July 2008 1 

### An Update on DOE/NETL’s Mercury Control Technology Field Testing Program

Thomas J. Feeley, III 1 and Andrew P. Jones 2

1 U.S. Department of Energy, Na tional Energy Technology Laboratory

2 Science Applications International Corporation

The U.S. Department of Energy’s National Energy Technology Laboratory (NETL), under the Office of Fossil Energy’s Innova tions for Existing Plants (IEP) Program,manages the premier mercury (Hg) research and development (R&D) program for coalfired power generation facilities in the wo rld. Working collaboratively with the U.S. Environmental Protection Agency (EPA), the Electric Power Research Institute (EPRI), power plant operators, state and local agenc ies, and a host of re search organizations and academic institutions, the IEP Program has identified the major factors that affect Hg speciation and capture in coal combustion flue gas and funneled this knowledge into the development of a suite of Hg-specific cont rol technologies for the diverse fleet of U.S. coal-fired power plants. The high performan ce observed during many of these field tests has given coal-fired power plant operators the confidence to begin deploying technology. As of April 2008, over 44 gigawatts (GW) of coal-based electric generating capacity have placed orders for full-scale activa ted carbon injection (ACI) systems.



### BACKGROUND

Since first being identified for potential regulation in the 1990 Clean Air Act Amendments, there has been concern within the industry whether it would be possible to develop cost-effective emission control technologies for Hg because of its low concentration and reactivity during coal co mbustion. However, while technical issuesremain, the U.S. Department of Energy’s NETL has been successful, through publicprivate partnerships, in significantly impr oving both the cost and performance of Hg control technology.

NETL initiated comprehensive Hg research under the Office of Fossil Energy’s IEP Program in the early 1990s to ensure that cost-effective and reliable pollution control technologies are available for the existi ng fleet of coal-fir ed utility boilers. 1 To comprehensively address the life-cycle of Hg released during coal combustion, NETL has directed over $80 million in Federal fundi ng over the last decade toward external (extramural) and in-house res earch projects focusing on six inter-related research areas (see Figure 1):

• Emissions characterization;

• Development and testing of total a nd speciated measurement devices;

• Speciation research;

• Development and testing of control technologies;July 2008 2 • Coal utilization by-products (CUB) characterization; and

• Fate and transport of emissions.

Figure 1 – Overview of Hg R&D Co nducted under NETL’s IEP Program

Emissions characterization performed by NETL and others in the early 1990s showed that Hg was not effectively captured across existing air pollution c ontrol device (APCD) configurations. Further conclu sions were limited by the lack of a reliable method to measure the different chemical forms of Hg in coal combustion flue gas. To overcome this hurdle, NETL co-funded the development and validation of the Ontario Hydro (OH) method through a Jointly Sponsored Research Program with the University of North Dakota’s Energy and Environmenta l Research Center (UNDEERC).

Analysis of OH method sampling campaigns reveal ed that the tr ace amount of Hg present in coal is volatilized during combustion a nd converted to gaseous elemental mercury (Hg 0 ). Subsequent cooling of the coal combusti on flue gas and interaction of the gaseous Hg 0 with other flue gas constituents, such as chlorine (Cl) and unburned carbon (UBC), result in a portion of the Hg 0 being converted to gaseou s oxidized forms of mercury (Hg 2+ ) and particulate-bound mercury (Hg P ). As a result, coal combustion flue gas contains varying percentages of Hg P , Hg 2+ , and Hg 0 and the exact speciation has a profound effect on the Hg capture efficiency of existing APCD configurations, which has been found to range from 0 to over 90%. 2 The Hg P fraction is typically removed by a particulate control device such as an electrostatic precipitator (ESP) or fabric filter (FF). The Hg 2+ portion is water-soluble and therefore a relatively high per cent can be captured in wet flue gas desulfurization (FGD) systems, while the Hg 0 fraction is generally not captured by existing APCD. DOE/NETL’s Hg R&D

* ORD (In-house R&D) - CUB characterization - Control technology R&D
* Technology transfer
* Economic analyses
* Regulatory analysis Emissions Research

* HAP characterization stack testing

CUB Research

* Fate characterization * Impact of controls

Speciation Research
* OH sampling campaigns

* Co-benefit enhancements Fate & Transport
* Wet deposition monitoring * Stack plume measurements Control Technology R&D
* Bench- & pilot-scale tests

* Full-scale field tests Measurement R&D

* OH method

* SCEMsJuly 2008 3 Insight into the factors that influence Hg sp eciation and capture in coal combustion flue gas allowed NETL to focus its R&D effort s on the most promising technologies for controlling Hg emissions from coal-based power systems. One obvious cost-effective strategy for power plants that ha ve or plan to install FGD w ould be to take advantage of the “co-benefit” capture of Hg. However, wet scrubbers do not achieve 1 00% capture of Hg 2+ , nor as noted above is all the Hg in an oxidized form, even for bituminous coal. Moreover, this approach is not a viable Hg control option for power generation facilities not equipped with FGD systems. As such, NE TL initiated an R&D program in the mid1990s directed at two general approaches fo r controlling Hg -- (1 ) Hg-specific control technology such as sorbent injection and (2) Hg 0 oxidation concepts.

In 2000, following laboratory through pilot- scale development of these technology approaches, NETL launched a three-phase fiel d testing program. This program called for the installation and full-scale and slip-stream testing of the most promising Hg control technologies at operating coal-f ired power plants. The ini tial field testing (Phase I) focused on untreated ACI and improving the capture of Hg across wet FGD systems, while Phase II, which began in 2003, was e xpanded to include testing of chemicallytreated ACI, sorbent (i.e., activated carbon) enhancement additives, and Hg 0 oxidation catalysts. The goal of Phases I and II was to develop Hg control tec hnologies (available for commercial demonstration by year-end 2007 fo r all coal ranks) that could achieve 50 to 70% Hg capture at costs 25 to 50% less than the baseline (1999) estimate of about $60,000 per pound of Hg removed ($/lb Hg remove d). Phase III of the field testing program was initiated in 2006 and directed at continued field testing of advanced Hg control technologies that coul d achieve 90% or greater captu re at a 50 to 75% cost
reduction and that would be available for commercial demonstration by 2010. In addition, the Phase III field testing emphasized the assessment of potentia l balance-of-plant impacts associated with c ontinuously operating a Hg-sp ecific control technology.

This paper focuses on results from the Ph ase II Hg control tec hnology field testing program with the data segr egated by technology. In addi tion, the results of NETL’s economic analysis of Hg control via ACI ar e presented, along with a discussion of potential coal utilization by- product (CUB) impacts. Pre liminary results from NETL’s Phase III Hg field testing program are also presented.



### Field Testing of Advanced Mercury Control Technologies

Building on promising advances from the Ph ase I field testing program, NETL selected eight new full-scale projects in Septembe r 2003 to test and evaluate Hg control technologies under a Phase II, Round 1 (Phase II-1) field testing solicitation. The Phase II-1 projects shown in Table 1 were initiated in 2004 and completed in 2007. An additional six projects – repr esenting seven technologies a - were subsequently awarded in October 2004 under a Phase II, Round 2 (Phase II-2) solicitation that were also

a The seven Phase II-2 Hg control technologies ar e: TOXECONTM, TOXECONTM II, high-temperature Hg sorbents, brominated PAC injection, chemically-treated PAC injecti on via the Mer-CureTM process, wet FGD chemical additives, and an integrated approach to Hg control that includes combustion modifications.July 2008 4 completed in 2007 (Table 2). Total funding for the Phase II program was about $45 million with the various research teams provi ding nearly $13 million in cost sharing.

The Phase II projects focus on longer-term (~ 1 month at optimized conditions), largescale field testing on plants burning primarily low-rank coals or blends (with some units burning bituminous coal) and equipped with a va riety of APCD configurations. Most of the 14 projects fall under two general categorie s of Hg control – so rbent injection or oxidation enhancements. Sorbent injection gene rically describes conventional (untreated) ACI, chemically-treated ACI, or the injection of non-carbon sorb ents into the flue gas for Hg control. Mercury oxidation enhancements are intended to improve the Hg capture efficiency of conventional ACI or downstream APCD by converting Hg 0 to a more reactive oxidized state. For instance, coal or flue gas additives are being investigated both alone, and in conjunction with conventional AC I. Additional Hg control technologies are being tested to enhance Hg capture at coal-f ired units equipped with wet FGD systems.These FGD-related technologies include coal and flue gas chemical additives and fixedbed catalysts to incr ease levels of Hg 2+ in the combustion flue gas, and wet FGD chemical additives to promote Hg capture and prevent re-emission of Hg 0 from the FGD
absorber vessel.July 2008 5 Table 1 -- NETL’s Phase II-1 Field Testing Projects

Project Title Lead Company Test Location Coal Rank APCD Configuration

Sunflower Electric’s

Holcomb Unit 1 PRB SDA/FF

AmerenUE’s Meramec Unit 2 PRB CS-ESP (320 SCA)

Missouri Basin Power Project’s Laramie River Unit 3 PRB SDA & CS-ESP (599 SCA) DTE Energy’s
Monroe Unit 4 PRB/Bit.
Blend SCR & CS-ESP (258 SCA)
American Electric Power’s
Conesville Unit 6 High-Sulfur
Bituminous CS-ESP (301 SCA)
& Wet FGD Evaluation of Sorbent Injection for Mercury

Control ADA-ES

AmerenUE’s Labadie Unit 2 PRB CS-ESP (279 SCA) Southern Company’s

Plant Yates Unit 1 Low-Sulfur
Bituminous CS-ESP (173 SCA)
& Wet FGD Southern Company’s

Plant Yates Unit 2 Low-Sulfur
Bituminous CS-ESP (144 SCA) Sorbent Injection

for Small ESP Mercury Control URS Group

Reliant Energy’s
Shawville Unit 3 Mid-Sulfur
Bituminous Two CS-ESPs (82 & 230 SCA)
Basin Electric’s
Leland Olds Unit 1 ND Lignite CS-ESP (320 SCA)

Great River Energy’s
Stanton Unit 10 ND Lignite SDA/FF

Basin Electric’s Antelope Valley Unit 1 ND Lignite SDA/FF

Great River Energy’s
Stanton Unit 1 PRB CS-ESP (470 SCA) Enhancing

Carbon Reactivity in Mercury Control in Lignite-Fired Systems UNDEERC

Montana-Dakota Utilities Co.
Lewis & Clark Station ND Lignite Mechanical
Collector & Wet
Venturi Scrubber DTE Energy’s
St. Clair Unit 1 PRB/Bit.
Blend CS-ESP (SCA 467) Advanced Utility Mercury Sorbent

Field-Testing

Program Sorbent Technologies Duke Energy’s
Buck Unit 6 Low-Sulfur
Bituminous HS-ESP (240 SCA)

Demonstration

of Amended
Silicates for Mercury Control Amended
Silicates Duke Energy’s
Miami Fort Unit 6 Mid-Sulfur
Bituminous CS-ESP (353 SCA)

Luminant Power’s
Monticello Unit 3 TX Lignite/PRB
blend CS-ESP (452 SCA)
& Wet FGD Pilot Testing of Mercury
Oxidation Catalysts for Upstream of Wet

FGD Systems URS Group Southern Company’s
Plant Yates Unit 1 Low-Sulfur
Bituminous CS-ESP (173 SCA)
& Wet FGD

Great River Energy’s
Stanton Unit 10 ND Lignite SDA/FF Evaluation of
MerCAPTM for

Power Plant Mercury Control URS Group Southern Company’s
Plant Yates Unit 1 Low-Sulfur
Bituminous CS-ESP (173 SCA)
& Wet FGD

Minnkota Power’s Milton R. Young Unit 2 ND Lignite CS-ESP (375 SCA)
& Wet FGD Mercury
Oxidation Upstream of an

ESP and Wet
FGD UNDEERC Luminant Power’s
Monticello Unit 3 TX Lignite/PRB
blend CS-ESP (452 SCA)
& Wet FGDJuly 2008 6 Table 2 -- NETL’s Phase II-2 Field Testing Projects

Project Title Lead Company Test Location Coal Rank APCD Configuration Field Testing of
Activated Carbon Injection Options for

Mercury Control UNDEERC Luminant Power’s Big Brown Unit 2 TX Lignite/PRB
Blend CS-ESP (162 SCA)
& COHPAC ® FF

PacifiCorp’s
Dave Johnston Unit 3 PRB CS-ESP (600 SCA)

Basin Electric’s
Leland Olds Unit 1 ND Lignite CS-ESP (320 SCA) Field Demonstration
of Enhanced Sorbent Injection for Mercury
Control ALSTOMPPL Reliant Energy’s
Portland Unit 1 Mid-Sulfur
Bituminous CS-ESP (284 SCA)

Entergy’s Independence Unit 1 PRB CS-ESP (542 SCA)

MidAmerican’s

Louisa Unit 1 PRB HS-ESP (459 SCA) Low Cost Options for

Moderate Levels of

Mercury Control ADA-ES

MidAmerican’s
Council Bluffs Unit 2 PRB HS-ESP (224 SCA)

Progress Energy’s
Lee Unit 1 Low-Sulfur
Bituminous CS-ESP (300 SCA)

Midwestern
Generation’s
Crawford Unit 7 PRB CS-ESP (112 SCA) Brominated Sorbents
for Small Cold-Side ESPs, Hot-Side ESPs,

and Fly Ash use in
Concrete Sorbent Technologies
Midwestern
Generation’s Will County Unit 3 PRB HS-ESP (233 SCA)

Luminant Power’s
Monticello Unit 3 TX Lignite/PRB
blend CS-ESP (452 SCA)
& Wet FGD Southern Company’s

Plant Yates Unit 1 Low-Sulfur
Bituminous CS-ESP (173 SCA)
& Wet FGD Field Testing of a Wet

FGD Additive for Enhanced Mercury
Control URS Group Indianapolis Power & Light’s Petersburg Unit 2 High-Sulfur
Bituminous CS-ESP (430 SCA)
& Wet FGD

Demonstration of Integrated Approach to Mercury Control GE-EER Progress Energy’s
Lee Unit 3 Low-Sulfur
Bituminous CS-ESP (300 SCA)

The intent of NETL's Phase I and II Hg control technology fi eld testing programs was to work with industry to evaluate the most pr omising Hg control technologies at full-scale in a variety of configurati ons. Although 30-day long-term te sts were conducted in Phase II, the test period was not sufficient to an swer many fundamental questions about longterm consistency of Hg removal and reliability of the system when integrated with plant processes. As the technologies move toward s commercial implementation, it is critical to accurately define the Hg removal performan ce and costs so that power companies and policy makers can make informed decisions. NETL awarded nine new projects in 2006 to conduct Hg control tests at full-scale coal-fir ed units and in the laboratory, under a Phase III Hg control solicitation. Table 3 presents general information about each of the Phase III projects selected by NETL. Total funding fo r the Phase III program was just over $27 million with the various research teams pr oviding nearly $9 million in cost sharing. Building on advances from the Phase I and II mercury projects, Phas e III has four topic

areas.July 2008 7 3⁄4 Topic Area I – Phase III Field Testing of Mercury Control Technology Capable of Achieving 90% or Greater Removal of Mercury 3⁄4 Topic Area II – Additional (Round 3) Phase II Fiel d Testing of Mercury Control Technology Capable of Achievi ng 50-70% Mercury Removal 3⁄4 Topic Area III – Novel Combustion and Post-C ombustion Control Technologies 3⁄4 Topic Area IV – Novel Pre-combustion Control Technology

Table 3 -- NETL’s Phase III Merc ury Control Technology Projects

Project Title Lead Company Test Location Coal Rank APCD Configuration

T T T o

o o p p p i

i i c c c A

A A r

r r e e e a a a I

I I P

P P r

r r o o o

j j j e e e c c c t t t s s s

Demonstration of MerCureTM Technology ALSTOMPPL Lower Colorado River Authority’s Fayette Unit 3 PRB Blends CS-ESP (640 SCA)
& Wet FGD Kansas City Power & Light’s Hawthorne Unit 5 PRB SCR & SDA/FF Long-Term
Demonstration of SEA Technology for Mercury Control UNDEERC E.ON America’s
Mill Creek Unit 4 High-Sulfur
Bituminous SCR, CS-ESP (232 SCA) & Wet FGD
Full-Scale Field Trial
of the Low Temperature Mercury Capture Process CONSOL Energy TBD TBD TBD

Long-Term ACI Field
Test for >90% Mercury Removal ADA-ES Rocky Mountain Power’s
Hardin Station PRB SDA/FF

T T T o

o o p p p i

i i c c c A

A A r

r r e e e a a a I

I I I I I P

P P r

r r o o o

j j j e e e c c c t t t s s s Full-Scale Testing of Mercury Oxidation Catalyst URS Group LCRA’s Fayette Unit 3 PRB Blends CS-ESP (640 SCA)
& Wet FGD

Mercury Control for Plants Firing Texas Lignite and Equipped
with ESP-Wet FGD URS Group NRG Texas Power LLC’s
Limestone Station Unit 1 TX Lignite/PRB
blend CS-ESP (452 SCA)
& Wet FGD

Evaluation of Mercury Control Strategies on a

Cyclone Boiler with
SCR ADA-ES Public Service of New Hampshire Company’s
Merrimack Unit 2 Mid-Sulfur
Bituminous SCR & (2) CS-ESPs in series (120 & 230 SCAs)

T T T o

o o p p p i

i i c c c A

A A r

r r e e e a a a I

I I I I I I I I P

P P r

r r o o o

j j j e e e c c c t t t
Utilization of Partially
Gasified Coal for Mercury Removal GE-EER Boiler Simulator Facility Multiple Multiple

T T T o

o o p p p i

i i c c c A

A A r

r r e e e a a a I

I I V V V P

P P r

r r o o o

j j j e e e c c c t t t
Pilot Testing of WRI’s Novel Mercury Control Technology WRI WRI & UNDEERC’s PTC Multiple Multiple

The following is a discussion of results ob tained during NETL’s Phase II Hg control technology field testing program. While multiple Hg control technologies were explored at many of the Phase II field testing s ites, the results are grouped by the technologyJuly 2008 8 selected for evaluation during the 30-day exte nded tests. In additi on, preliminary results
from the Phase III field te sting sites are presented.

Elemental Hg Oxidation Enhancements Oxidation of flue gas Hg 0 followed by absorption of Hg 2+ across a wet FGD system has the potential to be a reliable and cost-effec tive Hg control strategy for coal-fired power plants. To optimize Hg capture across FGD systems, NETL is funding the development of technologies that promote Hg 0 oxidation in coal combusti on flue gas: retrofit Hg 0 oxidation catalysts and chemical additives. Th e impact of combustion modifications, such as coal reburn, on flue gas Hg 0 oxidation has also been examined under the IEP Program. 3 In addition, NETL field tested F GD additives designe d to suppress Hg 0 reemissions across the scrubber.

Combustion Modifications General Electric Energy and Environmental Research Corporation (GE EER) evaluated a novel multi-pollutant control technology to reduce Hg, NOx, and carbon monoxide emissions, while simultaneously improving plan t efficiency and reliability, at Progress Energy’s bituminous coal-fired Lee Station Un it 3 that is equipped with a CS-ESP and
SO 3 flue gas conditioning (FGC) system. 4 The primary objective of this Phase II project was to achieve at least 70% incremental Hg capture via: (1) combustion modifications designed to enhance “co-benefit” Hg capture by fly ash; (2) duct humidification to reduce ESP temperature; and (3) ACI upstream of the ESP for polishing control. Preliminary results indicate a 38% improvement in “co -benefit” Hg capture following combustion optimization activities. Meanwhile, untreated ACI at about 18 lb/MMacf achieved 80% total Hg removal with SO 3 conditioning idled, but the rem oval efficiency was limited to approximately 55% with the operation of SO 3 FGC.

Elemental Hg Oxidation Catalysts URS Corporation (URS), in collaboration w ith EPRI, Great River Energy (GRE), City Public Service (CPS) of San Antonio, a nd the North Dakota Industrial Commission, conducted pilot-scale testing of Hg 0 oxidation catalysts at GRE’s North Dakota (ND) lignite-fired Coal Creek Station (CCS) and CPS of San Antonio’s J.K. Spruce Plant, which burns PRB coal. CCS is equipped with a wet FGD system downstream of a CSESP, while Spruce is equipped with a wet FGD downstream of a reverse-gas FF. Pilot catalyst skids installed at bot h plants were loaded with a palladium (Pd#1) catalyst, a selective catalytic reduction (SCR) catalyst, and an experimental activated carbon (C#6) catalyst. In addition, a subbituminous ash-base d (SBA#5) catalyst was installed at CCS, while a gold (Au) cata lyst was evaluated at Spruce. In a full-scale application, the fixedbed catalysts would be installed downstream of an ESP or FF, to: (1) minimize fly ash deposition on the catalysts; (2) prevent or mi nimize catalyst erosion; and (3) ensure a low flue gas temperature and flow rate, which reduces the catalyst space velocity and minimizes the length of catalyst required.

High levels of baseline Hg 2+ downstream of the FF at Spruce made it difficult to evaluate the Hg 0 oxidation catalysts. Final catalyst ac tivity measurements, conducted at CCS in June 2004, showed 79% Hg 0 oxidation across the C#6 catalyst, with nearly 13 months ofJuly 2008 9 operation, and about 67% oxidation across the Pd#1 catalyst after more than 20 months of operation. 5 Significantly lower activity was measured for the SCR and SBA#5 catalysts. In an attempt to extend th e effective life of the catalysts, in-situ thermal catalyst regeneration tests were performed. Following thermal regeneration, Hg 0 oxidation across the Pd#1 catalyst increased from 67 to 88% (nea r the 95% activity of the fresh catalyst), while the C#6 catalyst showed no improvement. It is important to note that these “proof of concept” tests were conducted simply to de termine if the catalysts could be thermally regenerated, and conditions were not adju sted to optimize thermal regeneration. Meanwhile, 79% total Hg capture was obser ved across the pilot-scale wet limestone forced oxidation (LSFO) FGD, with 84% Hg 2+ at the FGD inlet.

URS has completed pilot-scale testing of Hg 0 oxidation catalysts at Luminant Power’s Monticello Steam Electric Station (MoSES) Unit 3, which fires a blend of Texas (TX) lignite and PRB coals. 6 In January 2005, four Hg 0 oxidation catalysts were installed downstream of the CS-ESP: (1) Au; (2) SCR; (3) regenerated Pd#1 from CCS; and (4) fresh Pd#1. During catalyst inspection, URS observed severe fly ash buildup on the catalyst surfaces, likely caused by frequent p ilot unit outages during the test campaign. Following in-situ catalyst cleaning in August 2006, Hg 0 oxidation was approximately 72% across the regenerated Pd#1 catalyst an d 66% across the Au catalyst, after 17 months of pilot-scale operation. Tests comple ted in April 2005 indicated total Hg capture across a pilot-scale wet FGD ranged from 76 to 87%, compared to only 36% removal
under baseline conditions. This equates to about 70% increm ental Hg capture due to the catalysts.

URS has also completed pilot-scale testing of the catalytic Hg oxidation technology at Southern Company’s Plant Yates Unit 1, whic h fires a low-sulfur Eastern bituminous coal. The pilot catalyst skid, installed downs tream of a CS-ESP, was loaded with fresh Pd#1 and Au catalysts in December 2005, along with regenerated SCR and Au catalysts from J.K. Spruce. After nearly 11 months of operation, Hg 0 oxidation measured 58% across the fresh Au catalyst, 38% across the fresh Pd#1 catalyst, 32% across the regenerated SCR catalyst, and 26% across the regenerated Au catalyst. The pilot catalyst skid was taken off-line in January 2007 to accommodate an SO 3 injection test plan.

Under a Phase III award, URS began a fu ll-scale field test of a gold-based Hg 0 oxidation catalyst at Lower Colorado River Authority’s Fayette Power Project Unit 3 in May 2008. The test is intended to confirm the require d catalyst quantities and catalyst life for achieving an average of 70% or greater Hg 0 oxidation in PRB flue gases over a two-year period. The project represents the next logical advancemen t of the catalytic oxidation technology from its current pilo t-scale. It will an swer technical questions such as the catalyst quantity required to achieve high Hg oxidation percentages, catalyst life, the efficiency of catalytically-oxidized Hg captu re in full-scale wet FGD systems, and the ability to keep the catalysts clean of fly ash buildup at full-scale with sonic horns.

Chemical Additives NETL is funding Phase II field tests of chemi cal additives designed to promote flue gas Hg 0 oxidation and enhance FGD Hg capture. 7 The additives, collectively referred to asJuly 2008 10 sorbent enhancement additives (SEA) by UNDE ERC and as oxidation additives (OA) by URS, are sprayed onto the coal as an aque ous salt solution. This approach maximizes the residence time available for interactions with Hg 0 . Full-scale field testing of this technology has been completed at Minnkot a Power Cooperative’s Milton R. Young (MRY) Unit 2 and Luminant Power’s MoSES Unit 3.

MRY Unit 2 fires ND lignite coal in a cyclone boiler and is equipped with a CS-ESP and
wet FGD. UNDEERC evaluated three additives during short-term parametric tests: SEA1, calcium chloride (CaCl 2 ); SEA2, a proprietary ch emical formulation; and magnesium chloride (MgCl 2 ). SEA2 yielded the best results, achieving approximately 44% total Hg capture across the ESP/FGD co mbination with injection at 75 ppm (on a dry coal basis), as compared to less than 20% Hg capture with SEA1 and MgCl 2 injection at 500 ppm. About 60% total Hg capture was observed with SEA2 injection at 50 ppm (on a dry coal basis) , coupled with DARCO ® Hg (an untreated PAC developed by NORIT Americas, Inc.) injection at 1 lb/MMa cf. During the 30-day long-term test, total Hg capture across the ESP/FGD configur ation ranged from 50 to 65% with SEA2 injection at 60-100 ppm (on a dry coal basis) and DARCO ® Hg injection at 0.15
lb/MMacf.

During parametric testing at MoSES Unit 3, URS evaluated the performance of OA1 (CaCl 2 ) and OA2 (calcium bromide - CaBr 2 ). These trials clearly displayed the superior performance of CaBr 2 as 72% Hg 2+ was observed at the ESP outle t with an injection rate of 100 ppm Br in the coal ( on a dry basis). As a result, long-term testing was conducted
with CaBr 2 . The two-week test, at a CaBr 2 injection rate equivalent to 55 ppm Br in the coal, oxidized 67% of the Hg entering the FGD, resulting in an aver age total Hg capture
of 65%. At a CaBr 2 injection rate equivalent to 113 ppm Br in the coal, Hg 0 oxidation reached 85%, resulting in an average total Hg capture of 86% over the subsequent twoweek test. In addition, a short- term test conducted with a CaBr 2 injection rate equivalent to 330 ppm Br in the coal resulted in 92% total Hg capture across the ESP/FGD configuration.

Addressing Hg Re-emissions across FGD Systems Originally thought to be a sampling artifact, Hg 0 re-emissions have been observed at
several coal-fired uni ts and occur when Hg 2+ captured by a wet FGD is chemicallyreduced within the vessel and re-emitted as Hg 0 . Through funding provided by NETL, URS is conducting bench-scale testing to dete rmine the mechanisms and kinetics of the aqueous reactions of Hg absorbed by wet FG D systems, and to develop a kinetics model that predicts Hg reduction and re-emission reactions in wet FGD systems over a wide range of chemical conditions. 8 The underlying hypothesis of this project is that Hg reemission reactions (apparently driven by SO 2 -derived "sulfite" species in the liquid phase) are limited by kinetics rather than e quilibrium. Results indicate that low FGD chloride concentrations can slow Hg 2+ reduction, while high chlori de concentrations may completely inhibit the sulfur reactions, preventing Hg 2+ reduction within the FGD vessel. Moreover, results show that the rate of Hg 2+ reduction increases by a factor of about 10 as the pH decreases from 5 to 6 down to a bout pH 3, in the presen ce of chloride. TheseJuly 2008 11 results suggest that Hg 0 re-emissions in full-scale wet FGD systems could be greatly influenced by factors such as chloride concentration and slurry droplet pH.

A chemical kinetics model has been develope d to describe the aqueous Hg reactions in FGD systems. The model predicts the basic tr ends seen experimentally for pH, sulfite, thiosulfate, and chloride effects, and pr ovides fairly good numerical agreement with experimental data. The model is currently be ing verified through a se ries of bench-scale wet FGD tests using simulated flue gas to determine if it accurately predicts the tendency for Hg 0 re-emissions, and the phase in whic h Hg is found in the FGD by-products. Preliminary results indicate that mercuric mono-chlo rosulfite (ClHgSO 3 - ) is a key species since the rate constant for decomposition of ClHgSO 3 - to Hg 0 is much smaller than that for the mercuric sulfite complex, thus contribut ing to the inhibiting effect of chloride on Hg 0 re-emissions. In addition, thiosulfate appears to inhibit Hg 0 re-emissions at low pH, but accelerate this phenomenon at high pH. The validated model will be run over a wide range of potential wet FGD operating condi tions with and without the use of FGD additives to determine conditions that: (1 ) optimize FGD Hg capture; and (2) influence the phase in which Hg leav es in the FGD by-products.

Wet FGD Additives URS also conducted pilot- and full-scale fi eld tests of a wet FGD additive, Degussa Corporation’s TMT-15, to determine whether th e additive can precipitate absorbed Hg as a stable salt, thereby minimizing Hg 0 re-emissions and lo wering FGD liquor Hg
concentrations. 9 This project is also assessing whether this same additive can be used to minimize Hg in reused FGD solid by-produc ts, through separation of the fine Hgcontaining salts from the remainder of th e byproduct. The project included pilot-scale testing at MoSES Unit 3 and Plant Yates Unit 1. Full-scale field tests have been completed at Indianapolis Power & Light’s Petersburg Station Unit 2, which fires highsulfur bituminous coal, and Plant Yates.

The effectiveness of Degussa Corporation’s TMT-15 additive in suppressing Hg 0 reemissions was inconclusive at pilot-scale due to: (1) the absence of re-emissions, even without chemical addition, at Monticello Station; and (2) Hg measurement issues at Southern Company’s bituminous-fired Pl ant Yates. However, TMT-15 had the anticipated impact on FGD by-products as the FGD liquor Hg concentrations were significantly reduced during both tests. During a full-scale field test at Indianapolis Power & Light’s Petersburg Station, which bur ns high-sulfur bituminous coal, a modest decline in Hg 0 emissions was observed during an eight -day TMT-15 injection test, but the additive did not impact the partitioning of Hg in FGD by-products at this site. Meanwhile, full-scale results obtained duri ng a 30-day evaluation of Nalco Company’s
8034 additive at Plant Yates we re confounded by low baseline Hg 0 re-emission levels.

A third wet FGD additive, Babcock & Wilcox’ s Absorption Plus(Hg)TM, was evaluated at E.ON America’s high-sulfur bituminous-fired M ill Creek Station afte r parametric trials revealed that untreated ACI had little, if any, impact on Hg removal. 10 During long-term testing, total Hg removal averaged about 92% with the addi tion of AbsorptionJuly 2008 12 Plus(Hg)TM. Note that over 80% total Hg removal was observed under baseline
conditions.

Sorbent Injection NETL’s Phase II portfolio of full-scale field te sting projects encompass several variations of sorbent injection technology: untreated AC I, untreated ACI with chemical additives, chemically-treated ACI, EPRI’s TOXECO NTM configuration, TOXECON IITM, as well as non-carbon and “concrete-friendly” PAC so rbents. The development, and subsequent field testing, of chemically-treated ACI and chemical additives, in conjunction with untreated ACI, represents a concerted effortto enhance Hg capture at units firing lowrank coal after Phase I results at the PRB-fired Pleasant Prai rie Unit 2 showed total Hg
removal via untreated ACI was limited to about 65%. 11 These advanced Hg-specific control technologies are designe d to introduce excess halogens into the Cl-deficient flue gas emitted from low-rank coals to promote Hg 0 oxidation and adsorption. Meanwhile, minimizing the impact of ACI on fly ash uti lization is the driving force behind Phase II field testing of the TOXECONTM configur ations and non-carbon/ “concrete-friendly” sorbent injection.

Untreated PAC In addition to serving as a benchmark duri ng nearly all of NETL’s Phase II full-scale field tests, untreated ACI has also been ev aluated during two 30-day long-term tests. At Plant Yates Unit 1, URS selected RWE Rhin ebraun’s Super HOK sorbent and total Hg capture varied from 50 to 86% with inject ion rates ranging from 4.5 to 9.5 lb/MMacf. 12 Plant Yates was selected for long-term testing, in part, to gain a be tter understanding of the effect of ACI on small-SCA ESP (173 SCA) and wet FGD operation. URS observed an increase in the ESP arcing ra te during continuous ACI, part icularly at high load. While the 30-day long-term injection test caused no visible physical damage to the ESP, it
remains unclear what effect the increased ar cing rate will have on ESP performance over longer time periods.

ADA-ES chose DARCO ® Hg for the 30-day long-term test conducted at DTE Energy’s Monroe Station Unit 4, which burns a 60% P RB and 40% bituminous coal blend and is equipped with an SCR and CS-ESP. 13 Total Hg removal averaged 78% with DARCO ® Hg injection at 4.9 lb/MMacf. Th e performance of untreated DARCO ® Hg during select
Phase I and II full-scale field te sts is presented in Figure 2.July 2008 13 Figure 2 – Phase I and II Performance Curves for Untreated ACI

Chemically-Treated PAC The limited Hg removal achieved by untreated ACI at Pleasant Prairie spurred the development and full-scale field testing of alternatives, such as PAC chemically-treated
with bromine. Two brominated PACs – NORIT Americas’ DARCO ® Hg-LH and Sorbent Technologies’ B-PACTM - have consisten tly been top performers at Phase II field testing units burning lower-rank coals. In fact , the outstanding performance (see Figure 3)
of these brominated sorbents has accelerat ed the commercialization of Hg-specific controls technologies and drasti cally reduced the estimated co st of Hg control due to a reduction in the ACI rate required to achieve a given level of control, which offsets the higher cost of these sorbents.

ADA-ES selected brominated DARCO ® Hg-LH for 30-day long-te rm field tests at two
PRB-fired units: Sunflower Electric’s Holcomb Station Unit 1 and AmerenUE’s Meramec Station Unit 2. At Meramec, 93% average total Hg removal was achieved
across the CS-ESP with DARCO ® Hg-LH injection at 3.3 lb/MMacf. 14 Total Hg capture averaged 93% across the spray dryer absorber and fabric filter (SDA/ FF) configuration at
Holcomb with DARCO ® Hg-LH injection at 1.2 lb/MMacf. 15 UNDEERC also conducted a 30-day evaluation of DARCO ® Hg-LH at GRE’s ND lignite-fired Stanton Station Unit
10. With DARCO ® Hg-LH injection at 0.7 lb/MMacf , total Hg capture across the SDA/FF configuration averaged 59%. 16 However, greater than 90% Hg capture was achieved at this unit during para metric trials with both DARCO ® Hg-LH and B-PACTM injection at 1.5 lb/MMacf. 

### ACI Concentration (lb/MMacf)Mercury Removal (%)

0 20 40 60 80 100

0 5 10 15 20 Brayton Point (Bit/ESP)

Pleasant Prairie (PRB/ESP)

Leland Olds (ND Lignite/ESP)

Monroe (60:40 PRB-Bit blend/ESP) E.C. Gaston (Bit/FF)

Holcomb (PRB/FF)

Antelope Valley (ND Lignite/FF)

Big Brown (70:30 TX Lignite-PRB blend/FF)

* All data generated using NORIT Americas’ DARCO ® Hg 

### ACI Concentration (lb/MMacf)Mercury Removal (%)

0 20 40 60 80 100

0 5 10 15 20 Brayton Point (Bit/ESP)

Pleasant Prairie (PRB/ESP)

Leland Olds (ND Lignite/ESP)

Monroe (60:40 PRB-Bit blend/ESP) E.C. Gaston (Bit/FF)

Holcomb (PRB/FF)

Antelope Valley (ND Lignite/FF)

Big Brown (70:30 TX Lignite-PRB blend/FF)

* All data generated using NORIT Americas’ DARCO ® HgJuly 2008 14 The brominated B-PACTM sorbent has also been selected for 30-day long-term trials at three of NETL’s Phase II field testing sites. At GRE’s PRB-fired St anton Station Unit 1, URS observed 85% average total Hg removal across the CS-ESP with B-PACTM injection
at 1.7 lb/MMacf. 17 Sorbent Technologies conducted long- term field tests with B-PACTM at DTE Energy’s St. Clair Station Unit 1, which burns an 85% PRB and 15% bituminous coal blend, and Progress Energy’s bituminous-fir ed Lee Station Unit 1. At St. Clair, 94% average total Hg removal was achieved across the CS-ESP with B-PACTM injection at 3
lb/MMacf. 18 Total Hg capture averaged 85% across the CS-ESP at Lee with B-PACTM injection at 8 lb/MMacf. 17 Note that the 30-day long-term test at Lee was conducted with
the SO 3 FGC system idled and opacity levels remained acceptable.

ADA-ES is conducting Phase III testing at Rocky Mountain Power’s PRB-fired Hardin Generating Station to evaluate the Hg re moval performance, long-term emissions variability, and associated ope rating and maintenance costs of PAC injection for greater than 90% Hg control during a te n- to twelve-month full-sca le demonstration. Baseline Hg capture at Hardin ranged from 20 to 30% across the SCR and SDA/FF configuration. 19 During parametric testing, an in jection rate of about 1 lb/M Macf was required to attain slightly more than 90% total Hg removal with DARCO ® Hg-LH and Calgon Carbon’s
brominated FLUEPACTM-MC Plus. In addition, injection of a DARCO ® Hg and
FLUEPACTM-MC Plus mixture achieved 90% total Hg at 0.14 lb/M Macf, with a low KNXTM additive rate. The long-term test be gan in September 2007 and will continue through August 2008 using DARCO ® Hg-LH. At low load (80 to 90 MW), a DARCO ® Hg-LH injection rate of 1.5 lb /MMacf is required to mainta in 90% removal compared to
3.0 lb/MMacf at 120 MW. This is likely due the high fraction of Hg 2+ produced at low load (up to 50%) that is captured in the SDA.

URS conducted Phase III field testing at NRG Texas Power LLC’s Limestone Electric Generating Station Unit 1, which fires a 70:30 bl end of TX lignite and PRB coals and is equipped with a CS-ESP and wet FGD. Baselin e Hg removal was highly variable ranging from about 5 to 50%. Since this unit markets its fly ash for reuse, two Hg control technologies designed to preser ve ash quality were evaluate d during parametric tests: low-ash impact sorbent in jection and TOXECON IITM. 20 During injection upstream of the ESP, the brominated B-PACTM and DARCO ® Hg-LH sorbents performed similarly with about 90% ACI Hg removal at 2 to 3 lb/MMacf. Untreated DARCO ® Hg also achieved 90% ACI Hg removal with injection at sligh tly less than 6 lb/MMacf. Injection of the “concrete-friendly” C-PACTM sorbent at a bout 1.5 lb/MMacf resulted in approximately 73% ACI Hg removal. During parametric tr ials with the TOXECON IITM configuration, ACI Hg removal was limited to about 60% with DARCO ® Hg and DARCO ® Hg-LH injection at about 5 to 6 lb/MMacf. Note that DARCO ® Hg-LH injection into the TOXECON IITM configuration took place w ith the unit firing 100% PRB coal. A twomonth continuous injection test was completed with DARCO ® Hg-LH injection at 2 lb/MMacf and preliminary resu lts indicate that the project goal of 50 to 70% ACI Hg
removal across the ESP was achieved. In ad dition, URS is confident that the low
DARCO ® Hg-LH injection rate will not prohibit fly ash reuse, but analysis is ongoing.July 2008 15 Another chemically-treated ACI technology, AL STOM Power, Inc. – U.S. Power Plant Laboratories’ (ALSTOM-PPL) Me r-CureTM process, is unique in that injection takes place in the high-temperature region upstream of the air preheater (APH) and the process employs a proprietary “proce ssor” to prevent chemically -treated Mer-CleanTM sorbent agglomeration and ensure uniform sorbent dispersion. 21 Three 30-day long-term field tests of Mer-CureTM have been completed at Phase II sites equipped with a CS-ESP: (1) PacifiCorp’s PRB-fired Dave Johnston Unit 3; (2) Leland Olds Unit 1; and (3) Reliant Energy’s medium-sulfur (2%) bituminous-fir ed Portland Station Unit 1. Chemicallytreated Mer-CleanTM 8 injection rates of 0.63 and 1.4 lb/MMacf achieved average total Hg removals of 92 and 90% at Dave Johnston and Leland Olds, respec tively. At Portland, about 95% average total Hg capture was obs erved with chemically-treated Mer-CleanTM 8-21 injection at 8.5 lb/MMacf. The reduced efficiency of the Mer-CleanTM sorbents at Portland may have been caused by elevated levels of flue gas SO 3 , resulting from the
combustion of medium-sulfur bituminous coal.

A Phase III evaluation of Mer-CureTM was completed at LCRA’s Fayette Unit 3 in April
2007. 22 Baseline Hg capture was approximately 50% across the CS-ESP and wet FGD.Note that all results are based on the incremental (or ACI) level of Hg control. ALSTOMPPL evaluated three sorbents (eSorbTM 11, eSorbTM 13, and eSorbTM 18) designed to preserve fly ash quality, along with Mer-Cle anTM 8, during parametric testing. Excluding eSorbTM 18, 80% ACI Hg capture wa s achieved with inje ction at 0.4 to 0.5 lb/MMacf. At an injection at abou t 0.8 lb/MMacf, eSorbTM 11 and Mer- CleanTM 8 attained 90% ACI Hg capture. Preliminary results indicate that fl y ash remains marketable with eSorbTM 13 at about 0.5 lb/MMacf (85% ACI Hg capture). The testing program was halted prematurely due to an unscheduled plant outage.

Figure 3 – Phase II Performance Curves for Chemically-treated ACI



### ACI Concentration (lb/MMacf)Mercury Removal (%)

0 20 40 60 80 100

0369 Dave Johnston - PRB/ESP (Mer-Clean 8) Meramec - PRB/ESP (DARCO Hg-LH) Stanton 1 - PRB/ESP (B-PAC) Holcomb - PRB/FF (DARCO Hg-LH) Leland Olds - ND Lignite/ESP (Mer-Clean 8) Stanton 10 - ND Lignite/FF (DARCO Hg-LH) St Clair - 85:15 PRB-Bit blend/ESP (B-PAC)
Portland - Bit/ESP (Mer-Clean 8-21) Lee - Bit/ESP (B-PAC)



### ACI Concentration (lb/MMacf)Mercury Removal (%)

0 20 40 60 80 100

0369 Dave Johnston - PRB/ESP (Mer-Clean 8) Meramec - PRB/ESP (DARCO Hg-LH) Stanton 1 - PRB/ESP (B-PAC) Holcomb - PRB/FF (DARCO Hg-LH) Leland Olds - ND Lignite/ESP (Mer-Clean 8) Stanton 10 - ND Lignite/FF (DARCO Hg-LH) St Clair - 85:15 PRB-Bit blend/ESP (B-PAC)
Portland - Bit/ESP (Mer-Clean 8-21) Lee - Bit/ESP (B-PAC)July 2008 16 SO 3 Impacts NETL Hg control R&D has shown that flue gas SO 3 , even at low concentrations, can interfere with the pe rformance of ACI. SO 3 is generated in coal combustion flue gas via three mechanisms: (1) oxidation of SO 2 within the furnace; (2) further oxidation of SO 2 across SCR catalysts; and (3) SO 3 FGC systems. It appears that SO 3 competes with Hg for adsorption sites on the PAC surface thereb y limiting its performance and/or requiring much higher ACI rates to achieve a give n level of Hg control (see Figure 4). 23

Figure 4 - Impact of SO 3 on ACI Performance

During Phase II field testing at AEP’s high-su lfur (3-4%) bituminous-fired Conesville Station Unit 6, ADA-ES evaluated over 50 ca ndidate sorbents and total Hg removal was limited to approximately 30% with chemica lly-treated PAC injection at 12 lb/MMacf. 24 Consequently, a 30-day long-te rm field test was not conducte d at this unit; instead, NETL funding was used to eval uate the impact of SO 3 FGC on brominated DARCO ® Hg-LH at
AmerenUE’s PRB-fired Labadie Station. 25 As shown in Figure 4, turning the SO 3 FGC system off at Labadie increased total Hg removal from about 50 to 80% with DARCO ® Hg-LH injection at 8 lb/MMacf. In addition, greater than 90% Hg removal was observed
with no SO 3 injection and DARCO ® Hg-LH injection upstream of the APH at about 5 lb/MMacf. The performance of brominated B-PACTM was also impacted by SO 3 FGC at Lee Station. With B-PACTM injection at 8 lb /MMacf, Hg capture increased from 32 to
82% when SO 3 FGC was idled at Lee. One possible solution to this problem is the dual injection of PAC and alkaline materials. Prel iminary results from a few Phase II and III field testing sites are encouraging.Mercury Removal (%)

ACI Concentration (lb/MMacf) 0 20 40 60 80 100

0 5 10 15 20 Lee (B-PAC/15 ppm SO3)

Labadie (DARCO Hg-LH/10.3 ppm SO3)

Conesville Unit 6 (DARCO Hg) Lee (H-PAC/Hot-side/15 ppm SO3)

Labadie (DARCO Hg-LH/Hot-side/10.3 ppm SO3) Lee (B-PAC/No SO3)

Labadie (DARCO Hg-LH/No SO3)

Labadie (DARCO Hg-LH/Hot-side/No SO3)Mercury Removal (%)

ACI Concentration (lb/MMacf) 0 20 40 60 80 100

0 5 10 15 20 Lee (B-PAC/15 ppm SO3)

Labadie (DARCO Hg-LH/10.3 ppm SO3)

Conesville Unit 6 (DARCO Hg) Lee (H-PAC/Hot-side/15 ppm SO3)

Labadie (DARCO Hg-LH/Hot-side/10.3 ppm SO3) Lee (B-PAC/No SO3)

Labadie (DARCO Hg-LH/No SO3)

Labadie (DARCO Hg-LH/Hot-side/No SO3)July 2008 17 ADA-ES is conducting a Phase III field test at Public Service of New Hampshire Company’s Merrimack Station Unit 2, which utilizes a cyclone-fired boiler to burn a blend of bituminous coals (1.0 - 1.3% sulfur content) and is equipped with an SCR system followed by two CS-ESPs in series. 26 This is a challenging environment for ACI
due to elevated SO 3 levels and high flue gas temperat ure. During parametric testing, several Hg sorbents were evaluated both w ith and without the in jection of magnesium oxide (MgO) or sodium sesquicarb onate (trona) – two potential SO 3 mitigation additives that also permit a reduction in flue gas temper ature. Results indicate that trona injection enhanced ACI performance to a greater degr ee than MgO; however, the sodium content of trona may limit fly ash recycling opportunities.

Without SO 3 mitigation, Hg removal was limited to about 22% with brominated
DARCO ® Hg-LH injection between the two ESPs at 8 lb/MMacf. Untreated DARCO ® Hg injection at 8 lb/MMacf, coupled with trona injection, resulted in about 65% Hg removal. During a continuous injection test completed in March 2008, 50% Hg removal was achieved with trona injection upstr eam of the APH at 500 lb/hr and DARCO ® HgLH injection between the two ESPs at about 4 lb/MMacf.

Conventional PAC with Chemical Additives As an alternative to using ch emically-treated PAC, NETL al so has sponsored field tests using conventional PAC supplemented with chemi cal additives applied to the coal and/or flue gas to overcome the poor performance of conventional PAC in low-rank coal applications. Through funding provided by NETL, UNDEERC conducted two 30-day long-term field tests at full-scale units firi ng ND lignite coal to determine whether SEA coal treatment enhances the performance of untreated ACI at units burning lower-rank
coals. 16 Indeed, SEA coal treatment improved the Hg capture efficiency of untreated ACI at both of these Phase II field testing sites. During the 30-day trial at Basin Electric’s Leland Olds Station Unit 1, 58% average to tal Hg capture was observed across the CSESP with DARCO ® Hg injection at 2.7 lb /MMacf, coupled with the addition of an aqueous CaCl 2 solution to the ND lignite coal at a rate of 2.9 lb/ MMacf. UNDEERC also evaluated this advanced Hg-specific contro l technology at Basin Electric’s Antelope Valley Station Unit 1. Total Hg removal aver aged 92% across the SDA/FF configuration with the addition of SEA2 to the ND lignite coal at a rate of 0.033 lb/MMacf and
DARCO ® Hg injection at 0.81 lb/MMacf.

UNDEERC conducted additional Phase II Hg c ontrol field testing at Montana-Dakota Utilities Company’s Montana lignite-fired Lewi s & Clark Station that is equipped with a
mechanical collector and wet venturi scrubber. Parametric tests evaluated the Hg capture efficiency of SEA1 and SEA2 addition to th e coal with and without ACI upstream of the
wet venturi scrubber. 27 With SEA1 injection at 600 pp m coal equivalent, about 90% Hg
removal is achieved with untreated DARCO ® Hg injection at 3 lb/MMacf. Slight improvements in performance were observed with higher SEA1 and DARCO ® Hg injection rates. Ninety percent Hg removal wa s also observed with SEA2 injection at 100 ppm coal equivalent and DARCO ® Hg injection at 1 lb/MMacf. Note that in the absence of PAC injection, Hg remova l was limited to about 55% wi th SEA2 injection at 100 ppmJuly 2008 18 coal equivalent. A one-week, optimized fiel d test was also conducted, but results are currently unavailable.

Under a Phase III award, UNDEERC is evalua ting PAC and SEA injection, as well as, the SEA2 technique 2 (SEA2 T2) technol ogy, which involves co-injection of the proprietary SEA2 additive and PAC upstream of the particulate control device. Full-scale field testing is currently on-going at Kansas City Power & Light's Hawthorn Unit 5 that burns PRB coal and is equipped with an SCR and SDA/FF conf iguration. During parametric testing at Hawthorne, greater th an 90% total Hg capture was achieved with SEA1 added to the coal at 1200 ppm and DARCO ® Hg-LH injection at 3 lb/MMacf. 28

With the SEA2 T2 technol ogy, the co-injection of DARCO ® Hg at 2.8 lb/MMacf and SEA2 at 0.14 lb/lb of PAC, resulted in abou t 85% total Hg remova l. In addition, >90% Hg removal was achieved with SEA1 a dded to the coal at ~500 ppm and DARCO ® Hg injection at 2 lb/MMacf. A 45-day long-term is scheduled for Hawthorne where
UNDEERC will further evaluate SEA1 additi on to the coal, coupl ed with untreated
DARCO ® Hg injection upstream of the ESP.

ACI Upstream of a Hot-Side ESP NETL is also evaluating Hg control technol ogies designed specifica lly for hot-side ESP (HS-ESP) applications, where the elevated fl ue gas temperature limits the Hg capture efficiency of ACI. A four-day trial conducte d at Duke Energy’s low-sulfur bituminous coal-fired Buck Plant achieved approximately 70% total Hg removal with the injection of Sorbent Technologies’ chemically-t reated H-PACTM at 10 lb/MMacf. 18 Sorbent Technologies conducted additiona l field testing at Midweste rn Generation’s PRB-fired Will County Unit 3. A high temperature version of the brominated, “concrete-friendly” C-PACTM sorbent was evaluated since fly ash from this unit is marketed for reuse. Using a newly developed X-a-Lance distributing la nce design, 73% Hg removal was achieved during a parametric trial with C-PACTM injection at 5 lb/MMacf. 29 During a six-day continuous test, Hg removal ranged from a bout 60 to 73% with C-PACTM injection at 5
lb/MMacf.

Under a separate Phase II project, ADA-ES evaluated the impact of adding hightemperature liquid sorbents to the pre-combus ted coal and/or upstream of the HS-ESP on Hg control at MidAmerican’s P RB-fired Louisa Station Unit 1. 30 While Alstom’s brominated KNXTM coal additive promoted Hg 0 oxidation, the lack of a downstream FGD at this unit led to no increase in Hg removal.

Alternative Sorbent In jection Technologies The typical ACI system is located upstream of a particulate control device to enable simultaneous capture of the spent PAC and fl y ash. This Hg control strategy leads to commingling of the PAC and fly ash that can pr ohibit certain fly ash recycling efforts. In particular, fly ash collected at coal-fired units that employ sorbent injection for Hg control is banned from serving as a feedst ock at cement kilns following a December 2006 final rule issued by EPA. 31 Note that this ruling is based on the potential for increased Hg
emissions at cement kilns rather than car bon contamination con cerns. In 2006, over 4July 2008 19 million tons of fly ash served as alternative feedstock to shale or clay at about 34 U.S.
cement kilns. 32

Meanwhile, one of the highest-value reuse app lications for fly ash is use as a substitute for Portland cement in concrete production. The utilization of fly ash in concrete production is particularly sensitive to carbon co ntent as well as th e surface area of the carbon present in the fly ash. PAC injection wi ll increase the carbon content of the fly ash with the degree of carbon contamination de pendent upon the ACI conc entration required to achieve a given level of Hg control. In addition, PAC has a high surface area that is ideal for Hg capture, but also promotes the adsorption of surfactants known as air entraining admixtures (AEA) th at are added to the concrete slurries to stabilize an optimum amount of air in the concrete pr oduct, thus improving its workability and durability to freeze-thaw cycles. 33,34 The adsorption of AEA by the injected PAC will lead to an increased Foam Index value, whic h refers to the quantity of AEA required to saturate the fly ash and cement mixture, re sulting in an inferior concrete product. Furthermore, the association of fly ash wi th Hg capture may influence marketability simply due to a perceived connection with th e hazards of Hg. As a result, NETL’s Phase II Hg control technology field testing program includes evaluations of alternative sorbent injection technologies designed to minimize, or completely eliminate, fly ash carbon contamination caused by ACI upstream of a particulate control device.

TOXECONTM Configuration Based on the promising Phase I results at E.C. Gaston (see Figur e 5), TOXECONTM was
selected for a first-of-a-kind commercia l Hg control technology demonstration at WeEnergies’ Presque Isle Power Plant in Marquette, Michigan, under DOE’s Clean Coal Power Initiative. Currently operational, th e TOXECONTM configuration has achieved about 90% total Hg removal with untreated DARCO ® Hg and brominated DARCO ® HgLH injection at a bout 1.7 and 1.2 lb/MMacf, respectively. 35 During an extended testing period, greater than 90% total Hg removal wa s maintained for 48 consecutive days with
both DARCO ® Hg and DARCO ® Hg-LH injection.

Under the Phase II program, NETL has also funded a full-scale field test of the TOXECONTM configuration at Luminant Ener gy’s Big Brown Unit 2, which fires a 70% TX lignite and 30% PRB coal blend. 36 UNDEERC evaluated the performance of untreated ACI, co-injection of SEA and unt reated PAC, and UN DEERC’s proprietary enhanced PAC during parametric tests. Due to concerns about the cumulative impact ofSEA and PAC injection on differential pressure across the relatively small FF (air-tocloth ratio of 12:1), UNDEERC’s enhanced PAC was selected for the 30-day long-term demonstration and total Hg capture average about 74% with an in jection rate of 1.5
lb/MMacf.

According to an in-depth BOP analys is performed by UNDEERC, enhanced PAC injection at 1.5 lb/MMacf in creased the pressure drop ac ross the FF at Big Brown by
about 1” H 2 O at high load (~600 MW). Handling a nd storage issues with the PAC/ash
mixture have also been observed at both Pr esque Isle and Big Br own. In particular, a portion of the PAC/ash mixture was found to be very hot and smoldering at each unit andJuly 2008 20 preliminary results indicate that plant pers onnel will need to monitor and empty the FF hoppers on a regular basis to avoid self-heat ing and ignition of the PAC/ash mixture.

TOXECON IITM Configuration EPRI’s TOXECON IITM technology injects so rbents directly into the downstream collecting field(s) of an ESP. Since the majo rity of fly ash (~90%) is collected in the upstream ESP fields, only a small portion of the total collected ash contains spent sorbent. The technology requires minimal capital investment compared to the TOXECONTM configuration, because a retr ofit FF is not required. A full-scale
TOXECON IITM field test was conducte d by ADA-ES at Entergy’s PRB-fired Independence Station Unit 1. 37 The CS-ESP at Independence c ontains four electric fields (542 SCA) and ACI took place between the se cond and third fields. During a long-term field test in November 2005, about 60% aver age total Hg removal was observed with
DARCO ® Hg-LH injection at 4 to 5 lb/MMacf. While the project goal of 50 to 70% Hg capture was attained, ADA-ES felt that performance was limited by the injection lance design. During subsequent full-scale field te sting at Independence in February 2007,
DARCO ® Hg-LH injection at 5.5 lb/MMacf ach ieved 90% total Hg removal with ADAES’ new TOXECON IITM lance design. A rema ining concern with any Hg control strategy involving sorbent in jection, particularly the TO XECON IITM technology that limits the ESP residence time, is the potential for increased particulate emissions that could trigger New Source Review requirements.

Figure 5 – Phase I and II TOXECONTM Performance CurvesMercury Removal (%)



### ACI Concentration (lb/MMacf) 0 20 40 60 80 100

01234567 Big Brown - 70:30 TX Lignite/PRB blend (DARCO Hg) Big Brown - 70:30 TX Lignite/PRB blend (DARCO Hg & SEA4) Big Brown - 70:30 TX Lignite/PRB blend (EERC Enhanced PAC) Big Brown - PRB (EERC Enhanced PAC)

Presque Isle - PRB (DARCO Hg)

E.C. Gaston - Bituminous (DARCO Hg)Mercury Removal (%)



### ACI Concentration (lb/MMacf) 0 20 40 60 80 100

01234567 Big Brown - 70:30 TX Lignite/PRB blend (DARCO Hg) Big Brown - 70:30 TX Lignite/PRB blend (DARCO Hg & SEA4) Big Brown - 70:30 TX Lignite/PRB blend (EERC Enhanced PAC) Big Brown - PRB (EERC Enhanced PAC)

Presque Isle - PRB (DARCO Hg)

E.C. Gaston - Bituminous (DARCO Hg)July 2008 21 Non-carbon & “Concrete-fri endly” PAC Sorbents NETL is funding full-scale field tests of altern ative Hg sorbents that would allow coalfired power generators to continue marketi ng fly ash commingled with the spent sorbent as a suitable replacement for Portland cemen t in concrete. Two approaches are discussed
below: non-carbon based sorbent in jection and injection of PA C that is passivated during production to limit AEA adsorption.

The performance of Amended Silicates ’ non-carbon Amended SilicatesTM sorbent (comprised of a chemically-amended silicate substrate) was evalua ted during a 30-day long-term field test at Duke Energy’s medium-sulfur (~2.3%) bituminous-fired Miami
Fort Unit 6. 38 Total Hg capture across the CS -ESP averaged 40% with Amended SilicatesTM injection at 5 to 6 lb/MMacf. Once again, flue gas SO 3 may have had a detrimental effect on sorbent performance at Miami Fort.

Under a separate Phase II project, Sorbent Technologies conducted a 30-day long-term evaluation of their brominated, “concrete-frien dly” C-PACTM at Midw estern Generation’s
PRB-fired Crawford Station Unit 7. 39 With C-PACTM injecti on at about 4.6 lb/MMacf, total Hg removal across the small CS-ESP aver aged 81%. Most importantly, preliminary results indicate that fly ash samples collec ted during sorbent injection at these units would satisfy the criteria used to determ ine the suitability for reuse in concrete production.



### Novel Hg Control Concepts

Innovative techniques for Hg control that c ould eventually replace and/or augment the more mature technologies discussed above are also being explored under the IEP Program. The following is a brief disc ussion of these NETL-funded efforts.

MerCAPTM The Hg control via adsorption process (Mer CAPTM), developed by EPRI, relies on fixed structure sorbents positioned in the flue gas st ream to adsorb Hg and then, as the sorbent becomes saturated, regenerate the sorbent and recover the Hg. An initial retrofit application of the MerCAPTM technology is for “polishing” control of Hg 0 downstream of FGD systems. During two six-month extended pi lot-scale tests, the performance of goldcoated MerCAPTM plates was evaluated downstream of a: (1) spray dryer adsorber and fabric filter (SDA/FF) configuration at Great River Energy’s Stanton Station Unit 10; and (2) wet FGD system at Plant Yates Unit 1. 40

After more than 6,000 hours of continuous op eration at Stanton Station, Hg removal averaged 30 to 35% across the acid-treated MerCAPTM plates and 10 to 30% across the untreated plates. Testing also revealed that regeneration via acid treatment and tighter plate spacing (1⁄2-inch vs. 1-inch) improved th e Hg capture efficiency of the MerCAPTM technology. At Plant Yates, Hg removal decrea sed from 15 to 3% during the first three days of pilot-scale MerCAPTM operation. It was believed that limestone slurry carryover from the FGD system was inhibiting Hg r eactions. Subsequent use of a water wash system for the plates was able to restore Hg removal to 15%.July 2008 22 Utilization of Partially Gasified Coal for Mercury Removal GE EER will evaluate the Hg capture efficien cy of sorbents produced from coal in an insitu gasification process at coal burning plants. Proposed Phase III work will optimize the gasification process to maximize sorbent reac tivity while minimizing sorbent production

costs. 41 Optimization will be conducted with resp ect to coal type, gasification process parameters, and the sorbent injection rate re quired to achieve at le ast 70% Hg removal. Among the gasification process parameters to be optimized are: (1) composition of solid fuel/air mixture, (2) temperature, and (3) mixture residence time. GE EER will also evaluate the stability of captured Hg and the potential impact on fly ash marketability.

Low Temperature Mercury Capture Process CONSOL Energy, Inc. (CONSOL) will conduc t a Phase III field test of the Low Temperature Mercury Capture (LTMC) process at a bituminous-fired power plant that is equipped with a CS-ESP. LTMC has the ability to reduce Hg emissions by over 90%, as was recently shown by CONSOL on a slip-s tream pilot plant at Allegheny Power’s Mitchell Station. The LTMC process controls Hg by cooling the flue gas temperature to about 220°F, which promotes Hg adsorption on the UBC inherent in fly ash. To avoid corrosion at the low-temp erature conditions, the SO 3 concentration will be controlled through magnesium hydroxide slurry injection. The project will also demonstrate that water spray humidification can ma intain ESP performance under low-SO 3 conditions. A
two-month test will be conduc ted to evaluate long-term performance and any potential balance-of-plant impacts.

Pilot Testing of WRI’s Novel Mercury Control Technology Western Research Institute (WRI) will devel op and evaluate pre-combustion Hg removal of raw coal by thermal treatment. 42 Key process steps in the WRI technology include treating the fuel at two selected temperature windows. In the first stage, the moisture in the fuel is driven-off; in the second stage, coal is heated by nearly inert ga s resulting in significant removal of coal-bound Hg. Bench-s cale testing has reveal ed that residence time is an important parameter for Hg release in some coals - an increase of 8 minutes of residence time results in almost 80% of Hg released from coal. The percentage of Hg
released from the coals varied from 50 to 87% depending on residence time. In addition,
initial results from a fixed-be d test unit indicate that high temperature sorbents will be available to remove Hg from the process r ecycle sweep gas in the temperature range of
550 to 600°F. Pilot-scale testi ng (100 lb/hr) is currently be ing conducted to assess and scale-up results from the bench-scale tests. The pilot unit will examine two different Hg removal configurations: a vibratory fluid bed, and a proprietary vertical reactor.

NETL in-house development of novel control technologies After studying numerous sorbents for Hg ca pture in simulated coal-derived gases, scientists at NETL discovered and patented th ree trace metal capture technologies that are
now licensed and in commercial demonstrati on. The Thief process, licensed to NalcoMobotec USA, is a cost-effectiv e alternative to ACI for Hg removal from flue gas as Thief carbon sorbents range from $90 to $200 per ton. The Photochemical Oxidation (PCO) process, licensed to Powerspan Corpor ation, introduces a 254-nm ultraviolet light into the flue gas, leading to enhanced Hg oxidation and capture. NETL researchersJuly 2008 23 received the 2005 Award for Excellence in Technology Transfer from the Federal Laboratory Consortium (F LC) for the PCO method.

Recognizing the need for a low-cost technique to remove Hg from coal-based Integrated Gasification Combined Cycle power plants, NETL researchers have invented a new sorbent that works on fuel gas at elevated te mperatures. The new sorbent is palladium (Pd) on an inert support. Un like conventional sorbents su ch as activated carbon, which operate at ambient temperature, high temperat ure Pd sorbents remove Hg and arsenic at temperatures above 500°F, and have more than twice the capacity of previously existing sorbents, resulting in a major improvement in overall energy efficiency of the power combustion process. NETL researchers re ceived the 2008 Award for Excellence in Technology Transfer from the FLC for developing the Pd-based Hg sorbents licensed to Johnson Matthey.



### Economic Analysis of ACI

NETL published an updated economi c analysis of Hg control via ACI at 12 of the Phase II ACI field testing sites. 43 The May 2007 report provides “s tudy-level”, plant-specific cost estimates and was carried out to provide NETL a gauge in measuring its success in achieving the target of reducing the baseli ne (1999) Hg control cost estimate of $60,000/lb Hg removed by 25 to 50%. As shown in Figure 6, 20-year levelized cost estimates for the incremental cost of Hg c ontrol ($/lb Hg removed) were calculated for 90% ACI Hg removal at seven Phase II field te sting sites. Note that chemically-treated ACI was the Hg control technology ev aluated at each of these units.

The Phase II field testing results are very en couraging both in terms of the level of Hg
removal achieved and the estimated cost of control on a 20-year levelized basis. Specifically, the economics of Hg control via chemically-treated ACI at units burning lower-rank PRB and lignite coals is notew orthy. The 20-year levelized incremental increase in cost of electricity (COE) fo r 90% ACI Hg removal remains below 1.30 mills per kilowatt-hour (mills/kWh) for the four P RB units (Holcomb, Meramec, Stanton Unit 1, and Dave Johnston), as well as the units fi ring a PRB/bituminous blend (St. Clair), and ND lignite (Leland Olds), wh en CUB impacts are excluded. b For comparison, the increase in COE calculated for 90% ACI Hg removal at the medium-sulfur bituminousfired Portland Station is over 1.90 mills /kWh, when CUB impacts are excluded. Meanwhile, the incremental cost of 90% AC I Hg removal ranges from less than $10,000 to about $30,000/lb Hg removed, wh en CUB impacts are excluded.

The increase in COE resulting from Hg c ontrol via ACI is primarily determined by annual PAC consumption costs that are depe ndent on the required ACI rate, delivered PAC price, and the volume of flue gas bei ng treated. Chemical composition also affects PAC price since manufacturers charge a higher price for chemically-treated PAC to offset the additional production costs required to alter the sorbent’s molecular structure. The

b As shown in Figure 6, the economic analysis also included an assessment of the potential for ACI to negatively impact the sale and disposal of CUB (fly ash) and therefore impact the overall cost of Hg
control.July 2008 24 ACI rate required to achieve a given level of Hg control can be impacted by a host of plant-specific dynamics, includi ng, but not limited to: chlorine and sulfur contents of the coal being burned, APCD confi guration, flue gas temperatur e, boiler efficiency, UBC content of the fly ash, and ductwork geometry in proximity to the ACI location. The impact of PAC manufacturing location on delivered sorben t price has taken on added significance following the U.S. Department of Commerce’s decision to impose tariffs, ranging from 62 to 228%, on Chinese activated carbon manufacturers. 44 The February 26, 2007 determination responds to concerns th at Chinese manufacturers were dumping
activated carbon at less than th e fair U.S. market value.

Figure 6 – 20-Year Levelized Increment al Cost of 90% ACI Hg Control

The cost on a $/lb Hg removed basis is impact ed largely by the level of “co-benefit” Hg capture exhibited by the existing APCD confi guration and coal Hg content. For example, the incremental cost of Hg control will increase when: (1) “co-benefit” Hg capture is high; and/or (2) coal Hg content is low, because a smaller quantity of Hg is removed from the flue gas for a given level of control.

Additional factors can influence the cost of Hg control, includi ng: economic factors (labor rate, taxes and continge ncies, economic life of capital equipment, etc.), process disruptions (unexpected or excessive outages, etc.), pr oximity to a reliable PAC manufacturer, and modifications to existing equipment. The estimates developed here assume an uncomplicated retrofit and minimal economic impact due to the installation of the ACI system, assuming that the installation occurs during a regul arly scheduled plant outage. The estimates are also based on the a ssumption that Hg cont rol via ACI will not cause any BOP impacts. In addition, the pot ential demand for a si gnificant quantity of ACI systems within a relatively short timef rame, to ensure nationwide compliance with CAMR and the patchwork of state-level re gulations, could place a strain on qualified $0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 with By-product Impacts a

Meramec

PRB / ESP
DARCO ® Hg-LH Dave Johnston

PRB / ESP
Mer-CleanTM 8 Holcomb

PRB / FF
DARCO ® Hg-LH St. Clair

PRB-Bit blend / ESP
B-PACTMIncremental Cost of Control, $/lb Hg Removed

a For units equipped with an ESP, by-product impacts include the fly ash disposal cost ($17/ton) and lost revenue from fly ash sa les ($18/ton), assuming 100% utilization. For the SDA/FF configuration, only the cost of SDA by-product disposal ($17/ton) is inclu ded. without By-product Impacts

Leland Olds #1

Lignite / ESP
Mer-CleanTM 8 Stanton #1

PRB / ESP
B-PACTM Portland

Bit / ESP
Mer-CleanTM 8-21 DOE Cost target:
≤ $45,000/lb Hg removed

$0 $10,000 $20,000 $30,000 $40,000 $50,000 $60,000 with By-product Impacts a

Meramec

PRB / ESP
DARCO ® Hg-LH Dave Johnston

PRB / ESP
Mer-CleanTM 8 Holcomb

PRB / FF
DARCO ® Hg-LH St. Clair

PRB-Bit blend / ESP
B-PACTMIncremental Cost of Control, $/lb Hg Removed

a For units equipped with an ESP, by-product impacts include the fly ash disposal cost ($17/ton) and lost revenue from fly ash sa les ($18/ton), assuming 100% utilization. For the SDA/FF configuration, only the cost of SDA by-product disposal ($17/ton) is inclu ded. without By-product Impacts

Leland Olds #1

Lignite / ESP
Mer-CleanTM 8 Stanton #1

PRB / ESP
B-PACTM Portland

Bit / ESP
Mer-CleanTM 8-21 DOE Cost target:
≤ $45,000/lb Hg removedJuly 2008 25 engineers, skilled laborers, and the raw materi als required to erect both retrofit and new PAC storage and injection systems.



### Technology Commercialization

Although the Federal regulatory structure for Hg emissions from coal-fired power plants is once again uncertain following the vacat ur of EPA’s Clean Air Mercury Rule on February 8, 2008, 45 NETL’s field testing program ha s successfully brought Hg control technologies to the point of commercial-deplo yment readiness. As of April 2008, nearly 90 full-scale ACI systems, a signature technolo gy of the IEP Program, have been ordered by U.S. coal-fired power generators. 46 These contracts represent over 44 gigawatts (GW) of coal-fired electric generating capacity. Th is includes approximately 33 GW of existing capacity (~10% of total U.S. coal-fired capacity ) that will be retrofit with ACI systems to control Hg emissions. The ACI systems have th e potential to remove more than 90% of the Hg in most applications, at a cost that can dip below $10,000/lb Hg removed. Although the results achieved during NETL’s field tests met or exceeded program goals, site-specific Hg characterization and testing may be required to evaluate alternative methods and their Hg capture efficiency on individual power plant generating units.



### COAL UTILIZATION BY-P RODUCTS R&D PROGRAM

In addition to developing cost-effective co ntrol technologies for coal-fired power generation facilities, NETL’s Hg research also focuses on CUB characterization. 47 CUB research is in response to the transfer of Hg and other trace metals from flue gas to the solid and liquid effluent streams as a result of implementing pollu tion controls on coalbased power systems, and driven by the goal of increasing the overall beneficial use of CUB. At least partly attribut able to NETL’s research effort s, CUB beneficial utilization
has increased from 25% in 1990 to over 43% in 2006, while annual CUB production in
the United States has risen from about 80 to nearly 125 million tons over this time period. 32 NETL’s overall goal is to increase CUB reuse to 50% by 2010, and nearly 100% by 2020.

CUB are currently regulated as non-hazardous under the Re source Conservation and Recovery Act, and it is expected that they will continue to be regulated as such. However, EPA has left the door open for futu re review of the regul atory status of CUB because of continuing concern over the fate of Hg and other trace metals in by-products. This concern is heightened in light of the deployment of Hg capture technology under CAMR. In response, NETL has sponsored a number of projects that focus on an evaluation of the potential leaching and volat ilization of Hg and other trace metals from CUB, particularly FGD by-products, such as synthetic gypsum, and fly ash.



### Determining the Fate of Hg in FGD By-products

The use of FGD as a Hg capture technology highlights the importance of better understanding the chemistry of Hg and FGD solids and synthetic gypsum products in order to predict the environmental fate of the CUB-bound Hg. The following NETL-July 2008 26 sponsored research is examining the mob ility and ultimate fate of Hg in FGD byproducts.

NETL’s Office of Research and Developmen t (NETL/ORD) is conducting an in-house
research effort directed at determin ing the fate of Hg in FGD materials. 48 This activity focuses on Hg stability dur ing FGD gypsum drying, Hg st ability during wallboard production using FGD gypsum, Hg leachability from FGD gypsum, and the Hg-binding phase in FGD gypsum. The stability of Hg during FGD gypsum drying was studied by collecting samples before and after a natura l gas-fired heating unit, which reduces the
moisture content of the FGD solids for ease of handling during the wallboard manufacturing process. Results indicated that within analytical precision, no Hg desorbed during drying of free moisture.

The stability of Hg in FGD gypsum dur ing wallboard production was analyzed by NETL/ORD by collecting samples of FGD gypsum feedstock and the corresponding wallboard products from five wallboard ma nufacturing plants. The Hg present in the unprocessed FGD gypsum and the finished wallboard product ranged from 0.04 to 1.5 ppm on a dry basis. The quantity of Hg retain ed in the finished wallboard product varied, with three samples showing nearly complete Hg retention during the wallboard manufacturing process. For the other tw o samples, Hg losses were 12 and 58%, suggesting that the quantity and thermal stab ility of Hg in FGD gypsum and wallboard depends on the origin of the gypsum and/or the nature of processing.

NETL/ORD also conducted settling and leachin g experiments using FGD slurry samples in an attempt to isolate the Hg-binding phase from bulk gypsum. During settling, Hg partitioned almost exclusively to the top, slower-settling layer of the FGD slurry. Analysis of this residue reveal ed that both Hg and iron (Fe) were enriched in the top layer by factors of about 20 and 10, respectively. Meanwhile, Hg was not mobilized during FGD slurry leaching experiments using a co ntinuous, stirred-tank extractor. This is indicative of a strong chemisorption rather than physical adsorption of Hg. As a result, it is believed that Hg sequestered in FGD gyps um is primarily bound to an iron-rich phase, such as iron-coated clay mate rials or iron oxide/hydroxide part icles, probably introduced
with the limestone used as the FGD reagent. Additional research 49 has also shown that some Hg retained in FGD gypsum requires hyd rogen peroxide oxidation for release, such as a phase containing sulfides or carboneous materials. Mercury not bound in either of these two fractions is likely a precursor to Hg 0 that could form via mechanisms being investigated through URS’ be nch-scale kinetics model.

Leach testing is also being used to evalua te the impacts of pH and oxidation-reduction potential (ORP) on Hg mobility in FGD bypr oducts. Leaching of si x FGD materials to pH > 2 under aerobic conditions failed to m obilize appreciable amounts of Hg. While no Hg was released to the leachate during experiments with pH > 4 and ORP > 100 millivolts (mV), dissolution of the major immob ilized form of Hg was complete with pH < 1 and an ORP of approximately 350 mV . Consequently, NETL/ORD researchers concluded that the Hg-retaining phase will immobilize Hg in many reuse applications,July 2008 27 with one possible exception being placement in mine-land reclamation areas where the FGD by-products could be exposed to aci dic, anaerobic conditions.

The extramural thrust of NETL’s CUB resear ch is focused on the fate of Hg in FGD gypsum during wallboard producti on and ultimate disposal. For instance, the Tennessee Valley Authority (TVA) evaluated Hg retentio n in FGD gypsum from three sources: a Hg-amended commercial calcium sulfate, a la boratory-scale wet FGD system, and a fullscale wet FGD system. 50 TVA researchers concluded that no Hg would evolve from disposed FGD byproducts up to a maximu m temperature of 140°F, although thermal desorption of Hg from FGD gypsum did occur at approximately 400°F.

USG Corporation is providing data on the ex tent and location of Hg loss during the wallboard production process, and also provi ding information on the potential for Hg leaching at the end of the wallboard life-cycle, when it is disposed in municipal
landfills. 51 FGD gypsum evaluation tests from six different power pl ant/FGD feedstock variations have been complete d to investigate the impact of different configurations on the stability of Hg during wallboard produc tion. Testing included the use of FGD gypsum produced during TMT-15 injection into a power plant scrubber.

Results to date indicate that use of fine s blowdown in wet FGD systems significantly reduced Hg content in the FGD gypsum. For FGD gypsum generated without fines blowdown, Hg loss amounted to less than 8%, while tests using FGD gypsum from power plants employing fines blowdown i ndicated Hg loss of 46 to 55% during wallboard production.



### Determining the Fate of Hg in Fly Ash

Beginning with the Phase I full-scale field testing program, NETL ha s required that field contractors evaluating Hg control via sorb ent injection collect and analyze fly ash samples. Fly ash analyses are focused on determining the stability and ultimate fate of Hg during potential utilization a pplications and disposal. More recently, NETL awarded a contract to Frontier Geosciences, Inc. (Fro ntier) to conduct independent laboratory analysis of CUB generated during NETL’s Phas e II full-scale Hg control technology field testing program. 52 The purpose of the independent la boratory analysis is to ensure accurate and consistent laboratory procedures are used to determine the environmental fate of Hg in CUB. NETL/ORD has also been conducting in-house leaching experiments with fly ash collected from ACI field testing sites.

The Frontier work includes leaching studies using the Synthetic Precipitation Leaching Procedure (SPLP, EPA Method 1312), low- (40 ° C for 30 days), medium- (190 ° C for 1 hour), and high-temperature (900-1200 ° C for 5 minutes) Hg volatility tests, microbial methylation experiments, and halide analysis. Preliminary SPLP results indicate that little to no Hg would be released under normal di sposal conditions. In addition, Hg bound to PAC sorbents, particularly those that have b een chemically-treated, appears to be more stable than the UBC-bound Hg. During the low-te mperature volatility te sts, essentially no Hg was emitted from the fly ash samples. Thermal desorption of Hg has been observedJuly 2008 28 during the medium- and high-temperature volat ility tests conducted by Frontier; however, the extent of release is still under investigation.

Using a pure culture of sulfate reducing bact eria known to methylate Hg, the production of methyl-mercury, over a 30 da y period, is being monitored to assess the methylation potential of Hg present in CUB. Preliminar y results from this “worst-case-scenario” microbial mobilization study indicate an increase in methyl-mercury production. However, microbial activity has also st abilized a number of target metals.

NETL/ORD researchers have also conducted leaching expe riments on the Phase II byproducts using the modified SPLP, the NETL Serial Batch Leaching Procedure (SBLP), and NETL Column Leaching on a select numbe r of sample pairs. During a five-month continuous column experiment using four leachants: water (pH=5.7), dilute sulfuric acid (pH=1.2), dilute acetic acid (pH= 2.9), and sodium carbonate (pH=11.1), 53 the PAC/ash mixtures were generally found to effectivel y immobilize the captured Hg over a range of laboratory conditions. Overall, very little of the Hg (always below 0.5% and often under 0.1%) contained in the ash samples was sol ubilized during leaching. Neither the pH nor
the nature of the anion had a noticea ble effect on the leachate mercury.

Not only have the Hg control technologies demonstrated capture of Hg that would otherwise be released into the environment, but the Hg has generally been shown to be retained in the control technology by-products under conditions of laboratory leaching
tests. For some of these mate rials, the tests performed in this study show these control technology ashes, in spite of their higher Hg c ontent, to be environmentally more stable with respect to Hg release than the corresponding baseline ashes of lower Hg content. 54



### SUMMARY

Over the past seven years, NETL has mana ged full-scale field tests of Hg control technologies at nearly 50 U.S. coal-fired pow er generation facilities. The flexible nature of this program allowed NETL to quickly in corporate insights a nd lessons learned from its network of partners into the development of advanced Hg control technologies tailored to specific areas of need. For instance, a de termination that chlorine released during coal combustion promotes Hg 0 oxidation in flue gas led to the development of technologies designed to provide a halogen “boost” for coal s, such as subbituminous and lignite, that
tend to contain low levels of chlorine and t hus lower concentrations of the more reactive oxidized form(s) of Hg.

NETL has observed a step-change improvement in both the cost and performance of Hg control during full-scale field tests with chemically-treated (or brominated) ACI. The improved Hg capture efficiency of these advanced sorbent injection systems has given coal-fired power plant operato rs the confidence to begi n deploying technology. As of April 2008, nearly 90 full-scale ACI systems have been ordered by U.S. coal-fired power generators. These contracts include both new and retrofit installati ons and represent over 44 GW of coal-based electric generating capac ity. The ACI systems have the potential to remove more than 90% of the Hg in many applications based on results from NETL’sJuly 2008 29 field testing program, at a co st estimated to dip below $10,000/lb Hg removed. However, while the results achieved during NETL’s fiel d tests met or exceeded program goals, only through experience gained during long-term continuous operation of these advanced technologies in a range of full- scale commercial applications will their actual costs and performance be determined.



### ACKNOWLEDGEMENT

This report would not have been possible without the efforts of the NETL project managers and researchers who pr ovided valuable technical in put. The authors would like to acknowledge the contributions of Lynn Brickett, Andrew O’ Palko, Bruce Lani, Charles Miller, Sara Pletcher, Pierina Noceti, Barbara Carney, William Aljoe, Evan Granite, Henry Pennline, and James Murp hy. The authors would also like to acknowledge the efforts of EPA, EPRI, coal-fir ed power generators who participated in the program, and the research organizations and academic institutions who were active participants.



### DISCLAIMER

References in this article to any specific commercial product or service are to facilitate understanding and do not imply endorsement by the U.S. Department of Energy.



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25 Sjostrom, S.; Dillon, M.; Donnelly, B.; Bustard, J.; Filippelli, G.; Glesmann, R.; Orscheln, T.; Wahlert, S.; Chang, R.; O’Palko, A. Influence of SO 3 on Mercury Removal with Activated Carbon: Full-Scale
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26 Campbell, T.; Bustard, J.; Brignac, P.; Sjostrom, S. ; Raichle, P.; Auclair, A. ; Keyes, H.; Senior, C.; O’Palko, A. Evaluation of Control Strategies to Effectivel y Meet 70-90% Mercury Reduction on an Eastern Bituminous Coal Cyclone Boiler with SCR. In Proceedings of the Air Qua lity VI Conference, Arlington, VA, September 24-27, 2007.

27 Brickett, L. An Update of DOE’s Phase II & III Mercury Control Technology Program. Presented at the Air Quality VI Conference, Arlington, VA, September 24-27, 2007.

28 Laumb, J.; Pavlish, B. Long-Term Demonstration of Sorbent Enhancement Additive Technology for Mercury Control. Presented at the Electric Utilities Environm ental Conference, Tucson, AZ, January 22- 24, 2007.

29 Landreth, R.; Nelson, S.; Liu, X.; Tang, Z.; Donoc hod, D.; Kulpinski, K.; Wanninger, K.; Brickett, L. Additional B-PACTM, H-PACTM, and C-PACTM Trial Results. In Proceedings of the Air Quality VI Conference, Arlington, VA, September 24-27, 2007.July 2008 32 30 Campbell, T.; O’Palko, A. Low Cost Options for Moderate Level s of Mercury Control – TOXECON IITM and High Temperature Sorbents. Presented at the DOE/NETL Mercury Control Technology Conference, Pittsburgh, PA, December 11-13, 2006. http://www.netl.doe.gov/publications/proceedings/0 6/mercury/presentations/Campbell_presentation_12110 6.pdf

31 National Emission Standards for Hazardous Air Pollutants From the Portland Cement Manufacturing Industry; Final Rule and Proposed Rule; 40 CFR Part 63, EPA–HQ–OAR–2002–0051; FRL–8256–4; U.S. Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 2006, http://a257.g.akamaitech.net/7/2 57/2422/01jan20061800/e docket.access.gpo.gov/2 006/pdf/E6- 21405.pdf

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33 Brominated Sorbents for Small Cold-Side ESPs, Hot-Side ESPs and Concrete; Project Kickoff Meeting for the U.S. Department of Energy under Cooperative Agreement No. DE-FC26-05NT42308; Sorbent Technologies Corporation: Twinsburg, OH, 2005.

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35 Derenne, S.; Sartorelli, P.; Bustar d, J.; Stewart, R.; Sjostrom, S.; Jo hnson, P.; McMillian, M.; Sudhoff, F.; Chang, R. TOXECONTM Clean Coal Demonstration for Mercury and Multi-Pollutant Control at the Presque Isle Power Plant. In Proceedings of the Air Quality VI Conference, Arlington, VA, September 24- 27, 2007.

36 Pavlish, J.; Thompson, J.; Martin, C.; Hamre, L.; Wiemuth, B.; Pletcher, S. Fabric Filter Bag Investigation Following Field Testing of Sorbent Injection for Mercury Control at TXU’s Big Brown
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37 Campbell, T.; Sjostrom, S.; Bustard, J.; Donnelly, B.; Sapp, C.; Hantz, J.; Br adberry, T.; Chang, R.; O’Palko, A. TOXECON IITM Demonstration: A Testing Update. In Proceedings of the Air Quality VI Conference, Arlington, VA, September 24-27, 2007.

38 Butz, J.; Broderick, T.; Turchi, C.; Geers, J. Trial of Amended SilicatesTM for Mercury Control at Miami
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39 Nelson, S.; Landreth, R.; Liu, X.; Tang, Z.; Miller, J.; Brickett, L. Brominated Sorbents for Small ColdSide ESPs, Hot-Side ESPs, and Fly Ash Use in Concrete. Presented at the DOE/NETL Mercury Control Technology Conference, Pittsburgh, PA, December 11-13, 2006. http://www.netl.doe.gov/publications/proceedings/0 6/mercury/presentations/Nelson_presentation_121106. pdf

40 Machalek, T. Mercury Control by EPRI MerCAPTM Process. Presented at the DOE/NETL Mercury Control Technology Conference, Pitts burgh, PA, December 11-13, 2006, http://www.netl.doe.gov/publications/proceedings/0 6/mercury/presentations/Machalek_presentation_12130 6.pdf

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41 Samuelson, C.; Lissian ski, V.; McNemar, A. Utilization of Partially Gasified Coal for Mercury Removal. Presented at the DOE/NETL Mercury Control Techno logy Conference, Pittsbur gh, PA, December 11-13, 2007, http://www.netl.doe.gov/publi cations/proceedings/07/mercur y/panels/Samuelson_Panel.pdf

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43 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: UPDATED Ec onomic Analysis of Activated Carbon Injection. Prepared for the U.S. Department of Energy, 2007, http://www.netl.doe.gov/technologies /coalpower/ewr/mercury/pubs/ Phase_II_UPDATED_Hg_Control_Ec onomic_Analysis.pdf

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49 Schroeder, K.; Beatty, L.; Cardon e, C.; Hreha, D.; Kair ies, C.; Rohar, P.; Thompson, R.; White, F. Leach Testing of FGD Materials. Presented at the DOE/NETL Mercury Control Technology Conference, Pittsburgh, PA, December 11-13, 2006, http://www.netl.doe.gov/publications/proceedings/06/ mercury/presentations/Schroeder_presentation_12120 6.pdf

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52 Hensman, C.; Dahl, A.; McIntosh, B.; Hawkins, L. ; Kilner, P.; Hien, J.; Pr estbo, E.; Gilmour, C.; Brickett, L. The Impact of Hg Control Technologies on Mobility Pathways for Hg, Ni, As, Se, Cd and Pb from Coal Utilization Byproducts. In Proceedings of the Air Quality VI Conference, Arlington, VA, September 24-27, 2007.

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