SafetyinDesignandInstalla0onofHeatRecoverySteamGenerator
CEPSI2016byJohnnyKwong
24Oct2016
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Content
● Introduc9on● HRSGsinLammaPowerSta9on● CommonRisksandFailuresofHRSG● SafetyforDesign● SafetyforInstalla9on● Conclusion
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Introduc0on
Stage I L1-3 : 250 MW x 3 (1982-84) Stage II L4-6 : 350 MW x 3 (1987-92) Stage III L7-8 : 350 MW x 2 (1995-97)
8 Coal-Fired Units 2,500 MW
GT1 : 55 MW (1978) GT2,3,4,6 : 125 MW x 4 (1989-90)
5 Oil-Fired Open Cycle GT Units 555 MW
2 Gas/Oil Dual-Fired CCGT Units
GT57CC : 345 MW (2002) L9 : 335 MW (2006) 335 MW
345 MW
~3,737 MW (Incl. Renewable)
Total Installed Capacity :
800kW
1MW
● Lamma Power Station and Extension
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Introduc0on
● Heat Recovery Steam Generators (HRSG) have been adopted widely due to growth in CCGT plants
● HRSG is essentially a Boiler but without firing; it captures residual heat of high temperature flue gas (typically 540-650oC) and generate steam for power generation and/or district heating;
● Heat present in flue gas falls typically within 40-70% of initial fuel energy of a F-class CCGT
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HRSGsinLammaPowerSta0onCCGT Unit GT 5&7 L9 L10 (future)
Flue Gas Flow Vertical Vertical Horizontal
Pressure Stages HP, LP HP, IP, LP; With Reheat
HP, IP, LP; With Reheat
Drum Type ü ü ü SCR/CO Catalyst X X SCR catalyst
Supplementary Firing X X X
Casing design Cold/Hot casing Cold Cold
Steam Output 195.15 t/hr 512 oC
73.5 kg/cm2g
279.7 t/hr 539.9 oC
109.4 kg/cm2g
294.7 t/hr 582 oC
139.4 kg/cm2g
1 Preheater 2 LP evaporator 3 LP superheater 4 HP economizer 5 Catalyst 6 HP evaporator 7 NH3 injection 8 HP superheater
Typical Vertical Design HP drum
LP drum Feedwater tank
1 2 3 4 5 6 7 8
Typical Horizontal Design Feedwater tank LP drum HP drum
8 7 6 5 4 3 2 1
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CommonRisksandFailuresofHRSG● Corrosion
Ø General Corrosion Ø Stress Corrosion Cracking Ø Flow Accelerated Corrosion
● Low Cycle Fatigue ● Water/Steam Cycle Chemistry
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SafetyforDesignofHRSG
● General Corrosion – Rate of corrosion
Relative Corrosion Rate of Fe and Cu
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SafetyforDesignofHRSG
● Prevention Measures Ø Materials Selection + Water Chemistry (pH, conductivity..)
SA 299
/Deaerator
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Flow Mal-distribution
• Mechanical configuration
• Un-even heat absorption during transient/load change
• High duct firing • Poor venting/drainage
Off-design Water
Chemistry
• Poor control of water quality (global FAC effects)
Poor Materials Selection
for vulnerable
section
• Low grade CS vs Higher Cr alloy steel (e.g. Grade 11 or above)
SafetyforDesignofHRSG
● Flow Accelerated Corrosion
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SafetyforDesignofHRSG
● Wear Rate of Carbon Steel and Various Alloy Steels
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SafetyforDesignofHRSG
● Wear Rate of Carbon Steel and Various Alloy Steels
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SafetyforDesignofHRSG
● Fatigue (Low Cycle Fatigue)
Two-shift Cycling
• Fast Start up/Shut down would increase thermal stress
Presence of condensate
• High difference in tube-to-tube temperature
• Inadequate drains/vents
Unresolved thermal
expansion at harps
• Configuration that inhibit expansion, thus induces stress
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SafetyforDesignofHRSG● Fatigue (Low Cycle Fatigue)
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SafetyforDesignofHRSG
● Stress Corrosion Cracking
Corrosive Environment
Tensile Stress
Susceptible
Material
SCC
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SafetyforDesignofHRSG● Water Cycle Chemistry
Failure Mechanisms
Affected by Water Cycle Chemistry
CF
FAC SCC
Hydrogen Damage Pitting
Deposit Related – Overheating or
Caustic Gouging
Controlled parameters: Oxygen, pH, Conductivity Insoluble, Carryover, TDS
Independent of Cycle Chemistry
LCF/HCF, Weld Failure,
Thermal Fatigue, Creep,
Cold end tube corrosion
With established Action Plan, such as blow down, chemical dosing, etc. in case of deviation
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SafetyforDesignofHRSG● All Volatile Treatment (Oxidizing) – AVT(O) ● Reddish color is the Hematite (Fe2O3) formed on the wall
while the black color is mainly the Magnetite (Fe3O4). AVT(R) AVT(O
)
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SafetyforDesignofHRSG
● HRSG Dry Lay-up Arrangement (Preservation) Ø Dry Lay-up
Dehumidifier
FWP
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SafetyforInstalla0onofHRSG
● WelderQualifica0onTest
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SafetyforInstalla0onofHRSG
● Pre-WeldingInspec0on
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SafetyforInstalla0onofHRSG● HRSGModuleMovingInandLiMing(HorizontalHRSG)
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Conclusion
● Safety in design and installation is a must in securing the performance of HRSG within its design life (~30 years).
● Design-code compliance is the minimum requirement only;
More attention to be paid on the HRSG failure mechanisms and the prevention measures in design stage.
● Live monitoring of water chemistry & metal temperature with good maintenance /lay-up practice are required to ensure the operation is within design boundaries.
KopKhunKrap!ThankYou!
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