Final Notes from Site Visit at RRI Energy’s Keystone Generating Station

on February 1, 2010

EPA conducted a site visit at RRI Energy’s Keystone Generating Station (Keystone) located in 

Shelocta, PA on February 1, 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 2, located at the end of these notes, identifies the site visit 

participants. The presentation that the RRI Energy personnel gave during the site visit is

provided as Attachment 1 to these notes. Additionally, an overall water balance diagram for the 

plant (Attachment 2), a process flow diagram for the FGD system (Attachment 3), process flow 

diagrams for the FGD wastewater treatment system (Attachment 4), the design engineer’s report

for the FGD wastewater treatment system (Attachment 5), and an excerpt from the plant’s permit 

providing the internal outfall and final outfall limitations for the FGD wastewater treatment 

system (Attachment 6) are provided as attachments to the site visit notes. 

Plant Overview

• Keystone operates two coal-fired generating units at the power plant. Units 1 and 

2, which began operation in 1967 and 1968, respectively, each have a gross 

generating capacity of 900 megawatts (MW). The total net generating capacity 

for the plant is of 1,700 MW. Both generating units are operated as baseload 

units. The table below contains some general information for the two generating 

units.

Table 1: Plant Summary

Unit

Installation 

Date

Gross 

Capacity 

(MW)

Particulate 

Control NOx Control SO2 Control

1 1967 900 Electrostatic 

Precipitator 

(ESP) 

(cold-side)

Low NOx Burners 

(1994), Selective 

Catalytic Reduction 

(SCR) (2003)

Wet FGD installed 

in September 2009

2 1968 900 ESP (coldside)Low NOx Burners 

(1995), SCR (2003)

Wet FGD installed 

in November 2009

• Keystone recently retrofitted the two units with FGD scrubber systems to control 

the sulfur dioxide (SO2) releases from the plant. The FGD systems were installed 

in September 2009 (Unit 1) and November 2009 (Unit 2). The wet FGD 

scrubbers are designed to achieve greater than 98 percent removal of SO2 from 

the flue gas; however, the actual SO2 removal achieved by the scrubbers is 75 

percent when using two spray levels. With the recent addition of the FGD 

scrubber system, Keystone also installed an FGD wastewater treatment system to 

control the discharges of the wastewater generated during the operation of the 

FGD scrubbers.
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• Keystone operates electrostatic precipitator (ESPs) to control fly ash and 

particulate emissions from the plant. Keystone also operates selective catalytic 

reduction (SCR) systems to control nitrogen oxide (NOx) emissions from the 

plant. In January 2009, the plant began operating the SCRs year round. 

Additionally, the boilers are operated with low-NOx burners.

• Plum Creek and Crooked Creek supply the plant with water.

• Coal arrives by train and truck. Keystone burns only eastern bituminous coal

(mostly from Pennsylvania). Around five million tons of coal is burned per year. 

The plant receives coal from several dozen sources. The coal has a sulfur content 

of 1.2 to 2.2 pounds of sulfur per million BTU. Keystone states that the coal 

content varies greatly with the supplier. Over the last couple of months the sulfur 

content has been 1.5 to 1.7 pounds of sulfur per million BTU. Keystone’s five 

year business plan is to buy the cheapest coal as long as the sulfur content is less 

than 2 to 2.25 pounds per million BTU.

• When necessary (not routinely), Keystone takes feeder samples of coal and tests 

for BTU, chloride, sulfur, ash content, moisture, carbon, hydrogen, and nitrogen. 

Keystone does not test for metals unless there is a specific reason to do so. 

• Keystone has no plans to install activated carbon technologies or any other flue 

gas mercury controls. However, the plant has done some testing on mercury 

control systems for both units. 

• The plant has no sulfur trioxide controls except for the benefits from the FGD 

system.

• Keystone operates dry fly ash handling systems. The fly ash handling systems 

were installed when the plant began initial operation. The dry fly ash is 

transported to silos pneumatically. After the silos, it is conditioned and 

transported to the on-site ash site. Keystone is looking to sell fly ash for 

beneficial reuse, but has no current contracts. Keystone stated that they are 

having difficulty marketing the fly ash due to the plant location.

• Keystone operates wet bottom ash handling systems. The plant sluices the bottom

ash to hydrobins. The dewatered bottom ash is transported to the ash site. The 

hydrobin overflow is transported to the ash settling ponds. The plant operates

three ash settling ponds; each is about half an acre. From the ash settling ponds, 

the wastewater travels to a thermal cooling pond, which covers approximately

seven acres. The ash wastewater is then transferred through the lagoon and 

finally discharges to Crooked Creek.

• Keystone combines fly ash and bottom ash at the ash site (i.e., landfill). The 

landfill is lined and has a leachate collection system. The leachate collection 
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system produces a continuous waste stream. The flow of the east valley landfill

leachate is 100 gpm. The flow of the west valley landfill leachate is 42 gpm (in 

2010). 

• The Keystone plant is located on approximately 1,000 acres in Armstrong 

County, Pennsylvania. Keystone has approximately 200 employees. 

Main Plant Wastewater Treatment System

• Keystone operates a main plant wastewater treatment system that treats leachate 

from the ash site, contact storm water, coal pile runoff, bottom ash sluice water, 

wastewater from the sewage treatment plant, and plant drain wastewater. 

• The treatment system consists of conventional pH neutralization, flocculation, 

clarification, and/or extended aeration.

• The effluent from the treatment system is discharged to Crooked Creek via outfall 

003. 

Flue Gas Desulfurization System

• The plant operates two forced oxidation wet FGD systems (one per unit). Each 

FGD absorber has five spray levels with a dual flow tray system and a two stage 

mist eliminator. 

• Keystone uses a limestone slurry as the sorbent for the sulfur dioxide absorption. 

The limestone is delivered to the plant via truck and rail. Keystone uses ball mills 

onsite to pulverize the limestone. From the ball mills, the slurry is transferred to 

hydrocyclones to collect limestone particles that are too large for use in the FGD 

system. The underflow from the hydrocyclones is returned to the ball mill for 

additional processing. The overflow from the hydrocyclones, which is 

approximately 25 to 30 percent limestone, is transferred to a storage tank prior to 

being fed to the FGD system.

• The fresh limestone slurry is fed to the reaction tank of the FGD system and the 

recycle pumps pump the slurry to the various levels of the FGD absorber. Both 

absorbers have five spray levels. The slurry is pressurized and sprayed downward 

into the absorber through spray nozzles. As the slurry falls downward and the 

flue gas flows counter-current to the slurry, the spray droplets of the limestone 

slurry contact the flue gas and absorb the sulfur dioxide, which reacts with the 

limestone particles and produces calcium sulfite. Additionally, the dual flow tray 

generates a layer of sorbent slurry in the absorber that the flue gas must pass 

through, which provides additional contact time for the reactions to occur. The 

sorbent slurry passes through the tray and flows downward in the absorber until it 

reaches the reaction tank. Keystone bubbles air through the reaction tank to 

oxidize the calcium sulfite to calcium sulfate (i.e., gypsum).
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• Keystone does not use and does not have the capability to add any additives in the 

FGD system. 

• Keystone intermittently blows down the gypsum slurry from the reaction tank to 

control the chlorides concentration in the absorbers. The chlorides concentration 

in the absorbers is maintained between 18,000 and 20,000 ppm, with a design 

maximum chlorides concentration of 25,000 ppm. The typical percent solids 

within the absorber is 40 to 60 percent.

• Keystone transfers the blowdown from the absorber to the gypsum dewatering 

operations. The blowdown is first transferred to the primary hydrocyclones where

the solid gypsum is separated from the water by centrifugal force. The solid 

gypsum is forced outward to the walls of the hydrocyclones and falls downward, 

while the water exits the top of the hydrocyclones. The gypsum from the primary 

hydrocyclones is transferred to the filter feed tank, which is then transferred to the 

vacuum belt filters. Keystone washes the gypsum with service water as it is 

applied to the vacuum belt filter to reduce the chlorides in the gypsum. The 

filtrate from the vacuum belt filter is transferred to the purge tank and then 

transferred to the FGD wastewater treatment system.

• Keystone generates around 2,000 tons of gypsum a day. The gypsum that is 

generated contains less than 120 ppm of chlorides and less than 10 percent 

moisture. Keystone is attempting to market the gypsum; however, they do not 

have any current contracts to sell the gypsum. Therefore, the plant is transferring 

all the gypsum to the on-site ash site for disposal. According to plant personnel, if

100% of the gypsum was placed in the landfill, the expected life of Stages III and 

IV of the landfill would be 2015 and 2028, respectively. If, however, none of the 

gypsum produced is placed in the landfill, then the expected life of Stages III and 

IV of the landfill would be 2020 and 2046, respectively.

• Keystone monitors the solids level and chlorides level in the primary

hydrocyclone overflow because if the chloride or solids level is low, the plant 

sends the overflow back to the absorber. The primary hydrocyclone overflow is 

transferred back to the absorber when the concentration of chlorides is measured 

at 14,000 mg/L or the concentration of solids is 18 percent. Otherwise, the 

primary hydrocyclone overflow is transferred to the secondary hydrocyclone feed 

tank and then pumped to the secondary hydrocyclones.

• The underflow from the secondary hydrocyclones is returned to the absorber. The 

overflow from the secondary hydrocyclones is transferred to a purge tank, which 

also receives the filtrate from the vacuum belt filter. The wastewater in the purge 

tank is intermittently transferred to the FGD wastewater treatment system. 
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FGD Wastewater Treatment System

• A block flow diagram and more detailed process flow diagrams of the FGD 

wastewater treatment system are provided as Attachment 4 to these notes. 

• The wastewater from the purge tank, which includes both secondary 

hydrocyclone overflow and filtrate from the vacuum belt filters, is transferred to 

the equalization tank of the FGD wastewater treatment system. The equalization 

tank also receives the filter press filtrate, gravity filter backwash, polishing filter 

backwash, and off-specification recycle. The FGD wastewater treatment system

only treats wastewater from the FGD process. It was designed by Siemens and 

consists of gypsum desupersaturation, metal sequestration, clarification, pH 

adjustment, and filtration.

• The plant began sending wastewater to the FGD wastewater treatment system in 

September 2009, which was three to four weeks after the first FGD system began 

operation. At the time of the site visit, the plant was still in the process of 

optimizing the system.

• The flow rate through the wastewater treatment system depends on the amount of 

wastewater recirculated through the system. The average 24-hour flow rate is 

approximately 260 gpm. Keystone personnel attempt to keep the flow through 

the system constant by staggering the blowdown from the scrubbers. However, 

the flow can range from 400-450 gpm if both scrubbers are blowing down to zero 

gpm if neither is operating. The design flow rate for the treatment system is 450 

gpm.

• Overflow from the secondary hydrocyclones enters into the wastewater treatment 

system and is first sent to the equalization tank. This overflow has a solids level 

of around 2 percent. There is a sample point immediately upstream of the 

equalization tank. The equalization tank also receives water from the filtrate 

sump and effluent from the FGD wastewater treatment system, which the plant 

recirculates to maintain a steady flow of wastewater through the system.

• The wastewater then flows into the desaturation tank where the pH is adjusted

from 6.0-7.0 to 8.0-8.5 with the addition of a lime slurry. The plant receives dry 

lime and slakes the lime on site, to generate 10% of lime slurry. The plant adds 

lime to the desaturation tank to form metal hydroxides, which precipitate out of 

solution. The pH is optimal at this range because a higher pH would cause 

magnesium hydroxide to precipitate. 

• After the desaturation tank, the wastewater flows by gravity into the heavy metals 

reaction tank where Keystone adds organosulfide (TMT-15) to the wastewater. 

The organosulfide is added to precipitate residual metals as sulfide complexes.
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• From the heavy metals reaction tank, the wastewater flows to the flow splitter 

tank where Keystone adds ferric chloride to the wastewater. The ferric chloride is 

used to assist in the coagulation of the solids precipitated in the desaturation tank 

and the heavy metals reaction tank.

• After the flow splitter tank, the wastewater is directed to two clarifiers, and the 

plant adds polymer to the wastewater as it flows to the clarifier. The wastewater 

is divided equally between the two clarifiers. The clarifiers are solids contact 

clarifiers that contain a sludge bed that attracts the solids in the wastewater. A 

portion of the sludge from the clarifiers is recycled to the desaturation tank, while 

the majority is transferred to a sludge tank and then pumped to a filter press for 

dewatering. The dewatered sludge is sent to the ash site. The filtrate from the 

filter press is transferred to the filtrate sump. Wastewater in the filtrate sump is

returned to the equalization tank.

• The overflow from the clarifiers flow by gravity to the heat exchanger feed tank. 

The plant operates two heat exchangers in parallel. Before the wastewater goes 

through the heat exchangers, Keystone adds hydrochloric acid and antiscalant to 

the wastewater. The heat exchangers lower the temperature of the wastewater 

from 110°F to 85°F. Keystone uses cooling water in the heat exchanger. 

According to plant personnel, the wastewater cooling is necessary to control scale 

formation in the 16-mile discharge pipeline.

• From the heat exchangers, the wastewater is transferred to three continuous 

backwash gravity filters, using sand as the filter media, operating in parallel. The 

gravity filters main purpose is to reduce the level of total suspended solids (TSS)

in the wastewater. The backwash from the gravity filters is transferred to the 

filtrate sump, which is eventually returned to the equalization tank.

• After the sand filters, the wastewater flows by gravity to the effluent tank.

• After the effluent tank, the wastewater flows through the polishing filters. Even 

though the FGD wastewater treatment system was originally designed so that the 

polishing filters could be bypassed, Keystone plans to use the polishing filters full 

time. Keystone states that the polishing filters and gravity filters are necessary to 

keep the TSS level below the limit. (The permit authority lowered Keystone’s 

limit on TSS in exchange for allowing the plant to discharge a higher 

concentration of selenium.)

• Keystone has a composite sampler after the polishing filter in the discharge pump 

house. Keystone typically runs its compliance monitoring composite samples on 

Monday and Tuesday. The gauge pressure in the pipe at the sample point is 

approximately 156 psi. The flow of the effluent is much more consistent than the 

influent flow. Keystone tries to maintain a relatively constant flow of 180-220 

gpm. Based on the Design Engineer’s Report, the residence time of the treatment 

system is calculated to be 9.9 hours, based on the design flow of 450 gpm.
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• In the Design Engineer’s Report, Attachment 5, Keystone provided the design 

wastewater influent characteristics and the projected monthly average discharge 

levels for the treated wastewater. Keystone states that the influent characteristics 

are based on coal and limestone data. However, the actual influent values can 

vary greatly from those in the table. This table gives an indication of what species 

the FGD wastewater treatment system is targeting and to what degree. According 

to this table, the wastewater treatment system targets the following pollutants: 

TSS, pH, total aluminum, total cadmium, chromium III, total cobalt, total copper, 

total and dissolved iron, total lead, total manganese, total mercury, total nickel, 

and total zinc.

• The effluent from the FGD wastewater treatment system is regulated by

Keystone’s NPDES permit (PA0002062) via internal outfall 101. Attachment 6 

includes Keystone’s permit limitations for internal outfall 101. Additionally, 

Keystone is required to sample the influent for the following parameters: total and 

dissolved selenium, TSS, total dissolved solids, and pH.

• The treated FGD wastewater is discharged to the Allegheny River via final outfall 

001. The plant was prohibited to discharge to Crooked Creek because they could 

not meet the chloride limitations or the limitations for other trace metals such as

selenium. Therefore, Keystone built a 16 mile pipeline so that they could 

discharge to the Allegheny River. Discharge from the FGD wastewater treatment 

system is the only wastewater at the plant that is discharged to the Allegheny 

River. According to plant personnel, the estimated cost for the piping alone was 

1.3 million dollars ($1,300,000).

• According to Keystone personnel, the plant has not had any performance 

problems with the FGD wastewater treatment system. 

Sampling Information

• Keystone stated that they are not allowed to schedule planned outages from June 

15 through August 30. Information on planned outages in September and October 

is confidential business information (CBI), but Keystone will provide this 

information upon request, if EPA decides to sample at this location.

• When shipping packages to the plant, Keystone stated that Mark Jacklin should be 

the plant contact. 

• The nearest hospital to the plant is in Indiana. During the daylight shift there is a 

person on call at the plant to respond to medical emergencies.

 
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Table 2. Site Visit Attendees

Name Organization (Representing) Telephone E-mail

Sara Marie Baldi RRI Energy - Water Quality Group 724-597-8633 smbaldi@rrienergy.com

Donna Hill Southern Company/UWAG 205-257-5234 dbhill@southernco.com

Mark Jacklin RRI Energy - Keystone Tech Dept 724-354-5475 mjacklin@rrienergy.com

John Kosinski RRI Energy - Keystone Tech FGD Not Provided Not Provided

Josh Hall Environmental Protection Agency (EPA) 202-566-1002 hall.josh@epa.gov

TJ Finseth Eastern Research Group (Contractor to EPA) 703-633-1698 thomas.finseth@erg.com

Becky Schwantes Eastern Research Group (Contractor to EPA 703-633-1715 becky.schwantes@erg.com

Roger Smith Siemens Water Not Provided Not Provided

James Krizner Siemens Water Not Provided Not Provided

Rod Berkebile RRI - Keystone Not Provided Not Provided

Note: RRI Energy requested that all questions be submitted to Sara Marie Baldi and Mark Jacklin; therefore, RRI Energy did not 

provide contact information for the other site visit attendees.