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ULTRA SUPERCRITICAL. Pulverized Coal-Fired Steam Generators. Introduction. Q: What is Ultra Supercritical (USC)? A: Not universally defined, but generally can be considered to be >3800 psig and >1100 F final steam conditions Q: Why Consider Ultra Supercritical?

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ULTRA SUPERCRITICAL

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ULTRA SUPERCRITICAL

Pulverized Coal-Fired Steam Generators


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Introduction

Q: What is Ultra Supercritical (USC)?

A: Not universally defined, but generally can be considered to be >3800 psig and >1100 F final steam conditions

Q: Why Consider Ultra Supercritical?

A: Dramatic Improvement in Plant Efficiency

  • Economic Pressures – Fuel Prices

  • Environmental Pressures

    • Clean Air Act

    • Clear Skies

    • Local BACT

    • Future CO2

  • Social/Political Pressures

  • Quest for Permit


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Introduction

CYCLE HEAT RATE IMPROVEMENT


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Operating Results

Supercritical: Evolution

  • Early Supercritical Units had problems

    • Lengthy start-ups

    • Poor load following flexibility

    • Poor availability

    • Slagging/fouling/corrosion

  • Some of those problems not related to supercritical but other boiler evolution issues

  • Most early design issues have been effectively addressed and availability has improved, though maintenance costs are relatively high

  • Current supercritical designs in Europe and Japan have availability and maintenance commensurate with subcritical units


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Operating Results

  • Availability of Subcritical versus Supercritical Units – N. America

    • (Data from NERC 1982-1997)


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Operating Results

Availability Data for Supercritical verses Subcritical Units (Europe)


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Design Criteria

  • Size

    • Current commercial range from 300-1100 MW

  • Steam Conditions

    • Trade off efficiency gains (fuel savings) vs. capital cost

    • Example: Change from 1000/1000 to 1100/1100 results in 3-5% overall increase in plant cost

  • Fuel

    • More difficult fuels (often less expensive) require designs higher in capital costs

  • Feedwater Temperature

    • Affected by cycle design

  • Operating Requirements

    • Base load, load following, cycling, on-off peaking

  • Emissions Limits

    • Current and future, including CO2


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Advanced Designs and Materials

  • DOE/NETL - Cost and Performance Baseline for Fossil Energy Plants – 2007

  • EPRI – CoalFleet Guideline for Advanced Pulverized Coal Power Plants – 2008

  • EPRI - Engineering and Economic Assessment of Ultra-Supercritical Pulverized Coal Power Plants for Near Term Development – Ongoing

  • Thermie (Europe)

  • Japanese Program

  • U.S. - DOE and State of Ohio

  • Shandong Technical Exchange – Henan Design Institute – Henan Province, PRC

Recent Activities Assessing Ultra Supercritical Designs and Materials


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Advanced Designs and Materials

Ultra Supercritical: Current State-of-the-Art

  • Latest Units in Europe 4000 psig, 1105/1110 F

  • China moving up to 3800 psig, 1120/1135 F

  • Most aggressive unit in Japan 3950 psig, 1121/1153 F

  • U.S. Market generally around 3700 psig, 1080/1080 F

  • Most advanced U.S. plant in Engineering Phase at 3800 psig, 1112/1135 F

  • With advanced materials and careful design, Ultra Supercritical units have maintenance and availability similar to more recent standard supercritical units.


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Advanced Designs and Materials


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Advanced Design and Materials

Significant Issues with Ultra Supercritical Project Implementation

  • Long term validation of materials

    • ASME/ASTM Re-rating of materials: Grade 91, 92, 122, 23, etc.

    • Creep-Rupture, exfoliation, corrosion resistance

  • Fabrication

    • Welding procedures, heat treatment, bending, etc.

  • Construction

    • Qualified crafts, qualification of procedures, tight Q/A

  • Compatibility of valves, fittings and appurtenances

    • Many shapes, valves, etc. not available in advanced materials

Above issues present risks to project costs, schedule, and performance which are significant in comparison to standard subcritical or supercritical cycles.


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Future Generation USC

  • Increase steam conditions to further improve efficiency:

    • For typical US facility, efficiencies up to 48% (HHV) achievable

    • Benefits include:

      • Reduced emissions (including CO2)

      • Lower CO2 capture costs per MWh

  • Materials for advanced boilers:

Current

1150°F (630°C)

Ferritic Steels

AD700 Program

UltraGen II

1295°F (700°C)

Austenetic alloys and nickel based superalloys

  • UltraGen III

  • 1400°F (760°C)

  • Nickel based super alloys


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Future Generation USC

100,000 Creep-Rupture Stress for USC Boiler Materials

P.J. Maiasz, I.G. Wright, J.P Shingeldecker, T.B. Gibbons, and R.R. Romanosky, “Defining the Materials Issues and Research for Ultra-Supercritical Steam Turbines,” Proceedings to the Fourth International Conference on Advances in Materials Technology for Fossil Power Plants (Hilton Head, SC, Oct. 25-28, 2004). ASM-International, Materials Park, OH, 2005.


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Future Generation USC

Beyond Advanced Steam Conditions

  • Double Reheat

  • Reduction of Boiler Exit Gas Temperature

  • Low Level Exit Gas Heat Recovery

  • Coal Drying

  • Combustion Air Preheating

  • Feedwater Heater External Desuperheater

  • Multi-Pressure Condenser

  • Maximizing Cooling Tower Performance

  • Optimized Turbine Cycle for Ambient Conditions

  • Variable Speed Drives


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