pp%A United States
M^tUIV Environmental Protection
Agency	
E P A-600/R-04-147
November 2004
Selective Catalytic
EPISI Reduction Mercury Field
Sampling Project

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EPA-600/R-04/147
November 2004
Selective Catalytic Reduction Mercury
Field Sampling Project
by
Dennis L. Laudal, Jeffrey S. Thompson, Chad A. Wocken
Energy & Environmental Research Center
University of North Dakota
PO Box 9018
Grand Forks, ND 58202-9018
EPA Cooperative Agreement No. R 83060601
Project Officer: Chun Wai Lee
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
U.S. Environmental Protection Agency
Washington DC 20460

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Disclaimers
This report was prepared as an account of work cosponsored by an agency of the United
States Government. Neither the United States Government, nor any agency thereof, nor any
of their employees makes any warranty, express or implied, or assumes any legal liability or
responsibility for the accuracy, completeness, or usefulness of any information, apparatus,
product, or process disclosed or represents that its use would not infringe privately owned
rights. Reference herein to any specific commercial product, process, or service by trade
name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its
endorsement, recommendation, or favoring by the United States Government or any agency
thereof. The views and opinions of authors expressed herein do not necessarily state or
reflect those of the United States Government or any agency thereof.
This report was prepared with the support of the U.S. Department of Energy (DOE)
National Energy Technology Laboratory Cooperative Agreement No.
DE-FC26-98FT40321. However, any opinions, findings, conclusions, or recommendations
expressed herein are those of the author(s) and do not necessarily reflect the views of DOE.
EERC DISCLAIMER
LEGAL NOTICE: This research report was prepared by the Energy & Environmental
Research Center (EERC), an agency of the University of North Dakota, as an account of
work sponsored by EPA, EPRI, and DOE. Because of the research nature of the work
performed, neither the EERC nor any of its employees makes any warranty, express or
implied, or assumes any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, apparatus, product, or process disclosed, or represents that its
use would not infringe privately owned rights. Reference herein to any specific commercial
product, process, or service by trade name, trademark, manufacturer, or otherwise does not
necessarily constitute or imply its endorsement or recommendation by the EERC.
11

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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting
the Nation's land, air, and water resources. Under a mandate of national environmental laws,
the Agency strives to formulate and implement actions leading to a compatible balance
between human activities and the ability of natural systems to support and nurture life. To meet
this mandate, EPA's research program is providing data and technical support for solving
environmental problems today and building a science knowledge base necessary to manage
our ecological resources wisely, understand how pollutants affect our health, and prevent or
reduce environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) is the Agency's center for
investigation of technological and management approaches for preventing and reducing risks
from pollution that threaten human health and the environment. The focus of the Laboratory's
research program is on methods and their cost-effectiveness for prevention and control of
pollution to air, land, water, and subsurface resources; protection of water quality in public
water systems; remediation of contaminated sites, sediments and ground water; prevention
and control of indoor air pollution; and restoration of ecosystems. NRMRL collaborates with
both public and private sector partners to foster technologies that reduce the cost of
compliance and to anticipate emerging problems. NRMRL's research provides solutions to
environmental problems by: developing and promoting technologies that protect and improve
the environment; advancing scientific and engineering information to support regulatory and
policy decisions; and providing the technical support and information transfer to ensure
implementation of environmental regulations and strategies at the national, state, and
community levels.
This publication has been produced as part of the Laboratory's strategic long-term research
plan. It is published and made available by EPA's Office of Research and Development to
assist the user community and to link researchers with their clients.
Sally Gutierrez, Acting Director
National Risk Management Research
Laboratory
111

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EPA Review Notice
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency and approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
iv

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Abstract
Many utilities are actively investigating methods to control and reduce mercury (Hg)
emissions, particularly since EPA announced in 2000 its intent to regulate Hg emissions
from coal-fired power plants. Even though this research has obtained some data, a lack of
sound data still exists as to the effect of selective catalytic reduction (SCR), selective
noncatalytic reduction (SNCR), and flue gas conditioning on the speciation and removal of
Hg at power plants. Although both SCR and SNCR systems effectively reduce nitrogen
oxide emissions, each system may impact Hg speciation differently. In addition, some
utilities have utilized ammonia (NH3) or sulfur trioxide to improve electrostatic precipitator
(ESP) performance, thereby changing the flue gas and ash chemistry.
This project investigates the impact that SCR, SNCR, and flue gas-conditioning systems
have on total and speciated Hg emissions. If SCR or SNCR systems enhance Hg conversion/
capture, then they could be thought of as multipollutant control technologies. Data from this
project can be used for environmental planning purposes as well as to provide information
for regulatory decisions. Previous Energy & Environmental Research Center pilot-scale tests
investigated the role that coal type plays in Hg speciation, both with and without SCR. The
results indicated that SCR, and possibly NH3 injection for flue gas conditioning, may
enhance Hg capture, although it appeared that the impact was highly coal-specific.
However, there were significant concerns as to the applicability of the pilot-scale results to
full-scale power plants. To validate and expand the pilot-scale results, sampling was
conducted at the full-scale level.
Twelve power plants were chosen for full-scale sampling to investigate the role that
SCR, SNCR, flue gas conditioning, and coal blending have on Hg speciation. For a
10-12-day period, sampling was conducted both prior to and after the SCR unit or ESP
using both the wet-chemistry Ontario Hydro method and near-real-time continuous Hg
monitors. Hg variability, speciation, and concentration were evaluated. Fly ash and coal
samples were also collected to obtain the Hg balance across the control devices.
The results indicate that SCR can assist in converting elemental Hg to oxidized Hg.
However, the effect appears to be coal-specific and, possibly, catalyst-specific. Ammonia,
whether injected directly as a gas or indirectly as urea, did not appear to have a significant
v

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effect on Hg speciation and removal.
This project was a joint effort of EPRI, the U.S. Department of Energy National Energy
Technology Laboratory, the U.S. Environmental Protection Agency (EPA) National Risk
Management Research Laboratory, and the utility industry.
The cover illustration incorporates the Alchemist's symbol for mercury as shown in
Medicinisch-Chymisch- undAlchemistisches Oraculum, Ulm, 1755 and is a little different
from other renditions such as the one used in the Oak Ridge National Laboratory Website.
vi

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Table of Contents
Section	Page
Abstract	v
List of Figures	 viii
List of Tables 	x
Nomenclature	 xi
Executive Summary 	 1
Introduction 		11
Potential Impacts of SCR on Hg Speciation		12
Pilot-Scale Screening Tests Conducted at the EERC		13
Experimental Approach 		15
Results and Discussion	27
Effect of Flue Gas Conditioning and Coal Blending on Hg Speciation	27
Effect of an SCR on Hg Speciation 	28
Effect of SCR Catalyst Age on Hg Speciation	32
SCR/Wet FGD Combination for Hg Control	34
Conclusions	37
References	39
vii

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List of Figures
Figure	Page
ES-1 Non-elemental Hg concentrations at the inlet of the particulate control
device with and without the SCR 	 6
ES-2 Comparison of Hg speciation results from 2001, 2002, and 2003 at Site S2 .... 6
ES-3 Comparison of Hg speciation results from 2001, 2002, and 2003 at Site S4 .... 7
1	Schematic of Site SI showing sample locations from horizontal and vertical
perspectives 	 19
2	Schematic of Site S2 showing sample locations from horizontal and vertical
perspectives 	 19
3	Schematic of Site S3 showing sample locations from horizontal and vertical
perspectives 	 20
4	Schematic of Site S4 showing sample locations from horizontal and vertical
perspectives 	 20
5	Schematic of Site S5 for the unit with SCR showing sample locations from
horizontal and vertical views	 21
6	Schematic of Site S5 for the unit with no SCR showing sample locations from
horizontal and vertical views	 21
7	Schematic of Unit 1 at Site S6 with SCR in service showing sample locations
from horizontal and vertical views 	 22
8	Schematic of Unit 2 at Site S6 with SCR bypassed showing sample locations
from horizontal and vertical views 	 22
9	Side-view schematic of Site S8 Units 1 and 2 showing sampling locations	 23
10	Schematic of Site S9 Units 1 and 2 showing sample locations from horizontal and
vertical views	 24
11	Schematic of Site A1 showing sample locations from horizontal and vertical
views 	 25
12	Schematic of Site A2 showing sample locations from horizontal and vertical
views 	 25
13	Schematic of Unit 2 at Site A3 showing sample locations from horizontal and
vertical perspectives	 26
14	Schematic of Site A4 showing sample locations from horizontal and vertical
perspectives 	 26
viii

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List of Figures (continued)
Figure	Page
15	Example of mercury variability at the stack from a site burning a high-sulfur
eastern bituminous (Site S5) coal	30
16	Percent of Hg2+ at the inlet of the SCR system as a function of chloride content
of the coal (note: data points without labels are results from plants without SCR
units where Hg speciation was measured at the air heater inlet) 	30
17	Hg concentrations at the inlet of the particulate control device with and
without the SCR	31
18	CMM data showing the effect of bypassing the SCR reactor 	32
19	Comparison of Hg speciation results from 2001, 2002, and 2003 at Site S2	33
20	Comparison of Hg speciation results from 2001, 2002, and 2003 at Site S4	33
IX

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List of Tables
Table	Page
ES-l Configuration of Power Plants Tested	 3
ES-2 Summary of Coal Analyses	 4
ES-3 Change in Hg Oxidation Across the SCR Catalyst (95% confidence intervals) . . 5
ES-4 Effect of the SCR on Hg° Concentration Across the Wet FGDs (95%
confidence intervals) 	 8
1.	Configuration of Power Plants Tested	 16
2.	Summary of the Selection Criteria for Each Plant	 17
3.	Summary of Coal Analyses	 18
4.	Speciation Results at the ESP Inlet for Facilities With and Without Flue Gas
Conditioning 	 28
5.	Hg Speciation Results at the ESP Inlet When Blending PRB and Eastern
Bituminous Coals	 28
6.	Change in Hg Oxidation Across the SCR Catalyst (95% confidence interval)	 29
7.	Effect of the SCR on Hg° Concentration Across the Wet FGDs	 34
x

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Nomenclature
AH
air preheater
APCD
air pollution control device
Btu
British thermal units
CMM
continuous mercury monitor
DOE
U.S. Department of Energy
EERC
Energy & Environmental Research Center
EPA
U.S. Environmental Protection Agency
ESP
electrostatic precipitator
FGD
flue gas desulfurization
Hg
mercury
Hg°
elemental mercury
Hg2+
oxidized mercury
Hgp
particulate-bound mercury
nh3
ammonia
nh4hso4
ammonium bi sulfate
NOx
nitrogen oxides
OH
Ontario Hydro mercury speciation method
pm25
particulate matter less than 2.5 |im
PRB
Powder River Basin
SCR
selective catalytic reduction of NOx
SNCR
selective noncatalytic reduction of NOx
S03
sulfur trioxide
Ti02
titanium dioxide
v205
vanadium oxide
XI

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Executive Summary
This report provides a summary of the results of the Selective Catalytic Reduction
Mercury Field Sampling Project sponsored by EPRI, the U.S. Department of Energy (DOE)
National Energy Technology Laboratory, the U.S. Environmental Protection Agency
National Risk Management Research Laboratory, and the utility industry. This report
outlines the field research conducted and the results.
Introduction
During combustion, elemental mercury (Hg°) is liberated from coal. However,
depending on the coal type, a significant fraction of the mercury (Hg) can be oxidized or can
become associated with the fly ash particles in the post-combustion environment of a
coal-fired boiler. Relative to Hg°, oxidized Hg (Hg2+) and particulate-bound Hg (Hgp) are
generally more effectively captured in conventional pollution control systems, such as flue
gas desulfurization (FGD) systems, fabric filters, and electrostatic precipitators (ESPs)
[1-4]. The identification of a process for converting Hg° to Hg2+ and/or Hgp forms could
potentially improve the Hg removal efficiencies of existing pollution control systems.
Potential Impacts of Selective Catalytic Reduction on Hg
Speciation
Selective catalytic reduction (SCR) units achieve lower nitrogen oxide (NOx) emissions
by using ammonia (NH3) to reduce NOx to molecular nitrogen (N2) and H20 over a catalyst.
Laboratory, pilot-, and full-scale testing indicate that SCR catalysts promote the conversion
of Hg° to Hg2+ and/or Hgp [5-7], Possible mechanisms that could result in the SCR of NOx
impacting Hg speciation include:
•	Catalytically oxidizing the Hg.
•	Changing the flue gas chemistry.
•	Providing additional residence time.
•	Changing the fly ash chemical composition.
Description of the Power Plants and Coal
For the purposes of this report, the plants using SCR (eight plants) are referred to as
Sites SI through S9. The two plants with flue gas conditioning are referred to as Sites A1
and A3; the plant using selective noncatalytic reduction (SNCR) (urea injection) is Site A2;
1

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and the plant using different coal blends is Site A4. For consistency, the numbering system
is the same that has been used for the annual reports. Site S7 is not included, as that site was
not part of this project. Information about each of the plants and the coals fired at these
plants is provided in Tables ES-1 and ES-2.
Effects of Flue Gas Conditioning and Fuel Blending on Hg
Speciation
At Site A1 Unit A, which fired a blend of 50% Powder River Basin (PRB) and 50%
eastern bituminous, there was an increase in Hgp with NH3 and sulfur trioxide (S03)
conditioning compared to S03 conditioning alone. There was no difference at Unit B, where
100%) PRB was fired.
At Site A2, urea was injected into the boiler producing NH3 gas (the SNCR process).
Compared to the baseline case (no urea injection), the addition of urea had little if any effect
on Hg speciation.
At Site A3 where ammonium bisulfate (NH4HS04) is added when firing 100% Texas
lignite, the overall Hg removal (comparing the total Hg concentration at the ESP inlet and
the stack) is about the same with and without NH4HS04. However, without NH4HS04
injection, the removal is primarily by the wet FGD and with NH4HS04 injection, by the
ESP. This is a result of an increase in Hgp when NH4HS04 is added compared to the baseline
case. When 20% PRB is added to the coal feed, there appears to be a decrease in the overall
Hg removal (from less than 5% to around 50%).
At Site A4, tests were conducted at three different blend ratios of PRB and eastern
bituminous coals with no flue gas-conditioning agents. Comparison of the results from each
of the blends clearly shows an increase in Hg° and decrease in Hgp with an increase in the
fraction of PRB in the blend.
Effect of SCR on Hg Speciation
Table ES-3 presents results showing the impact of SCR operation on Hg oxidation.
There is an increase in Hg oxidation across the SCR catalyst for those plants firing an
eastern bituminous coal. The two plants that showed the lowest increase in oxidation across
the SCR (SI and S9) both fired 100% PRB coal. The amount of oxidation that occurs across
the catalyst is highly variable. It appears to be affected by coal properties as well as catalyst
design and, possibly, catalyst age.
2

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Table ES-1. Configuration of Power Plants Tested
Plant3
NOx Control
or Flue Gas
Conditioning
Coal
Boiler Type
Boiler
Size
(MW)
Low-NOx
Burners
Catalyst
Vendor and
Type
Catalyst
Ageb
SCR
Space
Velocity
(hr1)
Particulate
Control
Sulfur
Control
S1
SCR
PRBC
cyclone
650
no
Cormetech
honeycomb
-8000 hr
1800
ESP
none
S2de
SCR
OH bit.'
wall-fired
1300
yes
Siemens/
Westinghouse
plate
1, 2, & 3 ozone
seasons
2125
ESP
wet
scrubber
S3
SCR
PA bit.9
tanqentially
fired
750
yes, with
overfire air
KWH
honeycomb
1 ozone season
3930
ESP
none
S4de
SCR
KY bit.
cyclone
650
no
Cormetech
honeycomb
1, 2, & 3 ozone
seasons
2275
Venturi
scrubber
lime Venturi
scrubber
S5
SCR
WV bit.
wall-fired
684
yes
Haldor Topsoe
plate
3 months
3700
ESP
wet FGD
S6
SCR
low sulfur KY &
WV bit.
concentrically
fired
700
yes
Cormetech
honeycomb
2 ozone
seasons
3800
ESP
none
S8
SCR
PRB/bit. blend
wall-fired
820
yes
Cormetech
honeycomb
2 months
3100
ESP
none
tt>
CD
Q.
SCR
PRB
opposed-fired
617
no
Cormetech
honeycomb
3 months
2800
ESP
none
A1
Unit A
NH3/S03h
conditioning
PRB/bit. blend
opposed-fired
500
yes
NA
NA
NA
ESP
none
A1
Unit B
NH3/S03
conditioning
PRB
opposed-fired
500
yes
NA
NA
NA
ESP
none
A2
SNCR
OH bit.9
tanqentially
fired
160
no
NA
NA
NA
ESP
none
A3
nh4hso4j
conditioning
TX lig. & TX
lig./PRB blend
tanqentially
fired
793
no
NA
NA
NA
ESP
wet FGD
A4
none
3 PRB/bit.
blends
wall-fired
156
no
NA
NA
NA
ESP
none
a Site S7 was not part of this project.
b Approximate catalyst age at the time tested.
0	PRB = Powder River Basin
d Two identical units sampled, one with and one without SCR.
6 Sampled three times, 1 year apart.
' bit = bituminous.
9 Two different bituminous coals were used.
h ammonia/sulfur trioxide.
1	NA = not applicable.
'Ammonium bisulfate.
k lig. = lignite

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Table ES-2. Summary of Coal Analyses3
Constituent
S1b
S2,
Yr 1
S2,
Yr 2
S2,
Yr 3
S3
S4,
Yr 1
S4,
Yr 2
S4,
Yr 3
S5
S6
(/)
00
O
S9b
Hg, ng/g dry
0.10
0.17
0.14
0.14
0.40
0.13
0.18
0.08
0.13
0.07
0.07
0.04
Chlorides, |ig/g dry
<60
1333
523
411
1248
357
270
577
472
1020
1160
10
Moisture, %
27.5
7.6
6.1
10.3
7.0
10.5
8.3
7.0
4.6
6.1
19.3
30.3
Ash, %
3.7
11.7
9.4
8.7
14.0
9.1
9.1
9.1
12.1
11.6
6.6
5.4
Sulfur, %
0.19
3.9
3.9
2.8
1.7
2.9
3.0
3.3
3.6
1.0
1.4
0.40
Heating Value, Btu/lb
8960
11,092
12,097
11,803
11,421
11,341
12,077
12,260
12,120
12,019
12,721
8185
Constituent
A1d
A1-Bb
A2e
A2e
A3f
A39
A4b
A4h
A4'



Hg, |ig/g dry
0.12
0.12
0.09
0.14
0.17
0.17
0.05
0.07
0.07



Chlorides, |ig/g dry
806
153
1263
1087
133
18
18
210
241



Moisture, %
17.3
27.3
6.2
7.3
35.4
32.1
26
24
23.6



Ash, %
7.0
4.8
7.0
8.2
13
12.6
3.89
4.93
5.33



Sulfur, %
0.61
0.36
2.6
2.6
0.92
0.82
0.36
0.67
1.0



Heating Value, Btu/lb
10,377
9400
12,535
11,907
6147
7123
9078
9589
9744



a As-received unless otherwise noted.
b 100% PRB coal.
c Nominal 60% PRB and 40% eastern bituminous blend.
d Nominal 50% PRB and 50% eastern bituminous blend.
e Two different eastern bituminous coals.
f 100% Texas lignite.
9 Nominal 80% Texas lignite and 20% PRB blend.
h Nominal 85% PRB and 15% eastern bituminous blend.
1 Nominal 70% PRB and 30% eastern bituminous blend.

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Table ES-3. Change in Hg Oxidation Across the SCR Catalyst (95% confidence
intervals)
Site3
Year
Sampled
SCR Inlet Hg2+, %
of Total Hg
SCR Outlet Hg2+,
% of Total Hg
Percentage Point
Increase13
S1
2001
8
17
9
S2
2001
48±21
91±6
43
S2
2002
54±61
87±10
33
S2
2003
44±7
89±1
45
S3
2001
55±9
65±10
10
S4
2001
9±9
80±7
71
S4C
2002
33±8
63±20
30
S4C
2003
47±4
90±2
43
S5
2002
43±11
76±8
33
S6
2002
60±3
82±2
22
S8
2003
45±17
93±5
48
S9
2003
3±2
7±1
4
a Sites S1 and S9 fired a PRB coal; site S8 fired a blend of PRB and eastern bituminous coal; the others used
only eastern bituminous coals; site S7 was not part of this project.
b Defined as (SCR outlet % - SCR inlet %) and based on the average value.
c Work was performed by Western Kentucky University.
Although there is strong evidence that an SCR catalyst does promote Hg oxidation, to
determine the overall effect of SCR, it was useful to conduct tests both with and without
SCR in service at each site. Figure ES-1 shows the comparison. For four of the six sites (S2
through S8) that fired eastern bituminous coal, there is a higher concentration of
non-elemental Hg (Hg2+ and Hgp) when an SCR unit was present, based on measurements
made at the inlet to the particulate control device. For the other two sites, S3 and S6,
non-elemental Hg was more than 90% of total Hg, both with and without an SCR unit in
service. For the two sites that fired PRB coal (SI and S9), there was very little increase in
nonelemental Hg as a result of operating an SCR.
Effect of SCR Catalyst Age on Hg Speciation
Data indicate that additional Hg oxidation can be expected if an SCR unit is installed on
a unit firing an eastern bituminous coal. A potential concern is "Does the Hg oxidation
potential of an SCR decrease with time?" Therefore, two of the facilities, S2 and S4, were
tested over three years (both burned eastern bituminous coal). As Figures ES-2 and ES-3
show, there appears to be little, if any, aging effect over a 3-year period.
5

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EERC DL23046.CDR


fe,



I

i i Inlet to Part. Control Device - No SCR
f777i Inlet to Part. Control Device - With SCR
F
V,
21
24
v:
A
E

I
S1
S2
S3
S6
S8
S4 S5
Site
Figure ES-1. Non-elemental Hg concentrations at the inlet of the
particulate control device with and without the SCR.
S9
100 -
EERC DL23048.CDR
I I SCR Inlet
IZZ2 SCR Outlet
[=] ESP Inlet

2001
2003
Figure ES-2.
2002
Site S2
Comparison of Hg speciation results from 2001, 2002, and
2003 at Site S2.
6

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gERC DL23089.CDR
100 -
80 -
O)
X
T3
0)
N
~o
X
O
60 -
40 -
20 -
SCR Inlet
IZZ2 SCR Outlet
i i Air Preheater Outlet
2001
2002
2003
Site 34
Figure ES-3 Comparison of Hg speciation results from 2001, 2002, and
2003 at Site S4.
Effect of the SCR on Wet FGD Performance for Hg Control
In general, wet FGDs remove more than 90% of Hg2+. However, there is evidence that
some of the captured Hg21 can be reduced in the wet FGD to Hg°.[6] Although the sample
set is very small (three facilities) and the wet FGDs tested to date are not representative of
the most common FGD design in the United States (forced oxidation system), the data from
this project support this statement. As shown in Table ES-4, in all cases there is a percentage
of Hg2H that is chemically reduced to Hg° in the wet FGD. This FlgO is relatively insoluble
and is, therefore, either reemitted or directly passes through the FGD, resulting in an
increase of Hg° across the FGD. Also, the data seem to indicate the operation of the SCR
unit ameliorates this effect.
7

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Table ES-4. Effect of the SCR on Hg° Concentration Across the Wet FGDs (95%
confidence intervals)
FGD Inlet Hg° FGD Outlet Hg° 0 lncreasea Total Hg
Site e Year	Cq	Cq	Hg '"crease, Removed,
Sampled	... '3	... '3	iig/Nm3	0/
r	jig/IM m	jig/Nm	%
With SCR





S2
2001
0.4±0.2b
0.9±0.1
0.5
89
S2
2002
0.3±0.2
1,3±0.2
1.0
84
S2
2003
0.3±0.1
0.6±0.2
0.3
90
S4
2001
1,0±0.4
1,3±0.3
0.3
91
S4
2002
0.5±0.1
0.8±0.1
0.3
90
S4
2003
0.3±0.1
0.4±0.1
0.1
91
S5
2002
0.7±0.2
1,0±0.3
0.3
91
Without SCR




S2
2001
3.4±0.1b
5.0±1.0
1.6
51
S4
2001
5.6±1.0
7.1±0.2
1.5
46
S4
2002
5.7±0.6
8.0±1.3
2.3
44
S5
2002
4.7±1.0
6.1±0.6
1.4
51
a Defined as (FGD outlet Hg° conc. - FGD inlet Hg° conc.).
b The ESP inlet data were used for site S2 in 2001 because FGD inlet Hg concentration values are clear
outliers.
Conclusions
The primary conclusions based on the test results are:
•	For plants firing eastern bituminous coals, Hg° can be oxidized across the SCR
catalysts. The effect that SCR has on Hg speciation (i.e., extent of additional
oxidation that occurs) depends on the coal characteristics and, possibly, catalyst
properties. The increase of Hg2+ at the SCR outlet ranged from 10% at Site S3 to 71%
at Site S4.
•	Over a 3-year period, catalyst age appears to have little effect on the oxidation
potential of the SCR.
•	Based on the limited data at three plants, SCR operation reduced the extent of Hg°
reemission across a wet FGD.
•	The effects of flue gas conditioning (including SNCR) on Hg speciation appears to be
minimal. However, for the plant firing a Texas lignite, the addition of NH4HS04 did
increase the percentage of Hgp.
8

-------
References
1.	U.S. Environmental Protection Agency. Study of Hazardous Air Pollutant Emissions
from Electric Utility Steam Generating Units Final Report to Congress, EPA/453/R-
98/004A [NTIS PB98-131774]; Office of Air Quality Planning and Standards and Office
of Research and Development, Executive Summary, Feb 1998.
2.	EPRI. An Assessment of Mercury Emissions from U.S. Coal-Fired Power Plants; EPRI
Report No. 1000608; Oct 2000.
3.	Hargrove, O.W. Jr.; Peterson, J.R.; Seeger, D.M.; Skarupa, R.C.; Moser, R.E. Update of
EPRI Wet FGD Pilot-Scale Mercury Emissions Control Research. Presented at the
EPRI-DOE International Conference on Managing Hazardous and Particulate Air
Pollutants, Toronto, ON, Canada, Aug 1995.
4.	Holmes, M.J.; Redinger, K.E.; Evans, A.P.; Nolan, P.S. Control of Mercury in
Conventional Flue Gas Emissions Control Systems. Presented at the Managing
Hazardous Air Pollutants 4th International Conference, Washington, DC, Nov 12-14,
1997.
5.	Gutberlet, H.; Schliiten, A.; Lienta, A. SCR Impacts on Mercury Emissions on
Coal-Fired Boilers. Presented at the EPRI SCR Workshop, Memphis, TN, April 2000.
6.	EPRI. Pilot-Scale Screening Evaluation of the Impact of Selective Catalytic Reduction
for NOx on Mercury Speciation, EPRI Report No. 1000755, EPRI, Palo Alto, CA, 2000.
7.	EPRI. Power Plant Evaluation of the Effect of Selective Catalytic Reduction on
Mercury, EPRI Report No. 1005400, EPRI, Palo Alto, CA, 2002.
9

-------
10

-------
Introduction
The objective of this report is to document the results and provide a summary of the tests
associated with the "Selective Catalytic Reduction Mercury Field Sampling Project." The
testing was sponsored by EPRI, with additional funds provided by the utility industry, the
U.S. Department of Energy (DOE) National Energy Technology Laboratory, and the U.S.
Environmental Protection Agency (EPA) National Risk Management Research Laboratory.
Over a 3-year period, mercury (Hg) measurements were completed at 12 power plants, 8 of
which had selective catalytic reduction (SCR) for nitrogen oxides (NOx) reduction. Three of
the plants injected ammonia (NH3) or NH3 compounds either for conditioning electrostatic
precipitators (ESPs) or for NOx reduction. The final plant was tested to help evaluate the
effects on Hg speciation of blending Powder River Basin (PRB) subbituminous coal and
eastern bituminous coals.
Coal combustion by electric utilities is a large source of anthropogenic Hg emissions in
the United States, according to the most recent data, accounting for 45 tons/yr of total
point-source Hg emissions. [1] In December 2000, EPA issued an intent to regulate Hg from
coal-fired utility boilers and, in 2004, issued a proposed rule for public comment. [2] As a
result, many utilities have become proactive in evaluating the effectiveness of current air
pollution control technologies, as well as new technologies for Hg control. [1, 3-5]
Hg emissions from coal-fired boilers can be empirically classified, based on the
capabilities of currently available analytical methods, into three main forms: elemental Hg
(Hg°), oxidized Hg (Hg2+), and particulate-bound Hg (Hgp). The Hgp can be removed from
flue gas by conventional air pollution control devices (APCDs) such as an ESP or a
baghouse. Hg2+ compounds are readily captured in flue gas desulfurization (FGD) units. Hg°
is most likely to escape APCDs and be emitted to the atmosphere. Total Hg concentrations
in coal combustion flue gas typically range from 3 to 15 |ig/Nm3; however, Hg°, Hg2+, and
Hgp concentrations are quite variable depending on coal composition and combustion
conditions. [6]
In addition to Hg, coal-burning power plants are a significant anthropogenic source of
NOx emissions to the atmosphere. These NOx emissions are an environmental concern
primarily because they are associated with increased acidic precipitation, as well as fine
11

-------
particle and ozone formation. Depending on the size and type of boiler, the 1990 Clean Air
Act Amendments require specific reductions in NOx emissions from coal-fired electric
utilities. The most common NOx reduction strategy is the installation of low-NOx burners.
These burners have the capability of reducing NOx emissions by 40%-60%. However, with
possible establishment of fine particulate (PM2 5), regional haze, ozone regulations, and NOx
state implementation plans, there is increased incentive to reduce NOx emissions to a level
below what can be achieved using low-NOx burners. SCR technology, which can reduce
NOx emissions by more than 90%, is, therefore, becoming more attractive, particularly
because catalyst costs continue to decrease and the knowledge base for using SCR reactors
is expanding. It is planned that approximately 100 gigawatts of coal-fired electrical capacity
will have SCRs installed by 2005. [7]
Potential Impacts of SCR on Hg Speciation
SCR units achieve lower NOx emissions by catalytically reducing NOx to molecular
nitrogen (N2) and H20 in the presence of NH3. The catalysts used in SCR units are generally
metal oxides such as titanium dioxide (Ti02) supported vanadium oxide (V205). These units
are generally operated at about 650-750 °F (343-399 °C). Initial laboratory-scale tests
indicated that metal oxides, including V205 and Ti02, promoted the conversion of Hg° to
Hg2+ or Hgp in relatively simple flue gas mixtures. [8] In addition, pilot- and full-scale Hg
speciation measurements in European and U.S. coal-fired boilers equipped with SCR
reactors have shown the potential to promote the formation of Hg2+. [9-11] Therefore, it was
hypothesized that the use of SCR may improve the Hg-control efficiency of existing APCDs
by promoting Hg2+ or Hgp formation.
Possible mechanisms by which SCR operation could affect Hg speciation include:
•	Catalytic oxidation of the Hg. Evidence indicates that vanadium-based catalysts can
promote the formation of Hg2+.
•	Changing the flue gas chemistry. The significant reduction in flue gas NOx and slight
increase in NH3 concentrations associated with SCR may affect Hg speciation. It is
well known thatNOx, particularly nitrogen dioxide (N02), has a substantial effect on
Hg speciation. [12] The gas-phase effects of NH3 on Hg are unknown. SCR units also
have the potential to catalyze the formation of sulfur trioxide (S03) and, potentially,
alter the formation of chlorine, which may then react with Hg. [13-17]
•	Providing additional residence time for the oxidation of Hg to take place.
•	Changing the fly ash chemical composition. It is possible that SCR operation may
change the surface chemistry of the fly ash particles such that their ability to adsorb or
convert Hg species is altered.
12

-------
Pilot-Scale Screening Tests Conducted at the EERC
To investigate the effects of SCR on Hg speciation in a coal combustion system, EPRI,
DOE, and EPA funded a pilot-scale project at the Energy & Environmental Research Center
(EERC). [9] The primary objective for the pilot-scale tests was to determine whether NH3
injection or the catalyst in a representative SCR system promote the conversion of Hg° to
Hg2+ or Hgp. Although this project was a screening evaluation and not a complete parametric
study, it was designed to evaluate potential mechanisms for Hg conversion and the various
coal parameters (like chemical composition) that may affect the degree of conversion.
Three bituminous coals and a PRB subbituminous coal were burned in a pilot-scale
combustion system equipped with an NH3 injection system, SCR reactor, and ESP. The
selection criteria for the four coals investigated were the significant differences in their
sulfur and chloride contents.
The results from the tests indicated thatNH3 injection and, possibly, the SCR catalyst
promote the conversion of Hg2+ to Hgp in the coal combustion flue gases for two of the
bituminous coals, but this was not the case for the PRB coal. The results were inconclusive
for the third bituminous coal. When the limited data are used in a linear regression analysis,
it appears that the chloride, sulfur, and calcium contents of the coal correlate with Hg
speciation across the SCR unit. Because of the inherent concerns related to small pilot-scale
tests (surface area-to-volume ratios, different flue gas chemistries, and time and temperature
profiles), it was decided that sampling at full-scale power plants was necessary. Therefore,
beginning in 2001, EPRI, DOE, EPA, and the utility industry funded projects with the
EERC and others to conduct Hg sampling at power plants.
13

-------

-------
Experimental Approach
The principal objective of the project was to determine the impact of SCR operation and
flue gas conditioning on Hg speciation and, ultimately, on Hg emissions. To achieve this
objective for each unit/coal, a sampling plan was developed for various operating conditions
so that the effects of SCR or flue gas conditioning could be determined. At each site, tests
were conducted (where feasible) under operating conditions with and without the SCR in
operation or flue gas conditioning agents added. For the purposes of this report, the plants
using SCR (eight plants) are referred to as Sites SI through S9. The two plants with flue gas
conditioning are referred to as Sites A1 and A3; the plant using selective noncatalytic
reduction (SNCR) (urea injection) is Site A2; and the plant using different coal blends is
Site A4. For consistency, the numbering system is the same that has been used for the
annual reports. Site S7 is not included because that site was not part of this project. A
summary of the configuration of each plant tested and the purpose for testing at that plant
are provided in Tables 1 and 2, respectively.
During the first year of testing at the four sites with SCR (Sites SI, S2, S3, and S4),
three conditions were evaluated. The first test condition was with the SCR unit on-line and
fully operational. Specifically, the flue gas was passed through the SCR catalyst, and NH3
was added to reduce the NOx. The second test condition was with the NH3 turned off.
During this condition, the flue gas was flowing through the SCR, but no NH3 was added.
The third was a baseline condition where SCR was either completely bypassed or a sister
unit that did not have an SCR was tested. Based on the results of the first year of field work,
it was decided that additional testing at plants with SCR would not include the NH3-off test
condition because it would not be expected that an SCR would be operated in this mode.
Therefore, most of the subsequent work focused on the impact of SCRs on Hg speciation
and emissions.
In addition to SCR, factors that were identified that could potentially contribute to Hg
oxidation include coal type, specifically chlorine and sulfur content, and catalyst age.
Therefore, at each plant, coal samples were taken and analyzed. A summary of coal data for
each plant is provided in Table 3. Additionally, as shown in Table 2, two plants (Sites S2
and S4) were tested during each of 3 years to help determine the impact of catalyst age on
15

-------
Table 1. Configuration of Power Plants Tested
NOx Control
Plant3 or Flue Gas
Conditioning
Boiler
Coal Boiler Type Size
(MW)
S1
S2d,e
SCR
SCR
PRBC
OH bit.'
cyclone
wall-fired
650
1300
S3
S4d,e
55
56
S8
c\ S9d
A1
Unit A
A1
Unit B
A2
A3
A4
SCR
SCR
SCR
SCR
SCR
SCR
NHj/SCV1
conditioning
NH3/SO3
conditioning
SNCR
nh4hso4j
conditioning
none
PA bit.9
KY bit.
WV bit.
low sulfur KY &
WV bit.
PRB/bit. blend
PRB
tanqentially
fired
cyclone
wall-fired
concentrically
fired
wall-fired
opposed-fired
PRB/bit. blend opposed-fired
PRB	opposed-fired
OH bit.9
TX lig. & TX
lig./PRB blend
3 PRB/bit.
blends
tanqentially
fired
tanqentially
fired
wall-fired
750
650
684
700
820
617
500
500
160
793
156
a Site S7 was not part of this project.
b Approximate catalyst age at the time tested.
0	PRB = Powder River Basin
d Two identical units sampled, one with and one without SCR.
6 Sampled three times, 1 year apart.
' bit = bituminous.
9 Two different bituminous coals were used.
h ammonia/sulfur trioxide.
1	NA = not applicable.
' Ammonium bisulfate.
k lig. = lignite
Low-NOx
Burners
Catalyst
Vendor and
Type
Catalyst
Ageb
SCR
Space
Velocity
(hr1)
Particulate
Control
Sulfur
Control
no
yes
yes, with
overfire air
no
yes
yes
yes
no
yes
yes
no
no
no
Cormetech
honeycomb
Siemens/
Westinghouse
plate
KWH
honeycomb
Cormetech
honeycomb
Haldor Topsoe
plate
Cormetech
honeycomb
Cormetech
honeycomb
Cormetech
honeycomb
NA
NA
NA
NA
NA
-8000 hr
1, 2, & 3 ozone
seasons
1 ozone season
1, 2, & 3 ozone
seasons
3 months
2 ozone
seasons
2	months
3	months
NA
NA
NA
NA
NA
1800
2125
3930
2275
3700
3800
3100
2800
NA
NA
NA
NA
NA
ESP
ESP
ESP
Venturi
scrubber
ESP
ESP
ESP
ESP
ESP
ESP
ESP
ESP
ESP
none
wet scrubber
none
lime Venturi
scrubber
wet FGD
none
none
none
none
none
none
wet FGD
none

-------
Table 2. Summary of the Selection Criteria for Each Plant
Vpar
Plant jested	Purpose of Test
S1
2001
S2
2001-
S3
2001
S4
2001-
S5
2002
S6
2002
S8
2003
S9
2003
A1
2001
A2
2001
A3
2001
A4
2003
PRB coal with SCR
high-sulfur bituminous coal with SCR, a wet FGD system; catalyst aging
effects
medium-sulfur bituminous coal with SCR
high-sulfur bituminous coal with SCR, a wet FGD system; catalyst aging
effects
high-sulfur bituminous coal with SCR, a wet FGD system
low-sulfur bituminous coal with SCR
PRB-bituminous coal blend with SCR
PRB coal with SCR
PRB and PRB-bituminous coal blends with NH3 and S03 conditioning
medium-sulfur bituminous coal with SNCR
Texas lignate-PRB blends with NH4HS04 conditioning
PRB-bituminous coal blends
Hg speciation and ultimately on Hg emissions. In addition to coal samples, in effort to
complete a Hg balance at each plant, samples were collected from each of the APCDs.
Schematics showing the sampling locations for each of the plants are shown in Figures
1-14. As can be seen in the figures, Ontario Hydro (OH) sampling was done at the inlet and
outlet of each of the APCDs. In addition, continuous mercury monitors (CMMs) were
located at all sampling locations after the particulate control device. Flue gas samples were
also taken to measure the total particulate loading, chlorides, S03 concentrations and, when
the SCR was operating, NH3 slip, which is the amount of NH3 that passes unreacted through
the SCR.
17

-------
Table 3. Summary of Coal Analyses3
Constituent
S1b
S2,
Yr 1
S2,
Yr 2
S2,
Yr 3
S3
S4,
Yr 1
S4,
Yr 2
S4,
Yr 3
S5
S6
(/)
00
O
S9b
Hg, ng/g dry
0.10
0.17
0.14
0.14
0.40
0.13
0.18
0.08
0.13
0.07
0.07
0.04
Chlorides, |ig/g dry
<60
1333
523
411
1248
357
270
577
472
1020
1160
10
Moisture, %
27.5
7.6
6.1
10.3
7.0
10.5
8.3
7.0
4.6
6.1
19.3
30.3
Ash, %
3.7
11.7
9.4
8.7
14.0
9.1
9.1
9.1
12.1
11.6
6.6
5.4
Sulfur, %
0.19
3.9
3.9
2.8
1.7
2.9
3.0
3.3
3.6
1.0
1.4
0.40
Heating Value, Btu/lb
8960
11,092
12,097
11,803
11,421
11,341
12,077
12,260
12,120
12,019
12,721
8185
Constituent
A1d
A1-Bb
A2e
A2e
A3f
A39
A4b
A4h
A4'



Hg, |ig/g dry
0.12
0.12
0.09
0.14
0.17
0.17
0.05
0.07
0.07



Chlorides, |ig/g dry
806
153
1263
1087
133
18
18
210
241



Moisture, %
17.3
27.3
6.2
7.3
35.4
32.1
26
24
23.6



Ash, %
7.0
4.8
7.0
8.2
13
12.6
3.89
4.93
5.33



Sulfur, %
0.61
0.36
2.6
2.6
0.92
0.82
0.36
0.67
1.0



Heating Value, Btu/lb
10,377
9400
12,535
11,907
6147
7123
9078
9589
9744



a As-received unless otherwise noted.
b 100% PRB coal.
c Nominal 60% PRB and 40% eastern bituminous blend.
d Nominal 50% PRB and 50% eastern bituminous blend.
e Two different eastern bituminous coals.
f 100% Texas lignite.
9 Nominal 80% Texas lignite and 20% PRB blend.
h Nominal 85% PRB and 15% eastern bituminous blend.
1 Nominal 70% PRB and 30% eastern bituminous blend.

-------
EERCJTieOI7.CDR
NH, Injection—
Boiler
SCR
Outlet
Stack
EERC 01301*4 COR
SCR Inlet
Sample Location
ESP Inlet
Sample Location
Stack Sample
Location
SCR Outlet
Sample Location
Stack
Unit 2
Boiler
SCR
AH
ESP
Figure 1. Schematic of Site S1 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
EEFK;J719295.CC*!
NH3 Injection
SCR \ SCR
Outlet
Stack
Boiler
SCR
Inlet
AH
ESP
Inlet
ESP
Outlet
FGD
ESP
ESP Inlet	ESP Outlet
Sample Location Sample Location
SCR Inlet	SCR Qut|et
Sample Location Samp|e Locatjon
Stack Sample
Location
Boiler
SCR
ESP
Figure 2. Schematic of Site S2 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
19

-------
EERCJr204S9.CDR
NH3 Injection
ESP
Outlet
Boiler
ESP
SCR
y
1 AH „
^SCR
Outlet
SCR
Inlet
ESP
Inlet
SCR Outlet	ESP Outlet
Sample Location Sample Location
SCR Inlet
Sample Location
From
B Side
ESP Inlet
Sample Location
Stack
AH
Unit 1
Boiler	SCR	ESP
Figure 3. Schematic of Site S3 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
EERCJTZ>430,CCR
NH3 Injection
Boiler
SCR
Stack
Lime Venturi
Scrubber
XSCR
Outlet
SCR
AH Outlet
AH
Air Heater Outlet
Sample Location
SCR Outlet
Sample Location
SCR Inlet
Sample Location
Stack Sample
Location
Stack
Boiler
Lime Venturi
SCR	aH	Scrubber
Figure 4. Schematic of Site S4 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
20

-------
E£RCCW2n3VCDR
NH3 Injection
Boiler
Outlet
, Stack
ESP
Outlet
SCR Inlet
Sample Location
SCR Outlet
Sample Location
ESP Outlet
Sample Location
Stack Sample
Location
ESP Inlet
Sample Location
Boiler
SCR
ESP ESP
Stack
Figure 5. Schematic of Site S5 for the unit with SCR showing sample
locations from horizontal and vertical views (AH = air preheater).
EEHOCW2JI57-OOB
Stack
Boiler
ESP
Inlet
ESP
Outlet
AH
FGD
ESP
Stack Sample
ESP Inlet	Location
Sample Location
Stack
ESP
AH
Boiler
ESP Outlet
Sample Location
\ r-O-
Figure 6. Schematic of Site S5 for the unit with no SCR showing sample
locations from horizontal and vertical views (AH = air preheater).
21

-------
EEHC CWZt&OCDR
NH3 Injection—
ESP
Boi er
Outlet
Stack
SCR
Inlet i AH
SCR Inlet
Sample Location
SCR Outlet
Sample Location
ESP Inlet
Sample Location
Stack Sample
Location
Boiler
SCR
ESP ESP
Stack
Figure 7. Schematic of Unit 1 at Site S6 with SCR in service showing
sample locations from horizontal and vertical views (AH = air preheater).
EERC CW21281.CDR
ESP
Stack
Boiler
SCR
SCR
Bypass
ESP
Inlet
AH
ESP Inlet	Stack Sample
Sample Location Location
SCR
AH
ESP ESP
Stack
Boiler
Bypass
Figure 8. Schematic of Unit 2 at Site S6 with SCR bypassed showing sample
locations from horizontal and vertical views (AH = air preheater).
22

-------
Unit 1
EERC DL21921.CDR
NH3 Injection
S03 Injection
SCR
Upper ESP
Boiler
AH
Lower ESP
SCR Outlet
ESP Outlet
Stack
SCR In lei
L- ESP Inlet
Unit 2
Upper ESP
S03 Injection
Boiler
AH
Lower ESP
ESP Outlet
ESP Inlet-
Figure 9. Side-view schematic of Site S8 Units 1 and 2 showing
sampling locations (AH = air preheater).
23

-------
WH3 Injection
Unit 2
BERG Oi.2Mm.CDft
S03 Injection
SCR
Upper ESP
Boiler
AH
Lower ESP
\ SCR Outlet
SCR Middle
ESP Outlet
Stack
SCR Inlet
ESP Inlet
Unit 1
Upper ESP
S03 Injection
Boiler
AH
Lower ESP
ESP Outlet
ESP inlet'
Unit 2
amoumm,-
SCR
AH
Upper and
Lower ESP
Boiler
AH
SCR
ESP Outlet
SCR Inlet j
SCR Middle
ESP Inlet
SCR Outlet
Unit
AH
Upper and
Lower ESP
Boiler
AH
ESP Outlet
ESP Inlet
Figure 10. Schematic of Site S9 Units 1 and 2 showing sample locations
from horizontal and vertical views (AH = air preheater).
24

-------
Air Preheater
ESP Inlet
Sample
Location
ESP
Nh and SO,
Injects
Air Heater Inlet
Sample Location

tSP Inlet
Sample Location
ESP Outlet
Sample Location
\
.
Stack
Figure 11. Schematic of Site A1 showing sample locations
from horizontal and vertical views (AH = air preheater).
Air Preheater
Sample
Location
Stack
Sample
Location
Urea
injection
Unite
Boiler
Stack
ESP

Air Heater Inlet
Sample Location
Urea
Injection
~I
ESP Wat
Sample Location
Site A2
Boitet
ESP Outlet
Sample Location
From
Unit 5
ESP
3
Stack
Figure 12. Schematic of Site A2 showing sample locations from
horizontal and vertical views (AH = air preheater).
25

-------
E£RCDl23mS,C£m
Boiler
¦Stack
AH
FGD
ESP
ESP
Inlet
ESP
Outlet
ESP
ESP
Inlet
ESP
Outlet
APH
FGDs
Stack
Boiler
Figure 13. Schematic of Unit 2 at Site A3 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
EEBCOt.2f828.COB
Boiler
ESP
AH
Stack
ESP Inlet
Stack
ESP
Side A
AH
Boiler
ESP
Side B
AH
Stack
Stack
ESP Iniet
Figure 14. Schematic of Site A4 showing sample locations from
horizontal and vertical perspectives (AH = air preheater).
26

-------
Results and Discussion
The primary focus of this project was to evaluate changes in flue gas chemistry and
determine how this impacts Hg speciation. This was accomplished by testing at facilities
that fired different coals and had different APCDs, as shown in Table 1. As stated
previously, the use of SCR to reduce NOx emissions has the potential to improve the Hg
control efficiency of existing particulate removal and FGD systems by promoting Hg2+ or
Hgp formation. As data were compiled at the various facilities, several factors were
identified which may potentially impact the oxidation potential of SCR. Among these
factors, coal type and catalyst type, structure, and age were specifically identified as factors
that have the potential to influence Hg speciation.
To evaluate the effect of SCR on Hg speciation and, ultimately, on Hg emission at each
plant, the following were determined:
•	The change in Hg oxidation across the SCR unit.
•	The effect of SCR on Hg oxidation at the particulate control device (obtained by
comparing Hg speciation results with and without SCR in service).
•	The overall Hg removal with and without SCR.
The following is a summary discussion of the results. Detailed results were presented in
the annual reports submitted in 2001 and 2002 as well as individual reports of the plants
sampled in 2003 (see bibliography of project reports).
Effect of Flue Gas Conditioning and Coal Blending on Hg
Speciation
The results of the tests at the three facilities where flue gas conditioning agents were
used to enhance ESP performance are shown in Table 4. At Sites A1 and A3, it appeared
that NH3 injection tends to increase Hgp but inhibits Hg oxidation. It must be stressed that
these are very limited tests, and the results are quite variable. In fact, at Site A2, where urea
was injected into the boiler, the results are somewhat different. Here there was little effect
on the Hgp, and the effect of urea injection on Hg oxidation appeared to give different results
for the two coals tested. It is unknown if this was because NH3 is injected at a much higher
temperature compared to NH3 injection to improve ESP performance or if the effect is
simply coal dependent. In Table 5, the results are shown when different blends of a PRB and
27

-------
an eastern bituminous coal are fired. The results are what would be expected; there is a
decrease in Hgp and an increase in Hg° when increasing amounts of PRB are used in the
blend.
Table 4. Hg Speciation Results at the ESP Inlet for Facilities With and Without Flue Gas
Conditioning
A1-1a	A1-2	A2-1b	A2-2	A3-1c	A3-1
Hg 50% PRBd &	100% Bit. 100% Bit.	f 80% TX Lig.
Species 50% Bit.8	Coal 1	Coal 2 100/oTXLig. &20%PRB

with
without
with
without
with
without
with
without
with
without
with
without
Hgp, %
80
50
11
9
1
2
1
8
54
24
28
5
Hg°, %
2
7
67
72
37
17
12
13
10
10
35
17
Hg2+, %
18
43
22
19
62
81
87
79
36
66
37
78
Total Hg
65.3
45.8
21.1
9.8
19.2
-11.4
0.1
1.8
75.5
75.6
51.9
48.4
removed












a	A1 used both NH3 and SOs injected just upstream of the ESPs. Only the NH3 was turned off for tests without
conditioning.
b	A2 was an SNCR unit, so urea was injected into the boiler.
c	A3 injected NH4HS04 just upstream of the ESPs.
d	PRB = Powder River Basin.
e	Bit. = bituminous.
f	Lig. = lignite.
Table 5. Hg Speciation Results at the ESP Inlet When Blending PRB and Eastern
Bituminous Coals
A4-1	A4-2	A4-3
Hg Species 70% PRBd & 85% PRB &	odd
30% Bit.8 15% Bit.
Hgp, %
46
13
1
Hg°, %
20
53
95
Hg2+, %
35
34
4
Total Hg removed
47.3
23.7
6.3
a PRB = Powder River Basin.
b Bit. = bituminous.
Effect of an SCR on Hg Speciation
The percentage of Hg2+ was measured at both the inlet and outlet of the SCR unit at each
facility. It should be noted that all of the OH samples taken at these two locations were prior
to the air preheater; therefore, the temperature ranged from 640 to 700 °F (338 to 371 °C).
Table 6 presents the results for all of the plants tested that had SCR. In all cases, there was
28

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an increase in Hg oxidation across the SCR catalyst. However, the amount of oxidation that
occurs across the catalyst is highly variable. Some factors that may have affected the level of
oxidation are coal type and catalyst chemistry, structure, and age.
Table 6. Change in Hg Oxidation Across the SCR Catalyst (95% confidence interval)
Year SCR Inlet Hg2+, % SCR Outlet Hg2+, Percentage Point
Sampled	of Total Hg	% of Total Hg	Increase"
S1
2001
8
17
9
S2
2001
48±21
91±6
43
S2
2002
54±61
87±10
33
S2
2003
44±7
89±1
45
S3
2001
55±9
65±10
10
S4
2001
9±9
80±7
71
S4C
2002
33±8
63±20
30
S4C
2003
47±4
90±2
43
S5
2002
43±11
76±8
33
S6
2002
60±3
82±2
22
S8
2003
45±17
93±5
48
S9
2003
3±2
7±1
4
a Sites S1 and S9 fired a PRB coal; site S8 fired a blend of PRB and eastern bituminous coal; the others used
only eastern bituminous coals; site S7 was not part of this project.
b Defined as (SCR outlet % - SCR inlet %) and based on the average value.
c Work was performed by Western Kentucky University.
There was substantial variability in the percentage of Hg2+ at both the SCR inlet and
outlet locations. An example showing this variability is shown in Figure 15. However, there
was also variability among the other sites firing eastern bituminous coal. For example,
repeat testing conducted at Site S4 indicated a substantial increase in the percentage of Hg2+
when the coal chloride concentration increased from 2001 to 2002 testing. As shown in
Figure 16, one factor that appears to relate to the percentage of Hg2+ at the inlet to SCR unit
is the chloride concentration in the coal. It appears there is a threshold chloride
concentration at about 300-500 ppm chloride above which 40%-60% Hg oxidation results
at the SCR inlet. What effect this has on overall Hg oxidation is unclear.
Factors that may affect Hg oxidation are catalyst type and space velocity. Without
substantially more data, it is very difficult to determine the effects of these parameters. For
example, Sites S2 and S4 had space velocities less than 2300 hr"1; Sites S3, S5, and S6 had
29

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20
EERC DL21M C-OR
# Hg SCEM Total Gas-Phase Hg
O Hg SCEM Elemental Hg
i » OH Total Gas-Phase Hg
3

240 264 288 312 336 360 384 408 432 456 480 504 528 552 576 600 624 648 672 696 720 744 768 792 816 840
Hours into Test
Figure 15. Example of mercury variability at the stack from a site burning a high-sulfur
eastern bituminous (Site S5) coal.
100
DC
O 80-
co
CD
EERC DL23047.CDR
60
+
CM
CD H
J O
o r
CD O
O)
CO Q_
C CO
CD CO 40
O O
& s
^ 20 -I
S1
~ S9
S5#
S2 - 2002
S2-2001
S8
S4 - 2002
S4 - 2001
n	1	r
0 200 400 600 800 1000 1200 1400 1600
Average Chloride Cone, in the Coal (dry), pg/g
Figure 16. Percent of Hg2+ at the inlet of the SCR system as a function of chloride content
of the coal (note: data points without labels are results from plants without SCR units
where Hg speciation was measured at the air heater inlet).
30

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space velocities greater than 3700 hr-1; but there does not appear to be a clear correlation.
However, as shown in Table 1, the catalysts were also different. An attempt was made to
evaluate catalyst aging effects by retesting two plants (Sites S2 and S4). The results are
discussed in next section. EPRI is currently in the process of trying to develop models that
would predict the effects of the SCR catalysts based on catalyst properties.
Although there is strong evidence that an SCR catalyst does promote Hg oxidation, to
determine the overall effect of SCR, it was useful to conduct tests both with and without
SCR in service at each site. Figure 17 shows the comparison. For three of the five sites,
there is a higher concentration of non-elemental Hg (Hg2H and Hgp) when an SCR unit was
present based on measurements made at the inlet to the particulate control device. For the
other two sites, S3 and S6, non-elemental Hg was greater than 90% of the total both with
and without an SCR unit in service. Once the SCR unit is bypassed, the change in Hg
oxidation occurs rapidly, as is shown by the CMM data presented in Figure 18.
100
EERC DL2304S.CDR
.3 80-
60-
V- 40-
20-
0
2
I

h


1
j
I
Inlet to Part. Control
V7~7~a Inlet to Part. Control
M l l l l M l
Device
Device
V,
No SCR
With SCR
M
V.
I

il
S1
S2
S3
S4 S5
Site
S6
i
I
I
S8
f
I
'A
S9
Fiqure 17. Hq concentrations at the inlet of the particulate control device with and without
the SCR.
31

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CO
E
20 -
O)


18 -
c

o
16 -
CO

-1—'
c
14 -
CD

O

c
12-
o
O

>
10 -
13

O
i—
8 -
CD


6 -
CD

(/)

CO
4 -
-C

CL

CO
? -
CO

a


0 -
(O
-f—'
,o
1b
1-

EERC JT20353.CDR
16:00
17:00 18:00 19:00 20:00 21:00 22:00
Time
Figure 18. CMM data showing the effect of bypassing the SCR reactor.
Effect of SCR Catalyst Age on Hg Speciation
Flue gas monitoring was conducted over 3 consecutive years at two power plants (Sites
S2 and S4) to evaluate the impact catalyst age had on Hg speciation. The concern was that
the oxidation potential of an SCR catalyst could be reduced with time. The first tests were
conducted after approximately 3.5 months of catalyst age at Site S2 and after about 5
months at Site S4. Follow-up testing was then conducted after two additional ozone seasons
at each plant. Figures 19 and 20 show the results of the testing at these two sites.
It appeared that there was a decrease in Hg oxidation across the SCR catalyst by the
second season, particularly for Site S4. However, this was not apparent following the third
season. Although the plant indicated the coal was from the same mine, it is possible there
may have been some difference in the coal fired during the tests conducted in 2001 and
2002. The chlorine content was somewhat lower and the Hg concentration a little bit higher
in 2002. Although there may have been some differences in the oxidation across the SCR
catalyst, there was no significant difference at the inlet to the particulate control device at
either site from the first season to the third.
32

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EERC DL23048.CDR
100
80
C2>
X
"O
0J 60
N
X
O
xp 40
20
2001
i
I
SCR Inlet
r777i SCR Outlet
ESP Inlet
2002
Site S2
I
'A
2003
Figure 19. Comparison of Hg speciation results from 2001, 2002, and 2003 at Site S2,
EERC DL23Q89.CDR
100 -
80 -
O)
I
-o 60
CD
N
-q
x
O 40
20 -
W,
H
SCR Inlet
I777I SCR Outlet
Air Preheater Outlet

I,

2001
2002
Site S4
2003
Figure 20. Comparison of Hg speciation results from 2001, 2002, and 2003 at Site
S4.
33

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SCR/Wet FGD Combination for Hg Control
The underlying intent of understanding Hg oxidation via SCR technology is to determine
its potential to improve the Hg collection efficiency of existing ESPs, fabric filters, and FGD
systems in particular. In general, wet FGD systems remove more than 90% of Hg2+. There
has been evidence, however, that some of the captured Hg2+ can be reduced in the wet FGD
system to Hg°.[l 1, 18] Three sites have been tested that have wet FGD systems. Sites S2 and
S5 employ magnesium-enhanced lime FGDs, and Site S4 is a combined particulate-S02
venturi-spray tower scrubber. It is important to note that approximately 60% of wet FGD
systems in the United States are limestone forced-oxidation systems. As can be seen in
Table 7, there is a measurable increase in Hg° across the FGD unit at all of the sampling
sites when SCR was not in service. For the tests with SCR in service, there was an increase
in Hg°, but the increase appears to be very small and is generally within the variability of the
data. It should also be noted that there was little difference in the results each time Sites S2
and S4 were sampled, again indicating the catalyst age does not appear to effect Hg
speciation and overall Hg removal.
Table 7.
Effect of the SCR on Hg° Concentration Across Wet FGDs

Site
Year
Sampled
FGD Inlet Hg°
Conc.,
ng/Nm3
FGD Outlet Hg°
Conc.,
|ig/Nm3
Hg° Increase3,
|ig/Nm3
Total Hg
Removed,
%
With SCR




S2
2001
0.4±0.2b
0.9±0.1
0.5
89
S2
2002
0.3±0.2
1,3±0.2
1.0
84
S2
2003
0.3±0.1
0.6±0.2
0.3
90
S4
2001
1,0±0.4
1,3±0.3
0.3
91
S4
2002
0.5±0.1
0.8±0.1
0.3
90
S4
2003
0.3±0.1
0.4±0.1
0.1
91
S5
2002
0.7±0.2
1,0±0.3
0.3
91
Without SCR




S2
2001
3.4±0.1b
5.0±1.0
1.6
51
S4
2001
5.6±1.0
7.1±0.2
1.5
46
S4
2002
5.7±0.6
8.0±1.3
2.3
44
S5
2002
4.7±1.0
6.1±0.6
1.4
51
a Defined as (FGD outlet Hg° conc. - FGD inlet Hg° conc.).
b The ESP inlet data were used for site S2 in 2001 because FGD inlet Hg concentration values are clear
outliers.
34

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The mechanism for FGD reemission is not well understood, but it is speculated that
sulfite in the FGD slurry may reduce Hg2+ to Hg°. The impact of forced oxidation may alter
the sulfite chemistry, potentially giving different results than those obtained for the plants
shown in Table 7. Because the mechanism of reemission is not well understood and it is not
known how SCR units may impact reemission, the reader is cautioned in attempting to
extrapolate the results from these three sites to all FGD systems. Additional studies are
recommended and planned at plants with limestone forced-oxidation FGD systems.
35

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-------
Conclusions
For plants firing eastern bituminous coals, Hg oxidization occurs across SCR catalysts.
However, it appears to be variable and most likely related to a variety of factors. Some
potential factors are coal characteristics; catalyst chemistry, structure, and age; and space
velocity.
It appears that addition of an SCR unit, when an eastern bituminous coal is fired, will
provide additional Hg2+. With the exception of Sites S3 and S6 (where the Hg was
essentially all Hg2+ or Hgp both with and without SCR), all facilities showed increased
oxidation at the inlet to the particulate control device. The increase ranged from 15 to 39
percentage points.
At both sites where sampling was done over a 3-year period, it appeared there was a
decrease in Hg oxidation across the SCR catalyst between the first and second season,
particularly for Site S4. However, this was not apparent following the third season. In
addition, the overall mercury removal was the same for all 3 years. Although the plant
personnel at Site S4 indicated the coal was from the same mine, it is possible there may have
been some difference in the coal fired during the tests conducted in 2001 and 2002. The
chlorine content was somewhat lower and the Hg concentration a little bit higher in 2002.
Although there may have been some differences in the oxidation across the SCR catalyst, at
the inlet to the particulate control device, there was no significant difference at either site
from the first season to the third.
Based on the limited data at three plants, it appears there is some reemission of the
captured Hg across the wet FGDs. For the tests with SCR in service, the increase appears to
be very small and is generally within the variability of the data. Nevertheless, at all three
plants (over all three ozone seasons for Sites S2 and S4), there was an increase in Hg°. When
an SCR unit is not present, it appears that the reemission is more pronounced.
At two of the sites where flue gas conditioning agents were used to enhance ESP
performance, it appeared that NH3 injection tended to increase Hgp but inhibit Hg oxidation.
However, at Site A2 where urea was injected into the boiler (SNCR), this was not the case.
Therefore, it must be stressed that these are very limited tests, and the results are quite
37

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variable.
When different blends of a PRB and eastern bituminous coal were fired, the results
showed there was a decrease in Hgp and an increase in Hg° with increasing amounts of PRB.
38

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REFERENCES
1.	U.S. Environmental Protection Agency. Study of Hazardous Air Pollutant Emissions
from Electric Utility Steam Generating Units Final Report to Congress, EPA/453/R-
98/004A [NTIS PB98-131774]; Office of Air Quality Planning and Standards and Office
of Research and Development, Executive Summary, Feb 1998.
2.	Proposed National Emission Standards for Hazardous Air Pollutants; and, in the
Alternative, Proposed Standards of Performance for New and Existing Stationary
Sources: Electric Utility Steam Generating Units. 40 CFR Part 60 and 40 CFR Part 63,
Fed. Reg:, 69, No. 20 4652-4752, 2004.
3.	EPRI. An Assessment of Mercury Emissions from U.S. Coal-Fired Power Plants; EPRI
Report No. 1000608, Oct 2000.
4.	Hargrove, O.W. Jr.; Peterson, J.R.; Seeger, D.M.; Skarupa, R.C.; Moser, R.E. Update of
EPRI Wet FGD Pilot-Scale Mercury Emissions Control Research. Presented at the
EPRI-DOE International Conference on Managing Hazardous and Particulate Air
Pollutants, Toronto, ON, Canada, Aug 1995.
5.	Holmes, M.J.; Redinger, K.E.; Evans, A.P.; Nolan, P.S. Control of Mercury in
Conventional Flue Gas Emissions Control Systems. Presented at the Managing
Hazardous Air Pollutants 4th International Conference, Washington, DC, Nov 12-14,
1997.
6.	Information Collection Request Reports, http://www.epa.gov/ttn/uatw/combust/utiltox/
utoxpg.html (accessed Oct 7, 2000).
7.	Cichanowizc, J.E. Muzio, L.J. Factors Affecting Selection of a Catalyst Management
Strategy. In Proceedings of the Combined Power Plant Air Pollutant Control Mega
Symposium; Washington, DC, May 2003.
8.	Gutberlet, H.; Schliiten, A.; Lienta, A. SCR Impacts on Mercury Emissions on
Coal-Fired Boilers. Presented at the EPRI SCR Workshop, Memphis, TN, April 2000.
9.	EPRI. Pilot-Scale Screening Evaluation of the Impact of Selective Catalytic Reduction
for NOx on Mercury Speciation, EPRI Report No. 1000755, EPRI, Palo Alto, CA, 2000.
10.	EPRI. Power Plant Evaluation of the Effect of Selective Catalytic Reduction on
Mercury, EPRI Report No. 1005400, EPRI, Palo Alto, CA, 2002.
11.	U. S. Environmental Protection Agency. Effect of Selective Catalytic Reduction on
Mercury, 2002 Field Studies Update, EPA-600/R-04/032, National Risk Management
Research Laboratory, Air Pollution Prevention and Control Division, Research Triangle
Park, NC: April 2004.
12.	Miller, S.J; Dunham, G.E.; Olson, E.S. Controlling Mechanisms That Determine
Mercury Sorbent Effectiveness, Paper No. 99-898. Presented at the 92nd Annual
Meeting & Exhibition of the Air & Waste Management Association, St. Louis, MO,
June 1999.
13.	Shashkov, V.I.; Mukhlenov, I.P.; Be_yash, E.Y.; Ostanina, V.I.; Shokarev, M.M.;
Vershinina, F.I. Effect of Mercury Vapors on the Oxidation of Sulfur Dioxide in a
39

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Fluidized Bed of Vanadium Catalyst. Khim. Prom. (Moscow); ¥7, 288-290, 1971.
14.	Carey, T.R.; Skarupa, R.C.; Hargrove, O.W. Jr. Enhanced Control of Mercury and Other
HAPs by Innovative Modifications to Wet FGD Processes; Phase I Report for U.S.
Department of Energy Contract No. DE-AC22-95PC95260; Aug 28, 1988.
15.	Hitchcock, H.L. Mercury Sorption on Metal Oxides. M.S. Thesis, University of North
Dakota; 83 p, Dec 1996.
16.	Galbreath, K.C.; Zygarlicke, C.J. Mercury Transformations in Coal Combustion Flue
Gas. Fuel Process. Technol, 65 66, 289-310, 2000.
17.	Ghorishi, S.B.; Lee, C.W.; Kilgroe, J.D. Mercury Speciation in Combustion Systems:
Studies with Simulated Flue Gases and Model Fly Ashes. Presented at the 92nd Annual
Meeting & Exhibition of the Air & Waste Management Association, St. Louis, MO,
June 1999.
18.	Nolan, P.; Redinger, K.; Amrhein, G.; Kudlac, G. Mercury Emissions Control in Wet
FGD Systems. Presented at the International Conference on Air Quality III: Mercury,
Trace Elements, and Particulate Matter, Arlington, VA, Sept 9-12, 2002.
40

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BIBLIOGRAPHY OF REPORTS COMPLETED
FOR THIS PROJECT
1.	EPRI. Pilot-Scale Screening Evaluation of the Impact of Selective Catalytic Reduction
for NOx on Mercury Speciation, EPRI Report No. 1000755, EPRI, Palo Alto, CA, 2000.
2.	EPRI. Power Plant Evaluation of the Effect of Selective Catalytic Reduction on
Mercury, EPRI Report No. 1005400, EPRI, Palo Alto, CA, 2002.
3.	U. S. Environmental Protection Agency. Effect of Selective Catalytic Reduction on
Mercury, 2002 Field Studies Update, EPA-600/R-04/032, National Risk Management
Research Laboratory, Air Pollution Prevention and Control Division, Research Triangle
Park, NC: April 2004.
4.	Interim Reports for Sites S8, S9, A4, and the third-year sampling at Site S2. These
reports are in publication, but copies have been provided to the U.S. Department of
Energy, EPRI, U.S. Environmental Protection Agency, and specific power plants.
41

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/R-04/147
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Selective Catalytic Reduction Mercury Field Sampling Project
5. REPORT DATE
November 2004



6. PERFORMING ORGANIZATION CODE
7. AUTHORS
Dennis L. Laudal, Jeffrey S. Thompson, Chad A. Wocken (EERC, U.
of North Dakota)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Energy & Environmental Research Center

10. PROGRAM ELEMENT NO.
University of North Dakota
PO Box 9018
Grand Forks, ND 58202-9018


11. CONTRACT/GRANT NO.
R 83060601
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. EPA, Office of Research and Development

13. TYPE OF REPORT AND PERIOD COVERED
Final Summary; 03/01/01-06/30/04
Air Pollution Prevention and Control Division
Research Triangle Park, North Carolina 27711

14. SPONSORING AGENCY CODE
EPA/600/13
15. SUPPLEMENTARY NOTES
The EPA Project Officer is Chun Wai Lee, Mail Drop E305-01, phone (919) 541-7663, e-mail lee.chun-
wai@epamail.epa.gov.
16. ABSTRACT
The report provides a summary of the testing of the Selective Catalytic Reduction Mercury Field Sampling
Project. The electric utility industry is investigating methods to control and reduce mercury (Hg) emissions
because EPA proposed in 2000 to regulate Hg emissions from coal-fired power plants. The project
investigated the impact of selective catalytic reduction (SCR), selective noncatalytic reduction (SNCR), flue
gas-conditioning systems, and coal blending on speciation and capture of Hg from coal-fired electric utility
boilers. The results indicate that SCR can assist in converting elemental Hg to an oxidized form. However,
the effect appears to be coal-specific and, possibly, catalyst-specific. Significant increase in Hg oxidation
across the SCR reactor was observed for plants firing an eastern bituminous coal. The two plants that
showed very little increase in oxidation across the SCR fired Power River Basin subbituminous coal; results
of the repeated tests for the two plants show very little aging effect of the SCR catalyst for reducing Hg
oxidation over a 3-year period. Ammonia-based flue gas conditioning agents, whether injected directly as
NH3 gas or indirectly as NH2CONH2 and NH4HS04, did not appear to have a significant effect on Hg
speciation and removal. Results of the coal blending tests show significant increase of particulate-bound Hg
and decrease of Hg° with increasing amounts of bituminous coal in the coal blends.
17.
KEY WORDS AND DOCUMENT ANALYSIS


a. DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Air Pollution Mercury (metal)
Electric Power Plants Oxidation
Boilers Public Health
Coal
Combustion
Emission
Flue Gases
Pollution Control
Stationary Sources
13B 07B
10B
13A 06E
21D
21B
14G
18. DISTRIBUTION STATEMENT

19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
60
Release to Public

20. SECURITY CLASS (This Page)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77 ) PREVIOUS EDITION IS OBSOLETE

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