Draft Notes from Site Visit at We Energies’ Pleasant Prairie Power Plant on March 2, 2010

EPA conducted a site visit at We Energi es’ Pleasant Prairie Po wer Plant (Pleasant Prairie) located in Pleasant Pr airie, WI on Tuesday, March 2, 2010 to learn about the operations at the plant, specifically the fl ue gas desulfurization (FGD) wast ewater treatment system. These notes describe the information collected during the site visit. Table 1, located at the end of these notes, identifies the site visit participants. An FGD wastewater flow diag ram and an overall plant water balance diagram are provided as Attach ments 1 and 2, respectively, to these notes.

Plant Overview

 Pleasant Prairie operates two coal-fired ge nerating units at the power plant. Units 1 and 2, which began operation in 1980 and 1985, respectively, each have a capacity of 615 megawatts (MW). Both un its are operated as baseload units.

 Pleasant Prairie retr ofitted Units 1 and 2 with F GD scrubber systems to control the sulfur dioxide (SO 2 ) releases from the plant. The FGD scrubber systems were

installed in November 2006 (Unit 1) and March 2007 (Unit 2). With the addition of the FGD scrubber systems, Pleasant Prai rie also installed an FGD wastewater treatment plant to control the discharges of the wastewater generated during the operation of the FGD scrubbers.

 SCR systems were retrofit additions to the plant and were installed on Unit 2 in 2003 and Unit 1 in 2006. [QUESTION FO R PLEASANT PRAIRIE: Did the plant install the FGD scrubber system and SCR system on Unit 1 at the same time?] SCRs are used to c ontrol nitrogen oxide (NO

x ) emissions. The plant operates the SCR systems year round.

 Pleasant Prairie operates cold side electro static precipitators (ESPs) on both Units 1 and 2. The ESPs remove approximately 99.7 percent of the particulates in the flue gas. Pleasant Prairie opera tes a dry fly ash handling system.

 Pleasant Prairie recently installed a ca lcium bromide injection system for the boiler. The system injects a solution of calcium bromide into the boiler which enhances the oxidation of mercury in the flue gas. The oxidized mercury is more easily removed in the FGD scrubber system and, therefore, lowers the plant’s mercury emissions. The bromide injecti on system has been achieving 60-70 percent mercury removal, or better.

 Pleasant Prairie burns Powder River Basi n (PRB) coal in both units. The plant burns approximately 5.5 million tons of coal per year.

 Pleasant Prairie is located about 5 mile s away from Lake Michigan. The plant discharges to Lake Michigan. During the site visit, Unit 1 was in a sc heduled maintenance outage. During this outage, the air heater baskets were se rviced and the annual boiler work was completed.

Carbon Capture Study

 Pleasant Prairie participated in a pilot-scale carbon capture technology study in

collaboration with EPRI and Alstom th at started in 2007 and ended in October 2009. The study used a slip stream of the flue gas to test Alstom’s chilled ammonia carbon capture technology. Alstom and EPRI operated the pilot-scale system at the plant for approximately tw o years before the study was completed. [QUESTION FOR PLEASANT PRAIRIE: From which unit was the slip stream taken and treated?]

 Plant personnel stated that the carbon cap ture system was successful in removing up to 90 percent of the carbon dioxide from the flue gas.

 Pleasant Prairie stated that the plant is located over sub solid rock, limiting the ability to sequester any captured carbon in the ground; therefore, the carbon dioxide captured during the study was transferred off site.[QUESTION FOR

PLEASANT PRAIRIE: Where and how wa s the captured carbon transferred offsite?]

 Plant personnel stated that the lessons learned from the study at Pleasant Prairie were incorporated into the pilot study that is taking place at AEP’s Mountaineer plant in New Haven, WV.

 Plant personnel explained th at the system at the Pleas ant Prairie site utilized aqueous ammonia and sulfuric acid for pH adjustment in the absorber. The process generated a waste stream consis ting of an ammonium sulfate solution. The plant’s wastewater treatment system does not treat for ammonia; therefore, the wastewater stream from the study wa s collected and transferred off site. The generated wastewater was tr ansferred off-site and trea ted at Beaver Royal in Illinois. [QUESTION FOR PLEASANT PRAIRIE: How was the wastewater treated by Beaver Royal and what did they do with the wastewater after treatment?]

 Pleasant Prairie stated that because the carbon capture system was operated by Alstom and EPRI, they were uncertain of the generation rate for the wastewater stream. Additionally, Pleasant Prairie does not have any analytical results characterizing the waste stream; however , the plant believes that EPRI should

have characterization data. Pleasant Prairi e stated that they do not know if the

characterization data will be included in the final re port prepared for the study. [QUESTION FOR PLEASANT PRAIRIE: Please provide the letter that was submitted to the DNR that estimated that characteristics of the waste stream.] EPRI collected water and air samples from the system during the study. Plant personnel stated that a fina l report, from EPRI, may be available by the end of

2010.

FGD Operation

 Pleasant Prairie has two identically de signed FGD scrubber systems on Units 1

and 2.

 The FGD spray tower has three spray head er levels; however, the plant typically only operates two of the spray levels at one time. The FGD scrubber systems are also equipped with one dual flow tray.

 The plant does not add any organic acids to the scrubber (e.g., DBA) because the plant’s FGD wastewater treatment system does not have the capability to remove the BOD from the system. Pleasant Prairie st ated that if they did add organic acids they would have to send the wast ewater to a POTW for treatment.

 The plant has experienced some problems w ith foaming in the absorber; therefore, they have been adding a s ilicone-based antifoamant to control this issue. The plant adds between 10 and 20 gallons of the antifoamant per day.

 The plant uses a limestone slurry as the sorbent for sulfur dioxide (SO 2 ) absorption. Each unit has its own ball mill where the limestone is ground and mixed with water to 40 to 50 percent solids by weight. The plant uses hydrocyclones to classify the limestone a nd ensure the correc t size particles are used in the FGD scrubber system.

 Pleasant Prairie maintains the solids c oncentration in the FGD scrubber systems between 15 and 18 percent solids. When the solids concentration exceeds 18 percent, the plant blows down from the FGD scrubber. Plant personnel estimated

that each unit blows down for about 8 to 10 hours each day. The plant tries to stagger the blow down from the two units.

 Pleasant Prairie also mainta ins the chloride concentration in the FGD scrubber systems between 3,000 and 10,000 ppm. The pl ant tries to keep the chlorides concentration around 6,000 ppm. The maximu m design chlorides concentration is 15,000 ppm.

 Plant staff indicated that the chloride c oncentration in Unit 1 tends to be higher than in Unit 2 because water from Unit 2 is recycled to Unit 1.

 The blowdown for each FGD scrubber syst em is transferred to its primary hydrocyclone. Each FGD scrubber system has a dedicated hydrocyclone. The underflow from the primary hydrocyclones, which is 50 percent solids, istransferred to the vacuum belt filters wh ere the plant washes the gypsum to lower the chlorides concentration in the gyps um. Each primary hydrocyclone feeds a

dedicated vacuum belt filter. The vacuum belt filter dries the gypsum to less than 10 percent moisture. Pleasant Prairie sells the gypsum to a wallboard manufacturing in Waukegan, IL, as well as for agricultural uses.

 The filtrate from the vacuum belt filters is collected and transferred back to the FGD scrubber systems. All the filtrate is typically transferred back to the Unit 1 FGD scrubber system; however the plant has the capability to also send the filtrate to the Unit 2 FGD scrubber system.

 The primary hydrocyclone overflow from th e two units are commingled together and transferred to a common secondary hydrocyclone. The underflow from the secondary hydrocyclone is recycled b ack to the FGD scrubber systems. The overflow from the second hydrocyclone is transferred to the FGD wastewater

treatment system.

FGD Wastewater Treatment System

 The FGD wastewater treatment system is designed to receive intermittent discharges of FGD wastewater from the s econdary hydrocyclones at a flow rate of approximately 40 gpm. The design flow ra te for the FGD wastewater treatment system is 75 gpm.

 The secondary hydrocyclone overflow is tr ansferred directly to the equalization tank, where intermittent flows from the hydrocyclone are equalized allowing the plant to pump a constant flow rate of FGD wastewater through the treatment system. The equalization tank also receives wastewater from the filtrate sump, which consists of filter press filtrate and treated effluent recycle.

 The wastewater flows from the equaliz ation tank to reaction tank 1, where hydrated lime is added to raise the pH of the wastewater from 5.6 to about 8.5

S.U. Reaction tank 1 also receives so me of the sludge from the downstream primary clarifier which provide se ed crystals for gypsum nucleation.

 From reaction tank 1, the wastewater flows to the primary clarif ier. The clarifier contains approximately 2 to 4 feet of settled solids in the bottom of the clarifier. Pleasant Prairie adds a polymer to the prim ary clarifier to aid the settling of the

solids.

 The overflow from the primary clarifier flows to reaction tank 2, where the plant adds organosulfide and hydr ochloric acid. When the pl ant first began operating the treatment system, they used TMT 15® as the organosulfide. Since that time, the plant has switched to using Nalmet® 1689, which is an organosulfide that has a longer polymer chain, and therefore, a higher molecular weight, which helps aid in the settling of precipitates. Pleasan t Prairie also began adding hydrochloricacid to reaction tank 2, which wasn’t in th e initial design of the treatment system, because the plant determined that the they got better removals of mercury when the treatment system operated at a lowe r pH. The pH in reaction tank 2 is targeted at 7.0 to 7.2 S.U.

 The wastewater flows next to reaction ta nk 3, where ferric chloride is added. The

wastewater then flows to the flash mi x tank, where polymer is added. From the flash mix tank, the wastewater flows to the flocculation tank where a gentler mixing takes place.

 The wastewater from the flocculation then flows to the secondary clarifier. The secondary clarifier se ttles the solids created from chemical conditioning steps. The secondary clarifier is an inclined-plate lamella separator type clarifier. Hydrochloric acid is added to the overflow from the secondary clarifier to meet discharge standards for pH.

 The treated wastewater is collected in tw o effluent tanks prior to discharging to Lake Michigan.

 Pleasant Prairie commingles the effluent from the FGD wastewater treatment system with other plant wastewaters, t ypically cooling tower blowdown, at a ratio

of 30:1 to meet the final outfall merc ury and chloride limits, 80 ng/L and 1,514 mg/L, respectively.

 The plant stated that when they chlo rinate the cooling system, they do not discharge cooling tower blowdown. Because there is no discharge of cooling tower blowdown during chlorination, the plant does not disc harge the treated

FGD wastewater because there is no t enough other plant wastewaters to commingle with the FGD wastewater to m eet the final outfall mercury limit. The treated wastewater is held in the effluent tank during chlorination until discharged. [QUESTION FOR PLEASANT PRAIRIE: How long can the plant keep from discharging without need ing to go into re circulation mode?]

 The FGD wastewater treatment system typically operates Monday through Saturday. The plant performs weekly maintenance on the system starting Saturday evening. This maintenance includes draini ng and flushing the second clarifier, to avoid flocculation build up, whic h can impact its performance.

 The first FGD scrubber, installed in N ovember 2006, ran for several months with 100% recirculation before blowing down to the FGD wastewater treatment system. The plant had several start up and performance issues with the FGD wastewater treatment system and did not discharge from the system until the end of calendar year 2007. Pleasant Prairie wa s able to operate the wastewater treatment system in recirculation mode for a long period of time because the chlorides in the system do not build up qui ckly due to the low chlorine content in

the PRB coal. When the plant does not blowdown for severa l weeks, fines and colloidal particles begin to build up in the FGD wastewater treatment system because they are being recirculated throughout the system wit hout being discharged. As the fines concentration begins to increase, the mercury concentration also begins to increase. If the mercury concentration rises above the NPDES permit limit, the plant is unable to discharge and, theref ore, the mercury concentration would continue to rise. To help remove the fines and associated mercury from the wastewater, Pleasant Prairie installed a set of cartridge filters that can be used as a polishing step. The plant used the cartridge filters to remove the mercury from the FGD wastewater treatment syst em after the initial start up phase. The plant is still able to treat the wastewater through the cartr idge filters, but they try not to do this unless necessary because the filters are e xpensive. Currently the plant can stop discharging for approximately a week before they can notice chlorine concentrations increases. [QUE STION FOR PLEASANT PRAIRIE: How frequently do the cartridge filters need to be replaced when used?]

 Pleasant Prairie has made a few modificat ions to the FGD wastewater treatment system since the system first began operat ing in early 2007. The following is a list

of the modifications Pleasant Prairie has made to the FGD wastewater treatment

system:

 Changed the type of organosulfide used in the system from TMT 15® to Nalmet® 1689;

 Added a hydrochloric acid addition point to reaction tank 2 because the system achieves better mercury removals at a lower pH;

 Bypassed a set of sand filters which were located after the secondary clarifiers becaus e of scaling issues; and

 Added the capability to use cartrid ge filtration to remove colloidal particles from the wastewater af ter the effluent tanks, which may build up in the system if the pl ant recirculates the wastewater without discharging for several weeks; however the cartridge filtration is not used regularly.

Wastewater Treatment System Performance

 Pleasant Prairie is required to sample me rcury twice per week, according to their NPDES permit. The plant also collects samples Monday through Friday off the secondary clarifier for co nfirmation of system performance. The plant uses Method DMA 80 to test mercury, which is comparable to Method 1631E, but is usually biased high. For example, some samples analyzed using Method 1631E resulted in mercury concentrations of 0.22 to 0.25 ppb, and the Method DMA 80 resulted in mercury concentrations of 0.35 to 0.4 ppb. When mercury concentrations start to approach 1.2 or 1.3 ppb; the plant will begin discharging from the FGD wastewat er treatment system in batches. The

wastewater is transferred to one of the e ffluent tanks and then isolated when it is full. The plant will then analyze a sample for mercury to ensure it is below the permit limit of 1.5 ppb. Once the mercury co ncentration is confirmed, the plant discharges the wastewater from the effluent tank.

 The plant tries to keep the effluent me rcury levels below 0.4 ppb. The wastewater treatment system is currently achieving the lowest mercury concentrations since the installation of the system without the use of polishing filtration, 0.25 ppb.

 FGD wastewater from units burning PRB coal has a higher influent mercury concentration, compared to bituminous coal. PRB coal produces an FGD

wastewater treatment influent with a mercury concentration of 2,000 ppb ± 500, compared to 500 ppb for an influent concentration from bituminous coal.

 Pleasant Prairie believes that high mercur y levels in the FGD wastewater are a result of the scrubber chemistry and burning PRB coal. Pleasant Pr airie stated that the effluent from their treatment system is an order of magnitude higher than the effluent from a similar treatment syst em burning bituminous coal. The average mercury concentration reached after tr eatment for bituminous coal is 0.03-0.04 ppb; some even reaching 14 ppt.

 Pleasant Prairie has performed pilot tests using microfiltration for the reduction of mercury and other heavy metals in the final effluent. In September/October 2008, the plant performed a series of membrane pilot tests. The pilot tests used a 1 gpm slip stream from the primary clarifier effl uent as the basis for the study. The pilot tests included the following:

 Pleasant Prairie tested Siemens’ Memcor® technology microfiltration system. The system achieved effluent mercury concentrations of 0.1 ppb, but the system experienced signifi cant scaling issues. [QUESTION FOR PLEASANT PRAIRIE: Please clarify if the plant tested a microfiltration or ultrafiltration system. What speci fic configuration did you test at the plant? How long was the system test ed at the plant? How quickly did scaling occur?]

 Pleasant Prairie tested GE’s Zeewee d microfiltration system, which also achieved effluent mercury concen trations of 0.1 ppb. [QUESTION FOR PLEASANT PRAIRIE: Please clarify if the plant tested a microfiltration or ultrafiltration system.] The syst em used air scouring and backwashing to remove scale from the system. Pleasant Prairie stated that the system performed well and appeared to be more promising than the Memcor® system. However, the plant stated that they would want the system to be tested on a larger scale before they would purchase the system. Pleasant Prairie also tested an absorptive media system and an iron cementation system.

 Selenium levels are also higher in PRB co al than bituminous coal. Total selenium

in the influent FGD wastewater at Pleas ant Prairie is abou t 15,000 ppb, mostly in the solids phase. The effluent from the system is between 3,000 and 5,000 ppb.

Pleasant Prairie believes that the selenium in their wastewater is difficult to treat because there is more selenate (which has a higher solubility) in the system, than selenite. Pleasant Prairie believes the pr esence of more selenate is due to the scrubber chemistry associated with PRB coal.

Information for Sampling

 EPA identified the FGD wastewater treatme nt system influent sampling point as the tap off the secondary hydrocyclone. EP A would use this sample to represent

the influent to the FGD wastewater treatme nt system. Pleasant Prairie stated that they could install a smaller hose barb on the tap to accommodate the sample collection. There is plenty of space su rrounding the secondary hydrcyoclone in order to set up tables an d store coolers/supplies.

 EPA identified the FGD wastewater treatme nt system effluent sampling point as the tap located after the effl uent tank, prior to recircul ation or discharge, at the sample panel. Prairie stated that they c ould install a smaller hose barb on the tap to accommodate the sample collection. There is available space in the FGD wastewater treatment building to set up tables and store coolers.

 Pleasant Prairie stated that all on-site sampling personnel would be required to attend a 30 minute health and safety tr aining session. In cas e of emergencies during the sampling episode, the samplers should contact the control room immediately. Additionally, all personnel will be equipped with key phone

numbers and sound awareness cards for a ny sound signals occurring at the plant during sampling.Table 1. Site Visit AttendeesNameOrganization (Representing)TelephoneE-mailElizabeth Hellman We Energies 414-221-3235 elizabeth.hellman@we-energies.comPete Kutzora We Energies 414-221-3926 pete.kutzora@we-energies.comDavid LeeWe Energies414-221-2158 david.lee@we-energies.comDonna HillSouthern Company/UWAG205-587-4846 dbhill@southernco.comJezebele AliceaUS EPA202-566-1755 alicea.jezebele@epa.govRon JordanUS EPA202-566-1003 jordan.ronald@epa.govTJ FinsethERG703-633-1698 thomas.finseth@erg.comElizabeth SabolERG703-633-1659 elizabeth.sabol@erg.com