Draft Notes from Site Visit to GenOn Energy’s Conemaugh Generating Station on August 23, 2012

EPA conducted a site visit at GenOn Energy Northeast Management Company ’s Conemaugh Generating Station (Conemaugh) located in New Florence, Pennsylvania on Thursday, August 23, 2012 to learn about operations at the plant and discuss recent up g rades to the FGD wastewater treatment system. These notes describe the information collected during the site visit. Table 2 identifies the site visit participants.

Pla nt Overview

• Conemaugh operates two electric generating units, both of which are baseload coal

- fired units. The plant’s net generating capacity is 1,700 MW. The table below contains some general information on the current operation of each steam electric generating unit.

Table 1. Steam Electric Generating Unit Operations

SE Unit Fuel Capacity (MW) Fly Ash Bottom Ash FGD

1 Coal : Bituminous 850 Dry Ash Handling

– Combined Vacuum and Pressure System Wet Sluiced Wet System

2 Coal : Bituminous 850 Dry Ash Handling

– Combined Vacuum and Pressure System Wet Sluiced Wet System

• In January 2012, Conemaugh added an ion exchange system and an anaerobic bioreactor to the existing FGD wastewater treatment system. These systems were added in response to more stringent limits on boron and selenium in their NPDES permit set by the State Commonwealth of Pennsylvania.

• Conemaugh also recently added a clarifier to treat cooling tower blowdown. The clarifier targets removal s of iron, ma g n gan es e ium , and aluminum

.

• The plant is planning to install selective catalytic reduction ( SCR ) systems on Units 1 and 2 over the next two years. The use of the SCR systems will reduce the nitrogen oxide emissions from the plant, but will also oxidize the mercury and result in addi tional mercury remov al from the flue gas in the FGD system.

• Conemaugh is also planning to make upgrades to the FGD systems for both units. The upgrades include adding a tray to each of the absorbers and adding secondary hydro cy clone s to the systems

. Fly Ash Handling

• Units 1 and 2 handle the fly ash collected from the electrostatic precipitators (ESPs) dry using combined vacuum and pressure systems.

• The f ly ash is transferred to two silos for each generating unit (four silos total) . Each set of silos has the capacity to hold 4 to 5 days worth of fly ash.

• Conemaugh unloads fly ash from the silos five days per week using pugmills. Conemaugh use s cooling tower blowdown to moisten the ash in the pugmills prior to load ing it into trucks

.

• Most fly ash is sent to the on

- site landfill with only a small percentage being reused or sold for concrete products, structural fill, or for mining applications.Bottom Ash Handling

• Conemaugh wet sluices pyrites and the bottom ash from Units 1 and 2 to dewatering bins. Overflow from the dewatering bins is transferred to a set of two of three ash settling ponds operated in parallel . The solids from the dewatering bins are sent to the plant’s on

- site landfill. From the ash settling ponds, water is st ored in a recycle basin and is recycle d and reused within the bottom ash sluice system. Solids from these ponds are periodically dredged and transferred to the landfill. Makeup water to the bottom ash handling system includes , but is not limited to, cooling tower blowdown , boiler blowdown, and treated effluent from the landfill leachate and coal pile and yard runoff

.

• After During periods of heavy precipitation, excess water collecting in the ash settling pond is transferred to the desilting pond. Effluent from this desilting pond is used as FGD make

- up or , as FGD reagent and slurry prep aration water , or is discharged from Outfall 004

. Because the bottom ash transport water may be reused in the FGD system, it can eventually be discharged af ter being treated in the FGD wastewater treatment system. Normally, no bottom ash transport water is discharged and the wastewater is completely recycled.

Flue Gas Desulfurization (FGD) System

• Conemaugh is currently operating a limestone forced oxidation FGD system on both Units 1 and 2. The scrubbers achieve a sulfur dioxide ( SO 2 ) removal efficiency of between 97 and 99 percent.

• DBA is currently used as an additive in the FGD system . Conemaugh personnel indicated that it may be possible to discontinue the use of DBA once planned upgrades have been made to the FGD system (i.e., installation of trays) . The plant will evaluate this option once the trays and secondary hydro cy clone s have been installed.

• Conem augh operates the FGD system with a c hloride s concentration of a pproximately 16,000
ppm.

• Blowdown from the FGD system is transferred to the primary hydrocyclones for initial solids separation. Overflow from the hydrocyclones is sent to the lamella clarifie r s for additional solids separation before reuse in the absorbers or being sent to the FGD wastewater treatment system.

• Underflow from both the primary hydrocyclone s and the lamella clarifier s is sent to the vacuum belt filter. The solid gypsum from the filter is currently landfilled or used as byproduct in wallboard . The filtrate from the vacuum belt filt er is recycled back to the lamella clarifier.

• Overflow from the lamella clarifier has a typical solids concentration of 100 ,000 to 200 ,000 ppm ( 0.00 1 t o 0.00 2 percent solids) . This wastewater is sent to the FGD wastewater treatment system.

• Conemaugh has not done any manipulation of oxidation reduction potential (ORP) within the scrubber to determine what its e ffects are on FGD wastewater composition.

• Co nemaugh personnel stated that they do not expect to see any significant increase in the mercury concentration in the FGD scrubber purge after the installation of the SCR systems because they expect that the additional mercury removed in the scrubber will partition to the gypsum solids.

• With the addition of the secondary hydrocyclone s, the overflow from the primary hydrocyclones will be transferred to the secondary hydrocyclones instead of the lamella clarifier s . The overflow from the secondary hydrocyclone s will be transferred to the lamella clarifier and recycled to the scrubber to conveyed to the FGD WWTP . The underflow from both the secondary hydrocyclone s will be recycled back to absorber.

FGD Wastewater Treatment System• Conemaugh completed the upgrade of the FGD wastewater treatment system in January 2012. The upgrades were in response to a 2004 consent order and agreement, as amended in 2010 decree between the Conemaugh Generating Station and Pennsylvania Department of Environmental Protection requiring compliance with more stringent selenium, boron, manganese

, and iron limitations by February 1, 2012. A block flow diagram of the new FGD wastewater treatment system is included as Attachment 1.

• As discussed previously, C onemaugh recently added an ion exchange system to target boron removal

, and an anaerobic biological reactor system to target selenium removal , and a more automated pH adjustment system to target manganese

. Both These systems were added to the plant’s existing FGD wastewater system which included primary and secondary clarification and a set of aerobic sequencing batch reactors (SBR).

• Overflow from the plant’s lamella clarifier is sent to the FGD surge tank, which is the beginning of the FG D wastewater treatment system.

• From the surge tank the wastewater is sent to the industrial wastewater treatment (IWT) portion of the system . The IWT system contains two pH adjustment sump s operated in series; however, Conemaugh only adds lime to the prim ary pH adjustment sump. Conemaugh add s lime to adjust the pH to approximately 9.3 S.U. to target boron and manganese removal. The wastewater flows through the secondary sump and is then transferred to two primary clarifi ers operated in parallel.

• Cone maugh injects ferric chloride and trimercapto

- s

- triazine (TMT) into the wastewater upstream of the clarifiers. Conemaugh also adds a polymer directly to the clarifiers. Underflow from primary clarifiers is sent to a thickener and then to filter presses fo r dewatering. The solids are landfilled and the filtrate from the filter press is recycled back to the pH adjustment sump.

• The overflow from the clarifiers is sent to the boron pH adjustment tank where the plant adds hyrdrochloric acid to lower the pH to approximately 8 S.U. in preparation for the boron ion exchange system.

• After adjust ing the pH

, Conemaugh transfers the wastewater to the boron equalization tank, which feeds the ion exchange system. T he ion exchange system consists of two parallel train s , each capable of handling 75 percent of the flow. First, the wastewater is split and pumped through the two pressure sand filter s operating in parallel. The wastewater is then sent through the ion exchange resin vessels. Each train contains two vessels. As designed the vessels operate in series, except when one of the vessels is being regenerated , which was designed to occur every six hours . However, because of scaling issues, Conemaugh has needed to operate the system such that one of the vessel s in eac h train is always being regenerated

. As the regeneration of one vessel is complete, the other vessel begins its regeneration process. Conemaugh is evaluating alternatives to minimize scaling issues within the resin and resin regeneration treatment system

.

• Conemaugh uses sulfuric acid and caustic soda washes to regenerate the resins. The waste from the regeneration process is transferred to a boron regeneration waste tank and then fed to the boron precipitation tank where the plant adds ferric chloride and lime. The plant then feeds the water to a clarifier where a polymer is added. The underflow from the clarifiers is pumped to a storage tank and then to filter presses. The filter cake is landfilled and the filtrate is transferred to the filtrate sump an d recycled to the boron regeneration waste tank or to the IWT for reprocessing

. The overflow from the clarifier is sent to the IWT for reprocessing or to a continuous backwash sand gravity filter and /or then to the boron effluent tank where it is commingle d with the effluent from the ion exchange vessels. The backwash from the gravity filters is transferred to the filtrate sump and then to the IWT for reprocessing

.

• As part of the ion exchange system, Conemaugh added several in

- line boron analyzers to more closely monitor when the resin s need to be regenerat ed

. The performance of the in

- line boron analyzers continue to be optimized.

• Conemaugh personnel reported seeing a roughly 85 5 0 % reduction in boron concentrations across the ion exchange system. Co nemaugh has measured boron concentrations between 400 and 500 Formatted: Font: (Default) Times New Roman600 ppm in the purge stream and concentrations of 2 0 to 75 90 ppm in the wastewater transferred to the anaerobic reactor system, with a roughly 30% 45% removal coming reduction in boron concentrations across from the primary clarifier s

.

• From the ion exchange system, wastewater is transferred directly into the anaerobic reactor with phosphoric acid, micro

- nutrients, a sugar solution, and a urea solution added inline prior to entering the r eactor. Wastewater goes through a series of two reactors before a clarification and filtration step used to remove recover and return the bio solids to the reactors . The wastewater is then transferred to the aerobic SBR feed tank while the excess biosolids liquid sludge is are hauled offsite for disposal.

• The anaerobic reactors utilize a slow mix to keep the mix the biological material suspended in

with the wastewater but not create an aerobic environment

.

• The anaerobic biological reactor system doe s not include a heat exchanger to cool wastewater before entering the reactor. Conemaugh personnel indicated that the retention time in the system allows for sufficient heat loss before the wastewater reaches the anaerobic reactor system. The system is i nsulated for cold weather.

• With the addition of the anaerobic reactors targeting selenium removal, Conemaugh has achieved selenium concentrations of approximately 150 ppb and lower in the final effluent. This is below the plant’s NPDES permit limit on sel enium, which is 250 ppb.

• Conemaugh has seen the best selenium removals while maintaining the ORP of the anaerobic biological reactor system between

- 250 and

- 350 mV.

• Conemaugh worked with Infilco Degremont on the design of the upgrades to the FGD wastewate r system, including the ion exchange system and anaerobic reactor system. The system is guaranteed to achieve effluent concentrations that are approximately 20 15 percent less than the permit limits required by the State Commonwealth of Pennsylvania. The FGD wastewater system is designed to achieve a boron concentration of 80 83 ppm and a selenium concentration of ?? 210 ppb. [ QUESTION TO CONEMAUGH: Please provide the design concentration for selenium guaranteed by Infilco.]

• The anae robic biological reactor system took approximately six months to start

- up and reach equilibrium. During this period no plant wide shutdown was required. Conemaugh was able to by

- pass modulate flow s to acclimatize individual reactors as they were initially brought online.

• Based on information from the Infilco Degremont, during a period of plant shutdown the anaerobic biological reactor system would only need to be fed nutrients. No wastewater recirculation would n eed to take place. The biomass would go dormant and a specific start

- up process would need to be followed to bring the biomass back to its active state.

• A permit is required in order to dispose of the anaerobic reactor sludge in the on

- site landfill.

• From the anaerobic biological reactors, the wastewater is transferred to a clarifier where ferric chloride and polymer are added. The majority of the underflow is recycled back to the first anaerobic biological reactor, while a small percentage is sent to the selenium waste tank and disposed of as a liquid sludge . Conemaugh needs to modify their a permit to dewater and dispose of this waste in its landfill, so currently the waste is sent off site as a liquid until they can ge receive t the permit modification to send it to the landfill.

• The overflow from the clarifier is transferred to a continuous backwash sand gravity filter. The backwash from the filter is also recycled to the first anaerobic biological reactor. The effluent from the gravity filter is transfer red to the a former pH adjustment sump, which acts as the sequencing batch reactor (SBR) feed tank and no longer receives any chemicals for pH adjustment.

• Wastewater from the SBR feed tank is sent to the SBR reactor tanks. With the addition of the ion exchange system and anaerobic reactors, the SBR reactors are currently used as an aeration and polishing step prior to discharge.• The plant adds urea and phosphoric acid to the SBRs. The SBRs reduce the BOD and iron present in the wastewater.

• The SBRs do not have an anaerobic stage and therefore, do not achieve denitrification of the wastewater after the nitrification of the wastewater is achieved through the aeration of the
wastewater

.

• The solids collected in the SBRs are transferred to a thickener and a portion is recycled to the SBR feed tank while the remainder is transferred to the landfill for dewatering and disposal. The effluent from the SBRs is sent to a clearwell and then sent through two of three pressure sand filters operated in parallel. The backwash from the pressure filters is recycled to the SBR feed tank while the effluent from the pressure filters is commingled with several other was te streams and discharged to the Conemaugh River via Outfall 007

.

• The entire treatment system has a residence time of roughly 3 to 4 days, with each biological reactor having a residence time between 6 and 9 hours.

• Prior to installing both the ion exchan ge system and anaerobic biological reactor system

, Conemaugh evaluated several alternatives to each system. A magnesium hydroxide process and zero liquid discharge systems were evaluated as possible alternatives to the ion exchange system. The magnesium h ydroxide process did not achieve comparable boron removal while the zero liquid discharge system was prohibitively expensive. A two

- stage chemical precipitation system and a GE ABMet system were evaluated as alternatives to the anaerobic biological reacto r system, with the ABMet system also being piloted at the plant. The chemical precipitation system alone was not able to achieve the required effluent concentrations. While the ABMet system use s similar chemistry to the anaerobic biological reactor system installed

, Conemaugh stated that they were concern ed about potential scaling and plugging of the activated carbon media in the ABMet system

.

• A pilot

- scale anaerobic biological reactor system was operate d at Conemaugh in 2009 prior to treatment system upgrades. Plant representatives stated that they observed similar removals and performance in the full

- scale system with what was demonstrated in the pilot

- scale system.

Landfills and Leachate Treatment Sys tems

• Conemaugh operates one landfill including an active landfill (Stage II) and one retired landfill (Stage I) . The plant also has plans to expand the existing for a future landfill (Stage III)

.

• The currently active landfill receives bottom ash, fly ash, calcium sulfate (gypsum), and other plant solid wastes. Th is e Stage II landfill is lined and leachate is collected and commingled with coal pile runoff, stormwater from the landfill and station , and leachate from the retired landfill

. This commingled was tewater is collected in a lined pond and transferred to a leachate treatment system.

• The combined wastewater in the leachate collection pond is generally very acidic with a pH between 2 and 3 S.U. From the pond, the wastewater is transferred to a reacto r where lime is added to bring the pH up to between 4 and 4.5 S.U . The wastewater is then sent to a second reactor where more lime is added to raise the pH to between 8 and 9 S.U . The effluent is then sent to a high density solids clarifier. Solids from the clarifier are pumped into a portion of the leachate collection pond where they can dewater prior to being trucked to the plant’s on

- site landfill. Overflow from the clarifier is reused within the plant in the FGD system and as bottom ash sluice make

- up water.

• Conemaugh is not currently adding new solids to the retired landfill but this landfill does hold fly ash, bottom ash, and calcium sulfate (gypsum) coal refuse waste. Leachate collected from the retired landfill is combined with leachate from the active landfill and treated in the plant’s leachate treatment system. Comment [FS1]: Note that the SBRs undergo settling and decant steps where the DO decreases. We have not evaluated whether this could provide for denitrification.• Plant representatives indicated that plans are in place to expand the current landfill. This expansion is not expected to open until 2016 and is known as ‘Stage 3’ III’ . This landfill will receive the same type of waste that is currently held in the active Stage II of the landfill, fly ash, bottom ash, calcium sulfate (gypsum), and other plant wastes.

### Table 2 . Site Visit Attendees

Name Organization (Representing) Telephone E

- mail

Steve Frank GenOn

- Canonsburg, PA (724) 597

- 8310 Stephen.frank@genon.com

Keith Schmidt GenOn

- Canonsburg, PA (724) 597

- 8193 Keith.schmidt@genon.com

Jim Brunson GenOn

- Conemaugh (724) 235

- 4596 James.brunson@genon.com

John Balog GenOn

- Conemaugh (724) 255

- 3352 John.ba y log@ ganon genon .com
Tony Garaventa GenOn

- Conemaugh (724) 235

- 4597 Anthony.garaventa@ ganon genon .com
Shelley Wjciechowski GenOn

- Conemaugh (724) 235

- 4465 Shelley.wojciechowski@genon.com

Dave Benson Keystone

- Conemaugh Projects (724) 357

- 1727 dbenson@kcpo.com

David Read GenOn (724) 354

- 5470 David.read@ ganon genon .com

Donna Hill Southern Company (205) 257

- 5234 dbhill@southernco.com

Ron Jordan EPA/Office of Water (202) 566

- 1003 Jordan.ronald@epa.gov

Cuc Schroeder EPA/Office of Water (202) 566

- 2397 Schroeder.cuc@epa.gov

James Covington EPA/Office of Water (202) 566

- 1034 Covington.james@epa.gov

T.J. Finseth ERG (Contractor to EPA) (703) 633

- 1698 Thomas.finseth@erg.com

Danielle Lewis ERG (Contractor to EPA) (703) 633

- 1703 Danielle.lewis@erg.com Field Code Changed

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