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 Power Plant (Pleasant Prairie) located in Pleasant Prairie, WI on Tuesda y, March 2, 2010 to learn about the operations at the plant, specifically the flue gas desulfur ization (FGD) wastewater treatment system. These notes describe the information collected during the si te visit. Table 1, located at the end of these notes, identifies the site visit participants. An FGD wastewater flow diagram and an overall plant water balance diagram are provided as Attachments 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 units are operated as baseload units.

 Pleasant Prairie retrofitted Units 1 and 2 with FGD 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 Pr airie 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 th e plant and were installed on Unit 2 in 2003 and Unit 1 in 2006. [QUESTION FOR PLEASANT PRAIRIE: Did the plant install the FGD scrubber system and SCR system on Unit 1 at the same time?] SCRs are used to control 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 operates a dry fly ash handling system.

 Pleasant Prairie recently installed a calcium bromide injection system for the boiler. A liquid form of 50% calcium bromide is sprayed on to the coal at the inlet to the ball mills used to pulverize the coal. The bromide addition results in conditions that lead to the oxidation of mercury into a form that increases its removal in the wet FGD system. The bromide injection system has been achieving 60-70 percent mercury removal, or better. Mercury is ultimately removed from the wet FGD blowdown at the treatment facility and the dried wastewater sludge is landfilled. Increased amounts of flue gas merc ury removal (adsorbed to the fly ash) in the precipitators has also been observed. 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, lowe rs the plant’s mercury emissions

. Comment [dml1]: Yes. The SCR and FGD systems for U1 installed and placed into service at

the same time.

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

 Pleasant Prairie is located about 5 miles awa y from Lake Michigan. The plant discharges to Lake Michigan.

 During the site visit, Unit 1 was in a scheduled maintenance outage. During this outage, the air heater baskets were serviced 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 that started in 2007 and ended in October 2009. The study used a slip stream of the Unit 1 flue gas from either P4 Unit 2 or

P4 Unit 1 to test Alstom’s chilled ammonia carbon capture technology. Alstom and EPRI operated the pilot-scale system at the plant for approximately two years before the study was completed. [QUESTION FOR PLEASANT PRAIRIE: From which unit was the slip stream taken and treated?] The carbon capture pilot was set up to obtain flue gas from P4 Unit 2. A back up connection was later added to allow the carbon capture pilot to remain in service when P4 Unit 2 was shut down for its annual scheduled maintenance outage, or was off line due to a forced outage.

 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. Following capture the carbon dioxide was routed to the flue gas and emitted to the stack.

 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 FORPLEASANT PRAIRIE: Where and how was the captured carbon transferred offsite?]

 Plant personnel stated that the lessons l earned 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 that the system at the Pleasant Prairie site utilized aqueous ammonia and sulfuric acid for pH adjustment in the absorber. The process generated a waste stream consisting of an ammonium sulfate solution. The plant’s wastewater treatment system does not treat for ammonia; therefore, the wastewater stream from the study was collected and transferred off site. The generated non-hazardous wastewater was transferred off-site and treated at Formatted: Font: Bold

Comment [dml2]: This research was to evaluate capture, not sequestration. See edit to bullet point above. Note – this project did not involve an evaluation of the potential to store CO2 below P4, nor anywhere else in SE Wis. Therefore, I’d remove this bullet point completely.Beaver Royal Oil Company in Illinois. [QUESTION FOR PLEASANT

PRAIRIE: How was the wastew ater treated by Beaver Royal Oil and what did they do with the wastewater after treatment?] Beaver Oil Company received the

dilute ammonium sulfate waste stream from Alstom Power's Chilled Ammonia Carbon Capture Pilot at We Energies P4, and placed it "into their general waste treatment feed." It was mostly water and was used for pH adjustment of incoming feeds to allow for precipitation in their batch treatment tanks.

 Pleasant Prairie stated that because th e carbon capture system was operated by Alstom and EPRI, they were uncertain of the generation rate for the wastewater stream. Additionally, Pleasant Prairie do es 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 report 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 final report, from EPRI, may be available by the end of

2010.

FGD Operation

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

and 2.

 The FGD spray tower has three spray header 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 wastewater to a POTW for treatment.

 The plant has experienced some problems with foaming in the absorber; therefore, they have been adding a silicone-based an tifoamant 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. The two scrubber systems share two Each unit has its own ball s mill where the limestone is ground and mixed w ith water to 40 to 50 percent solids by weight. The plant uses hydrocyclones to classify the limestone and ensure the correct size particles are used in the FGD scrubber system. Formatted: Font: (Default) Times New Roman,

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Comment [dml3]: Copies of our submittal and the DNR response are attached. Pleasant Prairie maintains the solids concentration in the FGD scrubber systems

between 1 5 8 and 2 1 8 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 maintains the chloride concentration in the FGD scrubber systems between 3,000 and 10,000 ppm. The plant tries to keep the chlorides concentration around 6,000 ppm , or lower . The maximum design chlorides concentration is 15,000 ppm.

 Plant staff indicated that the chloride co ncentration 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 system 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, is transferred to the vacuum belt filters where the plant washes the gypsum to lower the chlorides concentration in the gypsum. Each primary hydrocyclone feeds

either of two common a dedicated vacuum belt filter s . 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; howev er the plant has the capability to also send the filtrate to the Unit 2 FGD scrubber system.

 The primary hydrocyclone overflow from the two units are commingled together and transferred to a common secondary hydrocyclone. The underflow from the secondary hydrocyclone is recycled back 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 secondary hydrocyclones . Normal system

flow is at a flow rate of approximately 40 gpm. The design flow rate for the FGD wastewater treatment system is 75 gpm.

 The secondary hydrocyclone overflow is transferred 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 equalization 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 some of the sludge from the downstream primary clarifier which provide seed crystals for gypsum nucleation.

 From reaction tank 1, the wastewater flow s to the primary clarifier. The clarifier contains approximately 2 to 4 feet of settle d solids in the bottom of the clarifier. Pleasant Prairie adds a polymer to the pr imary 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 hydrochloric acid. When the plant 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 hydrochloric acid 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 lower pH. The pH in reaction tank 2 is targeted at 7.0 to 7.2 S.U.

 The wastewater flows next to reaction tank 3, where ferric chloride is added. The wastewater then flows to the flash mix 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 settles the solids creat ed from chemical conditioning steps. The secondary clarifier is an inclined-p late lamella separato r type clarifier. Hydrochloric acid is can be added to the overflow from the secondary clarifier to meet discharge standards for pH. Under normal operation, hydrochloric acid is only added to reaction tank 2.

 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, typi cally cooling tower blowdown, at a ratio of 30:1 to meet the final outfall mercury and chloride limits, 80 ng/L and 1,514 mg/L, respectively.

 The plant stated that when they chlorinate the cooling system, they do not discharge cooling tower blowdown. Because there is no discharge of cooling tower blowdown during chlorination, th e plant does not discharge the treated FGD wastewater because there is not enough other plant wastewaters to Formatted: Indent: Left: 0.5", Hanging: 0.5", Bulleted + Level: 1 + Aligned at: 0" + Tab after: 0.25" + Indent at: 0.25", Tab stops: 1",

List tab + Not at 0.25"commingle with the FGD wastewater to me et 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 needing to go into recirculation 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 draining and flushing the second clarifier, to avoid flocculation build up, which can impact its performance.

 The first FGD scrubber, installed in November 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 was 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 quickly due to the low chlorine content in

the PRB coal.

 When the plant does not blowdown for seve ral weeks, fines and colloidal particles begin to build up in the FGD wastewater treatment system because they are being recirculated throughout the system without 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, therefore, the mercury concentration would continue to rise. To help remove the fines and associated mercury from the wastewater, Pleasant Prairie inst alled a set of cartridge filte rs that can be used as a polishing step. The plant used the cartridge filters to remove the mercury from the FGD wastewater treatment system after the in itial start up phase. The plant is still

able to treat the wastewater through the cartridge filters, but they try not to do this unless necessary because the filters are expensive. Currently the plant can stop discharging for approximately a week before they can notice chlorine concentrations increases. [QUEST ION FOR PLEASANT PRAIRIE: How frequently do the cartridge filters need to be replaced when used?]

 Pleasant Prairie has made a few modifica tions to the FGD wastewater treatment system since the system first began opera ting 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; Comment [dml4]: PGK: The working volume of the two effluent tanks is about 18,000 gallons so the plant can interrupt discharge of treated effluent for about 8 hours before needing to go into recirculation

mode.

Comment [dml5]: Cartridge filters were replaced every 24-36 hours based on flow rate and solids loading. Bypassed a set of sand filters which were located after the secondary clarifiers because of scaling issues; and

 Added the capability to use cartridge filtration to remove colloidal particles from the wastewater after the effluent tanks, which may build up in the system if the plant 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 mercury twice per week, according to their NPDES permit. The plant also collects samples Monday through Friday off the secondary clarifier for confirmation of system performance. The plant uses a Method DMA 80 Hg analyzer 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 exceed 1. 1 2 or 1.3 ppb ;
, the plant will begin discharging from the FGD wastewater treatment system in batches. The

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

 The plant staff has been working to optimize the performance of the system and typically achieves tries to keep the effluent mercury concentrations 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 bitumino us coal. PRB coal produces an FGD

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

 Pleasant Prairie believes that high merc ury levels in the FGD wastewater are a result of the scrubber chemistry and burning PRB coal. Pleasant Prairie stated that

the mercury concentration measured in the effluent from their treatment system is an order of magnitude higher than the effluent from a similar treatment system burning bituminous coal at another of We Energies facility . The average mercury concentration reached after treatment 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 specific configuration did you test at the plant? How long was the system tested at the plant? How quickly did scaling occur?]

 Pleasant Prairie tested GE’s Zeeweed membranes during a 2-3 week period, but not the entire GE Zeeweed microfiltration system . The pilot test involved the use of organosulfide, iron co-precipitation and

microfiltration that

, which also achieved effluent mercury concentrations of 0.1 ppb. [QUESTION FOR PLEASANT PRAIRIE: Please clarify if the plant tested a microfiltration or ultrafiltration system.] The microfiltration

system incorporated a small Zeeweed hollow fiber membrane module that operated at about 1 gpm. The Zeeweed membranes were removed and manually cleaned used air scouring and backwashing to remove scale

from the system several times during the duration of the pilot test . 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 Pleasan t Prairie is about 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 presence of more selenate is due to the scrubber chemistry associated with PRB coal.

Information for Sampling

 EPA identified the FGD wastewater treatment system influent sampling point as the tap off the secondary hydrocyclone. EPA 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 surrounding the secondary hydrcyoclone in order to set up tables and store coolers/supplies. Comment [dml6]: This pilot, described in detail in EPRI report 1020576, used the Memcor hollow

fiber microfiltration with flow inside to outside as a pre-filter to the solids absorption tanks. The system was only tested over a one week period due to significant scaling which developed in less than 24 hours of operation.

Comment [dml7]: No -- The entire Zeeweed system is a microfiltration unit that includes an integrated air scour and chemical cleaning system.

This standard GE Zeeweed unit was not tested because of potential corrosion concerns. We did, however, incorporate a small Zeeweed hollow fiber membrane module (0.1 micron, with flow outside to inside) into a custom built system used in the pilot test described in this paragraph. Reference: EPRI report 1016813. EPA identified the FGD wastewater treatment system effluent sampling point as the tap located after the effluent tank, prior to recirculation or discharge, at the sample panel. Prairie stated that they could 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 training session. In case 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 any 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.comEd MorrisWe Energies262-947-5625ed.morris@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.comFormatted:Font: (Default) Times NewRoman, 12 pt, Not Italic, Font color: Black