Sorbent Injection for Mercury Control Upstream of SmallSCA ESPs 

Paper #65 

Katherine Dombrowski, Carl Richardson, Tom Machalek 

URS Corporation, 9400 Amberglen Boulevard, Austin, TX 78729

Dawn Chapman 

U.S. DOE-NETL, PO Box 880, Morgantown, WV 26507-0880 

Ramsay Chang 

EPRI, 3412 Hillview Avenue, Palo Alto, CA 94304

Larry Monroe, Mark Berry, Nick Irvin 

Southern Company Generation and Energy Marketing, PO Box 2641 BIN 14N-8195, 

Birmingham, Alabama 35291

Ken McBee 

Georgia Power - Plant Yates, 708 Dyer Road, Newnan, GA 30263

Sharon Sjostrom 

ADA-ES, 8100 South Park Way Unit B, Littleton, CO 80120

ABSTRACT 

URS Group, in conjunction with EPRI, Southern Company, Georgia Power, and ADA-ES is 

evaluating sorbent injection for mercury control upstream of small-SCA ESPs in flue gas derived 

from low-sulfur Eastern bituminous fuel. The project is funded by DOE-NETL and is divided 

into two phases, parametric testing and long-term testing. This paper reports the results from the 

full-scale parametric testing conducted at Georgia Power’s Plant Yates Units 1 and 2. Both units 

are equipped with cold-side ESPs and fire the same fuel. In addition, Unit 1 also has a wet 

scrubber, and Unit 2 typically runs with SO3 and NH3 flue gas conditioning. Parametric tests 

were performed with three sorbent materials to determine the effect of addition rate upstream of 

the ESP on mercury removal and supplemental removal across the wet scrubber. Parametric tests 

also evaluated the effect of sorbent addition rate and flue gas conditioning on sorbent 

performance. 

INTRODUCTION 

Sorbent injection is currently the most studied mercury control technology for coal-fired utilities. 

The technology has been tested in numerous pilot and full-scale demonstrations sponsored by 

DOE-NETL, EPRI, and others. Most previous activated carbon injection testing has been 

performed on units with relatively large ESPs (electrostatic precipitators). In these tests, high 

levels of mercury removal were possible, and little to no detrimental effects were observed on 

the ESP. However, in the current fleet of U.S. coal-fired utility ESPs, over 70% have specific 

collection areas (SCAs) less than 300 ft2/1000 acfm. The mercury removal capabilities and 

balance of plant effects for sorbent injection have not been tested on plants with small ESPs. 
2

The purpose of this project is to evaluate full-scale sorbent injection on two small size ESPs for a 

plant that fires eastern bituminous coal. One of the ESPs is equipped with a dual flue-gas 

conditioning system, allowing for the effects of NH3 and SO3 injection on mercury removal to be 

explored. 

Short-term parametric tests were conducted on Georgia Power’s Plant Yates Units 1 and 2 to 

evaluate the performance of activated carbon sorbents. In addition, the effects of the dual flue 

gas conditioning system on mercury removal performance were evaluated as part of the shortterm parametric test on Unit 2. Based on the results of the parametric tests, a single sorbent will 

be selected for longer term full-scale tests on Unit 1 to observe long term performance of the 

sorbent, and its effects on ESP and JBR FGD (jet bubbling reactor flue gas desulphurization) 

system operations and combustion byproduct properties. The results of this study will provide 

data required for assessing the performance, long-term operational impacts, and estimating the 

costs of full-scale sorbent injection processes for flue gas mercury removal. 

DESCRIPTION OF PLANT YATES UNITS 1 AND 2 

Various sorbent materials were injected upstream of small SCA ESP systems at Georgia Power’s 

Plant Yates Unit 1 and Unit 2. Both Unit 1 and Unit 2 fire a low sulfur bituminous coal. Unit 1 is 

equipped with a JBR wet FGD system downstream of the ESP for SO2 control. Unit 2 is not 

equipped with downstream SO2 controls; however, a dual flue gas conditioning system is used to 

enhance ESP performance. The dual flue gas conditioning system consists of SO3 and NH3

injection. 

Figures 1 and 2 show the basic plant configuration, sorbent injection points, and flue gas sample 

locations for Units 1 and 2, respectively. Characteristics of each unit are summarized in Table 1. 

TEST METHODS 

For the short-term parametric tests, a sorbent injection system was installed to service both the 

Unit 1 and Unit 2 ESP inlet injection points. This portable dry injection system pneumatically 

conveys a predetermined and adjustable amount of powdered activated carbon (PAC) from bulk 

bags into the flue gas stream via six sorbent injection lances. The PAC is metered using a 

volumetric feeder into a pneumatic eductor, where the air supplied from the regenerative blower 

provides the motive force needed to transport the carbon to the final injection locations. The 

Porta-PAC (portable powdered activated carbon) system can deliver from 20 – 400 lb/hr of 

activated carbon. 

The mercury measurements for baseline and injection testing were performed with mercury 

semi-continuous analyzers, which are described below in more detail. For each unit, flue gas 

extraction probes and mercury analyzers were situated at the ESP inlet and outlet locations. For 

Unit 1, a mercury analyzer was also placed at the JBR scrubber outlet. The analyzers 

continuously monitored the flue gas mercury concentration throughout the test program. 

For each sorbent injection test, particulate loading was measured via single-point Method 17. 

Solid and liquid samples, such as makeup water, fly ash, and coal, were collected and analyzed 

for mercury content. Fly ash and coal mercury were digested with ASTM 3684 and analyzed for 

mercury by CVAA. 
3

Figure 1. Unit 1 Configuration and Flue Gas Sample Locations

Figure 2. Unit 2 Configuration and Flue Gas Sample Locations 

JBR 

Absorber

Boiler

Stack

APH 

Inlet Flue Gas 

Sampling 

ESP Outlet Flue 

Gas Sampling 

FGD Outlet 

Sampling 

Sorbent

Injection

CS ESP

Stack

APH 

Inlet Flue Gas 

Sampling 

ESP Outlet 

Sampling 

Flue Gas 

Conditioning

CS ESP 

Sorbent 

Injection 
4

Table 1. Plant Yates Unit 1 and 2 configurations. 

Yates Unit 1 Yates Unit 2 

Boiler 

Type CE Tangential Fired 

Nameplate (MW) 100 

Coal 

Type Eastern Bituminous 

Sulfur (wt %, dry) 1.0 

Mercury (mg/kg, dry) 0.06-0.14 

Chloride (mg/kg, dry) 150-450 

ESP 

Type Cold-Side 

ESP Manufacturer Buell (1968 and 1971 vintage, refurbished in 1997) 

Specific Collection Area 

(ft2

/1000afcm) 

173 144 

Plate Spacing (in.) 11 

Plate Height (ft) 30 

Electrical Fields 3 2 

Mechanical Fields 4 3 

ESP Inlet Temp. (°F) 310 300 

ESP Design Flow Rate (ACFM) 490,000 420,000 

NOx Controls Low NOx Burners None 

SO2 Controls Chiyoda CT-121 wet 

scrubber (JBR) 

None 

Flue Gas Conditioning None Dual NH3/SO3

 

EPRI SCEM Mercury Analyzer 

Flue gas vapor-phase mercury analyses were made using EPRI semi-continuous analyzers 

depicted in Figure 3. At each sample location, a sample of the flue gas is extracted from the duct 

and then drawn through an inertial gas separation (IGS) filter to remove particulate matter. This 

IGS filter consists of a heated stainless steel tube lined with sintered material. A secondary 

sample stream is pulled across the sintered metal filter and then is directed through the mercury 

analyzer at a rate of approximately 1-2 L/min thus providing near real-time feedback during the 

various test conditions. The analyzer consists of a cold vapor atomic absorption spectrometer 

(CVAAS) coupled with a gold amalgamation system (Au-CVAAS). Since the Au-CVAAS 

measures mercury by using the distinct lines of the UV absorption characteristics of elemental 

mercury, the non-elemental fraction is converted to elemental mercury prior to analysis using a 

chilled reduction solution of acidified stannous chloride. Several impingers containing alkaline 

solutions are placed downstream of the reducing impingers to remove acidic components from 

the flue gas; elemental mercury is quantitatively transferred through these impingers. 

To measure elemental mercury only, an impinger containing either 1M potassium chloride (KCl) 

or 1M Tris Hydroxymethyl (aminomethane) and EDTA is placed upstream of the alkaline 

solution impingers to capture oxidized mercury. Oxidized forms of mercury are captured and 

maintained in the KCl or Tris impingers while elemental mercury passes through to the gold 

system. Comparison of “total” and “elemental” mercury measurements yields the extent of 
5

mercury oxidation in the flue gas. All mercury concentrations reported in this paper are 

normalized to 3% O2. 

Figure 3. Semi-continuous Mercury Analyzer 

Gas exiting the impingers flows through a gold amalgamation column where the mercury in the 

gas is adsorbed (<60 C). After adsorbing mercury onto the gold for a fixed period of time 

(typically 1-3 minutes), the mercury concentrated on the gold is thermally desorbed (>400 C) in 

nitrogen or air, and sent as a concentrated mercury stream to a CVAAS for analysis. Therefore, 

the total flue gas mercury concentration is measured semi-continuously with a 1 to 3-minute 

sample time followed by a 2-minute analytical period. 

TEST MATRIX 

Three different sorbents were selected for testing on Plant Yates Unit 1. A description of the 

each sorbent is provided in the table below. The Darco FGDcarbon will serve as the 

benchmark sorbent since it has been used in numerous other sorbent injection test programs and 

its performance characteristics are well defined. The Super HOK sorbent is a German lignitederived activated carbon selected for its cost, performance in previous tests and availability in 

quantities necessary for this test program. The third sorbent (NH carbon) is an iodated activated 

carbon which was not originally included in the test plan, but it was made available at no cost to 

the project. The project team made the decision to test this chemically treated activated carbon 

because it offered the potential for higher removals, although the cost is about 75% higher than 

that of the benchmark Darco FGDcarbon. 

Table 2. Sorbents selected for test program.

Carbon Name Manufacturer Description Cost ($/lb) 

Darco FGDTM Norit Americas Lignite-derived activated carbon; baseline 

carbon (19 μm mean particle size) 

0.50 

Super HOK RWE Rhinebraun German lignite-derived activated carbon (23 

μm mean particle size) 

0.35 

NH Carbon 

Ningxia Huahui 

Activated Carbon Co. 

LTD 

Chinese iodated bituminous-derived activated 

carbon (24 μm mean particle size) 

0.88 

Flue Gas

Duct

IGS Filter

Pump

EPRI SemiContinuous

Mercury

Analyzer

Sample

Impingers

Data Acquisition

Bypass

Pump
6

The test conditions for Units 1 and 2 are summarized in Tables 3 and 4. All testing occurred with 

the units at full load. Prior to commencement of injection tests, a week of baseline (no sorbent 

injection) testing was conducted on each unit. For injection testing, baseline mercury 

concentrations were measured at the beginning and end of each test day. On each injection test 

day, one to four injection rates were tested. At least two hours were needed at each test condition 

in order to achieve steady outlet mercury concentrations. Once steady concentrations were 

achieved, the carbon injection rate was changed to a new value. 

Table 3. Unit 1 test conditions.

Sorbent Test Week Range of Carbon Injection Rates 

Tested (lb/MMacf) 

Baseline (no sorbent) 2/24/04 - 2/27/04 0 

Darco FGDTM 3/1/04 - 3/5/04 2.1 - 12.7 

Super HOK 4/6/04 - 4/7/04 3.3 - 17.0 

NH Carbon 3/29/04 - 3/30/04 4.2 - 12.5 

Table 4. Unit 2 test conditions.

Sorbent Test Week Range of Carbon Injection Rates 

Tested (lb/MMacf) 

Baseline (no sorbent) 3/15/04 - 3/19/04 0 

Darco FGDTM 3/22/04 - 3/26/04 2.1 - 12.7 

RESULTS 

Baseline Results 

During baseline testing on Unit 1 (SCA = 173 ft2/1000 acfm), the average vapor-phase ESP inlet 

mercury concentration was 4.02 g/Nm3

 and the average ESP outlet concentration was 2.64 

g/Nm3

 (at 3% O2). On average, a 34% native removal across the ESP was measured during the 

baseline period. For Unit 2 (SCA = 144 ft2/1000 acfm) during the baseline week of testing, the 

average ESP inlet mercury concentration was 6.04 g/Nm3and the outlet was 3.89g/Nm3, 

indicating 36% native removal across the ESP. 

Inlet and outlet mercury concentrations at full load varied during the course of the day, 

depending upon the coal mercury content and the temperature of the flue gas. Baseline mercury 

measurements were also made before and after each injection test day. ESP inlet mercury was 

typically between 4.0 and 7.0g/Nm3

,while ESP outlet concentrations were between 2.5 and 5.0 

g/Nm3

. 

Coal and ash samples were collected during the baseline testing week and measured for mercury 

content. The fly ash had a high LOI content, typically in the 9-13% range. As seen in Figure 4, 

the mercury content of the ash increased proportionately to the LOI content, indicating that the 

LOI of the ash may play a role in the high native removals observed across the ESP. 
7

Figure 4. Ash mercury content as a function of the LOI content 

Injection Results 

Three carbon-based sorbents were tested at Plant Yates Unit 1 for their ability to remove 

mercury from the flue gas. These sorbents were injected at various rates and the resulting 

mercury concentrations at the ESP outlet and JBR outlet were monitored. In order to assess the 

performance of the sorbents, two different mathematical metrics were used. The first metric was 

the percent removal of mercury across the ESP, which was calculated as 

 % Removal Across ESP = 1- (HgVaporESP,out)t / (HgVaporESP,in)t

where (HgVaporESP,out)t is the vapor phase mercury concentration at the ESP outlet measured at 

time t, and (HgVaporESP,in)t is the vapor phase mercury concentration at the ESP inlet measured 

at time t. The percent removal metric incorporates native mercury removal across the ESP. 

Because at times native removals were as high as 50%, a second metric was designed in order to 

attribute the percent mercury reduction at the ESP outlet due to sorbent injection. The mercury 

reduction was calculated as 

 % Reduction at ESP Outlet = 1- (HgVaporESP,out)t / (HgVaporESP,out)0

where (HgVaporESP,out)t is the vapor phase mercury concentration at the ESP outlet measured at 

time t, and (HgVaporESP,out)0 is the vapor phase mercury concentration at the ESP outlet 

measured just prior to the start of injection (i.e. the baseline ESP outlet mercury concentration). 

Similar metrics were devised in order to evaluate the percent removal across the combined 

ESP/JBR system and the percent mercury reduction at the JBR outlet.

Figures 5 through 8 summarize the results from the three sorbents tested on the Unit 1 ESP. 

Figures 5 and 6 show the percent removal across the ESP and the percent mercury reduction at 

the ESP outlet, respectively, as a function of sorbent injection rate. All three carbons exhibited 

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 5 10 15 20 25

LOI (%)

Ash Mercury Content (g/g)

Unit 1 Ash

Unit 2 Ash bottom ash
8

similar performance in the Unit 1 ESP. Overall mercury removal (due to both native removal and 

removal by PAC) across the ESP plateaued between 50 and 70% for injection rates greater than 6 

lb/MMacf. For the three carbons, the maximum achieved percent reduction of mercury at the 

ESP outlet was about 40%. The curves for the Darco FGDTM and the NH carbon are nearly 

identical, and the Super HOK curve is just slightly lower. 

Figures 7 and 8 show the percent removal across the combined ESP/JBR and the percent 

mercury reduction at the JBR outlet, respectively, as a function of sorbent injection rate. The NH 

carbon resulted in the highest combined removal across the ESP/JBR. However, the native 

removal across the combined system was higher during the NH carbon injection testing week 

than during the other injection test weeks. The reduction of mercury at the stack was higher for 

the NH carbon. The Darco FGDTM and the Super HOK curves were nearly identical. 

Sorbent injection tests were conducted with Darco FGDTM upstream of the Plant Yates Unit 2 

ESP, which employs dual flue gas conditioning. Results from the tests are shown in Figure 9. 

These short-term test data indicate an additional 30 to 40 percent reduction in total vapor-phase 

mercury was achieved at an injection rate of 2 lb/MMacf. No additional reduction was observed 

at higher injection rates up to 13 lb/MMacf. It should be noted that the higher injection rates 

were tested on a day when the baseline ESP outlet mercury concentration was lower than normal 

(2.6 rather than 5.0 g/Nm3), which could bias low the mercury reduction measured. Figure 9 

also indicates the set points for the dual flue gas conditioning system during each test period. The 

dual flue gas conditioning system appeared to have no effect on the reduction in total vaporphase mercury at the ESP outlet. 

Native removals across the Unit 2 ESP ranged from 20-60% during the testing weeks, which is 

similar to the Unit 1 ESP. For the Unit 2 ESP system, the removal curve (Figure 10) flattens out 

near 70 percent for sorbent injection rates of 6 lb/MMacf and above. 

Figure 5. Comparison of Mercury Removal Efficiency Across the ESP 

of the Three Sorbents Tested on Unit 1 
9

Figure 6. Comparison of Mercury Reduction at the ESP Outlet 

 for the Three Sorbents Tested on Unit 1 

Figure 7. Comparison of Mercury Removal Efficiency Across the 

 Combined ESP/JBR of the Three Sorbents Tested on Unit 1 
10

Figure 8. Comparison of Mercury Reduction at the JBR Outlet 

 for the Three Sorbents Tested on Unit 1 

Figure 9. Percent Reduction in Vapor Phase Mercury at Unit 2 ESP Outlet

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 2 4 6 8 10 12 14

% Reduction in Vapor Phase Hg at ESP Outlet

Full

Half

Low NH3

None

Conditioning:
11

Figure 10. Removal of Vapor Phase Mercury Across Unit 2 ESP 

ESP Performance 

The impact of sorbent injection on the ESP performance was quantified by taking single point 

Method 17 particulate samples during each injection rate and by monitoring the arc rate in each 

field. Figure 11 shows the Unit 1 ESP outlet particulate concentrations measured during baseline 

and injection testing. During baseline conditions (sorbent injection rate = 0 lb/MMacf), the ESP 

outlet particulate concentration ranged from 0.024 to 0.052 grains/dscf at 3% O2, with an average 

of 0.036 gr/dscf. For the tested carbon injection rates of 2 to 17 lb/MMacf, the measured outlet 

particulate concentrations were mostly within or below the range of concentrations measured 

during baseline testing. These results indicate that carbon injection caused no significant increase 

in ESP outlet particulate concentration. Similar results were seen for Unit 2. 

Figure 11. Particulate Emissions as Measured by Single Point Method 17 at Unit 1 ESP Outlet 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 2 4 6 8 10 12 14

% Removal of Vapor Phase Hg Across ESP

Day 1

Day 2

Day 3

Day 4

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 2 4 6 8 10 12 14 16 18

Injection Rate (lb/MMacf)

Particulate Emission Concentration from ESP( gr/dscf @ 3% O2)

Darco FGD

NH Carbon

HOK

Baseline (no sorbent injection)

Range of Baseline 

Measurements
12

CONCLUSIONS 

Three sorbents were tested during short-term parametric tests on Plant Yates Units 1 and 2 for 

their ability to remove flue gas mercury. The results from baseline (no sorbent injection) and 

parametric testing indicated: 

 During baseline testing, the mercury content of the ash increased proportionately to the 

LOI content, likely contributing to the native mercury removal observed during this 

period (Unit 1 = 34% average Hg removal, Unit 2 = 36% average Hg removal). 

 All three tested sorbents (Darco FGDTM, Super HOK, and NH Carbon) had 

approximately the same dose-response curve for mercury removal from the flue gas, 

reaching 30-40% additional reduction in ESP outlet mercury at a sorbent injection 

concentration of approximately 6 lb/MMacf. 

 Mercury removal reached a plateau at 6 lb/MMacf and injecting additional sorbent did 

not result in additional mercury removal. 

 Carbon injection caused no significant increase in ESP outlet particulate concentration on 

Unit 1 or Unit 2 as measured by single-point EPA Method 17. 

 The dual flue gas conditioning system appeared to have no effect on the reduction in total 

vapor-phase mercury at the ESP outlet. 

Longer term tests, to be conducted in Fall 2004, will enable better assessment of sorbent 

injection performance and balance-of-plant impacts.