## Duke Energy Carolinas’ WFGD Retrofit Program: Operation at Marshall and Belews Creek Stations

Paper #: 48

Ronald E. Laws, P.E. Consulting Engineer, Program Engineering (relaws@duke-energy.com ph. 704-382-8411, fax 704-382-9769) Duke Energy Carolinas
526 S. Church Street Charlotte, NC 28202

Ed Byers
FGD Area Coordinator (ecbyers@duke-energy. com ph. 336-445-0388) Duke Energy Carolinas
Belews Creek Steam Station
3195 Pine Hall Road Belews Creek, NC 27009

Jürgen Dopatka, P.E. Technology Manager (jurgen.dopatka@power.alstom.co m ph. 865-694-5342, fax 865-694-5213)
Rita Mardini Senior Process Engineer (rita.h.mardini@power.alstom.co m ph. 865-560-1393, fax 865-694-5213)
Alstom Power Environmental Control Systems 1409 Centerpoint Boulevard Knoxville, TN 37932

Jim McCarthy, P.E. Chief Engineer Mechanical/Piping, Power Divisi on – Fossil Sector, Shaw Group (James.McCarthy@Shawgrp.com ph.704-331-6043, fax 704-331-1310) 128 S. Tryon St., Suite 400 Charlotte, NC 28202

Presented at: MEGA Symposium 2008 Baltimore, MD August 25-28, 2008

Page 1 of 18 10.3155/2008CP175.48

### 1. ABSTRACT

Duke Energy-Carolinas committed to a multiphase fleet-wide SO 2 emissions reduction. Four of eight coal-fired stations are being retrofitted with high efficiency WFGD by 2012. Engineering started in 2003, two stati ons are already operating, one is being commissioned, and anot her being constructed.

The state-of-the-art WFGD system s at Marshall and Belews Cr eek Stations have been in operation between 8-20 months. Performan ce testing on the absorbers and overall systems has been completed. Operating e xperience, maintenance requirements, and performance results are the main focus of this paper. Specifics include:

• Absorber performance without the presence of spare spray levels

• Damperless open-bypass system employing unique materials

• Selection of FRP outlet flues and stack liners

• HDPE piping: engineering, construction, operation

• Duke’s Gypsum Recycling Program: G ypsum quality, contract approach, transportation arrangement, dedicated supply.

• Biological and wetlands removal of selenium and mercury from WFGD
blowdown

• Overall operating and maintenance e xperience, including O&M provisions and equipment reliability during the recent 20 months at Marshall Steam Station and eight months at Belews Creek Station.

Page 2 of 18

### 2. INTRODUCTION

In 2002 Duke Energy Carolinas embarked on an ambitious program to retrofit flue gas desulphurization equipment on 12 of its largest units over the course of the next 10 years. The total affected generating capacity exceed s 6,000 MW. This is the largest and most complex plant modification program ever undertaken on the Duke Energy Carolinas fossil fleet. Total predicted costs approach $1.5 billion. The affected stations are

summarized in Table 1

.

Table 1. Stations Affected by Desulphurization.
Station/Unit Location Approx. Net Capacity Each (MW) Expected or Actual* Startup

Allen 1 and 2 Belmont, NC 165 2009 Allen 3, 4 and 5 Belmont, NC 275 2009

Belews Creek 1 and 2 Walnut Cove, NC 1,120 2008*

Cliffside 5 Cliffside, NC 560 2010

Marshall 1 and 2 Terrell, NC 385 2007*

Marshall 3 and 4 Terrell, NC 660 2007*/2006*

Duke Energy Carolinas has teamed with Alst om Power and Shaw to engineer, procure, construct and commission these systems. Th e size and importance of this program has posed numerous challenges and opportuni ties for innovative engineering solutions. Implementation of the SO 2 emission reduction program is based on a staged approach. Using the results of the fleetwide Phase I study as a starting point, a site-specific Phase II study was conducted for each unit. Actual implementation (Phase III) commenced upon approval of funding, usually 3 – 4 months after completion of the Phase II study.

The first of these retrofits, Marshall Steam Station with its four boiler units, has been operating with a new state-of-the art WFGD system for 20 months. The second WFGD retrofit, Belews Creek Station with its two large boilers, has been operating its absorbers as much as eight months. Allen Station with its five boilers and two absorbers is close to completion of construction. The operating experience, maintenance requirements, and performance results at Marshall and Belews Creek are the main focus of this paper. A discussion of the overall program approach is discussed elsewhere. 1, 2

Page 3 of 18

### 3. CURRENT PROGRAM STATUS
Figure 1. Marshall’s New Stack with
all three FGD units in service. Marshall Steam Station The Marshall Station is located on Lake Norman, approximately 35 miles northwest of Charlotte, North Carolina. The plant was c onstructed in the 1970s and consists of four (4) tangen tially fired pulverized coal units. Units 1 and 2 have an approximate net capacity of 385 MW each while Units 3 and 4 are larger at 660 MW (net) each.

Construction on the Unit 4 FGD absorber started in summer 2004. In late fall 2006, Unit 4 FGD was the first one of the program to go into service, and Unit 3 followed in March 2007. The final two boiler units, Units 1 and 2, have been operating with a WFGD since May 2007. Figure 1 shows cleaned flue gas from Marshall leaving the stack.

Belews Creek Steam Station
The Belews Creek Station is the largest coal-burning power plant operated by Duke Energy Carolinas, and is located on Belews Lake near Walnut Cove, North Carolina. The plant was
constructed in the 1970s and consists of two (2) coal-fired units, each of which can generate 1,120 MW net output. Figure 2. Belews Creek Units 1 & 2 WFGD, Dec. 2007

Construction at the Belews Creek Station began in May 2005. The two absorbers serving Unit 1 went into service in January 2008, followed by the absorbers for Unit 2 in April 2008. Figure 2 shows the recently completed Belews Creek WFGD System.

Allen Steam Station
The Allen Station is a five unit station located in Belmont, North Carolina on the
Catawba River. Units 1 and 2 (165 MW net each) be gan operating in 1957; unit 3 in 1959; unit 4 in 1960 and unit 5 in 1961 (all 275 MW net each). Allen is the only Duke Energy Carolinas station with five units under one roof. The current c onstruction status of the Allen WFGD system is shown in Figure 3

.

Page 4 of 18The Phase III construction is approximately 70% complete as of June 2008. The first absorber is expected to go on line in spring
2009. Figure 3. Allen Inlet Duct, Absorbers 1 & 3 and Stack (June 2008)

Cliffside Unit 5
Cliffside Steam Station is a five-unit coal generating facility located in Cliffside, North Carolina. Units 1 – 4 are part of the original plant built in 1940. Due to their small size and age they will not be
retrofitted with WFGD and will be retired in 2012. Although part of the same station, Unit 5 (560 net MW) is located in Cleveland Co unty 1/2 mile from the other four units. This unit is equipped with a sel ective catalytic reduction system.

Unit 5 WFGD was part of the original fleetwi de program, the scope has been expanded to include AQCS equipment associated with a new, 800 MW ultra supe rcritical unit (Unit 6). Detailed engineering st arted in the summer of 2007 and is approximately 25% complete as of June 2008, with construction recently started. Un it 5 FGD is scheduled for Commercial Operation in the Fall of 2010. Unit 6 is scheduled for Commercial Operation in the Spring of 2012.



### 4. COMMON FEATURES OF THE WFGD SYSTEMS OF EACH
STATION

4.1. Absorber Design

The absorber design for all the stations repr esents the proven state-of-the-art Alstom Power open spray tower system with a number of features to improve efficiency and operational flexibility and at the same time reduce capital cost.

• At several stations, multiple boilers are feeding into a single absorber vessel (Marshall, Allen, see Table 2 ), afforded by the reliability of recent open spray tower designs.

• The absorbers were designed without a de dicated spare spray level, resulting in capital cost savings associated with the reduced tower height and the spray system (i.e. pumps, piping, valves, motors, switchgear , etc.). In the event of an unplanned spray pump outage, organic acid (DBA) will be injected into the system allowing the required SO 2 removal performance to be maintain ed with one pump out of service. The design also allows for the flexibility to achieve 99% SO 2 removal with all recycle pumps in service and DBA addition for enhanced performance when desired.

Page 5 of 18• The absorber is equipped with Alstom Power’s patented Performance Enhancement Plates (PEPs), also known as wall rings. These PEPs minimize ‘sneakage’ of untreated gas along the absorber wall, and at the same time re-entrain slurry that got
lost to the absorber walls.

• In addition, the PEPs are complemented by st ate-of-the-art dual orifice spray nozzles, which spray both vertically up and down in all but the upper spray elevation. This increases the retention time of droplets fo r increased mass transfer with the acidic gases compared to conventional down-spra y only configurations, with favorable impact on the draft loss. Both of the above absorber components afford high efficiency operation with practically no extra energy input.



### 4.2. FRP Outlet Duct and Stack Liners

All absorber vessels are equipped with fiberglass reinforced plastic (FRP) outlet ducts as well as FRP flues. A summary of the key absorber outlet duct and flue gas outlet flue data is provided in Table
2 . While Marshall ( Figure 4 ) utilizes extended outlet ducts, the FGDs at the remaining stations utilize more closely coupled
extended absorber outlets and extended stack breeches (See Figure 2 for Belews Creek). Figure 4. Marshall Unit 4 Absorber FRP Outlet Duct

Table 2. Overview of FRP Outlet Duct s and Stack Liners at each Station Station Unit Absorber Outlet
Duct Diameter Flue
Diameter Windscreen
Diameter Stack height

Allen 1, 2, 5 29’+6” (Common Absorber) 29’+6”

3, 4 29’+6” (Common Absorber) 29’+6” 74’ (Common Stack) 365’+0”

Belews
Creek 1 26’+2” ea (2 Abs.) 36’+0” 47’+10” Top

63’+0” Bottom 500’+0”

2 26’+2” ea (2 Abs.) 36’+10” 47’+10” Top

63’+0” Bottom 500’+0”

Cliffside 5 25’+0” 25’+0”

6 29’+0” 29’+0” 72’+0” (Common Stack) 575”+0”

Marshall 1, 2 29’+6” (Common Absorber) 29’+6”

3 29’+ 6” 29”+6”

4 29’+ 6” 29’+6” 80’+2” (Common Stack) 315’+0” (Common Stack)

Page 6 of 18The conceptual design was based on 317LMN ou tlet ducts and flue ga s liners. The cost and lead-time for this material escalated rapi dly early in the design process, thus other options were evaluated. FRP was eventually se lected for both the outlet duct and the flue gas liners. The decision to switch to FRP was based on 20-year life cycle cost, superior
corrosion resistance and reasonable lead-time. Other materials examined in addition to
317LMN and FRP included C-276 clad over car bon steel and epoxy ma stic/borosilicate glass block.

FRP had previously been used successfully in similar applicati ons within the power industry. Due to the size and importance of this equipment, steps were taken to build on this experience as outlined below:

• Design Conditions – The maximum expect ed normal flue gas temperature exiting the absorbers was approxi mately 125 oF. The normal operating design temperature for the outlet duct a nd flue gas liners was established at 140 oF along with a transient desi gn temperature of 200 oF. The normal operating mode of the FGD system precl uded use of the new stack without the FGD system in operation. A diesel driven emergency quench system was installed upstream of each absorber in order to protect the FRP outlet duct and flue gas liners, as well as the ab sorber internals, in case of a system upset. This system was sized to provide protection for approximately 10 minutes based on flue gas excursion temperatures of approximately 500 oF.

• Liquid Collection – Both physical mode l testing and computational fluid dynamic analysis were used to design liquid collection devices within the outlet ducts and flue gas liners. A ma ximum flue gas velocity of 55 – 60
ft/sec was used to size th e ductwork and liners. Th is is the recommended design velocity for FRP ductwork to minimize droplet entrainment from liquid on the duct/liner walls. Special a ttention was paid to the FRP joint
that connected the indivi dual duct and liner sections. The contour of the joint was configured to minimize prot rusion on the inside diameter of the duct/liner, thus reducing th e potential for re-entraining liquid drops into the gas path.

• Third Party Review – The duct and liner s were designed and constructed in accordance with ASTM D5364 “Standard Guide for Design, Fabrication, and Erection of Fiberglass Reinforced Plastic Chimney Liners with Coal Fired Units” and constructed by an ASME RTP-1 stamp holder. Although helpful, these standards do not cover a ll critical aspects of FRP design and construction. An experienced third part y consultant was hired to review all engineering assumptions, calculation s, material specifications and fabrication drawings as well as prov ide onsite quality assurance of the
fabrication and installati on of the FRP sections. A ll FRP sections were spun in an onsite facility.

Page 7 of 18

### 4.3. HDPE Piping

High density polyethylene (HDPE) pipe was used extensively throughout the Fleetwide WFGD retrofits. In excess of 150,000 ft is installed across all th e projects. HDPE was used almost exclusively for both water a nd slurry piping in above and below ground services. Notable exceptions include absorb er recycle pump suction and discharge, oxidation air, and compressed air.

Duke had experienced numerous problems over the years with corrosion, tuberculation
and Asiatic clam infestation in carbon steel raw water piping at it s generating stations. Early in the conceptual phase of the progr am, the decision was made to investigate
alternatives to Duke’s trad itional use of carbon steel pi ping for these services. The investigation examined various ways to deal with these issues such as pigging, chemical treatments, etc.; however, the primary focu s was on alternate materials. Duke had recently completed a similar study for the raw water systems at other generating stations. This study served as the foundation for the FGD investigation. Alternate materials examined in the FGD study included stainle ss steel, PVC, rubber lined carbon steel and HDPE. The study examined corrosion resistan ce, pressure drop, capital cost, long term operating and maintenance costs, imp act resistance, availability, etc.

HDPE was ultimately chosen due to its superior corrosion resistance, low net present value cost and good experience to date with a test section of HDPE. The test section did not show any signs of corrosion or biological buildup after a 6-year trial run. During this study the erosion resistant capab ilities of HDPE also became apparent. Duke had some experience with HDPE for ash sluicing with good results. The decision to use HDPE was expanded to the WFGD slurry services as well.

The benefits of using HDPE were clear; how ever, it did pose numerous engineering and construction challenges as outlined below. It should be noted that although ASME B31.1 allows the use of non-metallic pipe, it doe s not provide any mandatory design rules.

• Temperature sensitive – HDPE loses strength rapidly with increasing temperature. The pressure rating at 1 30 oF is only 65% of the rating at 100 oF. This was a particular issue w ith slurry piping on these FGD projects as approximately 50% of this piping ha d a design temperature greater than 125 oF. If mitered fittings are used, an additional reduction in pressure rating is required. In order to control costs, two line classes were established for HDPE. The “hot” line class design cond itions were established at 95 psig, 125 oF and utilized SDR 7 piping with both fabricated and molded fittings. The “cold” line class design conditions were 95 psig at 110 oF and utilized SDR 9 piping with both fabricated a nd molded fittings. In addition, the thermal expansion coefficient of HDPE is much greater than carbon steel and must be accounted for in piping layouts.

• Supports – HDPE piping has a low modulus of elasticity wh en compared to carbon steel and requires approximately twice the number of pipe supports,

Page 8 of 18which was accounted for in the economic analysis. A side benefit of the low modulus of elasticity is redu ced nozzle loads on equipment.

• Sizing – Although the smooth walls of HD PE pipe offer reduced pressure drop when compared to carbon steel, the required wall thickness often necessitated using the next larger size pipe to maintain a reasonable fluid velocity. Adapter plates were required to accommodate differences between pipe inside diameter and valve insi de diameter. Pressure drop data for HDPE, especially fittings, are not as extensive as th at for carbon steel. This introduced a degree of uncertainty in pressure drop calculations, which had to be considered when sizing pumps.

• Layout – Long radius bends were us ed wherever possible to minimize erosion in slurry lines. D/r ranged from 2 to 5. Although mitered fittings were permitted, a source for “hot forged” sweep bends (D/r = 3) was identified and used for most bends. The decision to use HDPE long radius bends was not made until after much of the Marshall equipment layout was in place, thus accommodating the lo ng radius bends was particularly challenging.

• Construction – Spools of HDPE piping were prefabricated and lifted into place similar to carbon steel. Flanged connections were used for connecting the spools.

The Marshall WFGD system has been operati ng since late 2006, and there have been no noteworthy issues identified by the station with regard to the use of HDPE piping.



### 4.4. CWTS General

While Constructed Wetlands Treatment System (CWTS) was the initial choice for FGD Waste Water treatment, early in the Belews Creek preliminary engineering there was concern developing about the viability of th e CWTS. For Belews Creek, a biological treatment system was chosen to provide the bulk of the FGD waste water treatment downstream of a conventional physico-chemical treatment system. CWTS was expected to provide polishing treatment in case of a shortfall in the biological treatment system. The Allen and Cliffside FGD projects have not incorporated CWTS in their designs. Rather, biological treatment systems have been chosen as the FGD waste water treatment
system.

The predicted selenium concentration for Be lews Creek was bracket ed to 6.4 ppm min., 8.2 ppm avg., and 17.5 ppm max. Th e predicted mercury con centrations were 0.04 ppm min., 0.11 ppm avg., and 0.44 ppm max. Detailed in formation discussing the prediction of the purge stream compositions and the design of the constructed wetlands treatment system (CWTS) is found elsewhere. 1, 3, 4, 5

Page 9 of 18With the predicted ranges in mind, the Belews Creek WWTS was designed for a selenium concentration of 4.00 ppm max. a nd a mercury concentration of 0.30 ppm max..

During the tuning process in February 2008 at Belews Creek, WWTS inlet samples were analyzed and the selenium concentration ranged between 1.7 – 10.1 ppm for digested Se, between 0.56 – 1.86 for dissolved Se, a nd between 0.0011 – 0.0021 ppm for mercury. It must be noted that as of this writing the unde rlying inlet concentrations of these elements in coal, limestone and water at that particul ar time were not cross-checked to see where they ended up in comparison to the value ranges used for the prediction. This would allow an assessment of the prediction quality.



### 4.5. Gypsum Recycling Program

Recognizing the solid waste disposal vol ume the FGD Program represented and the success other utilities have had with recy cling FGD byproducts, Duke searched for a partner for recycling the bypr oduct that would be generate d by the FGD Program. A partnership was developed with a wallboard manufacturer, and plans were developed for the manufacturer to build a new wallboard pr oduction plant with D uke being the sole provider of byproduct gyps um for the facility.

A new wallboard production facility was built in the town of Mt. Holly, North Carolina. This facility began operation in August 2007 and will be capable of consuming a significant portion of the gypsum byproduct annu ally. The wallboard facility has been
scheduled to accommodate the build out schedu le of the Duke FGD Program as well as
meet the needs of the wallboard market in the Carolinas. To date , the gypsum produced in the Marshall and Belews Creek FGD Systems have met the quality requirements of the wallboard facility.



### 5. 20 MONTHS OF OPERATION AT MARSHALL

Marshall’s first WFGD absorber has been ope rating since October 2006. Since that time, the remaining two absorbers have come on-lin e, and all performance testing has been completed. This section discu sses some of the features unique to Marshall’s FGD system and the station’s operations and maintena nce (O&M) experience during the first 20 months of operation.



### 5.1. Absorber Performance

Performance of the Marshall FGD System ha s met expectations. Unit 4 performance testing was conducted in January 2007. Due to the station’s dispatch requirements, the performance testing was staggered in January to operate at steady state for at least three solids residence times prior to testing. Two phases of testing were completed for Unit 4 – phase I at 2.4 lb SO 2 /MMBtu without DBA and phase II at 2.8 lb SO 2 /MMBtu with

DBA.

Page 10 of 18Unit 3 performance testing was conducted in May 2007. Only one phase of testing was completed for Unit 3 – phase I at 2.4 lb SO 2 /MMBtu without DBA. Note that there was no testing performed at the 2.8 lbSO 2 /MMbtu, 99% SO 2 removal parameter for Unit 3.
This was the result of boiler issues as a result of burning these higher sulfur fuels. Due to system load constraints and continued difficulties burning these fuels, this performance
test was waived.

Performance testing for the Marshall Unit 1&2 Absorber was conducted in August 2007. Two phases of testing were completed for Unit 1&2 – phase I at 2.4 lb SO 2 /MMBtu without DBA and phase II at 2.8 lb SO 2 /MMBtu with DBA. The agitator out of service and Electrical Consumption testing was not performed due to Non-FGD operational issues which curtailed the testing. Table 3 summarizes the key performance parameter results from the Marshall performance testing.

Table 3. Marshall Performance Testing Summary.
Test Results
Unit 1&2 Unit 3 Unit 4

SO 2 Removal without DBA, Design/Actual 95.0% / 95.3% 94.8%* / 95.9% 95.7%** /
96.2%

SO 2 Removal with DBA 99% / 99.4% † Not Tested 99.4% ††

Particulate Emission, lb/MMBtu (Design of 0.03 lb/MMBtu) 0.0014 0.008 0.006

Gypsum Quality Purity (Design 95 ± 2 %) Moisture (Design <10 %) 97.7 wt%

7.7 wt % 96.7 wt%
8.1 wt% 94.4 wt%
9.1 wt%

*Actual SO 2 inlet condition was 2.63 lb/MMBtu **Corrected for actual gas flow and actual SO 2 inlet conc. lower than design during testing † Actual SO2 Inlet Condition was 2.53 lb/MMBtu ††Actual SO 2 inlet condition was 2.65 lb/MMBtu



### 5.2. Damperless Open Bypa ss Configuration

The selection of an open bypass flue gas ha ndling configuration is one of the unique
features at Marshall. As indicated in Figure 5 , open bypass means that the gas paths to the WFGD system and to the old stack, which serves as start-up/emergency bypass, are not physically separated by a damper, but in stead, are in permanent open connection to each other, hence open bypass. The main func tion of the open bypass is to protect the boiler from undesired flue gas pressure ex cursions during transient conditions. The incentive to utilize an open bypass arrangement in lieu of dampers is the inherent simplicity of operation and lack of constant maintenance attention to dampers, which are required to operate within seconds if neede d. In order to prevent untreated flue gas leaving through the open bypass, the pressure at the bypass c onnection (stack base) must

Page 11 of 18be slightly negative. At the same time the in flow of ambient air th rough the existing stack
must be limited to not more than 5% of the to tal flue gas flow to avoid corrosion in the ductwork and unnecessary expense associ ated with the excess gas volume.

Figure 5. Damperless Open Bypass Flow Diagram.



### Boiler ESP

ID Fan Existing

Stack

Booster

Fan FGD System New

Stack

S-TEN 1 material was selected for the majo rity of the WFGD inlet duct with a thick polyurethane asphaltic mastic applied in th e cold air turbulent mixing zones at the junction between the existing ID fans, the existing stacks, and the new ductwork. Borosilicate block directly applied to the mastic on the inside of the duct has been used to protect the mastic. To provide mechanical protection during inspec tion and maintenance, a 1-1⁄4 inch thick Tuffchem masonry was installed on floor areas accessible for inspection.

Due to low ambient air velocities in the exis ting stack, there has been some uncertainty about the accuracy of a flow meter to measure this flow. Performance testing at Marshall
confirmed the ambient air flow to be within the design limit of 5% of total ID Fan outlet flue gas volume.



### 5.3. Constructed Wetland Treatment System at Marshall

The construction of the Marshall CWTS began in September 2004. The wastewater leaving the wastewater solids removal system
is blended with service water to assist in decreasing the chloride
content of the wastewater. This pretreated wastewater is then
treated in a CWTS. The final CWTS configuration includes dual equalization basins and three parallel series of four treatment cells. The system was constructed Figure 6. Wetlands at Marshall, July 2006.

Page 12 of 18to achieve gravity flow throughout the system including discharging into the existing ash basin. The total acreage of the equalization ba sins and treatment cells is approximately 15 acres with the total area required to construc t the CWTS approaching 46 acres. The first scrubber unit was placed in se rvice in the fall of 2006, when introduction of the scrubber purge stream to the CWTS began. Wetlands Cells 1A, 1B, 1C shown in Figure 6 are the first treatment cells downstream of the equali zation basin and are planted with Bulrush.

The CWTS has proven effective in mercury re duction but selenium removal has not fully met expectations. Pilot testing comple ted by Clemson/Entrix in November 2006
concluded that boron levels as low as 25 ppm could impact the wetlands plants. In addition, DBA levels of 200 ppm impacted the performance of the wetlands system in the pilot testing. Actual boron levels in the wastewater are impacting the wetlands plants; however, the selenium removal in the wastewat er solids removal system clarifier and the
dilution in the Ash Basin downstream of th e CWTS have resulted in the National Pollutant Discharge Elimination System (NPDES) data being well within the projected limits even though no current Marshall NPDES limits for selenium or mercury exist. To date there has been limited DBA addition to the FGD System; therefore, limited
concentrations have been observed in the wetlands.



### 5.4. O&M and Reliability

Duke Energy Carolinas’ power stations must op erate at high levels of reliability and availability during the periods between planned outages. Careful consideration was given to the reliability, consequences of failure, and time to repair for critical process and auxiliary equipment. Efforts were made to en sure that the failure of a single piece of equipment would not impact the performance or availability of the WFGD system. 1
Low cost, reliable operation is key to the success of the Duke Energy Carolinas’ FGD Program, and therefore also uses multiple boi lers feeding into one absorber at two stations. The Fleetwide Program is f ounded on this premise. The Duke Energy Carolinas’ FGD Program relies on a small opera ting staff for the day-to-day operations. The Marshall FGD operation is staffed around the clock by two operators (although commissioning personnel are still assisting this role). While routine maintenance (e.g., oil changes, greasing rotating equipment, etc. ) is typically handled by the plant staff, maintenance activities of a more significant nature will be handled by a Maintenance

Contractor.

O&M Operations at Marshall have been fairly uneventful. There have been a couple of incidences of foaming in the Absorber resu lting in overflows of the Reaction Tank. One event was related to the misoperation of the Reagent Feed System, which resulted in a low pH excursion. The other occurrences seem to be related to oil firing of the boiler during startup.

Other than routine maintenance activities, th ere have been no major maintenance events thus far. Marshall Unit 4 has had an outage to perform some internal inspections of the Absorber after 4 months of operation. The only observations were some scale buildup

Page 13 of 18around the Absorber Inlet Nozzle and some minor scaling of the mist eliminators, which was removed by manual washing. More deta iled inspections of Marshall Unit 4 Absorber occurred in the Spring of 2008 to assess both performance of materials of
construction and formation of scale inside th e vessel. Areas of significant scale buildup appears to be limited to the wet/dry interface at the Absorber Inlet Nozzle. Corrosion
was observed on the 317LMN material as well as some small areas of C-276. Mist
Eliminator materials were found to be clean with only a few small areas of solids buildup.

The HDPE piping is performing well. The only issue after 20 months has been a sweep elbows on the mill return line (cla ssifier underflow) to the ball mill. This line is the most abrasive service in the FGD System. Since th e line is a gravity flow line, a temporary repair was performed which consisted of ba nding a sheet of rubber to the exterior

Reliability Appropriate application of e quipment redundancy has been a pplied to the Fleetwide FGD Program. The Marshall FGD has experien ced a only few impact s to reliability.



### 6. EIGHT MONTHS OF OPER ATION AT BELEWS CREEK

6.1. Absorber Performance

Performance of the Belews Creek FGD System has met expectations as of July 2008. The Unit 1 tuning process was conducted in Febr uary 2008 with lower sulfur coal 1.6
lbSO 2 /MMBtu. Performance testing is scheduled for the overall whol e plant in August, 2008 while burning design sulfur coal of 2.4 lbSO 2 /MMBtu. Table 4 summarizes the key performance parameter results from the Unit 1 & 2 Tuning processes.

Table 4. Belews Creek Tuning Results Summary. Unit 1 Unit 2

SO 2 Removal without DBA (Design 95%) >96.0% >96.0%*

Gypsum Quality Purity (Design 95% ± 2%) Moisture (Design <10%) 96.5%
8.7% 96.3% 8.5%, *Three out of four spray levels operating wh ile burning low sulfur coal of 1.4-1.6 lb

SO 2 /MMBtu.

Performance testing for the Belews Creek Unit 1&2 Absorber has not been fully completed as of July 2008. All performance te sting is expected to be completed by the end of August 2008. One phase of testing is planned for Unit 1 & 2 - at 2.4 lb

SO 2 /MMBtu without DBA. In a ddition to the emission tes ting, the common performance guarantees will be measured.

Page 14 of 18

### 6.2. Waste Water Treatment System – Mercury and Selenium

The FGD purge stream is unsuitable for re use by other power plant facilities and therefore must be treated separately before being discharged. The characteristics of this wastewater stream are such that it requires extensive treatment. A dedicated wastewater treatment system has been provided that c onsists of physical-chemical, biological, and constructed wetlands (CWTS) treatment steps.

Physical-Chemical Treatment

The physical-chemical process consists of hydrated lime addition to elevate pH to effect the precipitation of soluble metals as insoluble hydroxides and oxyhydroxides. An organosulfide reagent is added also to form organosulfide heavy metal complexes, which have very low solubility products thus resulting in maximum heavy metal removal (mercury). Ferrous or ferric chloride and Po lymer are added too to form a dense floc and enhance the settling characteristics of the pr ecipitate. Hydrochloric acid is added to readjust the pH value to meet effluent requirements.

Performance of the Belews Creek Waste water Mercury Removal System has met and exceeded expectations. Belews Creek Mercury Removal testing was conducted in February 2008. Table 5 summarizes the key performance parameter results from the testing.

Table 5. Belews Creek Mercury Removal Testing Summary Design Avg. Test Result FGD Purge Effluent Mercur y Concentration, ppm 0.30 0.0016 EQ Tank Effluent Mercury Concentration, ppm 0.0014 Clarifier Influent Mercury Concentration, ppm 0.0010 Clarifier Effluent Mercury Concentration, ppm BRL*

Bioreactor 1 Influent Mercur y Concentration, ppm BRL*

Bioreactor 2 Influent Mercur y Concentration, ppm BRL*

Bioreactor 2 Effluent Mercur y Concentration, ppm 0.001 BRL* * BRL: Below Reporting Limit of 0.0002 ppm

Biological Selenium Removal

The physical and chemical treatment will be followed by a biologi cal treatment where
microbes will be utilized to re duce selenite and selenate to elemental selenium. A nutrient is sdded to the system to ensure a viable biogrowth.

Performance of the Belews Creek Biologica l Selenium Removal System has met and exceeded expectations. Testing of the Selenium in the waste water influent stream from the FGD has yielded constituent levels frequently exceeding the Selenium design value.
Belews Creek Selenium Removal te sting was conducted in February 2008. Table 6 summarizes the key performance parameter results from that testing.

Page 15 of 18Table 6. Belews Creek Biological Selenium Removal Testing Summary. Design Avg. Test Results

Influent dissolved Se Concentration, ppm 4.00 1.12 Influent digested Se Concentration, ppm 4.00 4.28 Effluent dissolved Se Concentration, ppb 100 31 Effluent digested Se Concentration, ppb 100 12

CWTS at Belews Creek

The Belews Creek CWTS design is very similar to that constructed for the Marshall FGD Project. Unfortunately, plant growth has been very frustra ting. The initial planting of Bulrushes did not root well and became displ aced in the cells resu lting in loss of the plants. The resultant replanting was destr oyed by a flock of geese who feasted on the young plants. The third replanting has been pe rformed with the addition of geese counter measures including wolf effigies and the use of Kevlar wire strung over the planted cells.

These numerous replantings caused the CW TS schedule to exte nd beyond the First Absorber startup. Subsequently, it is fair to classify the CWTS as not performing at this writing due to plant infancy.

As already mentioned in section 4.4, the CWTS at Belews Creek was intended for polishing only in case of a s hortfall of the biological treatme nt system. Since start-up of the FGD system, the effluent limits were met already ahead of the CWTS.



### 6.3. O & M and Reliability

Initial operation of Unit 1 was fairly uneventful. Operations was challenged maintaining Reaction Tank chlorides below the 12,000 ppm limit. Some of this challenge was a function of burning low sulfur co al with near maximum coal chloride content. Piping design issues compounded operations ability to address this issue. The piping resolution involved adding vents to gravity return lines which seemed to be scavenging the Purge Stream and reducing the ability to purge chlorides. The low sulfur/high chloride fuel issue was anticipated and the provisions were incorporated in the design to accommodate this prospect. Some additional modifications are being implemented to make the task of dealing with low sulfur-high chloride coals more palatable.

Initial operation of Unit 2 has been experiencing signifi cant foaming due to a booster fan lube oil leak. Due to high system demand on generation, the Station was unable to take a load reduction or Unit outage to resolve the leak for several weeks. The leak has been resolved early July, although the foaming i ssue continued through most of July 2008 due to the accumulated oil. However, the FGD performance has been meeting design requirements for SO 2 removal and gypsum quality since start-up.

Page 16 of 18Performance Testing has been dela yed due to test fuel (2.4 lb SO 2 /MMBtu) availability. As of this writing, the testing is sc heduled to occur in early August 2008.

The typical maintenance issues with starti ng up new systems have occurred at Belews Creek. These include bearings, electrical equipment, etc. While these have been troubling, none have resulted in forced outages of the Units.



### 7. SUMMARY AND CONCLUSIONS

The Duke Energy Carolinas’ WFGD retrofit program is well underway with all units operating at Marshall and Belews Creek while progress is being made toward project completion at the other stations. Th e Marshall and Belews Creek WFGDs are successfully operating and mee ting performance guarantees since coming online in late 2006/early 2007 at Marshall and early 2008 for Belews Creek. This paper has highlighted some of the unique features of the Marshall and Belews Creek system and noted any pertinent experience with those f eatures since the WFGD system has been operating. While the damperless open bypass, the FRP outlet duct, and the HDPE piping required special design considerations, they ha ve proven to meet the requirements of the WFGD system. Many of these unique featur es will require further evaluation due to impacts expected from operation, such as the impacts of DBA use on the CWTS effectiveness to remove mercury and sele nium. Finally, O&M and reliability was
discussed with some noted lessons le arned and further evaluations pending.

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### 8. REFERENCES

1. McCarthy, J., J. Dopatka, R. Mardini, P.C. Rader, and C. Bussell, Duke Power WFGD Retrofit Program: Compliance via Stan dardization and Selective Site-specific

Innovations. Proceedings POWER-GEN International, Las Vegas, 2005.

2. McCarthy, J., J. Dopatka, K. Barger, P.C. Rader, and C. Bussell, D uke Energy– Carolinas’ WFGD Retrofit Program: S ite-specific Innovations and their Implementation. Proceedings MEGA Symposium, Baltimore, 2006.

3. Emission Factors Handbook: Guidelines fo r Estimating Trace Substance Emissions from Fossil Fuel Steam Electric Plants , EPRI, Palo Alto, CA: (2002) 105402.

4. McCarthy, J., D.T. Shuping, J.H. Rodgers Jr., J. Dopatka, P.C. Rader, and C. Bussell, Duke Power WFGD Retrofit Program: Achieving the Lowest System-Wide Cost of Compliance. Proceedings Combined Power Plant Air Pollutant Control Mega Symposium, Washington, 2004.

5. Mierzejewski, M. K., Clean Air Shouldn't Mean Dirty Water: FGD Wastewaters and
Their Treatment , Proceedings Power-Gen, Orlando, USA, pp 531-542 (1991).



### 9. KEYWORDS

Alstom Power, Duke Energy-Carolinas, Shaw , North Carolina, Clean Air, FGD, WFGD, Flue Gas Desulfurization, SO 2 , Removal, Retrofit, Open Bypass, Wastewater treatment, Biological, Wastewater solids removal system , Constructed Wetlands, Selenium removal, Belews Creek Steam Station, Marshall Steam Station, O&M, Reliability, FRP ductwork, Open spray tower, HDPE piping, Gypsum recycling

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