## Sorbent Injection for Mercury Control Upstream of SmallSCA ESPs

Paper #65

Katherine Dombrowski, Carl Richardson, Tom Machalek URS Corporation, 9400 Ambergle n 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 Ener gy 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 ups tream of small-SCA ESPs in flue gas derived from low-sulfur Eastern bituminous fuel. The pr oject 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 c onducted 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 ty pically runs with SO 3 and NH 3 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 s upplemental removal across the we t scrubber. Para metric tests also evaluated the effect of sorbent additi on rate and flue gas conditioning on sorbent performance.


### INTRODUCTION Sorbent injection is currently the most studied mercury control technolog y for coal-fired utilities. The technology has been tested in numerous pilo t 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 ft 2 /1000 acfm. The mercury removal capabilities and balance of plant effects for sorbent injection ha ve not been tested on plants with small ESPs.2 The purpose of this project is to evaluate full-s cale 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 NH 3 and SO 3 injection on mercur y removal to be explored. Short-term parametr ic tests were c onducted on Georgia Power’s Plan t Yates Units 1 and 2 to evaluate the performance of activ ated carbon sorbents. In addition, the effects of the dual flue gas conditioning system on mercur y removal performance were eval uated 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 (j et 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 pr ocesses 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 syst em downstream of the ESP for SO 2 control. Unit 2 is not equipped with downstream SO 2 controls; however, a dual flue gas conditioning system is used to enhance ESP performance. The dual flue gas conditioning system consists of SO 3 and NH 3 injection. Figures 1 and 2 show the basic pl ant configuration, sorbent injecti on points, and flue gas sample locations for Units 1 and 2, respectively. Charact eristics 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 pneuma tic 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 de tail. 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 lo ading 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 Fl ue Gas Sample Locations

Figure 2. Unit 2 Configuration and Fl ue Gas Sample Locations JBR Absorber

Boile r 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 Injection4 Table 1. Plant Yates Unit 1 a nd 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 (ft 2 /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 NO x Controls Low NOx Burners None SO 2 Controls Chiyoda CT-121 wet scrubber (JBR) None

Flue Gas Conditioning None Dual NH 3 /SO 3



### EPRI SCEM Mercury Analyzer Flue gas vapor-phase mercury analyses were made using EPRI se mi-continuous analyzers depicted in Figure 3. At each sample location, a sa mple 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 merc ury prior to analysis using a chilled reduction solution of acidified stannous ch loride. Several impingers containing alkaline solutions are placed downstream of the reducin g 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 of5 mercury oxidation in the flue gas. All mercur y concentrations reporte d in this paper are normalized to 3% O 2 . 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 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.


### TEST MATRIX

Three different sorbents were selected for te sting on Plant Yates Unit 1. A description of the each sorbent is provided in the table below. The Darco FGD carbon will serve as the benchmark sorbent since it has been used in numer ous 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 incl uded in the test plan, but it was made available at no cost to the project. The project t eam 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 FGD carbon.
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 Pump6 The test conditions for Units 1 and 2 are summarize d 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 conduc ted on each unit. For injecti on testing, baseline mercury concentrations were measured at the beginning a nd end of each test day. On each injection test day, one to four injecti on rates were tested. At least two hours were needed at each test condition in order to achieve steady ou tlet 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 FGD TM 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 FGD TM 3/22/04 - 3/26/04 2.1 - 12.7



### RESULTS
Baseline Results During baseline testing on Unit 1 (SCA = 173 ft 2 /1000 acfm), the average vapor-phase ESP inlet mercury concentration was 4.02  g/Nm 3 and the average ESP ou tlet concentration was 2.64
 g/Nm 3 (at 3% O 2 ). On average, a 34% native removal across the ESP was measured during the baseline period. For Unit 2 (SCA = 144 ft 2 /1000 acfm) during the baseline week of testing, the average ESP inlet mercur y concentration was 6.04  g/Nm 3 and the outlet was 3.89  g/Nm 3

, 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 c ontent and the temperature of th e flue gas. Baseline mercury measurements were also made before and after each injection test day. ESP inlet mercury was typically between 4.0 and 7.0  g/Nm 3 ,while ESP outlet concentra tions were between 2.5 and 5.0
 g/Nm 3

. Coal and ash samples were collected during the baseline testing week and measured for mercury content. The fly ash had a high LOI content, typi cally in the 9-13% range. As seen in Figure 4, the mercury content of the ash increased proportiona tely to the LOI content, indicating that the LOI of the ash may play a role in the hi gh 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 Pl ant 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 m onitored. 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- (HgVapor ESP,out ) t / (HgVapor ESP,in ) t where (HgVapor ESP,out ) t is the vapor phase merc ury concentration at the ESP outlet measured at time t, and (HgVapor ESP,in ) t is the vapor phase mercury concen tration 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 re duction at the ESP outlet due to sorbent injection. The mercury reduction was calculated as % Reduction at ESP Outlet = 1- (HgVapor ESP,out ) t / (HgVapor ESP,out ) 0 where (HgVapor ESP,out ) t is the vapor phase merc ury concentration at the ESP outlet measured at time t, and (HgVapor ESP,out ) 0 is the vapor phase mercury c oncentration 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 me rcury 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 acro ss the ESP and the percen t mercury reduction at the ESP outlet, respectively, as a function of so rbent 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 ash8 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 ach ieved percent reduction of mercury at the ESP outlet was about 40%. The curves for the Darco FGD TM and the NH carbon are nearly identical, and the Super HOK curve is just slightly lower. Figures 7 and 8 show the percent removal acr oss 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 remova l across the ESP/JBR. However, the native removal across the combined system was high er 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 FGD TM and the Super HOK curves were nearly identical. Sorbent injection tests were conducted with Darco FGD TM 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 indi cate an additional 30 to 40 percen t reduction in to tal vapor-phase mercury was achieved at an inj ection rate of 2 lb/MMacf. No additional reducti on 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/Nm 3 ), which could bias low the merc ury reduction measured. Figure 9 also indicates the set points for the dual flue gas conditioning sy stem during each test period. The dual flue gas conditioning system appeared to have no effect on the re duction 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 injecti on rates of 6 lb/MMacf and above.

Figure 5. Comparison of Mercur y Removal Efficiency Across the ESP of the Three Sorbents Tested on Unit 19 Figure 6. Comparison of Mercury Re duction at the ESP Outlet for the Three Sorbents Tested on Unit 1

Figure 7. Comparison of Mercury Rem oval Efficiency Across the Combined ESP/JBR of the Three Sorbents Tested on Unit 110 Figure 8. Comparison of Mercury Re duction at the JBR Outlet for the Three Sorbents Tested on Unit 1

Figure 9. Percent Reduction in Vapor Phas e 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 perfo rmance was quantified by taking single point Method 17 particulate samp les during each injection rate and by monitoring the arc rate in each field. Figure 11 shows the Unit 1 ESP outlet partic ulate concentrations m easured during baseline and injection testing. During ba seline conditions (sorbent injecti on rate = 0 lb/MMacf), the ESP outlet particulate concentr ation ranged from 0.024 to 0.052 grains/dscf at 3% O 2 , with an average of 0.036 gr/dscf. For the tested carbon injection ra tes of 2 to 17 lb/MMacf, the measured outlet particulate concentrations were mostly within or below the range of c oncentrations measured during baseline testing. These results indicate th at 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 Measurements12 

### 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 in creased proportionately to the LOI content, likely contributing to the na tive mercury removal observed during this period (Unit 1 = 34% average Hg removal, Unit 2 = 36% average Hg removal).

 All three tested sorbents (Darco FGD TM , Super HOK, and NH Carbon) had approximately the same dose -response curve for mercury removal from the flue gas, reaching 30-40% additional re duction in ESP outlet mercur y at a sorbent injection concentration of approx imately 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 particul ate 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 ba lance-of-plant impacts.