Effects of HCl and SO2 Concentration on Mercury Removal by Activated Carbon Sorbents in Coal Derived Flue Gas. Energy & Fuels. 2009, 23, 47344739. (80) Pitoniak, E.; Wu, C. Y.; Mazyck, D. W.; Powers, K. W.; Sig mund, W. Adsorption enhancement mechanisms of silicatitania nanocomposites for elemental mercury vapor removal. Environmental Science & Technology. 2005, 39, 12691274. (81) McDowell, M. A.; Dillon, C. F.; Osterloh, J.; Bolger, P. M.; Pellizzari, E.; Fe rnando, R.; de Oca, R. M.; Schober, S. E.; Sinks, T.; Jones, R. L.; Mahaffey, K. R. Hair mercury levels in US children and women of childbearing age: Reference range data from NHANES 19992000. Environmental Health Perspectives. 2004, 112, 11651171. (82) Cheuk, D. K. L.; Wong, V. Attention deficit hyperactivity disorder and blood mercury level: a casecontrol study in Chinese children. Neuropediatrics. 2006, 37, 234240. (83) USDOE Mercury Emission Control R&D. 2005. http://www.fossil.energy.gov/progr ams/powersystems/pollutioncontrols/overview_ mercurycontrols.html

PAGE 90

90 (84) CATM Annual Report: Toxic Metal Transformation in Fossil Fuel Combustion Systems. 2008 www.undeerc.org/catm/pdf/area1/2008ToxicMetalTransformations.pdf (85) Mercury Control Plan for Sherco Units 1 & 2 Pursuant to the Minnesota Mercury Emission Reduction Act of 2006. 2009. (86) Li, Y.; Daukoru, M.; Suriyawong, A.; Biswas, P. Mercury Emissions Control in Coal Combustion Systems Using Potassium Iodide: BenchScale and Pilot Scale Stud ies. Energy & Fuels. 2009, 23, 236243. (87) Winder, C.; Balouet, J. C. The toxicity of commercial jet oils. Environmental Research. 2002, 89, 146164. (88) Devilliers, D. Semiconductor photocatalysis: still an active research area despite barriers to commercialization. Energeia. 2006, 17, 13. (89) Stokke, J. M.; Mazyck, D. W. Effect of Catalyst Support on the Photocatalytic Destruction of VOCs in a PackedBed Reactor. 2007, (90) Stokke, J. M.; Mazyck, D. W. Photocatalytic Degradation of Methanol Using Silica Titania Composite Pellets: Effect of Pore Size on Mass Transfer and Reaction Kinetics. Environmental Science & Technology. 2008, 42, 38083813. (91) Termaath, C.; Holmes, F.; Drwiega, J.; Londeree, D.; Mazyck, D.; Powers, K.; Chadik, P.; Wu C. Comparison of nanoparticles for the photocatalytic destruction of organic pollutants for water recovery. In 33rd International Conference on Environmental Systems 2003, 2003012334, Vancouver, BC.. 2003. (92) Holmes, F. R.; Chadik, P. A.; Mazyck, D. W.; Wu, C. Y.; Garton, M. J.; Powers, K. W.; Londeree, D. J. Photocatalytic oxidation of selected organic contaminants in a continuous flow reactor packed with titaniadoped silica. In 34th International Conference on Environmental Systems. Colorado Springs, CO, USA. 2004. (93) Ludwig, C. Y.; Byrne, H. E.; Stokke, J. M.; Chadik, P. A.; Mazyck, D. W. Performance of SilicaTitania Carbon Composites for Photocatalytic Degradation of Gray Water. Journal of Environmental Engineering. 2011, 137, 38. (94) Garton, M. J.; Chadi k, P. A.; Mazyck, D. W Photocatalytic oxidation of selected organic contaminants and inactivation of microorganisms in a continuous flow reactor packed with titaniadoped silica Master of Engineeri ng Thesis. University of Florida. 2005. (95) Michaelis, S.; Loraine, T. Aircraft Cabin Air Filtration and Related Technologies: Requirements, Present Practice and Prospects. Air Quality in Airplane Cabins and Similar Enclosed Spaces. 2005, 267 289.

PAGE 91

91 (96) ASHRAE STANDARD 161: Air Quality within Commercial Aircraft, American Society of Heating, Refrigerating and Air Conditioning Engineers. 2007. (97) NCASI Chilled Impinger Test Method for Use on Pulp Mill Sources to Quantify Met hanol Emissions. Nation al Council for Air and Stream Improvement. Method CI/GS/PULP 94.03. February 2005. (98) Ginestet, A.; Pugnet, D.; Rowley, J.; Bull, K.; Yeomans, H. Development of a new photocatalytic oxidation air filter for aircraft cabin. Indoor Air. 2005, 15, 326 334 (99) Sun, Y.; Fang, L.; Wyon, D. P.; Wisthaler, A.; Lagercrantz, L.; Strm Tejsen, P. Experimental research on photocatalytic oxidation air purification technology applied to aircraft cabins. Building and Environment. 2008, 43, 258268.

PAGE 92

92 BIOGRAP HICAL SKETCH Alexander Ferdinand Gruss was born in Filderstadt, Germany in September of 1982. He attended the Swiss Federal Institute of Technology from October 2002 until October 2004, receiving the equivalent of an associates degree in Civil Engineering. After transferring to the University of Florida in 2005, he graduated Magna cum Laude with a B.S. in Civil Engineering in May of 2007. During his last semester, he began working on air phase mercury removal using a novel photocatalytic silicatitania composite material. He continued this work in graduate school under the guidance of Dr. David Mazyck and received his Ph.D. from the University of Florida in the summer of 2011.