Full-Scale Activated Carbon Injection for Mercury Control 

in Flue Gas Derived from North Dakota Lignite 

Paper 83 

Tom Machalek, Carl Richardson, Katherine Dombrowski 

URS Corporation, 9400 Amberglen Boulevard, Austin, TX 78729 

Trevor Ley, Tim Ebner, Kevin Fisher 

Apogee Scientific, 2895 W. Oxford Ave. Suite 1, Englewood, CO 80110 

Lynn Brickett 

U.S. DOE-NETL, P.O. Box 880, Morgantown, WV 26508 

Ramsay Chang 

EPRI, 3412 Hillview Avenue, Palo Alto, CA 94304

Mark Strohfus 

Great River Energy, 17845 E. Hwy. 10 Elk River, MN 55330 

Steve Smokey 

Stanton Station, 4001 Highway 200A, Stanton, ND 58571 

Sharon Sjostrom 

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

ABSTRACT 

URS Group, in conjunction with DOE-NETL, EPRI, Great River Energy, North Dakota 

Industrial Commission, Apogee Scientific, and ADA-ES, is evaluating the effectiveness of 

sorbent injection for reducing mercury emissions from flue gas derived from North Dakota 

lignite. This paper reports full-scale tests performed at Great River Energy’s Stanton Station 

Unit 10 to evaluate sorbent injection performance across a spray dryer-baghouse combination. 

Six mercury sorbents were chosen based upon pre-determined selection criteria and were 

evaluated during short-term parametric tests on each unit. Parametric tests determined optimal 

process conditions for each sorbent and were used to select a sorbent for longer-term testing. 

Results provide insight to the long-term performance and variability of this process as well as 

any effects on plant operations. Data from this program will also be used to perform an 

economic analysis of the costs associated with full-scale implementation of a sorbent-based 

injection system. 

INTRODUCTION 

Carbon injection technology is one of the most studied mercury control technologies available 

for coal-fired power plants. The technology has shown the capability to achieve fairly high 

mercury removals in plants burning specific coals and employing specific pollution control 

devices. For plants firing lignite fuels, injection of untreated activated carbons has shown lower 

mercury removal performance than for other coals, such as bituminous coals. The low chlorine 

and high calcium content of lignite fuel results in low reactivity between the mercury and 

sorbent, thereby resulting in poorer performance. The reactivity between mercury and sorbent 

can be improved by using chemically-treated carbons or by using furnace additives to increase 
2

the chloride content of the flue gas. Both of these technologies have been successfully 

demonstrated in short-term, full-scale tests. 

Full-scale testing of chemically treated carbons was undertaken at Stanton Station as part of a 

larger DOE-NETL program investigating methods to enhance the capability of carbon sorbents 

to remove mercury from lignite combustion gases. In this program sorbent injection will be 

tested at plants equipped with electrostatic precipitators (ESPs) only and at plants equipped with 

spray dryer/baghouse (SD/BH) combination. Stanton Station consists of two units. Unit 1 is 

equipped with an ESP, while Unit 10 is equipped with a spray dryer/baghouse. For each unit 

parametric testing of various carbons will be performed in order to evaluate the effect of 

chemical treatment on flue gas mercury adsorption. Based on the results from the parametric 

tests, a single sorbent will be selected for long-term testing. The long-term testing provides an 

opportunity to evaluate balance-of-plant effects of sorbent injection. 

The parametric and long term testing on Stanton Unit 10 has been completed and the results are 

presented in this paper. Testing on Unit 1 has yet to commence. 

DESCRIPTION OF STANTON UNIT 10 

Various sorbent materials were injected upstream of spray dryer/baghouse (SD/BH) combination 

at Great River Energy’s Stanton Station Unit 10. Unit 10 fires North Dakota lignite and is rated 

for a load of 60 MW. Figure 1 shows the basic plant configuration, sorbent injection points, and 

flue gas sample locations for Units 10. Characteristics of the Unit 10 (and Unit 1) are 

summarized in Table 1. 

Coal

s

Unit 10

Boiler

Bottom Ash

Spray

Dryer

s s

s

s

Reverse

Gas

Baghouse

Stack

Reagent

Slurry

Prep.

Lime

Makeup

Water

Spray Dryer Solids

Combined Solids

Stack

Gas

Sorbent

Injection Baghouse Solids

Coal

ss

Unit 10

Boiler

Bottom Ash

Unit 10

Boiler

Bottom Ash

Spray

Dryer

ss s

ss

ss

Reverse

Gas

Baghouse

Stack

Reagent

Slurry

Prep.

Lime

Makeup

Water S

S

Spray Dryer Solids

Combined Solids

Stack

Gas

S Sample Location

Sorbent

Injection

S

Baghouse Solids

Figure 1. Stanton Unit 10 Configuration With Flue Gas and Solid Sample Locations
3

TEST METHODS 

For the short-term parametric tests, an EPRI sorbent injection system was installed to service the 

Unit 10 spray dryer inlet. 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. 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 mercury measurements for baseline and injection testing were performed with mercury 

semi-continuous analyzers, which are described below in more detail. Flue gas extraction probes 

and mercury analyzers were situated at the spray dryer inlet, baghouse inlet, and baghouse outlet. 

The analyzers continuously monitored the flue gas mercury concentration throughout the test 

program. 

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. 

Table 1. Stanton Unit 10 Configuration 

Stanton Unit 1 Stanton Unit 10 

Boiler

Type Foster Wheeler, 

PC Wall-Fired 

Combustion Engineering, 

PC Tangential 

Nameplate (MW) 150 Gross 60 Gross 

Fuel

Type ND Lignite 

Source Coteau Freedom Mine 

Moisture 37.8 

Sulfur (wt %, as received) 0.64 

Heating Value (Btu/lb, as received) 6,635 

Mercury (mg/kg, dry) 0.055 

Chloride (mg/kg, dry) <30 

Particulate Control

Type Cold-Side ESP Reverse Gas Baghouse 

Manufacturer Research-Cottrell Research-Cottrell 

ESP Specific Collection Area 

(ft2

/1000afcm) 

470 NA 

ESP Plate Spacing (in.) 9 NA 

Baghouse Air/Cloth Ratio (acf/ft2) NA 1.6 to 1 

Baghouse Cleaning Cycle NA 12-hr 

Device Inlet/Outlet Temp. (°F) 325 190 

NOx Controls LoNOx Burners LoNOx Burners 

SO2 Controls

 Type None Lime Spray Dryer 

Manufacturer NA Research-Cottrell 

 Design SO2 Removal (%) NA >80% 

 Recycle Rate (lb lime/lb recycle) NA 0 (no recycle) 

 Inlet / Outlet Temp (°F) NA 350 / 190 

Flue Gas Flow Rate (scfm) 360,000 160,000 
4

EPRI SCEM Mercury Analyzer 

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

depicted in Figure 2. At each sample location, a sample of the flue gas is extracted from the duct 

and then passes 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 that has been 

treated with a Restek Silcosteel coating. 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 

mercury oxidation in the flue gas. 

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. 

Figure 2. Semi-continuous mercury analyzer. 

Flue Gas

Duct

IGS Filter

Pump

EPRI SemiContinuous

Mercury

Analyzer

Sample

Impingers

Data Acquisition

Bypass 

Pump
5

TEST MATRIX 

Six sorbents were tested at Unit 10 as shown in Table 2. FGDTM carbon has been tested at 

Stanton and a number of other coal-fired plants and serves as a benchmark sorbent. Selection of 

the remaining five sorbents was based on the following criteria: 1) delivered cost; 2) mercury 

removal performance as verified in previous lab and/or field sorbent injection testing programs; 

and 3) vendor ability to supply the quantity of sorbent needed to conduct long-term testing. 

Barnebey Sutcliffe’s iodated carbon (CB 200xFTM and referred to in this paper as BS IAC) has 

been tested previously at Stanton Station and has shown up to 90% removal of mercury. It was 

tested again to verify performance and serve as a benchmark for the other treated carbons. While 

this sorbent has demonstrated higher mercury removal performance, its price is $7.71/lb, which 

is an order of magnitude higher than Norit FGDTM. 

As a lower price alternative product, an untreated, super-activated version of the Barnebey 

Sutcliffe carbon (208CPTM and referred to in this paper as BS SAC) was tested. The untreated 

carbon BS SAC has a price of $0.85/lb. 

Two chemically-treated carbons from Norit Americas were tested on Unit 10, FGD-E1 and 

FGD-E3. The sorbent FGD-E3 was expected to be a higher performing carbon than the FGDE1; however, it was more slightly more costly than FGD-E1 ($0.65/lb vs $0.60/lb). A 

brominated lignite-derived activated carbon from Sorbent Technologies (ST BAC) was also 

tested. This carbon has been demonstrated in full-scale tests at other sites to have high mercury 

removal efficiency at low injection rates. The projected price of ST BAC ranges from $0.50 to 

$1.00/lb. 

Table 2. Sorbents Selected for Test Program

Sorbent 

Name 

Unit to 

be 

Tested Manufacturer 

Average 

Particle 

Size 

(μm) Description 

F.O.B. 

Price 

($/lb) 

FGDTM Unit 10 Norit 

Americas 

19 Lignite-derived activated carbon; baseline 

carbon 

$0.50 

CB 

200xFTM 

BS IAC 

Unit 10 Barnebey 

Sutcliffe 

88 CB 200xF iodated coconut shell activated 

carbon; “by fines” particle size; received 

2004

$7.71 

FGD-E1 Unit 10 Norit 

Americas 

17 Chemically-treated, lignite-derived activated 

carbon 

$0.60 

FGD-E3 Unit 10 Norit 

Americas 

19 Halogenated, lignite-derived activated carbon $0.65 

208CPTM 

BS SAC 

Unit 10 Barnebey 

Sutcliffe 

46 Super activated coconut shell carbon $0.85 

ST BAC Unit 10 Sorbent 

Technologies 

20 Brominated lignite-derived activated carbon $0.50-1.00
6

All testing occurred with the unit at full load or very near to full load. Prior to commencement of 

injection tests, a week of baseline (no sorbent injection) testing was conducted on the 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. 

RESULTS 

Parametric Test Results 

Flue gas temperatures at the air heater outlet (spray dryer inlet), as measured by the plant, ranged 

from 312oF to 338oF. Flue gas temperatures at the baghouse outlet ranged from 175oF to 184oF. 

During the baseline and parametric evaluations, the targeted bag cleaning differential pressure 

for cleaning was 3.0-inches H2O with a time period between cleanings of about 3-4 hours. 

During parametric evaluations, the targeted bag cleaning differential pressure for cleaning was 

4.5-inches H2O with a time period between cleanings of about 7-8 hours. Neither the sorbent 

injection rate nor the sorbent type seemed to affect the baghouse cleaning frequency. 

No noticeable differences were observed in the operation of the spray dryer system during the 

baseline and the sorbent injection test periods. Slurry feed rates and water flows were run as 

under normal plant operations. Other plant parameters, including opacity, did not vary much 

during the evaluation period and no correlation with the amount of sorbent injected or sorbent 

type was observed. 

Baseline measurements were taken at the spray dryer inlet and baghouse outlet prior to each set 

of sorbent parametric evaluations. During baseline evaluations, the total vapor-phase mercury 

concentration ranged from 7.5 to 13 μg/Nm3

 for all sampled locations. The baseline flue gas 

contained little (< 10%) oxidized mercury. Native removal across the SD/BH configuration was 

less than 10% during baseline periods. 

Six sorbents were evaluated at various injection rates ranging from 0.5 to 6.0 lb/MMacf to 

achieve target removals ranging from 40% to greater than 90%. Mercury removals across the 

SD/BH for the six sorbents are presented in Figure 3. Removals were calculated by comparing 

the baghouse outlet mercury concentration to the spray dryer inlet concentration. 

The benchmark sorbent, Norit Darco FGDTM, achieved 75% mercury removal at an injection rate 

of 6.0 lb/MMacf. The super activated (but untreated) SAC carbon achieved higher removals 

than the Darco FGDTM, over the injection range of 0.5 to 1.5 lb/MMacf. At the maximum tested 

injection rate of 1.5 MMacf, the SAC carbon achieved almost 60% removal. 

The chemically treated carbons (BS IAC, Norit E-1, Norit E-3, and ST BAC) provided improved 

mercury removal performance over the untreated carbons. At an injection rate of 1.0 lb/MMacf, 

both the FGD E-3 and the ST BAC produced mercury removals greater than 85%. Mercury 

removals greater than 90% were achieved at an injection rate of 1.5 lb/MMacf with both 

sorbents. The Norit E-1 performed better than the untreated Darco FGDTM, but not as well as the 

Norit E-3. 
7

Figure 3. Results from Full-Scale Parametric Testing of Sorbents at Stanton Unit 10.

0

20

40

60

80

100

0 1 2 3 4 5 6 7

Injection Rate (lb/MMacf)

Hg Removal (%)

FGD

IAC

SAC

E1

E3

BAC

In this round of parametric testing the BS IAC carbon did not produce the 90+% mercury 

removals that it had achieved in previous test programs at Stanton Station. The BS IAC tested for 

this round of parametric tests was from a different manufacturer’s lot than the previous tests. BS 

IAC carbon sample from the previous (year 2000) lot were available on-site and was briefly 

tested. The older BS IAC carbon produced 90+% removals, indicating that there were 

significant differences between the two batches of carbon. Post test analysis showed that the 

average particle size of the 2004 lot was 87 m, while the 2000 lot had an average particle size 

of 47 m. 

Long-term Test Results 

After review of the parametric test results, Norit’s E-3 was selected for extended evaluations on 

Stanton Unit 10. This decision was based on the sorbent’s mercury removal performance, cost, 

and ability to be delivered in the quantity needed for the test program. A target removal of 60% 

to 75% mercury removal across the SD/BH was set for the long-term testing, which occurred 

over a period of 24 days. 

The spray dryer inlet mercury vapor-phase concentrations ranged from 7.5 to 12 μg/Nm3

 during 

the evaluation. For the long-term test period, an injection rate of 1.0 lb/MMacf was needed to 

achieve 65% to 75% mercury removal across the SD/BH. The outlet concentration from the 

SD/BH was typically in the range of 2.5-3.5 over the course of the long-term tests. An additional 

mercury-sampling probe was located after the sorbent injection point, but upstream of the SD, in 

order to observe any in-flight removal. No mercury removal was observed in-flight nor across 

the SD. 

The cleaning frequency of the baghouse increased to every three to four hours, as compared to 

six to eight hours during baseline operation (i.e. no sorbent injection). However, the slurry feed 

to the SD was not held constant during long-term testing because of coal sulfur variations. These 

coal sulfur variations did not occur during the baseline testing. The slurry feed rate can affect the 

frequency of cleaning; therefore, it is not possible to quantify the contribution of the sorbent 

injection to the compressed cleaning cycle. It is estimated that the added particulate loading due 

to sorbent injection was nominally 0.2% at 1 lb/MMacf. It is unlikely that this small increase in 
8

loading could influence the cleaning frequency of the baghouse. In addition to a change in 

cleaning frequency, a 4 - 6% increase in opacity was observed for a very short time period (< 5 

minutes) immediately after each baghouse clean. 

CONCLUSION 

Six sorbents were tested on Stanton Station Unit 10 for their ability to remove flue gas mercury. 

Two of the chemically treated sorbents (ST BAC and Norit E-3) were able to achieve mercury 

removals greater than 90% across the spray dryer/baghouse combination at sorbent injection 

rates as low as 1.5 lb/MMacf. In contrast, the non-treated sorbents were limited to 75% mercury 

removal, even at injection rates as high as 6 lb/MMacf. The Norit E-3 sorbent was selected for 

24 days of continuous sorbent injection testing. During the long-term tests, an injection rate of 1 

lb/MMacf was maintained in order to achieve 65-75% mercury removal across the spray 

dryer/baghouse combination. The resulting outlet mercury concentration was in the general 

range of 2.5-3.5 g/Nm3

. The most notable change in plant operation during sorbent injection 

was a doubling of the baghouse cleaning frequency. The increased particulate load to the 

baghouse was estimated to be less than 0.2%. Therefore, it is unlikely the increase in cleaning 

frequency is attributable to sorbent injection.