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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 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? 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
Introduction CYCLE HEAT RATE IMPROVEMENT
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
Operating Results • Availability of Subcritical versus Supercritical Units – N. America • (Data from NERC 1982-1997)
Operating Results Availability Data for Supercritical verses Subcritical Units (Europe)
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
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
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.
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.
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
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.
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