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 Mi ami 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, specifi cally the flue gas desulfurization (FGD) wastewater treatment system and ash handling practices. This me morandum describes the information collected during the site visit. Attached is the water balance diagram fo r 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 wastew ater treatment system influent and effluent, and analytical results from groundw ater 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 D ecember 2007. Additionally, there are four oilfired combustion turbine electric generati ng units located at the Miami Fort plant; however, they are operated by the non-regulated combusti on turbine fleet of Duke Energy. The plant has a total gross generati ng 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 info rmation for the coal-fired units.

Capacity

(MW) Unit Initial Year of Operation Nameplate Summer Winter Particulate Control NOx Control SO 2 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. Th e average sulfur content of the coal is 5.76 pounds SO 2 /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 oxid ation 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 genera ting unit. Bottom ash for all three units is handled wet.

 Miami Fort operates an ash pond with two adj acent 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 stacki ng method. This approach entails using equipment to maintain channels for the sl uice water to move th rough the mass of ash solids collected in the po nd. 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 tran sport water, the as h 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 plan t 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 a bove the surrounding elevation. Analytical results from the groundwater monitoring are attached to the notes.

 The ash pond discharges to the Ohio River th rough outfall 002. No water from the ash pond is recycled back to the plant as sluice water or fo r 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, ch romium, and copper. Daily monitoring of flow rate is also required.

FGD System and FGD Wastewater Management

 Miami Fort operates limestone forced oxida tion 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 ch lorides limit of 12,000 ppm. At the time of the site visit, unit 7 FGD absorber chlo rides were at 5,900 pp m and unit 8 absorber chlorides were at 5,800 ppm. According to pl ant staff, absorber ch lorides 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 vac uum belts for further dewatering. The overflow from the primary hydroclones is tr ansferred 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 wate r. 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 hydr oclones to the treatment system averages 150 gpm (averaged over a 24-hour period). Th e 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 3 rd party contractor, Synmat, has a staff of approximately 17 personnel dedicated to operating the entire FGD sy stem, including reagent preparation, gypsum dewatering, laboratory, and wastewater treat ment and solids handling. Synmat uses approximately 1.5-2 FTE of the total st affing to operate th e 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 equa lization tank where lime is added to promote desaturation and the formation of metal hydroxides. Wa stewater then flows to the coagulation tank, where organosulfide (TMT -15) and ferric chloride are added to promote iron coprecipitation and formation of metal sulf ides. 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 DensaD eg lamella clarifier. Polymer is added to the reaction tank for coagulation and flo cculation to improve solids removals. The overflow from both clarifiers is combined in the effluent tank, and then discharged to the ash pond. Clarifier underf low 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 specificat ions. If the wastewater cannot be treated to the necessary specifications within the wastew ater treatment facilit y, 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, c onductivity, total suspended solids, and total dissolved solids. The plant is not required to monitor F GD wastewater for metals, but has collected some data for the treatment sy stem influent and effluent. Analyticalresults for FGD wastewater treatment system effluent monitoring are attached to the
notes.

 Duke Energy, in conjunction with a vendor, pr eviously conducted bench-scale tests of FGD wastewater that evaluate d the effect that organosul fide addition has on mercury removals.

 Plant staff estimated the capital cost for the FGD wastewater treatment system at $12 million. Annual operating and maintenan ce (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