EPA/600/R-09/021
September 2009
Evaluation of the Impact of Chlorine
on Mercury Oxidation in a
Pilot-Scale Coal Combustor - the
Effect of Coal Blending
By
Shannon D. Seme
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
Cosponsor(s)
Electric Power Research Institute
EPRI 3420 Hillview Avenue, Palo Alto, California 94304
Principal Investigator: Paul Chu
Cormetech, Inc.
5000 International Drive
Durham, NC 27712
Principal Investigator: Tom Hastings
U.S. Environmental Protection Agency
Office of Research and Development
Washington, D.C. 20460
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Abstract
This project was a joint effort of the U.S. Environmental Protection Agency (EPA) National Risk
Management Research Laboratory. EPRI, and Cormetech.
Coal-fired power plants are a major source of mercury (Hg) released into the environment and
the utility industry is currently investigating options to reduce Hg emissions. One control option
is to utilize existing pollution control equipment such as wet flue gas desulfurization (FGD)
scrubbers. The split (speciation) between chemical forms of mercury (Hg) species has a strong
influence on the control and environmental fate of Hg emissions from coal combustion. The
high-temperature coal combustion process releases Hg in elemental form (Hg°). A significant
fraction of the Hg° can be subsequently oxidized in the low-temperature, post-combustion
n 94-
environment of a coal-fired boiler. Relative to Hg , oxidized Hg (Hg ) is more effectively
removed by air pollution control systems (APCS). For example, the water-soluble Hg2+ is much
more easily captured than insoluble Hg° in FGD units. Selective catalytic reduction (SCR)
technology widely applied for reducing NOx emissions from power plants also affects the
speciation of Hg in the coal combustion flue gases. Recent full-scale field tests conducted in the
U.S. showed increases in Hg oxidation across the SCR catalysts for plants firing bituminous
coals with sulfur (S) content ranging from 1.0 to 3.9%. However, plants firing subbituminous
Powder River Basin (PRB) coals which contains significantly lower chlorine (Cl) and sulfur (S)
content and higher calcium (Ca) content than those of the bituminous coals, showed very little
change in mercury speciation across the SCR reactors. A field study conducted by EPRI showed
blending of PRB coal with a bituminous coal (60% PRB/40% bituminous) resulted in increased
Hg2+ from 45% at the SCR inlet to 93% at the outlet. Coal blending appears to be a potentially
cost effective approach for increasing Hg oxidation for PRB coal-fired SCR systems.
A study has been undertaken to investigate the effect of blending PRB coal with an Eastern
bituminous coal on the speciation of Hg across an SCR catalyst. In this project, a pilot-scale (1.2
MWt) coal combustor equipped with an SCR reactor for NOx control was used for evaluating the
effect of coal blending on improving Hg oxidation across an SCR catalyst. Several parameters
such as the ratio of PRB/bituminous coal blend and the concentrations of hydrogen halides (HC1,
HBr, and HF) and halogens (Cb and Br2) in the flue gas were evaluated to determine their effects
on the oxidation of Hg° under typical SCR NOx emission control conditions. The objective of
this project was to evaluate the effectiveness of firing PRB/bituminous coal blends to enhance
mercury oxidation in a coal fired power plant equipped with an SCR system.
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Disclaimer
The U.S. Environmental Protection Agency through its Office of Research and
Development (funded and managed) or (partially funded and collaborated) in the
research described here. It has been subject to the Agency's review and has been
approved for publication as an EPA document.
Notice
Mention of trade names, products, or services does not convey, and should not be
interpreted as conveying, official EPA approval, endorsement, or recommendation.
IV
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CONTENTS
1 INTRODUCTION 1-1
2 EXPERIMENTAL APPROACH 2-1
3 RESULTS AND DISCUSSION 3-1
4 CONCLUSIONS 4-1
5 REFERENCES 5-1
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LIST OF FIGURES
Figure 2-1 Schematic of Multi-Pollutant Control Research Facility with Sampling
Locations Shown 2-1
Figure 3-1 Mercury Speciation Results for Different Coal Blend Combinations 3-2
Figure 3-2 Percent Oxidized Mercury for SCR Inlet and SCR Outlet for Different Coal
Blend Combinations 3-3
Figure 3-3 Gas-phase Chlorine (HCI + CI2) versus Theoretical Chlorine Concentration 3-5
Figure 3-4 Mercury Oxidation (absolute change) Across the SCR as a Function of Coal
Chlorine Content 3-6
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LIST OF TABLES
Table 2-1 Ultimate and Proximate Analysis for Coal Samples (as-received basis) 2-3
Table 2-2 Neutron Activation Results for Coal Samples 2-4
Table 2-3 Baghouse Hopper Ash Hg and LOI of Ash 2-5
Table 2-4 Operating Conditions for the Coal Blending Tests 2-6
Table 3-1 Hg Speciation Results from the SCR Inlet and SCR Outlet 3-1
Table 3-2 Sorbent Tube Results (post-baghouse) 3-3
Table 3-3 Method 26 Results for Coal Blending Tests 3-4
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1
INTRODUCTION
Coal-fired power plants are a major anthropogenic source of mercury emissions in the U.S. [1].
There are several control options for mercury emissions from coal-fired boilers. Mercury may be
captured as a co-benefit of paniculate matter (PM) controls, NOx controls, and 862 controls, as
well as through mercury-specific control technologies, such as activated carbon injection.
Available data show that the use of existing pollution control equipment can also be used to
control mercury emissions. It is known that mercury in its oxidized state (Hg +) is highly water
soluble and thus would be expected to be captured in plants with wet FGD systems. One of the
main obstacles with this approach is converting the elemental mercury into the water-soluble
mercuric chloride form. Selective catalytic reduction (SCR) has been shown as a method of
oxidizing mercury in some coal-fired boilers and results in increased mercury removal in the
downstream wet FGD system. The degree of this co-benefit varies with the type of coal being
burned and the specific control technology configuration.
Blending of coals of different ranks at pulverized coal-fired power stations is becoming
increasingly common as electric utilities attempt to save costs, meet 862 emission limits and
improve the combustion conditions in their plants. Many plants have begun to blend low-sulfur
Powder River basin (PRB) coal with Eastern bituminous coals to reduce SC>2 emissions. Little
data exists on the effect of blending on Hg speciation. One report by Laudal et al. [2] showed
that the overall Hg oxidation was greater than 99% at a plant that blended 40% PRB with 60%
bituminous coal (on a heat input basis) and operated an SCR unit. The goal of the current study
was to examine the oxidation of mercury using blends ranging from 10% PRB to 40% PRB with
the balance being Eastern bituminous coal, and compare those results to mercury oxidation when
firing pure bituminous and pure PRB fuel.
The results presented here focused on the effect of Cl concentration on the oxidation of Hg
across the SCR unit. In a full-scale power plant, oxidation will occur across the air pre-heater.
Additional tests to evaluate the air pre-heater on Hg oxidation were not performed because the
air pre-heater on the pilot plant is not representative of that at a full-scale power plant.
1-1
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2
EXPERIMENTAL APPROACH
The multi-pollutant control research facility (MPCRF), located at EPA's Research Triangle Park
campus, was used for the PRB and bituminous coal blending speciation tests. The MPCRF is a 4
MM Btu/hr (1.2 MWt) multi-fuel combustor that can fire pulverized coal, fuel oil, or natural gas.
A schematic of the facility is shown in Figure 2-1. The facility consists of the combustor, a series
of heat exchangers to simulate the convective section, a selective catalytic reduction (SCR) unit,
a fabric filter, and a lime slurry wet scrubber. The MPCRF is equipped with two sets of
continuous emissions monitors (CEMs) for measuring different flue gas species including sulfur
dioxide (802), nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CC^), and
oxygen (02). These measurements were taken at the inlet to the SCR and prior to the inlet of the
baghouse. NOx measurements were taken at the inlet and outlet of the SCR to determine the
NOx reduction efficiency.
NO
co Method 26 OH
C02 S J~
S02 ^l 0. • • >
O,
Coal
Figure 2-1
Schematic of Multi-Pollutant Control Research Facility with Sampling Locations Shown
2-1
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Experimental Approach
A low-sulfur PRB coal from the North Antelope seam located in Wyoming was used as the
baseline coal in these tests. A medium sulfur Eastern bituminous coal (Pittsburgh #8) was used to
increase the amount of chlorine in the fuel blends. The effect of the SCR unit on Hg speciation
was tested at four different PRB/bituminous blending ratios, 60%/40%, 70%/30%, 80%/20%,
and 90%/10%. Along with the two baseline tests of 100% PRB and 100% of bituminous, as well
as one repeated blend test, a total of seven tests were conducted for this study.
The separate coal blends were prepared in batches by calculating the amount of coal required to
obtain the specific blends. The blended coal batches were calculated based on the as-received
heating value for the two coals. The coal was then weighed and placed in a roll-off container for
blending. A front-end loader was used to blend the coal together prior to being pulverized in a
hammermill. Samples were taken for each blend after pulverization and sent for proximate and
ultimate analysis by an outside laboratory. The analysis results for the blends and baseline coals
are shown in Table 2-1. Neutron activation analysis (NAA) was used to determine the iodine (I),
bromine (Br), and chlorine (Cl) content of the coal and is shown in Table 2-2. The chlorine
ranged from 973 ppm for the bituminous coal to 35 ppm for the PRB. Bromine was 13.4 ppm for
the bituminous coal and 1.7 ppm for the PRB. Iodine was present in concentrations less than 2
ppm for all the fuel blends.
The facility is designed to be pre-heated on natural gas until the temperature exceeds 2000 °F at
which time the facility can be switched over to coal. During these tests, the facility was switched
over to coal in the afternoon prior to a test day. It takes about one hour for the flue gas
temperature to stabilize once the unit is fired on coal. The ammonia injection system was then
turned on about one hour after being switched to coal. Once a test day had finished the unit was
then switched back to natural gas to maintain temperature in the unit.
The SCR unit consists of three full length sections of honeycomb SCR catalyst elements (each
section containing nine honeycomb catalyst elements of 1190 mm length and 150 mm square
cross-section). Each section of the SCR catalyst is equipped with a flow straightener, a soot
blower, and the catalyst. The SCR was operated at a temperature of approximately 700-740 °F,
with a space velocity of 1900 h"1. A NHs/NOx ratio of 0.9-1 was used for these tests. Anhydrous
ammonia was metered using a mass flow controller and was injected into the flue gas duct about
4 feet prior to the SCR unit, which was designed to achieve 5% RMS deviation of NHs
concentration (i.e., reasonably well-mixed conditions simulating commercial practice). Ammonia
slip was not measured during these tests. Flue gas flow rates were measured at the outlet of the
SCR using a pitot tube. The SCR unit was designed with sample ports located between each
catalyst section. Soot blowers were used to clean the catalyst prior to the start of a test day and
approximately twelve hours into a test.
2-2
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Experimental Approach
Table 2-1
Ultimate and Proximate Analysis for Coal Samples (as-received basis)
Sample
100%
BIT
65%/35%
(PRB/BIT)
70%/30%
(PRB/BIT)
74%/26%
(PRB/BIT)
79%/21%
(PRB/BIT)
91%/9%
(PRB/BIT)
100% PRB
Proximate
Moisture
Volatile
Ash
Fixed Carbon
2.63
35.02
6.06
56.29
19.43
31.63
6.16
42.78
18.42
33.29
6.49
41.8
21.32
31.49
5.69
41.5
23.88
34.91
4.95
36.26
27.38
39.78
3.81
29.03
31.37
32.72
4.04
31.87
Ultimate
Carbon, %
Hydrogen, %
Nitrogen, %
Sulfur, %
Oxygen, %
Fluorine, ppm
76.80
5.36
1.79
1.40
8.49
94
59.58
6.0
1.05
0.63
26.55
52
57.04
4.71
0.97
0.54
30.23
N/A
58.82
5.93
0.97
0.48
28.09
52
54.58
5.61
0.98
0.43
33.43
72
51.3
5.93
0.91
0.30
37.75
88
51.02
5.95
<0.5
0.25
38.74
63
Heating Value,
Btu/lb
Hg, ppb (dry)
13,852
134
10,202
52
9,891
66
9,650
28
9,378
86
8,733
37
8,201
42
2-3
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Experimental Approach
Table 2-2
Neutron Activation Results for Coal Samples
Sample
100% Bit
65%/35% (PRB/BIT)
70%/30% (PRB/BIT)
74%/26% (PRB/BIT)
79%/21% (PRB/BIT)
91%/9% (PRB/BIT)
100% PRB
Iodine (ppm)
1.9
0.8
0.9
0.6
<0.5
<0.5
<0.5
Bromine (ppm)
13.4
5.0
3.6
3.6
2.9
1.9
1.7
Chlorine (ppm)
973
337
270
237
154
101
35
The catalyst that was used in this system was manufactured by Cormetech. The catalyst samples
tested in the EPA pilot combustor were extracted from a full-scale 300 MW unit after
approximately 15,000 hours in DeNOx service firing low sulfur Eastern bituminous fuel. The
DeNOx activity compared to fresh catalyst was estimated by Cormetech to have a 0.8-0.9 K/Ko
value. A used catalyst was selected to minimize the amount of time required for the catalyst to be
saturated with mercury, as new catalysts tend to adsorb mercury for a period after being
installed.
Several sampling locations were used during these tests and are noted in Figure 2-1. The primary
speciated mercury measurement was made using the Ontario Hydro (OH) method [3]. The in-
stack filter option was used for PM capture in place of the standard hot box filter. Two OH
impinger trains per day were pulled at the inlet and outlet of the SCR unit with a total sampling
time of approximately 1.5 hours per train. During the 100% bituminous test and the 70%
PRB/30% bituminous test an additional OH train was pulled after the second catalyst section. All
OH trains were recovered and analyzed on-site per the method.
Halogen measurements were taken at the inlet of the SCR once per test condition using EPA
Method 26. Sorbent tubes were used to obtain total gaseous mercury concentrations at the inlet
and outlet of the baghouse. lodated carbon sorbent tube measurements at the inlet to the
baghouse were biased due to the flyash buildup in the front section of the tube and the results are
not reported. The sorbent tubes would quickly fill up with ash in the high dust environment and
block off the flow of gas through the tube. The total mercury concentration in the sorbent tubes
was determined using the thermal decomposition method specified in Appendix K of the Code of
Federal Regulations, 40 CFR part 75 [4].
Flyash samples were collected from the baghouse hopper twice during each run. These samples
were used to measure loss on ignition (LOT) and Hg uptake by the ash. These results are shown
in Table 2-3. The flyash was analyzed using the thermal decomposition method using an Ohio
Lumex model RA-915+. The high LOT in the ash is a result of slag tubes that were installed in
the radiant section of the furnace.
2-4
-------
Experimental Approach
Table 2-3
Baghouse Hopper Ash Hg and LOI of Ash
Test Conditions
(PRB/BIT Ratio)
100% Bit
65%/35%
70%/30%
74%/26%
79%/21%
91%/9%
100% PRB
Average LOI, %
21
12.5
11.9
15.3
15.1
16.5
13.7
Hg in ash, jig/kg
2960
2590
2210
2000
1600
1560
1725
The operating conditions for the tests are shown in Table 2-4. The SCR inlet temperature ranged
from a high of 740 °F to a lower limit of 700 °F. The SCR outlet temperature was roughly 60-70
°F lower than the inlet temperature due to heat loss across the catalyst section, and ranged from
630 to 670 °F. The SCR inlet NOx concentration ranged from 530 to 625 ppm, with a greater
than 90% reduction in NOx achieved across the SCR. Sulfur dioxide ranged from a high of 990
ppm for the 100% bituminous test to 153 ppm for the 100% PRB test. Excess oxygen
concentrations in the flue gas were in the 5-6 % range.
2-5
-------
Experimental Approach
Table 2-4
Operating Conditions for the Coal Blending Tests
PRB/BIT
Ratio
0%/100%
65%/35%
70%/30%
74%/26%
79%/21%
91%/9%
100%/0%
SCR Inlet
NOX
ppm
625
570
575
530
545
530
580
SO2
ppm
990
457
421
365
263
169
153
CO2
%
14.7
13.7
14.6
14.1
14.3
13.5
15.8
02
%
5.1
6.7
5.4
6.2
5.9
6.8
4.7
Temperature
°F
725
700
720
740
710
730
725
SCR Outlet
NOX
ppm
65
28
42
32
13
10
48
SO2
ppm
988
432
400
349
175
77
126
CO2
%
14.4
13.5
14.2
14.2
13.6
13.1
15.1
02
%
5.0
6.6
5.6
5.6
6.3
7.1
5.0
Temperature
°F
660
630
660
670
650
665
665
2-6
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3
RESULTS AND DISCUSSION
Mercury concentration data from the coal blending tests are shown in Table 3-1. Elemental
mercury (Hg°), oxidized mercury (Hg2+), and total mercury (HgT) are shown for the SCR inlet
and SCR outlet. Two OH sampling trains were pulled during each test day. No particulate-bound
mercury was detected as the temperature of the in-stack filter was above 600 °F. Mercury
speciation results for the tests are shown graphically in Figure 3-1. The amount of Hg + is shown
as an average of the two runs for each coal blend at the SCR inlet and outlet. The percentage of
Hg2+ is higher at the SCR outlet than at the SCR inlet for all of the test cases except for the 100%
PRB run where the inlet and outlet oxidized concentrations were similar.
Table 3-1
Hg Speciation Results from the SCR Inlet and SCR Outlet
PRB/BIT Ratio
100% Bit -Sample 1
100% Bit -Sample 2
65%/35% - Sample 1
65%/35% - Sample 2
70%/30% - Sample 1
70%/30% - Sample 2
74%/26% - Sample 1
74%/26% - Sample 2
79%/21%- Sample 1
79%/21%- Sample 2
91 %/9%- Sample 1
91%/9%-Sample2
100% PRB- Sample 1
100% PRB -Sample 2
SCR Inlet
H9°3
jig/m3
8.99
9.64
5.86
6.56
7.70
5.09
4.73
8.38
6.36
5.51
5.09
5.23
5.52
5.89
Hg-
jig/m3
3.64
3.36
1.12
0.72
2.03
1.71
1.11
0.36
0.32
0.46
0.23
0.27
0.37
0.40
^^
jig/m3
12.63
13.01
6.98
7.28
9.74
6.80
5.83
8.74*
6.68
5.97
5.32
5.50
5.90
6.30
OxHg
%
28.8
25.9
16.0
9.8
20.9
25.2
19.0
4.1
4.8
7.6
4.3
4.9
6.4
6.4
SCR Outlet
H9°3
jig/m3
2.22
2.10
2.87
3.10
4.62
3.07
2.80
7.08
5.50
3.98
4.28
3.71
6.36
5.89
Hg-
jig/m3
10.34
12.23
4.68
4.95
5.26
4.03
3.13
1.23
0.52
1.89
1.04
0.94
0.15
0.21
^^
jig/m3
12.55
14.33
7.55
8.05
9.88
7.10
5.93
8.31*
6.02
5.87
5.31
4.65
6.51
6.10
OxHg
%
82.3
85.3
61.9
61.5
53.3
56.8
52.7
14.8
8.7
32.2
19.5
20.2
2.2
3.4
3-1
-------
Results and Discussion
*This run has been omitted from the data set due to facility problems during the sampling period.
Sorbent trap samples were used to characterize the total amount of Hg captured by the baghouse.
The HgT (post-baghouse) for each test condition is shown in Table 3-2. The initial intent of these
tests was to characterize Hg removal through the entire system including the scrubber. However,
little to no Hg passed through the baghouse due to adsorption on unburned carbon in the ash due
to the high LOT of the ash. Initial sorbent trap samples collected at the outlet of the scrubber
indicated that the total Hg concentration at the FGD outlet were extremely low (<0.1 |ig/m3). As
a result, additional sampling at this location was discontinued.
14
12 -
...
8
6 -
4 -
2 -
n -
SCR
SCR Outlet
Ir
lie
^
t
SCR SCR
Tnipt Outlet
SCR talet _
SCR Outlet g
Inlet
_
SCR SCR |
In
let
-
Outlet
n
1 1
-
SCR
• Oxidized Hg
D Elemental Hg
Inlet SCR
:
Outlet S
I
C
lie
~
SCR
SCR Outlet
H Ii
t SCR
Outlet
lie
=
t
100% BIT 65/35 Blend 70/30 Blend 74/26 Blend 79/21 Blend 91/9 Blend
100% PRB
Figure 3-1
Mercury Speciation Results for Different Coal Blend Combinations
3-2
-------
90
70 -
60 -
50 -
S 40 -
30 -
PH
20 -
10 -
Results and Discussion
n
100% BIT 65/35 Blend 70/30 Blend 74/26 Blend 79/21 Blend 91/9 Blend 100% PRB
Figure 3-2
Percent Oxidized Mercury for SCR Inlet and SCR Outlet for Different Coal Blend
Combinations
Table 3-2
Sorbent Tube Results (post-baghouse)
PRB/BIT Ratio
100% BIT
65%/35%
70%/30%
74%/26%
79%/21%
91%/9%
100% PRB
HgT- Sample 1
(H9/m3)
<0.1
1.6
0.18
0.20
<0.1
<0.1
0.10
HgT- Sample 2
(H9/m3)
<0.1
<0.1
0.15
0.13
<0.1
0.20
0.10
One of the main goals of this project was to determine the effect of halogen concentration on Hg
oxidation. EPA Method 26 was used to characterize the halogens in the flue gas. Table 3-3
contains the Method 26 results for these tests. As shown in Table 3-3 nearly all of the chlorine in
3-3
-------
Results and Discussion
the coal was found as hydrogen chloride (HC1). Bituminous coal had the highest Cl
concentration (see Table 2-2) which translated into an HC1 concentration of 60.8 ppm at the SCR
inlet, while PRB had the lowest fuel Cl concentration which translates into an HC1 concentration
of below 5 ppm at the SCR inlet. Bromine and hydrogen bromide (HBr) were not detected in the
flue gas at the SCR inlet, while hydrogen fluoride (HF) was present in concentrations of less than
5 ppm. It is therefore expected that the primary Hg oxidant is HC1. There is an excellent
correlation for the HC1 in the flue gas as a function of coal chlorine content, as shown in Figure
3-3. The one to one correlation is also shown in Figure 3-3 that indicates most of the chlorine is
in the vapor phase and available for reacting with Hg. Based on the results from these tests it was
determined that oxidation of Hg is highly dependent on the amount of chlorine in the coal and
less so for the amount of bromine and fluorine.
Table 3-3
Method 26 Results for Coal Blending Tests
PRB/BIT Ratio
100% BIT
65%/35%
70%/30%
74%/26%
79%/21%
91%/9%
100% PRB
HCI (ppm)
60.8
23.6
NS
15.2
10.2
5.6
NS
CI2(ppm)
0.09
0.07
NS
0.05
0.03
0.03
NS
HBr (ppm)
<0.1
<0.1
NS
<0.1
<0.1
<0.1
NS
Br2 (ppm)
<0.1
<0.1
NS
<0.1
<0.1
<0.1
NS
HF (ppm)
4.9
3.8
NS
2.5
1.4
1.7
NS
F2 (ppm)
<0.05
<0.05
NS
0.1
<0.05
<0.05
NS
NS=No Sample
5-4
-------
Results and Discussion
Data Fit
1:1 Correlation
20
40
60
80
100
120
Theoretical Chlorine in Gas (mg/m )
Figure 3-3
Gas-phase Chlorine (HCI + CI2) versus Theoretical Chlorine Concentration
The data from Figure 3-3 are shown in Figure 3-4 as the absolute percentage change of oxidized
mercury (SCR outlet minus SCR inlet) as a function of coal chlorine content. There is no net
increase with the PRB coal alone as compared to 58% for the bituminous coal. A modest
increase is achieved when adding 10 and 20% bituminous coal to the blend. Another distinct
increase of 35% was achieved with the addition of 30% bituminous to the blend. By adding 40%
bituminous to the blend the mercury oxidation approaches that of the pure bituminous coal alone.
From this graph one may estimate expected levels of oxidized mercury at the SCR outlet as a
function of coal chlorine content. Increasing the chlorine content three fold from 300 ppm to 900
ppm only nets an increase of roughly 30%, indicating that not all of the chlorine in the flue gas
reacts with the available mercury. Laudal et al. [2] reported that for a 60/40 blend (543 ppm Cl)
the amount of oxidized Hg at the exit of the SCR approached 99%.
5-5
-------
Results and Discussion
35
101 154 237 270
Chlorine in Coal (ppm)
337
973
Figure 3-4
Mercury Oxidation (absolute change) Across the SCR as a Function of Coal Chlorine
Content
3-6
-------
4
CONCLUSIONS
Coal blending tests were conducted to investigate the effect of blending PRB coal with an
Eastern bituminous coal on the speciation of Hg across an SCR catalyst. Tests were conducted in
which 100% bituminous coal and 100% sub-bituminous PRB were fired to examine the effect on
mercury oxidation. Several blends were run with bituminous coal comprising the minority
fraction. It was determined that a higher percentage of the total Hg was present as oxidized Hg at
the SCR outlet as the chlorine in the coal increased. The other hydrogen halides such as HBr and
HF are not present in sufficient concentrations in the flue gas to have an impact on Hg oxidation.
A blend that contained at least 35% bituminous coal was necessary to obtain an oxidized Hg
concentration of 60% oxidized Hg at the SCR outlet with 100% bituminous coal producing just
under 90% oxidized Hg at the SCR outlet. Very little Hg passed through the baghouse due to the
high LOT of the ash. Those power plants that are equipped with SCR and wet scrubbers may
have an additional option of utilizing existing DeNOx and SC>2 pollution control equipment to
improve mercury control by adding an additional source of chloride to the fuel through fuel
blending or other means.
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REFERENCES
1. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units -
Final Report to Congress, Volume 1, Office of Air Quality Planning and Standards, U.S.
Environmental Protection Agency, Research Triangle Park, NC; EPA-453R-98-004a,
February 1998; (NTIS PB98-131774).
2. Evaluation of the impact of selective catalytic reduction on Hg speciation for a power plant
firing blended coal at DTE Energy's Monroe Power Station, U.S. Department of Energy,
National Energy Technology Laboratory, Pittsburgh, PA, Report # 2005-EERC-04-01.
3. ASTM Method D 6784-02, "Standard Test Method for Elemental, Oxidized, Particle-Bound,
and Total Mercury in Flue Gas Generated from Coal-Fired Stationary Sources (Ontario-
Hydro Method)".
4. Code of Federal Regulations, 40 CFR part 75, including Appendices A through K, September
2007.
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