## 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 Ambergle n 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, EP RI, Great River Energy, North Dakota Industrial Commission, Apogee Scie ntific, and ADA-ES, is evalua ting the effectiveness of sorbent injection for reducing mercury emissi ons from flue gas derived from North Dakota lignite. This paper reports full-scale tests perfo rmed at Great River Energy’s Stanton Station Unit 10 to evaluate sorbent injection perform ance across a spray dryer-baghouse combination. Six mercury sorbents were c hosen based upon pre-determined selection criteria and were evaluated during short-term para metric tests on each unit. Para metric tests de termined 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. Th e 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, injec tion of untreated activated carbons has shown lower mercury removal performance than fo r other coals, such as bitumi nous coals. The low chlorine and high calcium content of lignite fuel resu lts 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 car bons or by using furnace additives to increase2 the chloride content of the flue gas. Both of these technologies ha ve been successfully demonstrated in short-term, full-scale tests. Full-scale testing of chemically treated carbons wa s undertaken at Stanton Station as part of a larger DOE-NETL program inves tigating 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. Stant on Station consists of two units. Unit 1 is equipped with an ESP, while Unit 10 is equippe d 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 th e 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-p lant effects of sorbent injection. The parametric and long term testing on Stant on Unit 10 has been completed and the results are presented in this paper. Tes ting on Unit 1 has yet to commence.



### DESCRIPTION OF STANTON UNIT 10

Various sorbent materials were injected upstream of spray drye r/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 pl ant configuration, sorben t injection points, and flue gas sample locations for Units 10. Ch aracteristics 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 s s
Unit 10 Boiler

Bottom Ash

Unit 10 Boiler

Bottom Ash Spray Dryer s s s s s

s s Reverse Gas Baghouse Stack

Reagent Slurry Prep. Lime

Makeup Water S S Spray Dryer Solids

Combined Solids Stack Gas

Sample Location S Sorbent Injection

S Baghouse Solids Figure 1. Stanton Unit 10 Configuration W ith Flue Gas and Solid Sample Locations3 

### 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 pneum atically conveys a predetermined and adjustable amount of powde red 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 supp lied 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 de tail. Flue gas extraction probes and mercury analyzers were situated at the spray dryer inlet, baghouse inle t, and baghouse outlet. The analyzers continuously monitored the flue gas mercury concentrati on 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 (ft 2 /1000afcm) 470 NA

ESP Plate Spaci ng (in.) 9 NA Baghouse Air/Clot h Ratio (acf/ft 2 ) NA 1.6 to 1 Baghouse Cleaning Cycle NA 12-hr Device Inlet/Outlet Temp. (°F) 325 190 NO x Controls LoNO x Burners LoNO x Burners SO 2 Controls

Type None Lime Spray Dryer

Manufacturer NA Research-Cottrell Design SO 2 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) 360,000 160,0004 EPRI SCEM Mercury Analyzer Flue gas vapor-phase mercury analyses were made using EPRI se mi-continuous analyzers depicted in Figure 2. At each sample location, a sa mple 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 str eam 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 absorpti on 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 characteris tics of elemental merc ury, the non-elemental fraction is converted to elementa l mercury prior to analysis us ing 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 c ontaining either 1M pot assium 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 concentr ated on the gold is thermally desorbed (>400  C) in nitrogen or air, and sent as a concentrated me rcury stream to a CVAAS for analysis. Therefore, the total flue gas mercury con centration is measured semi-con tinuously 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 Semi

Continuous

Mercury Analyzer Sample Impingers Data Acquisition

Bypass Pump5 

### 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 be nchmark sorbent. Selection of the remaining five sorbents was based on the follo wing criteria: 1) deliv ered cost; 2) mercury removal performance as verified in previous lab and/or field sorb ent injection testing programs; and 3) vendor ability to supply the quantity of so rbent 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% remova l of mercury. It was tested again to verify perform ance and serve as a benchmark fo r the other treated carbons. While this sorbent has demonstrated higher mercury removal performan ce, its price is $7.71/lb, which is an order of magnitude higher than Norit FGD TM

. As a lower price alternative product, an untreat ed, super-activated version of the Barnebey Sutcliffe carbon (208CPTM and referre d to in this paper as BS SA C) was tested. The untreated carbon BS SAC has a price of $0.85/lb. Two chemically-treated carbons from Norit Am ericas 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 co stly than FGD-E1 ($0.65/lb vs $0.60/lb). A brominated lignite-derived activated carbon fro m Sorbent Technologies (ST BAC) was also tested. This carbon has been demons trated in full-scale tests at ot her sites to have high mercury removal efficiency at low inj ection 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 $0.50-1.006 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 concen trations were achieved, the car bon 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 parametr ic evaluations, the targeted ba g cleaning differential pressure for cleaning was 3.0-inches H 2 O with a time period between cl eanings of about 3-4 hours. During parametric evaluations, the targeted ba g cleaning differential pressure for cleaning was 4.5-inches H 2 O 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 rate s and water flows were run as under normal plant operations. Ot her 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 evaluati ons. During baseline evaluations, the total vapor-phase mercury concentration ranged from 7.5 to 13 μg/Nm 3 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 inj ection rates ranging from 0.5 to 6.0 lb/MMacf to achieve target removals rangin g 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 c oncentration to the spray dryer inlet concentration. The benchmark sorbent, Norit Darco FGD TM , achieved 75% mercury remova l at an injection rate of 6.0 lb/MMacf. The super activated (but untreated) SAC carbon achieved higher removals than the Darco FGD TM , 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 in jection rate of 1.0 lb/MMacf, both the FGD E-3 and the ST BAC produced me rcury 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 FGD TM , 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 pr evious test programs at Stant on 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 th e two batches of carbon. Post te st 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, No rit’s E-3 was selected fo r 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 mercur y vapor-phase concentrations ranged from 7.5 to 12 μg/Nm 3 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 re moval 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 sorb ent injection point, but upstream of the SD, in order to observe any in-flight removal. No mercury removal wa s 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 ope ration (i.e. no sorbent injection) . However, the slurry feed to the SD was not held constant during long-term te sting because of coal sulfur variations. These coal sulfur variations did not occur during the base line testing. The slurry feed rate can affect the frequency of cleaning; therefore, it is not possi ble 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/MM acf. It is unlikely that this small increase in8 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 afte r 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 dr yer/baghouse combination at sorbent injection rates as low as 1.5 lb/MMacf. In contrast, th e non-treated sorbents we re 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. Du ring the long-term tests, an injection rate of 1 lb/MMacf was maintained in order to achie ve 65-75% mercury rem oval across the spray dryer/baghouse combination. The resulting outle t mercury concentrati on was in the general range of 2.5-3.5 g/Nm 3 . 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.