Final Notes from Site Visit at We Energies ’ Pleasant Prairie Power Plant

on March 2 , 2010

EPA conducted a site visit at We Energies ’ Pleasant Prairie Power Plant (Pleasant Prairie) located in Pleasant Prairie, WI on Tuesday

, March 2 , 2010 to learn about the operations at the plant , specifically the flue gas desulfurization (FGD) wastewater treatment system

. These notes describe the information collected during the site visit. Table 1 , located at the end of th ese
notes , identifies the site visit participants. A n 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 generating 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 ret rofitted 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 Prairie also installed a n 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. The FGD scrubber system and SCR system for Unit 1 were installed and placed into service 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 electrostatic precipitators (ESPs) on both Units 1 and 2. The ESPs remove approximately 99.7 % 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

. The bromide injection system has been achieving 60

- 70 % mercury removal, or better. 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 FG D system. 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 mercury removal (adsorbed to the fly ash) in the precipitators has also been observed

.

**•** Pleasant Prairie burns Powder River Basin (PRB) coal in both u nits. The plant burns approximately 5.5 million tons of coal per year.Pa ge 2

**•** Pleasant Prairie is located about 5 miles from Lake Michigan. The plant discharges to Lake Michigan.

**•** During the sit e visit, Unit 1 was in a scheduled maintenance outage. During this outage, the air heater baskets were serviced a nd 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 flue gas from either Unit 2 or Unit 1 t o 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

. The carbon capture pilot was initially set up to obtain flue gas
from only Unit 2. A back up connection was later added to allow the c arbon capture pilot to remain in service when Unit 2 was shut down for its annual scheduled maintenance outage, or was off line due to a forced outage.

**•** P lant personnel stated that the carbon capture system was successful in removing up to 90 % of the carb on dioxide from the flue gas. Following capture the carbon dioxide was routed to the flue gas and emitted to the stack. This project evaluated carbon dioxide capture, and did not involve an evaluation of the potential to store
carbon dioxide below the pla nt.

**•** Plant personnel stated that the lesson s 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 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 ammoni a ; 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
Beaver Oil Company in Illinois. Beaver Oil Company received the dilute
ammonium sulfate w aste stream from Alstom Power's Chilled Ammonia Carbon Capture Pilot at Pleasant Prairie , 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 batc h treatment tanks.

**•** 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

c haracterizing the waste stream; however, the plant believes that EPRI should
have characterization data

. Pleasant Prairie stated that they do not know if thePa ge 3

characterization data will be included in the final report prepared for the study.
The letter tha t was submitted by Pleasant Prairie to the D epartment of N atural
R esources (DNR) characterizing the waste stream and the DNR ’s response to this letter are provided in Attachment 3

.

**•** 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 scr ubber 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 du a l flow tray.

**•** The plant does not add any organic acids to the scrubber ( e.g. , dibasic acid ( DBA ) ) because the plant’s FGD wastewa ter treatment system does not have the capability to remove the BOD from the system. Pleasant Prairie stated that if they did add organic acids they would have to send the wastewater to a publicly owned treatment works ( POTW ) for treatment

.

**•** The plant has experienced some problems with foaming in the absorber ; therefore, they have been adding a silicone

- based antifoam ant to control this issue. The plant adds between 10 and 20 gallons of the antifoama nt per day

.

**•** The plant uses a limestone slurry as the sorb ent for sulfur dioxide (SO 2 ) absorption. The two scrubber systems share two ball mill s where the limestone is ground and mixed with water to 4 0 to 50 % solids by weight. The plant uses hydro cy clones to classify the limestone and ensure the correct size part icles are
used in the FGD scrubber system.

**•** Pleasant Prairie maintains the solids concentration in the FGD scrubber systems between 1 8 and 2 1 % solids. When the solids concentration exceeds 18 % , the plant blows down from the FGD scrubber . Plant personnel es timated that each
unit blows down for abou t 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.Pa ge 4

**•** Plant staff indicated that the chloride concentration 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 hydroc yc lone. Each FGD scrubber system has a dedicated hydro cy clone. The underflow from the primary hydro cy clones, which is 50 % solids, is transferred t o the vacuum belt filters where the plant washes the gypsum to lower the chlorides concentration in the gypsum. Each primary hydro cy clone feeds either of the two

common vacuum belt filter s

. The vacuum belt filter s dr y the gypsum to less than
10 % 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 hydro cy clone overflow from the two units are commingled together
and transferred to a common secondary hydro cy clone. The underflow from the secondary hydro cy clone is recycled back to the FGD scrubber systems. The
overflow from the second hydrocyclone is transferred to the FGD wastewater treatment sys tem

.

FGD Wastewater Treatment System

**•** The FGD wastewater treatment system is designed to receive intermittent discharges of FGD wastewater from the secondary hydrocyclone s . Normal system
flow is approximately 40 gpm. T he design flow rate for the FGD wast ewater 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

.

**•** Th e wastewater flow s from the equalization tank to reaction tank 1, where hydrated lime is added to ra ise 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, t he wastewater flows to the primary clarifier. The clarifier contains approximately 2 to 4 feet of settled solids in the bottom of the clarifier. Pleasant Prairie adds a polymer to the primary cl arifier to aid the settling of the
solids.Pa ge 5

**•** 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 org anosulfide. 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. Pleasant Prairie also began ad ding hydrochloric acid to reaction tank 2, which wasn’t in the 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 wher e a gentler mixing takes place.

**•** The wastewater from the flocculation then flows to the secondary clarifier. The secondary clarifier settles the solids created from chemical conditioning steps

. The secondary clarifier is an inclined

- plate lamella separator type clarifier. Hydrochloric acid 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 two effluent tank s prior to discharging to Lake Michigan.

**•** Pleasant Prairie commingles the effluent from the FGD wastewater treatment system with other plant wastewaters, typically 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 chlorinat e the cooling system , the y do not discharge cooling tower blowdown. Because the re is no discharge of cooling tower blowdown during chlorination, the plant does not discharge the treated
FGD wastewater because there is not enough other plant wastewaters to commingle with the FGD wastewater to meet the final outfall mercury limit. The treated wastewater is held in the effluent tank during chlorination until
d ischarged

. The working volume of the two treated 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.

**•** The FGD wastewater treatment system typically operates Monday through Saturday. The plant performs w eekly maintenance o n the system starting Saturday evening. This maintenance includes draining and flushing the second clarifier, to avoid flocculation build up , which can impact its performance

.Pa ge 6

**•** The fi rst 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 l ow chlorine content in
the PRB coal.

**•** When t he plant does not blowdown for several 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

, 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 system after the initial start up phase

. The filters were replaced every 24

- 36 hours depending on flow rate and solids loading. T he plant
is still able to treat the wastewater through the cartridge fil ters , 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.

**•** Pleasant Prairie has made a few modificatio ns to the FGD wastewater treatment system since the system first began operating 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 sy stem 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 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 week s; however the cartridge filtration is not used regularly.Pa ge 7

Wastewater Treatment System Performance

**•** Pleasant Prairie is required to sample mercury twice per week , according to their NPDES permit. The plant also collects samples M onday through Friday off the
second ary 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 sample s analyzed using
Method 1631E resulted in m ercury concentrations of 0.22 to 0.25 ppb, and the
DMA 80 result ed in mercury concentration s of 0.35 to 0.4 ppb.

**•** When mercury concentrations exceed 1. 1 ppb

, the plant will begin discharging
from the FGD wastewater treatment system in batches. The wastewat er 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 ensure it is below the permit limit of 1.5 ppb. Once the mercury concentration is confirmed, the plant discharge s the

wast ewater from the effluent tank

.

**•** The plant staff has been working to optimize the performance of the system and typically achieves mercury concentrations below 0 .4 ppb. The wastewater

treatment system is currently achieving the lowest mercury concentration s 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 mercury levels in the FGD wastewater are a
result of the scrubber chemistry and bur ning PRB coal. Pleasant Prairie stated that
the mercury concentration measured in the effluent fro m 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

- 0.0 4 ppb; some even reaching 14 ppt.

**•** Pleasant Prairie has performed pilot test s 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 effluent as the basis for the study. The pilot tests included the following :

**•** Pleasant Prairie tested Siemens’ Memcor ® hollow fiber microfiltration system . The system achieved effluent mer cury concentrations of 0.1 ppb

. The system was only tested over a one week period because it experienced significant scaling issues which started to develop within less than 24Pa ge 8

hours of operation

. This pilot study is described in detail in EPRI report
102 057 6.

**•** Pleasant Prairie tested GE’s Zeeweed membranes during a 2

- 3 week period, but not the entire GE Zeeweed microfiltration system

. The entire Zeeweed system is a microfiltration unit that includes an integrated air scour and chemical cleaning system. T his standard GE Zeeweed unit was not tested because of potential corrosion concerns. The pilot test involved
the use of o rganosulfide, iron co

- precipitation

, and microfiltration that
achieved effluent mercury concentrations of 0.1 ppb. The microfiltration system incorporated a small Zeeweed hollow fiber membrane module (0.1 micron) that operated at about 1 gpm. The Zeeweed membranes were removed and manually cleaned to remove scale several times during the duration of the pilot test . Pleasant Prairie state d tha t the system performed
well and appeared to be more promising than the Memcor ® system. However, t he plant stated that they would want the system to be tested on a larger scale before they would purchase the system. More information about this study can be found in EPRI report 1016813.

**•** Pleasant Prairie also tested an absorpti ve media system and an iron cementation system.

**•** Selenium levels are also higher in PRB coal than bituminous coal. Total selenium
in the influent FGD wastewater at Pleasant 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 s olubility) 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 hydro cy clone. EPA would use this sample to represent the influent to the FGD wastewater treatment 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 hydr cy oclone in order to set up tables and store coolers/supplies.

**•** EPA identified the FGD wastewater treatment system effluent sampling point as the tap located after the effluent tank, prior to recirc ulation 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.Pa ge 9

**•** 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 sampl ing 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.Page 10

Table 1

. Site Visit Attendees

Name Organization (Representing) Telephone E

- mail

Elizabeth Hellman We Energies 414

- 221

- 3235 elizabeth.hellman@we

- energies.com

Pete Kutzora We Energies 414

- 221

- 3926 pete.kutzora@we

- energies.com

David Lee We Energies 414

- 221

- 2158 david.lee@we

- energies.com

Ed Morris We Energies 262

- 947

- 5625 ed.morris@we

- energies.com

Donna Hill Southern Company/UWAG 205

- 587

- 4846 dbhill@southernco.com

Jezebele Alicea US EPA 202

- 566

- 1755 alicea.jezebele@epa.gov

Ron Jordan US EPA 202

- 566

- 1003 jordan.ronald@epa.gov

TJ Finseth ERG 703

- 633

- 1698 thomas.finseth@erg.com

Elizabeth Sabol ERG 703

- 633

- 1659 elizabeth.sabol@erg.com