Draft Notes from Site Visit at 

Duke Energy’s Miami Fort Station

on March 1, 2010

EPA conducted a site visit at Duke Energy’s Miami Fort Station (Miami Fort) located in 

North Bend, OH on Monday, March 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 1, located at the end of these notes, 

identifies the site visit participants. The presentation that the Duke Energy personnel gave during 

the site visit is provided as Attachment 1 to these notes and includes a FGD system process flow 

diagram, a simplified flow diagram of the FGD wastewater treatment system, and detailed view 

of the DensaDeg® clarifier. A more detailed process flow diagram of the FGD wastewater 

treatment system and an aerial view of the plant are provided as Attachments 2 and 3, 

respectively, to these notes.

Plant Overview

• Miami Fort operates three coal-fired steam electric generating units at the power 

plant. Unit 6, which began operation in 1960, has a generating capacity of 175 

MW. Units 7 and 8, which began operation in 1975 and 1978, respectively, each 

have a generating capacity of 550 megawatts (MW). All three units are operated 

as baseload units. The table below contains some general information regarding 

the three generating units.

Unit

Installation 

Date

Gross 

Capacity 

(MW)

Particulate 

Control NOx Control SO2 Control

6 1960 175 Electrostatic 

Precipitator 

(ESP)

(cold-side)

Low-NOx Burners None

7 1975 550 ESP (coldside)Selective Catalytic 

Reduction (SCR) 

(2003)

Wet FGD installed 

December 2007

8 1978 550 ESP (coldside)SCR (2001) Wet FGD installed 

in April 2007

• Duke Energy is a partial owner of all the units at the plant. Miami Fort explained 

that a joint committee that meets regularly makes decisions regarding the units. It 

was also stated that both parties split the expenses and revenue of the units. 

• Miami Fort retrofitted Units 7 and 8 in 2007 with FGD scrubber systems to 

control the sulfur dioxide (SO2) releases from the plant. Unit 6 was not retrofitted 

with a scrubber system and Miami Fort does not have any plans for a retrofit. 

• Miami Fort operates SCR systems on Units 7 and 8, installed in 2003 and 2001, 

respectively. Miami Fort runs the SCRs year round. The plant has not yet 

performed a catalyst regeneration on either of the SCRs. The plant takes samples 

of fly ash every day and measures the amount of ammonia present. Plant 
May 27, 2009

Page 2

personnel stated that more ammonia slip was noticed this year. Miami Fort is 

beginning to discuss the options for how to handle the SCR catalysts. Plant 

personnel explained that they are considering the following options:

o Install a new layer of catalyst;

o Regenerate an existing layer of catalyst; or 

o Replace an existing layer with a new layer of catalyst.

• Miami Fort stated that ash can build up on the catalysts in the SCR system, 

depending on the type of coal burned. Sonic horns are continuously used to 

remove ash from the catalysts; however, during quick outages, the plant uses a 

water spray to remove any remaining ash buildup. [QUESTION FOR MIAMI 

FORT: Is the above description accurate? Also, are pressure gauges used to 

activate either the sonic horns or an automatic wash cycle?]

• Miami Fort burns eastern bituminous coal in all three units. Miami Fort stated that 

the coal is delivered by barge from several different mines. Miami Fort explained 

that the source of the coal is a variable. 

• Miami Fort stated that the sulfur content of the coal ranges from 2.5 to 7.5 pounds 

of sulfur per million BTU and that the chlorine content of the coal can range from 

0.04 to 0.3 percent, depending on the source. 

• Miami Fort previously had issues with blue plume from the stack, associated with 

sulfur trioxide emissions. The plant now injects lime into the flue gas between the 

air heater and the ESP to control the sulfur trioxide emissions.

• Miami Fort operates dry fly ash handling systems on Units 7 and 8 and a wet fly 

ash handling system on Unit 6. The dry fly ash handling systems on Units 7 and 8 

are separate systems and the ash from each unit is stored in a separate silo. Wet 

fly ash from Unit 6 is sluiced to the plant’s ash pond.

• Miami Fort has both wet and dry fly ash loading capabilities for Units 7 and 8. 

Additionally, the plant has the capability to load rail cars from the Unit 7 silo.

• Miami Fort sells most of the ash to Ready Mix. Any fly ash that the plant cannot 

sell is transferred to their landfill located approximately three miles away, which

is owned by Duke Energy. [QUESTION FOR MIAMI FORT: Is the landfill 

operated by Duke Energy?] Miami Fort stated that if the ammonia in the fly ash 

exceeds 100 ppm, the ash is not able to be sold and is transferred to the landfill.

• Miami Fort operates wet bottom ash handling systems on all three units. A 

hydroveyor vacuum system sluices the bottom ash to the ash pond. Miami Fort 

uses cooling tower blowdown as the source for the hydroveyor water. The fly ash 

and bottom ash from Unit 6 are sluiced together to the ash pond. The plant sluices 

pyrites separately to the ash pond to enable the plant to market some of the 
May 27, 2009

Page 3

bottom ash. Miami Fort previously had a contract with Home Depot to reuse 

filtered bottom ash for cement board. The contract was dropped when the plant

switched to a higher density coal. Miami Fort is currently not selling any bottom 

ash for reuse.

• Miami Fort operates an ash pond with two adjacent cells operated in series. The 

fly ash and bottom ash sluice streams are transferred to the first cell. Miami Fort 

adds polymer to the ash pond near where the sluice pipes deposit the ash to 

improve solids removals. The plant operates the first cell using a rim ditch 

stacking method. This approach entails using equipment to maintain channels for 

the sluice water to move through the mass of ash solids collected in the pond. The 

plant removes the solids that settle out in the channels of the ash pond and stacks 

them in piles along the channels to allow the solids to dewater, while the water 

drains back into the pond.

• The plant hauls the dewatered ash from the pond to the landfill that is owned by 

Duke Energy for disposal. This ash is typically 18 percent moisture. Miami Fort 

stated that along with the fly ash, FGD gypsum wastes and FGD wastewater 

treatment solids are transferred to the landfill. [QUESTION FOR MIAMI FORT: 

What gypsum is sent to the landfill (e.g., off-specification, extra that can’t 

marketed)?]

• Miami Fort sends about 150,000 tons of ash to the pond per year. The plant 

estimates that the water in the ash pond has a three day retention time. The pond 

also receives the effluent from the FGD wastewater treatment system, which is 

transferred to the first cell (Pond A) after the stacking portion. The sumps from all 

three units are transferred directly to the second cell (Pond B). Coal pile runoff is 

also transferred to the ash pond, but it is collected in a smaller pond before being 

transferred to the ash pond. [QUESTION FOR MIAMI FORT: Is the coal pile 

runoff added to Pond A or Pond B?] Miami Fort has the capability to add carbon 

dioxide to the ash pond wastewater as it flows from Pond A to Pond B.

[QUESTION FOR MIAMI FORT: Has the plant added carbon dioxide to the 

pond? When does the plant add carbon dioxide?]

• Miami Fort discharges the ash pond effluent to the Ohio River via Outfall 002. 

The ash pond effluent flow rate is approximately 13 MGD.

• Leachate from the ash pond is collected in a dike along the outer edge of Pond B. 

The ash pond has 38 different drains that collect leachate and transfer it to the 

dike. The dike also collects rainfall and runoff from the ash pond berms. The 

removal of leachate from the ash pond keeps the pond from building too much 

pressure and makes the pond more stable. The leachate flows along the dike and 

is discharged to the Ohio River via a stormwater outfall. Plant personnel stated 

that the combined flow from all 38 drains is about two gpm.
May 27, 2009

Page 4

• Miami Fort has groundwater monitoring wells around the ash pond. [QUESTION 

FOR MIAMI FORT: How many wells does the plant have? Are they upgradient 

or downgradient? What analytes are monitored and at what frequency. When were 

the wells installed and when did monitoring begin? Does the plant have a 

monitoring well that measures background concentrations?]

• Miami Fort was recently issued a new NPDES permit on July 1, 2009. Miami Fort 

will provide EPA with an electronic copy of the permit. [NOTE: Miami Fort sent 

EPA the new NPDES permit on March 5, 2010.]

FGD System

• Miami Fort operates two limestone forced oxidation FGD systems (one each on 

Units 7 and 8). 

• The FGD systems have three spray levels; however, the plant typically only 

operates two of the spray levels at one time. The FGD systems are also equipped 

with dual flow trays. 

• River water is used as the source of makeup water to the FGD system. The plant 

does not use organic acids in the FGD systems.

• Miami Fort maintains the solids concentration in the FGD system between 21 and 

24 percent solids. According to plant staff, absorber chlorides are typically 

maintained at approximately 5,000-10,000 ppm. The FGD systems have a design 

maximum chlorides limit of 12,000 ppm. The plant blows down from the 

absorbers in batches, depending on the chlorides and solids concentrations in the 

absorber. The FGD system operates at a pH of 5 S.U.

• The blowdown for each FGD system is transferred to its primary hydrocyclone. 

Each FGD system has a dedicated hydrocyclone. The gypsum from the each 

primary hydrocyclone is sent to its own vacuum belt filter for further dewatering. 

The overflow from each primary hydrocyclone is transferred to its own secondary 

hydrocyclone. The underflow from the secondary hydrocyclones is sent to the 

reclaim tank, which is shared between the two units, and reused in the FGD 

system as make-up water. The overflow from the secondary hydrocyclones, which 

contains between 2.5 and 3.0 percent suspended solids, is sent to the FGD 

wastewater treatment system.

• As the gypsum slurry is applied to the vacuum belt filters, Miami Fort washes the 

gypsum with service water to reduce the chlorides in the gypsum to less than 100 

ppm. The vacuum belt filters dry the gypsum to a moisture content of 

approximately nine percent. The gypsum product produced at the plant is 

marketed. [QUESTION FOR MIAMI FORT: To what industries is the gypsum 

marketed?]
May 27, 2009

Page 5

• The filtrate from the vacuum belt filters is collected in the reclaim tank and 

transferred back to the FGD systems. [QUESTION FOR MIAMI FORT: Is the 

reclaim tank water reused in both FGD systems, or primarily in one of the FGD 

systems? If used primarily in one FGD system, which FGD system is the reclaim 

tank water used?]

• Miami Fort’s third party contractor, Synmat, operates the entire FGD system, 

including reagent preparation, gypsum dewatering and marketing, laboratory, and 

wastewater treatment and solids handling. 

FGD Wastewater Treatment System

• The FGD wastewater treatment system, which was designed by Infilco 

Degremont, is a chemical precipitation system that uses hydroxide and sulfide 

precipitation to remove metals and suspended solids from the wastewater. Ferric 

chloride and polymer are also added to enhance pollutant removals. The 

maximum design flow rate for the system is 200 gpm, but the average flow rate 

into the FGD wastewater treatment system is 150 gpm.

• Secondary hydrocyclone overflow from the scrubber is transferred directly to the 

equalization tank. Miami Fort adds lime to the equalization tank to raise the pH of 

the wastewater from approximately 5 S.U. to between 8.4 and 8.6 S.U. To 

promote desaturation of the gypsum, Miami Fort recycles some of the sludge 

from the downstream clarifiers which provides seed crystals for gypsum 

nucleation. The equalization tank also receives flush water from the recycle 

sludge lines, and wastewater from the wastewater treatment building sump, which 

consists of filter press filtrate. 

• From the equalization tank, the FGD wastewater flows to the coagulation tank, 

where Miami Fort adds organosulfide and ferric chloride to the wastewater. The 

ferric chloride is used to assist in the coagulation of the solids precipitated in the 

equalization tank, as well as promote iron coprecipitation of some residual metals 

in the wastewater. The organosulfide is added to precipitate residual metals as 

sulfide complexes.

• Flow from the coagulation tank splits into two parallel streams that flow to two 

DensaDeg® clarifiers. The DensaDeg® clarifier has an initial reactor section, 

where polymer is added for coagulation and flocculation to improve solids 

removals. From the reactor section, the wastewater enters the 

clarification/thickening section of the clarifier, where the solids settle out of the 

wastewater. As discussed previously, some of the sludge from the two clarifiers is 

recycled back to the equalization tank to provide seed crystals for gypsum 

nucleation. The remainder of the sludge is transferred to the sludge holding tank 

and then processed through the filter presses. The filtrate from the filter presses is 

collected in the wastewater treatment building sump and recycled to the 

equalization tank. The sludge from the filter presses is hauled off site for disposal 
May 27, 2009

Page 6

at a landfill. [QUESTION FOR MIAMI FORT: Is the wastewater treatment 

sludge sent to the same landfill as the ash?]

• The clarified wastewater from the two DensaDeg® clarfiers is combined in the 

effluent tank. The wastewater is pumped to the ash pond and discharged via 

Outfall 002. The transfers to the ash pond are based on level control within the 

effluent tank; therefore, the transfers are not continuous.

• If the effluent from the FGD wastewater treatment system does not meet system 

specifications and discharge limits, the FGD wastewater treatment system is 

stopped. The material within the system is treated until the effluent meets 

specifications and then is discharged.

• Miami Fort is currently testing the use of Nalmet® 1689 as the organosulfide in 

the FGD wastewater treatment system instead of TMT 15®, which was used by 

the plant when the FGD wastewater treatment system began operation. The plant 

is testing the effectiveness of Nalmet® 1689 by adjusting its feed rate, as well as 

the feed rates of the other FGD wastewater treatment additives (i.e., polymer, 

ferric chloride). Miami Fort personnel stated that the Nalmet® 1689 results look 

promising and that it has been effective in lowering mercury levels. 

• Miami Fort is also planning to test a General Electric organosulfide product in the 

summer using a slip stream. [QUESTION FOR MIAMI FORT: What GE 

organosulfide is being tested? From where in the FGD wastewater treatment 

system will the slip stream be pulled? What is the planned slip stream flow rate?]

• EPA stated that regardless of the testing being conducted in the FGD wastewater 

treatment system, EPA would like the plant to operate the FGD wastewater 

treatment system at stable operating conditions during EPA’s planned sampling 

episode.

• The plant stated that mercury data are available for the inlet and outlet of the FGD 

wastewater treatment system, Outfalls 601 and 608, respectively. EPA stated that 

these data would be helpful to review. Plant personnel stated that the data would 

be sent electronically to EPA. [NOTE: Miami Fort sent EPA the data on March 5, 

2010.]

Information for Sampling

• EPA identified the FGD wastewater treatment system influent sampling point as 

the tap off the secondary hydrocyclone flowing to the equalization tank. 

• EPA identified the FGD wastewater treatment system effluent sampling point as a 

tap on the pump discharge off the effluent tank. Miami Fort stated that they could 

install a smaller hose barb on the tap to accommodate the sample collection.
May 27, 2009

Page 7

There is plenty of table and cooler storage space near the sample point in the FGD 

wastewater treatment building.

• Plant personnel stated that all EPA/ERG sampling personnel would be required to 

go through a 45 minute health and safety orientation prior to the sample 

collection. 

• Plant personnel also stated that there is a first responder team on site and ERG 

would have access to the team in case of emergency.
Table 1. Site Visit Attendees

Name Organization (Representing) Telephone E-mail

Pat Coyle Duke Energy 513-287-2268 pat.coyle@duke-energy.com

Brian Huddleston Duke Energy 217-218-2985 huddlebj@muohio.edu

Joseph G. Potts Duke Energy 513-287-2609 joseph.potts@duke-energy.com

Jim Stieritz Duke Energy 513-287-2269 jim.stieritz@duke-energy.com

Tara Thomas Duke Energy 513-467-4950 Tara.thomas@duke-energy.com

JR Wood Duke Energy 513-467-4886 jr.wood@duke-energy.com

Donna B. 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