Notes from Site Visit at Allegheny Energy’s Harrison Power Station 

on September 10, 2008 

EPA conducted a site visit at Allegheny Energy’s Harrison Power Station located in Harrison, 

WV on Wednesday, September 10, 2008 to learn about the operations at the plant, specifically 

the FGD wastewater treatment system. Table 1, located at the end of this memorandum, 

identifies the site visit participants. The presentation that the Harrison personnel presented during 

the site visit is provided as an attachment to the memorandum. 

This memorandum describes the information collected during the site visit and the pre-site visit 

phone call, which was held on August 20, 2008. 

Plant Overview 

• Harrison operates three generating units at the power plant. Each unit generates 

650 MW. 

Unit 

Installation 

Date 

Capacity 

(MW) 

Particulate 

Control NOx Control SO2 Control 

1 December 

1972 

650 Cold-side 

ESP 

SCR installed 

May 2002 

Wet FGD installed 

January 1994 

2 December 

1973 

650 Cold-side 

ESP 

SCR installed 

May 2003 

Wet FGD installed 

January 1994 

3 December 

1974 

650 Cold-side 

ESP 

SCR installed 

May 2003 

Wet FGD installed 

January 1994 

• All three units have cold-side ESPs, which achieve between 98 and 99 percent 

removal of the fly ash and other particulates. 

• Harrison currently operates the SCRs during the ozone season. However, Harrison 

may begin year-round operation next year. 

• Harrison operates magnesium-enhanced lime inhibited oxidation FGD scrubbers 

on all three units. 

• Harrison burns eastern bituminous coal. The sulfur content of the coal, based on 

2008 data from the coal supplier, is approximately 2.85 lbs S/BTU or 3.45% 

sulfur. The chlorine content of the coal, based on 2008 data from the coal 

supplier, is 0.05-0.1% (dry basis). 

• Harrison is also beginning to burn PRB coal in addition to the eastern bituminous 

coal. Currently, PRB accounts for approximately 7 percent of the total burn for 

each unit. Harrison stated that the plant is using PRB because it is cheaper than 

eastern bituminous, even accounting for additional transportation costs. However, 

the PRB coal contains approximately 9,000 BTU/lb, while the eastern bituminous 

coal contains approximately 12,000 BTU/lb. 
Page 2 

• Harrison burns between 17,000 and 18,000 tons of coal per day and consumes 

450,000 tons of lime per year. 

• Harrison’s coal pile has its own settling pond which receives all coal runoff. The 

coal pile runoff pond drains to the wastewater lagoons. During the site visit, EPA 

collected a sample from the coal pile runoff pond and measured the pH of the 

sample using a pH meter. The pH of the coal pile runoff pond was measured as 

2.95 S.U. EPA observed that the pond water had a slight yellow tint. 

• Harrison operates a recirculating cooling water system with cooling towers. The 

cooling tower blowdown is either used as bottom ash sluice source water or 

transferred to the wastewater treatment lagoons and discharged to the West Fork 

River. A process flow diagram for the handling of the plant’s wastewater is 

provided as an attachment to this memorandum. 

• The level of the West Fork River is maintained by an upstream dam. In addition, 

two reservoirs are used to control the volume of the river. 

• Harrison stated that 80 percent of the mercury is removed from the flue gas by the 

combination of the SCR and FGD systems. 

FGD System 

• Harrison operates a wet magnesium-enhanced lime inhibited oxidation FGD 

scrubber on each of the three generating units. All three FGD scrubbers began 

operating in January of 1994. 

• Harrison’s lime supply naturally contains a small percentage of magnesium. The 

lime supplied to the plant typically contains 2.9 percent MgO and 90 percent 

CaO. Harrison stated that the ideal MgO content is 2.5 to 2.7 percent. Although 

the magnesium is naturally present in the lime acquired by Harrison, the plant can 

add additional magnesium if necessary. The FGD scrubber chemistry is enhanced 

by the addition of magnesium oxide. 

• The lime manufacturer calcines limestone into lime prior to delivering the lime to 

Harrison. The additional processing is one reason why lime is more expensive 

than limestone on a per unit mass basis. 

• The lime supplied to Harrison is first transported by barge and then by rail. 

Harrison receives 15-17 rail cars per day, 5 days a week. The lime is stored in 

two silos which each hold approximately 40,000 to 45,000 tons of lime 

(approximately a 30-35 day supply). 

• The lime is slaked into hydrated lime slurry consisting of calcium hydroxide and 

magnesium hydroxide. Harrison uses a ball mill to slake the lime. Both the 

calcium hydroxide and magnesium hydroxide reactions are exothermic and 

generate heat, which results in the lime slurry having a high temperature. The 

high temperature of the slurry helps to dissolve the magnesium in the slurry. 
Page 3 

• Magnesium enhances the FGD scrubber chemistry in the following ways: 

o MgSO3 is roughly 200 times more soluble than CaSO3 (three percent of 

the aqueous phase is dissolved MgSO3). For this reason, more sulfur can 

remain bonded in solution before MgSO3 is converted to CaSO3, which is 

precipitated out of solution. 

o Magnesium chemistry maintains a high alkalinity (1500-2000 ppm) and 

pH. Under these non-equilibrium conditions, SO2 absorption is favorable 

and the mass transfer resistance between the liquid and the gas is the rate 

limiting step. In forced oxidation, there is an additional resistance to mass 

transfer within the liquid phase because of the low solubility and alkalinity 

of calcium sulfate. 

o Magnesium sulfite is converted to magnesium bisulfite which captures 

twice as many sulfur dioxide molecules in solution as calcium sulfite. 

• Harrison stated that the FGD scrubbers remove approximately 98 percent of the 

SO2 in the flue gas. The flue gas emmision SO2 concentration is approximately 20 

ppm. 

• Harrison adds elemental sulfur to the FGD scrubbers to inhibit the oxidation of 

the calcium sulfite to calcium sulfate Adding emulsified sulfur to the FGD 

scrubbers forms the thiosulfate species (S2O3

2-), which is an oxygen scavenger 

and removes oxygen from the system before it oxidizes the calcium sulfite. 

• Although the Harrison plant operates an inhibited oxidation FGD scrubber 

system, Harrison estimates that 15 percent of the solids generated in the FGD 

scrubber are calcium sulfate due to natural oxidation. Harrison stated that this 

calcium sulfate is not present as gypsum in the product. Rather, there are crystals 

of calcium sulfate dispersed between crystals of calcium sulfite. 

• Harrison stated that elemental sulfur is typically only added to the FGD system 

during the ozone season, which is when the SCR system is operating. Harrison 

stated that when the SCR is operating it has caused issues with the oxidation of 

the calcium sulfite and, therefore, the elemental sulfur is needed. Harrison stated 

that operating the SCR without the elemental sulfur addition allows gypsum 

crystals to form. Allowing a combination of calcium sulfite and gypsum crystals 

to form would interfere with the solids separation process for the scrubber 

blowdown. 

• Harrison stated that the chlorides content within the scrubber is 4,000 to 5,000 

ppm. The scrubbers’ maximum chlorides design capacity is 12,000 ppm. The 

sulfite concentration in the scrubber is 4,000-6,000 ppm and the total dissolved 

solids concentration is 2.5-3.0 percent. The TDS is primarily MgSO3. TDS 

levels can cause operational problems if allowed to reach 4 percent. At these 

TDS levels, the density of the scrubber slurry begins to increase, which negatively 

affects the settling rates in the thickener and reduces the centrifuge performance. 
Page 4 

Harrison stated that the elevated TDS levels do not affect the sulfur dioxide 

removals in the FGD system. 

• Harrison stated that the pH in the scrubber is typically between 6.3 and 6.4. The 

scrubbers are operated to maintain the desired pH level. As pH drops, the plant 

adds more lime slurry to control pH levels. 

• Harrison stated that the FGD scrubber system works better with a high sulfur coal. 

Harrison stated that the sulfur content of the eastern bituminous coal ranges from 

3 to 3.5 percent, and has been approximately 3.4 percent in 2008. 

• Each of the FGD scrubbers has four spray levels; however, Harrison only operates 

three of the sprays levels at a time. Each spray level has its own recirculation 

pump. Each of the recirculation pumps recirculate the scrubber slurry at a flow 

rate of 125,000 gpm, for a total of 375,000 gpm of recirculation for each scrubber. 

• The FGD scrubber blowdown flow rate to the thickeners is 3,500 – 4,000 gpm. 

This stream flows from the scrubber through a pipe housing to the thickeners. 

Before the waste slurry is fed into the thickeners it flows through a distribution 

box which adds make up water from West Fork River and a polymer which aids 

in solids settling. A process flow diagram for the handling of the FGD 

wastewater is provided as an attachment to the memorandum. 

• Harrison has four thickeners which are not designated to a particular FGD 

scrubber (i.e., each thickener usually contains slurry from all three FGD 

scrubbers). However, Harrison has the ability to direct flow exclusively from any 

FGD scrubber to any of the thickeners. 

• Each thickener has a volume of 4,329,000 gallons. The average retention time for 

each of the thickeners is 17 hours. 

• The thickener overflow is recycled back to the FGD scrubbers. Because the FGD 

scrubber blowdown is commingled in the thickeners, the FGD wastewater 

returned to the FGD scrubbers is a combination of all the units. 

• There are two underflow pumps on each thickener. The underflow, which is 30 to 

40 percent solids, is sent to the centrifuges. Harrison has 15 centrifuges (three 

trains each with five centrifuges), but typically only four centrifuges from each 

train are in operation at any given time (i.e., a total of 12 centrifuges operating at 

a time). 

• Harrison’s centrifuges have variable-speed control, but the plant typically 

operates them at 2,000 rpm. The centrifuge spins and pushes the solids to the 

outside walls of the centrifuge. A rotating screw within the centrifuge rotates in 

the opposite direction of the centrifuge and pushes the solids back toward the inlet 

side of the centrifuge and out of the system. The water stays towards the inside of 

the screw and flows through holes located on the inner part of the screw to the 

opposite end of the centrifuge. 
Page 5 

• The water leaving the centrifuge, referred to as centrate, is transferred to one of 

two centrate tanks and is then recycled back to the FGD scrubbers. 

• Harrison adds Nalco flocculant to the centrifuges as needed. They may take 

samples from the centrifuge to determine the appropriate amount of Nalco 

flocculant to add. 

• The solids recovered from the centrifuges contain approximately 45 to 50 percent 

water. Harrison combines the centrifuged FGD cake with fly ash and hydrated 

lime in a pug mill. The pug mill typically operates continuously while the solid 

waste process is in operation (e.g., dewatering centrifuges and landfill activities). 

• The product from the pug mill is a cementitious material which falls from the pug 

mill conveyor to surge bins. The material is loaded directly from the surge bins 

into trucks which transport the solid waste to a landfill. Each truckload hauls 

approximately 100 tons of waste. The mixed material from the pug mill is solid 

enough to move/shape the waste with bulldozers. 

• Harrison stated that in the winter months it may be necessary to add more lime to 

the pug mill than in summer months. The higher lime ratio results in higher 

reaction temperatures and faster curing. This makes the final product easier to 

transport by truck. 

• Harrison stated that the solids handling system was designed to run 16 hours per 

day, 7 days per week. However, they have found that operating 24 hours per day, 

5 days per week and performing maintenance on the weekends resulted in less 

operational downtime. 

• Harrison stated that they do not need to operate with a chloride purge stream 

because the chlorides are being purged from the system with the FGD solids that 

are sent to the landfill. Because the centrifuged FGD cake contains 45 to 50 

percent water, a large amount of dissolved chlorides are present in the cake and 

are purged from the system. 

SCR System 

• Harrison stated that the SCR systems began in 2002 and 2003. 

• Harrison stores urea on site and converts it to ammonia for injection into the SCR 

systems. Harrison decided to use urea instead of storing anhydrous ammonia 

because of safety concerns. 

• Each SCR has four layers of catalyst. Harrison stated that three of the four layers 

are in operation. 

• Harrison stated that they will be regenerating the catalyst for the first time next 

year. The catalyst will be shipped to SCR Tech in Charlotte, NC for regeneration. 
Page 6 

Ash Handling and Wastewater Treatment 

• Harrison operates a wet bottom ash handling system. The bottom ash sluice is 

transferred to hydrobins to dewater the ash. Each unit has two hydrobins. The 

overflow from the hydrobins is sent to the wastewater treatment lagoons. Harrison 

has been marketing some of the bottom ash as a blasting agent, known as “black 

beauty”. Additionally, the plant uses the bottom ash to line the on-site landfill or 

sells some of the bottom ash to the state of West Virginia for use on roads for skid 

control. 

• The wastewater treatment lagoons also receive air preheater wastewater, floor 

drain wastewater, ion exchange wastewater, coal pile runoff (after settling), and 

other low-volume wastewaters. 

 

• Harrison has two treatment lagoons, but only one lagoon operates at any given 

time. The lagoon effluent is discharged directly into West Fork River. The last 

time Harrison switched lagoons was in October 2006. 

• Harrison operates a dry fly ash handling system. Most of the dry fly ash is used to 

create a cementitous material with the FGD by-product, which is then landfilled. 

In addition, some of the fly ash is landfilled and some is sold to make cheap 

cement used to fill in mine subsidence. 

Landfill 

• Harrison operates an on-site landfill for the disposal of the FGD solids material, 

as well as fly ash. 

• Originally, the landfill only received fly ash. Since the installation of the FGD 

scrubber, Harrison has added a geosynthetic lining; however, the original area 

where the fly ash was landfilled is still unlined. 

• The runoff and leachate from the lined portion of the landfill is collected in three 

water collection sedimentation ponds (A, B, and C). 

• The unlined portion of the landfill has an underdrain system that drains to a sump. 

This leachate collected in the sump is directed to Harrison’s wetlands treatment 

system by a system of ditches and underground collection pipes. 

Wetlands Treatment System 

• Harrison’s wetlands treatment system consists of 12 terraced cells and has been in 

operation for five years. There are two equalization basins. Terraced below the 

equalization cells are cells consisting of bull rush and cattail, for the removal of 

metals such as aluminum and iron, followed by peat moss cells for removal of 

trace metals, followed by limestone gravel cells for removal of manganese. 
Page 7 

• In November 2006, through an agreement with the State, Harrison’s wetland 

treatment system began treating acid mine drainage from an on-site abandoned 

mine. The acid mine drainage is blended with the leachate prior to entering the 

wetlands treatment system. Harrison stated that selenium is present in both 

wastestreams. 

• Harrison stated that no chemicals are added to the wetland treatment system. 

However, part of the treatment system consists of manganese oxidizing beds, 

which contain limestone gravel. 

• Harrison’s 2008 Constructed Wetlands Treatment System Report shows that the 

system met the NPDES permit limits for pH, aluminum, iron, manganese, 

hexavalent chromium, selenium, and TSS. In many cases, the influent to the 

treatment system was above the permit limits. 
Page 8 

 Table 1. Site Visit Attendees 

Name Organization (Representing) Telephone Joe Lapcevic Allegheny Energy (724) 838-6099 jlapcevic@Bill Cannon Allegheny Energy (724) 838-6018 wcannon@Dan Berisko Allegheny Energy (304) 584-2384 dberisk@aMarce Tennant Allegheny Energy (304) 584-2268 mtennan@Dennis Napier Allegheny Energy (304) 584-2263 dnapier@aBrent Banks Allegheny Energy (304) 584-2243 bbanks@aBill Glessner Allegheny Energy (304) 584-2262 wglessn@Julie Ford Allegheny Energy (304) 584-2329 jford@alleDonna Hill Southern Company (205) 257-5234 dbhill@soRon Jordan EPA/Office of Water (202) 566-1003 jordan.ronJosh Hall EPA/Office of Water (202) 566-1002 hall.josh@Deborah Bartram ERG (Contractor to EPA) (703) 633-1669 deborah.baTJ Finseth ERG (Contractor to EPA) (703) 994-7130 thomas.finKurt Blohm ERG (Contractor to EPA) (703) 633-1675 kurtis.bloh
ALLEGHENY ENERGY 

HARRISON POWER STATION 

D W BERISKO

FLUE GAS FLOW DIAGRAM - UNIT OPERATIONS

1 2 3 4

5

6

7

8

UNIT KEY:

1 COAL P[ILE2 MILLS3 BOILER4 SCR5 AIR HEATER6 ESP7 ABSORBER8 STACK

FLUE

GAS
ALLEGHENY ENERGY 

HARRISON POWER STATION 

D W BERISKO

FGD LIQUOR FLOW DIAGRAM - UNIT OPERATION

8 9

10

11

12

14

15

16

17

TO ST

TO

LANDFILL

UNIT KEY:

7 ABSORBER8 LIME LOADOUT9 DRY LIME SILO

10 LIME SLAKER11 SLAKED LIME SILO12 THICKENER13 THICKENER OVERFLOW TANK14 THICKENER UNDERFLOW TANK15 CENTRIFUGES16 CENTRATE TANK17 PUGMILLS
ALLEGHENY ENERGY 

HARRISON POWER STATION 

D W BERISKO

MAJOR CHEMICAL REACTIONS IN MG-LIME SCRUBB

1) SO2 + H2O ↔ H2SO3 Sulfur dioxide absorption into solu

2) H2SO3 + Ca(OH)2 → CaSO3↓ + 2 H2O Neutralization with calcium compo

lime to form insoluble calcium sul

3) H2SO3 + Mg(OH)2 → MgSO3 + 2 H2O Neutralization with magnesium com

of lime to form soluble magnesium 

4) H2SO3 + MgSO3 → Mg(HSO3)2 Critical neutralization reaction util

soluble magnesium sulfite.

5) Mg(HSO3)2 + Ca(OH)2 → CaSO3↓ + MgSO3

Neutralization reaction with calcium component of lime to form insoluble calcium sul

to regenerate soluble magnesium sulfite for reuse. ( Magnesium catalytic effect. )

7) SO3= + 1⁄2 O2 → SO4= Oxidation of sulfite to sulfate.

6) SO3= + H+ ↔ HSO3 ̄ Buffering equilibrium reaction of 

and bisulfite resulting in enhanced alkalinity in scrubber 
ALLEGHENY ENERGY 

HARRISON POWER STATION 

D W BERISKO

SOLUBILITY VALUES FOR VARIOUS SCRUBBER SPE

MgO 0.000 SOLID Magnesium Oxide

Calcium Sulfite CaSO3•2H2O 0.004 SOLIDCalcium Sulfate CaSO4•2H2O 0.260 SOLIDCalcium Chloride CaCl2•6H2O 74.5 LIQUOR

CaCO3 0.001 SOLID Calcium CarbonateMgSO3•6H2O 66.0 LIQUOR Magnesium SulfiteMgSO4•7H2O 71.0 LIQUOR Magnesium SulfateMgCl2•6H2O 116. LIQUOR Magnesium ChlorideMgCO3 0.010 SOLID Magnesium Carbonate

SOLUBILITY PHASE

(In 100 parts 

water)

NAME SYMBOL