Supercritical Power Plants Hike in Efficiency

7/28/2019 Supercritical Power Plants Hike in Efficiency

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Supercritical Power Plants Hike Efficiency, Gain World Market Share

During the Last Decade, Leading Industrial Countries Initiated a New Wave of Researchand Development

of supercritical (SC) steam power plants. This renewed interest, accompanied by a jumpfrom SC steam parameters to ultra-supercritical (USC) parameters, was driven mostlyby the increase in fuel costs on the world market and by increased environmentalregulations. New installations are under development in certain countries around theworld, but wider market penetration is still limited in some instances by cost andreliability concerns.

Units 17 and 18 steam at NIPSCO'ssupercritical Schahfer Generating Station.Photo courtesy of NIPSCO.

Click here to enlarge image

Based on a survey of independent power producers (IPPs) presented at the FifthAnnual Clean Coal Technology Conference in January 1997, IPPs consider advanced-steam cycle technologies (i.e., a SC steam generator) commercially proven, but morecostly and risky than conventional steam-plant technology. This high-risk perception

exists despite the reality that 350 SC units operate commercially worldwide, withreliabilities as high as those of conventional steam plants. Furthermore, EPRI reportsthat key SC plant performance parameters--availability, maintainability, cycling and low-load operation (with sliding pressure capability)--are equal to or better than those ofsubcritical cycles after an initial startup period.1


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Worldwide Status

As a leading country in developing and installing SC units in the 1960s and 1970s, the

United States today has about 86 GW of installed SC capacity. This capacity has notchanged since 1991, when the last SC plant (the 1,425 MW Zimmer 1 plant) came online. Of 162 operating units (as of 1998), 121 units burn coal, 40 units burn natural gasand 1 burns oil. Design capacities range from 300 MW to 1,400 MW. With the exceptionof two plants, all are designed for steam conditions of 3,300 to 3,700 psig (most at3,500 psig) and 1,000 to 1,100 F (most at 1,050 F).

Installations of SC plants in the United States peaked during the 1970s and fellprecipitously in the early 1980s. No new SC installations are planned in the UnitedStates except for speculation about a 796-MW lignite-fired unit in Texas with SCparameters of 3,910 psig/1,010 F/1,000 F.

In the United States, the Department of Energy's Federal Energy Technology Centerhas been developing technology for the next-generation of high-efficiency, low-emissionUSC boilers, called Low Emissions Boiler System (LEBS). Designed for main steamconditions of 4,500 psig and 1,100 F with two reheats, each at 1,100 F, LEBS utilizes anadvanced, low-NOx slagging combustion system and an optional copper oxide flue gascleanup system for NOx and SO2.

Several countries in Europe and Asia areintensively developing SC and USC power plants,including Japan, Denmark, Germany and Korea;

China is increasing activity as well. Figure 1 showsexpected growth in SC and USC installed capacityfor countries outside the United States,emphasizing the significant development programsin Japan and Korea.



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Japan has demonstrated the fastest growth ininstalled SC fossil capacity from 1990 to 1998. Italso has the largest development program in placefor building new SC coal-fired plants, scheduledfor 2000 to 2005. This growth is accompanied by a

continuous growth in single-unit capacity andsteam parameters. The typical size of a JapaneseSC coal unit in the mid-1990s was in the range of400 to 700 MW; recently commissioned units atthe Haramashi and Shinchi power plants are 1,000MW, and units planned to be commissionedbeyond 2000 will reach 1,050 MW.

Shinchi power station exemplifies Japan's efforts to push power plant technology to itslimits.2-3 With a measured thermal efficiency above 43 percent (LHV), Shinchi is one ofthe largest coal-fired power plants in the world using sliding-pressure technology, which

avoids losses associated with throttling valves at low loads. High-pressure steam ismaintained at 1,200 psig for loads up to 320 MW. As loads increase to 960 MW, high-pressure steam slides up to a maximum 3,700 psig.

Korea has an ambitious program for fossil power plant development, similar in design tothe "progressive standardization" method applied in the former Soviet Union. Under thisplan, Korea has built 16 "standard" 500 MW SC, once-through units between 1990 and1999, designed to burn bituminous coal with an ash content up to 17 percent and asulfur content up to 1 percent. These units are designed for a steam pressure of 3,600psig and superheated and reheated steam temperatures of about 1,005 F. The boilersare equipped with progressive NOx control features such as low-NOx burners and close-

coupled overfire air ports. This standard design has achieved: 1) substantial savings inengineering design and construction costs, 2) improved plant reliability and availability,3) reduced operational and maintenance problems, and 4) interchangeability and localreplacement of spare parts.

Danish power companies operate six SC power plants. All units are firing importedbituminous coal shipped to Denmark in large vessels at competitive prices. Fuel cost,stringent environmental standards, and access to cold sea water were factors in drivingthe Danish power sector toward higher steam parameters in SC and USC boilers. Unit 3at Nordjyllands has a planned net efficiency of 47 percent (LHV). This unit belongs to agroup of so-called USC convoy units consisting of natural gas-fired and coal-fired 400

MW boilers with identical steam conditions (4,500 psig/1,090/1,090 F).

Denmark's next approach for increasing net efficiency involves a conventional PCcombustion unit operated in parallel with a gas turbine for condensate/feedwaterpreheating. The startup of the first proposed unit of this kind, Avedore 2 in Copenhagen,was originally planned for 1999, but recently has been postponed. 4-5 The plant is acombined heat and power (CHP) unit that would meet a Danish requirement for burningbiomass and could fire either coal or gas as the main fuel. A gas-fired turbine is used to



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generate additional power, and its exhaust is used to heat the feedwater to the boiler,thereby enabling the steam turbine to generate more power. Supercritical steamconditions with 4,350 psig pressure and 1,076 F/1,112 F temperature, and a coolingwater temperature of 50 F, give the plant an efficiency of just over 48 percent (LHV).Boiler feedwater temperature is 590 F and condenser pressure is 2.9 psi.

Performance Improvement

Current SC/USC efficiencies for large power plants are in the range of 43 to 45 percent(LHV), while efficiencies up to 50 percent (LHV) are expected in new plants by 2010 to2015. Increasing the full-load efficiency of conventional SC fossil fuel units is generallybased on a step-by-step approach. Various measures can be used to increase thermalefficiency relative to current conventional SC practice (Figure 2).

Steam conditions: Increasing steam pressure and temperature from 3,630 psig/1,000 Fto 4,350 psig/1,110 F can increase efficiency by nearly 2 percentage points. Two

important issues related to increased steam pressure and temperature, however, mustbe addressed: 1) development of materials with high-temperature strength andcorrosion resistance for boiler and turbine pressurized metal parts, and 2) slagformation and fouling of waterwall and superheater tubes.

Materials used for manufacturing the boiler and the high-temperature turbine parts mustsatisfy the following mechanical criteria: adequate creep strength at operatingtemperature; adequate resistance to high-temperature corrosion; adequate formability,weldability and joining; and adequate thermal conductivity.

Second reheat: A second reheat stage can boost efficiency another 0.8 to 1.0

percentage points.

6

This concept has been in use since the 1960s on many subcriticalunits and at least five SC units. These systems, however, are still not cost-effective inmost cases and tend to limit operational flexibility. There are only two existing coal-firedUSC plants using double reheat design--Eddystone 1 & 2 in the United States (steamtemperature 1,280/1,050/1050 F) and the Nordjyllands convoy units (steam temperature1,080/1,076/1,076 F) in Denmark.

Condenser Pressure: Decreasing the condenser pressure from 9.42 psig to 4.35-3.62psig can further increase efficiency by 1.5 to 2.0 percentage points. The availability ofcold seawater for cooling is one of the reasons for the very high efficiencies achieved atDanish USC plants.


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Low temperature heat recovery: Every 10 F reduction in stack gas exit temperature(while recovering the heat involved) increases efficiency by 0.1 to 0.15 percent. Low-temperature corrosion concerns limit large temperature reductions, but the flue gas exittemperature can typically be maintained at 300 to 350 F depending of the fuel sulfurcontent.

The net efficiency trend for SC and USC units commissioned and planned to becommissioned between 1990 and 2000 is presented in Figure 3. The average netefficiency will increase up to 46 percent (LHV) by 2000, with higher numbers for units inDenmark (up to 48 percent LHV). In Japan and the Netherlands, this increase is more

conservative, and will be even lower for German power plants, because almost all unitsunder construction and planned for the near future are designed for lignite, which is oflower quality than coals used in Japan and Denmark.

Availability and Reliability

Studies of the relative reliability of coal-fired subcritical and supercritical plants haveshown that conventional subcritical boilers have had better reliability during their first 10years of operation.6 After 10 years, the average outage time caused by the pressureparts of SC units had leveled off at less than 500 hours/year (representing about 94percent availability), comparable to figures for subcritical plants. Availability of older SC

units is as good as subcritical units, but only when used for baseload duty. These datahave been confirmed by long-term experience with SC boiler operation in the formerSoviet Union and Italy.7-8 The average annual availability factor for all 300 MW units inthe former Soviet Union from 1990 to 1995 was 95 to 97 percent, which is higher thanSC power plant availability in the United States and Germany, where the best unitshave availability factors of 94 to 97 percent and average values lie between 75 and 85percent. The capacity factor for the 300 MW Soviet units before the collapse of theUSSR was also rather high, at 66 to 72 percent.


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An important feature of steam boilers is their load-following capability, which includestwo characteristics: 1) ability for fast startup from different conditions, and 2) ability tohandle sharp changes in load. SC once-through boilers, because of the absence of adrum and other thick-walled parts, require 15 to 20 percent less time for cold startupsthan conventional boilers. Using full/partial flow separators, modern once-through SC

boilers also are capable of very fast load changes, typically 3 to 4 percent per minute,and even 5 percent per minute when using an advanced control system.

References:

1. "Assessment of Supercritical Power Plant Performance," EPRI Report No. CS-4968, 1986.

2. "Flexibility, efficiency are hallmarks of latest coal-fired units," Power, April 1996,p. 43.

3. Jones, K., "Shinchi Leads Way for Large Advanced Coal-Fired Units," ElectricPower International, Third Quarter, 1997, p. 36.

4. Moscatelli, K. and G. Sormani, "Avedre No. 2 CHP Plant -- The Most AdvancedSteam Turbine in the World," Ansaldo Energia, POWER-GEN Americas '97.

5. "Parallel Powering for Avedre No. 2 Power Plant," Modern Power Systems, Vol.16:5. May 1996, pp. 31-36.

6. Couch, G. "OECD Coal-Fired Power Generation -- Trends in the 1990s," IEACoal Research, The Clean Coal Centre, 1997, 83 pp.

7. Lysko, V., et. al., "New Generation of Steam-Turbine Power Units," All-RussiaThermal Institute, Teploenergetika, No. 7, 1996.

8. Benaty, A., et. al., "Design, Construction And Operational Experience InSupercritical Boiler Of 660 MW Power Units," POWER-GEN Asia O95, Vol. 1, pp.611-645.

Acknowledgements:

This article is adapted from a paper presented at the 24th International TechnicalConference on Coal Utilization & Fuel Systems, Clearwater, Fla., March 1999.

Authors

Victor A. Gorokhov, Ph.D., is a senior engineer/project manager with ScienceApplication International Corp. He has more than 25 years' experience in powerengineering and environmental protection. Gorokhov holds a Ph.D. in powerengineering from the Ukrainian National Academy of Science, and an M.S. in powerengineering from the Azerbaijan Institute of Oil and Chemistry, Baku, USSR.


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Massood Ramezan, Ph.D., P.E., is principal engineer with Science ApplicationsInternational Corp. (formerly with Burns and Roe Services Corp.). He has more than 20years' experience in areas of energy and environmental control technologies. Ramezanholds B.S., M.S. and Ph.D. degrees in mechanical engineering from West VirginiaUniversity.

Lawrence A. Ruth, Ph.D., is senior management and technical advisor in the Office ofPower Systems Product Management at the U.S. Department of Energy's FederalEnergy Technology Center. He is responsible for coordinating the development of theVision 21 program. Ruth holds a Ph.D. in chemical engineering from the City Universityof New York.

Soung S. Kim, Ph.D., is project manager of the Low Emission Boiler System (LEBS)project at the U.S. Department of Energy's Federal Energy Technology Center. Prior tothis position, she was a supervisory engineer at the Westinghouse Electric Corp. Kimholds a Ph.D. degree in chemical engineering from Carnegie Mellon University

Design, Construction And Operational Experience In Supercritical Boiler Of 660 MWPower Units

Boilermakers help build first U.S. ultra-

supercritical unit

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Two Boilermakers help direct a tube section lift.Photos courtesy of MOST/MartinCommunications
http://www.boilermakers.org/files/news/photos/TurkPlant_TubeLift-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_TubeLift-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_TubeLift-11.jpg


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Air heaters are pictured in the foreground. At top is the extensive lay-down yard.

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Members work from suspended scaffolding in the boiler area.
http://www.boilermakers.org/files/news/photos/TurkPlant_Aerial4-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_SuspendedScaffolding.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_Aerial4-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_Aerial4-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_SuspendedScaffolding.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_SuspendedScaffolding.jpg


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Boilermakers perform one of the many high-pressure, heavy-wall boiler welds at the Turkproject.

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Aerial view of the J.W. Turk Plant. Courtesy of AEP / B&W. All other photos courtesy ofMOST/Martin Communications

Cutting-edge Turk Plant uses less coal and water, reduces

emissions

THE FIRST-EVER commercially-deployed, ultra-supercritical power generation unit in theUnited States is under construction in southwest Arkansas and Boilermakers are playing aleading role in the project.

The $2.1 billion, 600-MW J. W. Turk Jr. Plant will feature the latest environmental controls,according to majority owner Southwestern Electric Power Company (SWEPCO), an AmericanElectric Power (AEP) operating company.

Local 69 (Little Rock, Ark.) has jurisdiction over the project, which employed 350 Boilermakers

at its peak, including members from across the United States. More than 1.1 million Boilermakerman-hours have been worked since the project began in 2008. Boilermaker involvement isscheduled to conclude this spring, and the start-up operation is slated for the fourth quarter ofthis year.

Total construction jobs numbered 1,850 at the height of the project. The plant is expected toemploy 110 full-time workers and provide electricity to customers in Arkansas, Louisiana andTexas.
http://www.boilermakers.org/files/news/photos/TurkPlant_Weld3-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant2.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_Weld3-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant_Weld3-11.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant2.jpghttp://www.boilermakers.org/files/news/photos/TurkPlant2.jpg


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Shaw Constructors, Inc. is prime contractor for the project. Babcock & Wilcox received thecontract to supply and install the steam generator and air quality controls systems, with AlstomPower, Inc. supplying the turbine/generator and boiler feedwater pump turbine.

Project includes extensive work scope, presents many

challenges

WITH B&W HANDLING much of the construction effort, Boilermakers faced a substantialworkload with demanding deadlines. The B&W scope of work included the boiler, selectivecatalytic reduction equipment, dry scrubber, baghouse, fans, flues/ducts, pulverizers and piping.Through September of 2011, members had completed nearly 26,000 pressure-part welds, with arepair rate of just 1.17%.

Where practical, major components were assembled on the ground and rigged for lifting into theproper position. Erecting the Benson spiral furnace presented special challenges, as weldersattached tube panels in a three- dimensional fashion, working downward to a saw-tooth tub at the

furnace base.

We met every deadline we had, said Rodney Allison, who worked on the plant for two yearsbefore becoming business manager and secretary-treasurer for Local 69. Allison said manningthe job was a bit tricky because of opposition to the project by environmental groups. Theopposition created legal delays which idled workers, but AEP and SWPECO ultimately resolvedthe issues, and Boilermaker crews did their part to stay on schedule throughout the project.

In addition to environmental obstacles, the project faced severe weather impediments, includingrecord rain in 2010 and record heat in 2011. The heat was really bad, said Allison. I believe itwas about 125 on the outside of the ductwork on some days last year, and heat exhaustion

became a problem. The year before, we were rained or iced out for several days. That made ithard on the men.

Plant design offers numerous advantages

THE ULTRA-SUPERCRITICAL (USC) design of Turk Plant allows higher temperatures andpressures than can be handled by conventional power plants. This is achieved in part by usingchrome- and nickel-based super alloys in the steam generator, steam turbine and piping systems.

In a presentation to the MOST Tripartite Conference in Myrtle Beach, S.C., last fall, AEPrepresentatives Tom Householder and Chris Beam, and B&W's Jeff Hines discussed how theTurk Plant will use less resources and cut emissions. Householder is AEPs Managing Directorof Labor Relations; Chris Beam is Managing Director of Projects & Construction. Beamestimated that compared with conventional coal-fired plants of similar output, the Turk Plant willuse 180,000 tons less coal per year, 1,600 tons less lime and 14,000 tons less total ash. Thefacility will also use 1 million gallons less water per day.

Beam said environmental emissions will be much lower as well: 320,000 tons less carbondioxide, 150,000 tons less SO2, 100 tons less NOx and 25 tons less filterable particulate matter.


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Beam said he was very impressed with the quality of the workforce, particularly theBoilermakers' 1.17 weld reject rate.

Householder noted, The Boilermakers, with programs such as MOST and Common Arc, andmany other training programs, provided AEP the trained workforce with the skill sets needed to

complete this project safely, on schedule and within budget targets.

Householder added, Although we view the Boilermakers work on the project as a success, wecant be satisfied, because we did not attain our goal of zero jobsite injuries. However, B&Wsoverall OSHA recordable injury rate at Turk was 0.81, which is in the top 25% an excellentachievement.

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Supercritical Power Plants Hike in Efficiency