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. Serre
 

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
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (Hg0). A significant 

fraction of the Hg0 can be subsequently oxidized in the low-temperature, post-combustion 

environment of a coal-fired boiler. Relative to Hg0

, oxidized Hg (Hg2+) is more effectively 

removed by air pollution control systems (APCS). For example, the water-soluble Hg2+ is much 

more easily captured than insoluble Hg0 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 (HCl, 

HBr, and HF) and halogens (Cl2 and Br2) in the flue gas were evaluated to determine their effects 

on the oxidation of Hg0 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. 
 

 

 

 

 

 

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 
1 1

2 2

3 3

4 4

5 5

CONTENTS
 

INTRODUCTION ................................................................................................................. -1
 

EXPERIMENTAL APPROACH............................................................................................ -1
 

RESULTS AND DISCUSSION............................................................................................. -1
 

CONCLUSIONS .................................................................................................................. -1
 

REFERENCES .................................................................................................................... -1
 

 

 

 

 

 

 

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 (HCl + Cl2) 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

 

 

 

 

 

 

 

 

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
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 particulate matter (PM) controls, NOX controls, and SO2 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 (Hg2+) 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 SO2 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 SO2 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 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 (SO2), nitrogen oxides (NOX), carbon monoxide (CO), carbon dioxide (CO2), and 

oxygen (O2). 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. 

Scrubber

NOx 

CO Method 26 OH 

Coal 

Natural Gas Coal/Natural Gas Combustor

4 MM Btu/hr 

Heat-Exchanger 

Scrubber 

Stack 

Air Preheater 

Heat Exchanger 

Baghouse 

CO2 

SO2 

O2 

NOx 

CO2 

SO2 

O2 

Sorbent Tube 

SCR 

OH 

OH 

NH3 

Figure 2-1 

Schematic of Multi-Pollutant Control Research Facility with Sampling Locations Shown 

2-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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 o

F, 

with a space velocity of 1900 h-1. A NH3/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 NH3 

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 
 

 

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 2.63 19.43 18.42 21.32 23.88 27.38 31.37 

Volatile 35.02 31.63 33.29 31.49 34.91 39.78 32.72 

Ash 6.06 6.16 6.49 5.69 4.95 3.81 4.04 

Fixed Carbon 56.29 42.78 41.8 41.5 36.26 29.03 31.87 

Ultimate 

Carbon, % 76.80 59.58 57.04 58.82 54.58 51.3 51.02 

Hydrogen, % 5.36 6.0 4.71 5.93 5.61 5.93 5.95 

Nitrogen, % 1.79 1.05 0.97 0.97 0.98 0.91 <0.5 

Sulfur, % 1.40 0.63 0.54 0.48 0.43 0.30 0.25 

Oxygen, % 8.49 26.55 30.23 28.09 33.43 37.75 38.74 

Fluorine, ppm 94 52 N/A 52 72 88 63 

Heating Value, 

Btu/lb 

13,852 10,202 9,891 9,650 9,378 8,733 8,201 

Hg, ppb (dry) 134 52 66 28 86 37 42 

2-3
 
 

 

 

Experimental Approach 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2-2 

Neutron Activation Results for Coal Samples 

Sample Iodine (ppm) Bromine (ppm) Chlorine (ppm) 

100% Bit 1.9 13.4 973 

65%/35% (PRB/BIT) 0.8 5.0 337 

70%/30% (PRB/BIT) 0.9 3.6 270 

74%/26% (PRB/BIT) 0.6 3.6 237 

79%/21% (PRB/BIT) <0.5 2.9 154 

91%/9% (PRB/BIT) <0.5 1.9 101 

100% PRB <0.5 1.7 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 instack 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. Iodated 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 (LOI) 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 LOI 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) Average LOI, % Hg in ash, μg/kg 

100% Bit 21 2960 

65%/35% 12.5 2590 

70%/30% 11.9 2210 

74%/26% 15.3 2000 

79%/21% 15.1 1600 

91%/9% 16.5 1560 

100% PRB 13.7 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 

SCR Inlet SCR Outlet 

NOX 

ppm 

SO2 

ppm 

CO2 

% 

O2 

% 

Temperature 

°F 

NOX 

ppm 

SO2 

ppm 

CO2 

% 

O2 

% 

Temperature 

°F 

0%/100% 625 990 14.7 5.1 725 65 988 14.4 5.0 660 

65%/35% 570 457 13.7 6.7 700 28 432 13.5 6.6 630 

70%/30% 575 421 14.6 5.4 720 42 400 14.2 5.6 660 

74%/26% 530 365 14.1 6.2 740 32 349 14.2 5.6 670 

79%/21% 545 263 14.3 5.9 710 13 175 13.6 6.3 650 

91%/9% 530 169 13.5 6.8 730 10 77 13.1 7.1 665 

100%/0% 580 153 15.8 4.7 725 48 126 15.1 5.0 665 

2-6 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3 

RESULTS AND DISCUSSION
 

Mercury concentration data from the coal blending tests are shown in Table 3-1. Elemental 

mercury (Hg0

), 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 Hg2+ 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 

SCR Inlet SCR Outlet 

Hg0 

μg/m3 

Hg2+ 

μg/m3 

HgT 

μg/m3 

Ox Hg 

% 

Hg0 

μg/m3 

Hg2+ 

μg/m3 

HgT 

μg/m3 

Ox Hg 

% 

100% Bit - Sample 1 8.99 3.64 12.63 28.8 2.22 10.34 12.55 82.3 

100% Bit - Sample 2 9.64 3.36 13.01 25.9 2.10 12.23 14.33 85.3 

65%/35% - Sample 1 5.86 1.12 6.98 16.0 2.87 4.68 7.55 61.9 

65%/35% - Sample 2 6.56 0.72 7.28 9.8 3.10 4.95 8.05 61.5 

70%/30% - Sample 1 7.70 2.03 9.74 20.9 4.62 5.26 9.88 53.3 

70%/30% - Sample 2 5.09 1.71 6.80 25.2 3.07 4.03 7.10 56.8 

74%/26% - Sample 1 4.73 1.11 5.83 19.0 2.80 3.13 5.93 52.7 

74%/26% - Sample 2 8.38 0.36 8.74* 4.1 7.08 1.23 8.31* 14.8 

79%/21% - Sample 1 6.36 0.32 6.68 4.8 5.50 0.52 6.02 8.7 

79%/21% - Sample 2 5.51 0.46 5.97 7.6 3.98 1.89 5.87 32.2 

91%/9% - Sample 1 5.09 0.23 5.32 4.3 4.28 1.04 5.31 19.5 

91%/9% - Sample 2 5.23 0.27 5.50 4.9 3.71 0.94 4.65 20.2 

100% PRB - Sample 1 5.52 0.37 5.90 6.4 6.36 0.15 6.51 2.2 

100% PRB – Sample 2 5.89 0.40 6.30 6.4 5.89 0.21 6.10 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 LOI 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 μg/m3

). As 

a result, additional sampling at this location was discontinued. 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

 

 

SCR 

14 SCR Outlet 

Mercury Concentration (

μg/m3) 

Inlet 

12 

10 

8 

6 

4 

2 

0 

Oxidized Hg 

Elemental Hg 

SCR SCR 

SCR 

Outlet Inlet 

SCR Outlet 

Inlet 

SCR 

Outlet 

SCR 

Inlet 

SCR 

Outlet 

SCR 

Inlet 

SCR 

Outlet 

SCR 

Inlet 

SCR 

SCR Outlet 

Inlet 

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 
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Results and Discussion 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

Percent Oxidized Mercury 

SCR Outlet 

SCR Inlet 

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 HgT – Sample 1 

(μg/m3

) 

HgT – Sample 2 

(μg/m3

) 

100% BIT <0.1 <0.1 

65%/35% 1.6 <0.1 

70%/30% 0.18 0.15 

74%/26% 0.20 0.13 

79%/21% <0.1 <0.1 

91%/9% <0.1 0.20 

100% PRB 0.10 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 (HCl). Bituminous coal had the highest Cl 

concentration (see Table 2-2) which translated into an HCl concentration of 60.8 ppm at the SCR 

inlet, while PRB had the lowest fuel Cl concentration which translates into an HCl 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 HCl. There is an excellent 

correlation for the HCl 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 HCl (ppm) Cl2 (ppm) HBr (ppm) Br2 (ppm) HF (ppm) F2 (ppm) 

100% BIT 60.8 0.09 <0.1 <0.1 4.9 <0.05 

65%/35% 23.6 0.07 <0.1 <0.1 3.8 <0.05 

70%/30% NS NS NS NS NS NS 

74%/26% 15.2 0.05 <0.1 <0.1 2.5 0.1 

79%/21% 10.2 0.03 <0.1 <0.1 1.4 <0.05 

91%/9% 5.6 0.03 <0.1 <0.1 1.7 <0.05 

100% PRB NS NS NS NS NS NS 

NS=No Sample 

3-4 
 

 

R2 = 0.996 

0 

20 

40 

60 

80 

100 

120 

Actual Chlorine in Gas from M26 Data (mg/m3 ) 

Data Fit 

1:1 Correlation 

0 20 40 60 80 100 120 

Theoretical Chlorine in Gas (mg/m3

) 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results and Discussion 

Figure 3-3 

Gas-phase Chlorine (HCl + Cl2) 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%. 

3-5 
 

 

 

 

Results and Discussion 

0 

10 

20 

30 

40 

50 

60 

Mercury Oxidation Across Catalyst(%)

Delta Across Catalyst 

35 101 154 237 270 337 973
 

Chlorine in Coal (ppm)
 

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 LOI of the ash. Those power plants that are equipped with SCR and wet scrubbers may 

have an additional option of utilizing existing DeNOx and SO2 pollution control equipment to 

improve mercury control by adding an additional source of chloride to the fuel through fuel 

blending or other means. 

4-1 

 

 

 

 

 

 

 

 

 

 

 

5 

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 (OntarioHydro Method)”. 

4.	 Code of Federal Regulations, 40 CFR part 75, including Appendices A through K, September 

2007. 

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