Final Notes from Site Visit at Duke Energy’s Miami Fort Station 

on April 22, 2009 

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

North Bend, Ohio on April 22, 2009. The purpose of the site visit was to learn about the 

operations at the plant, specifically the flue gas desulfurization (FGD) wastewater treatment 

system and ash handling practices. This memorandum describes the information collected 

during the site visit. Attached is the water balance diagram for the plant, with annotations 

made during the site visit based on comments from plant staff. Also attached are analytical 

results provided by the plant for the FGD wastewater treatment system influent and effluent, 

and analytical results from groundwater monitoring of the ash ponds. 

Duke Energy contacts for the site visit: 

Name Phone Number E-mail

Jim Steiritz (513) 287-2269 jim.stieritz@duke-energy.com 

Joe Potts (513) 467-5873 joseph.potts@duke-energy.com 

Plant Overview 

 Miami Fort operates three baseload coal-fired steam electric generating units. A fourth 

coal-fired unit (unit 5) was retired in December 2007. Additionally, there are four oilfired combustion turbine electric generating units located at the Miami Fort plant; 

however, they are operated by the non-regulated combustion turbine fleet of Duke 

Energy. The plant has a total gross generating capacity of 1,275 MW from coal-fired 

units and 80 MW from the oil-fired units. The oil-fired units began commercial 

operation in 1971 and plant staff stated that the units are seldom used. The table 

below contains some general information for the coal-fired units. 

Capacity 

(MW) 

Unit 

Initial 

Year of 

Operation Nameplate Summer Winter 

Particulate 

Control 

NOx 

Control SO2 Control 

6 1960 175 163 163 Yes Low NOx 

Burners 

None 

7 1975 550 510 510 Yes SCR 

installed in 

2001 

Wet FGD 

installed in 

2007 

8 1978 550 510 510 Yes SCR 

installed in 

2001 

Wet FGD 

installed in 

2007 

 Miami Fort burns eastern bituminous coal. The average sulfur content of the coal is 

5.76 pounds SO2/mmBTU and the chlorine content of the coal is 0.069 pounds 

Cl/mmBTU. 

 Miami Fort operates SCRs on units 7 and 8, which are both operated year round. The 

plant also operates limestone forced oxidation wet FGD systems on units 7 and 8. The 

removal efficiency of both FGD systems is approximately 96 percent. 
Ash Handling 

 Miami Fort operates a wet fly ash handling system on unit 6 and dry fly ash handling 

systems for units 7 and 8. The dry fly ash handling systems for units 7 and 8 were 

installed as part of the initial installation of the electric generating unit. Bottom ash for 

all three units is handled wet. 

 Miami Fort operates an ash pond with two adjacent cells operated in series. Fly ash 

from unit 6 and bottom ash from all three units is sluiced to the cell nearest the plant. 

Polymer is added to the ash pond influent to improve TSS removals. Approximately 

one year ago, the plant changed its ash pond management practices and now operates 

the first cell using the 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. As solids removed from the channel dewater and 

accumulate, they are periodically hauled to a landfill three miles from the plant. 

 In addition to fly ash and bottom ash transport water, the ash pond also received 

treated FGD wastewater and mill rejects. 

 The overflow from the first cell enters the second cell for additional settling. Carbon 

dioxide can be added to the overflow to control the pH. 

 Both cells of the ash pond are unlined. According to plant staff, ground water 

monitoring has found elevated levels of arsenic, barium, calcium,iron, manganese, 

sulfate, and TDS. The highest level of the ash pond dike (on the river side of the pond) 

was estimated by plant staff to be 50 feet above the surrounding elevation. Analytical 

results from the groundwater monitoring are attached to the notes. 

 The ash pond discharges to the Ohio River through outfall 002. No water from the ash 

pond is recycled back to the plant as sluice water or for other purposes. The NPDES 

permit imposes effluent limits at outfall 002 for pH, TSS, and oil and grease. The 

permit also requires semi-annual monitoring (no limits) for nitrate+nitrite, selenium, 

arsenic, barium, zinc, cadmium, lead, chromium, and copper. Daily monitoring of 

flow rate is also required. 

FGD System and FGD Wastewater Management 

 Miami Fort operates limestone forced oxidation FGD scrubber systems on units 7 and 

8. The absorbers have three spray levels. River water is used as the source of makeup 

water to the FGD system. No dibasic acid (DBA) or other organic acids are added to 

the absorbers. 

 The FGD systems have a design maximum chlorides limit of 12,000 ppm. At the time 

of the site visit, unit 7 FGD absorber chlorides were at 5,900 ppm and unit 8 absorber 

chlorides were at 5,800 ppm. According to plant staff, absorber chlorides are typically 

maintained at approximately 5,000-10,000 ppm. The typical solids concentration in 

the absorbers is 21-24 percent solids. 
 Absorber blowdown is sent to primary hydroclones which separate the gypsum 

(hydroclone underflow) and send it to vacuum belts for further dewatering. The 

overflow from the primary hydroclones is transferred to secondary hydroclones. The 

underflow from the secondary hydroclones is sent to the Reclaim Water Tank to be 

reused in the process as make-up water. The overflow from the secondary 

hydroclones is sent to the FGD wastewater treatment system. 

 The FGD wastewater treatment plant is operated 24 hours per day, seven days per 

week. Influent flow from the secondary hydroclones to the treatment system averages 

150 gpm (averaged over a 24-hour period). The design maximum flow rate for the 

influent to the FGD wastewater treatment system is 200 gpm. The design maximum 

TSS concentration is 26,163 mg/L. 

 Miami Fort’s 3rd party contractor, Synmat, has a staff of approximately 17 personnel 

dedicated to operating the entire FGD system, including reagent preparation, gypsum 

dewatering, laboratory, and wastewater treatment and solids handling. Synmat uses 

approximately 1.5-2 FTE of the total staffing to operate the FGD wastewater 

treatment. 

 The FGD wastewater treatment system is a chemical precipitation system that uses 

hydroxide and sulfide precipitation to remove metals. Ferric chloride and polymer are 

also added to enhance pollutant removals. Secondary hydroclone overflow from the 

scrubber is sent to an equalization tank where lime is added to promote desaturation 

and the formation of metal hydroxides. Wastewater then flows to the coagulation 

tank, where organosulfide (TMT-15) and ferric chloride are added to promote iron 

coprecipitation and formation of metal sulfides. The pH of the coagulation tank is 

maintained at 8.2-8.4 S.U. Flow from the coagulation tank splits into two parallel 

trains of a reaction tank followed by a DensaDeg lamella clarifier. Polymer is added 

to the reaction tank for coagulation and flocculation to improve solids removals. The 

overflow from both clarifiers is combined in the effluent tank, and then discharged to 

the ash pond. Clarifier underflow is collected in a sludge tank and transferred to a 

plate-and-frame filter press for dewatering. The filter press filtrate, some sludge from 

the DensaDeg clarifier, and flush water are recycled back into the equalization tank. 

Figure 1 presents a simplified process flow diagram for the wastewater treatment 

system. 

 If the effluent from the FGD wastewater treatment system is not within specifications, 

the wastewater treatment facility is shut down. The material within the system is 

treated until the effluent is within specifications. If the wastewater cannot be treated to 

the necessary specifications within the wastewater treatment facility, the wastewater is 

sent to an outside concrete-lined pond. 

 Solids from the wastewater treatment system are sent to a landfill. 

 The treated effluent is sampled for pH, conductivity, total suspended solids, and total 

dissolved solids. The plant is not required to monitor FGD wastewater for metals, but 

has collected some data for the treatment system influent and effluent. Analytical 
results for FGD wastewater treatment system effluent monitoring are attached to the 

notes. 

 Duke Energy, in conjunction with a vendor, previously conducted bench-scale tests of 

FGD wastewater that evaluated the effect that organosulfide addition has on mercury 

removals. 

 Plant staff estimated the capital cost for the FGD wastewater treatment system at $12 

million. Annual operating and maintenance (O&M) costs were estimated at $1.5 

million. Chemical costs (lime, organosulfide, polymer, ferric chloride) and treatment 

sludge handling were each estimated at $1,000 per day, accounting for approximately 

$700,000-750,000 of the total annual O&M costs. 

Figure 1: Simplified Process Flow Diagram for the FGD Wastewater Treatment System